CHARACTERIZATION OF THE HUMAN BETA(3)-ADRENERGIC RECEPTOR GENE

Comparison of the rodent and human beta3-adrenergic receptor cDNAs wit h the respective genomic sequences has revealed unexpectedly that thes e genes contain two protein-coding exons. The rat gene was cloned rece ntly and was found to contain three exons and two introns. In the pres ent report, the human beta3 receptor gene was characterized and was fo und to consist of two exons and a single intron. Sequence analysis of the human beta3 receptor gene identified regions in the intron that we re homologous to the second exon and second intron of the rat gene. It appears that both species utilize homologous 5' donor sites in the fi rst 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 RN A and polymerase chain reaction-amplified cDNA demonstrated conclusive ly that beta3 receptor mRNA, containing two protein-coding exons, is e xpressed in human adipose and intestinal tissues. The pharmacological properties of the full length human beta3 receptor were determined for the first time in Chinese hamster ovary cells, where catecholamine ag onists activated adenylyl cyclase with low potency. The beta3 receptor agonists CGP 12177 and BRL 37344 also activated adenylyl cyclase. CGP 12177 was 10-15 times more potent than either isoproterenol or BRL 37 344 in stimulating adenylyl cyclase activity. These pharmacological pr operties 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.