Endothelin-1 Stimulates PAI-1 Protein Expression via Dual Transactivation Pathway Dependent ROCK and Phosphorylation of Smad2L

In addition to the carboxy region, Smad2 transcription factor can be phosphorylated in the linker region aswell. Phosphorylation of Smad2 linker region (Smad2L) promotes the expression of plasminogen activator inhibitor type1 (PAI-1) which leads to cardiovascular disorders such as atherosclerosis. The purpose of this study was to evaluate the role of dual transactivation of EGF and TGF-β receptors in phosphorylation of Smad2L and protein expression of PAI-1 induced by endothelin-1 (ET-1) in bovine aortic endothelial cells (BAECs). In addition, as an intermediary of G protein-coupled receptor (GPCR) signaling, the functions of ROCK and PLC were investigated in dual transactivation pathways. The experimental study is an in vitro study performed on BAECs. Proteins were investigatedby western blotting using protein-specific antibodies against phospho-Smad2 linker region residues (Ser245/250/255),phospho-Smad2 carboxy residues (465/467), ERK1/(Thr202/Thr204), and PAI-1. TGF (2 ng/ml), EGF (100 ng/ml) and ET-1 (100 nM) induced the phosphorylation of Smad2L. This response wasblocked in the presence of AG1478 (EGFR antagonists), SB431542 (TGFR inhibitor), and Y27632 (Rho-associated protein kinase (ROCK antagonist). Moreover, ET-1-increased protein expression of PAI-1 was decreased in the presence of bosentan (ET receptor inhibitor), AG1478, SB431542, and Y27632. The results indicated that ET-1 increases the phosphorylation of Smad2L and protein expression of PAI-1via induced the transactivation pathways of EGFR and TGFR. This study is the first attempt to scrutinize the significant role of ROCK in the protein expression of PAI-1.