The peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a member of the nuclear receptor superfamily of ligand-dependent transcription factors that is predominantly expressed in adipose tissue, adrenal gland and spleen. PPAR-gamma has been demonstrated to regulate adipocyte differentiation and glucose homeostasis in response to several structurally distinct compounds, including thiazolidinediones and fibrates. Naturally occurring compounds such as fatty acids and the prostaglandin D2 metabolite 15-deoxy-delta prostaglandin J2 (15d-PGJ2) bind to PPAR-gamma and stimulate transcription of target genes. Prostaglandin D2 metabolites have not yet been identified in adipose tissue, but are major products of arachidonic-acid metabolism in macrophages, raising the possibility that they might serve as endogenous PPAR-gamma ligands in this cell type. Here we show that PPAR-gamma is markedly upregulated in activated macrophages and inhibits the expression of the inducible nitric oxide synthase, gelatinase B and scavenger receptor A genes in response to 15d-PGJ2 and synthetic PPAR-gamma ligands. PPAR-gamma inhibits gene expression in part by antagonizing the activities of the transcription factors AP-1, STAT and NF-kappaB. These observations suggest that PPAR-gamma and locally produced prostaglandin D2 metabolites are involved in the regulation of inflammatory responses, and raise the possibility that synthetic PPAR-gamma ligands may be of therapeutic value in human diseases such as atherosclerosis and rheumatoid arthritis in which activated macrophages exert pathogenic effects.

fscabo@cnic.es or mricote@cnic.es.

Prostaglandin J2 (PGJ2) and its metabolites ⌬ 12 -PGJ2 and 15-deoxy-⌬ 12,14 -PGJ2 (15d-PGJ2) are naturally occurring derivatives of prostaglandin D2 that have been suggested to exert antiinflammatory effects in vivo. 15d-PGJ 2 is a high-affinity ligand for the peroxisome proliferator-activated receptor ␥ (PPAR␥) and has been demonstrated to inhibit the induction of inflammatory response genes, including inducible NO synthase and tumor necrosis factor ␣, in a PPAR␥-dependent manner. We report here that 15d-PGJ2 potently inhibits NF-B-dependent transcription by two additional PPAR␥-independent mechanisms. Several lines of evidence suggest that 15d-PGJ2 directly inhibits NF-B-dependent gene expression through covalent modifications of critical cysteine residues in IB kinase and the DNA-binding domains of NF-B subunits. These mechanisms act in combination to inhibit transactivation of the NF-B target gene cyclooxygenase 2. Direct inhibition of NF-B signaling by 15d-PGJ 2 may contribute to negative regulation of prostaglandin biosynthesis and inflammation, suggesting additional approaches to the development of antiinflammatory drugs. P rostaglandin J 2 (PGJ 2 ) and its metabolites are naturally occurring derivatives of prostaglandin D 2 (PGD 2 ). The pathway for formation of these compounds involves sequential conversion of PGD 2 to PGJ 2 , ⌬ 12 -PGJ 2 , and 15-deoxy-⌬ 12,14 -PGJ 2 (15d-PGJ 2 ) (1). The last of these metabolites, 15d-PGJ 2 , is a high-affinity ligand for peroxisome proliferator-activated receptor ␥ (PPAR␥) (2, 3). 15d-PGJ 2 represses several genes in activated macrophages, including the inducible NO synthase (iNOS) and tumor necrosis factor ␣ (TNF␣) genes, and this repression is at least partly dependent on PPAR␥ expression (4-6). 15d-PGJ 2 is present in vivo during the resolution phase of inflammation, suggesting that it may function as a feedback regulator of the inflammatory response (7).Previous studies evaluating PPAR␥-dependent inhibition of iNOS expression indicated that 15d-PGJ 2 was significantly more effective than synthetic PPAR␥ ligands, despite binding to PPAR␥ with lower affinity (4). PGJ 2 and its metabolites are characterized by the presence of a cyclopentenone ring system that contains an electrophilic carbon that can react covalently by means of the Michael addition reaction with nucleophiles such as the free sulfhydryls of glutathione and cysteine residues in cellular proteins (1,8,9). This reactive center is not present in the synthetic PPAR␥ ligands and has been proposed to account for some of the receptor-independent biological actions of PGJ 2 , its metabolites, and the related cyclopentenone prostaglandins PGA 2 and PGA 1 (8, 9).The transcription factor NF-B plays a key role in the activation of inflammatory response genes (10). In resting cells, NF-B is sequestered in the cytoplasm by association with an inhibitory protein IB. In response to signaling by inflammatory cytokines, IB kinase (IKK) is activated and phosphorylates IB on two serine residues. IB is then ubiquitinated...