Artículos de revistas: "Endocytosis"

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Bouchard, Beth A., Joseph M. Petty y Benjamin T. Suratt. "Endocytosis of Factor V by Ex Vivo-Derived Mouse Megakaryocytes is Dependent Upon Low Density Lipoprotein Receptor-Related Protein-1." Blood 114, n.º 22 (20 de noviembre de 2009): 4014. http://dx.doi.org/10.1182/blood.v114.22.4014.4014.

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Abstract Abstract 4014 Poster Board III-950 Subsequent to platelet activation at sites of vascular injury, numerous hemostatic proteins are released from platelet α-granules. As platelets possess little, if any, biosynthetic capability, these proteins are either synthesized by megakaryocytes (e.g. vonWillebrand) or endocytosed from the plasma by both megakaryocytes and platelets (e.g. fibrinogen). In contrast, in humans, factor V is endocytosed exclusively by megakaryocytes from the plasma via a specific, receptor-mediated, clathrin-dependent mechanism, requiring two membrane proteins. Factor V initially binds to a specific receptor. This binding event promotes an interaction between a second factor V molecule and low density lipoprotein receptor-related protein-1 (LRP-1), which subsequently mediates the endocytosis of bound factor V. In contrast, in mice, the platelet- and plasma-derived factor V pools appear to be biosynthetically distinct as demonstrated by Ginsburg and colleagues using transgenic animals (Blood 102:2856-61, 2003); however, the ability of mouse megakaryocytes to endocytose factor V was not determined. In the current study, the ability of ex vivo-derived mouse megakaryocytes to endocytose factor V is being assessed. Mouse megakaryocytes were identified by their morphology and expression of CD41. CD41 expression is apparent by Day 3 of culture. By Day 8, > 60% of the cells are positive for CD41 expression. Using a monoclonal anti-human factor V light chain antibody that cross-reacts with mouse factor V by western blotting, factor V was detected by immunohistochemistry in primary, bone marrow-derived mouse megakaryocytes, but not in cultured, ex vivo-derived mouse megakaryocytes (Day 11), when the cells are incubated in the absence of factor V, suggesting that under the conditions of this study ex vivo-derived mouse megakaryocytes are not capable of synthesizing factor V. To assess the ability of mouse megakaryocytes to endocytose factor V, cultures were incubated with fluorescently-labeled human factor V. Human and mouse factor V have an amino acid identity of ∼82% within their light chains, which mediates binding and/or endocytosis of factor V in the human system. Subsequent to incubation of ex vivo-derived mouse megakaryocyte cultures with fluorescently-labeled human factor V, substantial endocytosis was observed both by flow cytometry and fluorescence microcopy. Fluorescence microscopy indicated that these cells also endocytose fluorescently-labeled human fibrinogen, which colocalized substantially with endocytosed factor V. Fluorescence microscopy also demonstrated that while every cell expressed LRP-1 on its cell surface, only some of the cells were capable of endocytosing factor V. Furthermore, preincubation with polyclonal anti-LRP-1 antibodies inhibited 125I-factor V binding and endocytosis by ∼60%. Thus, while factor V binding and endocytosis are dependent, in part, upon the expression of LRP-1, LRP-1 expression by mouse megakaryocytes is not sufficient for factor V endocytosis, similar to observations with human megakaryocytes, and consistent with the notion that a second receptor is required. These combined observations demonstrate that ex vivo-derived mouse megakaryocytes endocytose human factor V and suggest that they may serve as an appropriate model system to study factor V endocytosis. Disclosures: No relevant conflicts of interest to declare.

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Fares, Hanna y Iva Greenwald. "Genetic Analysis of Endocytosis in Caenorhabditis elegans: Coelomocyte Uptake Defective Mutants". Genetics 159, n.º 1 (1 de septiembre de 2001): 133–45. http://dx.doi.org/10.1093/genetics/159.1.133.

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Abstract The coelomocytes of Caenorhabditis elegans are scavenger cells that continuously and nonspecifically endocytose fluid from the pseudocoelom (body cavity). Green fluorescent protein (GFP) secreted into the pseudocoelom from body wall muscle cells is endocytosed and degraded by coelomocytes. We show that toxin-mediated ablation of coelomocytes results in viable animals that fail to endocytose pseudocoelomic GFP, indicating that endocytosis by coelomocytes is not essential for growth or survival of C. elegans under normal laboratory conditions. We examined known viable endocytosis mutants, and performed RNAi for other known endocytosis genes, for coelomocyte uptake defective (Cup) phenotypes. We also screened for new genes involved in endocytosis by isolating viable mutants with Cup defects; this screen identified 14 different genes, many with multiple alleles. A variety of Cup terminal phenotypes were observed, consistent with defects at various steps in the endocytic pathway. Available molecular information indicates that the Cup mutant screen has identified novel components of the endocytosis machinery that are conserved in mammals but not in Saccharomyces cerevisiae, the only other organism for which large-scale genetic screens for endocytosis mutants have been performed.

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Bouchard, Beth A., Douglas J. Taatjes, Natalie T. Meisler y Paula B. Tracy. "Subsequent to Its Endocytosis by Megakaryocytes, Factor V Is Trafficked to the [Italic]cis[/Italic]-Golgi Network Prior to Its Storage in α-Granules." Blood 108, n.º 11 (16 de noviembre de 2006): 1697. http://dx.doi.org/10.1182/blood.v108.11.1697.1697.

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Abstract Human platelet-derived factor V originates from megakaryocyte endocytosis of its plasma counterpart. Circulating platelets do not endocytose plasma-derived factor V and little, if any, of this hemostatically relevant, and unique, cofactor protein is synthesized by megakaryocytes. Fibrinogen, another α-granule protein, is also endocytosed from plasma, whereas other similarly stored proteins are synthesized by megakaryocytes, e.g. vWF and P-selectin. Using CD34+ex vivo-derived megakaryocytes as a model, mechanisms defining megakaryocyte endocytosis of plasma-derived factor V and its intracellular trafficking to α-granules are being studied. Expression of the well-known megakaryocyte proteins αIIb, β3, vWF, and P-selectin increased in parallel concomitant with the loss of CD34 and increased cellular differentiation. Expression of these proteins was apparent within 4 days of cell culture and was maximal by day 10. In contrast, endocytosis of factor V by cells at earlier stages of megakaryocyte differentiation (day 7) occurred in the absence of αIIb and vWF expression. By day 10 in culture, all cells endocytosing factor V also expressed αIIb and vWF. Fibrinogen endocytosis occurred with the concomitant expression of αIIb/β3. The colocalization of fluorescently-labeled factor V and fibrinogen with various organelle-specific, fluorescent antibodies was determined by confocal microscopy using day 10 or 11 ex vivo-derived megakaryocytes. After a 1 hr endocytosis period, 87.8 ± 7.2% of the factor V colocalized with an antibody to Rab5, an early endosomal marker. Colocalization decreased over time such that only 5% of the Rab5 colocalized with factor V at 4 hrs. Endocytosed factor V also colocalized in a time-dependent manner with an antibody to GM130, a cis-Golgi element, consistent with the hypothesis that endocytosed, plasma-derived factor V is structurally modified to generate the unique platelet-derived molecule. After a 2 hr endocytosis period, 53.2 ± 23.0% of the GM130 specific antibody colocalized with factor V. Colocalization decreased 5-fold by 4 hrs. In contrast, little if any of the GM130 antibody colocalized with endocytosed fibrinogen, while >80% of the cis-Golgi element colocalized with vWF. After 19 hrs, substantial colocalization was also observed between endocytosed factor V and vWF (84.2 ± 3.7%) or P-selectin (54.8 ± 3.5%), which is consistent with their storage in α-granules and confirms flow cytometric analyses. The colocalization of endocytosed factor V and fibrinogen was also determined over time. These proteins colocalized quickly (1 hr) likely due to their uptake into early endosomes as suggested by previous studies in a megakaryocyte-like cell line. Colocalization reached a maximum and plateaued after endocytosis periods ≥ 8 hrs again consistent with their ultimate storage in α-granules. At endocytosis periods < 8 hrs, less factor V colocalized with fibrinogen consistent with the localization of factor V in the cis-Golgi network at these times. In conclusion, these combined observations suggest that following its endocytosis by megakaryocytes, factor V is taken up into early endosomes and trafficked through the Golgi complex prior to its storage in α-granules. Its transport through the Golgi is consistent with previous observations that platelet-derived factor V contains an O-linked glycosylation not found in its plasma counterpart.

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Roweth, Harvey G., Michael Malloy, Jodi A. Forward, Julia Ceglowski, Robert C. Flaumenhaft, Joseph E. Italiano y Elisabeth Battinelli. "The Effects of Antiplatelet Agents on Endocytosis". Blood 134, Supplement_1 (13 de noviembre de 2019): 1058. http://dx.doi.org/10.1182/blood-2019-131912.

