The Cyclic Adenosine Monophosphate-dependent Protein Kinase (PKA) Is Required for the Sustained Activation of Mitogen-activated Kinases and Gene Expression by Nerve Growth Factor

Induction of neuronal differentiation of the rat pheochromocytoma cell line, PC12 cells, by nerve growth factor (NGF) requires activation of the m itogen- a ctivated p rotein (MAP) kinase or e xtracellular signal- r egulated k inase (ERK). cAMP-dependent protein kinase (protein kinase A (PKA)) also can induce differentiation of these cells. Like NGF, the ability of PKA to differentiate PC12 cells is associated with a sustained activation of ERKs. Here we show that maximal sustained activation of ERK1 by NGF requires PKA. Inhibitors of PKA partially blocked activation of ERK1 by NGF but had no effect on activation of ERK1 by EGF. Inhibition of PKA also reduced the ability of NGF and cAMP, but not EGF, to activate the transcription factor Elk-1, reduced the induction of both immediate early and late genes after NGF treatment, and blocked the nuclear translocation of ERK1 induced by NGF. We propose that PKA is an important contributor to the activation of ERK1 by NGF and is required for maximal induction of gene expression by NGF.