Marcus S L, Miyata K S, Rachubinski R A, Capone J P
Department of Anatomy and Cell Biology, University of Alberta, Edmonton, Canada.
Gene Expr. 1995;4(4-5):227-39.
Peroxisome proliferator-activated receptors (PPARs) are orphan members of the nuclear hormone receptor superfamily. PPARs bind to cognate response elements through heterodimerization with retinoid X receptors (RXRs). Together PPAR/RXR regulate the transcription of genes for which products are involved in lipid homeostasis, cell growth, and differentiation. PPARs are activated by fatty acids and by nongenotoxic rodent hepatocarcinogens called peroxisome proliferators through as of yet undefined signal transduction pathways. In an effort to elucidate the requirements for PPAR function and the pathways of its activation, we expressed mouse PPAR alpha and human RXR alpha in the yeast Saccharomyces cerevisiae. Mouse PPAR alpha and human RXR alpha had little activity individually in yeast; however, when cosynthesized, they were able to synergistically activate transcription via cognate response elements. Transactivation was independent of exogenously added activators of either receptor but was potentiated by the addition of petroselinic acid, a fatty acid shown to activate PPARs in mammalian cells. Similar experiments were carried out in a mutant yeast strain lacking peroxisomes entirely or in a mutant strain deficient for 3-ketoacyl-CoA thiolase, the final enzyme of the peroxisomal beta-oxidation cascade. The findings showed that constitutive transactivation by PPAR/RXR did not require the complete beta-oxidation pathway or intact peroxisomes but required intact peroxisomes for potentiation by exogenously added petroselinic acid. This study demonstrates that at least part of the mammalian peroxisome proliferator-signaling pathway can be faithfully reconstituted in yeast and that activation of PPAR by at least one particular fatty acid requires the integrity of peroxisomes.
过氧化物酶体增殖物激活受体（PPARs）是核激素受体超家族的孤儿成员。PPARs通过与视黄酸X受体（RXRs）异源二聚化结合到同源反应元件上。PPAR/RXR共同调节那些其产物参与脂质稳态、细胞生长和分化的基因的转录。PPARs可被脂肪酸以及一类被称为过氧化物酶体增殖剂的非基因毒性啮齿动物肝癌致癌物通过尚未明确的信号转导途径激活。为了阐明PPAR功能的要求及其激活途径，我们在酿酒酵母中表达了小鼠PPARα和人RXRα。小鼠PPARα和人RXRα在酵母中单独几乎没有活性；然而，当共表达时，它们能够通过同源反应元件协同激活转录。反式激活不依赖于外源添加的任何一种受体的激活剂，但添加岩芹酸可增强这种激活作用，岩芹酸是一种已证实在哺乳动物细胞中可激活PPARs的脂肪酸。在完全缺乏过氧化物酶体的突变酵母菌株或缺乏3-酮酰基辅酶A硫解酶（过氧化物酶体β氧化级联反应的最后一种酶）的突变菌株中进行了类似实验。研究结果表明，PPAR/RXR的组成型反式激活不需要完整的β氧化途径或完整的过氧化物酶体，但外源添加岩芹酸增强激活作用则需要完整的过氧化物酶体。这项研究表明，至少部分哺乳动物过氧化物酶体增殖剂信号通路可以在酵母中如实地重建，并且至少一种特定脂肪酸对PPAR的激活需要过氧化物酶体的完整性。
