title: Insulin receptor substrate-1 and -2 mediate resistance to glucose-induced caspase-3 activation in human neuroblastoma cells.
abstract: Hyperglycemia in patients with type 2 diabetes causes multiple neuronal complications, e.g., diabetic polyneuropathy, cognitive decline, and embryonic neural crest defects due to increased apoptosis. Possible mechanisms of neuronal response to increased glucose burden are still a matter of debate. Insulin and insulin-like growth factor-1 (IGF-1) receptor signaling inhibits glucose-induced caspase-3 activation and apoptotic cell death. The insulin receptor substrates (IRS) are intracellular adapter proteins mediating insulin's and IGF-1's intracellular effects. Even though all IRS proteins have similar function and structure, recent data suggest different actions of IRS-1 and IRS-2 in mediating their anti-apoptotic effects in glucose neurotoxicity. We therefore investigated the role of IRS-1/-2 in glucose-induced caspase-3 activation using human neuroblastoma cells. Overexpression of IRS-1 or IRS-2 caused complete resistance to glucose-induced caspase-3 cleavage. Inhibition of PI3-kinase reversed this protective effect of IRS-1 or IRS-2. However, MAP-kinases inhibition had only minor impact. IRS overexpression increased MnSOD abundance as well as BAD phosphorylation while Bim and BAX levels remained unchanged. Since Akt promotes cell survival at least partially via phosphorylation and inhibition of downstream forkhead box-O (FoxO) transcription factors, we generated neuroblastoma cells stably overexpressing a dominant negative mutant of FoxO1 mimicking activation of the insulin/IGF-1 pathway on FoxO-mediated transcription. Using these cells we showed that FoxO1 is not involved in neuronal protection mediated by increased IRS-1/-2 expression. Thus, overexpression of both IRS-1 and IRS-2 induces complete resistance to glucose-induced caspase-3 activation via PI3-kinase mediated BAD phosphorylation and MnSOD expression independent of FoxO1.
authors.affiliation: Department of Internal Medicine II, Center for Molecular Medicine Cologne (CMMC), University of Cologne, Kerpener Str. 62, 50937 Cologne, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Stöhr
authors.forename: Johann
authors.initials: J
authors.lastname: Hahn
authors.forename: Lorna
authors.initials: L
authors.lastname: Moll
authors.forename: Uschi
authors.initials: U
authors.lastname: Leeser
authors.forename: Susanna
authors.initials: S
authors.lastname: Freude
authors.forename: Corinna
authors.initials: C
authors.lastname: Bernard
authors.forename: Katharina
authors.initials: K
authors.lastname: Schilbach
authors.forename: Andreas
authors.initials: A
authors.lastname: Markl
authors.forename: Michael
authors.initials: M
authors.lastname: Udelhoven
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Krone
authors.forename: Markus
authors.initials: M
authors.lastname: Schubert
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism*; D004789:Enzyme Activation; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D047468:Immunoprecipitation; D055504:Insulin Receptor Substrate Proteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009447:Neuroblastoma / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism; D013549:Sweetening Agents / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D051025:bcl-Associated Death Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C494819:BAD protein, human; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C526292:IRS1 protein, human; C526297:IRS2 protein, human; D055504:Insulin Receptor Substrate Proteins; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D013549:Sweetening Agents; D051025:bcl-Associated Death Protein; D013482:Superoxide Dismutase; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D053148:Caspase 3; D005947:Glucose