Functional analysis of nuclear ATF2 activity in endothelial cells exposed to prolonged shear and its dependence on KLF2. Nuclear extracts from HUVECs exposed to 5 days of pulsatile flow (A) or HUVECs overexpressing KLF2 (B) were assayed for the presence of functional Thr71-phosphorylated ATF2 protein. Data from 3 independent isolates are expressed relative to static or mock controls. (C) HUVECs containing lentiviral-delivered double-stranded siRNA directed against KLF2 or a control siRNA against FLUC were exposed for 5 days to shear stress or to static conditions and assayed for nuclear activated ATF2. The means of 3 different isolates are expressed relative to static FLUC. Error bars indicate SEM. Significant difference versus static control conditions is indicated (*P < .05; **P < .01).