Epidermal growth factor and cyclic AMP stimulation of distinct protein kinase activities in Leydig cell tumor membranes

Abstract

Epidermal growth factor (EGF) and cyclic AMP were found to stimulate distinct protein kinase activities in plasma membranes prepared from the M5480P murine Leydig cell tumor. EGF stimulated the phosphorylation of two protein bands with apparent molecular weights of 60,000 and 180,000, while cyclic AMP stimulated the phosphorylation of a minor component of molecular weight 220,000. The two types of kinases could also be distinguished on the basis of differential susceptibility to conditions of membrane preparation. These results suggest that EGF stimulates a cyclic AMP-independent protein kinase in murine Leydig cell tumors at the level of the plasma membrane.