Sterols regulate processing of carbohydrate chains of wild-type SREBP cleavage-activating protein (SCAP), but not sterol-resistant mutants Y298C or D443N.
Sterols regulate processing of carbohydrate chains of wild-type SREBP cleavage-activating protein (SCAP), but not sterol-resistant mutants Y298C or D443N.
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DOI：
10.1073/pnas.95.22.12848
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发表时间：
1998-10
影响因子：
11.1
通讯作者：
A. Nohturfft;Michael S. Brown;Joseph L. Goldstein
中科院分区：
文献类型：
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作者：
A. Nohturfft;Michael S. Brown;Joseph L. Goldstein
SREBP裂解激活蛋白（SCAP）是一种膜结合糖蛋白，调节固醇调节元件结合蛋白（SREBP）的蛋白水解激活，SREBP是控制动物细胞中脂质合成的膜结合转录因子。SCAP刺激的蛋白水解从内质网膜释放SREBP的活性片段，并允许它们进入细胞核，在那里它们激活转录。如25-羟基胆固醇的硬脂酸酯SCAP，抑制SREBP蛋白水解和关闭胆固醇合成。我们在这里报告的分离中国仓鼠卵巢细胞与点突变SCAP（Y298 C），使蛋白质抵抗抑制25-羟基胆固醇。与先前描述的D443 N突变一样，Y298 C突变发生在推定的固醇敏感结构域内，其是SCAP的多位膜附着区的一部分。表达SCAP（Y298 C）的细胞在25-羟基胆固醇存在下继续加工SREBP，因此它们抵抗这种固醇的杀伤。在野生型中国仓鼠卵巢细胞中，当细胞在含有25-羟基胆固醇的培养基中生长时，SCAP的N-连接糖链大多处于糖苷内切酶H-敏感的形式。相反，当细胞生长在甾醇耗尽的培养基中，这些链转化为糖苷内切酶H-抗性形式。25-羟基胆固醇在表达SCAP（D443 N）或SCAP（Y298 C）的细胞中几乎没有影响。这种受调控的碳水化合物加工与SCAP调控的SREBP蛋白水解之间的关系仍有待探讨。
SREBP cleavage activating protein (SCAP), a membrane-bound glycoprotein, regulates the proteolytic activation of sterol regulatory element binding proteins (SREBPs), which are membrane-bound transcription factors that control lipid synthesis in animal cells. SCAP-stimulated proteolysis releases active fragments of SREBPs from membranes of the endoplasmic reticulum and allows them to enter the nucleus where they activate transcription. Sterols such as 25-hydroxycholesterol inactivate SCAP, suppressing SREBP proteolysis and turning off cholesterol synthesis. We here report the isolation of Chinese hamster ovary cells with a point mutation in SCAP (Y298C) that renders the protein resistant to inhibition by 25-hydroxycholesterol. Like the previously described D443N mutation, the Y298C mutation occurs within the putative sterol-sensing domain, which is part of the polytopic membrane attachment region of SCAP. Cells that express SCAP(Y298C) continued to process SREBPs in the presence of 25-hydroxycholesterol and hence they resisted killing by this sterol. In wild-type Chinese hamster ovary cells the N-linked carbohydrate chains of SCAP were mostly in the endoglycosidase H-sensitive form when cells were grown in medium containing 25-hydroxycholesterol. In contrast, when cells were grown in sterol-depleted medium, these chains were converted to an endoglycosidase H-resistant form. 25-Hydroxycholesterol had virtually no effect in cells expressing SCAP(D443N) or SCAP(Y298C). The relation between this regulated carbohydrate processing to the SCAP-regulated proteolysis of SREBP remains to be explored.