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Almost every platelet-derived protein originates from either megakaryocytes (MKs), or the endocytosis of factors within blood circulation. These endocytosed factors can be locally released upon platelet activation to regulate hemostasis, or to promote the growth and neovascularization of solid tumors. Although platelet endocytosis has long been recognized, our mechanistic understanding remains largely confined to receptor-mediated endocytosis of fibrinogen via integrin αIIbβ3. Whether antiplatelet therapy and/or different disease states influence platelet endocytosis remain understudied areas of investigation. In this project, we examined how various antiplatelet agents affect the endocytosis of vascular endothelial growth factor (VEGF) and endostatin, which are broad pro-angiogenic and anti-angiogenic regulators, respectively. For our initial experiments, human platelets in platelet-rich plasma were exposed to either recombinant VEGF or endostatin for 1 hour, then washed to remove residual/unbound protein. Platelets were then lysed and changes in VEGF or endostatin concentration determined by ELISA. Using this approach, we demonstrated that platelets endocytose VEGF and endostatin in a concentration-dependent manner. We next established that following platelet activation, lysate concentrations of endocytosed VEGF and endostatin decreased and supernatant concentrations increased. This finding implies that endocytosed VEGF and endostatin are packaged into platelet alpha granules and are released following their activation, which we aim to confirm by measuring co-localization with endosomal and alpha granule markers. We have also developed two assays to track endocytosis into platelets, one where proteins are conjugated to pH-sensitive dyes that increase their fluorescence upon endosomal compartmentalization, and another utilizing fluorophore-targeting antibodies to quench eternal fluorescence of labeled factors. We next assessed if antiplatelet agents modulated endocytosis into platelets. We found that pre-treating platelets with aspirin, vorapaxar or ticagrelor resulted in dose-dependent inhibition of VEGF and fibrinogen but not endostatin endocytosis. This finding suggests that antiplatelet agents selectively inhibit the uptake of pro-angiogenic regulators, a statement we aim to support by measuring the endocytosis of additional angiogenic proteins. Our observations also affirm previous studies, claiming that fibrinogen and VEGF are differentially packaged into a subset of alpha granules distinct from endostatin. Experiments are ongoing to measure platelet levels of VEGF and endostatin in human subjects before and after aspirin intervention, to assess if our findings hold physiological relevance. The fact that several antiplatelet agents impaired VEGF endocytosis suggests a common inhibitory mechanism linked to suppressing basal levels of platelet activation. We tested this hypothesis by either simulating platelets with low-dose adenosine diphosphate or by chelating intracellular calcium to prevent basal activation. Neither of these processes influenced VEGF or endostatin endocytosis, suggesting that the process is not associated with basal platelet activation. We are currently investigating if antiplatelet agents alter the activity of small GTPases Arf6 and Dynamin-2, which have been shown to regulate receptor-mediated endocytosis of fibrinogen by platelets. Future experiments will aim to elucidate the mechanism by which antiplatelet agents inhibit protein uptake. It has previously been shown that platelets endocytose tumor-derived factors and RNA that may promote disease progression or act as biomarkers for liquid biopsies. We are currently studying if the daily administration of aspirin prevents the endocytosis of tumor-derived factors in a mouse model of tumor generation. In summary, our data show platelets endocytose and release key angiogenic regulators, a process which can be blocked through pre-treatment with various antiplatelet agents. Given the important role of platelets to tumor neovascularization, preventing the endocytosis of pro-angiogenic mediators could represent a novel mechanism that contributes to the inhibitory effects of antiplatelet agents on tumor growth and metastasis. Disclosures Flaumenhaft: Relay Therapeutics: Consultancy; PlateletDiagnostics: Consultancy, Other: Founder. Italiano:Platelet Biogenesis: Employment, Equity Ownership; Ionis Research Funding: Research Funding.

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Rivera, J., J. M. Mullins, K. Furuichi y C. Isersky. "Endocytosis of aggregated immunoglobulin G by rat basophilic leukemia cells; rate, extent, and effects on the endocytosis of immunoglobulin E." Journal of Immunology 136, n.º 2 (15 de enero de 1986): 623–27. http://dx.doi.org/10.4049/jimmunol.136.2.623.

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Abstract Rat basophilic leukemia (RBL) cells have distinct receptors for IgE and IgG. We assessed the endocytosis of chemically and immunochemically cross-linked mouse-IgG and its influence on the simultaneous endocytosis of IgE. We found that at 37 degrees C, aggregates of IgG and IgE were endocytosed at about the same rate with one-half of the maximal endocytosis occurring in 5 to 13 min, and the efficiency of endocytosis for both ligands ranging from 40 to 70%. We also found that endocytosis of cross-linked IgE and IgG occurred simultaneously and neither ligand significantly affected the rate or extent of endocytosis of the other. The cells accumulated the cross-linked IgG, and then released it to the extracellular environment, at a rate (less than 3%/hr) slower than the released endocytosed IgE (greater than 10%/hr). Using an assay that discriminates between unbound and receptor-bound oligomeric IgG, we found that oligomeric IgG is endocytosed with its receptor, and that the bulk of the ligand remains bound to its receptor for greater than 120 min after endocytosis. The differences in the rate of release of endocytosed IgG vs IgE suggests that the intracellular fate or pathway of these two oligomeric ligands may differ.

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Vocelle, Daniel, Olivia M. Chesniak, Amanda P. Malefyt, Georgina Comiskey, Kwasi Adu-Berchie, Milton R. Smith, Christina Chan y S. Patrick Walton. "Dextran functionalization enhances nanoparticle-mediated siRNA delivery and silencing". TECHNOLOGY 04, n.º 01 (marzo de 2016): 42–54. http://dx.doi.org/10.1142/s2339547816400100.

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Understanding the endocytosis and intracellular trafficking of short interfering RNA (siRNA) delivery vehicle complexes remains a critical bottleneck in designing siRNA delivery vehicles for highly active RNA interference (RNAi)-based therapeutics. In this study, we show that dextran functionalization of silica nanoparticles enhanced uptake and intracellular delivery of siRNAs in cultured cells. Using pharmacological inhibitors for endocytotic pathways, we determined that our complexes are endocytosed via a previously unreported mechanism for siRNA delivery in which dextran initiates scavenger receptor-mediated endocytosis through a clathrin/caveolin-independent process. Our findings suggest that siRNA delivery efficiency could be enhanced by incorporating dextran into existing delivery platforms to activate scavenger receptor activity across a variety of target cell types.

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Eyre, Jeanette, Kyriakos Ioannou, Blair D. Grubb, Moin A. Saleem, Peter W. Mathieson, Nigel J. Brunskill, Erik I. Christensen y Peter S. Topham. "Statin-sensitive endocytosis of albumin by glomerular podocytes". American Journal of Physiology-Renal Physiology 292, n.º 2 (febrero de 2007): F674—F681. http://dx.doi.org/10.1152/ajprenal.00272.2006.

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Glomerular podocytes are critical regulators of glomerular permeability via the slit diaphragm and may play a role in cleaning the glomerular filter. Whether podocytes are able to endocytose proteins is uncertain. We studied protein endocytosis in conditionally immortalized mouse and human podocytes using FITC-albumin by direct quantitative assay and by fluorescence microscopy and electron microscopy in mouse podocytes. Furthermore, in vivo uptake was studied in human, rat, and mouse podocytes. Both mouse and human podocytes displayed specific one-site binding for FITC-albumin with Kd of 0.91 or 0.44 mg/ml and Bmax of 3.15 or 0.81 μg/mg cell protein, respectively. In addition, they showed avid endocytosis of FITC-albumin with Km of 9.48 or 4.5 mg/ml and Vmax of 474.3 or 97.4 μg·mg cell protein−1·h−1, respectively. Immunoglobulin and transferrin were inefficient competitors of this process, indicating some specificity for albumin. Accumulation of endocytosed albumin could be demonstrated in intracellular vesicles by fluorescence confocal microscopy and electron microscopy. Endocytosis was sensitive to pretreatment with simvastatin. In vivo accumulation of albumin was found in all three species but was most pronounced in the rat. We conclude that podocytes are able to endocytose protein in a statin-sensitive manner. This function is likely to be highly significant in health and disease. In addition, protein endocytosis by podocytes may represent a useful, measurable phenotypic characteristic against which potentially injurious or beneficial interventions can be assessed.

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Bouchard, Beth A., Natalie T. Meisler, Michael E. Nesheim y Paula B. Tracy. "Uptake of Factor V by Megakaryocytes Requires a Specific Factor V Receptor Linked to a Low-Density Lipoprotein Receptor-Related Protein." Blood 106, n.º 11 (16 de noviembre de 2005): 688. http://dx.doi.org/10.1182/blood.v106.11.688.688.

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Abstract Factor V is endocytosed by megakaryocytes from plasma to form the platelet-derived factor V/Va pool via a receptor-mediated, clathrin-dependent mechanism. However, the megakaryocyte receptor that mediates the binding and subsequent endocytosis of plasma-derived factor V is unknown. Because of its known ability to interact with proteins involved in coagulation and fibrinolysis, the role of low-density lipoprotein receptor-related protein (LRP) or an LRP-like molecule was examined in factor V endocytosis by the megakaryocyte-like cell line CMK. As endocytosis by such proteins is Ca2+-dependent, binding and endocytosis of factor V ± added Ca2+ were examined. While endocytosis of factor V was absolutely dependent upon the presence of Ca2+, binding of factor V to megakaryocytes was unaffected by its absence allowing for the quantification of 125I-factor V binding in the absence of factor V endocytosis. The time-dependent, specific 125I-factor V binding to megakaryocytes reached a steady-state within 20–25 min and displayed a sigmoidal character. The steady state binding of a plasma concentration of 125I-factor V could be displaced 56.4 ± 7.8% by the addition of a 150-fold molar excess of the LRP ligand, receptor associated protein (RAP). In contrast, nearly all of the 125I-factor V bound could be displaced following the addition of a 50-fold molar excess of factor V alone or by the addition of both factor V and RAP. These observations suggest that factor V binds to two binding sites on megakaryocytes, which consist of a specific factor V receptor and LRP (or an LRP-like molecule). This notion of a two-receptor system was confirmed in steady state, concentration-dependent binding analyses of 125I-factor V in the presence or absence of RAP. Binding of factor V was saturable at a concentration ~15–20 times higher than the plasma concentration of factor V, which is consistent with observations that the platelet-derived factor V concentration is dependent upon and parallels the plasma-derived factor V concentration. Similar to the observations described above, concentration-dependent binding was also inhibited 40–50% by the presence of excess RAP. The binding curves in the presence or absence of RAP remained sigmoidal and were fit with confidence (r ≥ 0.95) to a two-receptor binding model. In support of these observations, AlexaFluor488-labeled factor V and AlexaFluor633-labeled RAP co-localized within the same cells subsequent to their endocytosis by megakaryocytes as demonstrated by confocal microscopy. Flow cytometric analyses of the same cell population confirmed these observations: All of the cells that endocytosed factor V also endocytosed RAP. Based upon the combined observations we propose a binding model where factor V endocytosis is mediated by a two-receptor system consisting of a specific factor V receptor and an LRP co-receptor closely linked on the cell surface. In this model, factor V binds to its specific receptor in a Ca2+-independent manner. Bound factor V is then transferred to LRP (or an LRP-like molecule) to allow for the binding of a second factor V molecule to the unoccupied site on the factor V receptor. Factor V bound to LRP is then endocytosed in Ca2+- and clathrin-dependent manners. As our flow cytometric analyses indicate that all of the cells bind and endocytose RAP, we hypothesize that it is the presence or absence of the specific factor V receptor that defines the megakaryocytes’ ability to endocytose factor V from plasma.

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Ivesic, Caroline, Stefanie Krammer, Marianne Koller-Peroutka, Aicha Laarouchi, Daniela Gruber, Ingeborg Lang, Irene K. Lichtscheidl y Wolfram Adlassnig. "Quantification of Protein Uptake by Endocytosis in Carnivorous Nepenthales". Plants 12, n.º 2 (11 de enero de 2023): 341. http://dx.doi.org/10.3390/plants12020341.

