Studies on heterogeneity of protein kinase C, their structures, regulations and functions.

蛋白激酶C(PKC)是一种多功能的丝氨酸/苏氨酸蛋白激酶，广泛参与多种细胞信号转导。在本研究中，我们通过分子克隆和酶学分析发现存在多个亚种的PKC。它们在几种组织和细胞类型中的相对活性、表达和细胞内定位的个体模式明显不同。到目前为止，从不同组织中获得的PKC亚种在其激活方式、酶学性质和佛波酯诱导的下调方面表现出细微的差异，此外，在HL-60细胞向粒细胞分化的过程中，PKC亚种的表达受到不同的调控。因此，我们强烈地认为，PKC家族的每个成员对底物蛋白表现出明显不同的偏好，这些底物蛋白位于表达底物的细胞类型的特定细胞内。用佛波醇酯或膜透性甘油通过PKC激活T淋巴细胞的分析表明，PKC具有双重作用，即膜受体的调节和基因表达的调节。短期的PKC激活可能是由肌醇磷脂的分解引起的，它提供了淋巴细胞表面TCR-CD3复合体的下调。另一方面，持续的PKC激活对于增强IL-2受体的表达最终导致细胞增殖是必要的。除了肌醇磷脂的水解之外，似乎还有几种额外的途径来提供延长酶激活所需的二酰甘油。这种导致PKC激活的新机制以及PKC亚种的功能特异性仍有待探索，以阐明PKC在基因表达调控和生长控制中的作用。

Protein kinase C (PKC) is a multifunctional protein Ser/Thr kinase and generally accepted to be involved in a wide variety of cellular signal transduction. In this study, we have found the existence of multiple subspecies of PKC through molecular cloning and enzymological analysis. Their relative activity and individual pattern of expression and intracellular locarization in several tissues and cell types are distinctly different one another. The PKC subspecies thus far obtained from various tissues exhibit subtle differences in their mode of activation, enzymological properties, and phorbol ester-induced down-regulation.In addition, the expressions of PKC subspecies are differently regulated during the differentiation of HL-60 cell toward granulocyte. Thus, it is strongly suggested that the members of PKC family each show distinctly different preference for substrate proteins that are located in specific intracellular comportments of the cell types in which they are expressed. Analysis of the activation of T-lymphocyte through PKC activation using phorbol esters or membrane-permeable diacylglycerols indicates a dual action of PKC, modulation of membrane receptor and regulation of gene expression. Short term PKC activation, which may be induced by the breakdown of inositol phospholipid, provides the down-regulation of TCR-CD3 complex on the surface of lymphocyte. On the other hand, sustained PKC activation is necessary to enhance the expression of IL-2 receptor eventually leading to cell proliferation.There appear to be several additional routes, other than the hydrolysis of inositol phospholipid, to provide the diacylglycerol that is needed for prolonged enzyme activation. This novel mechanisms leading to PKC activation as well as functional specificities of PKC subspecies remain to be explored to elucidate roles of PKC in the regulation of gene expression and growth control.