ERK5 and JNK Regulate the Expression of VCAM-1 Differentially in Insulin-and Tumor Necrosis Factor-α Stimulated Rat Aortic Endothelial Cells

Vascular Cell Adhesion Molecule-1 (VCAM-1) is a cell surface molecule that is expressed on vascular endothelial cells. One of the many functions of VCAM-1 is to interact with serum monocytes, causing them to adhere to the endothelium and transmigrate into the medial portion of the artery. Increased expression of VCAM-1 is part of the pathology of vascular inflammation and atherosclerosis. Insulin and Tumor Necrosis Factor-α (TNFα) are physiological stimulators of cell surface VCAM-1 expression and their intracellular signaling is regulated, in part, by intracellular kinases. We show here that Extracellular Signal-regulate Kinase-5 (ERK5) and c-Jun N-terminal Kinase (JNK) have opposing effects on insulin-and TNFα-stimulated VCAM-1 expression in Rat Aorta Endothelial Cells (RAEC). Using short hairpin ERK5 plasmid DNA and short hairpin JNK plasmid DNA we decreased the expression of ERK5 and JNK, respectively, producing ERK5 Knockdown (KD) and JNK KD cell lines when this hairpin-producing plasmid DNA were expressed in RAEC the following occurred: (1) the simultaneous expression of both ERK KD and JNK KD in the absence of insulin and TNFα increased the basal levels of cell surface VCAM-1, (2) expression of ERK KD decreased insulin and TNFα-stimulated VCAM-1 expression, (3) expression of JNK KD increased the expression of insulin and TNFα-stimulated VCAM-1 and (4) expression of ERK5 KD plus JNK KD stimulated an increase in both insulin and TNFα-stimulated VCAM-1 above that seen for positive controls alone.