Cyclic stretch-induced myocardin expression is mediated by the ERK pathway. (A and B) ERK pathway inhibitor (PD98059) and ERK siRNA knocked down total ERK protein expression. (A) Western blots for myocardin protein in VSMCs subjected to cyclic stretch in the absence or presence of inhibitors, siRNA, and vehicle (DMSO; Dimethyl sulfoxide 0.1%). CM = conditioned medium. (B) Quantitative analysis of myocardin protein levels. The values from stretched VSMCs have been normalized to values in control cells (n = 5 per group). *P < 0.01 vs. control. (C and D) Phosphorylation of ERK mediated stretch-induced myocardin expression, which was blocked by PD98059. Rat VSMCs were subjected to stretch for different periods of time in the presence or absence of inhibitors, and cell lysates were collected for western blot analysis using antibodies for total and phospho-ERK. T-ERK = total ERK. P-ERK = ERK phosphorylation. *P < 0.01 vs. control. #P < 0.01 vs. 18 h; (n = 3).