BRAF^V600E mutation is frequently found in human cancers particularly thyroid cancer and melanoma, and is involved in the regulation of gene expression through activating MAPK/Erk signaling. Trimethylation of histone 3 lysine 27 (H3K27me3) is a critical epigenetic mark for the maintenance of gene silencing in tumorigenesis. However, molecular mechanism underlying the complex interplay between these two molecular events remains to be explored. In the present study, we conducted chromatin immunoprecipitation combined with next-generation sequencing (ChIP-Seq) and expression microarray analysis in NIH3T3 cells to explore the relationship between H3K27me3 and transcriptional regulation by BRAF^V600E mutation. Our results showed that activated MAPK/Erk signaling by BRAF^V600E mutation was a trigger of this epigenetic processing at many downstream target genes in cancer cell lines and Braf^V600E-induced thyroid cancer of transgenetic mice. By integrating ChIP-Seq and gene expression microarray data, we identified 150 down-regulated loci with increased levels of H3K27me3 in BRAF-mutant cells relative to BRAF wild-type cells. Our data also demonstrated that c-Myc, a downstream key effector of BRAF^V600E signaling, was required for BRAF^V600E-induced changes in H3K27me3 through regulating the components of the polycomb repressive complex 2 (PRC2) genes Ezh2, Suz12 and Jarid2 at both transcriptional levels via direct binding to their regulatory elements and post-transcriptional levels via repressing the miR-26a, miR-200b and miR-155. In addition, BRAF^V600E also caused gene silencing through Erk1/2-induced RNA polymerase II (RNAPII) poising and chromatin architecture. Collectively, our data uncover a previously unknown epigenetic mechanism in the tumorigenesis of BRAF^V600E-driven cancers.

中文翻译：

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H3K27me3诱导BRAF ^V600E诱导表观遗传沉默需要c-Myc

BRAF ^V600E突变常见于人类癌症，尤其是甲状腺癌和黑色素瘤，并且通过激活MAPK / Erk信号传导参与基因表达的调控。组蛋白3赖氨酸27（H3K27me3）的三甲基化是维持肿瘤发生中基因沉默的重要表观遗传标记。但是，这两个分子事件之间复杂相互作用的分子机制仍有待探索。在本研究中，我们在NIH3T3细胞中进行了染色质免疫沉淀结合下一代测序（ChIP-Seq）和表达微阵列分析，以探索H3K27me3与BRAF ^V600E突变转录调控之间的关系。我们的结果表明，激活的MAPK / Erk信号通过BRAF ^V600E突变是本后生处理的触发在癌细胞系和BRAF许多下游靶基因^V600E -转基因小鼠中诱导的甲状腺癌。通过整合ChIP-Seq和基因表达微阵列数据，我们确定了150个下调的基因座，相对于BRAF野生型细胞，BRAF突变细胞中H3K27me3的水平升高。我们的数据还表明，c-Myc的，BRAF的下游关键效应^V600E信令，需要对BRAF ^V600EH3K27me3引起的变化，通过直接结合其调控元件的转录水平调节多梳抑制复合物2（PRC2）基因Ezh2，Suz12和Jarid2的成分以及通过抑制miR-26a，miR-200b在转录后水平进行和miR-155。此外，BRAF ^V600E还通过Erk1 / 2诱导的RNA聚合酶II（RNAPII）平衡和染色质结构导致基因沉默。总体而言，我们的数据揭示了BRAF ^V600E驱动的癌症的肿瘤发生中先前未知的表观遗传机制。