Agonist-induced phosphorylation of orthologues of the orphan receptor GPR35 as an activation biomarker

ABSTRACT: Mass spectrometry, mutagenesis and labelling with [32P] orthophosphate identified that each of the five hydroxy-amino acids in the intracellular C-terminal tail of human GPR35a became phosphorylated in response to agonist occupancy of the receptor and that, apart from Ser294, each of these contributed to the effectiveness of interaction of the receptor with arrestin-3. Key to such interactions was Ser303. Despite there being a greater number of hydroxy-amino acids in the C-terminal tail of both mouse and rat GPR35 the serine corresponding to residue 303 in human GPR35a also played a dominant role in arrestin-3 interactions for both rodent orthologues. Fully phospho-site deficient mutants of human GPR35a and mouse GPR35 failed to interact effectively with arrestin-3 and the human phospho-deficient variant was not internalized from the surface of cells in response to agonist treatment. Even in cells stably expressing species orthologues of GPR35 a substantial proportion of the expressed protein(s) was, however, immature. Phospho-site specific antisera targeting the region encompassing Ser303 in human (Ser301 in mouse) GPR35 identified only the mature forms of GPR35 and provided effective biomarkers of the activation status of the receptors both in immunoblotting and immunocytochemical studies. Such antisera may be useful tools to evaluate target engagement in drug discovery and target validation programmes.

INSTRUMENT(S): LTQ Orbitrap Elite

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Fibroblast, Bile

SUBMITTER: Adrian Butcher  

LAB HEAD: Graeme Milligan

PROVIDER: PXD030548 | Pride | 2022-04-04

REPOSITORIES: Pride