Distinct cAMP signaling pathways differentially regulate alpha2C-adrenoceptor expression: role in serum induction in human arteriolar smooth muscle cells.
The physiological role of alpha(2)-adrenoceptors (alpha(2)-ARs) in cutaneous, arteriolar, vascular smooth muscle cells (VSMs) is to mediate cold-induced constriction. In VSMs cultured from human cutaneous arterioles, there is a selective increase in alpha(2C)-AR expression after serum stimulation. In the present study, we examined the cellular mechanisms contributing to this response. Serum induction of alpha(2C)-ARs was paralleled by increased expression of cyclooxygenase-2 (COX-2), increased release of prostaglandins, and increased intracellular concentration of cAMP. Inhibition of COX-2 by acetyl salicylic acid (1 mM), NS-398 (5 microM), or celecoxib (3 microM) abolished the increase in cAMP and markedly reduced alpha(2C)-AR induction in response to serum stimulation. The cAMP agonists, forskolin (10 microM), isoproterenol (10 microM), and cholera toxin (0.1 microg/ml) each dramatically increased expression of alpha(2C)-ARs in human cutaneous VSMs. The A-kinase inhibitor H-89 (2 microM) inhibited phosphorylation of cAMP response element binding protein, but not the increase in alpha(2C)-AR expression in response to these agonists. cAMP-dependent but A-kinase independent signaling can involve activation of guanine nucleotide exchange factors for the GTP-binding protein, Rap. Indeed, pull-down assays demonstrated Rap1 activation by serum and forskolin in VSM. Transient transfections using alpha(2C)-AR promoter-luciferase reporter construct demonstrated that Rap1 increased reporter activity, whereas the A-kinase catalytic subunit decreased reporter activity. These results indicate that cAMP signaling can have dual effects in cutaneous VSMs:activation of alpha(2C)-AR transcription mediated by Rap1 GTPase and suppression mediated by A-kinase. The former effect predominates in serum-stimulated VSMs leading to a COX-2, cAMP, and Rap 1-dependent increase in alpha(2C)-AR expression. Such increased expression of alpha(2C)-ARs may contribute to enhanced cold-induced vasoconstriction and Raynaud's phenomenon.
Chotani
Maqsood A
MA
Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, USA. chotani-1@medctr.osu.edu
Mitra
Srabani
S
Eid
Ali H
AH
Han
Seon A
SA
Flavahan
Nicholas A
NA
D001160:Arterioles / Q000166:cytology / Q000378:metabolism*; D001790:Blood Physiological Phenomena; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D051546:Cyclooxygenase 2; D006801:Humans; D008565:Membrane Proteins; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism / Q000502:physiology; D020033:Protein Isoforms / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism
D008565:Membrane Proteins; D020033:Protein Isoforms; D018341:Receptors, Adrenergic, alpha-2; D000242:Cyclic AMP; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D020827:rap1 GTP-Binding Proteins