Oxygen-Regulated β 2 -Adrenergic Receptor Hydroxylation by EGLN3 and Ubiquitylation by pVHL

Abstract

Agonist-induced ubiquitylation and degradation of heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors (GPCRs) play an essential role in surface receptor homeostasis, thereby tuning many physiological processes. Although β-arrestin and affiliated E3 ligases mediate agonist-stimulated lysosomal degradation of the β₂-adrenergic receptor (β₂AR), a prototypic GPCR, the molecular cues that mark receptors for ubiquitylation and the regulation of receptor degradation by the proteasome remain poorly understood. We show that the von Hippel–Lindau tumor suppressor protein (pVHL)–E3 ligase complex, known for its regulation of hypoxia-inducible factor (HIF) proteins, interacts with and ubiquitylates the β₂AR, thereby decreasing receptor abundance. We further show that the interaction of pVHL with β₂AR is dependent on proline hydroxylation (proline-382 and -395) and that the dioxygenase EGLN3 interacts directly with the β₂AR to serve as an endogenous β₂AR prolyl hydroxylase. Under hypoxic conditions, receptor hydroxylation and subsequent ubiquitylation decrease dramatically, thus attenuating receptor degradation and down-regulation. Notably, in both cells and tissue, the abundance of endogenous β₂AR is shown to reflect constitutive turnover by EGLN3 and pVHL. Our findings provide insight into GPCR regulation, broaden the functional scope of prolyl hydroxylation, and expand our understanding of the cellular response to hypoxia.