Serine 363 of the δ-opioid receptor is crucial for adopting distinct pathways to activate ERK1/2 in response to stimulation with different ligands

Distinct opioid receptor agonists have been proved to induce differential patterns of ERK activation, but the underlying mechanisms remain unclear. Here, we report that Ser363 in the delta-opioid receptor (delta OR) determines the different abilities of the delta OR agonists DPDPE and TIPP to activate ERK by G-protein-or beta-arrestin-dependent pathways. Although both DPDPE and TIPP activated ERK1/2, they showed different temporal, spatial and desensitization patterns of ERK activation. We show that that DPDPE employed G protein as the primary mediator to activate the ERK cascade in an Src-dependent manner, whereas TIPP mainly adopted a beta-arrestin1/2-mediated pathway. Moreover, we found that DPDPE gained the capacity to adopt the beta-arrestin1/2-mediated pathway upon Ser363 mutation, accompanied by the same pattern of ERK activation as that induced by TIPP. Additionally, we found that TIPP-but not DPDPE-activated ERK could phosphorylate G-protein-coupled receptor kinase-2 and beta-arrestin1. However, such functional differences of ERK disappeared with the mutation of Ser363. Therefore, the present study reveals a crucial role for Ser363 in agonist-specific regulation of ERK activation patterns and functions.