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Carnivorous plants adsorb prey-derived nutrients partly by endocytosis. This study quantifies endocytosis in Drosophyllum lusitanicum, Drosera capensis, Drosera roseana, Dionaea muscipula and Nepenthes × ventrata. Traps were exposed to 1% fluorescent-labeled albumin (FITC-BSA), and uptake was quantified repeatedly for 64 h. Formation of vesicles started after ≤1 h in adhesive traps, but only after 16 h in species with temporary stomach (D. muscipula and N. × ventrata). In general, there are similarities in the observed species, especially in the beginning stages of endocytosis. Nonetheless, further intracellular processing of endocytotic vesicles seems to be widely different between species. Endocytotic vesicle size increased significantly over time in all species except in D. capensis. Fluorescence intensity of the endocytotic vesicles increased in all species except D. muscipula. After 64 h, estimates for FITC-BSA absorption per gland ranged from 5.9 ± 6.3 ng in D. roseana to 47.8 ± 44.3 ng in N. × ventrata, demonstrating that endocytosis substantially contributes to the adsorption of prey-derived nutrients.

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Parks, A. L., K. M. Klueg, J. R. Stout y M. A. Muskavitch. "Ligand endocytosis drives receptor dissociation and activation in the Notch pathway". Development 127, n.º 7 (1 de abril de 2000): 1373–85. http://dx.doi.org/10.1242/dev.127.7.1373.

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Endocytosis of the ligand delta; is required for activation of the receptor Notch during Drosophila development. The Notch extracellular domain (NotchECD) dissociates from the Notch intracellular domain (NotchICD) and is trans-endocytosed into delta;-expressing cells in wild-type imaginal discs. Reduction of dynamin-mediated endocytosis in developing eye and wing imaginal discs reduces Notch dissociation and Notch signalling. Furthermore, dynamin-mediated delta endocytosis is required for Notch trans-endocytosis in Drosophila cultured cell lines. Endocytosis-defective delta proteins fail to mediate trans-endocytosis of Notch in cultured cells, and exhibit aberrant subcellular trafficking and reduced signalling capacity in Drosophila. We suggest that endocytosis into delta-expressing cells of NotchECD bound to delta plays a critical role during activation of the Notch receptor and is required to achieve processing and dissociation of the Notch protein.

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Furuichi, K., J. Rivera, L. M. Buonocore y C. Isersky. "Recycling of receptor-bound IgE by rat basophilic leukemia cells." Journal of Immunology 136, n.º 3 (1 de febrero de 1986): 1015–22. http://dx.doi.org/10.4049/jimmunol.136.3.1015.

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Abstract Rat basophilic leukemia (RBL) cells have receptors for immunoglobulin E (IgE). We previously showed that unlike some other ligands, the binding of monomeric rat or mouse IgE to RBL cells does not induce endocytosis. However, aggregation of the cell-bound, monomeric mouse IgE anti-dinitrophenyl (DNP) with DNP-protein conjugates leads to endocytosis of the aggregated mouse IgE and to the co-endocytosis of some unaggregated monomeric rat IgE. In this study we analyzed and compared the fate of co-endocytosed and endocytosed IgE. We found that co-endocytosed rat IgE recycled back to the cell surface within 3 to 4 hr. In contrast, endocytosed, immunochemically cross-linked, receptor-bound mouse IgE anti-DNP was partially degraded and was released into the medium, with no observable recycling of receptors, by 3 hr. However, addition of the hapten, DNP-lysine, resulted in rapid recycling (t1/2 10 min) of the endocytosed receptor-bound IgE to the plasma membrane and blocked additional endocytosis. Recycling of the endocytosed mouse IgE was more pronounced when the hapten was added to cells within 20 min of the initiation of endocytosis. When the hapten was added to the cells at later times (60 to 180 min), progressively less IgE recycled to the surface. This may reflect shuttling of the internalized IgE from a 'prelysosomal' to a 'lysosomal' compartment. Thus we provide evidence for recycling of monomeric IgE receptor complexes, sorting between cross-linked and non-cross-linked IgE receptor complexes, the freeing of receptor-bound monomeric IgE from the endocytosed immune-complexed IgE, and the apparent dependence of the recycling efficiency upon intracellular localization.

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VEERAMACHANENI, D. N. RAO y RUPERT P. AMANN. "Endocytosis of Androgen‐Binding Protein, Cluster in, and Transferrin in the Efferent Ducts and Epididymis of the Ram". Journal of Andrology 12, n.º 5 (10 de septiembre de 1991): 288–94. http://dx.doi.org/10.1002/j.1939-4640.1991.tb01602.x.

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ABSTRACT: The amount of androgen‐binding protein (ABP) In luminal fluid from the central caput epididymidis of the ram, on a per sperm basis, remains the same as that in rete testis fluid (RTF) entering the ductuli efferentes, although >85% of the testicular protein is absorbed in proximal sites. To determine if ABP is spared from endocytosis in proximal sites and if proteins are differentially and selectively absorbed at specific sites in the excurrent ducts, we studied the endocytosis of ABP, clusterin, transferrin, and a 26/35‐kd dimer isolated from ovine RTF. Each protein was labeled with colloidal gold and microinjected into the lumen of a ductulus efferens and five specific sites in the ductus epididymidis; uptake was quantified by electron microscopy. Endocytosis of each protein, including ABP, was substantially greater in the ductuli efferentes than in any site in the ductus epididymidis. More ABP was endocytosed in proximal regions of the epididymis than any other protein studied. Endocytosis of the 26/35‐kd dimer, like ABP, was greater in proximal sites of the epididymis, whereas endocytosis of clusterin and transferrin was greater in distal sites. Thus, there was a differential absorption, since proteins were endocytosed in one or another specific region of the epididymis, depending on the protein. ABP was endocytosed in the ductuli efferentes and caput epididymidis in amounts similar to or greater than other major testicular proteins, and was not spared from endocytosis in the proximal excurrent ducts. Previously reported maintenance of a similar amount of ABP, on a per sperm basis, throughout the ovine caput epididymidis probably results from recycling of endocytosed ABP or from epididymal secretion of ABP.

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Bi, Yan, Dhriti Mukhopadhyay, Mary Drinane, Baoan Ji, Xing Li, Sheng Cao y Vijay H. Shah. "Endocytosis of collagen by hepatic stellate cells regulates extracellular matrix dynamics". American Journal of Physiology-Cell Physiology 307, n.º 7 (1 de octubre de 2014): C622—C633. http://dx.doi.org/10.1152/ajpcell.00086.2014.

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Hepatic stellate cells (HSCs) generate matrix, which in turn may also regulate HSCs function during liver fibrosis. We hypothesized that HSCs may endocytose matrix proteins to sense and respond to changes in microenvironment. Primary human HSCs, LX2, or mouse embryonic fibroblasts (MEFs) [wild-type; c-abl−/−; or Yes, Src, and Fyn knockout mice (YSF−/−)] were incubated with fluorescent-labeled collagen or gelatin. Fluorescence-activated cell sorting analysis and confocal microscopy were used for measuring cellular internalization of matrix proteins. Targeted PCR array and quantitative real-time PCR were used to evaluate gene expression changes. HSCs and LX2 cells endocytose collagens in a concentration- and time-dependent manner. Endocytosed collagen colocalized with Dextran 10K, a marker of macropinocytosis, and 5-ethylisopropyl amiloride, an inhibitor of macropinocytosis, reduced collagen internalization by 46%. Cytochalasin D and ML7 blocked collagen internalization by 47% and 45%, respectively, indicating that actin and myosin are critical for collagen endocytosis. Wortmannin and AKT inhibitor blocked collagen internalization by 70% and 89%, respectively, indicating that matrix macropinocytosis requires phosphoinositide-3-kinase (PI3K)/AKT signaling. Overexpression of dominant-negative dynamin-2 K44A blocked matrix internalization by 77%, indicating a role for dynamin-2 in matrix macropinocytosis. Whereas c-abl−/− MEF showed impaired matrix endocytosis, YSF−/− MEF surprisingly showed increased matrix endocytosis. It was also associated with complex gene regulations that related with matrix dynamics, including increased matrix metalloproteinase 9 (MMP-9) mRNA levels and zymographic activity. HSCs endocytose matrix proteins through macropinocytosis that requires a signaling network composed of PI3K/AKT, dynamin-2, and c-abl. Interaction with extracellular matrix regulates matrix dynamics through modulating multiple gene expressions including MMP-9.

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Wang, Zhixiang, Lianfeng Zhang, Tai K. Yeung y Xinmei Chen. "Endocytosis Deficiency of Epidermal Growth Factor (EGF) Receptor–ErbB2 Heterodimers in Response to EGF Stimulation". Molecular Biology of the Cell 10, n.º 5 (mayo de 1999): 1621–36. http://dx.doi.org/10.1091/mbc.10.5.1621.

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Epidermal growth factor (EGF) stimulates the homodimerization of EGF receptor (EGFR) and the heterodimerization of EGFR and ErbB2. The EGFR homodimers are quickly endocytosed after EGF stimulation as a means of down-regulation. However, the results from experiments on the ability of ErbB2 to undergo ligand-induced endocytosis are very controversial. It is unclear how the EGFR–ErbB2 heterodimers might behave. In this research, we showed by subcellular fractionation, immunoprecipitation, Western blotting, indirect immunofluorescence, and microinjection that, in the four breast cancer cell lines MDA453, SKBR3, BT474, and BT20, the EGFR–ErbB2 heterodimerization levels were positively correlated with the ratio of ErbB2/EGFR expression levels. ErbB2 was not endocytosed in response to EGF stimulation. Moreover, in MDA453, SKBR3, and BT474 cells, which have very high levels of EGFR–ErbB2 heterodimerization, EGF-induced EGFR endocytosis was greatly inhibited compared with that in BT20 cells, which have a very low level of EGFR–ErbB2 heterodimerization. Microinjection of an ErbB2 expression plasmid into BT20 cells significantly inhibited EGF-stimulated EGFR endocytosis. Coexpression of ErbB2 with EGFR in 293T cells also significantly inhibited EGF-stimulated EGFR endocytosis. EGF did not stimulate the endocytosis of ectopically expressed ErbB2 in BT20 and 293T cells. These results indicate that ErbB2 and the EGFR–ErbB2 heterodimers are impaired in EGF-induced endocytosis. Moreover, when expressed in BT20 cells by microinjection, a chimeric receptor composed of the ErbB2 extracellular domain and the EGFR intracellular domain underwent normal endocytosis in response to EGF, and this chimera did not block EGF-induced EGFR endocytosis. Thus, the endocytosis deficiency of ErbB2 is due to the sequence of its intracellular domain.

