ABIN-1 negatively Regulates μ-opioid Receptor Function

The μ-opioid receptor (MOR) is a Gi/o protein-coupled receptor that mediates analgesic, euphoric, and reward effects. Using a bacterial two-hybrid screen, we reported that the carboxyl tail of the rat MOR associates with A20-binding inhibitor of nuclear factor (NF)-κB (ABIN-1) (Zhou et al., 2015). This interaction was confirmed by direct protein - protein binding and co-immunoprecipitation of MOR and ABIN-1 proteins in cell lysates. Saturation binding studies showed that ABIN-1 had no effect on MOR binding. However, the interaction of ABIN-1 and MOR inhibited the activation of G-proteins induced by DAMGO ([D-Ala2,N-Me-Phe4,Gly5-ol]-Enkephalin). MOR phosphorylation, ubiquitination and internalization induced by DAMGO were decreased in Chinese hamster ovary cells that co-expressed MOR and ABIN-1. The suppression of forskolin-stimulated adenylyl cyclase by DAMGO was also inhibited by the interaction of ABIN-1 with MOR. In addition, ERK activation was also negatively regulated by overexpression of ABIN-1. These data suggest that ABIN-1 is a negative coregulator of MOR activation, phosphorylation, and internalization in vitro. ABIN-1 also inhibited morphine-induced hyper-locomotion in zebrafish larvae (AB strain). By utilization of an antisense morpholino oligonucleotide (MO) gene knockdown technology, the ABIN-1 MO-injected zebrafish larvae showed a significant increase (approximately 60%) in distance moved compared with control MO-injected larvae after acute morphine treatment (P<0.01). Taken together, ABIN-1 negatively regulates MOR function in vitro and in vivo.