Function and Regulation of SLC13A5 in the Liver

项目摘要 柠檬酸盐是一种关键的能量传感器，在碳水化合物代谢、能量生产和 组蛋白乙酰化。细胞内柠檬酸的水平通过生物合成和平衡受到严格控制。 运输。在肝脏中，溶质载体家族13成员5(SLC13A5)是一种钠偶联柠檬酸转运蛋白， 是将柠檬酸盐从循环输入到肝细胞所必需的，这一过程可以被 异种生物和内生刺激。最近的研究表明，SLC13A5的表达在 肥胖的非酒精性脂肪性肝病(NAFLD)患者，高脂饮食(HFD)治疗的恒河猴，以及 异种生物处理的人和大鼠肝细胞，提示SLC13A5的上调可能是 代谢紊乱。相反，SLC13A5的缺失可保护小鼠免受HFD诱导的肝脏脂肪变性的影响 黑腹葡萄球菌中SLC13A5同源基因的突变可以延长寿命。然而，尽管出现了 SLC13A5在能量平衡中的重要性，SLC13A5基因参与能量平衡的机制(S) 转录调控及临床用药是否干扰该转运蛋白的表达 很好的特点。此外，SLC13A5对肝功能的影响是否超出了脂质平衡，这在很大程度上是 未知。这项建议的总体目标是了解控制肝脏的分子机制。 目的：探讨SLC13A5基因在人肝细胞增殖中的作用。为此， 我们已经证明：1)构成雄烷受体(CAR)和孕烷的典型激活物 X受体(PXR)强烈诱导人SLC13A5的表达；2)敲除SLC13A5可减弱 3)SLC13A5的表达与肝细胞癌的发生呈负相关。 激活AMPK信号。根据这些初步结果，我们假设CAR和PXR是关键 SLC13A5在肝脏中诱导性表达的调节，以及SLC13A5的营养调节作用 通过调节AMPK/mTOR信号通路改变肝癌细胞的增殖。这个中心 假设将在以下特定目标中进行检验：目标1.确定CAR和PXR在异种生物中的作用- 诱导表达SLC13A5；目的2.阐明CAR和PXR介导的机制(S) 目的3.检测SLC13A5对肝癌细胞增殖的影响。结果是 有望为SLC13A5在肝脏中的转录调控提供基本的新知识， 并阐明SLC13A5在能量代谢与肝癌进展过程中的重要作用。

Project Summary Citrate is a key energy sensor that plays a central role in carbohydrate metabolism, energy production, and histone acetylation. The intracellular level of citrate is tightly controlled through a balance of biosynthesis and transport. In the liver, the solute carrier family 13 member 5 (SLC13A5), a sodium-coupled citrate transporter, is essential for the import of citrate from the circulation to hepatocytes, a process that can be perturbed by both xenobiotic and endobiotic stimuli. Recent studies have shown that expression of SLC13A5 was increased in obese, non-alcoholic fatty liver disease (NAFLD) patients, high-fat diet (HFD)-treated rhesus monkeys, and in xenobiotic-treated human and rat hepatocytes, suggesting upregulation of SLC13A5 can be a risk factor for metabolic disorders. In contrast, deletion of SLC13A5 protects mice from HFD-induced hepatic steatosis and mutations of the SLC13A5 ortholog in D. melanogaster promote longevity. However, despite the emerging importance of SLC13A5 in energy homeostasis, the mechanism(s) by which the SLC13A5 gene is transcriptionally regulated and whether clinically used drugs disturb the expression of this transporter are not well characterized. Moreover, whether SLC13A5 affects hepatic functions beyond lipid homeostasis is largely unknown. The overall objective of this proposal is to understand the molecular mechanisms governing hepatic SLC13A5 gene expression and to delineate the role of SLC13A5 in human liver cell proliferation. To this end, we have shown that 1) prototypical activators of the constitutive androstane receptor (CAR) and the pregnane X receptor (PXR) robustly induce expression of human SLC13A5; 2) knockdown of SLC13A5 attenuates the proliferation of hepatocellular carcinoma cells; and 3) expression of SLC13A5 is inversely correlated with the activation of AMPK signaling. Building on these preliminary results, we hypothesize that CAR and PXR are key regulators of the inductive expression of SLC13A5 in the liver, and SLC13A5 functions as a nutrient regulator altering the proliferation of hepatoma cells by modulating AMPK/mTOR signaling pathways. This central hypothesis will be tested in the following specific aims: Aim 1. Define the role of CAR and PXR in xenobiotic- induced expression of SLC13A5; Aim 2. Elucidate the mechanism(s) underlying CAR- and PXR-mediated induction of SLC13A5; Aim 3. Determine the effects of SLC13A5 on hepatoma cell proliferation. The outcomes are expected to provide fundamental novel knowledge on the transcriptional regulation of SLC13A5 in the liver, and to delineate a crucial role of SLC13A5 in bridging energy metabolism with liver cancer progression.