Characterization of cancer-related somatic mutations in the adenosine A_2B receptor

In cancer, G protein-coupled receptors (GPCRs) are involved in tumor progression and metastasis. In this study we particularly examined one GPCR, the adenosine A_2B receptor. This receptor is activated by high concentrations of its endogenous ligand adenosine, which suppresses the immune response to fight tumor progression. A series of adenosine A_2B receptor mutations were retrieved from the Cancer Genome Atlas harboring data from patient samples with different cancer types. The main goal of this work was to investigate the pharmacology of these mutant receptors using a 'single-GPCR-one-G protein' yeast assay technology. Concentration-growth curves were obtained with the full agonist NECA for the wild-type receptor and 15 mutants. Compared to wild-type receptor, the constitutive activity levels in mutant receptors F141L^4.61, Y202C^5.58 and L310P^8.63 were high, while the potency and efficacy of NECA and BAY 60-6583 on Y202C^5.58 was lower. A 33- and 26-fold higher constitutive activity on F141L^4.61 and L310P^8.63 was reduced to wild-type levels in response to the inverse agonist ZM241385. These constitutively active mutants may thus be tumor promoting. Mutant receptors F259S^6.60 and Y113F^34.53 showed a more than one log-unit decrease in potency. A complete loss of activation was observed in mutant receptors C29R^1.54, W130C^4.50 and P249L^6.50. All mutations were characterized at the structural level, generating hypotheses of their roles on modulating the receptor conformational equilibrium. Taken together, this study is the first to investigate the nature of adenosine A_2B receptor cancer mutations and may thus provide insights in mutant receptor function in cancer.