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Biological Role of the Intercellular Transfer of Glycosylphosphatidylinositol-Anchored Proteins: Stimulation of Lipid and Glycogen Synthesis. Int J Mol Sci 2022; 23:ijms23137418. [PMID: 35806423 PMCID: PMC9267055 DOI: 10.3390/ijms23137418] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 06/28/2022] [Accepted: 06/29/2022] [Indexed: 11/16/2022] Open
Abstract
Glycosylphosphatidylinositol-anchored proteins (GPI-APs), which are anchored at the outer leaflet of plasma membranes (PM) only by a carboxy-terminal GPI glycolipid, are known to fulfill multiple enzymic and receptor functions at the cell surface. Previous studies revealed that full-length GPI-APs with the complete GPI anchor attached can be released from and inserted into PMs in vitro. Moreover, full-length GPI-APs were recovered from serum, dependent on the age and metabolic state of rats and humans. Here, the possibility of intercellular control of metabolism by the intercellular transfer of GPI-APs was studied. Mutant K562 erythroleukemia (EL) cells, mannosamine-treated human adipocytes and methyl-ß-cyclodextrin-treated rat adipocytes as acceptor cells for GPI-APs, based on their impaired PM expression of GPI-APs, were incubated with full-length GPI-APs, prepared from rat adipocytes and embedded in micelle-like complexes, or with EL cells and human adipocytes with normal expression of GPI-APs as donor cells in transwell co-cultures. Increases in the amounts of full-length GPI-APs at the PM of acceptor cells as a measure of their transfer was assayed by chip-based sensing. Both experimental setups supported both the transfer and upregulation of glycogen (EL cells) and lipid (adipocytes) synthesis. These were all diminished by serum, serum GPI-specific phospholipase D, albumin, active bacterial PI-specific phospholipase C or depletion of total GPI-APs from the culture medium. Serum inhibition of both transfer and glycogen/lipid synthesis was counteracted by synthetic phosphoinositolglycans (PIGs), which closely resemble the structure of the GPI glycan core and caused dissociation of GPI-APs from serum proteins. Finally, large, heavily lipid-loaded donor and small, slightly lipid-loaded acceptor adipocytes were most effective in stimulating transfer and lipid synthesis. In conclusion, full-length GPI-APs can be transferred between adipocytes or between blood cells as well as between these cell types. Transfer and the resulting stimulation of lipid and glycogen synthesis, respectively, are downregulated by serum proteins and upregulated by PIGs. These findings argue for the (patho)physiological relevance of the intercellular transfer of GPI-APs in general and its role in the paracrine vs. endocrine (dys)regulation of metabolism, in particular. Moreover, they raise the possibility of the use of full-length GPI-APs as therapeutics for metabolic diseases.
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Galenova TI, Kyznetsova MY, Savchuk ON, Ostapchenco LI. [Low molecular weight regulators of the intracellular insulin signal transduction as a correction method of the insulin resistance in the treatment of type 2 diabetes]. BIOMEDITSINSKAIA KHIMIIA 2016; 62:31-7. [PMID: 26973184 DOI: 10.18097/pbmc20166201031] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Insulin resistance is the characteristic feature of type 2 diabetes. This condition is manifested in the reduction of peripheral tissues sensitivity to the biological action of insulin and is expressed in the inhibition of cellular glucose absorption and metabolism in response to hormonal stimulation. At the cellular level, disorders which are realized both at the receptor and the postreceptor levels can serve a prerequisite to the formation of insulin resistance and are associated with a change in the amount or dysfunction of major molecular signaling cascade. Thus, the insulin receptor, as well as the other related signaling molecules can be considered as ideal therapeutic targets for the correction of insulin resistance and thus low molecular weight effectors which act on the individual links of insulin signaling cascade may be positioned as a new generation of anti-diabetic agents. This report provides information on the regulators of insulin receptor cascade, main advantages and disadvantages of their impact on biological targets and prospects for their therapeutic use as anti-diabetic drugs.
