brl-37344 and carazolol

We present evidence that stimulation of the human beta-3 adrenergic receptor (AR), expressed in Chinese hamster ovary/K1 cells, specifically activates the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK)1 and 2, but not JNK or p38. The extent and kinetics of the ERK stimulation by the beta-3 AR are identical with those of the endogenic insulin receptor. However, insulin augments cellular proliferation, whereas beta-3 AR agonists inhibit proliferation due to the production of cyclic AMP. The pharmacological profile of the ERK activation by the beta-3 AR differs significantly from its activation of adenylyl cyclase. The order of potency and intrinsic activities of both natural ligands, norepinephrine and epinephrine, is inversed between both signaling pathways. In addition, BRL 37344 and propranolol, ligands that act as agonists in the stimulation of cyclase, act as antagonists for ERK activation. The activation of ERK1/2 is sensitive to pertussis toxin, suggesting that the beta-3 AR, in addition to its interaction with Gs, can couple to Gi/o. Furthermore, the activation of ERK by the beta-3 AR is sensitive to PD98059, wortmannin, and LY294002, indicating a crucial role for mitogen-activated protein kinase kinase and phosphatidylinositol-3 kinase (PI3K), respectively. A beta-3 AR-mediated stimulation of PI3K is confirmed by the observation that the selective agonist CGP 12177A specifically activates protein kinase B. As was observed for the activation of ERK, the activation of protein kinase B is inhibited by preincubation with pertussis toxin and PI3K inhibitors, suggesting that both are a consequence of a Gi/o-mediated activation of PI3K.

Topics: Adrenergic alpha-Agonists; Adrenergic alpha-Antagonists; Adrenergic beta-Agonists; Adrenergic beta-Antagonists; Animals; Bupranolol; Calcium-Calmodulin-Dependent Protein Kinases; CHO Cells; Colforsin; Cricetinae; Dioxoles; Enzyme Activation; Epinephrine; Ethanolamines; Humans; Insulin; Isoproterenol; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Norepinephrine; Phentolamine; Prazosin; Propanolamines; Receptors, Adrenergic, beta; Receptors, Adrenergic, beta-3; Signal Transduction; Yohimbine

Carazolol is a beta1/beta2 adrenoceptor antagonist of high potency used in the treatment of hypertension. Its affinity for the beta 3-adrenoceptor was determined in Chinese hamster ovary cells transfected with the gene of the human or the murine beta 3-adrenoceptor. Carazolol is recognized with a nanomolar affinity, which positions it among the best ligands for beta 3-adrenoceptors. The adenylyl cyclase stimulation was measured in transfected cells where carazolol acted as a full agonist on both murine and human receptor subtypes. Furthermore, in murine adipocyte-like 3T3-F442A cells, which express beta 3-adrenoceptor naturally, carazolol induced lipolysis. This compound also appeared to be a useful tool for molecular characterization of the beta 3-adrenoceptor, unlike the classical beta 3-adrenoceptor agonists, carazolol conferred an appreciable protection of receptor binding sites against inactivation by the reducing agent dithiothreitol. The major iodinated analog of carazolol retained its binding characteristics for the beta 3-adrenoceptor and remained an efficient adenylyl cyclase stimulator in cells expressing human beta 3-adrenoceptor.

Topics: Adenylyl Cyclases; Adrenergic beta-Agonists; Adrenergic beta-Antagonists; Animals; Binding, Competitive; Cells, Cultured; CHO Cells; Cricetinae; Dithiothreitol; Lipolysis; Propanolamines; Receptors, Adrenergic, beta