ROLE OF PROTEIN-KINASE-C IN MEDIATING NGF EFFECT ON NEUROPEPTIDE-Y EXPRESSION IN PC12 CELLS

Neuropeptide Y (NPY) is a 36 amino acid peptide present in the central and peripheral nervous systems. Treatment with Nerve Growth Factor (N GF) induces an increase in NPY mRNA in PC12 cells, a rat pheochromocyt oma cell line extensively used as a model of neuronal differentiation. Stimulators of both cAMP and calcium-phospholipid dependent protein k inases (PKA and PKC respectively) increase NPY mRNA levels in a simila r way to NGF. Nevertheless, H-89, a specific inhibitor of PKA failed t o block NGF stimulated NPY mRNA accumulation. Furthermore, direct meas urement of PKA activity in cell extracts showed no increase following NGF, in contrast to forskolin. H7, an inhibitor of both PKC and PKA sy stems completely abolished the NGF induced increase in NPY mRNA, sugge sting that PKC is necessary for NGF induction of the NPY gene. NGF als o increased PKC activity in cell extracts in a similar way to phorbol myristate acetate (PMA). Use of a reporter function, chloramphenicol a cetyl transferase, controlled by 700 base pairs of the 5' flanking reg ion of the NPY gene demonstrated that NGF and phorbol ester stimulated transcription of the NPY gene. This stimulation could be blocked by p re-incubating PC12 cells with calphostin C, a specific inhibitor of PK C. Our results indicate that NGF induces NPY gene expression via activ ation of PKC system. Although an increase in adenylate cyclase activit y affects the expression of the NPY gene, activation of PKA appears no t to be involved in mediating the NGF effects.