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Affiliation(s)
- T I Galenova
- Taras Shevchenko National University of Kyiv, Educational and Scientific Centre "Institute of Biology", Kyiv, Ukraine
| | - M Y Kyznetsova
- Taras Shevchenko National University of Kyiv, Educational and Scientific Centre "Institute of Biology", Kyiv, Ukraine
| | - O N Savchuk
- Taras Shevchenko National University of Kyiv, Educational and Scientific Centre "Institute of Biology", Kyiv, Ukraine
| | - L I Ostapchenco
- Taras Shevchenko National University of Kyiv, Educational and Scientific Centre "Institute of Biology", Kyiv, Ukraine
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Tuvshintulga B, Batmagnai E, Bazarragchaa E, Dulam P, Sugar S, Battsetseg B. Detection and molecular characterization of rabies virus in Mongolia during 2008-2010. INTERNATIONAL JOURNAL OF ONE HEALTH 2015. [DOI: 10.14202/ijoh.2015.26-31] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Hecht ML, Tsai YH, Liu X, Wolfrum C, Seeberger PH. Synthetic inositol phosphoglycans related to GPI lack insulin-mimetic activity. ACS Chem Biol 2010; 5:1075-86. [PMID: 20825209 DOI: 10.1021/cb1002152] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Insulin signaling has been suggested, at least in part, to be affected by an insulin-mimetic species of low molecular weight. These inositol phosphoglycans (IPGs) are generated upon growth hormone/cytokine stimulation and control the activity of a multitude of insulin effector enzymes. The minimal structural requirements of IPGs for insulin-mimetic action have been debated. Two types of IPGs were suggested, and the IPG-A type resembles the core glycan of glycosylphosphatidylinositol (GPI)-anchors. In fact, purified GPI-anchors of lower eukaryotic origin have been shown to influence glucose homeostasis. To elucidate active IPGs, a collection of synthetic IPGs designed on the basis of previous reports of activity were tested for their insulin-mimetic activity. In vitro and ex vivo assays in rodent adipose tissue as well as in vivo analyses in mice were employed to test the synthetic IPGs. None of the IPGs we tested mimic insulin actions as determined by PKB/Akt phosphorylation and quantification of glucose transport and lipogenesis. Furthermore, none of the IPGs had any effect in in vivo insulin tolerance assays. In stark contrast to previous claims, we conclude that neither of the compounds tested is insulin-mimetic.
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Affiliation(s)
- Marie-Lyn Hecht
- Department of Biomolecular Systems, Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, 14476 Potsdam, Germany
- Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany
- Laboratory of Organic Chemistry, Swiss Federal Institute of Technology (ETH) Zurich, 8093 Zurich, Switzerland
- Competence Center for Systems Physiology and Metabolic Diseases, Zurich, 8093 Zurich, Switzerland
| | - Yu-Hsuan Tsai
- Department of Biomolecular Systems, Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, 14476 Potsdam, Germany
- Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany
| | - Xinyu Liu
- Laboratory of Organic Chemistry, Swiss Federal Institute of Technology (ETH) Zurich, 8093 Zurich, Switzerland
| | - Christian Wolfrum
- Competence Center for Systems Physiology and Metabolic Diseases, Zurich, 8093 Zurich, Switzerland
- Institute of Molecular Systems Biology, Swiss Federal Institute of Technology (ETH) Zurich, 8093 Zurich, Switzerland
| | - Peter H. Seeberger
- Department of Biomolecular Systems, Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, 14476 Potsdam, Germany
- Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany
- Laboratory of Organic Chemistry, Swiss Federal Institute of Technology (ETH) Zurich, 8093 Zurich, Switzerland
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Müller G, Schulz A, Dearey EA, Wetekam EM, Wied S, Frick W. Synthetic phosphoinositolglycans regulate lipid metabolism between rat adipocytes via release of GPI-protein-harbouring adiposomes. Arch Physiol Biochem 2010; 116:97-115. [PMID: 20515260 DOI: 10.3109/13813455.2010.485205] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
A novel molecular mechanism for the regulation of lipid metabolism by palmitate, H2O2 and the anti-diabetic sulfonylurea drug, glimepiride, in rat adipocytes was recently elucidated. It encompasses the translocation of the glycosylphosphatidylinositol-anchored (GPI-) and (c)AMP degrading enzymes Gce1 and CD73 from detergent-insoluble glycolipid-enriched microdomains of the plasma membrane (DIGs) to intracellular lipid droplets (LD), the incorporation of Gce1 and CD73 into vesicles (adiposomes) which are then released from donor adipocytes and finally the transfer of Gce1 and CD73 from the adiposomes to acceptor adipocytes, where they degrade (c)AMP at the LD surface. Here the stimulation of esterification and inhibition of lipolysis by synthetic phosphoinositolglycans (PIGs), such as PIG37, which represents the glycan component of the GPI anchor, are shown to be correlated to translocation from DIGs to LD and release into adiposomes of Gce1 and CD73. PIG37 actions were blocked upon disruption of DIGs, inactivation of PIG receptor and removal of adiposomes from the incubation medium as was true for those induced by palmitate, H2O2 or glimepiride. In contrast, only the latter actions were dependent on the GPI-specific phospholipase C (GPI-PLC), which may generate PIGs, or on exogenous PIG37 in case of inhibited GPI-PLC. At submaximal concentrations PIG37 and palmitate, H2O2 or glimepiride acted in synergistic fashion. These data suggest that PIGs provoke the transfer of GPI-proteins from DIGs via LD and adiposomes of donor adipocytes to acceptor adipocytes and thereby mediate the regulation of lipid metabolism by palmitate, H2O2 and glimepiride between adipocytes.
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Affiliation(s)
- Günter Müller
- Sanofi-Aventis Deutschland GmbH, Research & Development, 65926 Frankfurt am Main, Germany.
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Goel M, Azev VN, d’Alarcao M. The biological activity of structurally defined inositol glycans. Future Med Chem 2009; 1:95-118. [PMID: 20390053 PMCID: PMC2853056 DOI: 10.4155/fmc.09.6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND: The inositol glycans (IGs) are glycolipid-derived carbohydrates produced by insulin-sensitive cells in response to insulin treatment. IGs exhibit an array of insulin-like activities including stimulation of lipogenesis, glucose transport and glycogen synthesis, suggesting that they may be involved in insulin signal transduction. However, because the natural IGs are structurally heterogeneous and difficult to purify to homogeneity, an understanding of the relationship between structure and biological activity has relied principally on synthetic IGs of defined structure. DISCUSSION: This article briefly describes what is known about the role of IGs in signal transduction and reviews the specific biological activities of the structurally defined IGs synthesized and tested to date. CONCLUSION: A pharmacophore for IG activity begins to emerge from the reviewed data and the structural elements necessary for activity are summarized.
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Affiliation(s)
- Meenakshi Goel
- Department of Chemistry, San José State University, One Washington Square, San José, CA 95192-90101, USA
| | - Viatcheslav N Azev
- AN Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova Str. 28, 119991, Moscow, Russia
| | - Marc d’Alarcao
- Department of Chemistry, San José State University, One Washington Square, San José, CA 95192-90101, USA
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Müller G, Wied S, Straub J, Jung C. Coordinated regulation of esterification and lipolysis by palmitate, H2O2 and the anti-diabetic sulfonylurea drug, glimepiride, in rat adipocytes. Eur J Pharmacol 2008; 597:6-18. [PMID: 18789917 DOI: 10.1016/j.ejphar.2008.08.034] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2008] [Revised: 07/23/2008] [Accepted: 08/08/2008] [Indexed: 10/21/2022]
Abstract
Inhibition of lipolysis by palmitate, H2O2 and the anti-diabetic sulfonylurea drug, glimepiride, in isolated rat adipocytes has previously been shown to rely on the degradation of cyclic adenosine monophosphate by the phosphodiesterase, Gce1, and the 5'-nucleotidase, CD73. These glycosylphosphatidylinositol (GPI)-anchored proteins are translocated from plasma membrane lipid rafts to intracellular lipid droplets upon H2O2-induced activation of a GPI-specific phospholipase C (GPI-PLC) in response to palmitate and glimepiride in intact adipocytes and, as demonstrated here, in cell-free systems as well. The same agents are also known to stimulate the incorporation of fatty acids into triacylglycerol. Here the involvement of H2O2 production, GPI-PLC activation and translocation of Gce1 and CD73 in the agent-induced esterification and accompanying lipid droplet formation was tested in rat adipocytes using relevant inhibitors. The results demonstrate that upregulation of the esterification and accumulation of triacylglycerol by glimepiride depends on the sequential H2O2-induced GPI-PLC activation and GPI-protein translocation as does inhibition of lipolysis. In contrast, stimulation of the esterification and triacylglycerol accumulation by palmitate relies on insulin-independent tyrosine phosphorylation and thus differs from its anti-lipolytic mechanism. As expected, insulin regulates lipid metabolism via typical insulin signalling independent of H2O2 production, GPI-PLC activation and GPI-protein translocation, albeit these processes are moderately stimulated by insulin. In conclusion, triacylglycerol and lipid droplet formation in response to glimepiride and H2O2 may involve the hydrolysis of cyclic adenosine monophosphate by lipid droplet-associated Gce1 and CD73 which may regulate lipid droplet-associated triacylglycerol-synthesizing and hydrolyzing enzymes in coordinated and inverse fashion.
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Müller G, Wied S, Walz N, Jung C. Translocation of glycosylphosphatidylinositol-anchored proteins from plasma membrane microdomains to lipid droplets in rat adipocytes is induced by palmitate, H2O2, and the sulfonylurea drug glimepiride. Mol Pharmacol 2008; 73:1513-29. [PMID: 18272749 DOI: 10.1124/mol.107.043935] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Inhibition of lipolysis by palmitate, H(2)O(2), and the antidiabetic sulfonylurea drug, glimepiride, in rat adipocytes has been shown previously to rely on the concerted degradation of cAMP by the glycosylphosphatidylinositol (GPI)-anchored phosphodiesterase Gce1 and 5'-nucleotidase CD73, which both gain access to the lipid droplets (LDs). The present report demonstrates the translocation of Gce1 and CD73, harboring the intact GPI anchor, from detergent-insoluble glycolipid-enriched plasma membrane domains (DIGs) to the LDs in response to palmitate, H(2)O(2), and glimepiride by analysis of their steady-state distribution using photoaffinity labeling and activity determination as well as of their redistribution after pulse or equilibrium metabolic labeling. We were surprised to find that palmitate, H(2)O(2), and glimepiride induced the activation of the GPI-specific phospholipase C (GPI-PLC) at DIGs of rat adipocytes, leading to anchorless Gce1 and CD73. Inhibition of the GPI-PLC or the presence of nonhydrolyzable substrate analogs of Gce1 and CD73 interfered with the palmitate-, H(2)O(2)-, and glimepiride-induced 1) lipolytic cleavage of Gce1 and CD73, 2) translocation of their GPI-anchored versions from DIGs to LDs, 3) up-regulation of cAMP degradation, and 4) inhibition of lipolysis. These data suggest a novel insulin-independent antilipolytic mechanism in rat adipocytes, which relies on the palmitate-, H(2)O(2)-, and glimepiride-induced and GPI-PLC-dependent translocation of (c)AMP-degrading GPI-anchored proteins from the adipocyte plasma membrane to LDs. The findings may shed new light on the biogenesis and degradation of LDs in response to physiological and pharmacological stimuli.
