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Protein kinase C and cAMP‐dependent protein kinase regulate the neuronal differentiation of immortalized raphe neurons

These studies examined the extent to which protein kinase C (PKC) and cAMP‐dependent protein kinase (PKA) regulate the neuronal differentiation of the raphe‐derived neuronal cell line, RN33B. A differentiation‐specific 2.25‐fold increase in soluble PKA activity was observed. Neither membrane‐associated‐PKA, ‐PKC, or soluble PKC activities changed concomitant with differentiation. The PKC activity was derived from PKC α, γ, ϵ, and θ isoenzymes. Activation of PKC inhibited the immunocytochemical expression of low and medium molecular weight neurofilament proteins, an effect due at least in part to decreased steady‐state levels of protein. PKC activation also decreased glutamate immunoreactivity and increased cell number, protein synthesis, and bromodeoxyuridine uptake by 2.4‐fold, 25%, and 32%, respectively. Coupled with the decrease in mature neuronal antigen expression, these data suggest that PKC activation inhibits neuronal differentiation by inducing proliferation. Inhibition of PKC markedly upregulated glutamate immunoreactivity. PKA activation potentiated the glutamatergic phenotype of RN33B cells, but inhibition of PKA was without effect on the expression of all neuronal antigens examined. Thus, both PKC and PKA regulate the differentiation of RN33B cells, although neither is absolutely necessary for expression of the differentiated neuronal phenotype. These results suggest the existence of parallel pathways regulating raphe neuronal differentiation. J. Neurosci. Res. 56:177–188, 1999.  © 1999 Wiley‐Liss, Inc.