Li Jun, Luo Jun, Zhu Jiangjiang, Sun Yuting, Yao Dawei, Shi Hengbo, Wang Wei
Shaanxi Key Laboratory of Molecular Biology for Agriculture, College of Animal Science and Technology, Northwest A&F University, Yangling 712100 Shaanxi, PR China.
Shaanxi Key Laboratory of Molecular Biology for Agriculture, College of Animal Science and Technology, Northwest A&F University, Yangling 712100 Shaanxi, PR China.
Comp Biochem Physiol B Biochem Mol Biol. 2015 Jun;184:44-51. doi: 10.1016/j.cbpb.2015.02.005. Epub 2015 Mar 1.
Fatty acid synthase (FASN) is a central enzyme of milk fat synthesis in the ruminant mammary gland. However, the mechanisms regulating goat FASN transcription remain elusive. The objective of this study was to investigate the mechanisms by which liver X receptor α (LXRα) regulates the FASN promoter in goat mammary epithelial cells (GMECs). In this study, T0901317 (T09), an agonist for LXRα, significantly enhanced the mRNA expression and promoter activity of FASN. Cloning of the dairy goat FASN promoter revealed the presence of one LXR response element (LXRE) and two sterol regulatory elements (SREs). Deletion or mutation of the FASN promoter LXRE reduced, but did not eliminate the transcriptional response of FASN to T09. While the LXRE and the SREs were both disrupted, basal transcription was severely reduced and there was no response to T09 treatment. This suggested that a complete response required one LXRE and two SREs. Knockdown of LXRα by siRNA did not alter the basal or T09-induced transcriptional activity of FASN. However, when sterol regulatory binding protein 1 (SREBP1) was knocked down, T09 significantly increased FASN transcription by wild-type GMECs, but had no effect on cells with LXRE-mutant promoters. The results suggested that LXR regulates FASN promoter activity through direct interaction with the LXRE as well as through increasing SREBP1 abundance. The present study provides insight into the transcriptional regulatory mechanisms controlling de novo fatty acid synthesis in GMECs.
脂肪酸合酶（FASN）是反刍动物乳腺中乳脂肪合成的关键酶。然而，调节山羊FASN转录的机制仍不清楚。本研究的目的是探讨肝X受体α（LXRα）调控山羊乳腺上皮细胞（GMECs）中FASN启动子的机制。在本研究中，LXRα激动剂T0901317（T09）显著增强了FASN的mRNA表达和启动子活性。奶山羊FASN启动子的克隆显示存在一个LXR反应元件（LXRE）和两个固醇调节元件（SREs）。FASN启动子LXRE的缺失或突变降低了，但并未消除FASN对T09的转录反应。当LXRE和SREs均被破坏时，基础转录严重降低，且对T09处理无反应。这表明完整的反应需要一个LXRE和两个SREs。用siRNA敲低LXRα并未改变FASN的基础或T09诱导的转录活性。然而，当固醇调节结合蛋白1（SREBP1）被敲低时，T09显著增加了野生型GMECs中FASN的转录，但对具有LXRE突变启动子的细胞无影响。结果表明，LXR通过与LXRE直接相互作用以及增加SREBP1丰度来调节FASN启动子活性。本研究为深入了解GMECs中从头脂肪酸合成的转录调控机制提供了依据。
