glucocorticoidmediated repression of nuclear factorkappabdependent transcription involves direct interference with transactivation glucocorticoids exert multiple antiinflammatory activities one of which is the inhibition of transcription dependent on the nuclear factor nfkappab it has been suggested that the effect of dexamethasone dex a glucocorticoid analog is attributed to an increased production of the inhibitory ikappab molecule which in turn would bind and remove activated dnabound nfkappab complexes in the cell nucleus upon investigating dexmediated repression of interleukin6 expression induced by tumor necrosis factor dex treatment was found to act directly on nfkappabdependent transcription without changing the expression level of ikappab neither the mrna of ikappab nor the protein was significantly elevated by a combined treatment with tumor necrosis factor and dex of murine endothelial or fibroblast cells the dnabinding activity of induced nfkappab also remained unchanged after stimulation of cells with dex evidence for a direct nuclear mechanism of action was obtained by analysis of cell lines stably expressing a fusion protein between the dnabinding domain of the yeast gal4 protein and the transactivating p65 subunit of nfkappab expression of a gal4dependent luciferase reporter gene activated by this nuclear fusion protein was also strongly repressed after addition of dex because the dnabinding activity of the gal4 fusion protein was not affected by dex it can be concluded that the reduction of gene activation was caused by interference of the activated glucocorticoid receptor with the transactivation potential of the nfkappab p65 subunit