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Gregory, Mark, Meng-Xin Yin, Malcolm J. McConville, Eleanor Williams, Alex N. Bullock, Stuart J. Conway, Antony W. Burgess, Bruno Catimel et Andrew B. Holmes. « Synthesis of Highly Water-Soluble Adamantyl Phosphoinositide Derivatives ». Australian Journal of Chemistry 68, no 4 (2015) : 543. http://dx.doi.org/10.1071/ch14543.
Texte intégralRésumé :
Phosphatidylinositol phosphates are key regulators of cell signalling pathways and membrane trafficking in eukaryotic cells, and there is a need for new chemical probes to further understand how they interact with lipid-binding proteins. Here, the synthesis of phosphatidylinositol phosphate analogues containing adamantyl carboxylic ester groups, in place of the natural lipid side chains, is described. These derivatives are considerably more soluble in water than analogues containing other lipid side chains and do not form large aggregates such as liposomes or micelles. These adamantyl analogues bind to known phosphoinositide-binding proteins with similar affinities to native ligands and will facilitate future studies on the substrate specificities of these proteins involving cocrystallisation studies with proteins.
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Ibrahim, Muktar Musa, Adamu Uzairu, Muhammad Tukur Ibrahim et Abdullahi Bello Umar. « Modelling PIP4K2A inhibitory activity of 1,7-naphthyridine analogues using machine learning and molecular docking studies ». RSC Advances 13, no 6 (2023) : 3402–15. http://dx.doi.org/10.1039/d2ra07382j.
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Smith, C. D., et K. J. Chang. « Regulation of Brain Phosphatidylinositol-4-phosphate Kinase by GTP Analogues ». Journal of Biological Chemistry 264, no 6 (février 1989) : 3206–10. http://dx.doi.org/10.1016/s0021-9258(18)94052-4.
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Boronenkov, Igor V., Joost C. Loijens, Masato Umeda et Richard A. Anderson. « Phosphoinositide Signaling Pathways in Nuclei Are Associated with Nuclear Speckles Containing Pre-mRNA Processing Factors ». Molecular Biology of the Cell 9, no 12 (décembre 1998) : 3547–60. http://dx.doi.org/10.1091/mbc.9.12.3547.
Texte intégralRésumé :
Phosphoinositide signal transduction pathways in nuclei use enzymes that are indistinguishable from their cytosolic analogues. We demonstrate that distinct phosphatidylinositol phosphate kinases (PIPKs), the type I and type II isoforms, are concentrated in nuclei of mammalian cells. The cytosolic and nuclear PIPKs display comparable activities toward the substrates phosphatidylinositol 4-phosphate and phosphatidylinositol 3-phosphate. Indirect immunofluorescence revealed that these kinases were associated with distinct subnuclear domains, identified as “nuclear speckles,” which also contained pre-mRNA processing factors. A pool of nuclear phosphatidylinositol bisphosphate (PIP2), the product of these kinases, was also detected at these same sites by monoclonal antibody staining. The localization of PIPKs and PIP2 to speckles is dynamic in that both PIPKs and PIP2 reorganize along with other speckle components upon inhibition of mRNA transcription. Because PIPKs have roles in the production of most phosphatidylinositol second messengers, these findings demonstrate that phosphatidylinositol signaling pathways are localized at nuclear speckles. Surprisingly, the PIPKs and PIP2 are not associated with invaginations of the nuclear envelope or any nuclear membrane structure. The putative absence of membranes at these sites suggests novel mechanisms for the generation of phosphoinositides within these structures.
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Morii, Hiroyuki, Tatsuo Okauchi, Hiroki Nomiya, Midori Ogawa, Kazumasa Fukuda et Hatsumi Taniguchi. « Studies of inositol 1-phosphate analogues as inhibitors of the phosphatidylinositol phosphate synthase in mycobacteria ». Journal of Biochemistry 153, no 3 (5 décembre 2012) : 257–66. http://dx.doi.org/10.1093/jb/mvs141.
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Pratt, Clifford, Yue-Jin Liu, Ting-Yi Chu, Karin Melkonian, Burton E. Tropp et Robert Engel. « Phosphonolipids. 3. Phosphonic acid analogues of phosphatidylinositol and related materials ». Canadian Journal of Chemistry 70, no 8 (1 août 1992) : 2135–41. http://dx.doi.org/10.1139/v92-268.
Texte intégralRésumé :
A convergent synthesis of an isosteric phosphonic acid analogue of phosphatidylinositol has been accomplished in which a non-hydrolyzable P—C—C linkage is present in place of the normal P—O—C esteric linkage joining the phosphate and diacylglycerol portions of the molecule. The synthetic route used provides the configuration at each stereogenic center to correspond to that present in the biologically generated phospholipid. In addition, the approach provides asymmetric introduction of acyl functions, placing saturated and unsaturated acyl groups in the terminal and internal positions respectively of the backbone portion of the analogue, corresponding to that present in the biologically generated phospholipid.
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Xu, Yong, Stephanie A. Lee, Tatiana G. Kutateladze, Diego Sbrissa, Assia Shisheva et Glenn D. Prestwich. « Chemical Synthesis and Molecular Recognition of Phosphatase-Resistant Analogues of Phosphatidylinositol-3-phosphate ». Journal of the American Chemical Society 128, no 3 (janvier 2006) : 885–97. http://dx.doi.org/10.1021/ja0554716.
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Graves, J. D., S. C. Lucas, D. R. Alexander et D. A. Cantrell. « Guanine nucleotide regulation of inositol phospholipid hydrolysis and CD3-antigen phosphorylation in permeabilized T lymphocytes ». Biochemical Journal 265, no 2 (15 janvier 1990) : 407–13. http://dx.doi.org/10.1042/bj2650407.
Texte intégralRésumé :
A method of membrane permeabilization of T lymphocytes with the bacterial cytotoxin streptolysin O has allowed the effect of guanine nucleotide analogues on phosphatidylinositol metabolism and protein kinase C (PKC) activation to be investigated. The data demonstrate that, in permeabilized cells, phosphorylation of the gamma subunit of the CD3 antigen can be induced in response to the PKC activator phorbol 12,13-dibutyrate, the polyclonal mitogen phytohaemagglutinin (PHA) and the stimulatory guanine nucleotide analogue guanosine 5′-[gamma-thio]triphosphate (GTP[S]). Application of a pseudo-substrate inhibitor of PKC indicated that CD3gamma-chain phosphorylation induced in response to all three agonists was mediated by PKC. PHA and GTP[S] also stimulated inositol phospholipid turnover and inositol phosphate accumulation. The kinetics and concentration-dependence of PHA-induced inositol phospholipid hydrolysis correlated with PHA-induced CD3gamma phosphorylation, suggesting that PHA may regulate CD3gamma phosphorylation via diacylglycerol produced as a consequence of inositol phospholipid hydrolysis. However, there was an inconsistency in that PHA induced greater (greater than 200%) levels of inositol phospholipid turnover than did GTP[S], but much weaker (less than 50%) levels of CD3-antigen phosphorylation. There was also a discrepancy between GTP[S] effects on phosphatidylinositol turnover and PKC activation, in that the half-maximal GTP[S] concentration for inositol phosphate production and CD3gamma-chain phosphorylation was 0.75 microM and 75 microM respectively. Moreover, 10 microM-GTP[S] induced maximal inositol phosphate production, but only 10% of maximal CD3gamma-chain phosphorylation. The data are consistent with the idea that other signal-transduction pathways, in addition to those involving inositol phosphate production, exist for the regulation of PKC in T lymphocytes.
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Taylor, S. J., et J. H. Exton. « Guanine-nucleotide and hormone regulation of polyphosphoinositide phospholipase C activity of rat liver plasma membranes. Bivalent-cation and phospholipid requirements ». Biochemical Journal 248, no 3 (15 décembre 1987) : 791–99. http://dx.doi.org/10.1042/bj2480791.
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The effect of the GTP analogue guanosine 5′-[gamma-thio]triphosphate (GTP[S]) on the polyphosphoinositide phospholipase C (PLC) of rat liver was examined by using exogenous [3H]phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]. GTP[S] stimulated the membrane-bound PLC up to 20-fold, with a half-maximal effect at approx. 100 nM. Stimulation was also observed with guanosine 5′-[beta gamma-imido]triphosphate, but not with adenosine 5′-[gamma-thio]triphosphate, and was inhibited by guanosine 5′-[beta-thio]diphosphate. Membrane-bound PLC was entirely Ca2+-dependent, and GTP[S] produced both a decrease in the Ca2+ requirement and an increase in activity at saturating [Ca2+]. The stimulatory action of GTP[S] required millimolar Mg2+. [8-arginine]Vasopressin (100 nM) stimulated the PLC activity approx. 2-fold in the presence of 10 nM-GTP[S], but had no effect in the absence of GTP[S] or at 1 microM-GTP[S]. The hydrolysis of PtdIns(4,5)P2 by membrane-bound PLC was increased when the substrate was mixed with phosphatidylethanolamine, phosphatidylcholine or various combinations of these with phosphatidylserine. With PtdIns(4,5)P2, alone or mixed with phosphatidylcholine, GTP[S] evoked little or no stimulation of the PLC activity. However, maximal stimulation by GTP[S] was observed in the presence of a 2-fold molar excess of phosphatidylserine or various combinations of phosphatidylethanolamine and phosphatidylserine. Hydrolysis of [3H]phosphatidylinositol 4-phosphate by membrane-bound PLC was also increased by GTP[S]. However, [3H]phosphatidylinositol was a poor substrate, and its hydrolysis was barely affected by GTP[S]. Cytosolic PtdIns(4,5)P2-PLC exhibited a Ca2+-dependence similar to that of the membrane-bound activity, but was unaffected by GTP[S]. It is concluded that rat liver plasma membranes possess a Ca2+-dependent polyphosphoinositide PLC that is activated by hormones and GTP analogues, depending on the Mg2+ concentration and phospholipid environment. It is proposed that GTP analogues and hormones, acting through a guanine nucleotide-binding protein, activate the enzyme mainly by lowering its Ca2+ requirement.
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Lobasso, Simona, Patrizia Lopalco, Roberto Angelini, Rita Vitale, Harald Huber, Volker Müller et Angela Corcelli. « Coupled TLC and MALDI-TOF/MS Analyses of the Lipid Extract of the Hyperthermophilic ArchaeonPyrococcus furiosus ». Archaea 2012 (2012) : 1–10. http://dx.doi.org/10.1155/2012/957852.
