Sterols regulate cycling of SREBP cleavage-activating protein (SCAP) between endoplasmic reticulum and Golgi
Sterols regulate cycling of SREBP cleavage-activating protein (SCAP) between endoplasmic reticulum and Golgi
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DOI：
10.1073/pnas.96.20.11235
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发表时间：
1999-09-28
影响因子：
11.1
通讯作者：
Brown, MS
中科院分区：
文献类型：
--
作者：
Nohturfft, A;DeBose-Boyd, RA;Brown, MS
固醇调节元件结合蛋白（SREBP）的蛋白水解裂解受SREBP裂解激活蛋白（SCAP）调节，SCAP与内质网（ER）膜中的SREBP形成复合物。在甾醇耗尽的细胞中，SCAP促进SREBP被Site-1蛋白酶切割，从而启动活性NH 2-末端片段从ER膜的释放，使得它们可以进入细胞核并激活基因表达。在固醇超载的细胞中，SCAP的活性被阻断，SREBP保持与膜结合，并且固醇调节基因的转录下降。在这里，我们提供的证据表明，甾醇类通过抑制ER和高尔基体之间的SCAP循环。我们使用糖苷酶，糖苷酶抑制剂，和糖基化缺陷的突变体细胞系，以证明N-连接的碳水化合物的SCAP修饰的高尔基体酶在甾醇耗尽的细胞。修饰后，SCAP返回ER，如实验所示，高尔基体修饰形式的SCAP在密度梯度上与ER膜共断裂。在固醇超载的细胞中，SCAP的高尔基体修饰不会发生，显然是因为SCAP未能离开ER。当用布雷菲德菌素A处理固醇过载的细胞时，SCAP的高尔基体修饰被恢复，这导致高尔基体酶易位到ER。这些研究表明，甾醇调节SREBP的切割，通过调节SCAP的能力，运输SREBP到后ER室，房子活性位点1蛋白酶。
The proteolytic cleavage of sterol regulatory element-binding proteins (SREBPs) is regulated by SREBP cleavage-activating protein (SCAP), which forms complexes with SREBPs in membranes of the endoplasmic reticulum (ER). In sterol-depleted cells, SCAP facilitates cleavage of SREBPs by Site-1 protease, thereby initiating release of active NH2-terminal fragments from the ER membrane so that they can enter the nucleus and activate gene expression. In sterol-overloaded cells, the activity of SCAP is blocked, SREBPs remain bound to membranes, and transcription of sterol-regulated genes declines. Here, we provide evidence that sterols act by inhibiting the cycling of SCAP between the ER and Golgi. We use glycosidases, glycosidase inhibitors, and a glycosylation-defective mutant cell line to demonstrate that the N-linked carbohydrates of SCAP are modified by Golgi enzymes in sterol-depleted cells. After modification, SCAP returns to the ER, as indicated by experiments that Show that the Golgi-modified forms of SCAP cofractionate with ER membranes on density gradients. In sterol-overloaded cells, the Golgi modifications of SCAP do not occur, apparently because SCAP fails to leave the ER. Golgi modifications of SCAP are restored when sterol overloaded cells are treated with brefeldin A,which causes Golgi enzymes to translocate to the ER. These studies suggest that sterols regulate the cleavage of SREBPs by modulating the ability of SCAP to transport SREBPs to a post-ER compartment that houses active Site-1 protease.