NERVE GROWTH-FACTOR AMPLIFIES CYCLIC-AMP PRODUCTION IN THE HT4 NEURONAL CELL FINE

There has been considerable interest and controversy in the relationsh ip between nerve growth factor (NGF) and the cyclic AMP (cAMP) second messenger system. We have used a novel, neuronal cell line (HT4) to in vestigate the effect of NGF on the adenylyl cyclase signaling system. Treatment of cells with NGF (100 ng/ml, 15 min) amplified cAMP accumul ation (approximate to 75%) in response to activation of adenosine A(2) receptors (5 min) with 5'-N-ethylcarboxamidoadenosine or activation o f adenylyl cyclase directly with forskolin. Basal cAMP accumulation wa s not altered by NGF. This amplification appears to be mediated by act ivation of protein kinase C (PKC) because (1) it was mimicked by activ ators (phorbol esters and a diacylglycerol analogue) of PKC, (2) the e ffects of NGF and phorbol ester on cAMP accumulation were not additive , (3) NGF amplification of cAMP accumulation was abolished by down-reg ulation of PKC, (4) NGF increased cytosolic PKC activity, and (5) inhi bitors of PKC blocked the NGF-induced amplification of cAMP accumulati on. Although NGF-induced amplification of cAMP accumulation was depend ent upon PKC, mechanisms other than the classic activation pathway (i. e., hydrolysis of inositol phospholipids or the production of diacylgl ycerol) appeared to mediate PKC activation by NGF. The tyrosine kinase inhibitor, lavendustin A, blocked NGF-mediated amplification of cAMP accumulation, suggesting a novel interaction between a tyrosine kinase and protein kinase C.