Journal articles: 'Intracellular lipid-binding protein'

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Soffientini, Ugo, and Annette Graham. "Intracellular cholesterol transport proteins: roles in health and disease." Clinical Science 130, no. 21 (September 22, 2016): 1843–59. http://dx.doi.org/10.1042/cs20160339.

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Effective cholesterol homoeostasis is essential in maintaining cellular function, and this is achieved by a network of lipid-responsive nuclear transcription factors, and enzymes, receptors and transporters subject to post-transcriptional and post-translational regulation, whereas loss of these elegant, tightly regulated homoeostatic responses is integral to disease pathologies. Recent data suggest that sterol-binding sensors, exchangers and transporters contribute to regulation of cellular cholesterol homoeostasis and that genetic overexpression or deletion, or mutations, in a number of these proteins are linked with diseases, including atherosclerosis, dyslipidaemia, diabetes, congenital lipoid adrenal hyperplasia, cancer, autosomal dominant hearing loss and male infertility. This review focuses on current evidence exploring the function of members of the ‘START’ (steroidogenic acute regulatory protein-related lipid transfer) and ‘ORP’ (oxysterol-binding protein-related proteins) families of sterol-binding proteins in sterol homoeostasis in eukaryotic cells, and the evidence that they represent valid therapeutic targets to alleviate human disease.

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Voelker, Dennis R. "Genetic analysis of intracellular aminoglycerophospholipid traffic." Biochemistry and Cell Biology 82, no. 1 (February 1, 2004): 156–69. http://dx.doi.org/10.1139/o03-075.

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Inter- and intramembrane phospholipid transport processes are central features of membrane biogenesis and homeostasis. Relatively recent successes in the molecular genetic analysis of aminoglycerophospholipid transport processes in both yeast and mammalian cells are now providing important new information defining specific protein and lipid components that participate in these reactions. Studies focused on phosphatidylserine (PtdSer) transport to the mitochondria reveal that the process is regulated by ubiquitination. In addition, a specific mutation disrupts PtdSer transport between mitochondrial membranes. Analysis of PtdSer transport from the endoplasmic reticulum to the locus of PtdSer decarboxylase 2 demonstrates the requirement for a phosphatidylinositol-4-kinase, a phosphatidylinositol-binding protein, and the C2 domain of the decarboxylase. Examination of NBD-phosphatidylcholine transport demonstrates the involvement of the prevacuolar compartment and a requirement for multiple genes involved in regulating vacuolar protein sorting for transport of the lipid to the vacuole. In intramembrane transport, multiple genes are now identified including those encoding multidrug resistant protein family members, DNF family members, ATP binding cassette transporters, and pleiotropic drug resistance family members. The scramblase family constitutes a collection of putative transmembrane transporters that function in an ATP-independent manner. The genetic analysis of lipid traffic is uncovering new molecules involved in all aspects of the regulation and execution of the transport steps and also providing essential tools to critically test the involvement of numerous candidate molecules.Key words: lipid transport, lipid sorting, membrane biogenesis, organelles, flippase.

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Voilquin, Laetitia, Massimo Lodi, Thomas Di Mattia, Marie-Pierre Chenard, Carole Mathelin, Fabien Alpy, and Catherine Tomasetto. "STARD3: A Swiss Army Knife for Intracellular Cholesterol Transport." Contact 2 (January 2019): 251525641985673. http://dx.doi.org/10.1177/2515256419856730.

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Intracellular cholesterol transport is a complex process involving specific carrier proteins. Cholesterol-binding proteins, such as the lipid transfer protein steroidogenic acute regulatory-related lipid transfer domain-3 (STARD3), are implicated in cholesterol movements between organelles. Indeed, STARD3 modulates intracellular cholesterol allocation by reducing it from the plasma membrane and favoring its passage from the endoplasmic reticulum (ER) to endosomes, where the protein is localized. STARD3 interacts with ER-anchored partners, notably vesicle-associated membrane protein-associated proteins (VAP-A and VAP-B) and motile sperm domain-containing 2 (MOSPD2), to create ER–endosome membrane contacts. Mechanistic studies showed that at ER–endosome contacts, STARD3 and VAP proteins build a molecular machine able to rapidly transfer cholesterol. This review presents the current knowledge on the molecular and cellular function of STARD3 in intracellular cholesterol traffic.

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Matsumura, Yoshihiro, Nobuhiro Ban, and Nobuya Inagaki. "Aberrant catalytic cycle and impaired lipid transport into intracellular vesicles in ABCA3 mutants associated with nonfatal pediatric interstitial lung disease." American Journal of Physiology-Lung Cellular and Molecular Physiology 295, no. 4 (October 2008): L698—L707. http://dx.doi.org/10.1152/ajplung.90352.2008.

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The ATP-binding cassette transporter ABCA3 mediates uptake of choline-phospholipids into intracellular vesicles and is essential for surfactant metabolism in lung alveolar type II cells. We have shown previously that ABCA3 mutations in fatal surfactant deficiency impair intracellular localization or ATP hydrolysis of ABCA3 protein. However, the mechanisms underlying the less severe phenotype of patients with ABCA3 mutation are unclear. In this study, we characterized ABCA3 mutant proteins identified in pediatric interstitial lung disease (pILD). E292V (intracellular loop 1), E690K (adjacent to Walker B motif in nucleotide binding domain 1), and T1114M (8th putative transmembrane segment) mutant proteins are localized mainly in intracellular vesicle membranes as wild-type protein. Lipid analysis and sucrose gradient fractionation revealed that the transport function of E292V mutant protein is moderately preserved, whereas those of E690K and T1114M mutant proteins are severely impaired. Vanadate-induced nucleotide trapping and photoaffinity labeling of wild-type and mutant proteins using 8-azido-[32P]ATP revealed an aberrant catalytic cycle in these mutant proteins. These results demonstrate the importance of a functional catalytic cycle in lipid transport of ABCA3 and suggest a pathophysiological mechanism of pILD due to ABCA3 mutation.

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Lee, Hyo-Geun, Yu-An Lu, Jun-Geon Je, Thilina U. Jayawardena, Min-Cheol Kang, Seung-Hong Lee, Tae-Hee Kim, et al. "Effects of Ethanol Extracts from Grateloupia elliptica, a Red Seaweed, and Its Chlorophyll Derivative on 3T3-L1 Adipocytes: Suppression of Lipid Accumulation through Downregulation of Adipogenic Protein Expression." Marine Drugs 19, no. 2 (February 4, 2021): 91. http://dx.doi.org/10.3390/md19020091.

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Grateloupia elliptica (G. elliptica) is a red seaweed with antioxidant, antidiabetic, anticancer, anti-inflammatory, and anticoagulant activities. However, the anti-obesity activity of G. elliptica has not been fully investigated. Therefore, the effect of G. elliptica ethanol extract on the suppression of intracellular lipid accumulation in 3T3-L1 cells by Oil Red O staining (ORO) was evaluated. Among the eight red seaweeds tested, G. elliptica 60% ethanol extract (GEE) exhibited the highest inhibition of lipid accumulation. GEE was the only extract to successfully suppress lipid accumulation among ethanol extracts from eight red seaweeds. In this study, we successfully isolated chlorophyll derivative (CD) from the ethyl acetate fraction (EA) of GEE by high-performance liquid chromatography and evaluated their inhibitory effect on intracellular lipid accumulation in 3T3-L1 adipocytes. CD significantly suppressed intracellular lipid accumulation. In addition, CD suppressed adipogenic protein expression such as sterol regulatory element-binding protein-1 (SREBP-1), peroxisome proliferator-activated receptor-γ (PPAR-γ), CCAAT/enhancer-binding protein-α (C/EBP-α), and fatty acid binding protein 4 (FABP4). Taken together, our results indicate that CD from GEE inhibits lipid accumulation by suppressing adipogenesis via the downregulation of adipogenic protein expressions in the differentiated adipocytes. Therefore, chlorophyll from G. elliptica has a beneficial effect on lipid metabolism and it could be utilized as a potential therapeutic agent for preventing obesity.

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Titus, Amber R., Ellyse N. Ridgway, Rebecca Douglas, Elena Sánchez Brenes, Elizabeth K. Mann, and Edgar E. Kooijman. "The C-Terminus of Perilipin 3 Shows Distinct Lipid Binding at Phospholipid-Oil-Aqueous Interfaces." Membranes 11, no. 4 (April 6, 2021): 265. http://dx.doi.org/10.3390/membranes11040265.