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Rosa, Juliana M., Cristina J. Torregrosa-Hetland, Inés Colmena, Luis M. Gutiérrez, Antonio G. García y Luis Gandía. "Calcium entry through slow-inactivating L-type calcium channels preferentially triggers endocytosis rather than exocytosis in bovine chromaffin cells". American Journal of Physiology-Cell Physiology 301, n.º 1 (julio de 2011): C86—C98. http://dx.doi.org/10.1152/ajpcell.00440.2010.

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Calcium (Ca2+)-dependent endocytosis has been linked to preferential Ca2+ entry through the L-type (α1D, CaV1.3) of voltage-dependent Ca2+ channels (VDCCs). Considering that the Ca2+-dependent exocytotic release of neurotransmitters is mostly triggered by Ca2+ entry through N-(α1B, CaV2.2) or PQ-VDCCs (α1A, CaV2.1) and that exocytosis and endocytosis are coupled, the supposition that the different channel subtypes are specialized to control different cell functions is attractive. Here we have explored this hypothesis in primary cultures of bovine adrenal chromaffin cells where PQ channels account for 50% of Ca2+ current ( ICa), 30% for N channels, and 20% for L channels. We used patch-clamp and fluorescence techniques to measure the exo-endocytotic responses triggered by long depolarizing stimuli, in 1, 2, or 10 mM concentrations of extracellular Ca2+ ([Ca2+]e). Exo-endocytotic responses were little affected by ω-conotoxin GVIA (N channel blocker), whereas ω-agatoxin IVA (PQ channel blocker) caused 80% blockade of exocytosis as well as endocytosis. In contrast, nifedipine (L channel blocker) only caused 20% inhibition of exocytosis but as much as 90% inhibition of endocytosis. Conversely, FPL67146 (an activator of L VDCCs) notably augmented endocytosis. Photoreleased caged Ca2+ caused substantially smaller endocytotic responses compared with those produced by K+ depolarization. Using fluorescence antibodies, no colocalization between L, N, or PQ channels with clathrin was found; a 20–30% colocalization was found between dynamin and all three channel antibodies. This is incompatible with the view that L channels are coupled to the endocytotic machine. Data rather support a mechanism implying the different inactivation rates of L (slow-inactivating) and N/PQ channels (fast-inactivating). Thus a slow but more sustained Ca2+ entry through L channels could be a requirement to trigger endocytosis efficiently, at least in bovine chromaffin cells.

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16

Smith, Corey y Erwin Neher. "Multiple Forms of Endocytosis In Bovine Adrenal Chromaffin Cells". Journal of Cell Biology 139, n.º 4 (17 de noviembre de 1997): 885–94. http://dx.doi.org/10.1083/jcb.139.4.885.

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We studied endocytosis in chromaffin cells with both perforated patch and whole cell configurations of the patch clamp technique using cell capacitance measurements in combination with amperometric catecholamine detection. We found that chromaffin cells exhibit two relatively rapid, kinetically distinct forms of stimulus-coupled endocytosis. A more prevalent “compensatory” retrieval occurs reproducibly after stimulation, recovering an approximately equivalent amount of membrane as added through the immediately preceding exocytosis. Membrane is retrieved through compensatory endocytosis at an initial rate of ∼6 fF/s. Compensatory endocytotic activity vanishes within a few minutes in the whole cell configuration. A second form of triggered membrane retrieval, termed “excess” retrieval, occurs only above a certain stimulus threshold and proceeds at a faster initial rate of ∼248 fF/s. It typically undershoots the capacitance value preceding the stimulus, and its magnitude has no clear relationship to the amount of membrane added through the immediately preceding exocytotic event. Excess endocytotic activity persists in the whole cell configuration. Thus, two kinetically distinct forms of endocytosis coexist in intact cells during perforated patch recording. Both are fast enough to retrieve membrane after exocytosis within a few seconds. We argue that the slower one, termed compensatory endocytosis, exhibits properties that make it the most likely mechanism for membrane recycling during normal secretory activity.

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17

Li, Chuang-Ye, Li Liu, Yao-Wang Zhao, Qian-Long Peng, Xin-Yuan Sun, Da Guo y Jian-Ming Ouyang. "Repair of Tea Polysaccharide Promotes the Endocytosis of Nanocalcium Oxalate Monohydrate by Damaged HK-2 Cells". Oxidative Medicine and Cellular Longevity 2020 (27 de abril de 2020): 1–12. http://dx.doi.org/10.1155/2020/2198976.

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Endocytosis is a protective mechanism of renal epithelial cells to eliminate retained crystals. This research investigated the endocytosis of 100 nm calcium oxalate monohydrate crystals in human kidney proximal tubular epithelial (HK-2) cells before and after repair by four kinds of tea polysaccharides with molecular weights (MWs) of 10.88 (TPS0), 8.16 (TPS1), 4.82 (TPS2), and 2.31 kDa (TPS3), respectively. When HK-2 cells were repaired by TPSs after oxalic acid injury, the cell viability, wound healing ability, mitochondrial membrane potential, percentage of cells with endocytosed crystals, and dissolution rate of the endocytosed crystals increased; the cell morphology recovered; and the reactive oxygen level and lactate dehydrogenase release decreased. Most of the endocytosed crystals were found in the lysosomes. The repair effects of the four TPSs were ranked in the following order: TPS2>TPS1>TPS3>TPS0. TPS2 with moderate MW presented the optimal repair ability and strongest ability to promote endocytosis.

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18

Shen, Yingjie, Lizhong Xu y David A. Foster. "Role for Phospholipase D in Receptor-Mediated Endocytosis". Molecular and Cellular Biology 21, n.º 2 (15 de enero de 2001): 595–602. http://dx.doi.org/10.1128/mcb.21.2.595-602.2001.

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ABSTRACT In response to epidermal growth factor (EGF), the EGF receptor is endocytosed and degraded. A substantial lag period exists between endocytosis and degradation, suggesting that endocytosis is more than a simple negative feedback. Phospholipase D (PLD), which has been implicated in vesicle formation in the Golgi, is activated in response to EGF and other growth factors. We report here that EGF receptor endocytosis is dependent upon PLD and the PLD1 regulators, protein kinase C α and RalA. EGF-induced receptor degradation is accelerated by overexpression of either wild-type PLD1 or PLD2 and retarded by overexpression of catalytically inactive mutants of either PLD1 or PLD2. EGF-induced activation of mitogen-activated protein kinase, which is dependent upon receptor endocytosis, is also dependent upon PLD. These data suggest a role for PLD in signaling that facilitates receptor endocytosis.

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19

Kuhn, Dagmar A., Dimitri Vanhecke, Benjamin Michen, Fabian Blank, Peter Gehr, Alke Petri-Fink y Barbara Rothen-Rutishauser. "Different endocytotic uptake mechanisms for nanoparticles in epithelial cells and macrophages". Beilstein Journal of Nanotechnology 5 (24 de septiembre de 2014): 1625–36. http://dx.doi.org/10.3762/bjnano.5.174.

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Precise knowledge regarding cellular uptake of nanoparticles is of great importance for future biomedical applications. Four different endocytotic uptake mechanisms, that is, phagocytosis, macropinocytosis, clathrin- and caveolin-mediated endocytosis, were investigated using a mouse macrophage (J774A.1) and a human alveolar epithelial type II cell line (A549). In order to deduce the involved pathway in nanoparticle uptake, selected inhibitors specific for one of the endocytotic pathways were optimized regarding concentration and incubation time in combination with fluorescently tagged marker proteins. Qualitative immunolocalization showed that J774A.1 cells highly expressed the lipid raft-related protein flotillin-1 and clathrin heavy chain, however, no caveolin-1. A549 cells expressed clathrin heavy chain and caveolin-1, but no flotillin-1 uptake-related proteins. Our data revealed an impeded uptake of 40 nm polystyrene nanoparticles by J774A.1 macrophages when actin polymerization and clathrin-coated pit formation was blocked. From this result, it is suggested that macropinocytosis and phagocytosis, as well as clathrin-mediated endocytosis, play a crucial role. The uptake of 40 nm nanoparticles in alveolar epithelial A549 cells was inhibited after depletion of cholesterol in the plasma membrane (preventing caveolin-mediated endocytosis) and inhibition of clathrin-coated vesicles (preventing clathrin-mediated endocytosis). Our data showed that a combination of several distinguishable endocytotic uptake mechanisms are involved in the uptake of 40 nm polystyrene nanoparticles in both the macrophage and epithelial cell line.

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20

Hua, Q., C. B. Knudson y W. Knudson. "Internalization of hyaluronan by chondrocytes occurs via receptor-mediated endocytosis". Journal of Cell Science 106, n.º 1 (1 de septiembre de 1993): 365–75. http://dx.doi.org/10.1242/jcs.106.1.365.

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Several studies have suggested that chondrocytes must have the capacity to internalize and degrade extracellular hyaluronan. In the present study we show direct evidence that hyaluronan is, in fact, endocytosed by chondrocytes and that the endocytosis is mediated via cell surface CD44/hyaluronan receptors. Cultures of bovine articular chondrocytes as well as rat chondrosarcoma chondrocytes were incubated with either fluorescein- or 3H-labeled hyaluronan. Intense binding and accumulation of labeled hyaluronan was visualized by fluorescence microscopy or bright-field/dark-field microscopy following autoradiography. Cell surface hyaluronan was removed with either trypsin or Streptomyces hyaluronidase in order to distinguish and quantify intracellular endocytosed hyaluronan. Labeled hyaluronan was visualized within small discrete intracellular vesicles distributed throughout the cytoplasm. Binding and endocytosis of fluorescein- or 3H-labeled hyaluronan was totally blocked by the addition of excess unlabeled hyaluronan or hyaluronan hexasaccharides, competitive inhibitors of hyaluronan/hyaluronan receptor interactions. Binding and endocytosis was also blocked by the addition of anti-CD44 monoclonal antibodies. Characterization of endocytosed 3H-labeled hyaluronan demonstrated that a significant portion of the hyaluronan was degraded by both the bovine articular and rat chondrosarcoma chondrocytes. Interestingly, a higher proportion of bound hyaluronan was internalized by the bovine chondrocytes. Therefore, hyaluronan receptor-mediated endocytosis and degradation of hyaluronan may provide a critical link to the maintenance and homeostasis of cartilage tissue.