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Affiliation(s)
- Günter Müller
- Sanofi-Aventis Pharma Germany GmbH, TD Metabolism, Industrial Park Höchst, Bldg. H821, 65926 Frankfurt am Main, Germany.
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Hunt GJ, Amdam GV, Schlipalius D, Emore C, Sardesai N, Williams CE, Rueppell O, Guzmán-Novoa E, Arechavaleta-Velasco M, Chandra S, Fondrk MK, Beye M, Page RE. Behavioral genomics of honeybee foraging and nest defense. Naturwissenschaften 2006; 94:247-67. [PMID: 17171388 PMCID: PMC1829419 DOI: 10.1007/s00114-006-0183-1] [Citation(s) in RCA: 166] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2006] [Revised: 10/08/2006] [Accepted: 10/16/2006] [Indexed: 12/20/2022]
Abstract
The honeybee has been the most important insect species for study of social behavior. The recently released draft genomic sequence for the bee will accelerate honeybee behavioral genetics. Although we lack sufficient tools to manipulate this genome easily, quantitative trait loci (QTLs) that influence natural variation in behavior have been identified and tested for their effects on correlated behavioral traits. We review what is known about the genetics and physiology of two behavioral traits in honeybees, foraging specialization (pollen versus nectar), and defensive behavior, and present evidence that map-based cloning of genes is more feasible in the bee than in other metazoans. We also present bioinformatic analyses of candidate genes within QTL confidence intervals (CIs). The high recombination rate of the bee made it possible to narrow the search to regions containing only 17–61 predicted peptides for each QTL, although CIs covered large genetic distances. Knowledge of correlated behavioral traits, comparative bioinformatics, and expression assays facilitated evaluation of candidate genes. An overrepresentation of genes involved in ovarian development and insulin-like signaling components within pollen foraging QTL regions suggests that an ancestral reproductive gene network was co-opted during the evolution of foraging specialization. The major QTL influencing defensive/aggressive behavior contains orthologs of genes involved in central nervous system activity and neurogenesis. Candidates at the other two defensive-behavior QTLs include modulators of sensory signaling (Am5HT7 serotonin receptor, AmArr4 arrestin, and GABA-B-R1 receptor). These studies are the first step in linking natural variation in honeybee social behavior to the identification of underlying genes.
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Affiliation(s)
- Greg J. Hunt
- Department of Entomology, Purdue University, West Lafayette, IN 47907 USA
| | - Gro V. Amdam
- School of Life Sciences, Arizona State University, P.O. Box 87451, Tempe, AZ 85287-4501 USA
| | - David Schlipalius
- Department of Entomology, Purdue University, West Lafayette, IN 47907 USA
| | - Christine Emore
- Department of Entomology, Purdue University, West Lafayette, IN 47907 USA
| | - Nagesh Sardesai
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907 USA
| | - Christie E. Williams
- Department of Entomology, Purdue University, West Lafayette, IN 47907 USA
- Crop Production and Pest Control Research Unit, USDA-ARS, West Lafayette, IN 47906 USA
| | - Olav Rueppell
- Department of Biology, University of North Carolina, 105 Eberhart Bldg., Greensboro, NC 27402 USA
| | - Ernesto Guzmán-Novoa
- Department of Environmental Biology, University of Guelph, N1G 2W1 Ontario, Canada
| | | | - Sathees Chandra
- Department of Biological, Chemical and Physical Sciences, Roosevelt University, Chicago, IL 60605 USA
| | - M. Kim Fondrk
- School of Life Sciences, Arizona State University, P.O. Box 87451, Tempe, AZ 85287-4501 USA
| | - Martin Beye
- Institut fuer Genetik, Heinrich-Heine Universitaet Duesseldorf, 40225 Duesseldorf, Germany
| | - Robert E. Page
- School of Life Sciences, Arizona State University, P.O. Box 87451, Tempe, AZ 85287-4501 USA
