Opioid Modulation of Extracellular Signal‐Regulated Protein Kinase Activity Is Ras‐Dependent and Involves G_βγ Subunits

Abstract

Although it is well-established that G protein-coupled receptor signaling systems can network with those of tyrosine kinase receptors by several mechanisms, the point(s) of convergence of the two pathways remains largely undelineated, particularly for opioids. Here we demonstrate that opioid agonists modulate the activity of the extracellular signal-regulated protein kinase (ERK) in African green monkey kidney COS-7 cells transiently cotransfected with mu-, delta-, or kappa-opioid receptors and ERK1- or ERK2-containing plasmids. Recombinant proteins in transfected cells were characterized by binding assay or immunoblotting. On treatment with corresponding mu- ([D-Ala2,Me-Phe4,Gly-ol5]enkephalin)-, delta- ([D-Pen2,D-Pen5]enkephalin)-, or kappa- (U69593)-selective opioid agonists, a dose-dependent, rapid stimulation of ERK1 and ERK2 activity was observed. This activation was inhibited by specific antagonists, suggesting the involvement of opioid receptors. Pretreatment of cells with pertussis toxin abolished ERK1 and ERK2 activation by agonists. Cotransfection of cells with dominant negative mutant N17-Ras or with a betagamma scavenger, CD8- beta-adrenergic receptor kinase-C, suppressed opioid stimulation of ERK1 and ERK2. When epidermal growth factor was used to activate ERK1, chronic (>2-h) opioid agonist treatment resulted in attenuation of the stimulation by the growth factor. This inhibition was blocked by the corresponding antagonists and CD8- beta-adrenergic receptor kinase-C cotransfection. These results suggest a mechanism involving Ras and betagamma subunits of Gi/o proteins in opioid agonist activation of ERK1 and ERK2, as well as opioid modulation of epidermal growth factor-induced ERK activity.

Activation of the kappa opioid receptor in the dorsal raphe nucleus mediates the aversive effects of stress and reinstates drug seeking

“…3B). These results confirm that the G␣i functionality of KOR was intact (25), in concordance with reports showing that KOR-mediated ERK activation does not require GRK3 or ␤-arrestin expression (24,26).…”

Mu Opioid Receptor Activation of ERK1/2 Is GRK3 and Arrestin Dependent in Striatal Neurons

“…However, two recent studies provided evidence that desensitization and endocytosis of MOR occurred with morphine treatment (17,18). Activation of ERK1/2 by the mu opioid agonist DAMGO has been demonstrated in MOR-transfected cells and in neurons from morphine-treated mice (8,9). However, the activation of ERK1/2 within the striatum and possible differences in the phosphorylation of ERK1/2 induced by MOR agonists has not been demonstrated.…”

“…Following agonist activation of MOR, the receptor becomes phosphorylated by G-protein receptor kinase (GRK), which initiates an arrestin-dependent desensitization process that involves clathrin-mediated endocytosis (7). The opioid activation of ERK1/2 by MOR agonist (D-Ala 2 ,Me-Phe 4 ,Gly-ol5) (DAMGO) was demonstrated in MOR-transfected cells (8), and ERK1/2 was activated in the pons and medulla of morphine-treated mice (9). However, the mechanism of ERK1/2 activation by opioids is not clear.…”

Ligand stabilization of CXCR4/δ‐opioid receptor heterodimers reveals a mechanism for immune response regulation

“…Synthetic ligands such as [D-Pen2, D-Pen5]enkephalin (DPDPE), which have greater affinity and selectivity for the DOR, were thus generated and are used in pharmacological studies [25]. After ligand binding, DOR activates Ga i , which induces adenylate cyclase inhibition, inhibits voltage-sensitive Ca 2+ channels, activates PKC, promotes Ca 2+ release from internal stores, recruits membrane proteins such as Ras-G protein regulatory factor, and activates the ERK/MAPK transduction cascade [26][27][28][29].We show that simultaneous stimulation of CXCR4-and DOR-expressing cells by their respective ligands, CXCL12 and DPDPE, does not trigger function. We excluded differences in cell surface receptor expression and receptor internalization, as well as heterologous desensitization processes, as the cause of this effect.…”