The effect of cancer-associated mutations on ligand binding and receptor function – A case for the 5-HT2C receptor

The serotonin 5-HT_2C receptor is a G protein-coupled receptor (GPCR) mainly expressed in the central nervous system. Besides regulating mood, appetite, and reproductive behavior, it has been identified as a potential target for cancer treatment. In this study, we aimed to investigate the effects of cancer patient-derived 5-HT_2C receptor mutations on ligand binding and receptor functionality. By filtering the sequencing data from the Genomic Data Commons data portal (GDC), we selected 12 mutations from multiple cancer types. We found that the affinity of the endogenous agonist serotonin (5-HT) and inverse agonist mesulergine were both drastically decreased by mutations L209H^ECL2 and F328S^6.52, which are located in the orthosteric binding pocket. In the calcium-flux assay, the potency of 5-HT was decreased at F328S^6.52, while a trend of increased efficacy was observed. In contrast, 5-HT displayed higher affinity at E306K^6.30 and E306A^6.30, while a trend of decreased efficacy was observed. These two mutations may disrupt the conserved ionic interaction between E^6.30 and R^3.50, and thus increase the constitutive activity of the receptor. The inhibitory potency of mesulergine was increased at E306A^6.30 but not E306K^6.30. Lastly, P365H^7.50 decreased the expression level of the receptor by more than ten-fold, which prevented further functional analyses. This study shows that cancer-associated mutations of 5-HT_2C receptor have diverse effects on ligand binding and function. Such mutations may affect serotonin-mediated signaling in tumor cells as well as treatment strategies targeting this receptor.