Oligomerization of opioid receptors with beta 2-adrenergic receptors: A role in trafficking and mitogen-activated protein kinase activation

Abstract

G-protein-coupled receptors (GPCRs) have recently joined the list of cell surface receptors that dimerize. Dimerization has been shown to alter the ligand-binding, signaling, and trafficking properties of these receptors. Recent studies have shown that GPCRs heterodimerize with closely related members, resulting in the modulation of their function. In this study, we have attempted to determine whether members of GPCR superfamilies that couple to different families of G-proteins can associate and form oligomers. We chose the ␤2 adrenergic receptor that couples to stimulatory G-proteins and ␦ & opioid receptors that couple to inhibitory G-proteins. ␤2 and ␦ receptors undergo robust agonist-mediated endocytosis, whereas receptors do not. We find that when coexpressed, ␤2 receptors can form heteromeric complexes with both ␦ and receptors. This heterooligomerization does not significantly alter the ligand binding or coupling properties of the receptors. However, it affects the trafficking properties of the receptors. For example, we find that ␦ receptors, when coexpressed with ␤2 receptors, undergo isoproterenol-mediated endocytosis. Conversely, ␤2 receptors in these cells undergo etorphine-mediated endocytosis. However, ␤2 receptors, when coexpressed with receptors, undergo neither opioid-nor isoproterenol-mediated endocytosis. Moreover, these cells exhibit a substantial decrease in the isoproterenol-induced phosphorylation of mitogen-activated protein kinases. Taken together, these results provide direct evidence of heteromerization of GPCRs that couple to different types of G-proteins, which results in the modulation of receptor trafficking and signal transduction.receptor subtypes ͉ G-protein-coupled receptor ͉ endocytosis ͉ dimers ͉ heterodimerization G -protein-coupled receptors (GPCRs), the largest and most diverse family of transmembrane receptors, are involved in the transduction of signals in response to a wide variety of stimuli. Until recently they were thought to function as monomers (1). However, a growing number of biochemical, biophysical, and functional studies suggest that GPCRs form functional, SDS-stable dimers (2). Heteromeric assembly of the nonfunctional ␥-aminobutyric acid receptor B R1a and ␥-aminobutyric acid receptor B R2 is necessary for ␥-aminobutyric acid receptor-mediated signaling in cultured cells and in rat superior ganglion neurons (3-8). In contrast, fully functional opioid receptors associate with each other, resulting in the generation of heterodimeric receptors with unique properties (9-11). Heterodimerization of fully functional somatostatin receptor 5 with somatostatin receptor 1 has also been found to alter the pharmacology and signaling of both receptors (12). Although there is increasing evidence for receptor dimerization between members of the same subfamily of GPCRs, not much is known about dimerization between members of different subfamilies.␤ 2 -Adrenergic receptors are prototypical receptors of the rhodopsin family that undergo rapid and robust agonistmediated endocyt...

A1R–A2AR heteromers coupled to Gs and Gi/0 proteins modulate GABA transport into astrocytes

“…The previous blockade of A 1 R or A 2A R prevents the internalization mediated by both A 1 R and A 2A R agonists, suggesting that internalization of heteromer in response to agonists is a consequence of heteromer overactivity. Confocal imaging of transfected HEK-293T cells confirmed that exposure to an A 1 R agonist led to internalization of not only A 1 R but also A 2A R and, conversely, exposure to an A 2A R agonist led to internalization of not only A 2A R but also A 1 R. Thus, in this aspect, A 1 -A 2A R heteromers behaved as the β2-adrenoceptor-δ-opioid [31] and μ-opioid-tachykinin NK1 [32] receptor heteromers but different from other heteromers whose protomers do not co-internalize [see 33]. It is technically difficult to know to what extent adenosine receptor internalization affects GABA transport in astrocytes.…”

G-Protein–Coupled Receptor Mas Is a Physiological Antagonist of the Angiotensin II Type 1 Receptor

“…In contrast to the effects of Mas, Ang II mobilization of [Ca 2ϩ ] i was unaffected by the presence of the G q/11 -coupled sphingosine-1-phosphate [S1P 3 ], urotensin II, or muscarinic M 3 acetylcholine receptors (Figure 2 23 The differential effects on AT 1 -mediated Ang II binding capacity on the one hand and signaling on the other by the coexpression of Mas suggested that the AT 1 receptor was physically altered by Mas such that the enhanced cell-surface expression of the AT 1 receptor was offset by reduced receptor functionality, most likely due to a conformational constraint on AT 1 signaling within the hetero-oligomer. The potential for such direct interactions between Mas and the AT 1 receptor was thus investigated with various forms of BRET.…”

Dimerization of G protein-coupled receptors: New avenues for somatostatin receptor signalling, control and functioning

“…Indeed, different receptors coexpressed in the same cell present certain promiscuity to heterodimerize (Jordan et al, 2001;McVey et al, 2001;Pfeiffer et al, 2002;Salim et al, 2002).…”