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21

Liu, Ke, Zhaolin Hua, Joshua A. Nepute y Todd R. Graham. "Yeast P4-ATPases Drs2p and Dnf1p Are Essential Cargos of the NPFXD/Sla1p Endocytic Pathway". Molecular Biology of the Cell 18, n.º 2 (febrero de 2007): 487–500. http://dx.doi.org/10.1091/mbc.e06-07-0592.

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Drs2p family P-type ATPases (P4-ATPases) are required in multiple vesicle-mediated protein transport steps and are proposed to be phospholipid translocases (flippases). The P4-ATPases Drs2p and Dnf1p cycle between the exocytic and endocytic pathways, and here we define endocytosis signals required by these proteins to maintain a steady-state localization to internal organelles. Internalization of Dnf1p from the plasma membrane uses an NPFXD endocytosis signal and its recognition by Sla1p, part of an endocytic coat/adaptor complex with clathrin, Pan1p, Sla2p/End4p, and End3p. Drs2p has multiple endocytosis signals, including two NPFXDs near the C terminus and PEST-like sequences near the N terminus that may mediate ubiquitin (Ub)-dependent endocytosis. Drs2p localizes to the trans-Golgi network in wild-type cells and accumulates on the plasma membrane when both the Ub- and NPFXD-dependent endocytic mechanisms are inactivated. Surprisingly, the pan1-20 temperature-sensitive mutant is constitutively defective for Ub-dependent endocytosis but is not defective for NPFXD-dependent endocytosis at the permissive growth temperature. To sustain viability of pan1-20, Drs2p must be endocytosed through the NPFXD/Sla1p pathway. Thus, Drs2p is an essential endocytic cargo in cells compromised for Ub-dependent endocytosis. These results demonstrate an essential role for endocytosis in retrieving proteins back to the Golgi, and they define critical cargos of the NPFXD/Sla1p system.

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22

Yao, Wenchao, Dankun Luo, Zhenyi Lv, Yang Yang, Liyi Wang, Biao Ma, Dongbo Xue, Chenjun Hao y Yingmei Zhang. "The Rabep1-Mediated Endocytosis and Activation of Trypsinogen to Promote Pancreatic Stellate Cell Activation". Biomolecules 12, n.º 8 (31 de julio de 2022): 1063. http://dx.doi.org/10.3390/biom12081063.

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Background: The pathogenesis of chronic pancreatitis is still unclear. Trypsinogen activation is an active factor in acute pancreatitis that has not been studied in the occurrence of chronic pancreatitis. Methods: Immunofluorescence was used to detect the location and expression of trypsinogen in chronic pancreatitis and normal tissues. Microarray and single-cell RNA-seq (scRNA-seq) were used to screen core genes and pathways in pancreatic stellate cells (PSCs). Western blotting and immunofluorescence were used to verify trypsinogen expression in PSCs after silencing Rabep1. Immunofluorescence and flow cytometry were used to validate trypsinogen activation and PSC activation after intervening in the endocytosis pathway. Results: Endocytosed trypsinogen was found in PSCs in CP clinical samples. Bioinformatic analysis showed that Rabep1 is a core gene that regulates trypsinogen endocytosis through the endocytosis pathway, verified by Western blot and immunofluorescence. Immunofluorescence and flow cytometry analyses confirmed the activation of trypsinogen and PSCs through the endocytosis pathway in PSCs. Conclusion: This study discovered a new mechanism by which trypsinogen affects the activation of PSCs and the occurrence and development of CP. Through communication between pancreatic acinar cells and PSCs, trypsinogen can be endocytosed by PSCs and activated by the Rabep1 gene.

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23

Li, Tianliang, Kewei Qin, Nan Li, Chaofeng Han y Xuetao Cao. "An endosomal LAPF is required for macrophage endocytosis and elimination of bacteria". Proceedings of the National Academy of Sciences 116, n.º 26 (12 de junio de 2019): 12958–63. http://dx.doi.org/10.1073/pnas.1903896116.

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Macrophages can internalize the invading pathogens by raft/caveolae and/or clathrin-dependent endocytosis and elicit an immune response against infection. However, the molecular mechanism for macrophage endocytosis remains elusive. Here we report that LAPF (lysosome-associated and apoptosis-inducing protein containing PH and FYVE domains) is required for caveolae-mediated endocytosis.Lapf-deficient macrophages have impaired capacity to endocytose and eliminate bacteria. Macrophage-specificLapf-deficient mice are more susceptible toEscherichia coli(E. coli) infection with higher bacterial loads. Moreover,Lapfdeficiency impairs TLR4 endocytosis, resulting in attenuated production of TLR-triggered proinflammatory cytokines. LAPF is localized to early endosomes and interacts with caveolin-1. Phosphorylation of LAPF by the tyrosine kinase Src is required for LAPF-Src-Caveolin complex formation and endocytosis and elimination of bacteria. Collectively, our work demonstrates that LAPF is critical for endocytosis of bacteria and induction of inflammatory responses, suggesting that LAPF and Src could be potential targets for the control of infectious diseases.

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24

Pandey, Madhu S., Edward N. Harris y Paul H. Weigel. "HARE-Mediated Endocytosis of Hyaluronan and Heparin Is Targeted by Different Subsets of Three Endocytic Motifs". International Journal of Cell Biology 2015 (2015): 1–12. http://dx.doi.org/10.1155/2015/524707.

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The hyaluronan (HA) receptor for endocytosis (HARE) is a multifunctional recycling clearance receptor for 14 different ligands, including HA and heparin (Hep), which bind to discrete nonoverlapping sites. Four different functional endocytic motifs (M) in the cytoplasmic domain (CD) target coated pit mediated uptake: (YSYFRI2485(M1), FQHF2495(M2), NPLY2519(M3), and DPF2534(M4)). We previously found (Pandey et al. J. Biol. Chem. 283, 21453, 2008) thatM1,M2, andM3mediate endocytosis of HA. Here we assessed the ability of HARE variants with a single-motif deletion or containing only a single motif to endocytose HA or Hep. Single-motif deletion variants lackingM1, M3, orM4(a different subset than involved in HA uptake) showed decreased Hep endocytosis, althoughM3was the most active; the remaining redundant motifs did not compensate for loss of other motifs. Surprisingly, a HARE CD variant with onlyM3internalized both HA and Hep, whereas variants with eitherM2orM4alone did not endocytose either ligand. Internalization of HA and Hep by HARE CD mutants was dynamin-dependent and was inhibited by hyperosmolarity, confirming clathrin-mediated endocytosis. The results indicate a complicated relationship among multiple CD motifs that target coated pit uptake and a more fundamental role for motifM3.

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25

Gasingirwa, Marie-Christine, Jacqueline Thirion, Jeannine Mertens-Strijthagen, Simone Wattiaux-De Coninck, Bruno Flamion, Robert Wattiaux y Michel Jadot. "Endocytosis of hyaluronidase-1 by the liver". Biochemical Journal 430, n.º 2 (13 de agosto de 2010): 305–13. http://dx.doi.org/10.1042/bj20100711.

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It has been suggested that intracellular Hyal-1 (hyaluronidase-1), which is considered a lysosomal enzyme, originates via endocytosis of the serum enzyme. To test this proposal we have investigated the uptake and intracellular distribution of rhHyal-1 (recombinant human Hyal-1) by mouse liver, making use of centrifugation methods. Experiments were performed on wild-type mice injected with 125I-labelled rhHyal-1 and on Hyal-1−/− mice injected with the unlabelled enzyme, which were killed at various times after injection. Activity of the unlabelled enzyme was determined by zymography. Intracellular distribution of Hyal-1 was investigated by differential and isopycnic centrifugation. The results of the study indicated that rhHyal-1 is endocytosed by the liver, mainly by sinusoidal cells, and follows the intracellular pathway described for many endocytosed proteins that are eventually located in lysosomes. However, Hyal-1 endocytosis has some particular features. First, endocytosed rhHyal-1 is quickly degraded. Secondly, its distribution, as analysed by differential centrifugation, differs from the distribution of β-galactosidase, taken as the reference lysosomal enzyme. Further analysis by isopycnic centrifugation in a sucrose gradient shows endocytosed rhHyal-1 behaves like β-galactosidase shortly after injection. However the Hyal-1 distribution is markedly less affected than β-galactosidase, following a prior injection of Triton WR-1339, which is a specific density perturbant of lysosomes. The behaviour in centrifugation of endogenous liver Hyal-1, identified by hyaluronan zymography, exhibits some similarity with the behaviour of the endocytosed enzyme, suggesting that it could originate from endocytosis of the serum enzyme. Overall, these results can be explained by supposing that active endocytosed Hyal-1 is mainly present in early lysosomes. Although its degradation half-time is short, Hyal-1 could exert its activity due to a constant supply of active molecules from the blood.

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26

Maxfield, Frederick R. "Characterization of endocytosis in intact cells by quantitative fluorescence microscopy". Proceedings, annual meeting, Electron Microscopy Society of America 49 (agosto de 1991): 234–35. http://dx.doi.org/10.1017/s0424820100085472.

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Endocytosis, the process by which extracellular macromolecules are taken into the cell is particularly amenable to quantitative analysis using fluorescence techniques. Fluorescently-labeled proteins and other macromolecules are taken up by cells via receptor-mediated endocytosis or fluid phase pinocytosis. Recently, fluorescent lipid probes have also been synthesized which label the endocytic pathway, allowing observation of lipid membrane traffic.Digital imaging allows the manipulation of images, background and autofluorescence subtractions, and fluorescence intensity measurements of individual endocytic compartments. Image intensification microscopy and digital image processing have been used extensively for studies of endocytosis, including the measurements of endosome pH, and the identification and quantitation of endocytic vesicle fusion. Recently, pathways taken by endocytosed fluorescent molecules have been followed using the confocal microscope, adding a powerful tool to investigate questions about endocytosis which were very difficult to study with conventional, full-field microscopy techniques.

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27

Subtil, A., A. Hemar y A. Dautry-Varsat. "Rapid endocytosis of interleukin 2 receptors when clathrin-coated pit endocytosis is inhibited". Journal of Cell Science 107, n.º 12 (1 de diciembre de 1994): 3461–68. http://dx.doi.org/10.1242/jcs.107.12.3461.

