Laboratory of Biochemistry, University of Crete Medical School and Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, Heraklion 71003, Greece.
Laboratory of Biochemistry, University of Crete Medical School and Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, Heraklion 71003, Greece.
Biochim Biophys Acta Gene Regul Mech. 2017 Mar;1860(3):327-336. doi: 10.1016/j.bbagrm.2017.01.007. Epub 2017 Jan 23.
Lipoprotein lipase (LPL) plays a major role in the hydrolysis of triglycerides (TG) from circulating TG-rich lipoproteins. The role of LPL in the liver has been controversial but recent studies in mice with liver LPL overexpression or deficiency have revealed important new roles of the enzyme in glucose and lipid metabolism. The objective of this study was to identify regulatory elements and factors that control the transcription of the human LPL gene in hepatocytes. Deletion analysis of the human LPL promoter revealed that the proximal region which harbors a binding site for the forkhead box transcription factor FOXA2/HNF-3β at position -47/-40 is important for its hepatic cell activity. Silencing of FOXA2 in HepG2 cells reduced the LPL mRNA and protein levels. Direct binding of FOXA2 to the novel binding site was established in vitro and ex vivo. Mutagenesis of the FOXA2 site reduced the basal activity and abolished the FOXA2-mediated transactivation of the LPL promoter. Ιnsulin decreased LPL mRNA levels in HepG2 cells and this was associated with phosphorylation of AKT and nuclear export of FOXA2. In summary, the data of the present study combined with previous findings on the role of FOXA2 in HDL metabolism and gluconeogenesis, suggest that FOXA2 is a key regulator of lipid and glucose homeostasis in the adult liver. Understanding the mechanisms by which FOXA2 exerts its functions in hepatocytes may open the way to novel therapeutic strategies for patients with metabolic diseases such as dyslipidemia, diabetes and the metabolic syndrome.
脂蛋白脂肪酶（LPL）在水解循环中富含甘油三酯（TG）的脂蛋白中的甘油三酯（TG）中起主要作用。LPL 在肝脏中的作用一直存在争议，但最近在肝脏 LPL 过表达或缺乏的小鼠中的研究揭示了该酶在葡萄糖和脂质代谢中的重要新作用。本研究的目的是鉴定控制人 LPL 基因在肝细胞中转录的调节元件和因子。人 LPL 启动子的缺失分析表明，近端区域在位置-47/-40 处含有一个结合叉头框转录因子 FOXA2/HNF-3β的结合位点，对于其肝细胞活性很重要。在 HepG2 细胞中沉默 FOXA2 降低了 LPL mRNA 和蛋白水平。体外和体内实验证实了 FOXA2 与新结合位点的直接结合。FOXA2 位点的突变降低了基础活性并消除了 FOXA2 介导的 LPL 启动子的转录激活。胰岛素降低了 HepG2 细胞中的 LPL mRNA 水平，这与 AKT 的磷酸化和 FOXA2 的核输出有关。总之，本研究的数据结合先前关于 FOXA2 在 HDL 代谢和糖异生中的作用的发现，表明 FOXA2 是成年肝脏中脂质和葡萄糖稳态的关键调节剂。了解 FOXA2 在肝细胞中发挥作用的机制可能为代谢疾病（如血脂异常、糖尿病和代谢综合征）患者开辟新的治疗策略。
