Wild-type or mutated human β3-adrenergic receptor (Trp64Arg) cDNAs were stably expressed in mouse 3T3-L1 cells. Saturation binding study using a β-adrenergic ligand revealed that there was no significant difference in the receptor density and the equilibrium dissociation constant between the two cell lines. However, the ability of the mutant β3-adrenergic receptor to accumulate cyclic AMP (cAMP) in response to isoproterenol was much reduced and Kact for cAMP accumulation was lowered as compared to the wild type receptor. The amount of alpha subunit of stimulatory GTP-binding protein (GSα) and adenylyl cyclase activity in response to forskolin were not different in the two cell lines. The responses of the mutant receptor to epinephrine, norepinephrine and L-755,507, a highly specific agonist for human β3-adrenergic receptor, were also reduced, but the reduction of Kact for L-755,507 was more evident than other agonists tested. The cAMP accumulation in response to some conventional β3 agonists was less than 10% of that to isoproterenol even in the cells expressing the wild type receptor. These results suggest that the Trp64Arg mutant β3-adrenergic receptor has less ability to stimulate adenylyl cyclase, and that lipolytic activity through the β3-adrenergic receptor by catecholamines in subjects carrying this mutation might be suppressed.
Key words
Obesity - cAMP - L-755,507 - β3-adrenergic Receptors - 3T3-L1 - GTP - Guanosine Triphosphate
