Role of β isoform of protein kinase C in hepatocyte growth factor-induced signal transduction in pigment cells

研究了肝细胞生长因子（HGF）通过其受体酪氨酸激酶c-Met在人正常黑色素细胞和恶性黑色素瘤细胞系中的信号通路。在黑素细胞和黑色素瘤细胞中均观察到hgf诱导的c-Met激活，而c-Met的下游靶点磷脂酰肌醇3-激酶（PI3K）在黑素细胞中未被激活，但在黑色素瘤细胞中增强。因此，我们分析了连接活化c-Met和PI3K的支架连接蛋白Gab1在这些细胞中的作用。Gab1在黑素细胞中的电泳迁移速度慢于黑色素瘤细胞，经碱性磷酸酶处理后迁移速度向黑色素瘤细胞转移，说明Gab1在黑素细胞中丝氨酸和苏氨酸被高度磷酸化。使用腺病毒载体将蛋白激酶C (PKC) βII引入黑色素瘤细胞，该蛋白在黑色素细胞中表达，但在黑色素瘤细胞中不存在，导致Gab1的丝氨酸和苏氨酸磷酸化。此外，pkc - β ii的引入抑制了hgf诱导的Pl3K的激活。这些结果表明，从Gab1到PI3K的HGF信号传导过程受到pkc - β ii的负调控。

The signaling pathway of hepatocyte growth factor (HGF) through its receptor-tyrosine kinase c-Met was examined in human normal melanocytes and malignant melanoma cell lines. HGF-induced c-Met activation was observed in both melanocytes and melanoma cells, whereas phosphatidylinositol 3-kinase (PI3K), a downstream target of c-Met, was not activated in the melanocytes but enhanced in the melanoma cells. Therefore, the role of Gab1, the scaffolding adapter protein that couples activated c-Met and PI3K, was analyzed in these cells. Gab1 in the melanocytes showed an electrophoretic mobility slower than that of the melanoma cells, and the mobility shifted to that of the melanoma cells after the treatment with alkaline phosphatase, indicating that Gab1 is highly phosphorylated on serine and threonine in the melanocytes. Introuction of protein kinase C (PKC) βII in the melanoma cells using adenovirus vector, that is expressed in the melanocytes but is absent in the melanoma cells, resulted in serine and threonine phosphorylation of Gab1. Furthermore, the introduction of PKCβII suppressed HGF-induced activation of Pl3K. These results indicate that the HGF signaling process from Gab1 to PI3K is negatively regulated by PKCβII.