Exposed thiols confer localization in the endoplasmic reticulum by retention rather than retrieval
Exposed thiols confer localization in the endoplasmic reticulum by retention rather than retrieval
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DOI：
10.1074/jbc.271.42.26138
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发表时间：
1996-10-18
影响因子：
4.8
通讯作者：
Sitia, R
中科院分区：
文献类型：
--
作者：
Isidoro, C;Maggioni, C;Sitia, R
存在于IgM链尾部（mu tp）的半胱氨酸阻止了未聚合的IgM中间体的分泌，并导致它们在内质网（ER）中积累。原则上，这可能是实际保留在该细胞器或从高尔基体中提取的结果。为了确定半胱氨酸依赖性内质网定位的两种机制中的哪一种，我们在这里分析了适当工程组织蛋白酶D （CD）分子的翻译后修饰。该蛋白酶的聚糖被er后磷酸转移酶磷酸化，并在反式高尔基体中进一步修饰，产生甘露糖6-磷酸溶酶体靶向信号。除非被外源性还原剂或临界半胱氨酸突变（CDM mu tpSer）逆转，否则只有微量的mu tp标记的CD （CDM mu tpCys）被磷酸化。相反，kdel标记的CD，从高尔基体进入内质网，获得磷酸盐，尽管主要抵抗碱性磷酸酶。与CDM mu tpSer类似，少数CDM mu tppcys分子逃脱保留并在顺式高尔基体中获得磷酸盐，被运输到KDEL检索室之外，这表明它们对碱性磷酸酶的敏感性。这些结果表明，巯基依赖性内质网定位主要来自于真正的保留，而不是通过高尔基体再循环。
The cysteine present in the Ig mu chain tailpiece (mu tp) prevents the secretion of unpolymerized IgM intermediates and causes their accumulation in the endoplasmic reticulum (ER). In principle, this can be the consequence of actual retention in this organelle or of retrieval from the Golgi. To determine which of the two mechanisms underlies the cysteine dependent ER localization, we analyze here the post-translational modifications of suitably engineered cathepsin D (CD) molecules. The glycans of this protease are phosphorylated by post-ER phosphotransferases and further modified in the trans-Golgi to generate a mannose 6-phosphate lysosome targeting signal. Only trace amounts of the mu tp-tagged CD (CDM mu tpCys) are phosphorylated, unless retention is reversed by exogenous reducing agents or the critical cysteine mutated (CDM mu tpSer). In contrast, a KDEL-tagged CD, that is retrieved from the Golgi into the ER, acquires phosphates, though mainly resistant to alkaline phosphatase. Similarly to CDM mu tpSer, the few CDM mu tpCys molecules that escape retention and acquire phosphates in the cis-Golgi are transported beyond the KDEL retrieval compartment, as indicated by their sensitivity to alkaline phosphatase. These results demonstrate that the thiol-dependent ER localization arises primarily from true retention, without recycling through the Golgi.