c-Myc is Required for BRAF(V600E)-Induced Epigenetic Silencing by H3K27me3 in Tumorigenesis.
c-Myc is Required for BRAF(V600E)-Induced Epigenetic Silencing by H3K27me3 in Tumorigenesis.
复制标题
c-Myc 是肿瘤发生中 H3K27me3 BRAF(V600E) 诱导的表观遗传沉默所必需的
作者：
Qu Y;Yang Q;Liu J;Shi B;Ji M;Li G;Hou P
BRAFV 600 E突变常见于人类癌症，特别是甲状腺癌和黑色素瘤，并通过激活MAPK/Erk信号通路参与基因表达的调节。组蛋白3赖氨酸27（H3 K27 me 3）的三甲基化是维持肿瘤发生中基因沉默的关键表观遗传标记。然而，这两个分子事件之间复杂的相互作用的分子机制仍有待探讨。本研究采用染色质免疫沉淀结合新一代测序技术（ChIP-Seq）和表达谱芯片技术，在NIH 3 T3细胞中研究H3 K27 me 3与BRAFV 600 E突变转录调控的关系。我们的研究结果表明，BRAFV 600 E突变激活的MAPK/Erk信号转导是癌细胞系和转基因小鼠中BraFV 600 E诱导的甲状腺癌中许多下游靶基因的表观遗传加工的触发因素。通过整合ChIP-Seq和基因表达微阵列数据，我们确定了150个下调位点，相对于BRAF野生型细胞，BRAF突变细胞中H3 K27 me 3水平增加。我们的数据还表明，c-Myc是BRAFV 600 E信号传导的下游关键效应子，通过在转录水平上通过直接结合其调控元件和转录后水平上通过抑制miR-26 a，miR-200 b和miR-155。此外，BRAFV 600 E还通过Erk 1/2诱导的RNA聚合酶II（RNAPII）平衡和染色质结构引起基因沉默。总的来说，我们的数据揭示了BRAFV 600 E驱动的癌症肿瘤发生中以前未知的表观遗传机制。
BRAFV600E 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 BRAFV600E mutation. Our results showed that activated MAPK/Erk signaling by BRAFV600E mutation was a trigger of this epigenetic processing at many downstream target genes in cancer cell lines and BrafV600E-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 BRAFV600E signaling, was required for BRAFV600E-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, BRAFV600E 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 BRAFV600E-driven cancers.