Delineation of the GPR15 receptor‐mediated Gα protein signalling profile in recombinant mammalian cells

The GPR15 receptor is a G protein‐coupled receptor (GPCR), which is activated by an endogenous peptide GPR15L(25–81) and a C‐terminal peptide fragment GPR15L(71–81). GPR15 signals through the G(i/o) pathway to decrease intracellular cyclic adenosine 3′,5′‐monophosphate (cAMP). However, the activation profiles of the GPR15 receptor within G(i/o) subtypes have not been examined. Moreover, whether the receptor can also couple to G(s), G(q/11) and G(12/13) is unclear. Here, GPR15L(25–81) and GPR15L(71–81) are used as pharmacological tool compounds to delineate the GPR15 receptor‐mediated Gα protein signalling using a G protein activation assay and second messenger assay conducted on living cells. The results show that the GPR15 receptor preferentially couples to G(i/o) rather than other pathways in both assays. Within the G(i/o) family, the GPR15 receptor activates all the subtypes (G(i1), G(i2), G(i3), G(oA), G(oB) and G(z)). The E(max) and activation rates of G(i1,) G(i2), G(i3,) G(oA) and G(oB) are similar, whilst the E(max) of G(z) is smaller and the activation rate is significantly slower. The potencies of both peptides toward each G(i/o) subtype have been determined. Furthermore, the GPR15 receptor signals through G(i/o) to inhibit cAMP accumulation, which could be blocked by the application of the G(i/o) inhibitor pertussis toxin.