Redox-dependent internalization of the purinergic P2Y₆ receptor limits colitis progression

After ligand stimulation, many G protein–coupled receptors (GPCRs) undergo β-arrestin–dependent desensitization, during which they are internalized and either degraded or recycled to the plasma membrane. Some GPCRs are not subject to this type of desensitization because they lack the residues required to interact with β-arrestins. We identified a mechanism of redox-dependent alternative internalization (REDAI) that promotes the internalization and degradation of the purinergic P2Y₆ receptor (P2Y₆R). Synthetic and natural compounds containing electrophilic isothiocyanate groups covalently modified P2Y₆R at Cys²²⁰, which promoted the ubiquitylation of Lys¹³⁷ and receptor internalization and degradation in various mouse and human cultured cell lines. Endogenous electrophiles also promoted ligand-dependent P2Y₆R internalization and degradation. P2Y₆R is highly abundant in inflammatory cells and promotes the pathogenesis of colitis. Deficiency in P2Y₆R protected mice against experimentally induced colitis, and mice expressing a form of P2Y₆R in which Cys²²⁰ was mutated to nonmodifiable serine were more sensitive to the induction of colitis. Several other GPCRs, including A_2BAR, contain cysteine and lysine residues at the appropriate positions to mediate REDAI, and isothiocyanate stimulated the internalization of A_2BAR and of a form of P2Y₂R with insertions of the appropriate residues. Thus, endogenous and exogenous electrophiles may limit colitis progression through cysteine modification of P2Y₆R and may also mediate internalization of other GPCRs.