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The lipidome of the marine hyperthermophilic archaeonPyrococcus furiosuswas studied by means of combined thin-layer chromatography and MALDI-TOF/MS analyses of the total lipid extract. 80–90% of the major polar lipids were represented by archaeol lipids (diethers) and the remaining part by caldarchaeol lipids (tetraethers). The direct analysis of lipids on chromatography plate showed the presence of the diphytanylglycerol analogues of phosphatidylinositol and phosphatidylglycerol, theN-acetylglucosamine-diphytanylglycerol phosphate plus some caldarchaeol lipids different from those previously described. In addition, evidence for the presence of the dimeric ether lipid cardiolipin is reported, suggesting that cardiolipins are ubiquitous in archaea.
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Huang, Wei, Honglu Zhang, Foteini Davrazou, Tatiana G. Kutateladze, Xiaobing Shi, Or Gozani et Glenn D. Prestwich. « Stabilized Phosphatidylinositol-5-Phosphate Analogues as Ligands for the Nuclear Protein ING2 : Chemistry, Biology, and Molecular Modeling ». Journal of the American Chemical Society 129, no 20 (mai 2007) : 6498–506. http://dx.doi.org/10.1021/ja070195b.
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Gold, M. R., J. P. Jakway et A. L. DeFranco. « Involvement of a guanine-nucleotide-binding component in membrane IgM-stimulated phosphoinositide breakdown. » Journal of Immunology 139, no 11 (1 décembre 1987) : 3604–13. http://dx.doi.org/10.4049/jimmunol.139.11.3604.
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Abstract Cross-linking of membrane immunoglobulin, the B cell receptor for antigen, activates the phosphoinositide signal transduction pathway. The initial event in this pathway is the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) by phospholipase C. This reaction yields two intracellular second messengers, diacylglycerol, which activates protein kinase C, and inositol trisphosphate, which causes an increase in cytoplasmic Ca2+. The experiments reported here demonstrate that activation of phospholipase C by membrane IgM (mIgM) involves a guanine nucleotide-dependent step. Saponin was used to permeabilize WEHI-231 B lymphoma cells and permit direct manipulation of nucleotide and Ca2+ concentrations. Very high levels of Ca2+ (greater than 100 microM) activated the phospholipase maximally without a requirement for cross-linking of mIgM. However, at much lower, physiologically relevant Ca2+ concentrations (100 to 500 nM), receptor-stimulated PtdInsP2 hydrolysis could be demonstrated. The ability of anti-IgM antibodies to activate phospholipase C in permeabilized WEHI-231 cells was greatly increased by nonhydrolyzable guanosine 5'-triphosphate (GTP) analogues (guanosine-5'-O-(3-thiotriphosphate) or 5'-guanylylimidodiphosphate), but not by guanosine diphosphate or guanosine diphosphate analogues or by a nonhydrolyzable analogue of adenosine triphosphate. This specificity for GTP analogues is consistent with the hypothesis that a GTP-binding regulatory protein analogous to those that couple receptors to adenylate cyclase is involved in the activation of phospholipase C by mIgM in WEHI-231 B lymphoma cells. In order to characterize this putative GTP-binding component, we examined the ability of pertussis toxin and cholera toxin to affect anti-IgM-stimulated inositol phosphate production. These bacterial toxins covalently modify and modulate the activity of various GTP-binding regulatory proteins and in some cell types can block receptor-stimulated PtdInsP2 breakdown. In WEHI-231 B lymphoma cells, neither toxin blocked signaling by mIgM. Thus mIgM appears to be coupled to the phosphoinositide signaling pathway by a GTP-dependent component that is insensitive to both pertussis toxin and cholera toxin.
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BRUZIK, K. S., G. LIN et M. D. TSAI. « ChemInform Abstract : Phosphorothioate Analogues of Phosphatidylinositol and Inositol 1,2- Cyclic Phosphate. Application to the Mechanism of Phospholipase C ». ChemInform 23, no 1 (22 août 2010) : no. http://dx.doi.org/10.1002/chin.199201338.
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Mannix, R. J., T. Moatter, K. A. Kelley et M. E. Gerritsen. « Cellular signaling responses mediated by a novel nucleotide receptor in rabbit microvessel endothelium ». American Journal of Physiology-Heart and Circulatory Physiology 265, no 2 (1 août 1993) : H675—H680. http://dx.doi.org/10.1152/ajpheart.1993.265.2.h675.
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The adenine nucleotide, ATP, elicits an elevation in intracellular ionized calcium concentration ([Ca2+]i) and phospholipase C-mediated phosphatidylinositol hydrolysis and stimulates the synthesis of the prostaglandins E2 and I2 in cultured endothelial cells derived from rabbit cardiac muscle. Use of various ATP analogues indicated that these events did not fit the classical definition of P1 or P2 purinergic receptors and, furthermore, indicated that the receptor(s) mediating these activities was not specific for purines. The rank order of agonist potency on prostaglandin release, elevations in [Ca2+]i, and inositol phosphate response was UTP > or = ATP > ADP > ADP[beta]S = 2-methylthio ATP > adenosine, suggesting that these three cellular responses are coupled to the same or similar receptors. However, the sensitivity of these three cellular responses to added nucleotides was somewhat different. The half-maximum effective concentration (EC50) for ATP stimulation of prostaglandin release was 100 microM, for inositol phosphate turnover it was 25 microM, and for elevations in [Ca2+]i it was < 1 microM. Similar discrepancies in EC50 UTP values for these three cellular responses were also noted. These observations indicate that purine and pyrimidine nucleotides elicit at least three cellular responses in rabbit cardiac muscle microvessel endothelial cells, all demonstrating similar rank orders of potency. However, the differences in EC50 suggest that if these responses are mediated by a single receptor type, it exhibits divergent coupling to various cellular signaling pathways.
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Qiao, Lixin, Fajun Nan, Mark Kunkel, Alfred Gallegos, Garth Powis et Alan P. Kozikowski. « 3-Deoxy-d-myo-inositol 1-Phosphate, 1-Phosphonate, and Ether Lipid Analogues as Inhibitors of Phosphatidylinositol-3-kinase Signaling and Cancer Cell Growth ». Journal of Medicinal Chemistry 41, no 18 (août 1998) : 3303–6. http://dx.doi.org/10.1021/jm980254j.
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Anderson, L., G. Milligan et K. A. Eidne. « Characterization of the gonadotrophin-releasing hormone receptor in αT3-1 pituitary gonadotroph cells ». Journal of Endocrinology 136, no 1 (janvier 1993) : 51—NP. http://dx.doi.org/10.1677/joe.0.1360051.
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ABSTRACT The present study has characterized the gonadotrophin-releasing hormone (GnRH) receptor in immortalized αT3-1 pituitary gonadotroph cells. GnRH and GnRH analogues produced both a dose- and time-dependent increase in total inositol phosphate (IP) accumulation. The rank order of potency of these analogues was the same as that obtained in parallel receptor-binding studies in αT3-1 cells. These responses were abolished following pretreatment with a GnRH antagonist. The use of a specific inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) assay demonstrated a rapid but short-lived rise in Ins(1,4,5)P3 production. Intracellular calcium ([Ca2+]i) was subsequently measured in αT3-1 cells using dual wavelength fluorescence microscopy combined with dynamic video imaging. GnRH produced a biphasic rise in [Ca2+]i. The initial calcium transient was complete within seconds while the smaller secondary plateau phase lasted several minutes. G-protein involvement in the IP response to GnRH in αT3-1 cells was investigated using sodium fluoride (NaF) and pertussis toxin (PTx) which activate and inactivate G-proteins respectively. Like GnRH, NaF produced a dose- and time-dependent increase in IP accumulation. Activation of phospholipase C in these cells by either GnRH or NaF was PTx-insensitive, suggesting that the G-protein involved was neither Gi nor Go but more probably Gq. Immunoblot analysis of αT3-1 cell membranes using antisera raised against the predicted C-terminal decapeptide of the α subunit of Gq demonstrated the presence of Gq in αT3-1 cells. Collectively these results show that the GnRH receptors expressed in αT3-1 cells are coupled to the phosphatidylinositol second messenger pathway via a specific G-protein. αT3-1 therefore represents a convenient model in which to study GnRH-related second messenger pathways. Journal of Endocrinology (1993) 136, 51–58
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Eberhard, D. A., et R. W. Holz. « Regulation of the formation of inositol phosphates by calcium, guanine nucleotides and ATP in digitonin-permeabilized bovine adrenal chromaffin cells ». Biochemical Journal 279, no 2 (15 octobre 1991) : 447–53. http://dx.doi.org/10.1042/bj2790447.
Texte intégralRésumé :
Both micromolar Ca2+ and guanosine 5′-[gamma-thio]triphosphate (GTP[S]) stimulated the formation of inositol phosphates (InsPs) in digitonin-permeabilized chromaffin cells prelabelled with [3H]inositol. The production of InsPs was potentiated by ATP. Guanosine 5′-[beta-thio]diphosphate (GDP[S]) caused a GTP-reversible shift to higher concentrations in the Ca(2+)-concentration-response curve for the release of InsPs without changing the maximal response. GTP[S] caused a shift to lower concentrations of Ca2+ and also increased the maximal response. The effects of GTP[S] and Ca2+ were synergistic. Although as much as 80% of the InsPs were derived from phosphatidylinositol 4-phosphate (PtdInsP) or 4,5-bisphosphate (PtdInsP2), the amount of InsPs produced could be several times the total amount of PtdInsP and PtdInsP2 in the cells and was largely accounted for by a decrease in PtdIns. The levels of labelled PtdInsP and PtdInsP2 increased on stimulation with Ca2+, but decreased on stimulation with GTP[S] or the combination of Ca2+ and GTP[S]. Preincubation with Ca2+ and ATP amplified the subsequent GTP[S]-induced production of InsPs. ATP and its gamma-thio and beta gamma-imido analogues stimulated the formation of InsPs in intact cells. However, only ATP potentiated the responses to Ca2+ and GTP[S] in permeable cells. Our main conclusions are: (1) a GTP-binding protein participates in the Ca(2+)-induced production of InsPs by phospholipase C, and (2) ATP markedly potentiates the stimulated formation of InsPs, an effect with arises from its role in polyphosphoinositide synthesis and does not involve purinergic receptor activation in permeabilized cells. The data also suggest that the different effects of Ca2+ and GTP[S] on polyphosphoinositide synthesis probably contribute to the synergistic action of Ca2+ and GTP[S] on the generation of InsPs.
