FK506 augments glucocorticoid-mediated cyclooxygenase-2 down-regulation inhuman rheumatoid synovial fibroblasts

Prostaglandins (PG) formed by cyclooxygenase (COX) enzymes are important me diators of inflammation in rheumatoid arthritis. The contribution of the in ducible COX-2 to inflammation in the rheumatoid synovium is well documented . We examined the regulation of COX-2 mRNA and protein expression in respon se to both glucocorticoids (GC) and FK506 using rheumatoid synovial fibrobl asts. Combined treatment of FK506 and a low concentration of dexamethasone (DEX) (10(-9) M) down-regulated synovial COX-2 mRNA and protein expression. In contrast, neither FK506 nor DEX (10-9 M) alone influenced COX-2 express ion. Immunocytochemical studies showed that pretreatment with FK506 enhance d the nuclear translocation of the glucocorticoid receptor (GR) in synovial fibroblasts in the presence of low concentrations of DEX (10(-9) M). Trans ient transfection experiments showed that treatment of cells with FK506 enh anced the expression of glucocorticoid-responsive gene reporter in the pres ence of DEX (10(-9) M). NF-kappa B is known to mediate the transcriptional activation of the COX-2 gene. Electrophoreiic mobility shift assay demonstr ated that DNA-binding activity of NF-kappa B was suppressed more profoundly by FK506 plus DEX (10(-9) M) treatment with those of DEX (10(-9) M) alone in IL-1 beta-stimulated synovial cells. Our results indicated that FK506-in duced potentiation of GR-mediated repression of synovial COX-2 gene transcr iption is the result of increased translocation of GR to the nucleus and su bsequent repression of NF-kappa B transactivation. Our results also suggest that FK506 may exert anti-inflammatory effects in the rheumatoid synovium by potentiating GR-mediated signal transduction.