The secretory pathway is normal in dithiothreitol-treated cells, but disulfide-bonded proteins are reduced and reversibly retained in the endoplasmic reticulum.
The secretory pathway is normal in dithiothreitol-treated cells, but disulfide-bonded proteins are reduced and reversibly retained in the endoplasmic reticulum.
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发表时间：
1993-09
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通讯作者：
H. F. Lodish;N. Kong
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作者：
H. F. Lodish;N. Kong
向HepG 2人肝癌细胞中加入2 mM二硫苏糖醇（DTT）可阻断新生成的白蛋白的分泌，并使其以还原状态积聚在内质网中。随后在不存在DTT的情况下孵育细胞允许还原的白蛋白形成明显正常的二硫键并正常分泌。类似地，DTT处理导致脱唾液酸糖蛋白受体的H1亚基的所有新形成的亚基以还原状态保留在内质网中;在去除DTT后，H1亚基通过正常的内质网折叠中间体形成二硫键并成熟为高尔基体。因此，在这两种蛋白质上的二硫键的明显正常形成可以在感染后发生，如先前对于流感HA血凝素所示（Braakman，I.，Helenius，J.，和Helenius，A.（1992）EMBO J. 11，1717-1722; Braakman，I.，Helenius，J.，和Helenius，A.（1992）Nature 356，260-262）。α 1-抗胰蛋白酶不含二硫键;在DTT持续存在的情况下，其获得复合寡糖的正常补体，并且仅以略微降低的速率分泌。因此，分泌途径即使在被DTT减少时也有效地发挥作用。在DTT治疗过程中，白蛋白和H1的内质网滞留可能是因为没有二硫键，这些蛋白质不能正确折叠，而不是因为囊泡转运和蛋白质分泌的整体过程中存在任何缺陷。
Addition of 2 mM dithiothreitol (DTT) to HepG2 human hepatoma cells blocks secretion of newly made albumin and causes it to accumulate in the endoplasmic reticulum in the reduced state. Subsequent incubation of the cells in the absence of DTT allows the reduced albumin to form apparently normal disulfide bonds and to be secreted normally. Similarly, DTT treatment causes all newly made subunits of the H1 subunit of the asialoglycoprotein receptor to be retained in the endoplasmic reticulum in the reduced state; following removal of DTT H1 subunits form disulfide bonds via a normal endoplasmic reticulum folding intermediate and mature to the Golgi. Thus, apparently normal formation of disulfide bonds on these two proteins can occur post-translationally, as has been shown previously for the influenza HA hemagglutinin (Braakman, I., Helenius, J., and Helenius, A. (1992) EMBO J. 11, 1717-1722; Braakman, I., Helenius, J., and Helenius, A. (1992) Nature 356, 260-262). alpha 1-Antitrypsin contains no disulfide bonds; in the continuous presence of DTT it acquires a normal complement of complex oligosaccharides and is secreted at an only slightly reduced rate. Thus, the secretory pathway functions efficiently even when it is reduced by DTT. Endoplasmic reticulum retention of albumin and H1 during treatment with DTT presumably occurs because, without disulfide bonds, these proteins cannot fold properly, not because of any defect in the overall processes of vesicular transport and protein secretion.