Characterization of the human beta 3-adrenergic receptor gene.

Comparison of the rodent and human beta 3-adrenergic receptor cDNAs with the respective genomic sequences has revealed unexpectedly that these genes contain two protein-coding exons. The rat gene was cloned recently and was found to contain three exons and two introns. In the present report, the human beta 3 receptor gene was characterized and was found to consist of two exons and a single intron. Sequence analysis of the human beta 3 receptor gene identified regions in the intron that were homologous to the second exon and second intron of the rat gene. It appears that both species utilize homologous 5' donor sites in the first intron and 3' acceptor sites of the final exon. However, splicing signals within the human intron that are homologous to the second exon of the rat gene are not used. Nuclease protection assays of tissue RNA and polymerase chain reaction-amplified cDNA demonstrated conclusively that beta 3 receptor mRNA, containing two protein-coding exons, is expressed in human adipose and intestinal tissues. The pharmacological properties of the full length human beta 3 receptor were determined for the first time in Chinese hamster ovary cells, where catecholamine agonists activated adenylyl cyclase with low potency. The beta 3 receptor agonists CGP 12177 and BRL 37344 also activated adenylyl cyclase. CGP 12177 was 10-15 times more potent than either isoproterenol or BRL 37344 in stimulating adenylyl cyclase activity. These pharmacological properties differed somewhat from those reported previously for Chinese hamster ovary cells expressing the truncated receptor. However, direct comparison indicates that it is unlikely that the amino acid sequence derived from the second exon can account for these differences.