Identification of Genes Activated By Bile Acids

描述（由申请人提供）：我们研究的主要目标是确定法内甾体X受体（FXR）的激活机制，并确定其在调节代谢途径中的作用。为此，我们鉴定了四种人类和小鼠FXR转录本，这些转录本来自一个编码四种不同蛋白质亚型的基因。我们发现了一个四氨基酸基序（MYTG），它位于四个亚型中的两个的DNA结合域附近，极大地改变了我们对这个转录因子的看法；新的和令人兴奋的数据表明，该基序的存在影响某些肝脏和肾上腺基因的转激活。我们最近发现，激活的FXR对小鼠的葡萄糖代谢有显著的影响，并对有毒外源性药物和IPS（脂多糖）的毒性作用产生的急性肝毒性具有高度的保护作用。我们最近也获得了FXR调节许多类固醇基因的证据，这表明FXR在肾上腺皮质中具有功能作用。基于这些数据，我们计划开展机制研究，以阐明FXR在以下方面的作用：1)控制血糖水平和肝脏糖代谢，2)控制血浆和肝脏脂质水平，3)保护肝脏免受对乙酰氨基酚等外源性药物的损伤，4)保护小鼠免受内毒素休克和细菌感染，5)调节肾上腺甾体源性细胞中的靶基因。这些研究将得到FXR转基因和FXR-/-小鼠，肝脏或肠道缺乏FXR的小鼠，以及表达单个FXR亚型的腺病毒的帮助。为了补充这些方法，将进行机制研究来阐明MYTG基序在四个FXR亚型中的两个中的功能。综上所述，这些研究将确定FXR异构体激活转录的新调控机制。此外，这些研究将阐明FXR在葡萄糖、类固醇和药物代谢以及对内毒素的抗性中的作用。

DESCRIPTION (provided by applicant): The major goals of our research have been to identify the mechanisms of activation of the farnesoid X receptor (FXR) and to define its role in regulating metabolic pathways. To this end, we have identified four human and murine FXR transcripts derived from a single gene that encode four different protein isoforms. Our identification of a four amino acid motif (MYTG), located immediately adjacent to the DNA binding domain of two of the four isoforms, dramatically altered our thinking about this transcription factor; new and exciting data suggest that the presence of this motif affects transactivation of certain hepatic and adrenal genes. We have recently discovered that activated FXR has a pronounced effect on glucose metabolism in mice and is highly protective against the acute hepatoxicity produced by toxic xenobiotics and from the toxic effects of IPS (lipopolysaccharide). We have also recently obtained evidence that FXR regulates a number of steroidogenic genes, suggesting a functional role for FXR in the adrenal cortex. Based on these data, generated during the current grant period, we propose to conduct mechanistic studies to elucidate the roles of FXR in i) the control of plasma glucose levels and hepatic glucose metabolism, ii) the control of plasma and hepatic lipid levels, iii) protection of the liver from damage induced by xenobiotics such as acetaminophen, iv) protecting mice from endotoxin shock and bacterial infection and v) the regulation of target genes in adrenal steroidogenic cells. These studies will be aided by the availability of FXR transgenic and FXR-/- mice, and mice lacking FXR in the liver or intestine, and adenovirus expressing individual FXR isoforms. To complement these approaches, mechanistic studies will be conducted to elucidate the function of the MYTG motif present in two of the four FXR isoforms. Taken together, these studies will identify novel regulatory mechanisms by which FXR isoforms activate transcription. In addition, these studies will elucidate the role of FXR in glucose, steroid and drug metabolism and in resistance to endotoxin.