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The cytokine interleukin 2 (IL2) is produced by activated helper T lymphocytes and modulates the growth and activity of cells expressing high-affinity surface IL2 receptors that transduce its signaling. After ligand binding to receptors on the plasma membrane, receptor-ligand complexes are rapidly endocytosed and IL2 is degraded in acidic compartments. The best known receptor-mediated endocytosis pathway involves clathrin-coated pits. Receptors that carry an internalization signal recognized by adaptors on the cytosolic side of the plasma membrane are clustered into the coated pits and enter cells very efficiently. Many receptors use this pathway, but other endocytic pathways have also been reported, for ricin, EGF and insulin, for instance, which seem to be less efficient than the coated one. We compared the endocytosis of IL2 and its receptors to that of transferrin, a marker of the coated pit pathway. Under normal conditions, the kinetics of entry of IL2 was two times slower than that of transferrin. When internalization via coated pits was inhibited by two different methods, potassium depletion and cytosol acidification, endocytosis of IL2 and its receptors was only partly inhibited, while transferrin entry was strongly affected. Treatment with the cationic amphiphilic drug chlorpromazine, which induces a redistribution of a clathrin-coated pit component, AP-2, to endosomes, reduced transferrin, but not IL2 internalization. Thus, unexpectedly, this cytokine and its receptors can still be rapidly endocytosed in the absence of functional clathrin-coated structures. We propose a model for receptor-mediated endocytosis that may account for these results and published data on other receptors.

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28

Hatakeyama, Riko, Masao Kamiya, Terunao Takahara y Tatsuya Maeda. "Endocytosis of the Aspartic Acid/Glutamic Acid Transporter Dip5 Is Triggered by Substrate-Dependent Recruitment of the Rsp5 Ubiquitin Ligase via the Arrestin-Like Protein Aly2". Molecular and Cellular Biology 30, n.º 24 (18 de octubre de 2010): 5598–607. http://dx.doi.org/10.1128/mcb.00464-10.

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ABSTRACT Endocytosis of nutrient transporters is stimulated under various conditions, such as elevated nutrient availability. In Saccharomyces cerevisiae, endocytosis is triggered by ubiquitination of transporters catalyzed by the E3 ubiquitin ligase Rsp5. However, how the ubiquitination is accelerated under certain conditions remains obscure. Here we demonstrate that closely related proteins Aly2/Art3 and Aly1/Art6, which are poorly characterized members of the arrestin-like protein family, mediate endocytosis of the aspartic acid/glutamic acid transporter Dip5. In aly2Δ cells, Dip5 is stabilized at the plasma membrane and is not endocytosed efficiently. Efficient ubiquitination of Dip5 is dependent on Aly2. aly1Δ cells also show deficiency in Dip5 endocytosis, although less remarkably than aly2Δ cells. Aly2 physically interacts in vivo with Rsp5 at its PY motif and also with Dip5, thus serving as an adaptor linking Rsp5 with Dip5 to achieve Dip5 ubiquitination. Importantly, the interaction between Aly2 and Dip5 is accelerated in response to elevated aspartic acid availability. This result indicates that the regulation of Dip5 endocytosis is accomplished by dynamic recruitment of Rsp5 via Aly2.

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29

Emma, F., H. W. Harris y K. Strange. "Acidification of vasopressin-induced endosomes in toad urinary bladder". American Journal of Physiology-Renal Physiology 267, n.º 1 (1 de julio de 1994): F106—F113. http://dx.doi.org/10.1152/ajprenal.1994.267.1.f106.

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It is well established that water channels (WC) are removed from the apical membrane of vasopressin-sensitive epithelia by endocytosis. The processing and the ultimate fate of endocytosed WC is, however, incompletely understood. In many cells, endosome acidification plays an important role in the processing and sorting of endocytosed proteins. Endosome acidification in the toad urinary bladder was therefore examined in vivo by fluorescence ratio video microscopy after induction of endocytosis by vasopressin removal and transepithelial water flow in the presence of the pH-sensitive fluid phase marker 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein-dextran. Fifteen minutes after induction of endocytosis, the majority of endosomes had a neutral or slightly acidic pH. The number of acidic endosomes increased progressively with time. Two hours after endocytosis began, 98% of the endosomes had a pH < 6.0. Bafilomycin completely blocked endosome acidification, indicating that H+ transport is mediated by a vacuolar H(+)-adenosinetriphosphatase. Bafilomycin had no effect on transepithelial water flow in bladders repetitively stimulated by vasopressin. These findings, as well as the work of other investigators, suggest that if WC recycling occurs, it is not dependent on acidification of the endosomal compartment. Acidification of vasopressin-induced endosomes most likely represents a terminal event in the endocytic pathway.

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30

Uhlin-Hansen, L. y M. Yanagishita. "Brefeldin A inhibits the endocytosis of plasma-membrane-associated heparan sulphate proteoglycans of cultured rat ovarian granulosa cells". Biochemical Journal 310, n.º 1 (15 de agosto de 1995): 271–78. http://dx.doi.org/10.1042/bj3100271.

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Rat ovarian granulosa cells were labelled with [35S]sulphate for 0.5-20 h and chased in the presence or absence of 1-2 micrograms/ml of brefeldin A (BFA) for up to 21 h. Heparan [35S]sulphate (HS) proteoglycans from the culture medium, plasma membrane and intracellular fractions were then analysed by gel chromatography. In the absence of BFA, about 85% of the plasma membrane-associated HS proteoglycans were endocytosed and subsequently degraded intracellularly. Recirculation of the HS proteoglycans between the intracellular pool and the cell surface was not observed. Exposing the cells to BFA for less than 1 h did not influence the turnover of the HS proteoglycans, whereas the effect of the drug on the Golgi functions reached a maximum in approx. 10 min. When the cells were treated with BFA for more than 1-2 h, the rate of endocytosis of HS proteoglycans was reduced to about 50% of the control. The delivery of endocytosed HS proteoglycans to lysosomes were not affected by the drug. Cycloheximide also reduced the endocytosis of HS proteoglycans, but not as much as BFA, indicating that the inhibitory effect of BFA can be only partly accounted for by a block of protein transport from the endoplasmic reticulum to the plasma membrane. In contrast with the endocytosis of HS proteoglycans, neither that of 125I-transferrin, known to be mediated by clathrin-coated vesicles, nor that of 125I-ricin, a marker molecule for bulk endocytosis, was affected by BFA. The half-life of 125I-transferrin and 125I-ricin in the plasma membrane was about 10 and 25 min respectively compared with about 5 h for the HS proteoglycans. Altogether, these results indicate that the endocytosis of plasma-membrane-associated HS proteoglycans is mediated by different mechanisms than the endocytosis of most other cell-surface proteins. Further, the mechanisms involved in the endocytosis of HS proteoglycans are sensitive to BFA.

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31

Handagama, PJ, DL Amrani y MA Shuman. "Endocytosis of fibrinogen into hamster megakaryocyte alpha granules is dependent on a dimeric gamma A configuration". Blood 85, n.º 7 (1 de abril de 1995): 1790–95. http://dx.doi.org/10.1182/blood.v85.7.1790.bloodjournal8571790.

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Two species of fibrinogen that differ only in the structure of their gamma chains, gamma A and gamma', are present in normal plasma. Fibrinogen stored in platelet alpha granules does not contain gamma' chains. Because platelet fibrinogen was recently shown to be derived exclusively by receptor-mediated endocytosis from plasma and not by endogenous megakaryocyte synthesis, we postulated that the gamma' fibrinogen present in plasma is not endocytosed by megakaryocytes and platelets. We tested this hypothesis by studying endocytosis of peak 1 (containing two gamma A chains) and peak 2 (containing one gamma A and one gamma' chain) fractions of human fibrinogen obtained from diethyl aminoethyl (DEAE) cellulose chromatography in an in vivo hamster model. When 10 mg of biotinylated, unfractionated, or peak 1 fibrinogen was injected intravenously, each protein was endocytosed into megakaryocytes and platelets within 24 hours. In contrast, equivalent doses of biotinylated peak 2 fibrinogen and bovine serum albumin were barely detectable within megakaryocytes and platelets. We conclude that gamma' fibrinogen is not endocytosed and incorporated into megakaryocytes and platelet alpha granules. Furthermore, a dimeric gamma A-chain configuration is required for receptor-mediated endocytosis of fibrinogen into these organelles.

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32

Schwake, Michael, Thomas Friedrich y Thomas J. Jentsch. "An Internalization Signal in ClC-5, an Endosomal Cl−Channel Mutated in Dent's Disease". Journal of Biological Chemistry 276, n.º 15 (14 de diciembre de 2000): 12049–54. http://dx.doi.org/10.1074/jbc.m010642200.

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The ClC-5 chloride channel resides mainly in vesicles of the endocytotic pathway and contributes to their acidification. Its disruption in mice entails a broad defect in renal endocytosis and causes secondary changes in calciotropic hormone levels. Inactivating mutations in Dent's disease lead to proteinuria and kidney stones. Possibly by recycling, a small fraction of ClC-5 also reaches the plasma membrane. Here we identify a carboxyl-terminal internalization motif in ClC-5. It resembles the PY motif, which is crucial for the endocytosis and degradation of epithelial Na+channels. Mutating this motif increases surface expression and currents about 2-fold. This is probably because of interactions with WW domains, because dominant negative mutants of the ubiquitin-protein ligase WWP2 increased surface expression and currents of ClC-5 only when its PY motif was intact. Stimulating endocytosis by expressing rab5 or its GTPase-deficient Q79L mutant decreased WT ClC-5 currents but did not affect channels with mutated motifs. Similarly, decreasing endocytosis by expressing the inactive S34N mutant of rab5 increased ClC-5 currents only if its PY-like motif was intact. Thus, the endocytosis of ClC-5, which itself is crucial for the endocytosis of other proteins, depends on the interaction of a carboxyl-terminal internalization signal with ubiquitin-protein ligases containing WW domains.

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33

Stephens, Richard S., Farah S. Fawaz, Kathleen A. Kennedy, Kelly Koshiyama, Barbara Nichols, Christiaan van Ooij y Joanne N. Engel. "Eukaryotic Cell Uptake of Heparin-Coated Microspheres: a Model of Host Cell Invasion by Chlamydia trachomatis". Infection and Immunity 68, n.º 3 (1 de marzo de 2000): 1080–85. http://dx.doi.org/10.1128/iai.68.3.1080-1085.2000.

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ABSTRACT Using polystyrene microspheres coated with heparin or heparan sulfate, it was shown that coated microspheres specifically bound eukaryotic cells and were endocytosed by nonprofessional phagocytic cells. Coated microspheres displayed properties of binding to eukaryotic cells that were similar to those of chlamydiae, and the microspheres were competitively inhibited by chlamydial organisms. Endocytosis of heparin-coated beads resulted in the tyrosine phosphorylation of a similar set of host proteins as did endocytosis of chlamydiae; however, unlike viable chlamydial organisms, which prevent phagolysosomal fusion, endocytosed beads were trafficked to a lysosomal compartment. These findings suggest that heparin-coated beads andChlamydia trachomatis enter eukaryotic cells by similar pathways.

