Receptor-mediated adenylyl cyclase activation through XLαs, the extra-large variant of the stimulatory G protein α-subunit

XLalphas, the large variant of the stimulatory G protein a subunit (Gsalpha), is derived from GNAS1 through the use of an alternative first exon and promoter. Gsa and XLalphas have distinct amino-terminal domains, but are identical over the carboxyl-terminal portion encoded by exons 2-13. XLalphas can mimic some functions of Gsalpha, including betagamma interaction and adenylyl cyclase stimulation. However, previous attempts to demonstrate coupling of XLalphas to typically Gs-coupled receptors have not been successful. We now report the generation of murine cell lines that carry homozygous disruption of Gnas exon 2, and are therefore null for endogenous XLalphas and Gsalpha (Gnas(E2-/E2-)). Gnas(E2-/E2-) cells transfected with plasmids encoding XLalphas and different heptahelical receptors, including the beta2-adrenergic receptor and receptors for PTH, TSH, and CRF, showed agonist-mediated cAMP accumulation that was indistinguishable from that observed with cells transiently coexpressing Gsalpha and these receptors. Our findings thus indicate that XLalphas is capable of functionally coupling to receptors that normally act via Gsalpha.