Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
J Cell Biochem. 2012 Jun;113(6):2064-76. doi: 10.1002/jcb.24078.
The liver is a major insulin-responsive tissue responsible for glucose regulation. One important mechanism in this phenomenon is insulin-induced glycogen synthesis. Studies in our laboratory have shown that protein kinase Cs delta (PKCδ) and alpha (α) have important roles in insulin-induced glucose transport in skeletal muscle, and that their expression and activity are regulated by insulin. Their importance in glucose regulation in liver cells is unclear. In this study we investigated the possibility that these isoforms are involved in the mediation of insulin-induced glycogen synthesis in hepatocytes. Studies were done on rat hepatocytes in primary culture and on the AML-12 (alpha mouse liver) cell line. Insulin increased activity and tyrosine phosphorylation of PKCδ within 5 min. In contrast, activity and tyrosine phosphorylation of PKCα were not increased by insulin. PKCδ was constitutively associated with IR, and this was increased by insulin stimulation. Suppression of PKCδ expression by transfection with RNAi, or overexpression of kinase dead (dominant negative) PKCδ reduced both the insulin-induced activation of PKB/Akt and the phosphorylation of glycogen synthase kinase 3 (GSK3) and reduced significantly insulin-induced glucose uptake. In addition, treatment of primary rat hepatocytes with rottlerin abrogated insulin-induced increase in glycogen synthesis. Neither overexpression nor inhibition of PKCα appeared to alter activation of PKB, phosphorylation of GSK3 or glucose uptake in response to insulin. We conclude that PKCδ, but not PKCα, plays an essential role in insulin-induced glucose uptake and glycogenesis in hepatocytes.
肝脏是一个主要的胰岛素反应组织，负责葡萄糖调节。这一现象的一个重要机制是胰岛素诱导的糖原合成。我们实验室的研究表明，蛋白激酶 C 三角洲（PKCδ）和阿尔法（α）在胰岛素诱导的骨骼肌葡萄糖转运中具有重要作用，它们的表达和活性受胰岛素调节。它们在肝细胞葡萄糖调节中的重要性尚不清楚。在这项研究中，我们研究了这些同工型是否参与胰岛素诱导的肝细胞糖原合成的可能性。这项研究在原代培养的大鼠肝细胞和 AML-12（α 鼠肝）细胞系上进行。胰岛素在 5 分钟内增加了 PKCδ 的活性和酪氨酸磷酸化。相比之下，胰岛素没有增加 PKCα 的活性和酪氨酸磷酸化。PKCδ 与胰岛素受体（IR）持续相关，胰岛素刺激可增加其相关性。用 RNAi 转染抑制 PKCδ 的表达，或过表达激酶失活（显性负）PKCδ，可降低胰岛素诱导的 PKB/Akt 激活和糖原合酶激酶 3（GSK3）的磷酸化，并显著降低胰岛素诱导的葡萄糖摄取。此外，罗特林纳（rottlerin）处理原代大鼠肝细胞可消除胰岛素诱导的糖原合成增加。过表达或抑制 PKCα 似乎都不会改变胰岛素对 PKB 激活、GSK3 磷酸化或葡萄糖摄取的作用。我们的结论是，PKCδ，而不是 PKCα，在胰岛素诱导的肝细胞葡萄糖摄取和糖生成中发挥着重要作用。
