NGX6a Is Degraded through a Proteasome-dependent Pathway without Ubiquitination Mediated by Ezrin, a Cytoskeleton-Membrane Linker*
NGX6a Is Degraded through a Proteasome-dependent Pathway without Ubiquitination Mediated by Ezrin, a Cytoskeleton-Membrane Linker*
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DOI：
10.1074/jbc.m114.584771
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发表时间：
2014-11
期刊：
影响因子：
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通讯作者：
Li Wang;X. Li;Bo Xiang;Ming Zhou;Xiayu Li;W. Xiong;Man Niu;Pingpin Wei;Zeyou Wang;Heran Wan
中科院分区：
文献类型：
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作者：
Li Wang;X. Li;Bo Xiang;Ming Zhou;Xiayu Li;W. Xiong;Man Niu;Pingpin Wei;Zeyou Wang;Heran Wan
背景：NGX6a是NGX6基因的一种新亚型，在鼻咽癌细胞中表达下调。结果：NGX6a经历了由ezrin介导的蛋白酶体依赖性降解，但没有泛素化。结论：Ezrin的高表达介导了肿瘤抑制因子NGX6a的降解，并有助于鼻咽癌细胞的高转移潜力。这些发现提供了NGX6a与ezrin相互作用的新分子机制。我们之前的研究表明NGX 6b基因在鼻咽癌（NPC）的侵袭和迁移中起抑制作用。最近，我们发现了新的异构体NGX6a，它比NGX6b长。在这项研究中，我们首次发现NGX6a在NPC细胞中被降解，并且这种降解是由ezrin介导的，ezrin是膜蛋白和细胞骨架之间的连接体。针对ezrin的特异性siRNA增加了这些细胞中NGX6a的蛋白水平。在降解过程中，NGX6a不是泛素化的，而是通过蛋白酶体依赖性途径降解的。在鼻咽癌组织芯片和胎儿多器官组织的免疫化学分析以及鼻咽癌和NPC细胞系的Western blot分析中，ezrin的分布模式与NGX6a呈负相关，表明ezrin和NGX6a相关，并参与NPC的进展和侵袭。通过定位相互作用的结合位点，发现NGX6a的七跨膜结构域是NGX6a降解的关键区域，而ezrin的氨基端是诱导NGX6a降解所必需的。敲低ezrin或转染具有EGF样结构域和跨膜1结构域的NGX6a突变体CO，导致没有降解，显著降低NPC细胞的侵袭和迁移能力。本研究为鼻咽癌细胞NGX6a低表达提供了一种新的分子机制，也为鼻咽癌细胞侵袭转移过程中的一个重要分子事件提供了理论依据。
Background: NGX6a, a novel isoform of the NGX6 gene, was found down-regulated in nasopharyngeal carcinoma cells. Results: NGX6a experienced proteasome-dependent degradation that is mediated by ezrin but without ubiquitination. Conclusion: High expression of ezrin mediates the degradation of tumor suppressor NGX6a and contributes to the high metastasis potential of nasopharyngeal carcinoma cells. Significance: These findings provide a novel molecular mechanism of NGX6a interacting with ezrin. Our previous study demonstrated that the NGX6b gene acts as a suppressor in the invasion and migration of nasopharyngeal carcinoma (NPC). Recently, we identified the novel isoform NGX6a, which is longer than NGX6b. In this study, we first found that NGX6a was degraded in NPC cells and that this degradation was mediated by ezrin, a linker between membrane proteins and the cytoskeleton. Specific siRNAs against ezrin increase the protein level of NGX6a in these cells. During degradation, NGX6a is not ubiquitinated but is degraded through a proteasome-dependent pathway. The distribution pattern of ezrin was negatively associated with NGX6a in an immunochemistry analysis of a nasopharyngeal carcinoma tissue microarray and fetus multiple organ tissues and Western blot analysis in nasopharyngeal and NPC cell lines, suggesting that ezrin and NGX6a are associated and are involved in the progression and invasion of NPC. By mapping the interacting binding sites, the seven-transmembrane domain of NGX6a was found to be the critical region for the degradation of NGX6a, and the amino terminus of ezrin is required for the induction of NGX6a degradation. The knockdown of ezrin or transfection of the NGX6a mutant CO, which has an EGF-like domain and a transmembrane 1 domain, resulted in no degradation, significantly reducing the ability of invasion and migration of NPC cells. This study provides a novel molecular mechanism for the low expression of NGX6a in NPC cells and an important molecular event in the process of invasion and metastasis of nasopharyngeal carcinoma cells.