Cannabinoid receptor-induced neurite outgrowth is mediated by Rap1 activation through Gαo/i-triggered proteasomal degradation of Rap1GAPII

The G alpha(o/i)-coupled CB1 cannabionoid receptor induces neurite outgrowth in Neuro-2A cells. The mechanisms of signaling through G alpha(o/i) to induce neurite outgrowth were studied. The expression of G alpha(o/i) reduces the stability of its direct interactor protein, Rap1GAPII, by targeting it for ubiquitination and proteasomal degradation. This results in the activation of Rap1. G alpha(o/i)-induced activation of endogenous Rap1 in Neuro-2A cells is blocked by the proteasomal inhibitor lactacystin. G alpha(o/i) stimulates neurite outgrowth that is blocked by the expression of dominant negative Rap1. Expression of Rap1GAPII also blocks the G alpha(o/i)-induced neurite outgrowth and treatment with proteasomal inhibitors potentiates this inhibition. The endogenous G alpha(o/i)-coupled cannabinoid ( CB1) receptor in Neuro-2A cells stimulates the degradation of Rap1GAPII; activation of Rap1 and treatment with pertussis toxin or lactacystin blocks these effects. The CB1 receptor-stimulated neurite outgrowth is blocked by treatment with pertussis toxin, small interfering RNA for Rap, lactacystin, and expression of Rap1GAPII. Thus, the G alpha(o/i)-coupled cannabinoid receptor, by regulating the proteasomal degradation of Rap1GAPII, activates Rap1 to induce neurite outgrowth.