Luiken Joost J F P, Ouwens D Margriet, Habets Daphna D J, van der Zon Gerard C M, Coumans Will A, Schwenk Robert W, Bonen Arend, Glatz Jan F C
Department of Molecular Genetics, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, PO Box 616, NL-6200 MD Maastricht, The Netherlands.
J Endocrinol. 2009 May;201(2):199-209. doi: 10.1677/JOE-09-0046. Epub 2009 Mar 9.
Insulin stimulates cardiac long-chain fatty acid (LCFA) and glucose uptake via translocation of human homolog of rat fatty acid translocase (CD36) and GLUT4 respectively, from intracellular membrane compartments to the sarcolemma, a process dependent on the activation of phosphatidylinositol-3 kinase. To identify downstream kinases of insulin signaling involved in translocation of CD36 and GLUT4 in the heart, we tested i) which cardiac protein kinase C (PKC) isoforms (alpha, delta, epsilon or zeta) are activated by insulin, and ii) whether PKC isoform-specific inhibition affects insulin-stimulated substrate uptake in the heart. Insulin-stimulated LCFA and glucose uptake were completely blunted by inhibition of PKC-zeta, but not by inhibition of conventional or novel PKCs. Concomitantly, translocation of CD36 and GLUT4 to the sarcolemma was completely blunted upon inhibition of PKC-zeta. However, insulin, in contrast to the diacylglycerol-analog phorbol-12-myristate-13-acetate (PMA), did not induce membrane-attachment of the conventional and novel PKCs-alpha, -delta, and -epsilon. PKC-zeta was already entirely membrane-bound in non-stimulated cells, and neither insulin nor PMA treatment had any effect on the subcellular localization of PKC-zeta. Furthermore, insulin treatment did not change phosphorylation of PKC-alpha, -delta, and -zeta or enzymatic activity of PKC-zeta towards a PKC-zeta substrate peptide. It is concluded that PKC-zeta, but not any other PKC isoform, is necessary for insulin-induced translocation of GLUT4 and CD36. However, PKC-zeta is already fully active under basal conditions and not further activated by insulin, indicating that its role in insulin-stimulated uptake of both glucose and LCFA is permissive rather than regulatory.
胰岛素分别通过大鼠脂肪酸转位酶（CD36）的人类同源物和葡萄糖转运蛋白4（GLUT4）从细胞内膜区室向肌膜的转位来刺激心脏长链脂肪酸（LCFA）和葡萄糖摄取，这一过程依赖于磷脂酰肌醇-3激酶的激活。为了确定参与心脏中CD36和GLUT4转位的胰岛素信号下游激酶，我们测试了：i）胰岛素激活哪些心脏蛋白激酶C（PKC）亚型（α、δ、ε或ζ）；ii）PKC亚型特异性抑制是否影响胰岛素刺激的心脏底物摄取。抑制PKC-ζ可完全抑制胰岛素刺激的LCFA和葡萄糖摄取，但抑制传统或新型PKC则无此作用。同时，抑制PKC-ζ后，CD36和GLUT4向肌膜的转位也完全受到抑制。然而，与二酰基甘油类似物佛波醇-12-肉豆蔻酸酯-13-乙酸酯（PMA）不同，胰岛素并未诱导传统和新型PKC-α、-δ和-ε的膜附着。PKC-ζ在未受刺激的细胞中已完全与膜结合，胰岛素和PMA处理均对PKC-ζ的亚细胞定位没有任何影响。此外，胰岛素处理并未改变PKC-α、-δ和-ζ的磷酸化或PKC-ζ对PKC-ζ底物肽的酶活性。结论是，PKC-ζ而非任何其他PKC亚型是胰岛素诱导的GLUT4和CD36转位所必需的。然而，PKC-ζ在基础条件下已完全激活，且不会被胰岛素进一步激活，这表明其在胰岛素刺激的葡萄糖和LCFA摄取中的作用是允许性的而非调节性的。
