Peroxisome proliferator-activated receptor gamma suppresses proximal alpha1(I) collagen promoter via inhibition of p300-facilitated NF-I binding to DNA in hepatic stellate cells.
Depletion of peroxisome proliferator-activated receptor gamma (PPARgamma) represents one of the key molecular changes that underlie transdifferentiation (activation) of hepatic stellate cells in the genesis of liver fibrosis (Miyahara, T., Schrum, L., Rippe, R., Xiong, S., Yee, H. F., Jr., Motomura, K., Anania, F. A., Willson, T. M., and Tsukamoto, H. (2000) J. Biol. Chem. 275, 35715-35722; Hazra, S., Xiong, S., Wang, J., Rippe, R. A., Krishna, V., Chatterjee, K., and Tsukamoto, H. (2004) J. Biol. Chem. 279, 11392-11401). In support of this notion, ectopic expression of PPARgamma suppresses hepatic stellate cells activation markers, most notably expression of alpha1(I) procollagen. However, the mechanisms underlying this antifibrotic effect are largely unknown. The present study utilized deletion-reporter gene constructs of proximal 2.2-kb alpha1(I) procollagen promoter to demonstrate that a region proximal to -133 bp is where PPARgamma exerts its inhibitory effect. Within this region, two DNase footprints with Sp1 and reverse CCAAT box sites exist. NF-I, but not CCAAT DNA-binding factor/NF-Y, binds to the proximal CCAAT box in hepatic stellate cells. A mutation of this site almost completely abrogates the promoter activity. NF-I mildly but independently stimulates the promoter activity and synergistically promotes Sp1-induced activity. PPARgamma inhibits NF-I binding to the most proximal footprint (-97/-85 bp) and inhibits its transactivity. The former effect is mediated by the ability of PPARgamma to inhibit p300-facilitated NF-I binding to DNA as demonstrated by chromatin immunoprecipitation assay.
Yavrom
Sharon
S
Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033-9141, USA.
Chen
Li
L
Xiong
Shigang
S
Wang
Jiaohong
J
Rippe
Richard A
RA
Tsukamoto
Hidekazu
H
D000818:Animals; D001483:Base Sequence; D024042:Collagen Type I / Q000235:genetics*; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D018983:DNA Footprinting; D003851:Deoxyribonucleases; D050881:E1A-Associated p300 Protein / Q000502:physiology*; D024202:Electrophoretic Mobility Shift Assay; D017353:Gene Deletion; D015870:Gene Expression / Q000187:drug effects; D049452:Green Fluorescent Proteins / Q000235:genetics; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D051839:NFI Transcription Factors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047495:PPAR gamma / Q000235:genetics / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D011993:Recombinant Fusion Proteins; D016329:Sp1 Transcription Factor / Q000378:metabolism; D014162:Transfection
D024042:Collagen Type I; D051839:NFI Transcription Factors; D047495:PPAR gamma; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D016329:Sp1 Transcription Factor; D049452:Green Fluorescent Proteins; D004247:DNA; D050881:E1A-Associated p300 Protein; C494362:Ep300 protein, rat; D003851:Deoxyribonucleases