title: Insulin regulates cleavage of procaspase-9 via binding of X chromosome-linked inhibitor of apoptosis protein in HT-29 cells.
abstract: Insulin significantly reduced tumor necrosis factor (TNF)-alpha-induced cleavage of procaspase-8, -9, and -3 and poly(ADP-ribose) polymerase when observed for up to 24 hours in a dose-dependent manner. Signaling pathways responsible for the inhibitory effects of insulin were investigated by using protein kinase inhibitors. Both phosphatidylinositol 3'-kinase (PI3K) and mitogen-activated protein kinase kinase pathways mediate the ability of insulin to decrease the TNF-alpha-induced cleavage of procaspase-8. In contrast, only the PI3K inhibitor reversed the effect of insulin on the TNF-alpha-induced cleavage of procaspase-9. Moreover, insulin decreased the apoptotic level induced by TNF-alpha, whereas the PI3K inhibitor enhanced it. The protein level of Apaf-1, an activator of procaspase-9, remained constant with the application of agents affecting the cleavage of procaspase-9. In examining another regulator of cleaved caspase-9, X chromosome-linked inhibitor of apoptosis protein (XIAP), we observed that TNF-alpha treatment induced fragmentation of XIAP, which was also enhanced by the PI3K inhibitor. In addition, XIAP was coimmunoprecipitated with procaspase-9. The treatment with TNF-alpha reduced the level of XIAP precipitated with procaspase-9, whereas insulin reversed this effect. Moreover, PI3K and Akt inhibitors, but not mammalian target of rapamycin inhibitor, inhibited the effect of insulin on the coprecipitation of procaspase-9 and XIAP. Our data suggest that insulin decreases the TNF-alpha-induced cleavage of procaspase-9 and subsequent apoptosis by regulating XIAP via the PI3K/Akt pathway.
authors.affiliation: Biological Engineering Division, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Ji-Eun
authors.initials: JE
authors.lastname: Kim
authors.forename: Steven R
authors.initials: SR
authors.lastname: Tannenbaum
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D002867:Chromones / Q000494:pharmacology; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019073:HT29 Cells; D006801:Humans; D047468:Immunoprecipitation; D007328:Insulin / Q000494:pharmacology*; D020935:MAP Kinase Signaling System; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000494:pharmacology; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D053453:Caspase 9; D020169:Caspases; D002867:Chromones; D004791:Enzyme Inhibitors; D007328:Insulin; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D014409:Tumor Necrosis Factor-alpha; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494918:AKT1 protein, human; C506433:CASP9 protein, human