NMD相关基因在鼻咽癌发生发展中的作用及机制研究

Nonsense-mediated mRNA decay (NMD) is a highly conserved RNA quality control pathway that protects cells from the deleterious effects of the truncated proteins by degrading aberrant mRNAs with premature translation termination (nonsense) codons (PTCs) generated by mutations or errors during gene expression. It was reported NMD was inhibited in tumors. However, NMD activity and expression of NMD-related genes have not been studied in nasopharyngeal carcinoma (NPC) until now. In our preliminary experiments, the important NMD components UPF1, UPF2, SMG1, SMG5, SMG6 and SMG7 was confirmed to be down-regulated in NPC tissues; knockdown of SMG1 enhanced NPC cell invasion significantly; Cox-2 and STC2, which were identified NMD targets and reported to enhanced NPC oncogenesis and metastasis, were up-regulated in UPF1-knockdown NPC cells. Based on these findings, this study will confirm the expression pattern and clinical significance of the key NMD components in NPC biopsies; elucidate the mechanism of NMD inhibition in NPC via the aspects of gene mutations, DNA methylation, transcription factors and miRNAs regulation, EBV infection and tumor microenvironments; identify the role and mechanism of NMD factors in NPC cell biological behaviors and tumor formation and metastasis in vitro and in vivo; screen and identify NMD targets through mRNA expression profile, mRNA variations with NMD triggering features, and verification in clinical samples; explore the role and mechanism of NMD targets regulated by NMD pathway in NPC oncogenesis and development. This study will help to elucidate the oncogenesis of NPC and provide new biomarkers for clinical treatment of NPC.

无义介导的mRNA降解（NMD）可降解清除异常转录产物，是一种重要的mRNA监控机制。有报道在肿瘤组织中NMD活性减弱。然而，NMD活性及其相关基因的研究在鼻咽癌中尚未见报道。我们在前期研究中发现NMD关键基因UPF1、UPF2、SMG1、SMG5、SMG6和SMG7在鼻咽癌活检样本中表达均显著降低；SMG1有抑制鼻咽癌细胞侵袭的作用；在鼻咽癌细胞中敲降UPF1后，有促癌促转移功能的NMD靶基因Cox-2和STC2表达上调。在前期研究的基础上，本项目拟阐明NMD相关基因低表达在鼻咽癌中的临床意义；分析EB病毒感染和肿瘤微环境等因素对NMD相关基因表达和NMD活性的影响，揭示鼻咽癌组织中NMD活性抑制的机制；验证NMD相关基因对鼻咽癌细胞的抑癌作用，并解析其作用机制；筛选鉴定NMD靶基因，探讨NMD途径通过降解靶基因参与鼻咽癌发生发展的分子机制。

无义介导的mRNA降解（NMD）是一种重要的mRNA降解机制，在肿瘤发生发展中可能有重要的作用。本研究首次探讨了NMD关键基因UPF1在鼻咽癌细胞中的功能和作用机制。我们发现NMD关键基因UPF1、UPF2、SMG1、SMG5、SMG6和SMG7在鼻咽癌组织中表达均显著降低；肿瘤中UPF1蛋白低表达的鼻咽癌患者远处转移率显著升高，生存时间显著较短，是独立预后因素。在鼻咽癌细胞中过表达或敲降UPF1后，细胞功能学实验和动物实验验证了UPF1在体内外有抑制鼻咽癌细胞增殖和转移的作用。对过表达或敲降UPF1的鼻咽癌细胞进行RNA测序分析，筛选鉴定差异基因并结合基因转录本序列分析发现COX2是可被NMD途径降解的靶基因，UPF1可下调COX2及其下游PD-L1和CYP1B1的表达。KEGG通路分析发现UPF1可抑制JAK/STAT3信号通路，回复实验证实UPF1通过抑制COX2下调STAT3通路活性。此外，我们还发现在鼻咽癌中miR-18a通过靶向抑制NMD通路重要因子SMG1，进而激活mTOR通路发挥促癌作用。综上所述，我们的研究发现在鼻咽癌细胞中NMD因子UPF1和SMG1分别通过COX2/JAK-STAT3和mTOR信号通路发挥抑癌作用。本研究对于阐明鼻咽癌致癌机制，以及鼻咽癌患者的个性化治疗和靶向治疗可能具有一定的临床价值。