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Lipid droplets (LDs) are ubiquitously expressed organelles; the only intracellular organelles that contain a lipid monolayer rather than a bilayer. Proteins localize and bind to this monolayer as they do to intracellular lipid bilayers. The mechanism by which cytosolic LD binding proteins recognize, and bind, to this lipid interface remains poorly understood. Amphipathic α-helix bundles form a common motif that is shared between cytosolic LD binding proteins (e.g., perilipins 2, 3, and 5) and apolipoproteins, such as apoE and apoLp-III, found on lipoprotein particles. Here, we use pendant drop tensiometry to expand our previous work on the C-terminal α-helix bundle of perilipin 3 and the full-length protein. We measure the recruitment and insertion of perilipin 3 at mixed lipid monolayers at an aqueous-phospholipid-oil interface. We find that, compared to its C-terminus alone, the full-length perilipin 3 has a higher affinity for both a neat oil/aqueous interface and a phosphatidylcholine (PC) coated oil/aqueous interface. Both the full-length protein and the C-terminus show significantly more insertion into a fully unsaturated PC monolayer, contrary to our previous results at the air-aqueous interface. Additionally, the C-terminus shows a preference for lipid monolayers containing phosphatidylethanolamine (PE), whereas the full-length protein does not. These results strongly support a model whereby both the N-terminal 11-mer repeat region and C-terminal amphipathic α-helix bundle domains of perilipin 3 have distinct lipid binding, and potentially biological roles.

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Scifres, Christina M., Baosheng Chen, D. Michael Nelson, and Yoel Sadovsky. "Fatty Acid Binding Protein 4 Regulates Intracellular Lipid Accumulation in Human Trophoblasts." Journal of Clinical Endocrinology & Metabolism 96, no. 7 (July 2011): E1083—E1091. http://dx.doi.org/10.1210/jc.2010-2084.

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Venkatachalam, Ananda B., Manoj B. Parmar, and Jonathan M. Wright. "Evolution of the duplicated intracellular lipid-binding protein genes of teleost fishes." Molecular Genetics and Genomics 292, no. 4 (April 7, 2017): 699–727. http://dx.doi.org/10.1007/s00438-017-1313-5.

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Kane, Christopher D., Natalie Ribarik Coe, Benjamin Vanlandingham, Peter Krieg, and David A. Bernlohr. "Expression, Purification, and Ligand-Binding Analysis of Recombinant Keratinocyte Lipid-Binding Protein (MAL-1), an Intracellular Lipid-Binding Protein Found Overexpressed in Neoplastic Skin Cells†." Biochemistry 35, no. 9 (January 1996): 2894–900. http://dx.doi.org/10.1021/bi952476e.

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Péresse, Tiphaine, David Kovacs, Mélody Subra, Joëlle Bigay, Meng-Chen Tsai, Joël Polidori, Romain Gautier, et al. "Molecular and cellular dissection of the oxysterol-binding protein cycle through a fluorescent inhibitor." Journal of Biological Chemistry 295, no. 13 (February 19, 2020): 4277–88. http://dx.doi.org/10.1074/jbc.ra119.012012.

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ORPphilins are bioactive natural products that strongly and selectively inhibit the growth of some cancer cell lines and are proposed to target intracellular lipid-transfer proteins of the oxysterol-binding protein (OSBP) family. These conserved proteins exchange key lipids, such as cholesterol and phosphatidylinositol 4-phosphate (PI(4)P), between organelle membranes. Among ORPphilins, molecules of the schweinfurthin family interfere with intracellular lipid distribution and metabolism, but their functioning at the molecular level is poorly understood. We report here that cell line sensitivity to schweinfurthin G (SWG) is inversely proportional to cellular OSBP levels. By taking advantage of the intrinsic fluorescence of SWG, we followed its fate in cell cultures and show that its incorporation at the trans-Golgi network depends on cellular abundance of OSBP. Using in vitro membrane reconstitution systems and cellular imaging approaches, we also report that SWG inhibits specifically the lipid transfer activity of OSBP. As a consequence, post-Golgi trafficking, membrane cholesterol levels, and PI(4)P turnover were affected. Finally, using intermolecular FRET analysis, we demonstrate that SWG directly binds to the lipid-binding cavity of OSBP. Collectively these results describe SWG as a specific and intrinsically fluorescent pharmacological tool for dissecting OSBP properties at the cellular and molecular levels. Our findings indicate that SWG binds OSBP with nanomolar affinity, that this binding is sensitive to the membrane environment, and that SWG inhibits the OSBP-catalyzed lipid exchange cycle.

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Herreros, Judit, Tony Ng, and Giampietro Schiavo. "Lipid Rafts Act as Specialized Domains for Tetanus Toxin Binding and Internalization into Neurons." Molecular Biology of the Cell 12, no. 10 (October 2001): 2947–60. http://dx.doi.org/10.1091/mbc.12.10.2947.

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Tetanus (TeNT) is a zinc protease that blocks neurotransmission by cleaving the synaptic protein vesicle-associated membrane protein/synaptobrevin. Although its intracellular catalytic activity is well established, the mechanism by which this neurotoxin interacts with the neuronal surface is not known. In this study, we characterize p15s, the first plasma membrane TeNT binding proteins and we show that they are glycosylphosphatidylinositol-anchored glycoproteins in nerve growth factor (NGF)-differentiated PC12 cells, spinal cord cells, and purified motor neurons. We identify p15 as neuronal Thy-1 in NGF-differentiated PC12 cells. Fluorescence lifetime imaging microscopy measurements confirm the close association of the binding domain of TeNT and Thy-1 at the plasma membrane. We find that TeNT is recruited to detergent-insoluble lipid microdomains on the surface of neuronal cells. Finally, we show that cholesterol depletion affects a raft subpool and blocks the internalization and intracellular activity of the toxin. Our results indicate that TeNT interacts with target cells by binding to lipid rafts and that cholesterol is required for TeNT internalization and/or trafficking in neurons.

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Kitamata, Manabu, Takehiko Inaba, and Shiro Suetsugu. "The roles of the diversity of amphipathic lipids in shaping membranes by membrane-shaping proteins." Biochemical Society Transactions 48, no. 3 (June 29, 2020): 837–51. http://dx.doi.org/10.1042/bst20190376.

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Lipid compositions of cells differ according to cell types and intracellular organelles. Phospholipids are major cell membrane lipids and have hydrophilic head groups and hydrophobic fatty acid tails. The cellular lipid membrane without any protein adapts to spherical shapes, and protein binding to the membrane is thought to be required for shaping the membrane for various cellular events. Until recently, modulation of cellular lipid membranes was initially shown to be mediated by proteins recognizing lipid head groups, including the negatively charged ones of phosphatidylserine and phosphoinositides. Recent studies have shown that the abilities of membrane-deforming proteins are also regulated by the composition of fatty acid tails, which cause different degrees of packing defects. The binding of proteins to cellular lipid membranes is affected by the packing defects, presumably through modulation of their interactions with hydrophobic amino acid residues. Therefore, lipid composition can be characterized by both packing defects and charge density. The lipid composition regarding fatty acid tails affects membrane bending via the proteins with amphipathic helices, including those with the ArfGAP1 lipid packing sensor (ALPS) motif and via membrane-deforming proteins with structural folding, including those with the Bin–Amphiphysin–Rvs167 (BAR) domains. This review focuses on how the fatty acid tails, in combination with the head groups of phospholipids, affect protein-mediated membrane deformation.

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Park, Jeong-Eun, Suk-Heung Oh, and Youn-Soo Cha. "Lactobacillus plantarumLG42 Isolated from Gajami Sik-Hae Inhibits Adipogenesis in 3T3-L1 Adipocyte." BioMed Research International 2013 (2013): 1–7. http://dx.doi.org/10.1155/2013/460927.

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We investigated whether lactic acid bacteria isolated from gajami sik-hae (GLAB) are capable of reducing the intracellular lipid accumulation by downregulating the expression of adipogenesis-related genes in differentiated 3T3-L1 cells. The GLAB,Lactobacillus plantarumLG42, significantly decreased the intracellular triglyceride storage and the glycerol-3-phosphate dehydrogenase (GPDH) activity in a dose-dependent manner. mRNA expression of transcription factors like peroxisome proliferator-activated receptor (PPAR)γand CCAAT/enhancer-binding protein (C/EBP)αinvolved in adipogenesis was markedly decreased by the GLAB treatment. Moreover, the GLAB also decreased the expression level of adipogenic markers like adipocyte fatty acid binding protein (aP2), leptin, GPDH, and fatty acid translocase (CD36) significantly. These results suggest that the GLAB inhibits lipid accumulation in the differentiated adipocyte through downregulating the expression of adipogenic transcription factors and other specific genes involved in lipid metabolism.

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Shigematsu, Hideki, Takashi Ebihara, Yasuko Yanagida, Tetsuya Haruyama, Eiry Kobatake, and Masuo Aizawa. "Site-directed lipid modification of IgG-binding protein by intracellular bacterial lipoprotein process." Journal of Biotechnology 75, no. 1 (September 1999): 23–31. http://dx.doi.org/10.1016/s0168-1656(99)00134-0.

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Peretti, Diego, Nili Dahan, Eyal Shimoni, Koret Hirschberg, and Sima Lev. "Coordinated Lipid Transfer between the Endoplasmic Reticulum and the Golgi Complex Requires the VAP Proteins and Is Essential for Golgi-mediated Transport." Molecular Biology of the Cell 19, no. 9 (September 2008): 3871–84. http://dx.doi.org/10.1091/mbc.e08-05-0498.

