PPAR agonists amplify iNOS expression while inhibiting NF-kappaB: implications for mesangial cell activation by cytokines.
In acute inflammation, the transcription factor NF-kappaB is activated and increases the expression of multiple pro-inflammatory genes. Agonists of peroxisome proliferator activated receptors (PPAR) have been reported to exert antiinflammatory effects in various systems. In keeping with such an antiinflammatory role, it was found that several PPAR agonists, including Wy14,643, clofibrate, carbaprostacyclin, and ciglitazone inhibited NF-kappaB activity and increased IkappaBalpha levels in cytokine-stimulated mesangial cells (MC). Activation of NF-kappaB has been found to be crucial to the cytokine-elicited expression of inducible nitric oxide synthase (iNOS). Despite the inhibitory effect of PPAR agonists on NF-kappaB activity, this study provides experimental data demonstrating that these agonists amplify cytokine-elicited NO generation in MC, potentiating iNOS protein expression approximately threefold. The upregulation of iNOS expression occurred at the mRNA level and apparently did not result from iNOS mRNA stabilization. Clofibrate and ciglitazone amplified the cytokine-elicited stimulation of a 16-Kb human iNOS promoter construct in stably transfected MC, suggesting that PPAR agonists potentiate iNOS induction through transcriptional mechanisms. MC express all three PPAR proteins. However, iNOS potentiation did not correlate with increased PPAR activity. In addition, Wy14,643-induced amplification of cytokine-elicited iNOS levels also occurred in RAW264.7 macrophages and in human epithelial Caco-2 and HT-29 cells. The observation that these epithelial cell lines express an inactive, truncated PPARalpha variant suggests that a classical PPARalpha agonist, such as Wy14,643, may act through PPARalpha-independent mechanisms. In conclusion, these results show that, despite reducing NF-kappaB activity, PPAR agonists may amplify the expression of certain NF-kappaB-dependent genes that are relevant to the inflammatory process, like iNOS.
Cernuda-Morollón
Eva
E
Department of Protein Structure and Function, Centro de Investigaciones Biológicas, C.S.I.C. and Instituto Reina Sofía de Investigaciones Nefrológicas, Madrid, Spain.
Rodríguez-Pascual
Fernando
F
Klatt
Peter
P
Lamas
Santiago
S
Pérez-Sala
Dolores
D
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D002478:Cells, Cultured; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D005920:Glomerular Mesangium / Q000166:cytology / Q000201:enzymology*; D020672:I-kappa B Proteins / Q000378:metabolism; D007375:Interleukin-1 / Q000494:pharmacology*; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors*; D009569:Nitric Oxide / Q000096:biosynthesis; D019001:Nitric Oxide Synthase / Q000235:genetics*; D052247:Nitric Oxide Synthase Type II; D020025:Peroxisome Proliferators / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D000970:Antineoplastic Agents; D020672:I-kappa B Proteins; D007375:Interleukin-1; D016328:NF-kappa B; C000606204:NFKBIA protein, human; C000606206:Nfkbia protein, rat; D020025:Peroxisome Proliferators; D011743:Pyrimidines; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha; D009569:Nitric Oxide; C006253:pirinixic acid; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat