GLUCOCORTICOID-MEDIATED REPRESSION OF NUCLEAR FACTOR-KAPPA-B-DEPENDENT TRANSCRIPTION INVOLVES DIRECT INTERFERENCE WITH TRANSACTIVATION

Glucocorticoids exert multiple anti-inflammatory activities, one of wh ich is the inhibition of transcription dependent on the nuclear Factor (NP)-kappa B, It has been suggested that the effect of dexamethasone (DEX), a glucocorticoid analog, is attributed to an increased producti on of the inhibitory I kappa B molecule, which in turn would hind and remove activated, DNA-bound NF-kappa B complexes in the cell nucleus. Upon investigating DEX-mediated repression of interleukin-6 expression induced by tumor necrosis factor, DEX treatment was found to act dire ctly on NF-kappa B-dependent transcription, without changing the expre ssion level of I kappa B. Neither the mRNA of I kappa B nor the protei n was significantly elevated by a combined treatment with tumor necros is factor and DEX of murine endothelial or fibroblast cells, The DNA-b inding activity of induced NF-kappa B also remained unchanged after st imulation of cells with DES. Evidence for a direct nuclear mechanism o f action was obtained by analysis of cell lines stably expressing a fu sion protein between the DNA-binding domain of the It-east Gall protei n and the transactivating p65 subunit of NF-kappa B, Expression of a G al-1-dependent luciferase reporter gent activated by this nuclear fusi on protein was also strongly repressed after addition of DEX. Because the DNA-binding activity elf the Gal-1 fusion protein was not affected by DEX, it tan be concluded that the reduction of gene activation was caused by interference of the activated. glucocorticoid receptor with the Irans;activation potential of the Nf-kappa B p65 subunit.