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Tamir, A., et N. Isakov. « Cyclic AMP inhibits phosphatidylinositol-coupled and -uncoupled mitogenic signals in T lymphocytes. Evidence that cAMP alters PKC-induced transcription regulation of members of the jun and fos family of genes. » Journal of Immunology 152, no 7 (1 avril 1994) : 3391–99. http://dx.doi.org/10.4049/jimmunol.152.7.3391.
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Abstract T lymphocyte stimulation via the Ag receptor results in activation of phospholipase C gamma 1 that catalyses the hydrolysis of phosphatidylinositol (PI). The hydrolysis generates inositol phosphate and diacylglycerol, which in turn, increase intracellular Ca2+ concentration and activates protein kinase C, respectively. Agonists operating via the adenylate cyclase pathway or cell permeable cAMP analogues inhibit T cell activation by interfering with the PI-turnover. We have shown that dbcAMP inhibits PI-independent mitogenic signals in T cells after stimulation with TPA plus ionomycin. dbcAMP inhibited the TPA plus ionomycin-induced transcription of IL-2 and IL-2R genes in EL4 cells, suggesting interference with biochemic events downstream to PI hydrolysis and upstream to transcription of early activation genes. Because many of the early genes operating in T cell mitogenesis possess a TPA-response element (TRE) in their promoter region, we tested the effect of cAMP on the TRE-binding protein, TPA-response element (TRE) in their promoter region, we tested the effect of cAMP on the TRE-binding protein, AP-1. dbcAMP increased the binding activity of nuclear proteins consisting of Fos:Jun heterodimers to a TRE-containing oligonucleotide, but altered the composition of Jun proteins in the AP-1. Furthermore, the TPA plus ionomycin-induced transcription program of members of the jun and fos family of genes was altered by dbcAMP, suggesting that inhibition of T cell proliferation by dbcAMP is a consequence of intervention in transcriptional regulation by TRE-binding proteins.
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Faili, A., J. Randon, I. M. Francischetti, B. B. Vargaftig et M. Hatmi. « Convulxin-induced platelet aggregation is accompanied by a powerful activation of the phospholipase C pathway ». Biochemical Journal 298, no 1 (15 février 1994) : 87–91. http://dx.doi.org/10.1042/bj2980087.
Texte intégralRésumé :
Platelet aggregation and stimulation of phosphoinositide-specific phospholipase C (PLC) by thrombin and by convulxin (Cvx), a non-enzymic snake venom glycoprotein, were compared. Cvx-stimulated production of inositol phosphates by washed platelets was independent of the cyclo-oxygenase pathway, formation of platelet-activating factor and ADP release, but prostacyclin (prostaglandin I2), a stimulator of cyclic AMP formation, suppressed its effects on platelet and PLC activation. Kinetic analysis showed that inositol 1,4,5-trisphosphate formation reached its maximal value 15 s after platelet stimulation with Cvx and persisted for at least 5 min. Neomycin sulphate (10 mM), which complexes phosphatidylinositol 4-phosphate and phosphatidyl-inositol 4,5-bisphosphate, decreased the production of inositol phosphates, partially prevented platelet aggregation induced by a high concentration of Cvx (10 nM) and abolished both platelet aggregation and inositol phosphate formation induced by thrombin (2 units/ml) and by a stable prostaglandin H2 analogue, U46619 (1 microM). In contrast with neomycin sulphate, Na2SO4 had no significant effect against all agonists tested. It is concluded that platelet activation by Cvx is partially mediated by PLC and involves other mechanisms as well.
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Harnett, M. M., et G. G. Klaus. « G protein coupling of antigen receptor-stimulated polyphosphoinositide hydrolysis in B cells. » Journal of Immunology 140, no 9 (1 mai 1988) : 3135–39. http://dx.doi.org/10.4049/jimmunol.140.9.3135.
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Abstract Cross-linking of the IgM and IgD Ag-R on mature B lymphocytes provokes the rapid hydrolysis of phosphatidylinositol 4,5-bisphosphate. We show here that in permeabilized, [3H]inositol-labeled mouse B cells the nonhydrolyzable GTP analogue GTP gamma S induces release of inositol phosphates, including inositol trisphosphate. The response is markedly augmented by the addition of polyclonal anti-Ig or anti-mu or anti-delta mAb. Inositol phosphate release provoked in intact B cells by any of the anti-receptor antibodies was not inhibited by pertussis toxin and only partially inhibited by cholera toxin. The results therefore indicate that both IgM- and IgD-R on B cells are coupled to the polyphosphoinositide-specific phosphodiesterase by one or more G proteins, which have yet to be identified.
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Camps, M., C. F. Hou, K. H. Jakobs et P. Gierschik. « Guanosine 5′-[γ-thio]triphosphate-stimulated hydrolysis of phosphatidylinositol 4,5-bisphosphate in HL-60 granulocytes. Evidence that the guanine nucleotide acts by relieving phospholipase C from an inhibitory constraint ». Biochemical Journal 271, no 3 (1 novembre 1990) : 743–48. http://dx.doi.org/10.1042/bj2710743.
Texte intégralRésumé :
Myeloid differentiated human leukaemia (HL-60) cells contain a soluble phospholipase C that hydrolysed phosphatidylinositol 4.5-bisphosphate and was markedly stimulated by the metabolically stable GTP analogue guanosine 5′-[gamma-thio]triphosphate (GTP[S]). Half-maximal and maximal (up to 5-fold) stimulation of inositol phosphate formation by GTP[S] occurred at 1.5 microM and 30 microM respectively. Other nucleotides (GTP, GDP, GMP, guanosine 5′-[beta-thio]diphosphate. ATP, adenosine 5′-[gamma-thio]triphosphate, UTP) did not affect phospholipase C activity, GTP[S] stimulation of inositol phosphate accumulation was inhibited by excess GDP, but not by ADP. The effect of GTP[S] on inositol phosphate formation was absolutely dependent on and markedly stimulated by free Ca2+ (median effective concn. approximately 100 nM). Analysis of inositol phosphates by anion-exchange chromatography revealed InsP3 as the major product of GTP[S]-stimulated phospholipase C activity. In the absence of GTP[S], specific phospholipase C activity was markedly decreased when tested at high protein concentrations, whereas GTP[S] stimulation of the enzyme was markedly enhanced under these conditions. As both basal and GTP[S]-stimulated inositol phosphate formation were linear with time whether studied at low or high protein concentration, these results suggest that (a) phospholipase C is under an inhibitory constraint and (b) GTP[S] relieves this inhibition, most likely by activating a soluble GTP-binding protein.
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Klima, Martin, Adriana Baumlova, Dominika Chalupska, Hubert Hřebabecký, Milan Dejmek, Radim Nencka et Evzen Boura. « The high-resolution crystal structure of phosphatidylinositol 4-kinase IIβ and the crystal structure of phosphatidylinositol 4-kinase IIα containing a nucleoside analogue provide a structural basis for isoform-specific inhibitor design ». Acta Crystallographica Section D Biological Crystallography 71, no 7 (30 juin 2015) : 1555–63. http://dx.doi.org/10.1107/s1399004715009505.
Texte intégralRésumé :
Phosphatidylinositol 4-phosphate (PI4P) is the most abundant monophosphoinositide in eukaryotic cells. Humans have four phosphatidylinositol 4-kinases (PI4Ks) that synthesize PI4P, among which are PI4K IIβ and PI4K IIα. In this study, two crystal structures are presented: the structure of human PI4K IIβ and the structure of PI4K IIα containing a nucleoside analogue. The former, a complex with ATP, is the first high-resolution (1.9 Å) structure of a PI4K. These structures reveal new details such as high conformational heterogeneity of the lateral hydrophobic pocket of the C-lobe and together provide a structural basis for isoform-specific inhibitor design.
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Vicentini, L. M., A. Ambrosini, F. Di Virgilio, J. Meldolesi et T. Pozzan. « Activation of muscarinic receptors in PC12 cells. Correlation between cytosolic Ca2+ rise and phosphoinositide hydrolysis ». Biochemical Journal 234, no 3 (15 mars 1986) : 555–62. http://dx.doi.org/10.1042/bj2340555.
Texte intégralRésumé :
The intracellular signals generated by carbachol activation of the muscarinic receptor [release of inositol phosphates as a consequence of phosphoinositide hydrolysis and rise of the cytosolic Ca2+ concentration ([Ca2+]i, measured by quin2)] were studied in intact PC12 pheochromocytoma cells that had been differentiated by treatment with nerve growth factor. When measured in parallel samples of the same cell preparation 30 s after receptor activation, the release of inositol trisphosphate and of its possible metabolites, inositol bis- and mono-phosphate, and the [Ca2+]i rise were found to occur with almost superimposable carbachol concentration curves. At the same time carbachol caused a decrease in the radioactivity of preloaded phosphatidylinositol 4,5-bisphosphate, the precursor of inositol trisphosphate. Neither the inositol phosphate nor the [Ca2+]i signal was modified by preincubation of the cells with either purified Bordetella pertussis toxin or forskolin, the direct activator of adenylate cyclase. Both signals were partially inhibited by dibutyryl cyclic AMP, especially when the nucleotide analogue was applied in combination with the phosphodiesterase inhibitors RO 201724 and theophylline. The latter drug alone profoundly inhibited the carbachol-induced [Ca2+]i rise, with only minimal effect on phosphoinositide hydrolysis. Because of the diverging results obtained with forskolin on the one hand, dibutyryl cyclic AMP and phosphodiesterase inhibitors on the other, the effects of the latter drugs are considered to be pharmacological, independent of the intracellular cyclic AMP concentration. Two further drugs tested, mepacrine and MY5445, inhibited phosphoinositide hydrolysis at the same time as the 45Ca2+ influx stimulated by carbachol. Taken together, our results concur with previous evidence obtained with permeabilized cells and cell fractions to indicate phosphatidylinositol 4,5-bisphosphate hydrolysis and [Ca2+]i rise as two successive events in the intracellular transduction cascade initiated by receptor activation. The strict correlation between the carbachol concentration curves for inositol trisphosphate generation and [Ca2+]i rise, and the inhibition by theophylline of the Ca2$ signal without major effects on inositol phosphate generation, satisfy important requirements of the abovementioned interpretation.
