Sphingomyelin depletion in cultured cells blocks proteolysis of sterol regulatory element binding proteins at site 1.
Sphingomyelin depletion in cultured cells blocks proteolysis of sterol regulatory element binding proteins at site 1.
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培养细胞中鞘磷脂的消耗会阻止位点 1 处甾醇调节元件结合蛋白的蛋白水解。
DOI：
10.1073/pnas.94.21.11179
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发表时间：
1997
影响因子：
11.1
通讯作者：
Goldstein,JL
中科院分区：
文献类型：
--
作者：
Scheek,S;Brown,MS;Goldstein,JL
目前的研究探讨了哺乳动物细胞鞘磷脂含量调节胆固醇合成酶基因转录的机制。其他人先前的研究已经表明，通过用中性鞘磷脂酶处理来消耗鞘磷脂导致一部分细胞胆固醇从质膜转移到内质网，在内质网中它扩大了一个调节池，导致胆固醇合成的下调和胆固醇酯化的上调。在这里，我们表明，鞘磷脂酶处理培养的中国仓鼠卵巢细胞，防止固醇调节元件结合蛋白-2（SREBP-2），一种膜结合的转录因子，参与胆固醇的生物合成和摄取的几个基因的转录所需的核进入。由于鞘磷脂酶处理抑制SREBP-2在位点1的蛋白水解切割，从而阻止活性NH 2末端片段从细胞膜释放，因此细胞核进入被阻断。因此，鞘磷脂酶处理模拟了当将外源固醇添加到细胞中时发生的对SREBP加工的抑制作用。鞘磷脂酶治疗没有阻止网站1蛋白水解SREBP-2在25-RA细胞，中国仓鼠卵巢细胞系，是抵抗抑制作用的甾醇，由于激活点突变的基因编码SREBP裂解激活蛋白。在25-RA细胞中，鞘磷脂酶处理也未能下调3-羟基-3-甲基戊二酰CoA合酶的mRNA，这是一种胆固醇生物合成酶，其转录依赖于SREBP的切割。与以前的数据一起考虑，目前的结果表明，细胞通过调节SREBP的蛋白水解裂解来调节胆固醇和鞘磷脂含量之间的平衡。
The current studies explore the mechanism by which the sphingomyelin content of mammalian cells regulates transcription of genes encoding enzymes of cholesterol synthesis. Previous studies by others have shown that depletion of sphingomyelin by treatment with neutral sphingomyelinase causes a fraction of cellular cholesterol to translocate from the plasma membrane to the endoplasmic reticulum where it expands a regulatory pool that leads to down-regulation of cholesterol synthesis and up-regulation of cholesterol esterification. Here we show that sphingomyelinase treatment of cultured Chinese hamster ovary cells prevents the nuclear entry of sterol regulatory element binding protein-2 (SREBP-2), a membrane-bound transcription factor required for transcription of several genes involved in the biosynthesis and uptake of cholesterol. Nuclear entry is blocked because sphingomyelinase treatment inhibits the proteolytic cleavage of SREBP-2 at site 1, thereby preventing release of the active NH2-terminal fragments from cell membranes. Sphingomyelinase treatment thus mimics the inhibitory effect on SREBP processing that occurs when exogenous sterols are added to cells. Sphingomyelinase treatment did not block site 1 proteolysis of SREBP-2 in 25-RA cells, a line of Chinese hamster ovary cells that is resistant to the suppressive effects of sterols, owing to an activating point mutation in the gene encoding SREBP cleavage-activating protein. In 25-RA cells, sphingomyelinase treatment also failed to down-regulate the mRNA for 3-hydroxy-3-methylglutaryl CoA synthase, a cholesterol biosynthetic enzyme whose transcription depends on the cleavage of SREBPs. Considered together with previous data, the current results indicate that cells regulate the balance between cholesterol and sphingomyelin content by regulating the proteolytic cleavage of SREBPs.