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 pheochromocytoma cells to evaluate their role in the action of nerve growth factor (NGF). Immunoblot analysis of whole cell lysates using antibodies against various PKC isoforms revealed that PC-12 cells contained PKC-alpha, -delta, -epsilon and zeta. Assay of the protein kinase activity in these different anti-PKC immunoprecipitates demonstrated that NGF 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. This increased phosphorylation observed in vitro is rapid, occurring maximally at 2.5 min and declining thereafter. Moreover, this effect of NGF is dose-dependent over physiological concentrations of the growth factor. Although the mechanistic basis for this specificity in PKC activation is not clear, NGF acutely stimulated the production of diacylglycerol without causing corresponding changes in intracellular Ca2+ concentrations. These results suggest that NGF may selectively stimulate the Ca2+-insensitive epsilon isoform of PKC by a phosphatidylinositol-independent mechanism.