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Lipid transport between intracellular organelles is mediated by vesicular and nonvesicular transport mechanisms and is critical for maintaining the identities of different cellular membranes. Nonvesicular lipid transport between the endoplasmic reticulum (ER) and the Golgi complex has been proposed to affect the lipid composition of the Golgi membranes. Here, we show that the integral ER–membrane proteins VAP-A and VAP-B affect the structural and functional integrity of the Golgi complex. Depletion of VAPs by RNA interference reduces the levels of phosphatidylinositol-4-phosphate (PI4P), diacylglycerol, and sphingomyelin in the Golgi membranes, and it leads to substantial inhibition of Golgi-mediated transport events. These effects are coordinately mediated by the lipid-transfer/binding proteins Nir2, oxysterol-binding protein (OSBP), and ceramide-transfer protein (CERT), which interact with VAPs via their FFAT motif. The effect of VAPs on PI4P levels is mediated by the phosphatidylinositol/phosphatidylcholine transfer protein Nir2, which is required for Golgi targeting of OSBP and CERT and the subsequent production of diacylglycerol and sphingomyelin. We propose that Nir2, OSBP, and CERT function coordinately at the ER–Golgi membrane contact sites, thereby affecting the lipid composition of the Golgi membranes and consequently their structural and functional identities.

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Wahlmüller, Felix Christof, Barbora Sokolikova, Daniela Rieger, and Margarethe Geiger. "New lipid interaction partners stimulate the inhibition of activated protein C by cell-penetrating protein C inhibitor." Thrombosis and Haemostasis 111, no. 01 (2014): 41–52. http://dx.doi.org/10.1160/th13-06-0478.

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SummaryProtein C inhibitor (PCI, SerpinA5) is a heparin-binding serpin which can penetrate through cellular membranes. Selected negatively charged phospholipids like unsaturated phosphatidylserine and oxidised phosphatidylethanolamine bind to PCI and stimulate its inhibitory activity towards different proteases. The interaction of phospholipids with PCI might also alter the lipid distribution pattern of blood cells and influence the remodelling of cellular membranes. Here we showed that PCI is an additional binding partner of phosphatidic acid (PA), cardiolipin (CL), and phosphoinositides (PIPs). Protein lipid overlay assays exhibited a unique binding pattern of PCI towards different lipid species. In addition PA, CL, and unsaturated, monophosphorylated PIPs stimulated the inhibitory property of PCI towards activated protein C in a heparin like manner. As shown for kallistatin (SerpinA4) and vaspin (SerpinA12), the incubation of cells with PCI led to the activation of protein kinase B (AKT), which could be achieved through direct interaction of PCI with PIPs. This model is supported by the fact that PCI stimulated the PIP-dependent 5-phosphatase SHIP2 in vitro, which would result in AKT activation. Hence the interaction of PCI with different lipids might not only stimulate the inhibition of potential target protease by PCI, but could also alter intracellular lipid signalling.

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FAIRN, Gregory D., and Christopher R. McMASTER. "Identification and assessment of the role of a nominal phospholipid binding region of ORP1S (oxysterol-binding-protein-related protein 1 short) in the regulation of vesicular transport." Biochemical Journal 387, no. 3 (April 26, 2005): 889–96. http://dx.doi.org/10.1042/bj20041915.

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The ORPs (oxysterol-binding-protein-related proteins) constitute an enigmatic family of intracellular lipid receptors that are related through a shared lipid binding domain. Emerging evidence suggests that ORPs relate lipid metabolism to membrane transport. Current data imply that the yeast ORP Kes1p is a negative regulator of Golgi-derived vesicular transport mediated by the essential phosphatidylinositol/phosphatidylcholine transfer protein Sec14p. Inactivation of Kes1p function allows restoration of growth and vesicular transport in cells lacking Sec14p function, and Kes1p function in this regard can be complemented by human ORP1S (ORP1 short). Recent studies have determined that Kes1p and ORP1S both bind phospholipids as ligands. To explore the function of distinct linear segments of ORP1S in phospholipid binding and vesicular transport regulation, we generated a series of 15 open reading frames coding for diagnostic regions within ORP1S. Purified versions of these ORP1S deletion proteins were characterized in vitro, and allowed the identification of a nominal phospholipid binding region. The in vitro analysis was interpreted in the context of in vivo growth and vesicle transport assays for members of the ORP1S deletion set. The results determined that the phospholipid binding domain per se was insufficient for inhibition of vesicular transport by ORP1S, and that transport of carboxypeptidase Y and invertase from the Golgi may be regulated differentially by specific regions of ORP1S/Kes1p.

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Backer, Jonathan M. "New methods for capturing the mystery lipid, PtdIns5P." Biochemical Journal 428, no. 3 (May 27, 2010): e1-e2. http://dx.doi.org/10.1042/bj20100688.

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The enormous versatility of phosphatidylinositol as a mediator of intracellular signalling is due to its variable phosphorylation on every combination of the 3′, 4′ and 5′ positions, as well as an even more complex range of phosphorylated products when inositol phosphate is released by phospholipase C activity. The phosphoinositides are produced by distinct enzymes in distinct intracellular membranes, and recruit and regulate downstream signalling proteins containing binding domains [PH (pleckstrin homology), PX (Phox homology), FYVE etc.] that are relatively specific for these lipids. Specific recruitment of downstream proteins presumably involves a coincidence detection mechanism, in which a combination of lipid–protein and protein–protein interactions define specificity. Of the seven intrucellular phosphoinositide, quantification of PtdIns5P levels in intact cells has remained difficult. In this issue of the Biochemical Journal, Sarkes and Rameh describe a novel HPLC-based approach which makes possible an analysis of the subcellular distribution of PtdIns5P and other phosphoinositides.

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Xu, Hongliang, Ann V. Hertzel, Kaylee A. Steen, Qigui Wang, Jill Suttles, and David A. Bernlohr. "Uncoupling Lipid Metabolism from Inflammation through Fatty Acid Binding Protein-Dependent Expression of UCP2." Molecular and Cellular Biology 35, no. 6 (January 12, 2015): 1055–65. http://dx.doi.org/10.1128/mcb.01122-14.

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Chronic inflammation in obese adipose tissue is linked to endoplasmic reticulum (ER) stress and systemic insulin resistance. Targeted deletion of the murine fatty acid binding protein (FABP4/aP2) uncouples obesity from inflammation although the mechanism underlying this finding has remained enigmatic. Here, we show that inhibition or deletion of FABP4/aP2 in macrophages results in increased intracellular free fatty acids (FFAs) and elevated expression of uncoupling protein 2 (UCP2) without concomitant increases in UCP1 or UCP3. Silencing of UCP2 mRNA in FABP4/aP2-deficient macrophages negated the protective effect of FABP loss and increased ER stress in response to palmitate or lipopolysaccharide (LPS). Pharmacologic inhibition of FABP4/aP2 with the FABP inhibitor HTS01037 also upregulated UCP2 and reduced expression of BiP, CHOP, and XBP-1s. Expression of native FABP4/aP2 (but not the non-fatty acid binding mutant R126Q) into FABP4/aP2 null cells reduced UCP2 expression, suggesting that the FABP-FFA equilibrium controls UCP2 expression. FABP4/aP2-deficient macrophages are resistant to LPS-induced mitochondrial dysfunction and exhibit decreased mitochondrial protein carbonylation and UCP2-dependent reduction in intracellular reactive oxygen species. These data demonstrate that FABP4/aP2 directly regulates intracellular FFA levels and indirectly controls macrophage inflammation and ER stress by regulating the expression of UCP2.

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Rutledge, Angela C., Qiaozhu Su, and Khosrow Adeli. "Apolipoprotein B100 biogenesis: a complex array of intracellular mechanisms regulating folding, stability, and lipoprotein assemblyThis paper is one of a selection of papers published in this special issue entitled “Canadian Society of Biochemistry, Molecular & Cellular Biology 52nd Annual Meeting — Protein Folding: Principles and Diseases” and has undergone the Journal's usual peer review process." Biochemistry and Cell Biology 88, no. 2 (April 2010): 251–67. http://dx.doi.org/10.1139/o09-168.

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Apolipoprotein B100 (apoB) is a large amphipathic lipid-binding protein that is synthesized by hepatocytes and used to assemble and stabilize very low density lipoproteins (VLDL). It may have been derived through evolution from other lipid-associating proteins such as microsomal triglyceride transfer protein or vitellogenin. The correct folding of apoB requires assistance from chaperone proteins in co-translational lipidation, disulfide bond formation, and glycosylation. Any impairment in these processes results in co-translational targeting of the misfolded apoB molecule for proteasomal degradation. In fact, most of the regulation of apoB production is mediated by intracellular degradation. ApoB that misfolds post-translationally, perhaps as a result of oxidative stress, may be eliminated through autophagy. This review focuses on the proposed pentapartite domain structure of apoB, the role that each domain plays in the binding of lipid species and regulation of apoB synthesis, and the process of VLDL assembly. The factors involved in the recognition, ubiquitination, and proteasomal delivery of defective apoB molecules are also discussed.

