DNA损伤诱导的细胞早衰过程中p21及p16 启动子低甲基化与mRNA高甲基化的并发机制

The upregulation of p21 and p16 in cellular senescence is achieved by regulation at multiple levels. However, the mechanisms underlying the concurrent initiation of different regulatory processes by DNA damage are not fully understood. In our previous study, we have found that: 1) In DNA damage-induced cancer cell senescence, the promoter hypomethylation and the mRNA hypermethylation of p21 and p16, the downregulation of Aurora-B and activation of p38MAPK, as well as the downregulation of DNMT1 and activation of NSun2 were concurrently existed; 2) NSun2 enhanced the expression of p21 by methylating the p21 3’UTR; 3) Ser456 of NSun2 protein is a potential phosphorylation target of p38MAPK; 4) NSun2-mediated p21 and p16 mRNA methylation may occur at the early stage of transcription. Based on these findings, we set out to further investigate the mechanisms underlying the coupling of promoter hypomethylation and mRNA hypermethylation of p21 and p16 in DNA damage-induced cellular senescence. We will also investigate the impact of this coupling in the regulation of p21 and p16 in DNA damage-induced cellular senescence. Our study will not only reveal the mechanisms underlying DNA damage-induced promoter hypomethylation and mRNA hypermethylation of p21 and p16 (at least in part), but also provide experimental evidence for revealing the essence of aging as well as for the treatment and prevention of human cancers.

细胞衰老过程中p21及p16显著上调是多层次共同调控的结果，但不同层次调控同时作用的机制不明。前期研究发现：1）DNA损伤诱导的HCT116 (p53-/-) 细胞早衰过程中，p21与p16 启动子低甲基化与mRNA高甲基化并发，Aurora-B下调与p38MAPK激活并发，DNMT1下调与NSun2激活并发；2）NSun2甲基化p21 mRNA并促进p21表达；3）NSun2 Ser456是p38MAPK的潜在靶点；4）NSun2对p21及p16 mRNA的甲基化在转录早期即可发生。在此基础上，本课题拟进一步探讨DNA损伤对p21与p16 启动子低甲基化与mRNA高甲基化的偶联（在概念上仍需商榷，见立项依据）及其机制，探讨这种偶联在细胞早衰过程中的意义。这些研究将部分阐释DNA损伤诱导p21及p16启动子低甲基化与 mRNA高甲基化的机制，也将为揭示衰老本质、防治肿瘤提供实验依据。

表观遗传修饰不仅发生在基因组层面，同样也存在于转录组层面。表观遗传修饰与多种疾病的发生发展密切相关，包括癌症、心血管疾病、代谢性疾病等。本课题围绕DNA甲基化和RNA甲基化修饰，以及二者的相互调控，探讨了DNA损伤下DNA甲基化与RNA甲基化相互偶联对衰老相关基因的调控及机制；RNA结合蛋白HuR及甲基化转移酶METTL3对脂代谢及血管内皮细胞炎症的调控及机制。结果显示：（1）DNA甲基转移酶DNMT1与RNA甲基转移酶NSUN2存在相互调控，DNA损伤下p21与p16表达上调导致细胞早衰，其机制涉及p38MAPK激活导致DNMT1表达抑制；（2）miR-509-3-5p通过抑制DNA损伤检验点重要分子PLK1的表达引起细胞异常有丝分裂及生长抑制；（3）肺癌细胞系对DNA损伤剂的敏感性与p53及DDR通路异质性相关；（4）HuR对脂代谢的调控涉及其对细胞核编码的氧化磷酸化相关基因的转录后调控；（5）甲基转移酶METTL3与血管炎症发生相关，其机制涉及YTHDF1调控 ICAM1等黏附分子的表达。本项目的研究成果有助于更好地认识衰老相关性疾病、肿瘤、动脉粥样硬化等的发生发展机制，也为相关的干预措施提供了实验依据。