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 kinase activated by NGF and several other factors in PC12 cells and other cell types. It is inhibited in vitro by purine analogs. In this work, we further characterize the modulation of PKN activity following exposure of PC12 cells to dexamethasone or NGF, which respectively direct these cells towards the chromaffin- or neuron-like phenotype. We show here that the two factors elicit opposite effects on the activation of the kinase: dexamethasone inhibits while NGF stimulates the basal level of PKN activity. Simultaneous addition to the cells of the factors causes no variation from basal kinase activity. Addition of dexamethasone not to the cells, but to partially purified PKN during the kinase assay, causes no modulation of the enzyme.