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Schindler, Maria, Mareike Pendzialek, Alexander Navarrete Santos, Torsten Plösch, Stefanie Seyring, Jacqueline Gürke, Elisa Haucke, Julia Miriam Knelangen, Bernd Fischer, and Anne Navarrete Santos. "Maternal Diabetes Leads to Unphysiological High Lipid Accumulation in Rabbit Preimplantation Embryos." Endocrinology 155, no. 4 (April 1, 2014): 1498–509. http://dx.doi.org/10.1210/en.2013-1760.

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According to the “developmental origin of health and disease” hypothesis, the metabolic set points of glucose and lipid metabolism are determined prenatally. In the case of a diabetic pregnancy, the embryo is exposed to higher glucose and lipid concentrations as early as during preimplantation development. We used the rabbit to study the effect of maternal diabetes type 1 on lipid accumulation and expression of lipogenic markers in preimplantation blastocysts. Accompanied by elevated triglyceride and glucose levels in the maternal blood, embryos from diabetic rabbits showed a massive intracellular lipid accumulation and increased expression of fatty acid transporter 4, fatty acid–binding protein 4, perilipin/adipophilin, and maturation of sterol-regulated element binding protein. However, expression of fatty acid synthase, a key enzyme for de novo synthesis of fatty acids, was not altered in vivo. During a short time in vitro culture of rabbit blastocysts, the accumulation of lipid droplets and expression of lipogenic markers were directly correlated with increasing glucose concentration, indicating that hyperglycemia leads to increased lipogenesis in the preimplantation embryo. Our study shows the decisive effect of glucose as the determining factor for fatty acid metabolism and intracellular lipid accumulation in preimplantation embryos.

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Nossoni, Zahra, Zahra Assar, Ipek Yapici, Meisam Nosrati, Wenjing Wang, Tetyana Berbasova, Chrysoula Vasileiou, Babak Borhan, and James Geiger. "Structures of holo wild-type human cellular retinol-binding protein II (hCRBPII) bound to retinol and retinal." Acta Crystallographica Section D Biological Crystallography 70, no. 12 (November 22, 2014): 3226–32. http://dx.doi.org/10.1107/s1399004714023839.

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Cellular retinol-binding proteins (CRBPs) I and II, which are members of the intracellular lipid-binding protein (iLBP) family, are retinoid chaperones that are responsible for the intracellular transport and delivery of both retinol and retinal. Although structures of retinol-bound CRBPI and CRBPII are known, no structure of a retinal-bound CRBP has been reported. In addition, the retinol-bound human CRBPII (hCRBPII) structure shows partial occupancy of a noncanonical conformation of retinol in the binding pocket. Here, the structure of retinal-bound hCRBPII and the structure of retinol-bound hCRBPII with retinol fully occupying the binding pocket are reported. It is further shown that the retinoid derivative seen in both the zebrafish CRBP and the hCRBPII structures is likely to be the product of flux-dependent and wavelength-dependent X-ray damage during data collection. The structures of retinoid-bound CRBPs are compared and contrasted, and rationales for the differences in binding affinities for retinal and retinol are provided.

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Jo, Youngah, Isamu Z. Hartman, and Russell A. DeBose-Boyd. "Ancient ubiquitous protein-1 mediates sterol-induced ubiquitination of 3-hydroxy-3-methylglutaryl CoA reductase in lipid droplet–associated endoplasmic reticulum membranes." Molecular Biology of the Cell 24, no. 3 (February 2013): 169–83. http://dx.doi.org/10.1091/mbc.e12-07-0564.

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Sterol-induced binding to Insigs in endoplasmic reticulum (ER) membranes triggers ubiquitination of the cholesterol biosynthetic enzyme 3-hydroxy-3-methylglutaryl CoA reductase. This ubiquitination, which is mediated by Insig-associated ubiquitin ligases gp78 and Trc8, is obligatory for extraction of reductase from lipid droplet–associated ER membranes into the cytosol for proteasome-mediated, ER-associated degradation (ERAD). In this study, we identify lipid droplet–associated, ancient, ubiquitous protein-1 (Aup1) as one of several proteins that copurify with gp78. RNA interference (RNAi) studies show that Aup1 recruits the ubiquitin-conjugating enzyme Ubc7 to lipid droplets and facilitates its binding to both gp78 and Trc8. The functional significance of these interactions is revealed by the observation that RNAi-mediated knockdown of Aup1 blunts sterol-accelerated ubiquitination of reductase, which appears to occur in lipid droplet–associated membranes and subsequent ERAD of the enzyme. In addition, Aup1 knockdown inhibits ERAD of Insig-1, another substrate for gp78, as well as that of membrane-bound precursor forms of sterol-regulatory, element-binding protein-1 and -2, transcription factors that modulate expression of genes encoding enzymes required for cholesterol synthesis. Considered together, these findings not only implicate a role for Aup1 in maintenance of intracellular cholesterol homeostasis, but they also highlight the close connections among ERAD, lipid droplets, and lipid droplet–associated proteins.

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Chen, Wentao, Jiajia Dong, Lars Plate, David E. Mortenson, Gabriel J. Brighty, Suhua Li, Yu Liu, et al. "Arylfluorosulfates Inactivate Intracellular Lipid Binding Protein(s) through Chemoselective SuFEx Reaction with a Binding Site Tyr Residue." Journal of the American Chemical Society 138, no. 23 (June 2, 2016): 7353–64. http://dx.doi.org/10.1021/jacs.6b02960.

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Lee, Hyo-Geun, Hyun-Soo Kim, Jun-Geon Je, Jin Hwang, K. K. Asanka Sanjeewa, Dae-Sung Lee, Kyung-Mo Song, Yun-Sang Choi, Min-Cheol Kang, and You-Jin Jeon. "Lipid Inhibitory Effect of (−)-loliolide Isolated from Sargassum horneri in 3T3-L1 Adipocytes: Inhibitory Mechanism of Adipose-Specific Proteins." Marine Drugs 19, no. 2 (February 8, 2021): 96. http://dx.doi.org/10.3390/md19020096.

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Sargassum horneri (S. horneri) is a well-known brown seaweed widely distributed worldwide. Several biological activities of S. horneri have been reported. However, its effects on lipid metabolism and the underlying mechanisms remain elusive. In the present study, we examined the inhibitory effect of the active compound “(−)-loliolide ((6S,7aR)-6-hydroxy-4,4,7a-trimethyl-5,6,7,7a-tetrahydro-1-benzofuran-2(4H)-one (HTT))” from S. horneri extract on lipid accumulation in differentiated adipocytes. MTT assays demonstrated that (−)-loliolide is not toxic to 3T3-L1 adipocytes in a range of concentrations. (−)-loliolide significantly reduced intracellular lipid accumulation in the differentiated phase of 3T3-L1 adipocytes as shown by Oil Red O staining. Western blot analysis revealed that (−)-loliolide increased the expression of lipolytic protein phospho-hormone-sensitive lipase (p-HSL) and thermogenic protein peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1). Additionally, (−)-loliolide decreased expression of adipogenic and lipogenic proteins, including sterol regulatory element-binding protein-1 (SREBP-1), peroxisome proliferator-activated receptor-γ (PPAR-γ), CCAAT/enhancer-binding protein-α (C/EBP-α), and fatty acid-binding protein 4 (FABP4) in 3T3-L1 adipocytes. These results indicate that (−)-loliolide from S. horneri could suppress lipid accumulation via regulation of antiadipogenic and prolipolytic mechanisms in 3T3-L1 cells. Considering the multifunctional effect of (−)-loliolide, it can be useful as a lipid-lowering agent in the management of patients who suffer from obesity.

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Kang, Jin Ku, Ok-Hee Kim, June Hur, So Hee Yu, Santosh Lamichhane, Jin Wook Lee, Uttam Ojha, et al. "Increased intracellular Ca2+concentrations prevent membrane localization of PH domains through the formation of Ca2+-phosphoinositides." Proceedings of the National Academy of Sciences 114, no. 45 (October 25, 2017): 11926–31. http://dx.doi.org/10.1073/pnas.1706489114.

