p21ras signaling is necessary but not sufficient to mediate neurotrophin induction of calcium channels in PC12 cells.

Nerve growth factor and basic fibroblast growth factor bind to and activate receptor tyrosine kinases, causing sequential signaling via the p21ras/extracellular signal-regulated kinase pathway. The necessity and sufficiency of this signaling pathway in transducing neuronal differentiation have been tested in the PC12 cell model. Although necessary for morphological changes, the sufficiency of p21ras-mediated signaling in these events has come into question. We report that growth factor induction of voltage-gated calcium channels, a hallmark of physiological differentiation, also requires p21ras-mediated signaling, but cannot be driven by p21ras activation alone. Thus, constitutive expression of the dominant negative N17ras mutant blocks growth factor-induced increases in Omega-conotoxin GVIA-sensitive, nimodipine-sensitive, and Omega-conotoxin GVIA/nimodipine-resistant calcium currents, but it does not block sodium current induction. However, manipulations that produce sustained activation of the p21ras signaling pathway and the neurite extension characteristic of morphological differentiation fail to increase calcium channel current densities. These results indicate the existence of distinct signaling requirements for morphological and physiological differentiation and further emphasize the importance of p21ras-independent signaling pathways in growth factor-mediated neuronal development.