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

本文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（PI 3 K）在黑素细胞中未激活，但在黑素瘤细胞中增强。因此，在这些细胞中分析了Gab 1的作用，Gab 1是将活化的c-Met和PI 3 K偶联的支架衔接蛋白。Gab 1在黑色素细胞中显示出比黑色素细胞慢的电泳迁移率，并且在用碱性磷酸酶处理后迁移率转移到黑色素细胞的迁移率，表明Gab 1在黑色素细胞中的丝氨酸和苏氨酸上高度磷酸化。蛋白激酶C（PKC）βII在黑色素细胞中表达，但在黑色素细胞中不表达，腺病毒介导的PKC βII在黑色素细胞中的转染导致Gab 1的丝氨酸和苏氨酸磷酸化。此外，PKCβII的引入抑制了HGF诱导的P13 K活化。这些结果表明，HGF信号通路从Gab 1到PI 3 K的过程受到PKCβII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.