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Lim J, Gowda DC, Krishnegowda G, Luckhart S. Induction of nitric oxide synthase in Anopheles stephensi by Plasmodium falciparum: mechanism of signaling and the role of parasite glycosylphosphatidylinositols. Infect Immun 2005; 73:2778-89. [PMID: 15845481 PMCID: PMC1087374 DOI: 10.1128/iai.73.5.2778-2789.2005] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Malaria parasite (Plasmodium spp.) infection in the mosquito Anopheles stephensi induces significant expression of A. stephensi nitric oxide synthase (AsNOS) in the midgut epithelium as early as 6 h postinfection and intermittently thereafter. This induction results in the synthesis of inflammatory levels of nitric oxide (NO) in the blood-filled midgut that adversely impact parasite development. In mammals, P. falciparum glycosylphosphatidylinositols (PfGPIs) can induce NOS expression in immune and endothelial cells and are sufficient to reproduce the major effects of parasite infection. These effects are mediated in part by mimicry of insulin signaling by PfGPIs. In this study, we demonstrate that PfGPIs can induce AsNOS expression in A. stephensi cells in vitro and in the midgut epithelium in vivo. Signaling by P. falciparum merozoites and PfGPIs is mediated through A. stephensi Akt/protein kinase B and a pathway involving DSOR1, a mitogen-activated protein kinase kinase, and an extracellular signal-regulated kinase. However, despite the involvement of kinases that are also associated with insulin signaling in A. stephensi cells, signaling by P. falciparum and by PfGPIs is distinctively different from signaling by insulin. Therefore, although mimicry of insulin by PfGPIs appears to be restricted to mammalian hosts of P. falciparum, the conservation of PfGPIs as a prominent parasite-derived signal of innate immunity can now be extended to include Anopheles mosquitoes, indicating that parasite signaling of innate immunity is conserved in mosquito and mammalian cells.
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Affiliation(s)
- Junghwa Lim
- Department of Medical Microbiology and Immunology, 3146 Tupper Hall, One Shields Avenue, University of California at Davis, School of Medicine, Davis, CA 95616, USA
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Müller G, Schulz A, Wied S, Frick W. Regulation of lipid raft proteins by glimepiride- and insulin-induced glycosylphosphatidylinositol-specific phospholipase C in rat adipocytes. Biochem Pharmacol 2005; 69:761-80. [PMID: 15710354 DOI: 10.1016/j.bcp.2004.11.014] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2004] [Accepted: 11/25/2004] [Indexed: 11/18/2022]
Abstract
The insulin receptor-independent insulin-mimetic signalling provoked by the antidiabetic sulfonylurea drug, glimepiride, is accompanied by the redistribution and concomitant activation of lipid raft-associated signalling components, such as the acylated tyrosine kinase, pp59(Lyn), and some glycosylphosphatidylinositol-anchored proteins (GPI-proteins). We now found that impairment of glimepiride-induced lipolytic cleavage of GPI-proteins in rat adipocytes by the novel inhibitor of glycosylphosphatidylinositol-specific phospholipase C (GPI-PLC), GPI-2350, caused almost complete blockade of (i) dissociation from caveolin-1 of pp59(Lyn) and GPI-proteins, (ii) their redistribution from high cholesterol- (hcDIGs) to low cholesterol-containing (lcDIGs) lipid rafts, (iii) tyrosine phosphorylation of pp59(Lyn) and insulin receptor substrate-1 protein (IRS-1) and (iv) stimulation of glucose transport as well as (v) inhibition of isoproterenol-induced lipolysis in response to glimepiride. In contrast, blockade of the moderate insulin activation of the GPI-PLC and of lipid raft protein redistribution by GPI-2350 slightly reduced insulin signalling and metabolic action, only. Importantly, in response to both insulin and glimepiride, lipolytically cleaved hydrophilic GPI-proteins remain associated with hcDIGs rather than redistribute to lcDIGs as do their uncleaved amphiphilic versions. In conclusion, GPI-PLC controls the localization within lipid rafts and thereby the activity of certain GPI-anchored and acylated signalling proteins. Its stimulation is required and may even be sufficient for insulin-mimetic cross-talking to IRS-1 in response to glimepiride via redistributed and activated pp59(Lyn).
