Nerve growth factor-induced neuronal differentiation after dominant repression of both type I and type II cAMP-dependent protein kinase activities.

Clonal PC12 lines deficient in cAMP-dependent protein kinase (PKA) were made by stably expressing mutant regulatory subunits (RI) of PKA that are deficient in cAMP binding (Correll, L. A., Woodford, T. A., Corbin, J. D., Mellon, P. L., and McKnight, G. S. (1989) J. Biol. Chem. 264, 16672-16678). Expression of the mutant RIs repressed cAMP-dependent activation of both PKAI and PKAII while having no effects on the cAMP binding to either free RI or RII or the level of catalytic subunit protein. These data suggest that RI and RII compete for the same pool of catalytic subunit and that the level of PKAI and PKAII are interdependent. We have used these cell lines to examine the requirement for PKA in mediating the effects of nerve growth factor (NGF) and agents that are thought to act exclusively via cAMP-dependent pathways. While several responses to cAMP were strongly compromised in these lines, NGF-dependent responses were comparable in parental and PKA-deficient cells, including: 1) protein phosphorylation, 2) transcriptional induction of the immediate early gene egr1, 3) expression of the gene for GAP-43, 4) induction of ornithine decarboxylase activity, and 5) formation of neurites. Furthermore, transient expression of the cAMP-dependent protein kinase inhibitor (RSVPKI; Day, R. N., Walder, J. A., and Maurer, R. A. (1989) J. Biol. Chem. 264, 431-436) blocked cAMP, but not NGF, induction of regulatory elements derived from the gene for egr1. These experiments support the idea that NGF can regulate neuronal differentiation by pathways that are independent of cAMP-activatable PKA.