An oncogenic Ezh2 mutation cooperates with particular genetic alterations to induce tumors in mice and redistributes H3K27m3 through the genome [RNA-seq]

B-cell lymphoma and melanoma harbor recurrent mutations in the gene encoding the EZH2 histone methyltransferase, but the carcinogenic role of these mutations is unclear. Here we describe a mouse model in which the most common somatic EZH2 gain-of-function mutation (Y646F in human, Y641F in the mouse) can be conditionally expressed. Expression of Ezh2Y641F in mouse B-cells or melanocytes caused high-penetrance lymphoma or melanoma, respectively. Bcl2 overexpression or p53 loss, but not c-Myc overexpression, further accelerated lymphoma progression, and expression of mutant B-Raf but not mutant N-Ras further accelerated melanoma progression. Although expression of Ezh2Y641F increased abundance of global H3K27 trimethylation (H3K27me3), it also caused a widespread redistribution of this repressive mark, including a loss of H3K27me3 associated with increased transcription at many loci. These results suggest that Ezh2Y641F induces lymphoma and melanoma through a vast reorganization of chromatin structure inducing both repression and activation of polycomb-regulated loci. B cells: 4 WT vs 4 Y641F samples, Melanoma: WT (480, 855) vs Y641F (480D, 855D) isogenic cell lines differing only for the presence of WT vs Y641F Ezh2.B细胞淋巴瘤与黑色素瘤在编码组蛋白甲基转移酶EZH2（EZH2 histone methyltransferase）的基因中携带有复发性突变，但此类突变的致癌功能尚未明确。本研究构建了一种可条件性表达最常见体细胞EZH2功能获得性突变的小鼠模型——人类对应突变为Y646F，小鼠对应突变为Y641F。在小鼠B细胞或黑素细胞中分别表达Ezh2Y641F，可分别诱导出高外显率的B细胞淋巴瘤或黑色素瘤。Bcl2过表达或p53缺失（而非c-Myc过表达）可进一步加速淋巴瘤进展；而突变型B-Raf（而非突变型N-Ras）的表达则可进一步加快黑色素瘤的发展进程。尽管Ezh2Y641F的表达可提升整体H3K27三甲基化（H3K27 trimethylation, H3K27me3）的水平，但同时也会导致该抑制性修饰标记发生广泛重分布，包括在众多基因座上伴随转录上调而出现的H3K27me3丢失现象。上述结果表明，Ezh2Y641F可通过大规模重塑染色质结构，同时实现对多梳调控基因座的抑制与激活，从而诱导B细胞淋巴瘤与黑色素瘤的发生。样本设置如下：B细胞组：4份野生型（Wild Type, WT）样本与4份Y641F突变型样本；黑色素瘤组：仅携带野生型Ezh2的同基因细胞系WT(480, 855)与仅携带Y641F突变型Ezh2的同基因细胞系Y641F(480D, 855D)。