title: Differential regulation of insulin receptor substrate-1 degradation during mannitol and okadaic acid induced apoptosis in human neuroblastoma cells.
abstract: Insulin receptor substrate (IRS) proteins are major docking molecules for the type I insulin like growth factor (IGF) receptor (IGF-IR) and mediate their effects on downstream signaling molecules. In this report, we investigated IRS-1 regulation during apoptosis in human neuroblastoma SH-EP cells. Treatment of SH-EP cells with mannitol or okadaic acid (OA) induces apoptosis with the typical characteristics of anoikis. Mannitol treatment results in IRS-1 degradation with concomitant appearance of smaller fragments, likely representing caspase cleavage products. In contrast OA-induced IRS-1 degradation is accompanied by a mobility shift in IRS-1, suggesting IRS-1 serine/threonine phosphorylation. Mannitol-induced, but not OA-induced, degradation is blocked by IGF-I. Pretreatment of the cells with caspase or proteasome inhibitors also partially blocks mannitol-induced IRS-1 degradation. These results suggest two independent pathways are involved in IRS-1 degradation; one pathway is dependent on caspase activation and is blocked by IGF-I, while a second pathway is caspase-independent and IGF-I-insensitive.
authors.affiliation: Department of Neurology, University of Michigan, 4414 Kresge III, 200 Zina Pitcher Place, Ann Arbor, MI 48109-0588, United States.
authors.forename: Bhumsoo
authors.initials: B
authors.lastname: Kim
authors.forename: SangSu
authors.initials: S
authors.lastname: Oh
authors.forename: Cynthia M
authors.initials: CM
authors.lastname: van Golen
authors.forename: Eva L
authors.initials: EL
authors.lastname: Feldman
mesh_terms: D017209:Apoptosis; D061945:Caspase Inhibitors; D045744:Cell Line, Tumor; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008353:Mannitol / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009447:Neuroblastoma; D019319:Okadaic Acid / Q000494:pharmacology*; D010750:Phosphoproteins / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D061988:Proteasome Inhibitors; D015398:Signal Transduction
chemical_list: D061945:Caspase Inhibitors; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D019319:Okadaic Acid; D008353:Mannitol; D007334:Insulin-Like Growth Factor I