Cheema S K, Agellon L B
Medical Research Council Group on Molecular and Cell Biology of Lipids and the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
J Biol Chem. 2000 Apr 28;275(17):12530-6. doi: 10.1074/jbc.275.17.12530.
We determined if fatty acids can regulate the murine Cyp7a1 and human CYP7A1 gene promoters via peroxisome proliferator-activated receptor alpha (PPARalpha)/9-cis-retinoic acid receptor alpha (RXRalpha). In transfected cells, the murine Cyp7a1 gene promoter displayed markedly lower basal activity, but greater sensitivity to fatty acid- or WY 14,643-activated PPARalpha/RXRalpha when compared with the human CYP7A1 gene promoter. PPARalpha/RXRalpha can bind to a site (Site II) located within the region at nucleotides -158 to -132 of both promoters. Mutagenesis of the human CYP7A1 Site II element abolished the response to activated PPARalpha/RXRalpha. The murine Cyp7a1 gene promoter contains an additional PPARalpha/RXRalpha-binding site (Site I) located within nucleotides -72 to -57. Replacement of a single residue in human CYP7A1 Site I with that found in the murine Cyp7a1 Site I sequence enabled PPARalpha/RXRalpha binding, and this mutation resulted in reduced basal activity, but substantially improved the response to activated PPARalpha/RXRalpha in transfected cells. We conclude that fatty acids can regulate the cyp7a gene promoter via PPARalpha/RXRalpha. The differential response of the murine Cyp7a1 and human CYP7A1 gene promoters to PPARalpha activators is attributable to the additional PPARalpha/RXRalpha-binding site in the murine Cyp7a1 gene promoter.
我们确定了脂肪酸是否能通过过氧化物酶体增殖物激活受体α（PPARα）/9-顺式视黄酸受体α（RXRα）调节小鼠Cyp7a1和人类CYP7A1基因启动子。在转染细胞中，与人类CYP7A1基因启动子相比，小鼠Cyp7a1基因启动子的基础活性明显较低，但对脂肪酸或WY 14,643激活的PPARα/RXRα更敏感。PPARα/RXRα可与位于两个启动子核苷酸-158至-132区域内的一个位点（位点II）结合。人类CYP7A1位点II元件的诱变消除了对激活的PPARα/RXRα的反应。小鼠Cyp7a1基因启动子包含另一个位于核苷酸-72至-57内的PPARα/RXRα结合位点（位点I）。用人CYP7A1位点I中的一个单残基替换小鼠Cyp7a1位点I序列中的残基可实现PPARα/RXRα结合，这种突变导致基础活性降低，但在转染细胞中显著改善了对激活的PPARα/RXRα的反应。我们得出结论，脂肪酸可通过PPARα/RXRα调节cyp7a基因启动子。小鼠Cyp7a1和人类CYP7A1基因启动子对PPARα激活剂的差异反应归因于小鼠Cyp7a1基因启动子中额外的PPARα/RXRα结合位点。
