DNA binding-independent induction of IkappaBalpha gene transcription by PPARalpha.
PPARs are ligand-activated transcription factors that regulate energy homeostasis. In addition, PPARs furthermore control the inflammatory response by antagonizing the nuclear factor-kappaB (NF-kappaB) signaling pathway. We recently demonstrated that PPARalpha activators increase IkappaBalpha mRNA and protein levels in human aortic smooth muscle cells. Here, we studied the molecular mechanisms by which PPARalpha controls IkappaBalpha expression. Using transient transfection assays, it is demonstrated that PPARalpha potentiates p65-stimulated IkappaBalpha transcription in a ligand-dependent manner. Site-directed mutagenesis experiments revealed that PPARalpha activation of IkappaBalpha transcription requires the NF-kappaB and Sp1 sites within IkappaBalpha promoter. Chromatin immunoprecipitation assays demonstrate that PPARalpha activation enhances the occupancy of the NF-kappaB response element in IkappaBalpha promoter in vivo. Overexpression of the oncoprotein E1A failed to inhibit PPARalpha-mediated IkappaBalpha promoter induction, suggesting that cAMP response element binding protein-binding protein/p300 is not involved in this mechanism. By contrast, a dominant-negative form of VDR-interacting protein 205 (DRIP205) comprising its two LXXLL motifs completely abolished PPARalpha ligand-mediated activation. Furthermore, cotransfection of increasing amounts of DRIP205 relieved this inhibition, suggesting that PPARalpha requires DRIP205 to regulate IkappaBalpha promoter activity. By contrast, DRIP205 is not involved in PPARalpha-mediated NF-kappaB transcriptional repression. Taken together, these data provide a molecular basis for PPARalpha-mediated induction of IkappaBalpha and demonstrate, for the first time, that PPARalpha may positively regulate gene transcription in the absence of functional PPAR response elements.
Delerive
Philippe
P
Institut National de la Santé et de la Recherche Médicale U.545, Département d'Athérosclérose, Institut Pasteur de Lille, 59019 Lille, France.
De Bosscher
Karolien
K
Vanden Berghe
Wim
W
Fruchart
Jean-Charles
JC
Haegeman
Guy
G
Staels
Bart
B
D000818:Animals; D001011:Aorta; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000494:pharmacology; D017362:Cyclic AMP Response Element-Binding Protein / Q000502:physiology; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics*; D004357:Drug Synergism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D020672:I-kappa B Proteins; D007163:Immunosorbent Techniques; D056913:Mediator Complex Subunit 1; D009131:Muscle, Smooth, Vascular / Q000737:chemistry; D016297:Mutagenesis, Site-Directed; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000235:genetics; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D020218:Response Elements; D051996:Transcription Factor RelA; D014157:Transcription Factors / Q000378:metabolism* / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D002352:Carrier Proteins; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; C538855:MED1 protein, human; D056913:Mediator Complex Subunit 1; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D051996:Transcription Factor RelA; D014157:Transcription Factors; D000072000:NF-KappaB Inhibitor alpha; D004247:DNA