ER quality control can lead to retrograde transport from the ER lumen to the cytosol and the nucleoplasm in plants
ER quality control can lead to retrograde transport from the ER lumen to the cytosol and the nucleoplasm in plants
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DOI：
10.1046/j.1365-313x.2003.01728.x
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发表时间：
2003-05-01
期刊：
影响因子：
7.2
通讯作者：
Hawes, C
中科院分区：
文献类型：
--
作者：
Brandizzi, F;Hanton, S;Hawes, C
分泌途径中的质量控制是防止可能由错误折叠的蛋白质释放到细胞或质外体中引起的有害作用的基本步骤。我们的目标是可视化和分析的处置路线，然后在体内使用荧光蛋白技术的植物细胞内的异常蛋白质。一个绿色荧光蛋白（GFP）的融合检测在胞质和核质中，尽管存在的N-末端分泌信号肽。与分泌的GFP相反，融合蛋白保留在细胞中，在那里它被缓慢降解，尽管速率远高于内质网（ER）保留的衍生物GFP-HDEL。该融合蛋白不能被运输或胞质蛋白酶体的抑制剂稳定。然而，该蛋白是一种强内腔结合蛋白（BiP）配体。完整的信号肽加工，即使在病毒感染的叶片中长期表达后，排除了记录的细胞质和核质中的积累是因为绕过易位孔的可能性。数据与融合蛋白通过逆行易位回到胞质溶胶而从ER处置的假设一致。此外，在核质中的积累被证明是微管依赖性的，不像有充分证据证明的扩散到核质中的细胞质表达的GFP。GFP融合物明显主动转运到核质中可能表明ER相关降解（ERAD）途径的一个尚未发现的特征，并解释了对蛋白酶体抑制剂降解的不敏感性。
Quality control in the secretory pathway is a fundamental step in preventing deleterious effects that may arise by the release of malfolded proteins into the cell or apoplast. Our aims were to visualise and analyse the disposal route followed by aberrant proteins within a plant cell in vivo using fluorescent protein technology. A green fluorescent protein (GFP) fusion was detected in the cytosol and the nucleoplasm in spite of the presence of an N-terminal secretory signal peptide. In contrast to secreted GFP, the fusion protein was retained in the cells where it was degraded slowly, albeit at a rate much higher than that of the endoplasmic reticulum (ER)-retained derivative GFP-HDEL. The fusion protein could not be stabilised by inhibitors of transport or the cytosolic proteasome. However, the protein is a strong lumenal binding protein (BiP) ligand. Complete signal peptide processing even after long-term expression in virus-infected leaves rules out the possibility that the documented accumulation in the cytosol and nucleoplasm is because of the bypassing of the translocation pores. The data are consistent with the hypothesis that the fusion protein is disposed off from the ER via a retrograde translocation back to the cytosol. Moreover, accumulation in the nucleoplasm was shown to be microtubule dependent unlike the well-documented diffusion of cytosolically expressed GFP into the nucleoplasm. The apparent active transport of the GFP fusion into the nucleoplasm may indicate an as yet undiscovered feature of the ER-associated degradation (ERAD) pathway and explain the insensitivity to degradation by proteasome inhibitors.