Ligand-induced overexpression of a constitutively active beta2-adrenergic receptor: pharmacological creation of a phenotype in transgenic mice.
Transgenic overexpression (40- to 100-fold) of the wild-type human beta2-adrenergic receptor in the hearts of mice leads to a marked increase in cardiac contractility, which is apparently due to the low level of spontaneous (i.e., agonist-independent) activity inherent in the receptor. Here we report that transgenic mice expressing a mutated constitutively active form of the receptor (CAM) show no such phenotype, owing to its modest expression (3-fold above endogenous cardiac beta-adrenergic receptor levels). Surprisingly, treatment of the animals with a variety of beta-adrenergic receptor ligands leads to a 50-fold increase in CAM beta2-adrenergic receptor expression, by stabilizing the CAM beta2-adrenergic receptor protein. Receptor up-regulation leads in turn to marked increases in adenylate cyclase activity, atrial tension determined in vitro, and indices of cardiac contractility determined in vivo. These results illustrate a novel mechanism for regulating physiological responses, i.e., ligand-induced stabilization of a constitutively active but inherently unstable protein.
Samama
P
P
Howard Hughes Medical Institute, Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.
Bond
R A
RA
Rockman
H A
HA
Milano
C A
CA
Lefkowitz
R J
RJ
D058672:Adrenergic beta-2 Receptor Antagonists; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D016275:Atrial Function; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction; D007545:Isoproterenol / Q000494:pharmacology; D008024:Ligands; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009154:Mutation; D010641:Phenotype; D011412:Propanolamines / Q000494:pharmacology; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology*; D015854:Up-Regulation; D016277:Ventricular Function, Left
D058672:Adrenergic beta-2 Receptor Antagonists; D000319:Adrenergic beta-Antagonists; D008024:Ligands; D011412:Propanolamines; D018343:Receptors, Adrenergic, beta-2; C026777:ICI 118551; D007545:Isoproterenol