Cai Y, Geutjes E-J, de Lint K, Roepman P, Bruurs L, Yu L-R, Wang W, van Blijswijk J, Mohammad H, de Rink I, Bernards R, Baylin S B
Department of Oncology and The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University, Baltimore, MD, USA.
Division of Molecular Carcinogenesis, Center for Biomedical Genetics and Cancer Genomics Centre, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
Oncogene. 2014 Apr 24;33(17):2157-68. doi: 10.1038/onc.2013.178. Epub 2013 May 27.
Many tumor suppressor genes (TSGs) are silenced through synergistic layers of epigenetic regulation including abnormal DNA hypermethylation of promoter CpG islands, repressive chromatin modifications and enhanced nucleosome deposition over transcription start sites. The protein complexes responsible for silencing of many of such TSGs remain to be identified. Our previous work demonstrated that multiple silenced TSGs in colorectal cancer cells can be partially reactivated by DNA demethylation in cells disrupted for the DNA methyltransferases 1 and 3B (DNMT1 and 3B) or by DNMT inhibitors (DNMTi). Herein, we used proteomic and functional genetic approaches to identify additional proteins that cooperate with DNMTs in silencing these key silenced TSGs in colon cancer cells. We discovered that DNMTs and the core components of the NuRD (Mi-2/nucleosome remodeling and deacetylase) nucleosome remodeling complex, chromo domain helicase DNA-binding protein 4 (CHD4) and histone deacetylase 1 (HDAC1) occupy the promoters of several of these hypermethylated TSGs and physically and functionally interact to maintain their silencing. Consistent with this, we find an inverse relationship between expression of HDAC1 and 2 and these TSGs in a large panel of primary colorectal tumors. We demonstrate that DNMTs and NuRD cooperate to maintain the silencing of several negative regulators of the WNT and other signaling pathways. We find that depletion of CHD4 is synergistic with DNMT inhibition in reducing the viability of colon cancer cells in correlation with reactivation of TSGs, suggesting that their combined inhibition may be beneficial for the treatment of colon cancer. Since CHD4 has ATPase activity, our data identify CHD4 as a potentially novel drug target in cancer.
许多肿瘤抑制基因（TSG）通过表观遗传调控的协同层面而沉默，包括启动子CpG岛的异常DNA高甲基化、抑制性染色质修饰以及转录起始位点上核小体沉积的增强。负责使许多此类TSG沉默的蛋白质复合物仍有待确定。我们之前的工作表明，在DNA甲基转移酶1和3B（DNMT1和3B）功能缺失的细胞中，通过DNA去甲基化或使用DNMT抑制剂（DNMTi），可使结肠癌细胞中多个沉默的TSG部分重新激活。在此，我们使用蛋白质组学和功能遗传学方法来鉴定在结肠癌细胞中与DNMT协同作用使这些关键沉默TSG沉默的其他蛋白质。我们发现，DNMT与NuRD（Mi-2/核小体重塑和去乙酰化酶）核小体重塑复合物的核心成分、染色体结构域解旋酶DNA结合蛋白4（CHD4）和组蛋白去乙酰化酶1（HDAC1）占据了其中一些高甲基化TSG的启动子，并在物理和功能上相互作用以维持它们的沉默。与此一致的是，我们在大量原发性结肠肿瘤中发现HDAC1和2的表达与这些TSG呈负相关。我们证明，DNMT和NuRD协同维持WNT及其他信号通路的几个负调控因子的沉默。我们发现，CHD4的缺失与DNMT抑制在降低结肠癌细胞活力方面具有协同作用，这与TSG的重新激活相关，表明联合抑制它们可能对结肠癌治疗有益。由于CHD4具有ATP酶活性，我们的数据将CHD4确定为癌症中一个潜在的新型药物靶点。
