EFFECT OF TNF-ALPHA ON SMIT MESSENGER-RNA LEVELS AND MYOINOSITOL ACCUMULATION IN CULTURED ENDOTHELIAL-CELLS

Previously we have shown that hyperosmolarity increases Na+-myo-inosit ol cotransporter (SMIT) activity and mRNA levels in cultured endotheli al cells. Because hyperosmolarity and cytokines, such as tumor necrosi s factor-alpha (TNF-alpha), activate similar signal transduction pathw ays, we examined the effect of TNF-alpha on SMIT mRNA levels and myo-i nositol accumulation. In contrast to the effect of hyperosmolarity, TN F-alpha caused a time-and concentration-dependent decrease in SMIT mRN A levels and myo-inositol accumulation. The effect of TNF-alpha on myo -inositol accumulation was found in large-vessel endothelial cells (de rived from the aorta and pulmonary artery) and cerebral microvessel en dothelial cells. In bovine aorta and bovine pulmonary artery endotheli al cells, TNF-alpha activated nuclear factor (NF)-kappa B. TNF-alpha, also increased ceramide levels, and C-2-ceramide mimicked the effect o f TNF-alpha on SMIT mRNA levels and myo-inositol accumulation in bovin e aorta endothelial cells, Pyrrolidinedithiocarbamate, genistein, and 7-amino-1-chloro-3-tosylamido-2-hepatanone, compounds that can inhibit NF-kappa B activation, partially prevented the TNF-alpha-induced decr ease in myo-inositol accumulation. The effect of TNF-alpha on myo-inos itol accumulation was also partially prevented by the protein kinase C inhibitor calphostin C but not by staurosporine. These studies demons trate that TNF-alpha causes a decrease in SMIT mRNA levels and myo-ino sitol accumulation in cultured endothelial cells, which may be related to the activation of NF-kappa B.