A ROLE FOR ZETA-PROTEIN-KINASE-C IN NERVE GROWTH FACTOR-INDUCED DIFFERENTIATION OF PC12 CELLS

Studies were undertaken to compare the signal-induced redistribution o f conventional protein kinase C (cPKC) to nonclassical protein kinase C (nPKC) family members in response to phorbol 12-myristate 13-acetate (PMA) or nerve growth factor (NGF) treatment of PC12 cells. cPKC-alph a and -beta and nPKC-delta and -epsilon were predominantly cytoplasmic , whereas PKC-zeta displayed approximately equal distribution between the cytoplasm and membrane fraction. Treatment of PC12 cells with PMA induced rapid translocation of both c- and nPKC isoforms to the membra ne fraction, although the kinetics varied between isoforms with epsilo n being most sensitive, followed by delta > zeta > alpha. Both PKC-eps ilon and delta translocated in the presence of minute concentrations o f PMA, whereas cPKC was less sensitive, and PKC-zeta was least sensiti ve. NGF treatment, on the other hand, induced translocation of cPKCs a nd delta and epsilon nPKC, albeit with differential magnitude, whereas PKC-zeta was found predominantly in the cytoplasm. Chronic treatment of PC12 cells with PMA (1 mu M) caused a rapid disappearance of alpha, beta, delta,and epsilon PKC isoforms, whereas the expression of PKC-z eta was unaltered over 4 days. NGF induced an increase in cytoplasmic PKC-zeta in control, or PMA down-regulated PC12 cells. Moreover, the i ncrease in cytoplasmic PKC-zeta was blocked by pretreatment with sphin gosine (2.5 mu M). Furthermore, PKC-zeta was activated by NGF in PMA d own-regulated PC12 cells, as determined by the extent of epsilon-pepti de phosphorylation using a permeabilized cell assay. In addition, the zeta-pseudosubstrate peptide inhibited NGF-induced activation of PKC-z eta. Immunocytochemical analysis of NCF differentiated PC12 cells docu mented the presence of PKC-zeta predominantly in the cell body and neu rite branch points. Taken together, these findings demonstrate that PK C-zeta plays a role in NGF signal coupling.