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Affiliation(s)
- Günter Müller
- Sanofi-Aventis, TD Metabolism, Industrial Park Frankfurt-Höchst, 65926 Frankfurt am Main, Germany.
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Martini CN, Vaena de Avalos SG, del Carmen Vila M. ACTH stimulates the release of alkaline phosphatase through Gi-mediated activation of a phospholipase C and the release of inositol-phosphoglycan. Mol Cell Biochem 2004; 258:191-9. [PMID: 15030184 DOI: 10.1023/b:mcbi.0000012855.94291.dd] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We have previously reported that ACTH activates a phospholipase C that hydrolyzes glycosylphosphatidylinositol (GPI), which would release inositolphosphoglycan (IPG) to the extracellular medium, and that an IPG purified from Trypanosoma cruzi is able to inhibit ACTH-mediated steroid production in adrenocortical cells. In the present paper, it was found that anti-inositolphosphoglycan antibodies (anti-CRD) increased ACTH-mediated corticosterone production, which indicates that an endogenous IPG is a physiological inhibitor of ACTH response. On the other hand, we investigated the release to the extracellular medium of the GPI-anchored enzyme, alkaline phosphatase, by ACTH. We found that: (a) the released enzyme appeared in the aqueous phase after Triton X-114 partitioning, consistent with loss of the GPI, (b) the phospholipase C inhibitor, U73122, impaired the release of the enzyme by the hormone and (c) two inhibitors of IPG uptake, inositol 2-monophosphate and 2 M NaCl, increased the amount of alkaline phosphatase in the extracellular medium. These results suggest that ACTH releases alkaline phosphatase by activation of a phospholipase C. Dibutyryladenosine-3',5'-cyclic monophosphate (db-cAMP) was able to increase the release of alkaline phosphatase from adrenocortical cells and this effect was inhibited by U73122, suggesting that cAMP is involved in the activation of phospholipase C. In addition, it was found that a pertussis-toxin sensitive G-protein is required for ACTH- and db-cAMP-mediated release of alkaline phosphatase and that incorporation of anti-Gi antibodies in adrenocortical cells inhibited the release of alkaline phosphatase by ACTH. Our results suggest that ACTH increases the release of alkaline phosphatase by activation of a phospholipase C through cAMP and Gi which would contribute to produce IPG It was also found that the two inhibitors of IPG uptake, inositol-2-monophosphate and 2 M NaCl, increased the amount of alkaline phosphatase in the extracellular medium of ACTH-treated cells more than in control cells, indicating that ACTH also stimulates the uptake of IPG These data support a role of GPI and the involvement of Gi in ACTH action.
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Affiliation(s)
- Claudia N Martini
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, 1428, Buenos Aires, Argentina
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Abstract
The structure of covalently-linked glycosylphosphatidylinositol (GPI) anchors of membrane proteins displayed on the cell surface is described. Evidence of how the GPI-anchors are sorted into membrane rafts in the plasma membrane is reviewed. Proteins are released by hydrolysis of the linkage to the GPI anchor and phospholipases from different sources involved in this process are characterised. The regulation of protein conformation and function resulting from phospholipase cleavage of the GPI anchor is discussed in the context of its role in signal transduction by insulin. In this signalling system, re-distribution of critical membrane components, including GPI-anchored proteins and non-receptor tyrosine kinases, between different raft domains appears to play a central role in the signal transduction pathway.
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Affiliation(s)
- Frances J Sharom
- Department of Chemistry and Biochemistry, University of Guelph, Guelph, Ontario, N1G 2W1 Canada
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