FK506 Augments Glucocorticoid-Mediated Cyclooxygenase–2 Down-Regulation in Human Rheumatoid Synovial Fibroblasts

Abstract

Prostaglandins (PG) formed by cyclooxygenase (COX) enzymes are important mediators of inflammation in rheumatoid arthritis. The contribution of the inducible COX-2 to inflammation in the rheumatoid synovium is well documented. We examined the regulation of COX-2 mRNA and protein expression in response to both glucocorticoids (GC) and FK506 using rheumatoid synovial fibroblasts. 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 expression. Immunocytochemical studies showed that pretreatment with FK506 enhanced the nuclear translocation of the glucocorticoid receptor (GR) in synovial fibroblasts in the presence of low concentrations of DEX (10−9 M). Transient transfection experiments showed that treatment of cells with FK506 enhanced the expression of glucocorticoid-responsive gene reporter in the presence of DEX (10−9 M). NF-κB is known to mediate the transcriptional activation of the COX-2 gene. Electrophoretic mobility shift assay demonstrated that DNA-binding activity of NF-κB was suppressed more profoundly by FK506 plus DEX (10−9 M) treatment with those of DEX (10−9 M) alone in IL-1β-stimulated synovial cells. Our results indicated that FK506-induced potentiation of GR-mediated repression of synovial COX-2 gene transcription is the result of increased translocation of GR to the nucleus and subsequent repression of NF-κB transactivation. Our results also suggest that FK506 may exert anti-inflammatory effects in the rheumatoid synovium by potentiating GR-mediated signal transduction.