title: A farnesylated G-protein suppresses Akt phosphorylation in INS 832/13 cells and normal rat islets: regulation by pertussis toxin and PGE₂.
abstract: Protein isoprenylation constitutes incorporation of either 15-carbon farnesyl or 20-carbon geranylgeranyl derivative of mevalonic acid onto the C-terminal cysteine, culminating in increased hydrophobicity of the modified proteins for optimal membrane anchoring and interaction with their respective effectors. Emerging evidence confirms the participatory role of prenylated proteins in pancreatic β-cell function including insulin secretion. Herein, we investigated the putative regulatory roles of protein farnesylation in cell survival signaling pathways in insulin-secreting INS 832/13 cells and normal rodent islets, specifically at the level of protein kinase-B/Akt phosphorylation induced by insulin-like growth factor [IGF-1]. Selective inhibitors of farnesylation [e.g., FTI-277 or FTI-2628] or knockdown of the β-subunit of farnesyl transferase by siRNA significantly increased Akt activation under basal and IGF-1-stimulated conditions. Consequentially, the relative abundance of phosphorylated FoxO1 and Bad were increased implicating inactivation of critical components of the cell death machinery. In addition, FTI-induced Akt activation was attenuated by the PI3-kinase inhibitor, LY294002. Exposure of INS 832/13 cells to pertussis toxin [PTx] markedly potentiated Akt phosphorylation suggesting involvement of a PTx-sensitive G-protein in this signaling axis. Furthermore, prostaglandin E₂, a known agonist of inhibitory G-proteins, significantly attenuated FTI-induced Akt phosphorylation. Taken together, our findings suggest expression of a farnesylated G-protein in INS 832/13 cells and normal rat islets, which appear to suppress Akt activation and subsequent cell survival signaling steps. Potential regulatory roles of the islet endogenous protein kinase-B inhibitory protein [Probin] in islet function are discussed.
authors.affiliation: Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, 259 Mack Avenue, Detroit, MI 48202, USA.
authors.forename: Chandrashekara N
authors.initials: CN
authors.lastname: Kyathanahalli
authors.forename: Anjaneyulu
authors.initials: A
authors.lastname: Kowluru
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D002470:Cell Survival; D002478:Cells, Cultured; D015232:Dinoprostone / Q000494:pharmacology*; D051231:Farnesyltranstransferase / Q000037:antagonists & inhibitors / Q000235:genetics; D051858:Forkhead Transcription Factors / Q000378:metabolism; D020868:Gene Silencing; D006160:Guanosine Triphosphate / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D037342:Pertussis Toxin / Q000494:pharmacology*; D010766:Phosphorylation; D054876:Prenylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D021122:Protein Subunits / Q000235:genetics; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D015398:Signal Transduction; D051025:bcl-Associated Death Protein / Q000378:metabolism; D000071161:Forkhead Box Protein O1
chemical_list: D064413:3-Phosphoinositide-Dependent Protein Kinases; D015232:Dinoprostone; D051231:Farnesyltranstransferase; D051858:Forkhead Transcription Factors; D006160:Guanosine Triphosphate; D007334:Insulin-Like Growth Factor I; D009419:Nerve Tissue Proteins; D037342:Pertussis Toxin; D017346:Protein Serine-Threonine Kinases; D021122:Protein Subunits; D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; D051025:bcl-Associated Death Protein; C494821:Bad protein, rat; C074639:Foxo1 protein, rat; D000071161:Forkhead Box Protein O1