Plasma membrane localization of the μ-opioid receptor controls spatiotemporal signaling

Abstract

Differential regulation of the μ-opioid receptor (MOR), a G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptor, contributes to the clinically limiting effects of opioid analgesics, such as morphine. We used biophysical approaches to quantify spatiotemporal MOR signaling in response to different ligands. In human embryonic kidney (HEK) 293 cells overexpressing MOR, morphine caused a Gβγ-dependent increase in plasma membrane-localized protein kinase C (PKC) activity, which resulted in a restricted distribution of MOR within the plasma membrane and induced sustained cytosolic extracellular signal-regulated kinase (ERK) signaling. In contrast, the synthetic opioid peptide DAMGO ([d-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin) enabled receptor redistribution within the plasma membrane, resulting in transient increases in cytosolic and nuclear ERK activity, and, subsequently, receptor internalization. When Gβγ subunits or PKCα activity was inhibited or when the carboxyl-terminal phosphorylation sites of MOR were mutated, morphine-activated MOR was released from its restricted plasma membrane localization and stimulated a transient increase in cytosolic and nuclear ERK activity in the absence of receptor internalization. Thus, these data suggest that the ligand-induced redistribution of MOR within the plasma membrane, and not its internalization, controls its spatiotemporal signaling.

Effect of Tamoxifen and Brain-Penetrant Protein Kinase C and c-Jun N-Terminal Kinase Inhibitors on Tolerance to Opioid-Induced Respiratory Depression in Mice

“…The precise mechanism underlying PKC-dependent desensitization of MOPr responsiveness is currently unknown, but PKC has clearly been shown to be activated following addition of morphine to cells and neurons expressing MOPr (Chu et al, 2010;Halls et al, 2016), and PKC activity may also be raised in vivo by concomitant activation of other G protein-coupled receptors that couple through Gq (Bailey et al, 2009a) or N-methyl-D-aspartate receptors to elevate intracellular calcium (Trujillo and Akil, 1995). The results also suggest that our previous finding that ethanol reverses morphine tolerance (Hill et al, 2016) could be mediated by ethanol or its metabolites somehow reversing the PKC-dependent mechanism.…”

Regulation of G protein‐coupled receptor signaling by plasma membrane organization and endocytosis

“…Receptor organization is likely dictated by the biochemical properties of the receptors themselves, lipid composition of the membrane, and the presence of a host of scaffolding proteins, although the mechanisms are still being elucidated. Once receptors bind a ligand, receptors rapidly reorganize to specific domains within the plasma membrane, which could help coordinate spatially restricted signaling . GPCRs are further regulated at the cell surface by agonist‐mediated endocytosis .…”

Impact of Lipid Composition and Receptor Conformation on the Spatio-temporal Organization of μ-Opioid Receptors in a Multi-component Plasma Membrane Model

“…Furthermore, although the exact role of MOR oligomerization in signaling is still under debate, the potential of developing new, more effective therapies in the treatment of pain [31] by selectively targeting MOR heterodimers makes these systems worthy of further investigation. Finally, while there is evidence both for [32] and against [33] the association of MOR with lipid rafts, CHOL has been shown to be important in the spatio-temporal signaling by MOR [34]. In fact, it has been shown to promote homodimerization of MOR [5], agonist binding [35], coupling with G-proteins [5,35], and translocation of β-arrestin [36].…”