title: Agonist-directed interactions with specific beta-arrestins determine mu-opioid receptor trafficking, ubiquitination, and dephosphorylation.
abstract: Morphine and other opiates mediate their effects through activation of the μ-opioid receptor (MOR), and regulation of the MOR has been shown to critically affect receptor responsiveness. Activation of the MOR results in receptor phosphorylation, β-arrestin recruitment, and internalization. This classical regulatory process can differ, depending on the ligand occupying the receptor. There are two forms of β-arrestin, β-arrestin1 and β-arrestin2 (also known as arrestin2 and arrestin3, respectively); however, most studies have focused on the consequences of recruiting β-arrestin2 specifically. In this study, we examine the different contributions of β-arrestin1- and β-arrestin2-mediated regulation of the MOR by comparing MOR agonists in cells that lack expression of individual or both β-arrestins. Here we show that morphine only recruits β-arrestin2, whereas the MOR-selective enkephalin [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO), recruits either β-arrestin. We show that β-arrestins are required for receptor internalization and that only β-arrestin2 can rescue morphine-induced MOR internalization, whereas either β-arrestin can rescue DAMGO-induced MOR internalization. DAMGO activation of the receptor promotes MOR ubiquitination over time. Interestingly, β-arrestin1 proves to be critical for MOR ubiquitination as modification does not occur in the absence of β-arrestin1 nor when morphine occupies the receptor. Moreover, the selective interactions between the MOR and β-arrestin1 facilitate receptor dephosphorylation, which may play a role in the resensitization of the MOR and thereby contribute to overall development of opioid tolerance.
authors.affiliation: Department of Molecular Therapeutics, The Scripps Research Institute, Jupiter, Florida 33458, USA.
authors.forename: Chad E
authors.initials: CE
authors.lastname: Groer
authors.forename: Cullen L
authors.initials: CL
authors.lastname: Schmid
authors.forename: Alex M
authors.initials: AM
authors.lastname: Jaeger
authors.forename: Laura M
authors.initials: LM
authors.lastname: Bohn
mesh_terms: D000701:Analgesics, Opioid; D000818:Animals; D019390:Arrestins / Q000819:agonists* / Q000378:metabolism*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D004745:Enkephalins; D051379:Mice; D010766:Phosphorylation; D021381:Protein Transport; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D054875:Ubiquitination; D000071557:beta-Arrestins
chemical_list: D000701:Analgesics, Opioid; D019390:Arrestins; D004745:Enkephalins; C404943:Oprm protein, mouse; D017450:Receptors, Opioid, mu; D000071557:beta-Arrestins; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-