Peroxisome proliferator-activated receptor α (PPARα) turnover by the ubiquitin-proteasome system controls the ligand-induced expression level of its target genes
Peroxisome proliferator-activated receptor α (PPARα) turnover by the ubiquitin-proteasome system controls the ligand-induced expression level of its target genes
复制标题
DOI：
10.1074/jbc.m110598200
复制
发表时间：
2002-10-04
影响因子：
4.8
通讯作者：
Glineur, C
中科院分区：
文献类型：
--
作者：
Blanquart, C;Barbier, O;Glineur, C
过氧化物酶体增殖物激活受体α（PPARalpha）是属于核受体家族的配体激活的转录因子。PPARalpha参与脂质和葡萄糖代谢的调节以及炎症反应的控制。近年来研究表明，许多核受体通过泛素-蛋白酶体途径被降解。由于PPARa表现出昼夜表达节律，并且由于PPARa在某些病理生理条件下如急性期炎症反应下被快速调节，我们假设PPARa蛋白水平必须处于严格控制之下。在这里，我们研究了控制PPARalpha蛋白水平的机制及其对PPARalpha靶基因转录控制的影响。使用脉冲追踪实验，它表明，PPARalpha是一种短寿命的蛋白质，并添加其配体稳定这种核受体。通过瞬时共转染实验，使用表达载体的PPARalpha和血凝素标记的泛素，它表明，PPARalpha蛋白是泛素化的，它的配体减少这种核受体的泛素化，从而提供了一种机制，在脉冲追踪实验中观察到的配体依赖性稳定。此外，用选择性蛋白酶体抑制剂MG 132处理，增加了泛素化PPARalpha的水平，并抑制其在转染细胞中的降解。此外，MG 132处理增强HepG 2细胞中内源性PPARalpha的水平。最后，瞬时转染和定量逆转录-PCR显示，抑制PPARalpha降解增加了其转录激活和靶基因如apoA-II和脂肪酸转运蛋白（FATP）的表达。综上所述，这些数据表明，PPARalpha降解的泛素-蛋白酶体系统中的配体依赖性的方式。其降解的调节提供了这种核受体的转录活性的新的调节机制。
Peroxisome proliferator activated-receptor alpha (PPARalpha) is a ligand-activated transcription factor belonging to the nuclear receptor family. PPARalpha is implicated in the regulation of lipid and glucose metabolism and in the control of inflammatory response. Recently, it has been demonstrated that a number of nuclear receptors are degraded by the ubiquitin-proteasome pathway. Since PPARa exhibits a circadian expression rhythm and since PPARa is rapidly regulated under certain pathophysiological conditions such as the acute phase inflammatory response, we hypothesized that PPARalpha protein levels must be under tight control. Here, we studied the mechanisms controlling PPARalpha protein levels and their consequences on the transcriptional control of PPARalpha target genes. Using pulse-chase experiments, it is shown that PPARalpha is a short-lived protein and that addition of its ligands stabilizes this nuclear receptor. By transient cotransfection experiments using expression vectors for PPARalpha and hemagglutinin-tagged ubiquitin, it is demonstrated that PPARalpha protein is ubiquitinated and that its ligands decrease the ubiquitination of this nuclear receptor, thus providing a mechanism for the ligand-dependent stabilization observed in pulse-chase experiments. In addition, treatment with MG132, a selective proteasome inhibitor, increases the level of ubiquitinated PPARalpha and inhibits its degradation in transfected cells. Furthermore, MG132 treatment enhances the level of endogenous PPARalpha in HepG2 cells. Finally, transient transfection and quantitative reverse transcription-PCR show that inhibition of PPARalpha degradation increases its transcriptional activation and expression of target genes such as apoA-II and fatty acid transport protein (FATP). Taken together, these data demonstrate that PPARalpha is degraded by the ubiquitin-proteasome system in a ligand-dependent manner. Regulation of its degradation provides a novel regulatory mechanism of transcriptional activity of this nuclear receptor.