A BRYOSTATIN-SENSITIVE PROTEIN-KINASE-C REQUIRED FOR NERVE GROWTH-FACTOR ACTIVITY

Nerve growth factor (NGF) stimulates rat pheochromocytoma cells (PC12) to differentiate into a neuronal-like cell that exhibits neurite exte nsions. The role of protein kinase C in signal transduction has been e xamined in PC12 cells treated with phorbol 12-myristate 13-acetate (PM A) and bryostatin, a macrocyclic lactone that activates protein kinase C at both the nuclear and the plasma membranes [Hocevar, B.A., & Fiel ds, A.P.(1991)J. Biol. Chem. 266,28-331. In contrast to PMA down-regul ation [Reinhold, D. S., & Neet, K. E. (1989) J. Biol. Chem. 264, 3538- 35441, chronic (24 h) treatment with bryostatin blocked the formation of neurites in response to NGF or basic fibroblast-derived growth fact or stimulation, but, like PMA, bryostatin did not block the induction of c-fos or c-jun protooncogenes by NGF. Chronic bryostatin treatment down-regulated protein kinase C activity in the cytosolic, membrane, a nd nuclear fractions. Acute (60 min) bryostatin or NGF treatment activ ated cytosolic and nuclear protein kinase C activity, suggesting possi ble translocation to the nucleus. Bryostatin did not induce neurite ou tgrowth, either alone or in combination with PMA. Thus, the bryostatin -sensitive protein kinase C is distinct from PMA- or K252a-sensitive k inases previously described. The bryostatin-sensitive protein kinase C is necessary, but not sufficient, for neurite outgrowth and acts in t he nucleus in a manner independent of c-fos and c-jun transcription.