NERVE GROWTH-FACTOR ACTIVATES CALCIUM-INSENSITIVE PROTEIN-KINASE C-EPSILON IN PC-12 RAT PHEOCHROMOCYTOMA CELLS

Protein kinase C (PKC) family members were examined in PC-12 rat pheoc hromocytoma cells to evaluate their role in the action of nerve growth factor (NGF). Immunoblot analysis of whole cell lysates using antibod ies against various PKC isoforms revealed that PC-12 cells contained P KC-alpha, -delta, -epsilon and zeta. Assay of the protein kinase activ ity in these different anti-PKC immunoprecipitates demonstrated that N GF stimulated the kinase activity of PKC-epsilon, but not PKC-alpha, - delta and -zeta. Both histone phosphorylation and autophosphorylation of PKC-epsilon were increased by treatment of PC-12 cells with NGF. Th is increased phosphorylation observed in vitro is rapid, occurring max imally at 2.5 min and declining thereafter. Moreover, this effect of N GF is dose-dependent over physiological concentrations of the growth f actor. Although the mechanistic basis for this specificity in PKC acti vation is not clear, NGF acutely stimulated the production of diacylgl ycerol without causing corresponding changes in intracellular Ca2+ con centrations. These results suggest that NGF may selectively stimulate the Ca2+-insensitive epsilon isoform of PKC by a phosphatidylinositol- independent mechanism.