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Golla, Rajasree, et Ramakrishna Seethala. « A Homogeneous Enzyme Fragment Complementation Cyclic AMP Screen for GPCR Agonists ». Journal of Biomolecular Screening 7, no 6 (décembre 2002) : 515–25. http://dx.doi.org/10.1177/1087057102238625.
Texte intégralRésumé :
In the new high-throughput screening (HTS) campaign, receptor functional assays, 3’,5’-cyclic adenosine mono-phosphate (cAMP), intracellular [Ca2+]i, phosphatidylinositol turnover, and reporter-based assays are being used as primary screens as they are now developed as homogeneous and automation-friendly assays. FlashPlate assay and scintillation proximity assay using radiolabeled cAMP have been used for measuring cAMP. A nonradioactive homogeneous HTS assay using HitHunter™ enzyme fragment complementation (EFC) technology was evaluated for measuring cAMP in adherent and suspension cells overexpressing a Gαs-coupled receptor. In the EFC-cAMP assay, the β-galactosidase (β-gal) donor fragment-cAMP (ED-cAMP) conjugate complements with the β-gal enzyme acceptor (EA) fragment to form an active β-gal enzyme. Binding of ED-cAMP conjugate to the anti-cAMP antibody prevents its complementation with the EA fragment to form an active enzyme. Cyclic AMP in the samples compete with ED-cAMP to bind to the anti-cAMP antibody, thus increasing the free ED-cAMP that can complement with the EA fragment to form an active enzyme that is assayed with a luminescent substrate. Thus, this assay results in a positive signal unlike other technologies, wherein the signal is completed by cAMP in the sample. Glucagon-like peptide (GLP)-1 binds to GLP-1 receptor (with a Kd of 0.2 nM) signals through Gαs to activate adenylate cyclase, which results in an increase of intracellular cAMP (EC50 of 0.3 nM). GLP-1 stimulation of cAMP levels measured by the EFC method was similar in both adherent and suspension cell formats (EC50 ~0.3 nM) at different cell numbers. The assay was further validated with forskolin, exendin, and several active GLP-1 peptide analogues. The stimulation of cAMP by GLP-1 and forskolin was effectively inhibited by the adenylate cyclase inhibitors MDL-12330A and SQ-22536, confirming that the increased cAMP is through the AC pathway. The assay tolerates dimethyl sulfoxide (DMSO) up to 10%, and tartrazine does not interfere with the assay with the adherent cells up to 1 mM and affects minimally up to 10 μM in suspension cells. The assay is very robust, with a Z value of 0.7 to 0.8. The assay was validated with several plates of low molecular weight nonpeptide compounds and peptide agonists with different potencies. The suspension cell protocol is a robust homogeneous assay that involves fewer steps than the adherent cell protocol and is suitable for HTS. The cAMP assay using EFC technology is advantageous in that it has a greater dynamic range of detection; is nonradioactive, very sensitive, robust; has minimal interference from DMSO and colored compounds; and is amenable for automation. An added advantage of this assay is that the cAMP is measured as a positive signal, thereby reducing the incidence of false positives.
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Van Haastert, P. J. M., M. J. De Vries, L. C. Penning, E. Roovers, J. Van der Kaay, C. Erneux et M. M. Van Lookeren Campagne. « Chemoattractant and guanosine 5′-[γ-thio]triphosphate induce the accumulation of inositol 1,4,5-trisphosphate in Dictyostelium cells that are labelled with [3H]inositol by electroporation ». Biochemical Journal 258, no 2 (1 mars 1989) : 577–86. http://dx.doi.org/10.1042/bj2580577.
Texte intégralRésumé :
The analysis of the inositol cycle in Dictyostelium discoideum cells is complicated by the limited uptake of [3H]inositol (0.2% of the applied radioactivity in 6 h), and by the conversion of [3H]inositol into water-soluble inositol metabolites that are eluted near the position of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] on anion-exchange h.p.l.c. columns. The uptake was improved to 2.5% by electroporation of cells in the presence of [3H]inositol; electroporation was optimal at two 210 microseconds pulses of 7 kV. Cells remained viable and responsive to chemotactic signals after electroporation. The intracellular [3H]inositol was rapidly metabolized to phosphatidylinositol and more slowly to phosphatidylinositol phosphate and phosphatidylinositol bisphosphate. More than 85% of the radioactivity in the water-soluble extract that was eluted on Dowex columns as Ins(1,4,5)P3 did not co-elute with authentic [32P]Ins(1,4,5)P3 on h.p.l.c. columns. Chromatography of the extract by ion-pair reversed-phase h.p.l.c. provided a good separation of the polar inositol polyphosphates. Cellular [3H]Ins(1,4,5)P3 was identified by (a) co-elution with authentic [32P]Ins(1,4,5)P3 and (b) degradation by a partially purified Ins(1,4,5)P3 5-phosphatase from rat brain. The chemoattractant cyclic AMP and the non-hydrolysable analogue guanosine 5′-[gamma-thio]triphosphate induced a transient accumulation of radioactivity in Ins(1,4,5)P3; we did not detect radioactivity in inositol 1,3,4-trisphosphate or inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4]. In vitro, Ins(1,4,5)P3 was metabolized to inositol 1,4- and 4,5-bisphosphate, but not to Ins(1,3,4,5)P4 or another tetrakisphosphate isomer. We conclude that Dictyostelium has a receptor- and G-protein-stimulated inositol cycle which is basically identical with that in mammalian cells, but the metabolism of Ins(1,4,5)P3 is probably different.
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Tokuoka, Suzumi M., Adolfo Saiardi et Stephen J. Nurrish. « The Mood Stabilizer Valproate Inhibits both Inositol- and Diacylglycerol-signaling Pathways in Caenorhabditis elegans ». Molecular Biology of the Cell 19, no 5 (mai 2008) : 2241–50. http://dx.doi.org/10.1091/mbc.e07-09-0982.
Texte intégralRésumé :
The antiepileptic valproate (VPA) is widely used in the treatment of bipolar disorder, although the mechanism of its action in the disorder is unclear. We show here that VPA inhibits both inositol phosphate and diacylglycerol (DAG) signaling in Caenorhabditis elegans. VPA disrupts two behaviors regulated by the inositol-1,4,5-trisphosphate (IP3): defecation and ovulation. VPA also inhibits two activities regulated by DAG signaling: acetylcholine release and egg laying. The effects of VPA on DAG signaling are relieved by phorbol ester, a DAG analogue, suggesting that VPA acts to inhibit DAG production. VPA reduces levels of DAG and inositol-1-phosphate, but phosphatidylinositol-4,5-bisphosphate (PIP2) is slightly increased, suggesting that phospholipase C-mediated hydrolysis of PIP2 to form DAG and IP3 is defective in the presence of VPA.
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Smith, C. D., D. Wen, S. L. Mooberry et K. J. Chang. « Inhibition of phosphatidylinositol 4-phosphate kinase by heparin. A possible mechanism for the antiproliferative effects of heparin ». Biochemical Journal 281, no 3 (1 février 1992) : 803–8. http://dx.doi.org/10.1042/bj2810803.
Texte intégralRésumé :
Heparin and related glycosaminoglycans are important modulators of vascular smooth muscle cell growth, and may be involved in pathological processes such as atherosclerosis. Since polyphosphoinositide metabolism is a major mechanism for regulating cellular activities, including proliferation, the effects of glycosaminoglycans and polyanionic compounds on the activities of phosphoinositide kinases were characterized. Heparin and heparan sulphate caused dose-dependent inhibitions of rat brain cytosolic phosphatidylinositol 4-phosphate (PIP) kinase activity, with half-maximal inhibitory concentrations of approx. 0.5 and 5 microM respectively. PIP kinase was also inhibited by several dextran sulphates, but was not sensitive to inhibition by keratin sulphate, chondroitin sulphate or hyaluronic acid. Polynucleotides and acidic polypeptides were only weakly inhibitory. Heparin did not alter either the PIP- or the Mg(2+)-dependence of PIP kinase. Addition of heparin to brain membranes suppressed PIP kinase activity without affecting phosphatidylinositol (PI) kinase activity. Heparin interfered with the ability of a GTP analogue to stimulate PIP kinase activity in these membranes, suggesting that it uncouples the kinase from an activating guanine-nucleotide-binding protein. In cultured A-10 vascular smooth muscle cells, heparin caused dose- and time-dependent inhibition of [3H]thymidine incorporation into DNA. Similar treatments with heparin decreased cellular levels of phosphatidylinositol 4,5-bisphosphate (PIP2) without changing PI and PIP levels. Therefore heparin-mediated inhibition of PIP kinase appears to lead to decreases in PIP2 levels which may attenuate cellular proliferation.
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Putney, J. W. « The role of phosphoinositide metabolism in signal transduction in secretory cells ». Journal of Experimental Biology 139, no 1 (1 septembre 1988) : 135–50. http://dx.doi.org/10.1242/jeb.139.1.135.
Texte intégralRésumé :
Activation of a variety of cell surface receptors results in a biphasic increase in the cytoplasmic Ca2+ concentration, due to the release, or mobilization, of intracellular Ca2+ stores and to the entry of Ca2+ from the extracellular space. Stimulation of these same receptors also results in the phospholipase-C-catalysed hydrolysis of the minor plasma membrane phospholipid, phosphatidylinositol 4,5-bisphosphate, with the concomitant formation of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and diacylglycerol. Analogous to the adenylyl cyclase signalling system, receptor-mediated stimulation of phospholipase C also appears to occur through one or more intermediary guanine nucleotide-dependent regulatory proteins. It is well established that phosphatidylinositol 4,5-bisphosphate hydrolysis is responsible for the changes in Ca2+ homeostasis. There is strong evidence that Ins(1,4,5)P3 stimulates Ca2+ release from intracellular stores. The Ca2+-releasing actions of Ins(1,4,5)P3 are terminated by its metabolism through two distinct pathways. Ins(1,4,5)P3 is dephosphorylated by a 5-phosphatase to Ins(1,4)P2; alternatively, Ins(1,4,5)P3 can also be phosphorylated to Ins(1,3,4,5)P4 by a 3-kinase. Whereas the mechanism of Ca2+ mobilization is understood, the precise mechanisms involved in Ca2+ entry are not known; a recent proposal that Ins(1,4,5)P3 by emptying an intracellular Ca2+ pool, secondarily elicits Ca2+ entry will be considered. This review summarizes our current understanding of the mechanisms by which inositol phosphates regulate cytoplasmic Ca2+ concentrations.