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Insulin resistance, a key etiological factor in metabolic syndrome, is closely linked to ectopic lipid accumulation and increased intracellular Ca2+concentrations in muscle and liver. However, the mechanism by which dysregulated intracellular Ca2+homeostasis causes insulin resistance remains elusive. Here, we show that increased intracellular Ca2+acts as a negative regulator of insulin signaling. Chronic intracellular Ca2+overload in hepatocytes during obesity and hyperlipidemia attenuates the phosphorylation of protein kinase B (Akt) and its key downstream signaling molecules by inhibiting membrane localization of pleckstrin homology (PH) domains. Pharmacological approaches showed that elevated intracellular Ca2+inhibits insulin-stimulated Akt phosphorylation and abrogates membrane localization of various PH domain proteins such as phospholipase Cδ and insulin receptor substrate 1, suggesting a common mechanism inhibiting the membrane targeting of PH domains. PH domain-lipid overlay assays confirmed that Ca2+abolishes the binding of various PH domains to phosphoinositides (PIPs) with two adjacent phosphate groups, such as PI(3,4)P2, PI(4,5)P2, and PI(3,4,5)P3. Finally, thermodynamic analysis of the binding interaction showed that Ca2+-mediated inhibition of targeting PH domains to the membrane resulted from the tight binding of Ca2+rather than PH domains to PIPs forming Ca2+-PIPs. Thus, Ca2+-PIPs prevent the recognition of PIPs by PH domains, potentially due to electrostatic repulsion between positively charged side chains in PH domains and the Ca2+-PIPs. Our findings provide a mechanistic link between intracellular Ca2+dysregulation and Akt inactivation in insulin resistance.

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Barrett, John, Nahid Saghir, Anna Timanova, Katie Clarke, and Peter M. Brophy. "Characterisation and Properties of an Intracellular Lipid-Binding Protein from the Tapeworm Moniezia expansa." European Journal of Biochemistry 250, no. 2 (December 1997): 269–75. http://dx.doi.org/10.1111/j.1432-1033.1997.0269a.x.

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Siarheyeva, Alena, and Frances J. Sharom. "The ABC transporter MsbA interacts with lipid A and amphipathic drugs at different sites." Biochemical Journal 419, no. 2 (March 27, 2009): 317–28. http://dx.doi.org/10.1042/bj20081364.

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MsbA is an essential ABC (ATP-binding cassette) transporter involved in lipid A transport across the cytoplasmic membrane of Gram-negative bacteria. The protein has also been linked to efflux of amphipathic drugs. Purified wild-type MsbA was labelled stoichiometrically with the fluorescent probe MIANS [2-(4′-maleimidylanilino)naphthalene-6-sulfonic acid] on C315, which is located within the intracellular domain connecting transmembrane helix 6 and the nucleotide-binding domain. MsbA–MIANS displayed high ATPase activity, and its folding and stability were unchanged. The initial rate of MsbA labelling by MIANS was reduced in the presence of amphipathic drugs, suggesting that binding of these compounds alters the protein conformation. The fluorescence of MsbA–MIANS was saturably quenched by nucleotides, lipid A and various drugs, and estimates of the Kd values for binding fell in the range of 0.35–10 μM. Lipid A and daunorubicin were able to bind to MsbA–MIANS simultaneously, implying that they occupy different binding sites. The effects of nucleotide and lipid A/daunorubicin binding were additive, and binding was not ordered. The Kd of MsbA for binding lipid A was substantially decreased when the daunorubicin binding site was occupied first, and prior binding of nucleotide also modulated lipid A binding affinity. These results indicate that MsbA contains two substrate-binding sites that communicate with both the nucleotide-binding domain and with each other. One is a high affinity binding site for the physiological substrate, lipid A, and the other site interacts with drugs with comparable affinity. Thus MsbA may function as both a lipid flippase and a multidrug transporter.

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Kim, Sou Hyun, Chawon Yun, Doyoung Kwon, Yun-Hee Lee, Jae-Hwan Kwak, and Young-Suk Jung. "Effect of Isoquercitrin on Free Fatty Acid-Induced Lipid Accumulation in HepG2 Cells." Molecules 28, no. 3 (February 3, 2023): 1476. http://dx.doi.org/10.3390/molecules28031476.

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Liver metabolic disorders and oxidative stress are crucial factors in the development of nonalcoholic fatty liver disease (NAFLD); however, treatment strategies to combat NAFLD remain poorly established, presenting an important challenge that needs to be addressed. Herein, we aimed to examine the effect of isoquercitrin on lipid accumulation induced by exogenous free fatty acids (FFA) using HepG2 cells and elucidate the underlying molecular mechanism. The cells were exposed to 0.5 mM FFA to induce intracellular lipid accumulation, followed by co-treatment with isoquercitrin to confirm the potential inhibitory effect on FFA-induced lipid production. HepG2 cells exposed to FFA alone exhibited intracellular lipid accumulation, compromised endoplasmic reticulum (ER) stress, and enhanced expression of proteins and genes involved in lipid synthesis; however, co-treatment with isoquercitrin decreased the expression of these molecules in a dose-dependent manner. Furthermore, isoquercitrin could activate AMP-activated protein kinase (AMPK), a key regulatory protein of hepatic fatty acid oxidation, suppressing new lipid production by phosphorylating acetyl-CoA carboxylase (ACC) and inhibiting sterol regulatory element-binding transcription factor 1 (SREBP-1)/fatty acid synthase (FAS) signals. Overall, these findings suggest that isoquercitrin can be employed as a therapeutic agent to improve NAFLD via the regulation of lipid metabolism by targeting the AMPK/ACC and SREBP1/FAS pathways.

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Cheng, Kwan H., Angela Graf, Amber Lewis, Thuong Pham, and Aakriti Acharya. "Exploring Membrane Binding Targets of Disordered Human Tau Aggregates on Lipid Rafts Using Multiscale Molecular Dynamics Simulations." Membranes 12, no. 11 (November 4, 2022): 1098. http://dx.doi.org/10.3390/membranes12111098.

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The self-aggregation of tau, a microtubule-binding protein, has been linked to the onset of Alzheimer’s Disease. Recent studies indicate that the disordered tau aggregates, or oligomers, are more toxic than the ordered fibrils found in the intracellular neurofibrillary tangles of tau. At present, details of tau oligomer interactions with lipid rafts, a model of neuronal membranes, are not known. Using molecular dynamics simulations, the lipid-binding events, membrane-damage, and protein folding of tau oligomers on various lipid raft surfaces were investigated. Tau oligomers preferred to bind to the boundary domains (Lod) created by the coexisting liquid-ordered (Lo) and liquid-disordered (Ld) domains in the lipid rafts. Additionally, stronger binding of tau oligomers to the ganglioside (GM1) and phosphatidylserine (PS) domains, and subsequent protein-induced lipid chain order disruption and beta-sheet formation were detected. Our results suggest that GM1 and PS domains, located exclusively in the outer and inner leaflets, respectively, of the neuronal membranes, are specific membrane domain targets, whereas the Lod domains are non-specific targets, of tau oligomers binding to neurons. The molecular details of these specific and non-specific tau bindings to lipid rafts may provide new insights into understanding membrane-associated tauopathies leading to Alzheimer’s Disease.

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31

Mahmood, Akhtar, Jian-su Shao, and David H. Alpers. "Rat enterocytes secrete SLPs containing alkaline phosphatase and cubilin in response to corn oil feeding." American Journal of Physiology-Gastrointestinal and Liver Physiology 285, no. 2 (August 2003): G433—G441. http://dx.doi.org/10.1152/ajpgi.00466.2002.

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Surfactant-like particles (SLP) are unilamellar secreted membranes associated with the process of lipid absorption and isolated previously only from the apical surface of enterocytes. In this paper, the intracellular membrane has been isolated from corn oil-fed animals, identified by its content of the marker protein intestinal alkaline phosphatase (IAP). Another brush-border protein, cubilin, and its anchoring protein megalin have been identified as components of extracellular SLP, but only cubilin is present to any extent in intracellular SLP. During fat absorption, IAP is modestly enriched in intracellular SLP, but full-length cubilin (migrating at 210 kDa in fat-fed mucosal fractions) falls by one-half, although fragments of cubilin are abundant in the intracellular SLP. Both IAP and cubilin colocalize to the same cells during corn oil absorption and colocalize around lipid droplets. This localization is more intense during feeding of corn oil with Pluronic L-81, a detergent that allows uptake of fatty acids and monoglycerides from the lumen, but blocks chylomicron secretion. Confocal microscopy confirms the colocalization of IAP and the ligand for cubilin, intrinsic factor. Possible roles for cubilin in intracellular SLP include facilitating movement of the lipid droplet through the cell and binding to the basolateral membrane before reverse endocytosis.

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32

Lee, Eun Byul, Pil Soo Sung, Jung-Hee Kim, Dong Jun Park, Wonhee Hur, and Seung Kew Yoon. "microRNA-99a Restricts Replication of Hepatitis C Virus by Targeting mTOR and De Novo Lipogenesis." Viruses 12, no. 7 (June 27, 2020): 696. http://dx.doi.org/10.3390/v12070696.

