Phenotypic regulation of the sphingosine 1-phosphate receptor Miles Apart by GRK2

The evolutionary conserved DRY motif at the end of the third helix of rhodopsin-like, class-A G protein-coupled receptors (GPCRs) is a major regulator of receptor stability, signaling activity, and β arrestin mediated internalization. Substitution of the DRY arginine by histidine in the human vasopressin receptor results in a loss-of-function phenotype associated with diabetes insipidus. The analogous R150H substitution of the DRY motif in the zebrafish sphingosine-1 phosphate receptor 2 (S1p2) produces a mutation, miles apart m93(mil m93), that disrupts not only signaling but also impairs heart field migration. We hypothesized that constitutive S1p desensitization is the underlying cause for this strong zebrafish developmental defect. We observed in cell assays that wild-type S1p2 receptor is at the cell surface whereas in distinct contrast the S1p2 R150H receptor is found in intracellular vesicles, blocking G protein but not arrestin signaling activity. Surface S1p2 R150H expression could be restored by inhibition of G protein coupled receptor kinase 2 (GRK2). Moreover, we observed that β arrestin 2 and GRK2 co-localize with S1p2 in developing zebrafish embryos and depletion of GRK2 in the S1p2 R150H miles apart zebrafish partially rescued cardia bifida. An ability of reduced GRK2 activity to reverse a developmental phenotype associated with constitutive desensitization supports efforts to genetically or pharmacologically target this kinase in diseases involving biased GPCR signaling.