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34

Xinhan, Lou, Masafumi Matsushita, Manami Numaza, Akira Taguchi, Keiji Mitsui y Hiroshi Kanazawa. "Na+/H+ exchanger isoform 6 (NHE6/SLC9A6) is involved in clathrin-dependent endocytosis of transferrin". American Journal of Physiology-Cell Physiology 301, n.º 6 (diciembre de 2011): C1431—C1444. http://dx.doi.org/10.1152/ajpcell.00154.2011.

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In mammalian cells, nine conserved isoforms of the Na+/H+ exchanger (NHE) are known to be important for pH regulation of the cytoplasm and organellar lumens. NHE1–5 are localized to the plasma membrane, whereas NHE6–9 are localized to distinct organelles. NHE6 is localized predominantly in endosomal compartments but is also found in the plasma membrane. To investigate the role of NHE6 in endocytosis, we established NHE6-knockdown HeLa cells and analyzed the effect of this knockdown on endocytotic events. The expression level of NHE6 in knockdown cells was decreased to ∼15% of the level seen in control cells. Uptake of transferrin was also decreased. No effect was found on the endocytosis of epidermal growth factor or on the cholera toxin B subunit. Moreover, in the NHE6-knockdown cells, transferrin uptake was found to be affected in the early stages of endocytosis. Microscopic analysis revealed that, at 2 min after the onset of endocytosis, colocalization of NHE6, clathrin, and transferrin was observed, which suggests that NHE6 was localized to endocytotic, clathrin-coated vesicles. In addition, in knockdown cells, transferrin-positive endosomes were acidified, but no effect was found on cytoplasmic pH. In cells overexpressing wild-type NHE6, increased transferrin uptake was observed, but no such increase was seen in cells overexpressing mutant NHE6 deficient in ion transport. The luminal pH in transferrin-positive endosomes was alkalized in cells overexpressing wild-type NHE6 but normal in cells overexpressing mutant NHE6. These observations suggest that NHE6 regulates clathrin-dependent endocytosis of transferrin via pH regulation.

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35

Beauwens, R., G. te Kronnie, J. Snauwaert y P. A. in't Veld. "Polycations reduce vasopressin-induced water flow by endocytic removal of water channels". American Journal of Physiology-Cell Physiology 250, n.º 5 (1 de mayo de 1986): C729—C737. http://dx.doi.org/10.1152/ajpcell.1986.250.5.c729.

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Several polycations added to the luminal solution were found to inhibit the vasopressin (ADH)-induced water flow in toad urinary bladder but not the ADH-induced increase in sodium transport or in urea permeability. Ultrastructural studies were conducted to evaluate the uptake of cationized ferritin. It was found that endocytosis of cationized ferritin by luminal cells was strikingly enhanced on exposure to ADH; this increased endocytosis was concomitant with inhibition of transepithelial ADH-induced water flow. Various maneuvers preventing endocytosis were also found to counteract the polycation-induced inhibition of the ADH effect. It is suggested that polycations are endocytosed in vesicles whose walls contain the water channels but not the urea or sodium channels.

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36

McGary, C. T., R. H. Raja y P. H. Weigel. "Endocytosis of hyaluronic acid by rat liver endothelial cells. Evidence for receptor recycling". Biochemical Journal 257, n.º 3 (1 de febrero de 1989): 875–84. http://dx.doi.org/10.1042/bj2570875.

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Hyaluronic acid (HA) is cleared from the blood by liver endothelial cells through receptor-mediated endocytosis [Eriksson, Fraser, Laurent, Pertoft & Smedsrod (1983) Exp. Cell Res. 144, 223-238]. We have measured the capacity of cultured rat liver endothelial cells to endocytose and degrade 125I-HA (Mr approximately 44,000) at 37 degrees C. Endocytosis was linear for 3 h and then reached a plateau. The rate of endocytosis was concentration-dependent and reached a maximum of 250 molecules/s per cell. Endocytosis of 125I-HA was inhibited more than 92% by a 150-fold excess of non-radiolabelled HA. HA, chondroitin sulphate and heparin effectively competed for endocytosis of 125I-HA, whereas glucuronic acid, N-acetylglucosamine, DNA, RNA, polygalacturonic acid and dextran did not compete. In the absence of cycloheximide, endothelial cells processed 13 times more 125I-HA in 6 h than their total (cell-surface and intracellular) specific HA-binding capacity. This result was not due to degradation and rapid replacement of receptors, because, even in the presence of cycloheximide, these cells processed 6 times more HA than their total receptor content in 6 h. Also, in the presence of cycloheximide, no decrease in 125I-HA-binding capacity was seen in cells processing or not processing HA for 6 h, indicating that receptors are not degraded after the endocytosis of HA. During endocytosis of HA at 37 degrees C, at least 65% of the intracellular HA receptors became occupied with HA within 30 min. This indicates that the intracellular HA receptors (75% of the total) function during continuous endocytosis. Hyperosmolarity inhibits endocytosis and receptor recycling in the asialoglycoprotein and low-density-lipoprotein receptor systems by disrupting the coated-pit pathway [Heuser & Anderson (1987) J. Cell Biol. 105, 230a; Oka & Weigel (1988) J. Cell. Biochem. 36, 169-183]. Hyperosmolarity inhibited 125I-HA endocytosis in liver endothelial cells by more than 90%, suggesting use of a coated-pit pathway by this HA receptor. We conclude that liver endothelial cell HA receptors are recycled during the continuous endocytosis and processing of HA.

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37

Koller-Peroutka, Marianne, Stefanie Krammer, Anselm Pavlik, Manfred Edlinger, Ingeborg Lang y Wolfram Adlassnig. "Endocytosis and Digestion in Carnivorous Pitcher Plants of the Family Sarraceniaceae". Plants 8, n.º 10 (24 de septiembre de 2019): 367. http://dx.doi.org/10.3390/plants8100367.

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Highly evolved carnivorous plants secrete digestive enzymes for degradation of trapped animals and absorb whole macromolecules from their prey by means of endocytosis. (1) Background: In the pitcher-plant family Sarraceniaceae, the production of enzymes is dubious and no evidence for endocytosis is known so far. (2) Methods: Heliamphora nutans, Darlingtonia californica, and nine taxa of Sarracenia are tested for cuticular pores, and for protease and endocytosis of the fluorescent protein analogue FITC-BSA, after 10–48 h of stimulation. (3) Results: Cuticular pores as a prerequisite for enzyme secretion and nutrient uptake are present in all tested species. Permeable cells form clusters in the inner epidermis of the pitchers, but are only little differentiated from impermeable epidermis cells. Proteases are found in S. psittacina, S. leucophylla, S. minor, S. oreophila, S. alabamensis, H. nutans, D. californica lacking only in S. flava and in S. purpurea ssp. purpurea, S. purpurea ssp. venosa, S. rosea, where enzyme production is possibly replaced by degradation via the extraordinary diverse inquiline fauna. S. leucophylla, S. minor, S. oreophila exhibit both protease production and endocytosis; S. psittacina, S. alabamensis, H. nutans, D. californica produce proteases only; no single species shows endocytosis without protease production. (4) Conclusions: Protease secretion seems to be a prerequisite for endocytotic nutrient uptake. Transport of FITC-BSA absorbed by endocytosis towards the vascular tissue of the trap leaves suggests that endocytosis of nutrients is more than a side effect of enzyme secretion.

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38

Gekle, M., S. Mildenberger, R. Freudinger y S. Silbernagl. "Endosomal alkalinization reduces Jmax and Km of albumin receptor-mediated endocytosis in OK cells". American Journal of Physiology-Renal Physiology 268, n.º 5 (1 de mayo de 1995): F899—F906. http://dx.doi.org/10.1152/ajprenal.1995.268.5.f899.

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In this study, we investigated the effects of endosomal alkalinization on kinetics of endocytotic uptake in intact proximal tubule-derived opossum kidney cells. We used fluorescein isothiocyanate (FITC)-labeled albumin and FITC-dextran as endocytotic substrates for receptor-mediated endocytosis and fluid-phase endocytosis, respectively. The pH in endosomes labeled with either FITC-albumin or FITC-dextran rose in the presence of the vacuolar-type ATPase inhibitor, bafilomycin A1, and in the presence of NH4Cl. Cytoplasmic pH, decreased in the presence of bafilomycin A1, but was not significantly different from control during prolonged exposure of the cells to NH4Cl. Endocytotic uptake of FITC-dextran was not affected by endosomal pH changes. Endocytotic uptake of FITC-albumin was reduced markedly by bafilomycin A1 (decrease of maximum transport rate and apparent affinity). Selective alkalinization of endosomes using NH4Cl (i.e., with the cytoplasmic pH not different from control) reduced FITC-albumin uptake in a similar way but to a lesser extent than did bafilomycin A1. Intracellular albumin degradation was impaired by bafilomycin A1 and NH4Cl. Prevention of endosome-lysosome fusion (lowering the temperature to 20 degrees C) abolished the effects of endosomal alkalinization. Furthermore, specific binding of albumin to the plasma membrane was reduced after incubation with bafilomycin A1, indicating an impairment of receptor recycling. These data show that endosomal pH is an important determinant for the kinetics of receptor-mediated endocytotic uptake of albumin in the proximal tubule but not for fluid-phase endocytosis. Endosomal alkalinization disturbs intracellular ligand handling and receptor trafficking, leading to a reduction of endocytotic capacity and affinity.

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39

Céfaï, Daniel, Helga Schneider, Oranart Matangkasombut, Hyun Kang, Joshua Brody y Christopher E. Rudd. "CD28 Receptor Endocytosis Is Targeted by Mutations That Disrupt Phosphatidylinositol 3-Kinase Binding and Costimulation". Journal of Immunology 160, n.º 5 (1 de marzo de 1998): 2223–30. http://dx.doi.org/10.4049/jimmunol.160.5.2223.

