Phosphorylation of the EGF receptor from A431 epidermoid carcinoma cells by three distinct types of protein kinase C.

Three distinct types of protein kinase C obtained from rat brain cytosol phosphorylated the EGF receptor of A431 epidermoid carcinoma cells at different rates. This receptor was phosphorylated most rapidly by type III protein kinase C, but slowly by type I enzyme. Type II enzyme showed intermediate activity. Chromatographic analysis indicated that A431 cells possessed only one of the three types found in rat brain, which apparently corresponded to type III enzyme. This type of protein kinase C, that is encoded by the alpha-sequence or a closely related sequence, appeared to be expressed commonly in many tissues and organs. The result implies that type III enzyme may play roles in growth promotion.