The main strategy against nasopharyngeal carcinoma (NPC) is radiotherapy. However, radioresistance mediated recurrence is a leading clinical bottleneck in NPC. Revealing the mechanism of NPC radioresistance will help improve the therapeutic effect. In this study, the role of TRIM21 (tripartite motif–containing 21) in NPC receiving ionizing radiation was firstly examined both in vivo and in vitro. Mass spectrometry analysis was performed to identify the downstream targets of TRIM21. NPC cells with TRIM21 or SERPINB5 (serpin family B member 5) overexpression or knockout were used to determine the epistatic relationship among SERPINB5, GMPS (guanine monophosphate synthase) and TRIM21. Flow cytometry, co-immunoprecipitation, western blot and immunofluorescence were employed to strengthen the results. Finally, immunohistochemistry using 4 radiosensitive and 8 radioresistent NPC patient samples was perform to examine the association between SERPINB5 or GMPS expression and patient radio-sensitivity. As an E3 ligase, TRIM21 was highly expressed in NPC. After ionizing radiation, TRIM21 repressed TP53 expression by mediating GMPS ubiquitination and degradation. Overexpression of TRIM21 protected NPC cells from radiation mediated cell apoptosis in vitro and in vivo. Further analysis revealed that TRIM21 mediated GMPS repression was dependent on SERPINB5, and SERPINB5 served as an adaptor which prevented GMPS from entering into the nucleus and introduced TRIM21 for GMPS ubiquitination. Moreover, the in vitro and in vivo results validated the finding that SERPINB5 promoted NPC cell radioresistance, and the radioresistant patients had higher SERPINB5 expression. Overall, our data showed that TRIM21–SERPINB5-mediated GMPS degradation facilitated TP53 repression, which promoted the radioresistance of NPC cells. This novel working model related to TP53 suppression provided new insight into NPC radioresistence clinically.

中文翻译：

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TRIM21–SERPINB5有助于抑制GMPS，以保护鼻咽癌细胞免于辐射诱导的凋亡

鼻咽癌（NPC）的主要治疗策略是放疗。然而，放射抵抗介导的复发是NPC的主要临床瓶颈。揭示NPC放射抗性的机制将有助于提高治疗效果。在这项研究中，首先在体内和体外研究了TRIM21（含三方基序的21）在接受电离辐射的NPC中的作用。进行质谱分析以鉴定TRIM21的下游靶标。使用具有TRIM21或SERPINB5（serpin家族B成员5成员）过表达或敲除的NPC细胞来确定SERPINB5，GMPS（鸟嘌呤单磷酸合酶）和TRIM21之间的上位性关系。流式细胞仪，免疫共沉淀，免疫印迹和免疫荧光技术被用来加强结果。最后，使用4个放射敏感性和8个放射抗性NPC患者样品进行免疫组织化学检查，以检查SERPINB5或GMPS表达与患者放射敏感性之间的关系。作为E3连接酶，TRIM21在NPC中高表达。电离辐射后，TRIM21通过介导GMPS泛素化和降解来抑制TP53表达。TRIM21的过表达可保护NPC细胞免受体外和体内辐射介导的细胞凋亡的影响。进一步的分析表明，TRIM21介导的GMPS抑制依赖于SERPINB5，而SERPINB5作为衔接子阻止GMPS进入细胞核，并引入了TRIM21进行GMPS泛素化。此外，体外和体内结果证实了SERPINB5促进了NPC细胞的放射抗性，并且耐放射的患者具有更高的SERPINB5表达。总体而言，我们的数据表明，TRIM21–SERPINB5介导的GMPS降解促进了TP53的抑制，从而促进了NPC细胞的放射抗性。这种与TP53抑制相关的新颖工作模型为临床NPC放射抵抗提供了新的见识。