Rac and Cdc42-dependent regulation of c-Jun N-terminal kinases by the δ-opioid receptor

Heptahelical opioid receptors utilize G_i proteins to regulate a multitude of effectors including the classical adenylyl cyclases and the more recently discovered mitogen-activated protein kinases (MAPKs). The c-Jun NH₂-terminal kinases (JNKs) belong to one of three subgroups of MAPKs. In NG108-15 neuroblastoma x glioma hybrid cells that endogenously express δ-opioid receptors, δ-agonist dose-dependently stimulated JNK activity in a pertussis toxin-sensitive manner. By using COS-7 cells transiently transfected with the cDNAs of δ-opioid receptor and hemagglutinin (HA)-tagged JNK, we delineated the signaling components involved in this pathway. Sequestration of Gβγ subunits by transducin suppressed the opioid-induced JNK activity. The possible involvement of the small GTPases was also examined. Expression of dominant negative mutants of Rac and Cdc42 blocked the opioid-induced JNK activation, and a partial inhibition was observed in the presence of the dominant negative mutant of Ras. In contrast, the dominant negative mutant of Rho did not affect the opioid-induced JNK activation. In addition, the receptor-mediated JNK activation was dependent on Src family tyrosine kinases, but independent of phosphatidylinositol-3 kinase and EGF receptor tyrosine kinases. Collectively, these results demonstrate functional regulation of JNK by the δ-opioid receptor, and this pathway requires Gβγ, Src kinases and the small GTPases Rac and Cdc42.