Tyrosine phosphorylation of S1PR1 leads to chaperone BiP-mediated import to the endoplasmic reticulum

Abstract

Cell surface G protein–coupled receptors (GPCRs), upon agonist binding, undergo serine–threonine phosphorylation, leading to either receptor recycling or degradation. Here, we show a new fate of GPCRs, exemplified by ER retention of sphingosine-1-phosphate receptor 1 (S1PR1). We show that S1P phosphorylates S1PR1 on tyrosine residue Y¹⁴³, which is associated with recruitment of activated BiP from the ER into the cytosol. BiP then interacts with endocytosed Y¹⁴³-S1PR1 and delivers it into the ER. In contrast to WT-S1PR1, which is recycled and stabilizes the endothelial barrier, phosphomimicking S1PR1 (Y¹⁴³D-S1PR1) is retained by BiP in the ER and increases cytosolic Ca²⁺ and disrupts barrier function. Intriguingly, a proinflammatory, but non-GPCR agonist, TNF-α, also triggered barrier-disruptive signaling by promoting S1PR1 phosphorylation on Y¹⁴³ and its import into ER via BiP. BiP depletion restored Y¹⁴³D-S1PR1 expression on the endothelial cell surface and rescued canonical receptor functions. Findings identify Y¹⁴³-phosphorylated S1PR1 as a potential target for prevention of endothelial barrier breakdown under inflammatory conditions.