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Kolb, J. P., D. Renard, B. Dugas, E. Genot, E. Petit-Koskas, M. Sarfati, G. Delespesse et J. Poggioli. « Monoclonal anti-CD23 antibodies induce a rise in [Ca2+]i and polyphosphoinositide hydrolysis in human activated B cells. Involvement of a Gp protein. » Journal of Immunology 145, no 2 (15 juillet 1990) : 429–37. http://dx.doi.org/10.4049/jimmunol.145.2.429.
Texte intégralRésumé :
Abstract Transduction through the CD23 molecule (Fc epsilon RII) was analyzed in human activated B lymphocytes using anti-CD23 mAb. B cell blasts expressing an increased amount of surface CD23 molecule were obtained by stimulation of normal peripheral blood B lymphocytes with Staphylococcus aureus strain Cowan I and IL-4. Anti-CD23 mAb were found to trigger polyphosphoinositide hydrolysis in these cells (and also in tumoral B cells expressing spontaneously CD23) and a rise in [Ca2+]i which could be attributed to mobilization from cytoplasmic pools. This increase in [Ca2+]i could be mimicked, with a comparable time-course, by the addition of InsP3 to permeabilized B cell blasts indicating that the increase in inositol phosphate accumulation induced by the antibodies was due to a preferential attack of phosphatidylinositol-bisphosphate by a specific phosphoinositidase C (PIC). In permeabilized cells, raising the free calcium concentration above 3 microM was found to induce polyphosphoinositides hydrolysis and to activate directly the PIC. Addition of 100 microM GTP-tetralithium salt, a non-hydrolyzable analogue of GTP, also resulted in an increased accumulation of inositol phosphates. A Ca2(+)-dependent PIC, linked to a GTP-binding protein (Gp protein), can thus be activated in B cell blasts. Addition of anti-CD23 antibodies to permeabilized B cells in the presence of a physiologic concentration of Ca2+ (100 nM) evoked, within 10 min, a rise in the various inositol phosphates. This ability of anti-CD23 antibodies to activate PIC was enhanced in the presence of GTP-tetralithium salt 100 microM. By contrast, preincubation with GDP-trilithium salt, a nonhydrolyzable analogue of GDP, caused a marked reduction in the release of inositol phosphates. Preincubation of B cell blasts with Pertussis toxin resulted in a total inhibition of the capacity of the toxin to ADP-ribosylate a 41-kDa protein, probably of the Gi type; in these conditions, no modification of anti-CD23-elicited polyphosphoinositide hydrolysis could be detected. These results suggest that the CD23 molecule may be coupled to the phosphoinositide signaling pathway by a GTP-dependent component that is insensitive to Pertussis toxin.
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Kang, Yuan-Lin, Yi-ying Chou, Paul W. Rothlauf, Zhuoming Liu, Timothy K. Soh, David Cureton, James Brett Case et al. « Inhibition of PIKfyve kinase prevents infection by Zaire ebolavirus and SARS-CoV-2 ». Proceedings of the National Academy of Sciences 117, no 34 (6 août 2020) : 20803–13. http://dx.doi.org/10.1073/pnas.2007837117.
Texte intégralRésumé :
Virus entry is a multistep process. It initiates when the virus attaches to the host cell and ends when the viral contents reach the cytosol. Genetically unrelated viruses can subvert analogous subcellular mechanisms and use similar trafficking pathways for successful entry. Antiviral strategies targeting early steps of infection are therefore appealing, particularly when the probability for successful interference through a common step is highest. We describe here potent inhibitory effects on content release and infection by chimeric vesicular stomatitis virus (VSV) containing the envelope proteins of Zaire ebolavirus (VSV-ZEBOV) or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (VSV-SARS-CoV-2) elicited by Apilimod and Vacuolin-1, small-molecule inhibitors of the main endosomal phosphatidylinositol-3-phosphate/phosphatidylinositol 5-kinase, PIKfyve. We also describe potent inhibition of SARS-CoV-2 strain 2019-nCoV/USA-WA1/2020 by Apilimod. These results define tools for studying the intracellular trafficking of pathogens elicited by inhibition of PIKfyve kinase and suggest the potential for targeting this kinase in developing small-molecule antivirals against SARS-CoV-2.
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Anderson, M. P., et M. J. Welsh. « Isoproterenol, cAMP, and bradykinin stimulate diacylglycerol production in airway epithelium ». American Journal of Physiology-Lung Cellular and Molecular Physiology 258, no 6 (1 juin 1990) : L294—L300. http://dx.doi.org/10.1152/ajplung.1990.258.6.l294.
Texte intégralRésumé :
Previous studies using phorbol esters and cell-free preparations suggest that protein kinase C (PKC) may regulate Cl- secretion and apical membrane Cl- channels in airway epithelium. To determine whether PKC may be involved in receptor-mediated control of secretion, we measured the mass of diacylglycerol (DAG) generated by two Cl- secretagogues, isoproterenol and bradykinin. Bradykinin increased cellular DAG at concentrations similar to those that increase inositol phosphates, suggesting that bradykinin stimulates phosphatidylinositol hydrolysis, as observed in other systems. Isoproterenol also increased cellular DAG at concentrations similar to those that stimulate adenosine 3',5'-cyclic monophosphate (cAMP) accumulation. The beta-adrenergic receptor antagonist, nadolol, blocked and cell-permanent analogues of cAMP mimicked the effect of isoproterenol. However, isoproterenol does not stimulate phosphatidylinositol turnover. Simultaneous addition of maximal concentrations of isoproterenol and bradykinin produced additive increases in DAG. To test the possibility that the isoproterenol-induced increase in DAG came from phosphatidylcholine turnover, we measured the release of water-soluble choline metabolites and the incorporation of choline into cellular lipids. Although phorbol ester and bradykinin stimulated phosphatidylcholine turnover, isoproterenol did not. These results suggest that isoproterenol and bradykinin generate DAG from the following different lipid sources: bradykinin stimulates phosphatidylinositol hydrolysis to produce DAG; isoproterenol stimulates an increase in DAG from unknown sources. The data suggest that simultaneous activation of cAMP-dependent protein kinase and PKC may occur during receptor-mediated stimulation of Cl- secretion.
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Stewart Campbell, A., et Gregory R. J. Thatcher. « Synthesis of an analogue of D,L-MYO-inositol-1,2-cyclic phosphate : inhibition of phosphatidylinositol-specific phospholipase C ». Tetrahedron Letters 32, no 20 (mai 1991) : 2207–10. http://dx.doi.org/10.1016/s0040-4039(00)79682-1.
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Apgar, J. R. « Polymerization of actin in RBL-2H3 cells can be triggered through either the IgE receptor or the adenosine receptor but different signaling pathways are used. » Molecular Biology of the Cell 5, no 3 (mars 1994) : 313–22. http://dx.doi.org/10.1091/mbc.5.3.313.
Texte intégralRésumé :
Crosslinking of the IgE receptor on rat basophilic leukemia (RBL) cells using the multivalent antigen DNP-BSA leads to a rapid and sustained increase in the filamentous actin content of the cells. Stimulation of RBL cells through the adenosine receptor also induces a very rapid polymerization of actin, which peaks in 45-60 s and is equivalent in magnitude to the F-actin response elicited through stimulation of the IgE receptor. However, in contrast to the IgE mediated response, which remains elevated for over 30 min, the F-actin increase induced by the adenosine analogue 5'-(N-ethylcarboxamido)-adenosine (NECA) is relatively transient and returns to baseline values within 5-10 min. While previous work has shown that the polymerization of actin in RBL cells stimulated through the IgE receptor is mediated by protein kinase C (PKC), protein kinase inhibitors have no effect on the F-actin response activated through the adenosine receptor. In contrast, pretreatment of the cells with pertussis toxin completely inhibits the F-actin response to NECA but has relatively little effect on the response induced through the IgE receptor. Stimulation of RBL cells through either receptor causes increased production of phosphatidylinositol mono-phosphate (PIP) and phosphatidylinositol bis-phosphate (PIP2), which correlates with the F-actin response. Production of PIP and PIP2 may be important downstream signals since these polyphosphoinositides are able to regulate the interaction of gelsolin and profilin with actin. Thus the polymerization of actin can be triggered through either the adenosine receptor or the IgE receptor, but different upstream signaling pathways are being used. The IgE mediated response requires the activation of PKC while stimulation through the adenosine receptor is PKC independent but involves a G protein.
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CAMPBELL, A. S., et G. R. J. THATCHER. « ChemInform Abstract : Synthesis of an Analogue of D,L-myo-Inositol-1,2-cyclic Phosphate : Inhibition of Phosphatidylinositol-Specific Phospholipase C. » ChemInform 23, no 10 (22 août 2010) : no. http://dx.doi.org/10.1002/chin.199210229.
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Pian, Phillip, Annalisa Bucchi, Richard B. Robinson et Steven A. Siegelbaum. « Regulation of Gating and Rundown of HCN Hyperpolarization-activated Channels by Exogenous and Endogenous PIP2 ». Journal of General Physiology 128, no 5 (30 octobre 2006) : 593–604. http://dx.doi.org/10.1085/jgp.200609648.
Texte intégralRésumé :
The voltage dependence of activation of the HCN hyperpolarization-activated cation channels is shifted in inside-out patches by −40 to −60 mV relative to activation in intact cells, a phenomenon referred to as rundown. Less than 20 mV of this hyperpolarizing shift can be due to the influence of the canonical modulator of HCN channels, cAMP. Here we study the role of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) in HCN channel rundown, as hydrolysis of PI(4,5)P2 by lipid phosphatases is thought to underlie rundown of several other channels. We find that bath application of exogenous PI(4,5)P2 reverses the effect of rundown, producing a large depolarizing shift in HCN2 activation. A synthetic short chain analogue of PI(4,5)P2, dioctanoyl phosphatidylinositol 4,5-bisphosphate, shifts the HCN2 activation curve to more positive potentials in a dose-dependent manner. Other dioctanoyl phosphatidylinositides with one or more phosphates on the lipid headgroup also shift activation, although phosphatidylinositol (PI) is ineffective. Several lines of evidence suggest that HCN2 is also regulated by endogenous PI(4,5)P2: (a) blockade of phosphatases slows the hyperpolarizing shift upon patch excision; (b) application of an antibody that binds and depletes membrane PIP2 causes a further hyperpolarizing shift in activation; (c) the shift in activation upon patch excision can be partially reversed by MgATP; and (d) the effect of MgATP is blocked by wortmannin, an inhibitor of PI kinases. Finally, recordings from rabbit sinoatrial cells demonstrate that diC8 PI(4,5)P2 delays the rundown of native HCN currents. Thus, both native and recombinant HCN channels are regulated by PI(4,5)P2.
