PT - JOURNAL ARTICLE AU - Anna E Hakalahti AU - Hamayun Khan AU - Miia M Vierimaa AU - Emilia H Pekkala AU - Jarkko J Lackman AU - Johanna Ulvila AU - Risto Kerkela AU - Ulla E Petaja-Repo TI - β-Adrenergic Agonists Mediate Enhancement of β1-Adrenergic eceptor N-terminal Cleavage and Stabilization in Vivo and in Vitro AID - 10.1124/mol.112.080440 DP - 2012 Jan 01 TA - Molecular Pharmacology PG - mol.112.080440 4099 - http://molpharm.aspetjournals.org/content/early/2012/10/11/mol.112.080440.short 4100 - http://molpharm.aspetjournals.org/content/early/2012/10/11/mol.112.080440.full 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. Here, 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 HEK293i 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 demonstrate that isoproterenol, S-propranolol, CGP-12177, pindolol and timolol, which displayed agonistic properties towards 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 that showed no agonistic activity had only marginal or no effect. Importantly, the agonists also stabilized intracellular receptor precursors, possibly via their pharmacological chaperone action, and they also 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 down-regulation and tendency toward up-regulation following long-term ligand treatments.