Inhibition of cholesterol biosynthesis by 25-hydroxycholesterol is independent of OSBP
Inhibition of cholesterol biosynthesis by 25-hydroxycholesterol is independent of OSBP
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DOI：
10.1111/j.1365-2443.2005.00879.x
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发表时间：
2005-08-01
期刊：
影响因子：
2.1
通讯作者：
Arai, H
中科院分区：
文献类型：
--
作者：
Nishimura, T;Inoue, T;Arai, H
25-羟基胆固醇（25-HC）是培养细胞中胆固醇合成基因转录的有效抑制剂。已从组织胞质溶胶中鉴定出一种25-HC的高亲和力结合蛋白，即氧固醇结合蛋白（OSBP）。在细胞培养物中加入25-HC后，OSBP从胞质溶胶易位至高尔基体膜，并被认为通过与高尔基体结合介导25-HC对胆固醇代谢的作用。然而，缺乏直接证据来证明这一假设。在这项研究中，我们敲低OSBP的表达，通过使用特异性的OSBP的双链siRNA检查OSBP和25-HC诱导的胆固醇合成基因转录抑制之间的关系。我们发现，降低OSBP表达的90%，并没有影响25-HC诱导的3-羟基-3-甲基戊二酰辅酶A（HMG-CoA）还原酶和角鲨烯环氧酶的转录抑制在任何程度上。外源性溶血磷脂酰胆碱（LPC），这是已知的，导致流出的细胞胆固醇进入培养基中，并增加胆固醇合成，被发现拯救25-HC诱导的下调固醇调节基因，而LPC不影响25-HC诱导的协会OSBP与高尔基体。这些结果表明，25-HC对胆固醇生物合成基因的抑制是OSBP非依赖性的。
25-hydroxycholesterol (25-HC) is a potent suppressor of cholesterol synthesis gene transcription in cultured cells. A high affinity binding protein for 25-HC, oxysterol-binding protein (OSBP), has been identified from tissue cytosol. OSBP translocates from the cytosol to the Golgi apparatus membranes after addition of 25-HC to cell cultures and is thought to mediate 25-HC action on cholesterol metabolism through association to the Golgi apparatus. However, direct evidence to prove this hypothesis was lacking. In this study, we knocked down expression of OSBP by using duplex siRNAs specific for OSBP to examine the relationship between OSBP and 25-HC-induced inhibition of cholesterol synthesis gene transcription. We found that decreasing OSBP expression by similar to 90% did not affect 25-HC-induced inhibition of transcription of 3-hydoxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and squalene epoxidase to any extent. Exogenous lysophosphatidylcholine (LPC), which is known to cause the efflux of cellular cholesterol into the medium and to increase cholesterol synthesis, was found to rescue the 25-HC-induced down-regulation of sterol regulated genes, while LPC did not affect 25-HC-induced association of OSBP with the Golgi apparatus. These results suggest that inhibition of cholesterol biosynthesis genes by 25-HC is OSBP-independent.