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In this study, we investigated the role of microRNA-99a (miR-99a) in hepatitis C virus (HCV) replication and lipogenesis in hepatocytes. Cell-culture-derived HCV (HCVcc) infection caused down-regulation of miR-99a in Huh-7 cells, and the relative levels of miR-99a were significantly lower in the sera of the HCV-infected patients than in those of healthy controls. Transfection of miR-99a-5p mimics resulted in a decrease in the intracellular and secreted HCV RNA levels. It also caused a decreased mammalian target of rapamycin (mTOR) protein level and phosphorylation of its downstream targets in HCV-replicating cells. Sterol regulatory element binding protein (SREBP)-1c expression and intracellular lipid accumulation decreased when either miR-99a-5p mimics or si-mTOR was transfected in oleic acid-treated Huh-7 cells. Overexpression of mTOR rescued HCV RNA replication and lipid droplet accumulation in miR-99a-5p mimics-transfected HCV replicon cells. Our data demonstrated that miR-99a ameliorates intracellular lipid accumulation by regulating mTOR/SREBP-1c and causes inefficient replication and packaging of intracellular HCV.

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Aw, Yvette C., Andrew J. Brown, Jia-Wei Wu, and Hongyuan Yang. "ORP1L, ORP1S, and ORP2: Lipid Sensors and Transporters." Contact 3 (January 2020): 251525642095681. http://dx.doi.org/10.1177/2515256420956818.

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Lipid transfer proteins are crucial for intracellular cholesterol trafficking at sites of membrane contact. In the OSBP/ORPs (oxysterol binding protein and OSBP-related proteins) family of lipid transfer proteins, ORP1L, ORP1S and ORP2 play important roles in cholesterol transport. ORP1L is an endosome/lysosome-anchored cholesterol sensor which may also move cholesterol bidirectionally at the interface between the endoplasmic reticulum and the endosome/lysosome. ORP2 delivers cholesterol to the plasma membrane, driven by PI(4,5)P2 hydrolysis. ORP1S may also transport cholesterol to the plasma membrane, although it is unclear if phosphoinositides are involved. The source of cholesterol delivered to the plasma membrane by ORP1S and ORP2 remains unclear. This review summarises the roles of these proteins in maintaining cellular cholesterol homeostasis and in human disease.

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Moore, David T., Patrik Nygren, Kathleen Molnar, Kathleen Boesze-Battaglia, Joel S. Bennett, and William F. DeGrado. "Protein-Protein and Protein-Lipid Interactions Modulate αIIbβ3 Inside-out Signaling." Blood 114, no. 22 (November 20, 2009): 152. http://dx.doi.org/10.1182/blood.v114.22.152.152.

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Abstract Abstract 152 Integrins are ubiquitously expressed α/β heterodimers that mediate cell-cell and cell-extracellular matrix interactions. The platelet integrin αIIbβ3 binds soluble fibrinogen following platelet activation, an event necessary for the formation of platelet aggregates. Integrins reside on plasma membranes in a highly regulated and dynamic equilibrium between inactive resting states and active ligand binding conformations. An essential feature of this equilibrium is the association and dissociation of integrin transmembrane (TM) and cytoplasmic domains. Thus, when integrins are inactive, the TM and cytoplasmic domains of their α and β subunits are in proximity; the domains separate when integrins assume their active conformations. Agonist-induced activation of αIIbβ3 in platelets (inside-out activation) requires binding of the FERM domain of the cytoskeletal protein talin to highly conserved membrane proximal and distal sequences in the β3 subunit cytoplasmic domain. FERM domain binding to the β3 cytoplasmic domain likely disrupts the αIIbβ3 TM domain-cytoplasmic domain heterodimer. As the β3 cytoplasmic domain exists in close apposition to the inner leaflet of the plasma membrane and the talin FERM domain is known to interact with the negatively-charged phospholipids that are common in eukaryotic membranes, we have investigated the effects of the membrane environment on β3 and talin structure and the talin-β;3 protein-protein interaction that regulates αIIbβ3 activation. A water soluble form of the β3 cytoplasmic domain was expressed, purified, and chemically conjugated to phospholipid bilayers, mimicking the native environment of the αIIb and β3 cytoplasmic domains as they exit the membrane. Using circular dichroism (CD) spectroscopy, the β3 cytoplasmic domain was found to have a significant increase in secondary structure and overall helicity when attached to the bilayer. Similarly, using hydrogen-deuterium exchange (HDX) mass spectrometry, we found that there is an overall decrease in amide backbone flexibility, particularly in the membrane proximal talin-interacting region. We also found significant changes in talin secondary structure in detergents by CD and by limited proteolysis mapping, supporting dramatic conformational changes in talin upon membrane binding. Using isothermal titration calorimetry (ITC) and integrin-conjugated lipid bilayers, we investigated the effects of lipid composition on talin-bilayer and talin-β3 cytoplasmic domain interactions. We found that the talin FERM domain likely has two binding sites for the membrane-conjugated β3 cytoplasmic domain, one in the canonical F3 subdomain and a second that depends on the F2 subdomain. Moreover, the talin head domain does not bind to β3 on neutral bilayers and requires a significant excess of phosphatidylserine (PS) relative to β3 to allow saturation. Interestingly phosphatidylinositol (4, 5)-bisphosphate containing bilayers have significantly higher affinity and mitigate the need for excess PS. Our results point toward a model in which β3 cytoplasmic domain structure is dependent on the lipid environment and its interaction with talin. Thus, αIIbβ3 activation is significantly regulated by lipid which may play a role in constraining αIIbβ3 activation by talin in the crowded platelet intracellular environment. Disclosures: No relevant conflicts of interest to declare.

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Prattes, S., G. Horl, A. Hammer, A. Blaschitz, W. F. Graier, W. Sattler, R. Zechner, and E. Steyrer. "Intracellular distribution and mobilization of unesterified cholesterol in adipocytes: triglyceride droplets are surrounded by cholesterol-rich ER-like surface layer structures." Journal of Cell Science 113, no. 17 (September 1, 2000): 2977–89. http://dx.doi.org/10.1242/jcs.113.17.2977.

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In addition to their central role in triglyceride storage, fat cells are a primary depot of unesterified cholesterol (FC) in the body. In comparison, peripheral cells contain very little FC. This difference in adipocytes versus peripheral tissues is inconsistent with the current theory of cholesterol homeostasis. Attempting to resolve this discrepancy, we examined intracellular storage sites of FC in murine 3T3-F442A adipocytes. Using the cholesterol-binding antibiotic, filipin, in combination with high resolution fluorescence microscopy, intense fluorescent staining characteristically decorated the periphery of triglyceride droplets (TGD) as well as the plasma membrane (PM) of fat cells. Filipin-staining was not visible inside the lipid droplets. Purification of TGD by subcellular fractionation demonstrated that the rise in total FC content of adipocytes upon differentiation was attributable to an increase in TGD-FC, which contributed up to one third of the total cellular FC. The protein component of purified TGD from cultured adipocytes as well as from murine adipocytes obtained from fresh tissues contained the lumenal endoplasmic reticulum (ER) immunoglobulin binding protein (BiP) and the integral ER membrane protein calnexin. Efflux experiments using the extracellular FC acceptors (β)-cyclodextrin or apolipoprotein A-I demonstrated that TGD-associated FC was releasable from TGD. Whereas FC efflux from adipocytes was unaffected in the presence of brefeldin A or monensin, the secretion of a control protein, lipoprotein lipase, was effectively reduced. In summary, our findings identify the TGD surface layer as primary intracellular storage site for FC within adipocytes. We suggest that the structural role of ER-resident proteins in this adipocyte TGD envelope has been previously neglected. Our findings support the suggestion that an ER-like structure, albeit of modified lipid composition, constitutes the lipid droplets' surface layer. Finally, the efflux process of FC from adipocytes upon extracellular stimulation with (beta)-cyclodextrin provides evidence for an energy-dependent intracellular trafficking route between the TGD-FC pool and the PM-FC sites which is distinct from the secretory pathway of proteins.

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Sacchettini, J. C., S. M. Hauft, S. L. Van Camp, D. P. Cistola, and J. I. Gordon. "Developmental and structural studies of an intracellular lipid binding protein expressed in the ileal epithelium." Journal of Biological Chemistry 265, no. 31 (November 1990): 19199–207. http://dx.doi.org/10.1016/s0021-9258(17)30644-0.

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Lai, Hong-Yue, Ling-Wei Hsu, Hsin-Hwa Tsai, Yu-Chih Lo, Shang-Hsun Yang, Ping-Yen Liu, and Ju-Ming Wang. "CCAAT/enhancer-binding protein delta promotes intracellular lipid accumulation in M1 macrophages of vascular lesions." Cardiovascular Research 113, no. 11 (July 11, 2017): 1376–88. http://dx.doi.org/10.1093/cvr/cvx134.

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Sakai, Juro, and Robert B. Rawson. "The sterol regulatory element-binding protein pathway: control of lipid homeostasis through regulated intracellular transport." Current Opinion in Lipidology 12, no. 3 (June 2001): 261–66. http://dx.doi.org/10.1097/00041433-200106000-00004.

