RT Journal Article SR Electronic T1 β-Adrenergic Agonists Mediate Enhancement of β1-Adrenergic Receptor N-terminal Cleavage and Stabilization In Vivo and In Vitro JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 129 OP 141 DO 10.1124/mol.112.080440 VO 83 IS 1 A1 Anna E. Hakalahti A1 Hamayun Khan A1 Miia M. Vierimaa A1 Emilia H. Pekkala A1 Jarkko J. Lackman A1 Johanna Ulvila A1 Risto Kerkelä A1 Ulla E. Petäjä-Repo YR 2013 UL http://molpharm.aspetjournals.org/content/83/1/129.abstract AB The β1-adrenergic receptor (β1AR) is the predominant βAR in the heart and is the main target for β-adrenergic antagonists, widely used in the treatment of cardiovascular diseases. Previously, we have shown that the human (h) β1AR is cleaved in its N terminus by a metalloproteinase, both constitutively and in a receptor activation–dependent manner. In this study, we investigated the specific events involved in β1AR regulation, focusing on the effects of long-term treatment with β-adrenergic ligands on receptor processing in stably transfected human embryonic kidney 293i cells. The key findings were verified using the transiently transfected hβ1AR and the endogenously expressed receptor in neonatal rat cardiomyocytes. By using flow cytometry and Western blotting, we demonstrated that isoproterenol, S-propranolol, CGP-12177 [4-[3-[(1,1-dimethylethyl)amino]2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one], pindolol, and timolol, which displayed agonistic properties toward the β1AR in either the adenylyl cyclase or the mitogen-activated protein kinase signaling pathways, induced cleavage of the mature cell-surface receptor. In contrast, metoprolol, bisoprolol, and CGP-20712 [1-[2-((3-carbamoyl-4-hydroxy)phenoxy)ethylamino]-3-[4-(1-methyl-4-trifluoromethyl-2-imidazolyl)phenoxy]-2-propanol], which showed no agonistic activity, had only a marginal or no effect. Importantly, the agonists also stabilized intracellular receptor precursors, possibly via their pharmacological chaperone action, and they stabilized the receptor in vitro. The opposing effects on the two receptor forms thus led to an increase in the amount of cleaved receptor fragments at the plasma membrane. The results underscore the pluridimensionality of β-adrenergic ligands and extend this property from receptor activation and signaling to the regulation of β1AR levels. This phenomenon may contribute to the exceptional resistance of β1ARs to downregulation and tendency toward upregulation following long-term ligand treatments.