The HECT ubiquitin E3 ligase Smurf2 degrades μ-opioid receptor 1 in the ubiquitin-proteasome system in lung epithelial cells.

Opioids are widely used for relieving clinical acute or chronic pain. The biological effects of opioids are through activating the μ-opioid receptors 1 (MOR1). Most studies have focused on the consequences of agonist-induced MOR1 phosphorylation, ubiquitination, and internalization. Agonist-mediated MOR1 degradation, which is crucial for receptor stability and responsiveness, has not been well studied. The HECT ubiquitin E3 ligase Smurf2 has been shown to regulate MOR1 ubiquitination and internalization, however, its role in MOR1 degradation has not been studied. Here, we demonstrate that Smurf2 mediates [D-Ala2 ,N-MePhe4 ,Gly5 -ol] encephalin (DAMGO, an agonist of MOR1)-induced MOR1 ubiquitination and degradation. DAMGO decreased MOR1 levels in the ubiquitin-proteasome system. MOR1 was modified by a lys48-linked polyubiquitin chain. Overexpression of Smurf2 induced MOR1 ubiquitination and accelerated DAMGO-induced MOR1 degradation, while down-regulation of Smurf2 attenuated MOR1 degradation. Further, DAMGO increased lung epithelial cells migration and proliferation, the effect was attenuated by over-expressed Smurf2. Collectively, these data unveil that Smurf2 negatively regulates MOR1 activity by reducing its stability. We also demonstrate an unrevealed biological function of MOR1 in lung epithelial cells. DAMGO/MOR1 promotes cell migration and proliferation in lung epithelial cells, suggesting a potential effect of DAMGO in lung repair and remodeling after lung injury.