Distinct cAMP signaling pathways differentially regulate 2C-adrenoceptor expression: role in serum induction in human arteriolar smooth muscle cells

Authors:
Chotani MA, Mitra S, Eid AH, Han SA and Flavahan NA
In:
Source: Am J Physiol Heart Circ Physiol
Publication Date: (2005)
Issue: 288(1): H69-H76
Research Area:
Cardiovascular
Cells used in publication:
SMC, vascular, human
Species: human
Tissue Origin:
Platform:
Nucleofector® I/II/2b
Abstract
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 muM), or celecoxib (3 muM) abolished the increase in cAMP and markedly reduced alpha(2C)-AR induction in response to serum stimulation. The cAMP agonists, forskolin (10 muM), isoproterenol (10 muM), and cholera toxin (0.1 mug/ml) each dramatically increased expression of alpha(2C)-ARs in human cutaneous VSMs. The A-kinase inhibitor H-89 (2 muM) 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.