A unique phenotype of 5-HT2C agonist-induced GTPγ35S binding, transferable to 5-HT2A and 5-HT2B, upon swapping intracellular regions

1 The human 5-HT2C receptor, when expressed heterologously in various mammalian cell lines (HEK293, SH-EP and NIH-3T3) at various receptor densities (6 to 45 pmol mg(-1) protein), mediates robust agonist-induced GTPgamma(35)S binding from coupling to G(i) subtypes of G proteins, in addition to G(q/11). Such a phenotype, however, was not seen with the human 5-HT2A and 5-HT2B receptors, indicating their common pathway with 5-HT2C limited to G(q/11), not including G(i). 2 Because intracellular regions are largely responsible for signalling pathways, we prepared the chimeras of the 5-HT2A and 5-HT2B receptors where the second and third intracellular loops, and the C-terminal region were replaced with the 5-HT2C counterparts. 3 The chimeras showed robust agonist-induced GTPgamma(35)S binding. Relative intrinsic efficacies of agonists from the GTPgamma(35)S binding were nearly identical to the reported values for their parent receptors as measured with Ca2+ or [H-3]-inositol phosphate accumulation. Also the chimeras displayed the same ligand-binding properties as the parent receptors. 4 We conclude that the phenotype of agonist-induced GTPgamma(35)S binding is unique to 5-HT2C among the 5-HT2 receptor family, and is transferable to 5-HT2A and 5-HT2B, upon swapping intracellular sequences, without altering their receptor pharmacology.