AN ACTIVATED MUTANT OF THE ALPHA-SUBUNIT OF G(0) INCREASES NEURITE OUTGROWTH VIA PROTEIN-KINASE-C

The GTP-binding protein, G(0), is present at very high concentration in the neuronal growth cone membrane [42]. The expression of activated mutants of the a subunit of G(0) increases neurite outgrowth [40]. To determine the intracellular mechanism for this outgrowth, we have examined activated alpha(0)-dependent outgrowth in the presence of agents which modulate different signal transduction cascades. Activation of protein kinase C with phorbol esters or with diacylglycerol prevents the alpha(0)-dependent increase in neurite extension. Inhibition of protein kinase C with staurosporine, with H7, or with long-term, high dose phorbol ester treatment resulted in greater neurite elongation, and no further increase after activated alpha(0) transfection. The protein phosphatase inhibitor, okadaic acid, also blocked the effect of activated alpha(0). In contrast, tyrosine kinase inhibitors and agents which alter cAMP levels did not alter activated alpha(0)-dependent neurite extension. We tested a number of compounds which alter intracellular calcium levels. TMB-8 and thapsigargin prevented an increase in outgrowth by activated alpha(0), but diltiazem, Bay K8644 and dantrolene had no effect on activated alpha(0)-dependent outgrowth. These studies suggest that activated alpha(0) increases neurite outgrowth by inhibiting protein kinase C and by modulating intracellular calcium release.