導致脂肪肝之斑馬魚第一型固醇調控序列結合蛋白基因被SREBP1, C/EBP apha, C/EBPbeta, 以及肝毒素thioacetamide活化

Abstract

固醇調控序列結合蛋白(SREBP)是一群與膽固醇脂肪酸的合成有關的轉錄因子，在哺乳類動物中可被分為三種型，分別為SREBP-1a，SREBP-1c與SREBP-2。他們可藉由活化許多的基因如與合成膽固醇有關的HMG CoA合成酶與還原酶、squalene合成酶以及與合成脂肪酸有關的乙醯輔酶A羧化酶、脂肪酸合成酶等來進行膽固醇與脂肪酸的生合成調控。在老鼠實驗模組中，老鼠可藉由過度表現第一型固醇調控序列結合蛋白而產生脂肪肝與有較大肝臟的表現型。在我們的研究中，我們已經選殖到斑馬魚的第一型固醇調控序列結合蛋白 (SREBP1) 全長序列（其中包括3540個鹼基以及1105個氨基酸序列）以及其長度為3006個鹼基的啟動子序列，包含兩個固醇調控序列結合蛋白與一個C/EBP的結合位置。在斑馬魚的第一型固醇調控序列結合蛋白啟動子的活性實驗中，轉錄因子：成熟型之第一型固醇調控序列結合蛋白、C/EBPα 以及C/EBPβ可以活化第一型固醇調控序列結合蛋白啟動子分別約為六倍、三倍與四倍，但是肝細胞核因子1α、1β和1γ則沒有明顯活化。此外，分別將綠色螢光肝臟轉基因斑馬魚以及人類C型肝炎病毒輔蛋白轉殖斑馬分別處理肝毒素TAA三週及一週後，斑馬魚的第一型固醇調控序列結合蛋白的表現會被明顯地誘導起來。

sterol regulatory element binding proteins (SREBPs) are transcription factors involved in fatty acid and cholesterol biosynthesis. Three isoforms: SREBP-1a, SREBP-1c, and SREBP-2 are found in mammals. They can turn on the fatty acid and cholesterol biosynthesis by activating multiple genes like acetyl CoA carboxylase(ACC) and fatty acid synthase(FAS) relating to fatty acid biosynthesis and 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) synthase, HMG CoA reductase, and squalene synthase relating to cholesterol biosynthesis. In mouse model, liver steatosis and enlarged liver by overexpressing SREBP-1 can be observed. In my study, I had cloned the full length zebrafish ( Danio rerio) SREBP1 (3540 bp) cDNA encoding 1105 amino acids and 3Kb promoter of zebrafish SREBP1 gene with two putative SREBP1 responsive elements (SRE) and one CCATT/enhancer binding protein (C/EBP) binding site. From the promoter assay of 3Kb zebrafish SREBP1 promoter, the transcription factors mature SREBP1, C/EBPα and C/EBPβ could activate the expression of SREBP1 gene at about 6, 3 and 4 folds, respectively whereas the hepatocyte nuclear factor 1α(HNF1α), 1β, and 1γ didn’t show significant transactivation activities. In addition to, zebrafish SREBP1 gene can be significantly induced by hepatotoxin thioacetamide (TAA) treatment at 3rd week in adult liver of green-fluorescent liver transgenic line and at 1st week in HCV-core protein transgenic line. Auto-activation of mature SREBP1 to SREBP1 gene in combination with C/EBP