Mechanosensitive transcription factors involved in endothelin B receptor expression

Growing evidence suggests an involvement of the endothelin B receptor (ET(B)-R) in blood pressure-dependent arterial remodeling. To study the molecular mechanisms leading to deformation-induced ET(B)-R expression, we have cultured rat aortic smooth muscle cells on flexible elastomers and, when grown to 70% confluence, periodically stretched them for 6 h (15% elongation, 0.5 Hz). The cells responded with an increase both in ET(B)-R mRNA (12-fold compared with control) and protein (4-fold). According to nuclear run-on analysis this increase in ET(B)-R expression occurred at the level of transcription. Among various kinase pathways, Rho kinase (ROCK) and p38 mitogen-activated protein kinase (p38 MAPK) mediated part of the deformation-induced increase in ET(B)-R expression, as judged by the inhibitory effect of Y27632 (1 microm, 38% inhibition) and SB202190 (10 microm, 44% inhibition), respectively. Gel shift assaying of the three transcription factors principally activated by these kinases revealed a transient deformation-induced activation of activator protein-1 (AP-1) and CCAAT/enhancer-binding protein (C/EBP), but not activating transcription factor, that was sensitive to both Y27632 and SB212190. The potential role of AP-1 and C/EBP in deformation-induced ET(B)-R expression was verified both by using decoy oligodeoxynucleotides mimicking the DNA-binding sites of these transcription factors and a nuclear run-on-based assay employing specific antibodies directed against AP-1 and C/EBP. Both techniques unequivocally demonstrated that activation of these transcription factors, namely that of C/EBP beta, contribute to the increase of ET(B)-R gene expression in response to cyclic stretch.