Osada S, Tsukamoto T, Takiguchi M, Mori M, Osumi T
Department of Life Science, Himeji Institute of Technology, Kamigori, Hyogo, Japan.
Genes Cells. 1997 May;2(5):315-27. doi: 10.1046/j.1365-2443.1997.1220319.x.
Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone receptor superfamily and regulate many genes of the proteins involved in lipid metabolism, including peroxisomal acyl-CoA oxidase (AOX). Through heterodimerization with retinoid X receptors (RXRs), PPAR was believed to recognize the sequence elements consisting of two directly repeating 6-bp half-sites spaced by one nucleotide (DR-1), located in the regulatory regions of these genes.
Employing the peroxisome proliferator-responsive enhancer of the rat AOX gene, we analysed the minimal sequence requirements for enhancer activity and PPARalpha/RXRalpha binding. We found that the sequence just downstream of the DR-1 motif is indispensable for both functions. By a direct selection procedure of high-affinity binding sites from a random sequence pool, we identified a consensus sequence at the four positions next to DR-1. We also suggest that PPARalpha binds to the downstream half-site, whereas RXRalpha binds to the upstream half-site of the AOX DR-1.
An extended half-site of 10-bp, but not a simple 6-bp half-site, is required for the PPARalpha binding, upon heterodimer formation with RXRalpha. The binding polarity of PPARalpha/RXRalpha seems to be opposite to that of other RXR-involving heterodimers.
过氧化物酶体增殖物激活受体（PPARs）属于核激素受体超家族，可调节许多参与脂质代谢的蛋白质基因，包括过氧化物酶体酰基辅酶A氧化酶（AOX）。人们认为，PPAR通过与视黄酸X受体（RXRs）异源二聚化，识别位于这些基因调控区域的由两个直接重复的6碱基对半位点组成、中间间隔一个核苷酸的序列元件（DR-1）。
利用大鼠AOX基因的过氧化物酶体增殖物反应性增强子，我们分析了增强子活性和PPARα/RXRα结合的最小序列要求。我们发现DR-1基序下游的序列对于这两种功能都是必不可少的。通过从随机序列库中直接筛选高亲和力结合位点，我们在DR-1旁边的四个位置确定了一个共有序列。我们还提出，PPARα结合下游半位点，而RXRα结合AOX DR-1的上游半位点。
与RXRα形成异源二聚体时，PPARα结合需要一个10碱基对的扩展半位点，而不是一个简单的6碱基对半位点。PPARα/RXRα的结合极性似乎与其他涉及RXR的异源二聚体相反。
