DEXAMETHASONE ABOLISHES THE ACTIVATION BY NERVE GROWTH-FACTOR OF PROTEIN KINASE-N - EFFECTS OF NERVE GROWTH-FACTOR AND DEXAMETHASONE ON PROTEIN KINASE-N

Protein kinase N (PKN) is a basic 45-47 kDa serine/threonine protein k inase activated by NGF and several other factors in PC12 cells and oth er cell types. It is inhibited in vitro by purine analogs. In this wor k, we further characterize the modulation of PKN activity following ex posure of PC12 cells to dexamethasone or NGF, which respectively direc t these cells towards the chromaffin- or neuron-like phenotype. We sho w here that the two factors elicit opposite effects on the activation of the kinase: dexamethasone inhibits while NGF stimulates the basal l evel of PKN activity. Simultaneous addition to the cells of the factor s causes no variation from basal kinase activity. Addition of dexameth asone not to the cells, but to partially purified PKN during the kinas e assay, causes no modulation of the enzyme.