Agonist-directed interactions with specific beta-arrestins determine mu-opioid receptor trafficking, ubiquitination, and dephosphorylation

Academic Article
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publication date

  • September 2011

abstract

  • Morphine and other opiates mediate their effects through activation of the ?-opioid receptor (MOR), and regulation of the MOR has been shown to critically affect receptor responsiveness. Activation of the MOR results in receptor phosphorylation, ?-arrestin recruitment, and internalization. This classical regulatory process can differ, depending on the ligand occupying the receptor. There are two forms of ?-arrestin, ?-arrestin1 and ?-arrestin2 (also known as arrestin2 and arrestin3, respectively); however, most studies have focused on the consequences of recruiting ?-arrestin2 specifically. In this study, we examine the different contributions of ?-arrestin1- and ?-arrestin2-mediated regulation of the MOR by comparing MOR agonists in cells that lack expression of individual or both ?-arrestins. Here we show that morphine only recruits ?-arrestin2, whereas the MOR-selective enkephalin [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO), recruits either ?-arrestin. We show that ?-arrestins are required for receptor internalization and that only ?-arrestin2 can rescue morphine-induced MOR internalization, whereas either ?-arrestin can rescue DAMGO-induced MOR internalization. DAMGO activation of the receptor promotes MOR ubiquitination over time. Interestingly, ?-arrestin1 proves to be critical for MOR ubiquitination as modification does not occur in the absence of ?-arrestin1 nor when morphine occupies the receptor. Moreover, the selective interactions between the MOR and ?-arrestin1 facilitate receptor dephosphorylation, which may play a role in the resensitization of the MOR and thereby contribute to overall development of opioid tolerance.
  • 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.