Hidden Bias: GPCR Polymorphisms and the Genomic Landscape of β- Arrestin Signaling
Clinically, no human diseases are currently diagnosed as being directly driven by {beta}- arrestins. Nonetheless, there is growing interest in developing {beta}-arrestin-biased drugs, due to the key regulatory role of {beta}-arrestins in modulating the cellular signaling of most G protein-coupled receptors (GPCRs). In cell-based studies of rhodopsin-family GPCRs, mutations in a conserved proline-hydrophobic (ProH) motif within the second intracellular loop (ICL2) have been shown to alter {beta}-arrestin signaling bias. The clinical relevance of such mutations in humans is unknown. However, if naturally occurring single nucleotide polymorphisms (SNPs) affecting this ProH motif exist across the GPCR family, then cross-referencing these genetic variants with large-scale population sequencing and epidemiologic data could reveal potential roles for {beta}-arrestin signaling in human health. In this report, we identify SNPs in human GPCRs that correspond to ProH substitutions, and we show that, in the neurotensin receptor NTSR1, these variants can indeed shift signaling bias. We also estimate a lower-bound population frequency for such SNPs, suggesting that although rare for any given receptor, their cumulative prevalence across the GPCR superfamily may be large enough to impact phenotypic variation. Together with emerging data from biased ligands, our findings support the idea that genetic variations in {beta}-arrestin signaling could represent a meaningful source of therapeutic relevance. Significance statementMutations altering G protein-coupled receptor (GPCR) signaling can affect health. We have identified a specific amino acid determinant in intracellular loop (ICL2) of human rhodopsin family GPCRs that influences {beta}-arrestin signaling. Although the medical consequences of this determinant remain unclear, we show that single nucleotide polymorphisms (SNPs) affecting the determinant routinely occur. By studying neurotensin receptor NTSR1, we confirm that the SNP alters {beta}-arrestin signaling bias. While individually rare per receptor, these SNPs may collectively contribute to {beta}-arrestin-related phenotypic changes in the human population. Our findings, combined with research on biased drugs, support the idea that {beta}-arrestin signaling might serve as a useful therapeutic target, opening new possibilities for precision medicine.