Carbohydrate regulation of hepatic gene expression - Evidence against a role for the upstream stimulatory factor
Carbohydrate regulation of hepatic gene expression - Evidence against a role for the upstream stimulatory factor
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DOI：
10.1074/jbc.272.11.7525
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发表时间：
1997-03-14
影响因子：
4.8
通讯作者：
Towle, HC
中科院分区：
文献类型：
--
作者：
Kaytor, EN;Shih, HM;Towle, HC
以高碳水化合物、低脂肪饮食诱导大鼠肝脏表达L-型丙酮酸激酶(L-PR)和S-14基因。在这两个基因的5‘侧翼区域都定位了一个含有两个CACGTG型E盒的碳水化合物反应元件(CHORE)。这种琐事的性质表明，碱性/螺旋-环-螺旋/亮氨酸拉链蛋白家族的一个成员可能负责调节对碳水化合物的反应。事实上，上游刺激因子(Usf)是一种普遍存在的碱性/螺旋-环-螺旋/亮氨酸拉链蛋白，存在于肝细胞核提取液中，并在体外与L-PK和S-14的家务结合。我们已经进行了实验，以确定USF是否参与了糖介导的L-PH和S-14的调节。为此，在原代肝细胞中表达了能够与内源性USF异源二聚体但不能与DNA结合的显性负性形式的USF。这些形式的表达都不能阻断葡萄糖对S-14或L-PK的诱导。此外，我们已经构建了突变的家务，保留了它们的碳水化合物响应性，但已经失去了与USF结合的能力。综上所述，这些数据表明，USF不是刺激S-14和L-PK表达的碳水化合物反应因子，一个不同的肝脏因素可能对转录反应负责。
Hepatic expression of the genes encoding L-type pyruvate kinase (L-PR) and S-14 is induced in rats upon feeding them a high carbohydrate, low fat diet. A carbohydrate response element (ChoRE) containing two CACGTG-type E boxes has been mapped in the 5'-flanking region of both of these genes. The nature of the ChoRE suggests that a member of the basic/helix-loop-helix/leucine zipper family of proteins may be responsible for mediating the response to carbohydrate. Indeed, the upstream stimulatory factor (USF), a ubiquitous basic/helix-loop-helix/leucine zipper protein, is present in hepatic nuclear extracts and binds to the ChoREs of L-PK and S-14 in vitro. We have conducted experiments to determine whether USF is involved in the carbohydrate-mediated regulation of L-PH and S-14. For this purpose, dominant negative forms of USF that are capable of heterodimerizing with endogenous USF but not of binding to DNA were expressed in primary hepatocytes. Expression of these forms did not block either S-14 Or L-PK induction by glucose. In addition, we have constructed mutant ChoREs that retain their carbohydrate responsiveness but have lost the ability to bind USF. Together, these data suggest that USF is not the carbohydrate-responsive factor that stimulates S-14 and L-PK expression and that a distinct hepatic factor is likely to be responsible for the transcriptional response.