Agonist-Specific Recruitment of Arrestin Isoforms Differentially Modify Delta Opioid Receptor Function

Abstract

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 2ϩ 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.

The role of regulator of G protein signaling 4 in delta-opioid receptor-mediated behaviors

“…Alternatively, these specific DOPr-mediated behaviors may be generated by a G protein-independent, arrestin-mediated signaling mechanism (Violin 2014). Previous studies demonstrated that DOPr activation leads to signaling through G protein-dependent and - independent pathways (Bradbury et al 2009; Charfi et al 2014; Charfi et al 2015); however, there are few reports connecting these distinct signaling mechanisms to specific behavioral outputs (Chiang et al 2016; Pradhan et al 2016). In conclusion, this study demonstrates that RGS4 differentially regulates SNC80-induced behaviors, suggesting that different molecular or cellular signaling pathways or neurocircuitry mediate these behavioral outcomes.…”

Allostatic Mechanisms of Opioid Tolerance Beyond Desensitization and Downregulation

“…Both high- and low-internalizing MOP and DOP agonists induce analgesic tolerance [19–22], albeit via different mechanisms. Moreover, MOP receptor agonists, independently of their internalization efficacy, exhibit comparable symptoms of physical withdrawal [20].…”

The delta opioid receptor tool box

“…Epitope tagging facilitates the detection of the receptor by high-affinity antibodies, and overcomes many of the difficulties posed by using delta opioid receptor specific antibodies (see section below). In addition, delta opioid receptors can also be modified for FRET/BRET- (fluores-cence/bioluminescence resonance energy transfer) based technologies, thus allowing for the direct visualization of specific protein-protein interactions (Audet et al, 2008, 2012; Richard-Lalonde et al, 2013; Charfi et al, 2014; Nagi et al, 2015b; Pradhan et al, 2016). …”

“…Differences in the inter-nalization properties of SNC80 and ARM390 have been found; while SNC80 produces robust receptor intemalization, ARM390 does not induce substantial delta opioid receptor sequestration (Marie et al, 2003a; Pradhan et al, 2009); and this can have an impact on short- and long-term tolerance following chronic use (Pradhan et al, 2009, 2010). Although ARM390 is a low-internalizing agonist, it does appear to recruit arrestin 3; and this interaction is limited to the cell membrane (Pradhan et al, 2016). Importantly, ARM390 is only effective when administered per os by gavage (AstraZeneca, personal communication).…”