The effect of mechanical stretch on cyclooxygenase type 2 expression and activator protein-1 and nuclear factor-κB activity in human amnion cells

Stretch of the uterus plays a role in parturition. Uterine stretch also leads to stretch of the fetal membranes, including the amnion, an important source of prostaglandin E-2 ( PGE(2)). We tested the hypothesis that stretch of the amnion leads to increased cyclooxygenase ( COX)-2 expression and PGE2 synthesis and investigated the mechanisms involved. We obtained amnion from women undergoing term elective cesarean section and isolated amnion epithelial cells. These cells were subjected to 11% static stretch. Stretch increased COX-2 expression and PGE2 production. EMSA studies showed that stretch increased both activator protein-1 ( AP-1) and nuclear factor-kappa B ( NF-kappa B) DNA binding at 1 and 6 h. In contrast, IL-1 beta increased both AP-1 and NF-kappa B DNA binding at 1 h only. Chromatin immunoprecipitation studies confirmed that stretch increased binding of NF-kappa B to the COX-2 promoter in vivo. Stretch had no effect on inhibitory-kappa B alpha ( I kappa B alpha) levels at the early time points but caused a decrease at 4 h. IL-1 beta stimulation decreased I kappa B alpha levels after 30 min. MG132, a proteasome inhibitor, inhibited only the second stretch-induced increase in NF-kappa B binding. This suggests that stretch initially activates NF-kappa B via a nonclassical pathway, which does not involve the inhibitory-kappa kinase-induced degradation of I kappa B alpha. The second peak of NF-kappa B activation may be mediated by the classical mechanism. Stretch of the amnion may contribute to increased expression of COX-2- and other AP-1- and NF-kappa B regulated genes with the onset of labor in the human.