title: Tonic inhibitory role for cAMP in alpha(1a)-adrenergic receptor coupling to extracellular signal-regulated kinases 1/2.
abstract: alpha(1a)-Adrenergic receptors (ARs) couple to phosphoinositide hydrolysis, adenylyl cyclase, and mitogen-activated protein kinase (MAPK) pathways. However, the interaction among these signaling pathways in activating extracellular signal-regulated kinase 1/2 (ERK1/2) is not well understood. We investigated the coupling of alpha(1a)-ARs to ERK1/2 in Chinese hamster ovary (CHO)-K1 cells stably transfected with mouse alpha(1a)-ARs, as well as the interaction between ERK1/2 and norepinephrine-induced cAMP accumulation. alpha(1a)-AR activation by norepinephrine increased the cytosolic Ca(2+) concentration and phosphorylated ERK1/2 in a time- and concentration-dependent manner. ERK1/2 phosphorylation was blocked by the MAPK kinase 1/2 inhibitor 2'-amino-3'-methoxyflavone (PD 98059) and the alpha(1)-AR antagonist prazosin. A transient elevation in intracellular Ca(2+) was required for the phosphorylation of ERK1/2; however, activation of protein kinase C did not seem to be required for ERK1/2 phosphorylation. Norepinephrine also stimulated cAMP accumulation in transfected CHO-K1 cells in a concentration-dependent manner via alpha(1a)-ARs, which was blocked by the Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. Norepinephrine-induced ERK1/2 phosphorylation was inhibited by the adenylyl cyclase activator forskolin and was enhanced by the adenylyl cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purine-6-amine (SQ 22536) and the protein kinase A inhibitor 4-cyano-3-methylisoquinoline. In conclusion, in transfected CHO-K1 cells, alpha(1a)-AR activation activates both phospholipase C and adenylyl cyclase-mediated signaling pathways. alpha(1a)-AR-mediated ERK1/2 phosphorylation was dependent on a rise in intracellular Ca(2+), and this pathway was reciprocally regulated by the concomitant activation of adenylyl cyclase, which inhibits ERK1/2 phosphorylation. Thus, alpha(1a)-AR stimulation of cAMP production may play an important role in regulating ERK1/2 phosphorylation in cell lines and native tissues.
authors.affiliation: Department of Pharmacology, Creighton University School of Medicine, Omaha, Nebraska 68178, USA.
authors.forename: Xiuxiang
authors.initials: X
authors.lastname: Jiao
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: Gonzalez-Cabrera
authors.forename: Lei
authors.initials: L
authors.lastname: Xiao
authors.forename: Michael E
authors.initials: ME
authors.lastname: Bradley
authors.forename: Peter W
authors.initials: PW
authors.lastname: Abel
authors.forename: William B
authors.initials: WB
authors.lastname: Jeffries
mesh_terms: D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism*; D003001:Cloning, Molecular; D006224:Cricetinae; D000242:Cyclic AMP / Q000502:physiology*; D007700:Kinetics; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D010766:Phosphorylation; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection
chemical_list: D018340:Receptors, Adrenergic, alpha-1; D011994:Recombinant Proteins; D000242:Cyclic AMP; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D009638:Norepinephrine