title: The G alpha(o/i)-coupled cannabinoid receptor-mediated neurite outgrowth involves Rap regulation of Src and Stat3.
abstract: The study of the signaling pathways regulating neurite outgrowth in culture is important because of their potential role in neuronal differentiation in vivo. We have previously shown that the G alpha(o/i)-coupled CB1 cannabinoid receptor (CB1R) activates Rap1 to induce neurite outgrowth. G alpha(o/i) also activates the Src-Stat3 pathway. Here, we studied the relationship between the G alpha(o/i)-Rap1 and Src-Stat3 pathways and the role of these signaling pathways in CB1R-mediated neurite outgrowth in Neuro-2A cells. The CB1 agonist HU-210 induced pertussis toxin-sensitive Src and Stat3 phosphorylation. Dominant negative (DN) mutants of Src and Stat3 blocked CB1R-induced neurite outgrowth. Constitutively active Rap 1B and Ral-activated Src and CB1R-induced Src phosphorylation was inhibited by Rap1-DN and Ral-DN, indicating that both Rap1 and Ral mediate downstream signaling from G alpha(o/i) for Src activation. Rap1-activated Ral and Ral-DN blocked Rap-induced Src phosphorylation. G alpha(o)-induced Stat3 activation was blocked by Ral-DN, whereas v-Src-induced Stat3 activation was not inhibited by Ral-DN, indicating that the CB1R, through G alpha(o), mediates the sequential activation of Rap1 to Ral to Src to Stat3 in Neuro-2A cells. Downstream of Src, the CB1R also activated Rac1 and JNK, which enhanced CBR1-mediated Stat3 activation. Rac-DN blocked CB1R-induced activation of JNK. Pharmacological inhibition of JNK blocked Src and CB1R activation of Stat3, indicating that Rac and JNK are also involved in CB1R-mediated neurite outgrowth. Overall, this study demonstrated that G alpha(o/i)-coupled CB1R triggers neurite outgrowth in Neuro-2A through the activation of a signaling network containing two pathways that bifurcate at Src and converge at Stat3.
authors.affiliation: Department of Pharmacology, Mount Sinai School of Medicine, New York, New York 10029, USA.
authors.forename: John Cijiang
authors.initials: JC
authors.lastname: He
authors.forename: Ivone
authors.initials: I
authors.lastname: Gomes
authors.forename: Tracy
authors.initials: T
authors.lastname: Nguyen
authors.forename: Gomathi
authors.initials: G
authors.lastname: Jayaram
authors.forename: Prahlad T
authors.initials: PT
authors.lastname: Ram
authors.forename: Lakshmi A
authors.initials: LA
authors.lastname: Devi
authors.forename: Ravi
authors.initials: R
authors.lastname: Iyengar
mesh_terms: D000818:Animals; D020134:Catalytic Domain; D045744:Cell Line, Tumor; D013759:Dronabinol / Q000031:analogs & derivatives / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic; D049452:Green Fluorescent Proteins / Q000737:chemistry / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D016501:Neurites / Q000502:physiology*; D010766:Phosphorylation; D043884:Receptor, Cannabinoid, CB1 / Q000378:metabolism*; D015398:Signal Transduction; D020827:rap1 GTP-Binding Proteins / Q000502:physiology*; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D043884:Receptor, Cannabinoid, CB1; D049452:Green Fluorescent Proteins; D013759:Dronabinol; D019061:src-Family Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020827:rap1 GTP-Binding Proteins; C062018:HU 211