Enhanced cAMP response of naturally occurring mutant of human β₃-adrenergic receptor

We have examined the functional significance of the naturally occurring mutation at position 64 of human β₃-adrenergic receptor (β₃AR), which changes the amino acid from tryptophan to arginine (W64R-β₃AR). The affinities of βAR agonists for W64R-β₃AR expressed in COS-7 cells were not significantly different from those for wild type β₃AR. When two receptors are expressed at various expression levels, and stimulated with CGP12177A, they showed essentially the same EC₅₀ values and maximal responses. Overexpression of G_i and G_o, or the treatment with pertussis toxin did not affect the agonist-induced cAMP response, suggesting that G_i and G_o did not contribute to the β₃AR-induced cAMP response. However, the enhanced cAMP response was observed when W64R-β₃AR was coexpressed with the adenylyl cyclase type III isoform, and stimulated by CGP12177A and isoproterenol. These results indicate that the cAMP response of W64R-β₃AR can be enhanced under the particular condition that adenylyl cyclase type III was coexpressed.