Coupling of cAMP/PKA and MAPK signaling in neuronal cells is dependent on developmental stage

Neurite formation, an essential feature of neuronal development, is believe d to involve participation of the ras-mitogen-activated protein kinase (MAP K) and cAMP-dependent protein kinase A (cAMP/PKA)-mediated signaling pathwa ys. These pathways have been studied extensively in the rat pheochromocytom a cell line PC12, and current hypotheses suggest a single effector mechanis m resulting from the convergence of cAMP/PKA and MAPK signaling. However, b ased on observations using a central neuronal progenitor cell line, AS583-8 , there also exists evidence that the two signaling pathways may act indepe ndently resulting in neurites with differing dynamic features. In the prese nt study, the upstream components of cAMP/PKA signaling were examined in AS 583-8 cells as well as possible interactions with the MAPK pathway. We foun d that activation of PKA is both necessary and sufficient for the elaborati on of rapidly forming processes, typical of the cAMP response. In addition, blockade of the MAPK pathway has no effect on the cAMP response, suggestin g that activation of the cAMP/PKA pathway can stimulate neurite formation i ndependent of the MAPK pathway. In order to evaluate which cell line model, PC12 vs AS583-8, best reflects the signaling features of developing centra l neurons, we examined interactions between cAMP/PKA and MAPK signaling in primary neuronal cultures from several brain regions. In immature cultures (1-day-old), at a point where the initiation of neurite formation is maxima l, no interaction was observed. In more mature cultures (7 days old), where synaptic contacts have been established, we found a weak but reproducible activation of MAPK following stimulation of the cAMP/PKA pathway. These res ults suggest that cAMP/PKA and MAPK signaling act independently at the init iation of neuritogenesis but become coupled during later stages of neuronal development. Therefore, the interaction of the two pathways may be cell st age (younger vs older) specific and may participate in cellular functions t hat take place after initial neurite formation. (C) 2001 Academic Press.