Inhibition of interleukin-1β–induced cyclooxygenase 2 expression in human synovial fibroblasts by 15-deoxy-Δ12,14-prostaglandin J2 through a histone deacetylase–independent mechanism

✍ Scribed by Katherine Farrajota; Saranette Cheng; Johanne Martel-Pelletier; Hassan Afif; Jean-Pierre Pelletier; Xinfang Li; Pierre Ranger; Hassan Fahmi

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 313 KB
• Volume: 52
• Category: Article
• ISSN: 0004-3591
• DOI: 10.1002/art.20714

✦ Synopsis

Objective. The cyclooxygenase (COX) metabolite, 15-deoxy-⌬ 12,14 -prostaglandin J 2 (15d-PGJ 2 ), has been reported to inhibit the expression of a number of genes involved in the pathogenesis of arthritis. However, its effects on COX-2 remain controversial. We undertook this study to investigate the effects of 15d-PGJ 2 on interleukin-1␤ (IL-1␤)-induced COX-2 expression in human synovial fibroblasts (HSFs).

Methods. HSFs were cultured with IL-1␤ in the absence or presence of 15d-PGJ 2 , and the levels of COX-2 protein and messenger RNA (mRNA) expression were evaluated using Western blotting and real-time reverse transcriptase-polymerase chain reaction, respectively. COX-2 promoter activity was analyzed in transient transfection experiments. Chromatin immunoprecipitation assays were performed to evaluate the level of histone acetylation and the recruitment of histone deacetylases (HDACs) 1, 2, and 3 and histone acetylase (HAT) p300 to the COX-2 promoter.

Results. IL-1␤-induced COX-2 protein and mRNA expression, as well as COX-2 promoter activation, were inhibited by 15d-PGJ 2 . Troglitazone, a selective peroxisome proliferator-activated receptor ␥ (PPAR␥) ligand, enhanced COX-2 expression, while GW9662, a specific PPAR␥ antagonist, relieved the suppressive effect of 15d-PGJ 2 . IL-1␤-induced histone H3 acetylation was selectively blocked by 15d-PGJ 2 . The reduction of histone H3 acetylation did not correlate with the recruitment of HDACs to the COX-2 promoter. Also, treatment with the specific HDAC inhibitor, trichostatin A, did not relieve the suppressive effect of 15d-PGJ 2 , indicating that HDACs are not involved in the inhibitory effect of 15d-PGJ 2 . Furthermore, 15d-PGJ 2 blocked IL-1␤-induced recruitment of p300 to the COX-2 promoter, which may be the mechanism for decreased histone H3 acetylation and COX-2 expression. In accordance with this, overexpression of p300, but not of a mutant p300 lacking HAT activity, relieved the inhibitory effect of 15d-PGJ 2 on COX-2 promoter activation.

Conclusion. These data suggest that 15d-PGJ 2 can inhibit IL-1␤-induced COX-2 expression by an HDAC-independent mechanism, probably by interfering with HAT p300.

There is increasing evidence suggesting a role of cyclooxygenase 2 (COX-2) in the pathogenesis of chronic arthritic diseases such as rheumatoid arthritis (RA) and osteoarthritis (OA). COX-2 expression and enzymatic activity are increased in articular tissues and cells of RA and OA patients (1,2). Furthermore, genetic ablation of COX-2 reduced the incidence and severity of collagen-induced arthritis in mice (3). Similar findings were reported in rats with adjuvant-induced arthritis Supported by grants from the Canadian Institutes of Health Research (IMH-63168), the Fonds de Recherche en Sante ´du Que ´bec (JC2836), and the