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Abstract Although the lipid kinase phosphatidylinositol 3-kinase (PI-3K) binds at high levels to the cytoplasmic tail of CD28, controversy exists regarding its role in CD28 costimulation. Potentially, the kinase could be linked to a signaling cascade or be needed indirectly in events such as receptor endocytosis. Indeed, little is known regarding both the fate of CD28 following receptor ligation and the events that control the process. In this study, we help to resolve this issue by providing evidence that PI-3K plays a role in regulating CD28 endocytosis. We show that ∼25 to 35% of wild-type CD28 becomes endocytosed following Ab binding (t1/2 = 10 min), followed by segregation into two pools; one pool is destined for degradation in lysosomal compartments and is blocked by chloroquine, and another pool that is recycled to the cell surface (t1/2 = 2.5 h). Recycling of CD28 could have an important impact on CD80/86-mediated costimulation by replenishing functionally active receptors on the cell surface. Several findings implicate PI-3K in the control of endocytosis. Modulation experiments indicate that CD28-PI-3K complexes are preferentially endocytosed, and mutations that alter PI-3K binding concordantly affect the efficacy of endocytosis. Importantly, mutations that inhibit receptor internalization also block cosignaling. Therefore, previous results documenting a requirement for PI-3K may be explained by a blockage of receptor internalization.

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40

DEAN, ROGER T. "Endocytosis". Biochemical Society Transactions 14, n.º 2 (1 de abril de 1986): 512. http://dx.doi.org/10.1042/bst0140512.

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41

Traub, Linton M. "Endocytosis". Cell 107, n.º 3 (noviembre de 2001): 272–74. http://dx.doi.org/10.1016/s0092-8674(01)00554-2.

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42

Hurley, James H. y Beverly Wendland. "Endocytosis". Cell 111, n.º 2 (octubre de 2002): 143–46. http://dx.doi.org/10.1016/s0092-8674(02)01044-9.

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43

Walker, J. H. "Endocytosis". Biochemical Education 14, n.º 4 (octubre de 1986): 198. http://dx.doi.org/10.1016/0307-4412(86)90236-0.

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44

Hubbard, A. L. "Endocytosis". Current Opinion in Cell Biology 1, n.º 4 (agosto de 1989): 675–83. http://dx.doi.org/10.1016/0955-0674(89)90033-1.

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45

Mukherjee, S., R. N. Ghosh y F. R. Maxfield. "Endocytosis". Physiological Reviews 77, n.º 3 (1 de julio de 1997): 759–803. http://dx.doi.org/10.1152/physrev.1997.77.3.759.

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Mammalian cells take up extracellular material by a variety of different mechanisms that are collectively termed endocytosis. Endocytic mechanisms serve many important cellular functions including the uptake of extracellular nutrients, regulation of cell-surface receptor expression, maintenance of cell polarity, and antigen presentation. Endocytic pathways are also utilized by viruses, toxins, and symbiotic microorganisms to gain entry into cells. One of the best-characterized endocytic mechanisms is receptor-mediated endocytosis via clathrin-coated pits. This type of endocytosis constitutes the major emphasis of this review, with a brief discussion of other endocytic mechanisms and their comparison with the receptor-mediated pathway. This review describes and evaluates critically current understanding of the mechanisms of entry of plasma membrane components such as the receptor-ligand complexes and membrane lipids as well as the extracellular fluid into cells. The intracellular sorting and trafficking of these molecules upon internalization are also described. The roles of endocytosis in physiological and pathological processes are discussed. These include maintenance of cell polarization, antigen presentation, glucose transport, atherosclerosis, Alzheimer's disease, and the endocytosis of toxins and viruses.

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46

Boyle, John A. "Endocytosis". Biochemistry and Molecular Biology Education 30, n.º 2 (marzo de 2002): 139. http://dx.doi.org/10.1002/bmb.2002.494030020025.

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47

Shi, Yuanyuan, Chen Wang, Xiaoshuang Zhou, Yafeng Li, Yuehong Ma, Rui Zhang y Rongshan Li. "Downregulation of PTEN promotes podocyte endocytosis of lipids aggravating obesity-related glomerulopathy". American Journal of Physiology-Renal Physiology 318, n.º 3 (1 de marzo de 2020): F589—F599. http://dx.doi.org/10.1152/ajprenal.00392.2019.

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With the increasing prevalence of obesity in adults worldwide, the incidence of obesity-related glomerulopathy (ORG) has increased yearly, becoming one of the leading causes of end-stage renal disease. Studies have demonstrated significant correlations between hyperlipidemia and impaired renal function in patients with ORG, indicating that hyperlipidemia causes damage in kidney cells. In podocytes, the endocytosis of lipids triggers an intracellular oxidative stress response that disrupts cellular integrity, resulting in proteinuria and glomerular sclerosis. However, the specific molecular mechanisms through which podocytes endocytose lipids remain unclear. Here, we demonstrated the enhanced endocytosis of lipids by podocytes from patients with ORG. This response was associated with decreased expression of phosphatase and tensin homolog (PTEN). In vitro silencing of PTEN promoted the endocytosis of low-density lipoprotein in mouse podocytes. Conversely, overexpression of PTEN inhibited the endocytosis of lipoproteins in podocytes. PTEN directly dephosphorylates and activates the actin-depolymerizing factor cofilin-1, leading to depolymerization of filamentous actin (F-actin), which is necessary for endocytosis. Notably, inhibition of PTEN resulted in the phosphorylation and inactivation of cofilin-1, leading to F-actin formation that enhanced the endocytosis of lipoproteins in podocytes. When hyperlipidemia was induced in mice with podocyte-specific deletion of PTEN, these mice recapitulated the major pathophysiological features of ORG. Thus, PTEN downregulation in podocytes may contribute to the pathogenesis of ORG.

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48

Lowther, Katie M., Viacheslav O. Nikolaev y Lisa M. Mehlmann. "Endocytosis in the mouse oocyte and its contribution to cAMP signaling during meiotic arrest". REPRODUCTION 141, n.º 6 (junio de 2011): 737–47. http://dx.doi.org/10.1530/rep-10-0461.

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Mammalian oocytes are arrested at prophase I of meiosis until a preovulatory surge of LH stimulates them to resume meiosis. Prior to the LH surge, high levels of cAMP within the oocyte maintain meiotic arrest; this cAMP is generated in the oocyte through the activity of the constitutively active, Gs-coupled receptor, G-protein-coupled receptor 3 (GPR3) or GPR12. Activated GPRs are typically targeted for desensitization through receptor-mediated endocytosis, but a continuously high level of cAMP is needed for meiotic arrest. The aim of this study was to examine whether receptor-mediated endocytosis occurs in the mouse oocyte and whether this could affect the maintenance of meiotic arrest. We found that constitutive endocytosis occurs in the mouse oocyte. Inhibitors of receptor-mediated endocytosis, monodansylcadaverine and dynasore, inhibited the formation of early endosomes and completely inhibited spontaneous meiotic resumption. A red fluorescent protein-tagged GPR3 localized in the plasma membrane and within early endosomes in the oocyte, demonstrating that GPR3 is endocytosed. However, overexpression of G-protein receptor kinase 2 and β-arrestin-2 had only a modest effect on stimulating meiotic resumption, suggesting that these proteins do not play a major role in GPR3 endocytosis. Inhibition of endocytosis elevated cAMP levels within oocytes, suggesting that there is an accumulation of GPR3 at the plasma membrane. These results show that endocytosis occurs in the oocyte, leading to a decrease in cAMP production, and suggest that there is a balance between cAMP production and degradation in the arrested oocyte that maintains cAMP levels at an appropriate level during the maintenance of meiotic arrest.

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49

Mc Dermott, Ray, Umit Ziylan, Danièle Spehner, Huguette Bausinger, Dan Lipsker, Mieke Mommaas, Jean-Pierre Cazenave et al. "Birbeck Granules Are Subdomains of Endosomal Recycling Compartment in Human Epidermal Langerhans Cells, Which Form Where Langerin Accumulates". Molecular Biology of the Cell 13, n.º 1 (enero de 2002): 317–35. http://dx.doi.org/10.1091/mbc.01-06-0300.

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Birbeck granules are unusual rod-shaped structures specific to epidermal Langerhans cells, whose origin and function remain undetermined. We investigated the intracellular location and fate of Langerin, a protein implicated in Birbeck granule biogenesis, in human epidermal Langerhans cells. In the steady state, Langerin is predominantly found in the endosomal recycling compartment and in Birbeck granules. Langerin internalizes by classical receptor-mediated endocytosis and the first Birbeck granules accessible to endocytosed Langerin are those connected to recycling endosomes in the pericentriolar area, where Langerin accumulates. Drug-induced inhibition of endocytosis results in the appearance of abundant open-ended Birbeck granule-like structures appended to the plasma membrane, whereas inhibition of recycling induces Birbeck granules to merge with a tubular endosomal network. In mature Langerhans cells, Langerin traffic is abolished and the loss of internal Langerin is associated with a concomitant depletion of Birbeck granules. Our results demonstrate an exchange of Langerin between early endosomal compartments and the plasma membrane, with dynamic retention in the endosomal recycling compartment. They show that Birbeck granules are not endocytotic structures, rather they are subdomains of the endosomal recycling compartment that form where Langerin accumulates. Finally, our results implicate ADP-ribosylation factor proteins in Langerin trafficking and the exchange between Birbeck granules and other endosomal membranes.

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50

Becuwe, Michel, Neide Vieira, David Lara, Jéssica Gomes-Rezende, Carina Soares-Cunha, Margarida Casal, Rosine Haguenauer-Tsapis, Olivier Vincent, Sandra Paiva y Sébastien Léon. "A molecular switch on an arrestin-like protein relays glucose signaling to transporter endocytosis". Journal of Cell Biology 196, n.º 2 (16 de enero de 2012): 247–59. http://dx.doi.org/10.1083/jcb.201109113.

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Endocytosis regulates the plasma membrane protein landscape in response to environmental cues. In yeast, the endocytosis of transporters depends on their ubiquitylation by the Nedd4-like ubiquitin ligase Rsp5, but how extracellular signals trigger this ubiquitylation is unknown. Various carbon source transporters are known to be ubiquitylated and endocytosed when glucose-starved cells are exposed to glucose. We show that this required the conserved arrestin-related protein Rod1/Art4, which was activated in response to glucose addition. Indeed, Rod1 was a direct target of the glucose signaling pathway composed of the AMPK homologue Snf1 and the PP1 phosphatase Glc7/Reg1. Glucose promoted Rod1 dephosphorylation and its subsequent release from a phospho-dependent interaction with 14-3-3 proteins. Consequently, this allowed Rod1 ubiquitylation by Rsp5, which was a prerequisite for transporter endocytosis. This paper therefore demonstrates that the arrestin-related protein Rod1 relays glucose signaling to transporter endocytosis and provides the first molecular insights into the nutrient-induced activation of an arrestin-related protein through a switch in post-translational modifications.

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