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Dunlop, M. E., et R. G. Larkins. « Muscarinic-agonist and guanine nucleotide activation of polyphosphoinositide phosphodiesterase in isolated islet-cell membranes ». Biochemical Journal 240, no 3 (15 décembre 1986) : 731–37. http://dx.doi.org/10.1042/bj2400731.
Texte intégralRésumé :
Stimulated hydrolysis of the inositol phospholipids phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] was investigated by studying the phosphoinositides produced in a suspended preparation of plasma membranes by transference of 32P from [gamma-32P]ATP. At basal Ca2+ concentration (calculated free Ca2+, 150 nM) phospholipid hydrolysis was stimulated either by the muscarinic agonists carbamoylcholine and bethanecol or by the addition of the non-hydrolysable analogue of GTP, guanosine 5′-[beta gamma-imido]triphosphate [p(NH)ppG]. GTP was without effect on basal hyrolysis. Both GTP and p(NH)ppG enhanced the rapid (within 10 s) hydrolysis of PtdIns4P and PtdIns(4,5)P2 induced by carbamoylcholine in a dose-dependent manner. A rightward shift in the competition curve of carbamoylcholine for bound L-[3H]quinuclidinyl benzilate was seen on addition of GTP or p(NH)ppG (100 microM) under phosphorylating conditions. Pretreatment of intact islet cells with Bordetella pertussis toxin, islet-activating protein (IAP) or treatment of membranes with IAP under conditions which elicited ADP-ribosylation of a protein of Mr 41,000 was without effect on muscarinic binding, phosphoinositide phosphorylation or subsequent hydrolysis by carbamoylcholine. The findings indicate the involvement of a GTP-binding protein in the coupling of the muscarinic receptor to phosphoinositide hydrolysis in the islet cell and suggest that this is distinct from the GTP-binding regulatory component of adenylate cyclase which is covalently modified by IAP.
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Antonny, Bruno, Joëlle Bigay et Bruno Mesmin. « The Oxysterol-Binding Protein Cycle : Burning Off PI(4)P to Transport Cholesterol ». Annual Review of Biochemistry 87, no 1 (20 juin 2018) : 809–37. http://dx.doi.org/10.1146/annurev-biochem-061516-044924.
Texte intégralRésumé :
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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Batty, Ian H., Jeroen van der Kaay, Alex Gray, Joan F. Telfer, Miles J. Dixon et C. Peter Downes. « The control of phosphatidylinositol 3,4-bisphosphate concentrations by activation of the Src homology 2 domain containing inositol polyphosphate 5-phosphatase 2, SHIP2 ». Biochemical Journal 407, no 2 (25 septembre 2007) : 255–66. http://dx.doi.org/10.1042/bj20070558.
Texte intégralRésumé :
Activation of class Ia PI3K (phosphoinositide 3-kinase) produces PtdInsP3, a vital intracellular mediator whose degradation generates additional lipid signals. In the present study vanadate analogues that inhibit PTPs (protein tyrosine phosphatases) were used to probe the mechanisms which regulate the concentrations of these molecules allowing their independent or integrated function. In 1321N1 cells, which lack PtdInsP3 3-phosphatase activity, sodium vanadate or a cell permeable derivative, bpV(phen) [potassium bisperoxo(1,10-phenanthroline)oxovanadate (V)], increased the recruitment into anti-phosphotyrosine immunoprecipitates of PI3K activity and of the p85 and p110α subunits of class Ia PI3K and enhanced the recruitment of PI3K activity stimulated by PDGF (platelet-derived growth factor). However, neither inhibitor much increased cellular PtdInsP3 concentrations, but both diminished dramatically the accumulation of PtdInsP3 stimulated by PDGF or insulin and markedly increased the control and stimulated concentrations of PtdIns(3,4)P2. These actions were accounted for by the ability of PTP inhibitors to stimulate the activity of endogenous PtdInsP3 5-phosphatase(s), particularly SHIP2 (Src homology 2 domain containing inositol polyphosphate 5-phosphatase 2) and to inhibit types I and II PtdIns(3,4)P2 4-phosphatases. Thus bpV(phen) promoted the translocation of SHIP2 from the cytosol to a Triton X-100-insoluble fraction and induced a marked (5–10-fold) increase in SHIP2 specific activity mediated by enhanced tyrosine phosphorylation. The net effect of these inhibitors was, therefore, to switch the signal output of class I PI3K from PtdInsP3 to PtdIns(3,4)P2. A key component controlling this shift in the balance of lipid signals is the activation of SHIP2 by increased tyrosine phosphorylation, an effect observed in HeLa cells in response to both PTP inhibitors and epidermal growth factor.
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Warburton, D., S. Buckley et L. Cosico. « P1 and P2 purinergic receptor signal transduction in rat type II pneumocytes ». Journal of Applied Physiology 66, no 2 (1 février 1989) : 901–5. http://dx.doi.org/10.1152/jappl.1989.66.2.901.
Texte intégralRésumé :
Extracellular ATP is a potent agonist of surfactant phosphatidylcholine (PC) exocytosis from type II pneumocytes in culture. We studied P1 and P2 receptor signal transduction in type II pneumocytes. The EC50 for ATP on PC exocytosis was 10(-6) M, whereas the EC50 for ADP, AMP, adenosine, and the nonmetabolizable ATP analogue alpha,beta-methylene ATP was 10(-4) M. The rank order of agonists for PC exocytosis was ATP greater than ADP greater than AMP greater than adenosine greater than alpha,beta-methylene ATP. The rank order of agonists for phosphatidylinositol (PI) hydrolysis was ATP greater than ADP, whereas AMP, adenosine, and alpha,beta-methylene ATP did not stimulate PI hydrolysis. ATP (10(-4) M) caused a 15-fold increase in adenosine 3′,5′-cyclic monophosphate (cAMP) production, and the nonmetabolizable adenosine analogue 5′-N-ethylcarboxyamidoadenosine (10(-6) M) increased cAMP production threefold. The effects of both these agonists on cAMP production were completely inhibited by the adenosine antagonist 8-phenyltheophylline (10(-5) M). The effects of ATP (10(-4) M) on PC exocytosis were inhibited 38% by 10(-5) M 8-phenyltheophylline. Thus, ATP regulates PC exocytosis by activating P2 receptors, which stimulate PI hydrolysis to inositol phosphate, as well as by activating P1 receptors, which stimulate cAMP production. Interactions between the P1 and P2 pathways may explain the high potency of extracellular ATP as an agonist of PC exocytosis.
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van der Schaar, Hilde M., Pieter Leyssen, Hendrik J. Thibaut, Armando de Palma, Lonneke van der Linden, Kjerstin H. W. Lanke, Céline Lacroix et al. « A Novel, Broad-Spectrum Inhibitor of Enterovirus Replication That Targets Host Cell Factor Phosphatidylinositol 4-Kinase IIIβ ». Antimicrobial Agents and Chemotherapy 57, no 10 (29 juillet 2013) : 4971–81. http://dx.doi.org/10.1128/aac.01175-13.
Texte intégralRésumé :
ABSTRACTDespite their high clinical and socioeconomic impacts, there is currently no approved antiviral therapy for the prophylaxis or treatment of enterovirus infections. Here we report on a novel inhibitor of enterovirus replication, compound 1, 2-fluoro-4-(2-methyl-8-(3-(methylsulfonyl)benzylamino)imidazo[1,2-a]pyrazin-3-yl)phenol. This compound exhibited a broad spectrum of antiviral activity, as it inhibited all tested species of enteroviruses and rhinoviruses, with 50% effective concentrations ranging between 4 and 71 nM. After a lengthy resistance selection process, coxsackievirus mutants resistant to compound 1 were isolated that carried substitutions in their 3A protein. Remarkably, the same substitutions were recently shown to provide resistance to inhibitors of phosphatidylinositol 4-kinase IIIβ (PI4KIIIβ), a lipid kinase that is essential for enterovirus replication, suggesting that compound 1 may also target this host factor. Accordingly, compound 1 directly inhibited PI4KIIIβ in anin vitrokinase activity assay. Furthermore, the compound strongly reduced the PI 4-phosphate levels of the Golgi complex in cells. Rescue of coxsackievirus replication in the presence of compound 1 by a mutant PI4KIIIβ carrying a substitution in its ATP-binding pocket revealed that the compound directly binds the kinase at this site. Finally, we determined that an analogue of compound 1, 3-(3-fluoro-4-methoxyphenyl)-2-methyl-N-(pyridin-4-ylmethyl)imidazo[1,2-a]pyrazin-8-amine, is well tolerated in mice and has a dose-dependent protective activity in a coxsackievirus serotype B4-induced pancreatitis model.
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Shirai, Y., K. Kashiwagi, N. Sakai et N. Saito. « Phospholipase A(2) and its products are involved in the purinergic receptor-mediated translocation of protein kinase C in CHO-K1 cells ». Journal of Cell Science 113, no 8 (15 avril 2000) : 1335–43. http://dx.doi.org/10.1242/jcs.113.8.1335.
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The signal transduction involved in the purinergic stimuli-induced activation of protein kinase C (PKC) in CHO-K1 cells was investigated. Purinergic stimuli such as adenosine triphosphate and uridine triphosphate induced a transient translocation of PKC epsilon, gamma, and delta from the cytoplasm to the plasma membrane. These translocations were blocked by an inhibitor of phosphatidylinositol-specific phospholipase C (PLC), but not by an inhibitor of phosphatidylcholine-specific PLC. A diacylglycerol (DAG) analogue also induced reversible translocations of PKC gamma, epsilon, and delta from the cytoplasm to the plasma membrane, while the calcium ionophore A23187 caused a similar translocation of only the gamma subtype. These results confirm that the hydrolysis of phosphatidylinositol-2-phosphate by PLC and the subsequent generation of DAG and increase in Ca(2+)are involved in the purinergic stimuli-induced translocation of PKC. A DAG antagonist, 1-o-hexadecyl-2-o-acetyl-glycerol, blocked the DAG analogue-induced translocations of all PKC subtypes tested but failed to inhibit the purinergic stimuli-induced translocations of PKC epsilon and gamma. The DAG antagonist could not block the ATP- and UTP-induced translocation of PKC epsilon even in the absence of extracellular Ca(2+). Co-application of the DAG antagonist and a phospholipase A(2) (PLA(2)) inhibitor such as aristolochic acid, arachidonyltrifluoromethyl ketone, or bromoenol lactone inhibited the purinergic receptor-mediated translocation of PKC epsilon although each PLA(2) inhibitor alone did not block the translocation. In contrast to the epsilon subtype, ATP-induced translocation of PKC gamma was observed in the presence of both the PLA(2) inhibitor and the DAG antagonist. However, it is noteworthy that re-translocation of PKC gamma was hastened by the PLA(2) inhibitor. Furthermore products of PLA(2), such as lysophospholipids and fatty acids, induced the translocation of PKC gamma and epsilon in a dose dependent manner, but not delta. These results indicate that, in addition to PLC and DAG, PLA(2) and its products are involved in the purinergic stimuli-induced translocation of PKC epsilon and gamma in CHO-K1 cells. Each subtype of PKC in CHO-K1 cell is individually activated in response to a purinergic stimulation.
