Braiman L, Alt A, Kuroki T, Ohba M, Bak A, Tennenbaum T, Sampson S R
Faculty of Life Sciences, Gonda-Goldschmied Center, Bar-Ilan University, Ramat-Gan, Israel.
Mol Endocrinol. 1999 Dec;13(12):2002-12. doi: 10.1210/mend.13.12.0393.
Insulin activates certain protein kinase C (PKC) isoforms that are involved in insulin-induced glucose transport. In this study, we investigated the possibility that activation of PKCdelta by insulin participates in the mediation of insulin effects on glucose transport in skeletal muscle. Studies were performed on primary cultures of rat skeletal myotubes. The role of PKCdelta in insulin-induced glucose uptake was evaluated both by selective pharmacological blockade and by over-expression of wild-type and point-mutated inactive PKCdelta isoforms in skeletal myotubes. We found that insulin induces tyrosine phosphorylation and translocation of PKCdelta to the plasma membrane and increases the activity of this isoform. Insulin-induced effects on translocation and phosphorylation of PKCdelta were blocked by a low concentration of rottlerin, whereas the effects of insulin on other PKC isoforms were not. This selective blockade of PKCdelta by rottlerin also inhibited insulin-induced translocation of glucose transporter 4 (GLUT4), but not glucose transporter 3 (GLUT3), and significantly reduced the stimulation of glucose uptake by insulin. When overexpressed in skeletal muscle, PKCdelta and PKCdelta were both active. Overexpression of PKCdelta induced the translocation of GLUT4 to the plasma membrane and increased basal glucose uptake to levels attained by insulin. Moreover, insulin did not increase glucose uptake further in cells overexpressing PKCdelta. Overexpression of PKCdelta did not affect basal glucose uptake or GLUT4 location. Stimulation of glucose uptake by insulin in cells overexpressing PKCdelta was similar to that in untransfected cells. Transfection of skeletal myotubes with dominant negative mutant PKCdelta did not alter basal glucose uptake but blocked insulin-induced GLUT4 translocation and glucose transport. These results demonstrate that insulin activates PKCdelta and that activated PKCdelta is a major signaling molecule in insulin-induced glucose transport.
胰岛素可激活某些参与胰岛素诱导的葡萄糖转运的蛋白激酶C（PKC）亚型。在本研究中，我们探讨了胰岛素激活PKCδ参与介导胰岛素对骨骼肌葡萄糖转运作用的可能性。实验在大鼠骨骼肌肌管原代培养物上进行。通过选择性药理阻断以及在骨骼肌肌管中过表达野生型和点突变失活的PKCδ亚型，评估了PKCδ在胰岛素诱导的葡萄糖摄取中的作用。我们发现胰岛素可诱导PKCδ的酪氨酸磷酸化并使其转位至质膜，同时增加该亚型的活性。低浓度的rottlerin可阻断胰岛素对PKCδ转位和磷酸化的诱导作用，而对胰岛素对其他PKC亚型的作用无影响。rottlerin对PKCδ的这种选择性阻断也抑制了胰岛素诱导的葡萄糖转运蛋白4（GLUT4）的转位，但不影响葡萄糖转运蛋白3（GLUT3），并显著降低了胰岛素对葡萄糖摄取的刺激作用。当在骨骼肌中过表达时，PKCδ和PKCδ均具有活性。PKCδ的过表达诱导了GLUT4转位至质膜，并使基础葡萄糖摄取增加至胰岛素所达到的水平。此外，在过表达PKCδ的细胞中，胰岛素并未进一步增加葡萄糖摄取。PKCδ过表达不影响基础葡萄糖摄取或GLUT4的定位。在过表达PKCδ的细胞中，胰岛素对葡萄糖摄取的刺激作用与未转染细胞相似。用显性负性突变体PKCδ转染骨骼肌肌管不改变基础葡萄糖摄取，但可阻断胰岛素诱导的GLUT4转位和葡萄糖转运。这些结果表明胰岛素激活PKCδ，且活化的PKCδ是胰岛素诱导的葡萄糖转运中的主要信号分子。
