Vascular cell adhesion molecule-1 gene expression during human smooth muscle cell differentiation is independent of NF-κB activation

Abstract

Vascular cell adhesion molecule-1 (VCAM-1) gene expression in cytokine- activated cells depends on two κB elements. Since VCAM-1 expression appears developmentally regulated and cytokine-inducible in smooth muscle cells (SMCs), we have studied the role of NF-κB in differentiated SMC VCAM-1 expression. Confluent SMCs were cultured either in a serum-free medium in order to induce differentiation, or in medium with serum, stimulated or not by tumor necrosis factor α (TNFα). The expression of smooth muscle myosin heavy chain, a SMC marker, and VCAM-1 was induced concomitantly in serum- free medium, whereas only VCAM-1 expression was induced by cytokine- treatment. We showed that the p50 and p65 subunits of NF-κB were localized in the cytoplasm of differentiating SMCs, whereas they were translocated into the nucleus of TNFα-activated SMCs. Electrophoretic mobility shift assays with VCAM-1 gene κB elements failed to detect any induction of DNA-protein complex with nuclear extracts of differentiating SMCs in contrast to the cytokine-activated SMC nuclear extracts. Furthermore, VCAM-1 mRNA induction was inhibited in TNF-α-stimulated SMCs, but not in differentiating SMCs, by pyrrolidine dithiocarbamate, an inhibitor of NF-κB protein activation. Taken together, these findings suggest that in contrast to TNF-α activation, NF- κB is not involved in VCAM-1 gene expression during SMC differentiation.