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Zhang, Si Qing, William G. Tsiaras, Toshiyuki Araki, Gengyun Wen, Liliana Minichiello, Ruediger Klein et Benjamin G. Neel. « Receptor-Specific Regulation of Phosphatidylinositol 3′-Kinase Activation by the Protein Tyrosine Phosphatase Shp2 ». Molecular and Cellular Biology 22, no 12 (15 juin 2002) : 4062–72. http://dx.doi.org/10.1128/mcb.22.12.4062-4072.2002.
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ABSTRACT Receptor tyrosine kinases (RTKs) play distinct roles in multiple biological systems. Many RTKs transmit similar signals, raising questions about how specificity is achieved. One potential mechanism for RTK specificity is control of the magnitude and kinetics of activation of downstream pathways. We have found that the protein tyrosine phosphatase Shp2 regulates the strength and duration of phosphatidylinositol 3′-kinase (PI3K) activation in the epidermal growth factor (EGF) receptor signaling pathway. Shp2 mutant fibroblasts exhibit increased association of the p85 subunit of PI3K with the scaffolding adapter Gab1 compared to that for wild-type (WT) fibroblasts or Shp2 mutant cells reconstituted with WT Shp2. Far-Western analysis suggests increased phosphorylation of p85 binding sites on Gab1. Gab1-associated PI3K activity is increased and PI3K-dependent downstream signals are enhanced in Shp2 mutant cells following EGF stimulation. Analogous results are obtained in fibroblasts inducibly expressing dominant-negative Shp2. Our results suggest that, in addition to its role as a positive component of the Ras-Erk pathway, Shp2 negatively regulates EGF-dependent PI3K activation by dephosphorylating Gab1 p85 binding sites, thereby terminating a previously proposed Gab1-PI3K positive feedback loop. Activation of PI3K-dependent pathways following stimulation by other growth factors is unaffected or decreased in Shp2 mutant cells. Thus, Shp2 regulates the kinetics and magnitude of RTK signaling in a receptor-specific manner.
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Harrison, D., J. H. Phillips et L. L. Lanier. « Involvement of a metalloprotease in spontaneous and phorbol ester-induced release of natural killer cell-associated Fc gamma RIII (CD16-II). » Journal of Immunology 147, no 10 (15 novembre 1991) : 3459–65. http://dx.doi.org/10.4049/jimmunol.147.10.3459.
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Abstract Two genes encode the CD16 low affinity IgG FcR. CD16-I (Fc gamma RIII-1) is expressed on PMN as a phosphatidylinositol-glycan anchored glycoprotein. CD16-II (Fc gamma RIII-2) is expressed on NK cells and macrophages as a transmembrane glycoprotein associated with CD3 zeta or Fc epsilon RI-gamma. NK cells spontaneously release soluble CD16-II from the cell surface and this is enhanced by activation with phorbol ester. In this study, we demonstrate that a metalloprotease is involved in the spontaneous and PMA-induced release of CD16-II from NK cells. 1,10-phenanthroline, an inhibitor of Zn(2+)-dependent metalloproteases, efficiently inhibits CD16-II release. 1,7-phenanthroline, an inactive analogue that doesn't chelate Zn2+ or other divalent metal cations, and inhibitors of serine proteases do not affect spontaneous or PMA-induced release of CD16-II. Murine P815 mastocytoma cells transfected with human CD16-II cDNA shed membrane CD16, and 1,10-phenanthroline inhibits this process. P815 transfectants expressing CD16-II molecules with truncated cytoplasmic domains also release soluble receptors, indicating that the cytoplasmic segment of CD16-II is not required for interaction with the protease or the cytoskeleton. By contrast, 1,10-phenanthroline does not inhibit PMA-induced release of CD16-I glycoprotein from PMN, indicating a different mechanism of release for this phosphatidylinositol-glycan anchored molecule. Prior studies have demonstrated that NK cells are activated via the inositol phosphate pathway after engagement of CD16-II by immune complexes or Ig-coated tumor cell targets. A membrane metalloprotease with substrate specificity for CD16-II that is activated by PKC stimulation may provide a mechanism for releasing the immune complex or target from the effector cells and halting signal transduction.
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Melamed, I., G. Wang et C. M. Roifman. « Antigen receptor-mediated protein tyrosine kinase activity is regulated by a pertussis toxin-sensitive G protein. » Journal of Immunology 149, no 1 (1 juillet 1992) : 169–74. http://dx.doi.org/10.4049/jimmunol.149.1.169.
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Abstract Ligation of the Ag receptor on B cells is associated with a rapid increase in phosphorylation on tyrosine residues of multiple substrates. One of the substrates is the phosphoinositide-specific phospholipase C-gamma 1. Because activation of phospholipase C-gamma 1 seems to be dependent on tyrosine phosphorylation, it is assumed that the two signaling pathways, phosphatidylinositol turnover and tyrosine phosphorylation, might be linked. However, since the Ag receptor does not possess a kinase domain, it remains unclear how these signaling pathways are regulated by the Ag receptor. Previous studies have proposed the existence of a receptor-coupled G protein that regulates inositol phosphate production in B cells. We confirm that phosphoinositide turnover is regulated by a pertussis toxin (PT)-sensitive G protein, most probably by controlling phosphorylation of phospholipase C-gamma 1. We show that treatment of permeabilized B cells with a nonhydrolyzable GTP analogue guanosine 5'-[3-thio]triphosphate induced an increase in tyrosine phosphorylation of multiple substrates that are identical to the proteins phosphorylated after anti-IgM stimulation. Furthermore, binding of the inactive form of G proteins with guanosine 5'-[2-thio]-triphosphate blocked anti-IgM induced tyrosine phosphorylation in permeabilized B cells. The results indicate that an Ag receptor-coupled G protein controls protein tyrosine kinase activity. We show that this G protein is sensitive to PT because tyrosine phosphorylation mediated by the Ag receptor was inhibited by this toxin in a concentration-dependent manner. Similar concentrations of PT also blocked tyrosine phosphorylation on phospholipase C-gamma 1 and generation of inositol phosphates. Preincubation of intact B cells with PT resulted in inhibition of c-fos mRNA expression and DNA synthesis in anti-IgM stimulated B cells, indicating that post-transcriptional events are also controlled by the Ag-receptor coupled G protein. We conclude that Ag receptor-associated protein tyrosine kinase activity is regulated by a G protein. This PT-sensitive G protein also regulates phosphorylation and activation of phospholipase C-gamma 1 as well as later events in B cell activation such as c-fos mRNA expression and proliferation.
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Ebanks, R., C. Roifman, A. Mellors et G. B. Mills. « The diacylglycerol analogue, 1,2-sn-dioctanoylglycerol, induces an increase in cytosolic free Ca2+ and cytosolic acidification of T lymphocytes through a protein kinase C-independent process ». Biochemical Journal 258, no 3 (15 mars 1989) : 689–98. http://dx.doi.org/10.1042/bj2580689.
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In this paper, we demonstrate that low concentrations (0.5-2.5 microM) of 1,2-sn-dioctanoylglycerol (DiC8), a potent diacylglycerol used in many previous studies to probe the role of protein kinase C (PKC) in cell activation, cause cytosolic alkalinization of human, mouse and pig T lymphocytes through PKC-mediated activation of the Na+/H+ antiport. However, at higher concentrations (greater than or equal to 12.5 microM), the effect on cytosolic pH (pHi) is reversed, resulting in a marked cytosolic acidification, followed by a gradual return of pHi to baseline values. DiC8 also induces marked changes in cytosolic free calcium concentrations ([Ca2+]i), initially by releasing calcium from intracellular stores, followed by a net transmembrane influx of calcium. The DiC8-induced cytosolic acidification, the resultant return to baseline pH and the increase in [Ca2+]i are independent of activation of PKC. Unlike many other agents which increase [Ca2+]i, DiC8 does not induce phosphatidylinositol hydrolysis with the resultant production of inositol phosphates. Other compounds known to activate PKC, including the closely related diacylglycerol analogues, 1,2-sn-dihexanoylglycerol and 1,2-sn-didecanoylglycerol, phorbol esters and mezerein, did not induce changes in [Ca2+]i or cytosolic acidification in T lymphocytes. Thus the action of DiC8 on intact lymphocytes is different from that of phorbol esters and other diacylglycerols, and is specific to the length of the acyl chains. Because changes in [Ca2+]i are often associated with cell proliferation and cell differentiation, some effects of DiC8 on intact cells may be a consequence of changes in [Ca2+]i.
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Chartash, E. K., A. Imai, M. C. Gershengorn, M. K. Crow et S. M. Friedman. « Direct human T helper cell-induced B cell activation is not mediated by inositol lipid hydrolysis. » Journal of Immunology 140, no 6 (15 mars 1988) : 1974–81. http://dx.doi.org/10.4049/jimmunol.140.6.1974.
