OR07-06 The Roles of GNAQ and GNA11 in Calcium-Sensing Receptor (CaSR) Signalling

Abstract

The G-protein subunits Gα 11 and Gα q, which share >90% peptide sequence identity and are encoded by the GNA11 and GNAQ genes, respectively, mediate signalling by the calcium-sensing receptor (CaSR), a class C G-protein coupled receptor (GPCR) that regulates extracellular calcium (Ca2+e) homeostasis. Germline Gα 11 inactivating and activating mutations cause familial hypocalciuric hypercalcaemia type-2 (FHH2) and autosomal dominant hypocalcaemia type-2 (ADH2), respectively, but such Gα q mutations have not been reported. We therefore investigated the DiscovEHR cohort database, which has exomes from 51,289 patients with matched phenotyping data, for such GNAQ mutations. The DiscovEHR cohort was examined for rare GNAQ variants, which were transiently expressed in CaSR-expressing HEK293A Gα q/11 knockout cells, and their effects on CaSR-mediated intracellular calcium (Ca2+i) release and MAPK activity, in response to increasing concentrations of extracellular calcium were assessed using a nuclear factor of activated T-cells response element (NFAT-RE) luciferase reporter construct and a serum response element (SRE) luciferase reporter construct, respectively. Responses were compared to those of wild-type (WT), inactivating FHH2-associated GNA11 mutations (Leu135Gln and Phe220Ser), and engineered GNAQ mutations that were equivalent to the FHH2-causing GNA11 mutations. Gα q/11 protein expression was confirmed by Western blot analysis. Six rare missense GNAQ variants (Arg19Trp, Ala110Val, Gln299His, Ala302Ser, Ala331Thr, Val344Ile) were identified in DiscovEHR individuals, all of whom had mean plasma calcium values in the normal range (8.30–10.00 mg/dL). Functional characterisation of all six Gα q variants showed no significant difference to WT Gα q responses, thereby indicating that these variants are unlikely to be disease-causing mutations. In addition, the FHH2-causing GNA11 mutations (Leu135Gln and Phe220Ser) had significantly reduced responses, compared to WT Gα 11; however, this could be compensated by WT Gα q. GNAQ Leu135Gln and Phe220Ser, in contrast to their Gα 11 counterparts, showed no differences in protein expression or signalling responses when compared to WT Gα q. Our study, which provides mechanistic insights into the differences between Gα q and Gα 11, indicates that Gα q, unlike Gα 11, does not play a major role in the pathogenesis of FHH2 or ADH2.