SERPINB5在鼻咽癌放疗抵抗中的作用及分子机制研究

The main reason of nasopharyngeal carcinoma (NPC) recurrence after radiotherapy lies in the radioresistance of tumor cells. The repression of cell apoptosis will lead to tumor cells’ radioresistance. Currently, we still know little about the mechanism governing NPC radioresistance. Our previous work found that: ①SERPINB5 was highly expressed in NPC cell lines with radioresistance, and SERPINB5 overexpression repressed NPC cell apoptosis in the condition of X-ray irradiation; ②Mass spectrometry results revealed that SERPINB5 can recruit E3 ligase TRIM21 to degrade GMPS, and thus blocking apoptotic process of tumor cells. Facilitated by the above results, we proposed that SERPINB5 represses tumor cell apoptosis through regulating the protein stability of GMPS, which leads to the radioresistance of NPC. The following research work will continue to perform: ①illustrating the exact interaction relationship among SERPINB5-TRIM21-GMPS, explore the mechanism governing SERPINB5 suppressing tumor cell apoptosis through in vivo and in vitro experiments; ②using NPC biopsy samples with radioresistance and mice model to study the functional role of SERPINB5 in radio-sensitivity of NPC. Based on our studies, we hope to shed light on the screening of the radioresistant NPC patients so as to provide personal clinical treatment.

鼻咽癌放疗后复发的主要原因是肿瘤细胞的放疗抵抗，导致肿瘤放疗抵抗的关键因素是细胞凋亡的抑制。我们的前期研究发现：①放射抵抗的鼻咽癌细胞系中SERPINB5表达升高，过表达SERPINB5可以抑制X射线诱导的鼻咽癌细胞凋亡；②质谱分析揭示SERPINB5可招募E3连接酶TRIM21降解GMPS，从而抑制鼻咽癌细胞的凋亡。由此我们提出假说，SERPINB5通过调控GMPS的蛋白稳定性抑制鼻咽癌细胞凋亡，从而导致放疗抵抗。拟开展以下研究予以验证：①通过体内外实验验证SERPINB5-TRIM21-GMPS三者调控的具体作用关系，探索其在射线照射下抑制细胞凋亡的分子机制；②利用鼻咽癌放疗抵抗患者组织标本结合动物实验，验证SERPINB5通过抑制细胞凋亡而促进鼻咽癌放疗抵抗。通过本项目的实施，为临床上筛选放疗抵抗鼻咽癌患者并进行个体化治疗提供理论指导。

治疗鼻咽癌的主要手段是放疗，然而由放疗抵抗引发的肿瘤复发是临床上鼻咽癌治愈的关键瓶颈。理解鼻咽癌放疗抵抗的机制有望提高疗效。鉴于TRIM21在以往研究中被发现有促进肿瘤放疗抵抗的功能，因此在本研究中，我们首先探索了鼻咽癌细胞接受放疗后TRIM21的变化和作用，并通过质谱分析筛选了TRIM21的下游作用蛋白。进一步利用过表达和敲除TRIM21及SERPINB5的鼻咽癌细胞进行基因调控的上下游分析，发现了GMPS在其中的关键作用。利用流式、免疫共沉淀、Western及免疫荧光等手段进一步验证了发现的结论。最后，我们通过免疫组化检测了4例放疗敏感和8例放疗抵抗鼻咽癌患者的样本中SERPINB5和GMPS的表达情况。TRIM21作为E3连接酶在NPC细胞中高表达。辐照后TRIM21会通过GMPS的泛素化降解抑制TP53的表达。体内体外实验验证过表达TRIM21能够免除辐照后NPC的凋亡。进一步的研究揭示TRIM21介导的GMPS抑制作用是通过SERPINB5实现，并且SERPINB5可作为适配体阻止GMPS入核同时促进TRIM21对GMPS的泛素化。与此同时，体内外实验证明SERPINB5能够促进鼻咽癌细胞的放疗抵抗，放疗抵抗的鼻咽癌患者活检样本中SERPINB5高表达。总体上，我们的数据揭示了TRIM21-SERPINB5介导的GMPS降解抑制了TP53，从而促进了鼻咽癌细胞的放疗抵抗，这一新发现为我们理解鼻咽癌的放疗抵抗提供了新的思路。