m6A independent genome-wide METTL3 and METTL14 redistribution drives senescence-associated secretory phenotype [RNA-seq]

Methyltransferase-like 3 (METTL3) and 14 (METTL14) are core subunits of the methyltransferase complex (MTC) that catalyzes mRNA N6-methyladenosine (m6A) modification. Despite the expanding list of m6A-dependent function of the MTC, m6A independent function of the METTL3 and METTL14 complex remains poorly understood. Here we show that genome-wide redistribution of METTL3 and METTL14 drives senescence-associated secretory phenotype (SASP) in a m6A-independent manner. METTL3 and METTL14 are necessary for SASP. However, SASP is not regulated by m6A mRNA modification. METTL14 is redistributed to the enhancers, while METTL3 is localized to the pre-existing NF-B sites within the promoters of the SASP genes during senescence. METTL3 interacts with NF-B and they are mutually dependent on their associations with the promoters of SASP genes. METTL14 but not METTL3 is necessary for function of SASP gene enhancers. METTL3 and METTL14 are required for both the tumor-promoting and immune surveillance functions of senescent cells mediated by SASP in vivo in mouse models. In summary, our results report a m6A independent function of the METTL3 and METTL14 complex in promoting SASP through regulating transcription by genome-wide redistribution of METTL14 to enhancers and METTL3 to promoters of SASP genes during senescence. RNA-seq in control and senescent IMR90 cell lines with different METTL14 status

甲基转移酶样蛋白3（Methyltransferase-like 3, METTL3）与甲基转移酶样蛋白14（Methyltransferase-like 14, METTL14）是催化mRNA N6-甲基腺苷（N6-methyladenosine, m6A）修饰的甲基转移酶复合物（methyltransferase complex, MTC）的核心亚基。尽管目前依赖m6A的MTC功能研究案例日益丰富，但METTL3与METTL14复合物的非m6A依赖性功能仍有待深入阐明。本研究证实，METTL3与METTL14的全基因组重分布可通过不依赖m6A的方式诱导衰老相关分泌表型（senescence-associated secretory phenotype, SASP）。METTL3与METTL14是SASP形成所必需的核心组分，但SASP的调控并不依赖于mRNA的m6A修饰。在细胞衰老进程中，METTL14会重分布至增强子区域，而METTL3则定位在SASP基因启动子内已存在的NF-κB结合位点。METTL3可与NF-κB发生相互作用，二者对于SASP基因启动子的结合存在相互依赖关系。METTL14（而非METTL3）是SASP基因增强子发挥正常功能所必需的。在小鼠体内模型中，METTL3与METTL14对于衰老细胞通过SASP介导的促肿瘤功能与免疫监视功能均不可或缺。综上，本研究揭示了METTL3与METTL14复合物的非m6A依赖性功能：在细胞衰老过程中，二者通过全基因组重分布，将METTL14重分布至SASP基因的增强子区域、将METTL3重分布至SASP基因的启动子区域，从而调控转录以促进SASP的产生。包含不同METTL14状态的对照组与衰老型IMR90细胞系的RNA测序数据集