Mechanism of insulin-induced GLUT4 down-regulation through retromer inhibition

长期胰岛素刺激导致GLUT4耗竭。这种作用主要是由于GLUT4的溶酶体加速降解引起的。我们发现胰岛素从3T3-L1脂肪细胞的LDM膜上急性解离逆转录物，这伴随着Vps35与sortilin相互作用的破坏。这种胰岛素效应依赖于蛋白激酶CK2，而不依赖于pi3激酶或Erk 1/2。敲低Vps26可将GLUT4降低至与胰岛素刺激时相当的水平4小时。CK2磷酸化基序突变的Vps35对胰岛素诱导的低密度微粒体膜解离具有抗性，其过表达可减弱GLUT4在胰岛素作用下的下调。胰岛素生成的过氧化氢是胰岛素作用于反转录物和GLUT4的上游介质。这些结果表明，胰岛素产生的氧化应激通过抑制ck2依赖的逆转录酶功能，将GLUT4的分选方向转向溶酶体。

Long term insulin stimulation causes GLUT4 depletion. This effect is caused mainly by accelerated lysosomal degradation of GLUT4. We show that insulin acutely dissociated retromer from the LDM membranes of 3T3-L1 adipocytes that was accompanied by disruption of the interaction of Vps35 with sortilin. This insulin effect was dependent on protein kinase CK2 but not PI3-kinase or Erk 1/2. Knockdown of Vps26 decreased GLUT4 to a level comparable with that with insulin stimulation for 4 h. Vps35 with a mutation in the CK2 phosphorylation motif was resistant to insulin-induced dissociation from the low density microsomal membrane, and its overexpression attenuated GLUT4 down-regulation with insulin. Insulin-generated hydrogen peroxide was an upstream mediator of the insulin action on retromer and GLUT4. These results suggested that insulin-generated oxidative stress switches the GLUT4 sorting direction to lysosomes through inhibition of the retromer function in a CK2-dependent manner.