Molecular mechanism of IRS-1 degradation by PLGγ and PP2C

我们发现，U 73122，这是磷脂酶C（PLC）抑制剂，阻断胰岛素诱导的3 T3-L1脂肪细胞的葡萄糖摄取。此外，PLCγ的过表达以剂量依赖性方式刺激葡萄糖摄取而不刺激胰岛素。PLCγ过表达不影响Akt的磷酸化，但增强非典型PKC的磷酸化。因此，PLCγ可能通过激活非典型的PKC来促进葡萄糖摄取，而蛋白磷酸酶2C（PP 2C）的过表达可引起PI 3-激酶p85丝氨酸残基的去磷酸化，从而正性调节胰岛素信号转导。另一方面，PP 2C的过表达加速胰岛素刺激的IRS-1降解。当我们通过sRNA干扰方法抑制PP 2C蛋白表达时，胰岛素诱导的IRS-1降解被抑制。蛋白酶体抑制剂lactasistine可完全抑制PP 2C诱导的IRS-1降解。PI 3-激酶抑制剂渥曼青霉素也部分抑制该作用。综上所述，PP 2C通过PI 3-激酶途径对胰岛素信号传导具有积极和消极的影响。

We found that U73122,which was phospholioase C(PLC) inhibitor, blocked insulin-induced glucose uptake in 3T3-L1 adipocytes. Moreover, overexpression of PLCγ stimulated glucose uptake without insulin stimulation in a dose dependent manner. Overexpression of PLCγ did not affect phosphorylation of Akt, but enhanced phosphorylation of atypical PKC. Thus, it suggests that PLCγ stimulates gluxoce uptake through activation of atypical PKC.Overexpression of protein phosphatase 2C(PP2C) caused dephosphorylation of serine residue of p85 of PI 3-kinase, and positively regulated insulin signaling. On the other hand, overexpression of PP2C accelerated insulin-stimulated IRS-1 degradation. When we suppressed PP2C protein expression by sRNA interference method, insulin-induced IRS-1 degradation was inhibited. Moreover, PP2C-induced IRS-1 degradation was completely inhibited by lactasistine treatment, which was proteasome inhibitor. PI 3-kinase inhibitor, wortmannin, also suppressed it, partially. Taken together, PP2C has both positive and negative effects on insulin signaling through PI 3-kinase pathway.