Regulation of adenylyl cyclase, ERK1/2, and CREB by G(z) following acute and chronic activation of the delta-opioid receptor

Opioid tolerance and physical dependence in mammals can be rapidly induced by chronic exposure to opioid agonists. Recently, opioid receptors have bee n shown to interact with the pertussis toxin (PTX)-insensitive G(z) (a memb er of the G(i) subfamily), which inhibits adenylyl cyclase and stimulates m itogen-activated protein kinases (MAPKs). Here, we established stable human embryonic kidney 293 cell lines expressing delta-opioid receptors with or without G(z) to examine the role of G(z) in opioid receptor-regulated signa ling systems. Each cell line was acutely or chronically treated with [D-Pen (2),D-Pen(5)]enkephalin (DPDPE), a delta-selective agonist, in the absence or presence of PTX. Subsequently, the activities of adenylyl cyclase, cycli c AMP (cAMP)-dependent response element-binding proteins (CREBs), and MAPKs were measured by determining cAMP accumulation and phosphorylation of CREB s and the extracellular signal-regulated protein kinases (ERKs) 1 and 2. In cells coexpressing G(z), DPDPE inhibited forskolin-stimulated cAMP accumul ation in a PTX-insensitive manner, but G(z) could not replace G(i) to media te adenylyl cyclase supersensitization upon chronic opioid treatment. DPDPE -induced adenylyl cyclase supersensitization was not associated with an inc rease in the phosphorylation of CREBs. Both G(i) and G(z) mediated DPDPE-in duced activation of ERK1/2, but these responses were abolished by chronic o pioid treatment. Collectively, our results show that although G(z) mediated opioid-induced inhibition of adenylyl cyclase and activation of ERK1/2, G( z) alone was insufficient to mediate opioid-induced adenylyl cyclase supers ensitization.