ROLE OF PROTEIN-KINASE-C-ALPHA IN NERVE GROWTH FACTOR-INDUCED ARACHIDONIC-ACID RELEASE FROM PC12 CELLS

Nerve growth factor (NGF) increases arachidonic acid (AA) release by P C12 pheochromocytoma cells. To explore the role of protein kinase C (P KC) in this action of NGF, PKC was down-regulated by long-term treatme nt of the cells with phorbol 12-myristate 13-acetate (PMA). Such prolo nged exposure to PMA (1 mu M) resulted in the inhibition of NGF-induce d AA release. Moreover, pretreatment of PC12 cells with the protein ki nase inhibitor staurosporine or with calphostin C, a specific inhibito r of PKC, also blocks the increase of AA release induced by NGF. These data, as well as that PMA alone can induce AA release in PC12 cells, suggest that PKC is necessary for NGF-induced AA release. Immunoblot a nalysis of whole cell lysates by using antibodies against various PKC isoforms revealed that our PC12 cells contained PKCs alpha, delta, eps ilon, and zeta. PMA down-regulation depleted PKCs alpha, delta, and ep silon, and partially depleted zeta. To see which isoform was involved in NGF-induced AA release, an isoform-specific PKC inhibitor was used. GO 6976, a compound that inhibits PKCs alpha and beta specifically, b locked NGF-induced AA release. In addition, thymelea-toxin, a specific activator of PKCs alpha, beta, and gamma, induced AA release from PC1 2 cells in amounts comparable with those seen with NGF. Taken together , these data suggest that PKC a plays a role in NGF-induced AA release .