Sterol upregulation of human CETP expression in vitro and in transgenic mice by an LXR element
Sterol upregulation of human CETP expression in vitro and in transgenic mice by an LXR element
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DOI：
10.1172/jci8573
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发表时间：
2000-02-01
影响因子：
15.9
通讯作者：
Tall, AR
中科院分区：
文献类型：
--
作者：
Luo, Y;Tall, AR
胆固醇酯转移蛋白（CETP）促进HDL胆固醇酯从血浆转移到肝脏。表达人CETP的转基因小鼠，受其天然侧翼区控制，增加该基因在高胆固醇血症中的表达。我们在分化的3 T3-L1脂肪细胞中建立了CETP启动子-荧光素酶报告基因测定，以定位甾醇上调元件。启动子诱变表明，由4个核苷酸（DR 4元件，-384至-339）分开的核受体结合序列的直接重复是导致这种活性的原因。使用携带正常或突变启动子序列的小鼠，我们证实了该元件对膳食固醇基因诱导的重要性。使用CETP DR 4元件和脂肪细胞核提取物鉴定含有LXR/RXR的凝胶阻滞复合物。LXR α/RXR α和LXR β/RXR α均通过其DR 4元件以甾醇响应方式反式激活CETP启动子。因此，CETP基因的正性固醇应答是由LXR激活的核受体结合位点介导的。Cyp 7a是肝脏中胆固醇转化为胆汁酸的限速酶，也受到LXR α的调节，这表明这类核受体协调肝脏中HDL胆固醇酯催化剂和胆汁酸合成的调节。
The cholesterol ester transfer protein (CETP) facilitates the transfer of HDL cholesterol esters from plasma to the liver. Transgenic mice expressing human CETP, controlled by its natural flanking region, increase expression of this gene in response to hypercholesterolemia. We established a CETP promoter-luciferase reporter assay in differentiated 3T3-L1 adipocytes to map the sterol upregulatory element. Promoter mutagenesis suggested that a direct repeat of a nuclear receptor binding sequence separated by 4 nucleotides (DR4 element, -384 to -339) was responsible for this activity. Using mice carrying normal or mutated promoter sequences, we confirmed the importance of this element for gene induction by dietary sterol. A gel retardation complex containing LXR/RXR was identified using the CETP DR4 element and adipocyte nuclear extracts. Both LXR alpha/RXR alpha and LXR beta/RXR alpha transactivated the CETP promoter via its DR4 element in a sterol-responsive fashion. Thus, the positive sterol response of the CETP gene is mediated by a nuclear receptor binding site that is activated by LXRs. That Cyp7a, the rate-limiting enzyme for conversion of cholesterol into bile acids in the liver, is also regulated by LXR alpha suggests that this class of nuclear receptor coordinates the regulation of HDL cholesterol ester catabolism and bile acid synthesis in the liver.