G-protein-coupled-receptor activation of the smooth muscle calponin gene

A hallmark of cultured smooth muscle cells (SMCs) is the rapid down-regulat ion of several lineage-restricted genes that define their in vivo different iated phenotype. Identifying factors that maintain an SMC differentiated ph enotype has important implications in understanding the molecular underpinn ings governing SMC differentiation and their subversion to an altered pheno type in various disease settings. Here, we show that several G-protein coup led receptors [a-thrombin, lysophosphatidic acid and angiotensin II (All)] increase the expression of smooth muscle calponin (SM-Calp) in rat and huma n SMC. The increase in SM-Calp protein appears to be selective for G-protei n-coupled receptors as epidermal growth factor was without effect. Studies using AII showed a 30-fold increase in SM-Calp protein, which was dose- and time-dependent and mediated by the angiotensin receptor-1 (AT(1) receptor) . The increase in SM-Calp protein with AII was attributable to transcriptio nal activation of SM-Calp based on increases in steady-state SM-Calp mRNA, increases in SM-Calp promoter activity and complete abrogation of protein i nduction with actinomycin D. To examine the potential role of extracellular signal-regulated kinase (Erk1/2), protein kinase B, p38 mitogen-activated protein kinase and protein kinase C in AII-induced SM-Calp, inhibitors to e ach of the signalling pathways were used. None of these signalling molecule s appears to be crucial for AII-induced SM-Calp expression, although Erk1/2 may be partially involved. These results identify SM-Calp as a target of A ll-mediated signalling, and suggest that the SMC response to All may incorp orate a novel activity of SM-Calp.