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Marcelino, Anna Marie C., Robert G. Smock, and Lila M. Gierasch. "Evolutionary coupling of structural and functional sequence information in the intracellular lipid-binding protein family." Proteins: Structure, Function, and Bioinformatics 63, no. 2 (February 13, 2006): 373–84. http://dx.doi.org/10.1002/prot.20860.

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Zhang, Chaoyi, Qianli Zhang, Zhihong Huang, and Quan Jiang. "Adropin inhibited tilapia hepatic glucose output and triglyceride accumulation via AMPK activation." Journal of Endocrinology 246, no. 2 (August 2020): 109–22. http://dx.doi.org/10.1530/joe-20-0077.

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Adropin plays a role in the maintenance of energy homeostasis, insulin resistance prevention, and impaired glucose tolerance. However, the molecular mechanisms by which adropin affects hepatic glucose and lipid metabolism in vitro are not entirely understood. This study intended to examine the roles and underlying mechanisms of adropin in glucose and lipid metabolism in Nile tilapia. In primary cultured tilapia hepatocytes, adropin significantly attenuated oleic acid (OA)-induced glucose output and reduced the activities and mRNA expression of cytosolic phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), which are involved in gluconeogenesis. In contrast, adropin facilitated glucose uptake activity via glucose transporter 1 (Glut1) upregulation in OA-treated hepatocytes. One-week of adropin treatment reduced the hepatic total lipid accumulation in OA-fed tilapia without changes in body weight. Subsequent studies revealed that adropin suppressed OA-induced intracellular triglyceride accumulation and decreased the expression of genes and proteins involved in lipid metabolisms such as sterol regulatory element-binding protein-1c (SREBP-1c), acetyl-CoA carboxylase α (ACCα) and CD36, but upregulated peroxisome proliferator-activated receptor α (PPARα) levels. In parallel studies, however, adropin had no detectable effects on fatty acid-binding protein 4 (Fabp4) and carnitine palmitoyltransferase 1α (Cpt1α) mRNA expression. Furthermore, adropin treatment dose-dependently increased the phosphorylation level of AMP-activated protein kinase (AMPK). Suppression of AMPK by compound C or AMPKα1 siRNA blocked adropin-induced decreases in the mature form of SREBP-1c expression, glucose output, and intracellular triglyceride content in OA-treated hepatocytes. These findings suggest that teleost adropin could suppress hepatic gluconeogenesis and triglyceride accumulation via a mechanism dependent on AMPK signalling.

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THUMSER, Alfred E. A., and David C. WILTON. "The binding of cholesterol and bile salts to recombinant rat liver fatty acid-binding protein." Biochemical Journal 320, no. 3 (December 15, 1996): 729–33. http://dx.doi.org/10.1042/bj3200729.

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The physiological role of liver fatty acid-binding protein (L-FABP) has yet to be clarified. An important feature of this member of the family of intracellular lipid-binding proteins is the wide range of compounds that have been identified as potential physiological ligands. By using recombinant L-FABP, the binding of cholesterol, bile salts and their derivatives has been investigated under conditions that allow a direct comparison of the binding affinities of these ligands for fatty acids. The results demonstrate an inability of L-FABP to bind cholesterol, although the anionic derivative, cholesteryl sulphate, will bind under similar assay conditions. Of the bile salts examined, lithocholate and taurolithocholate sulphate showed the greatest binding to L-FABP. It is proposed that an important function of L-FABP is to bind certain physiological amphipathic anions, thus preventing the ‘free’ concentrations of these compounds from exceeding their critical micelle concentration, which could result in cell damage.

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GUTIÉRREZ-GONZÁLEZ, Luis H., Christian LUDWIG, Carsten HOHOFF, Martin RADEMACHER, Thorsten HANHOFF, Heinz RÜTERJANS, Friedrich SPENER, and Christian LÜCKE. "Solution structure and backbone dynamics of human epidermal-type fatty acid-binding protein (E-FABP)." Biochemical Journal 364, no. 3 (June 15, 2002): 725–37. http://dx.doi.org/10.1042/bj20020039.

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Human epidermal-type fatty acid-binding protein (E-FABP) belongs to a family of intracellular 14–15kDa lipid-binding proteins, whose functions have been associated with fatty acid signalling, cell growth, regulation and differentiation. As a contribution to understanding the structure—function relationship, we report in the present study features of its solution structure and backbone dynamics determined by NMR spectroscopy. Applying multi-dimensional high-resolution NMR techniques on unlabelled and 15N-enriched recombinant human E-FABP, the 1H and 15N resonance assignments were completed. On the basis of 2008 distance restraints, the three-dimensional solution structure of human E-FABP was subsequently obtained (backbone atom root-mean-square deviation of 0.92±0.11Å; where 1Å = 0.1nm), consisting mainly of 10 anti-parallel β-strands that form a β-barrel structure. 15N relaxation experiments (T1, T2 and heteronuclear nuclear Overhauser effects) at 500, 600 and 800MHz provided information on the internal dynamics of the protein backbone. Nearly all non-terminal backbone amide groups showed order parameters S2>0.8, with an average value of 0.88±0.04, suggesting a uniformly low backbone mobility in the nanosecond-to-picosecond time range. Moreover, hydrogen/deuterium exchange experiments indicated a direct correlation between the stability of the hydrogen-bonding network in the β-sheet structure and the conformational exchange in the millisecond-to-microsecond time range. The features of E-FABP backbone dynamics elaborated in the present study differ markedly from those of the phylogenetically closely related heart-type FABP and the more distantly related ileal lipid-binding protein, implying a strong interdependence with the overall protein stability and possibly also with the ligand-binding affinity for members of the lipid-binding protein family.

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McDermott, Mark, Michael J. O. Wakelam, and Andrew J. Morris. "Phospholipase D." Biochemistry and Cell Biology 82, no. 1 (February 1, 2004): 225–53. http://dx.doi.org/10.1139/o03-079.

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Phospholipase D catalyses the hydrolysis of the phosphodiester bond of glycerophospholipids to generate phosphatidic acid and a free headgroup. Phospholipase D activities have been detected in simple to complex organisms from viruses and bacteria to yeast, plants, and mammals. Although enzymes with broader selectivity are found in some of the lower organisms, the plant, yeast, and mammalian enzymes are selective for phosphatidylcholine. The two mammalian phospholipase D isoforms are regulated by protein kinases and GTP binding proteins of the ADP-ribosylation and Rho families. Mammalian and yeast phospholipases D are also potently stimulated by phosphatidylinositol 4,5-bisphosphate. This review discusses the identification, characterization, structure, and regulation of phospholipase D. Genetic and pharmacological approaches implicate phospholipase D in a diverse range of cellular processes that include receptor signaling, control of intracellular membrane transport, and reorganization of the actin cytoskeleton. Most ideas about phospholipase D function consider that the phosphatidic acid product is an intracellular lipid messenger. Candidate targets for phospholipase-D-generated phosphatidic acid include phosphatidylinositol 4-phosphate 5-kinases and the raf protein kinase. Phosphatidic acid can also be converted to two other lipid mediators, diacylglycerol and lyso phosphatidic acid. Coordinated activation of these phospholipase-D-dependent pathways likely accounts for the pleitropic roles for these enzymes in many aspects of cell regulation.Key words: phospholipase D, phosphatidic acid, GTP-binding proteins, membrane transport, cytoskeletal regulation.

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Hofer, Peter, Ulrike Taschler, Renate Schreiber, Petra Kotzbeck, and Gabriele Schoiswohl. "The Lipolysome—A Highly Complex and Dynamic Protein Network Orchestrating Cytoplasmic Triacylglycerol Degradation." Metabolites 10, no. 4 (April 10, 2020): 147. http://dx.doi.org/10.3390/metabo10040147.

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The catabolism of intracellular triacylglycerols (TAGs) involves the activity of cytoplasmic and lysosomal enzymes. Cytoplasmic TAG hydrolysis, commonly termed lipolysis, is catalyzed by the sequential action of three major hydrolases, namely adipose triglyceride lipase, hormone-sensitive lipase, and monoacylglycerol lipase. All three enzymes interact with numerous protein binding partners that modulate their activity, cellular localization, or stability. Deficiencies of these auxiliary proteins can lead to derangements in neutral lipid metabolism and energy homeostasis. In this review, we summarize the composition and the dynamics of the complex lipolytic machinery we like to call “lipolysome”.

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Antonny, Bruno, Joëlle Bigay, and Bruno Mesmin. "The Oxysterol-Binding Protein Cycle: Burning Off PI(4)P to Transport Cholesterol." Annual Review of Biochemistry 87, no. 1 (June 20, 2018): 809–37. http://dx.doi.org/10.1146/annurev-biochem-061516-044924.

