Phospholipase C Epsilon Is a Critical Mediator of NF‐kB Activation and Vascular Cell Adhesion Molecule‐1 Expression in Endothelial Cells

Phospholipase C ε (PLCε) is an important effector of Rho and Ras supefamily of GTPases. We previously showed that RhoA is necessary for thrombin‐induced NF‐κB activation in endothelial cells. We now provide evidence that PLCε plays a key role in mediating the activation of NF‐κB and expression of its target gene, vascular cell adhesion molecule‐1 (VCAM‐1). Stimulation of human pulmonary artery endothelial (HPAE) cells with thrombin resulted in increased NF‐κB activity and VCAM‐1 expression and these responses were markedly inhibited in cells transfected with short interfering RNA (siRNA) targeting PLCε. RNAi knockdown of PLCε also inhibited IκBα phosphorylation on Ser32 and Ser36, and the subsequent IκBα degradation and the DNA binding of NF‐ κB. Depletion of PLCε was also effective in inhibiting phosphorylation of Ser‐536 within the transactivation domain 1 of RelA/p65, a critical event conferring transcriptional competency to the bound NF‐κB. Thus, PLCε controls NF‐κB activation and thereby VCAM‐1 expression by a dual mechanism involving IκBα phosphorylation/degradation‐dependent nuclear uptake and DNA binding of NF‐κB, and RelA/p65 phosphorylation‐dependent transcriptional capacity of the bound NF‐κB.