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Ligand-specific recruitment of arrestins facilitates functional selectivity of G-protein-coupled receptor signaling. Here, we describe agonist-selective recruitment of different arrestin isoforms to the delta opioid receptor in mice. A high-internalizing delta opioid receptor agonist (SNC80) preferentially recruited arrestin 2 and, in arrestin 2 knock-outs (KOs), we observed a significant increase in the potency of SNC80 to inhibit mechanical hyperalgesia and decreased acute tolerance. In contrast, the low-internalizing delta agonists (ARM390, JNJ20788560) preferentially recruited arrestin 3 with unaltered behavioral effects in arrestin 2 KOs. Surprisingly, arrestin 3 KO revealed an acute tolerance to these low-internalizing agonists, an effect never observed in wild-type animals. Furthermore, we examined delta opioid receptor-Ca(2+)channel coupling in dorsal root ganglia desensitized by ARM390 and the rate of resensitization was correspondingly decreased in arrestin 3 KOs. Live-cell imaging in HEK293 cells revealed that delta opioid receptors are in pre-engaged complexes with arrestin 3 at the cell membrane and that ARM390 strengthens this membrane interaction. The disruption of these complexes in arrestin 3 KOs likely accounts for the altered responses to low-internalizing agonists. Together, our results show agonist-selective recruitment of arrestin isoforms and reveal a novel endogenous role of arrestin 3 as a facilitator of resensitization and an inhibitor of tolerance mechanisms., Significance Statement: Agonists that bind to the same receptor can produce highly distinct signaling events and arrestins are a major mediator of this ligand bias. Here, we demonstrate that delta opioid receptor agonists differentially recruit arrestin isoforms. We found that the high-internalizing agonist SNC80 preferentially recruits arrestin 2 and knock-out (KO) of this protein results in increased efficacy of SNC80. In contrast, low-internalizing agonists (ARM390 and JNJ20788560) preferentially recruit arrestin 3 and, surprisingly, KO of arrestin 3 produces acute tolerance and impaired receptor resensitization to these agonists. Arrestin 3 is in pre-engaged complexes with the delta opioid receptor at the cell membrane and low-internalizing agonists promote this interaction. This study reveals a novel role for arrestin 3 as a facilitator of receptor resensitization., (Copyright © 2016 the authors 0270-6474/16/363541-11$15.00/0.)

Formation of receptor complexes between micro-opioid and alpha2A-adrenergic receptors has been demonstrated in transfected cells. The functional significance and underlying mechanisms of such receptor interactions remain to be determined in neuronal systems. We examined functional interactions between endogenous micro and alpha2A receptors in mouse dorsal root ganglion neurons. Acute application of the micro agonist [D-Ala2,N-MePhe4, Gly-ol5]enkephalin (DAMGO) or the alpha2 agonist clonidine inhibited voltage-gated Ca2+ currents in these neurons. Prolonged treatment with either DAMGO or clonidine induced a mutual cross-desensitization between micro and alpha2A receptor-mediated current inhibition. The cross-desensitization was closely associated with simultaneous internalization of micro and alpha2A receptors. Morphine, a mu agonist triggering little mu receptor endocytosis, induced neither cross-desensitization nor internalization of alpha2A receptors. Furthermore, inhibition of p38 MAPK prevented the cross-desensitization as well as cointernalization of micro and alpha2A receptors. Changes in receptor trafficking profiles suggested that p38 MAPK activity was required for initiating micro receptor internalization and maintaining possible micro-alpha2A association during their cointernalization. Finally, the micro-alpha2A cross-desensitization was absent in dorsal root ganglion neurons lacking beta-arrestin 2. These findings demonstrated p38 MAPK- and beta-arrestin 2-dependent cross-regulation between neuronal micro and alpha2A receptors. By promoting receptor cross-desensitization and cointernalization, such functional interactions may serve as negative feedback mechanisms triggered by prolonged agonist exposure to modulate the signaling of functionally related G protein-coupled receptors.