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To maintain an asymmetric distribution of ions across membranes, protein pumps displace ions against their concentration gradient by using chemical energy. Here, we describe a functionally analogous but topologically opposite process that applies to the lipid transfer protein (LTP) oxysterol-binding protein (OSBP). This multidomain protein exchanges cholesterol for the phosphoinositide phosphatidylinositol 4-phosphate [PI(4)P] between two apposed membranes. Because of the subsequent hydrolysis of PI(4)P, this counterexchange is irreversible and contributes to the establishment of a cholesterol gradient along organelles of the secretory pathway. The facts that some natural anti-cancer molecules block OSBP and that many viruses hijack the OSBP cycle for the formation of intracellular replication organelles highlight the importance and potency of OSBP-mediated lipid exchange. The architecture of some LTPs is similar to that of OSBP, suggesting that the principles of the OSBP cycle—burning PI(4)P for the vectorial transfer of another lipid—might be general.

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Hanadate, Yuki, Yumiko Saito-Nakano, Kumiko Nakada-Tsukui, and Tomoyoshi Nozaki. "Identification and Characterization of the Entamoeba Histolytica Rab8a Binding Protein: A Cdc50 Homolog." International Journal of Molecular Sciences 19, no. 12 (November 30, 2018): 3831. http://dx.doi.org/10.3390/ijms19123831.

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Membrane traffic plays a pivotal role in virulence in the enteric protozoan parasite Entamoeba histolytica. EhRab8A small GTPase is a key regulator of membrane traffic at the endoplasmic reticulum (ER) of this protist and is involved in the transport of plasma membrane proteins. Here we identified the binding proteins of EhRab8A. The Cdc50 homolog, a non-catalytic subunit of lipid flippase, was identified as an EhRab8A binding protein candidate by affinity coimmunoprecipitation. Binding of EhRab8A to EhCdc50 was also confirmed by reciprocal immunoprecipitation and blue-native polyacrylamide gel electrophoresis, the latter of which revealed an 87 kDa complex. Indirect immunofluorescence imaging with and without Triton X100 showed that endogenous EhCdc50 localized on the surface in the absence of permeabilizing agent but was observed on the intracellular structures and overlapped with the ER marker Bip when Triton X100 was used. Overexpression of N-terminal HA-tagged EhCdc50 impaired its translocation to the plasma membrane and caused its accumulation in the ER. As reported previously in other organisms, overexpression and accumulation of Cdc50 in the ER likely inhibited surface transport and function of the plasma membrane lipid flippase P4-ATPase. Interestingly, HA-EhCdc50-expressing trophozoites gained resistance to miltefosine, which is consistent with the prediction that HA-EhCdc50 overexpression caused its accumulation in the ER and mislocalization of the unidentified lipid flippase. Similarly, EhRab8A gene silenced trophozoites showed increased resistance to miltefosine, supporting EhRab8A-dependent transport of EhCdc50. This study demonstrated for the first time that EhRab8A mediates the transport of EhCdc50 and lipid flippase P4-ATPase from the ER to the plasma membrane.

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Ito, Jinichi, and Makoto Michikawa. "ApoA-I/HDL Generation and Intracellular Cholesterol Transport through Cytosolic Lipid-Protein Particles in Astrocytes." Journal of Lipids 2014 (2014): 1–9. http://dx.doi.org/10.1155/2014/530720.

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Exogenous apolipoprotein A-I (apoA-I) associates with ATP-binding cassette transporter A1 (ABCA1) on the cell surface of astrocytes like various peripheral cells and enhances the translocation of newly synthesized cholesterol from the endoplasmic reticulum/Golgi apparatus (ER/Golgi) to the cytosol. The cholesterol translocated to the cytosol is incorporated to cytosolic lipid-protein particles (CLPP) together with phospholipids and proteins such as sphingomyelin, phosphatidylcholine, caveolin-1, protein kinase Cα(PK-Cα), and cyclophilin A. The CLPP are high density lipoproteins- (HDL-)like cytosolic lipid-protein complex with densities of 1.09–1.16 g/mL and diameters of 17-18 nm. The association of exogenous apoA-I with cellular ABCA1 induces tyrosine phosphorylation, activation, and translocation to the CLPP of ABCA1-associated phospholipase Cγ(PL-Cγ) in rat astrocytes. Furthermore, PK-Cαis translocated and activated to/in the CLPP through the production of diacylglyceride in the CLPP. ApoA-I enhances both the association of CLPP with microtubules and the phosphorylation ofα-tubulin as a component of microtubules. The CLPP are dissociated from microtubules afterα-tubulin in microtubules is phosphorylated by the CLPP-associated PK-Cα. The association and dissociation between CLPP and microtubules may participate in the intracellular transport of cholesterol to the plasma membrane.

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Schaletzki, Yvonne, Marie-Luise Kromrey, Susanne Bröderdorf, Elke Hammer, Markus Grube, Paul Hagen, Sonja Sucic, et al. "Several adaptor proteins promote intracellular localisation of the transporter MRP4/ABCC4 in platelets and haematopoietic cells." Thrombosis and Haemostasis 117, no. 01 (2017): 105–15. http://dx.doi.org/10.1160/th16-01-0045.

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SummaryThe multidrug resistance protein 4 (MRP4/ABCC4) has been identified as an important transporter for signalling molecules including cyclic nucleotides and several lipid mediators in platelets and may thus represent a novel target to interfere with platelet function. Besides its localisation in the plasma membrane, MRP4 has been also detected in the membrane of dense granules in resting platelets. In polarised cells it is localised at the basolateral or apical plasma membrane. To date, the mechanism of MRP4 trafficking has not been elucidated; protein interactions may regulate both the localisation and function of this transporter. We approached this issue by searching for interacting proteins by in vitro binding assays, followed by immunoblotting and mass spectrometry, and by visualising their co-localisation in platelets and haematopoietic cells. We identified the PDZ domain containing scaffold proteins ezrin-binding protein 50 (EBP50/NHERF1), postsynaptic density protein 95 (PSD95), and sorting nexin 27 (SNX27), but also the adaptor protein complex 3 subunit β3A (AP3B1) and the heat shock protein HSP90 as putative interaction partners of MRP4. The knockdown of SNX27, PSD95, and AP3B1 by siRNA in megakaryoblastic leuk aemia cells led to a redistribution of MRP4 from intracellular structures to the plasma membrane. Inhibition of HSP90 led to a diminished expression and retention of MRP4 in the endoplasmic reticulum. These results indicate that MRP4 localisation and function are regulated by multiple protein interactions. Changes in the adaptor proteins can hence lead to altered localisation and function of the transporter.Supplementary Material to this article is available at www.thrombosis-online.com.

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Li, Ben, Muzammil H. Syed, Hamzah Khan, Krishna K. Singh, and Mohammad Qadura. "The Role of Fatty Acid Binding Protein 3 in Cardiovascular Diseases." Biomedicines 10, no. 9 (September 14, 2022): 2283. http://dx.doi.org/10.3390/biomedicines10092283.

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Fatty acid binding proteins (FABPs) are proteins found in the cytosol that contribute to disorders related to the cardiovascular system, including atherosclerosis and metabolic syndrome. Functionally, FABPs serve as intracellular lipid chaperones, interacting with hydrophobic ligands and mediating their transportation to sites of lipid metabolism. To date, nine unique members of the FABP family (FABP 1–9) have been identified and classified according to the tissue in which they are most highly expressed. In the literature, FABP3 has been shown to be a promising clinical biomarker for coronary and peripheral artery disease. Given the rising incidence of cardiovascular disease and its associated morbidity/mortality, identifying biomarkers for early diagnosis and treatment is critical. In this review, we highlight key discoveries and recent studies on the role of FABP3 in cardiovascular disorders, with a particular focus on its clinical relevance as a biomarker for peripheral artery disease.

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Raychaudhuri, Sumana, Young Jun Im, James H. Hurley, and William A. Prinz. "Nonvesicular sterol movement from plasma membrane to ER requires oxysterol-binding protein–related proteins and phosphoinositides." Journal of Cell Biology 173, no. 1 (April 3, 2006): 107–19. http://dx.doi.org/10.1083/jcb.200510084.

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Sterols are moved between cellular membranes by nonvesicular pathways whose functions are poorly understood. In yeast, one such pathway transfers sterols from the plasma membrane (PM) to the endoplasmic reticulum (ER). We show that this transport requires oxysterol-binding protein (OSBP)–related proteins (ORPs), which are a large family of conserved lipid-binding proteins. We demonstrate that a representative member of this family, Osh4p/Kes1p, specifically facilitates the nonvesicular transfer of cholesterol and ergosterol between membranes in vitro. In addition, Osh4p transfers sterols more rapidly between membranes containing phosphoinositides (PIPs), suggesting that PIPs regulate sterol transport by ORPs. We confirmed this by showing that PM to ER sterol transport slows dramatically in mutants with conditional defects in PIP biosynthesis. Our findings argue that ORPs move sterols among cellular compartments and that sterol transport and intracellular distribution are regulated by PIPs.

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Journal articles on the topic 'Intracellular lipid-binding protein'

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