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Abstract The Ag-specific interaction between cloned allospecific human Th cells and class II MHC determinants on the surface of allogeneic B cells induces a significant fraction of resting B cells to express a B cell specific activation Ag BLAST-2 (CD23). On the other hand, cross-linking of B cell surface Ig R by Ag analogues does not lead to BLAST-2 expression. By utilizing the BLAST-2 induction assay as a positive control for efficient Th-B cell interaction, we have investigated the biochemical basis of human B cell activation mediated by Ag and Th cells. Our data demonstrate that ligands for sIg R, including F(ab')2 goat anti-human IgM and Staphylococcus aureus protein A, stimulate the metabolism of B cell membrane inositol lipids as assessed by: 1) increased [3H]inositol phosphates formation in myo-[3H]inositol-labeled B cells; 2) selective incorporation of [32P]orthophosphate into phosphatidic acid and phosphatidylinositol, but not into phosphatidylethanolamine or phosphatidylcholine; and 3) rapid increase in B cell cytoplasmic ionized Ca2+ concentration ([Ca2+]i). In contrast, direct Th-B cell interaction leads to high intensity BLAST-2 expression on the B cell surface but this response is not mediated by changes in inositol lipid metabolism or [Ca2+]i. Further, Th-B cell interaction does not affect the changes in B cell inositol lipid metabolism or [Ca2+]i triggered by sIg cross-linking. Taken together, our results suggest that Ag and Th cells induce different functional B cell responses by activating distinct second messenger systems within the B cell.
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Kim, Ji-Eun, Hana Park et Tae-Cheon Kang. « CDDO-Me Distinctly Regulates Regional Specific Astroglial Responses to Status Epilepticus via ERK1/2-Nrf2, PTEN-PI3K-AKT and NFκB Signaling Pathways ». Antioxidants 9, no 10 (21 octobre 2020) : 1026. http://dx.doi.org/10.3390/antiox9101026.
Texte intégralRésumé :
2-Cyano-3,12-dioxo-oleana-1,9(11)-dien-28-oic acid methyl ester (CDDO-Me) is a triterpenoid analogue of oleanolic acid. CDDO-Me shows anti-inflammatory and neuroprotective effects. Furthermore, CDDO-Me has antioxidant properties, since it activates nuclear factor-erythroid 2-related factor 2 (Nrf2), which is a key player of redox homeostasis. In the present study, we evaluated whether CDDO-Me affects astroglial responses to status epilepticus (SE, a prolonged seizure activity) in the rat hippocampus in order to understand the underlying mechanisms of reactive astrogliosis and astroglial apoptosis. Under physiological conditions, CDDO-Me increased Nrf2 expression in the hippocampus without altering activities (phosphorylations) of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), phosphatidylinositol-3-kinase (PI3K), and AKT. CDDO-Me did not affect seizure activity in response to pilocarpine. However, CDDO-Me ameliorated reduced astroglial Nrf2 expression in the CA1 region and the molecular layer of the dentate gyrus (ML), and attenuated reactive astrogliosis and ML astroglial apoptosis following SE. In CA1 astrocytes, CDDO-Me inhibited the PI3K/AKT pathway by activating PTEN. In contrast, CDDO-ME resulted in extracellular signal-related kinases 1/2 (ERK1/2)-mediated Nrf2 upregulation in ML astrocytes. Furthermore, CDDO-Me decreased nuclear factor-κB (NFκB) phosphorylation in both CA1 and ML astrocytes. Therefore, our findings suggest that CDDO-Me may attenuate SE-induced reactive astrogliosis and astroglial apoptosis via regulation of ERK1/2-Nrf2, PTEN-PI3K-AKT, and NFκB signaling pathways.
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Lucas, David M., et Larry R. Rohrschneider. « A Novel Spliced Form of SH2-Containing Inositol Phosphatase Is Expressed During Myeloid Development ». Blood 93, no 6 (15 mars 1999) : 1922–33. http://dx.doi.org/10.1182/blood.v93.6.1922.406k21_1922_1933.
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SH2-containing Inositol Phosphatase (SHIP) is a 145 kD protein expressed in hematopoietic cells. SHIP is phosphorylated on tyrosine after receptor binding by several cytokines and has a negative role in hematopoiesis. We cloned a murine complementary DNA (cDNA) sequence for an isoform of SHIP with an internal 183 nucleotide deletion, encoding a protein 61 amino acids shorter than 145 kD SHIP. This deletion eliminates potential SH3-domain binding regions and a potential binding site for the p85 subunit of Phosphatidylinositol 3-Kinase. Using polyclonal anti-SHIP antibodies, we and others have previously observed a 135 kD SHIP isoform that is coexpressed with 145 kD SHIP. Here, we used monoclonal antibodies raised against the region deleted in the spliced form to show that the product of the novel spliced SHIP cDNA is antigenically identical to the 135 kD SHIP isoform. Like 145 kD SHIP, 135 kD SHIP expression was induced on differentiation of bone marrow cells. After macrophage colony-stimulating factor (M-CSF) stimulation of FDC-P1(Fms) myeloid cells, both 145 and 135 kD SHIP forms were tyrosine phosphorylated and could be coimmunoprecipitated with antibodies to Shc and Grb2. However, experiments showed only a weak association of 135 kD SHIP with p85. A potentially analogous 135 kD SHIP species also appears in human differentiated leukocytes.
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Desai, Trupti, Jill Gigg, Roy Gigg et Eloisa Martín-Zamora. « The preparation of racemic and enantiomerically pure myo-inositol derivatives as intermediates for the synthesis of phosphatidylinositol 3-, 3,4-bis-, and 3,4,5-tris-phosphates and for the synthesis of analogues of 1d-myo-inositol 1,3,4,5-tetrakisphosphate ». Carbohydrate Research 296, no 1-4 (décembre 1996) : 97–133. http://dx.doi.org/10.1016/s0008-6215(96)00211-x.
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Chiarini, Francesca, Cecilia Grimaldi, Francesca Ricci, Pierluigi Tazzari, Camilla Evangelisti, Andrea Pession, Pasqualepaolo Pagliaro, James McCubrey et Alberto M. Martelli. « Dual Inhibition of Phosphatidylinositol 3-Kinase and Mammalian Target of Rapamycin with NVP-BEZ235 as a New Therapeutic Option for T-Cell Acute Lymphoblastic Leukemia. » Blood 114, no 22 (20 novembre 2009) : 2025. http://dx.doi.org/10.1182/blood.v114.22.2025.2025.
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Abstract Abstract 2025 Poster Board II-2 Introduction: Recent findings have highlighted that constitutively active phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian Target of Rapamycin (mTOR) signaling is a common feature of T-cell acute lymphoblastic leukemia (T-ALL) where it strongly influences cell proliferation and survival. Pathway activation could be due to several reasons which include Notch1 activation leading to HES1-mediated transcriptional suppression of PTEN gene, PTEN phosphorylation or oxidation, and inactivation of SHIP1 phosphatase. These findings lend compelling weight for the application of PI3K/Akt/mTOR inhibitors in T-ALL. Rapamycin and its analogues have shown some promising effects in pre-clinical models of T-ALL. However, mTOR inhibitors are mainly cytostatic and could hyperactivate Akt due to the existence of feedback loops between mTOR, p70 S6 kinase, PI3K, and Akt. Recently, dual PI3K/mTOR inhibitors have been synthesized. Here, we have analyzed the therapeutic potential of the novel, dual PI3K/mTOR inhibitor, NVP-BEZ235, an orally bioavailable imidazoquinoline derivative, which has entered clinical trials for solid tumors, on both T-ALL cell lines and patient samples. Methods and Patients: We employed a panel of cell lines with up-regulated PI3K/Akt/mTOR signaling, including CEM-R cells [which overexpress high levels of the membrane transporter, 170-kDa P-glycoprotein (P-gp)], MOLT-4 and CEM-S cells (which lack PTEN expression), Jurkat cells (which do not express both PTEN and SHIP1), and RPMI-8402 and BE-13 cells. MOLT-4, CEM, and Jurkat cells have a non-functional p53 pathway. Moreover, both Jurkat and MOLT-4 cells have aberrant Notch1 signaling. Patients samples displayed pathway activation as documented by increased levels of p-Akt, p-4E-BP1, and p-S6 ribosomal protein, as well as low/absent PTEN expression. Results: NVP-BEZ235 was cytotoxic to the panel of cell lines as documented by MTT assays. NVP-BEZ235 IC50 ranged from 80 to 280 nM at 24 h. A comparison between NVP-BEZ235 and the dual PI3K/mTOR inhibitor PI-103, a small synthetic molecule of the pyridofuropyrimidine class with the same targets, demonstrated that NVP-BEZ235 was more effective than PI-103 when employed at equimolar concentrations. NVP-BEZ235 did not significantly affect the proliferation of peripheral blood T-lymphocytes from healthy donors stimulated with phytohemagglutinin and interleukin-2, whereas it blocked leukemic cells in the G1 phase of the cell cycle, and this was accompanied by decreased levels of phosphorylated Retinoblastoma protein. NVP-BEZ235 treatment also resulted in apoptotic cell death (about 20-30% at 6 h of exposure, when employed at 200 nM), as documented by Annexin V/propidium iodide staining and cytofluorimetric analysis. Moreover, NVP-BEZ235 activated caspase-8 and caspase-3, as demonstrated by western blot. Western blot documented a dose- and time-dependent dephosphorylation of Akt and its downstream target, GSK-3β, in response to NVP-BEZ235. mTOR downstream targets were also efficiently dephosphorylated, including p70S6 kinase, S6 ribosomal protein, and 4E-BP1. Remarkably, NVP-BEZ235 targeted the side population (SP, identified by Hoechst 33342 staining and ABCG2 expression) of T-ALL cell lines, which might correspond to leukemia initiating cells, and synergized with several chemotherapeutic agents (dexamethasone, vincristine, cyclophosphamide, Ara-C) currently employed for treating T-ALL patients. NVP-BEZ235 reduced chemoresistance to vincristine induced in Jurkat cells by co-culturing with MS-5 stromal cells which mimic the bone marrow microenvironment. NVP-BEZ235 was cytotoxic (IC50: 10-15 nM at 96 h) to primary lymphoblasts from patients with T-ALL, where the drug dephosphorylated 4E-BP1, at variance with rapamycin. Of note, NVP-BEZ235 targeted the SP also in T-ALL patient samples. Conclusions: NVP-BEZ235 was cytotoxic to T-ALL cell lines and patient lymphoblasts (including SP cells) at concentrations that have been previously reported to be achievable in vivo. Taken together, our findings indicate that longitudinal inhibition at two nodes of the PI3K/Akt/mTOR network with NVP-BEZ235, either alone or in combination with other drugs, may serve as an efficient treatment towards T-ALL cells (including those overexpressing P-gp and independently from p53 status) which require upregulation of this signaling pathway for their survival and growth. Disclosures: No relevant conflicts of interest to declare.