Kim Bhumsoo, Oh SangSu, van Golen Cynthia M, Feldman Eva L
Department of Neurology, University of Michigan, 4414 Kresge III, 200 Zina Pitcher Place, Ann Arbor, MI 48109-0588, United States.
Cell Signal. 2005 Jun;17(6):769-75. doi: 10.1016/j.cellsig.2004.11.001. Epub 2004 Nov 23.
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.
胰岛素受体底物（IRS）蛋白是I型胰岛素样生长因子（IGF）受体（IGF-IR）的主要对接分子，并介导其对下游信号分子的作用。在本报告中，我们研究了人神经母细胞瘤SH-EP细胞凋亡过程中IRS-1的调控。用甘露醇或冈田酸（OA）处理SH-EP细胞可诱导凋亡，并具有失巢凋亡的典型特征。甘露醇处理导致IRS-1降解，并伴随出现较小的片段，可能代表半胱天冬酶切割产物。相比之下，OA诱导的IRS-1降解伴随着IRS-1迁移率的改变，提示IRS-1丝氨酸/苏氨酸磷酸化。IGF-I可阻断甘露醇诱导而非OA诱导的降解。用半胱天冬酶或蛋白酶体抑制剂预处理细胞也可部分阻断甘露醇诱导的IRS-1降解。这些结果提示两条独立的途径参与了IRS-1降解；一条途径依赖于半胱天冬酶激活，并被IGF-I阻断，而第二条途径不依赖于半胱天冬酶且对IGF-I不敏感。
