The Key Laboratory of Developmental Genes and Human Diseases, Ministry of Education, Department of Medical Genetics and Developmental Biology, Medical School of Southeast University, Nanjing, China.
Oncogene. 2012 May 3;31(18):2298-308. doi: 10.1038/onc.2011.411. Epub 2011 Sep 12.
DNA methyltransferase 3B (DNMT3B) mediates gene silencing via epigenetic mechanisms during hepatocellular carcinoma (HCC) progression. We aimed to identify novel targets of DNMT3B and their potential regulatory mechanisms in HCC. Metastasis suppressor 1 (MTSS1) was one of the DNMT3B targets and selected for further study. DNMT3B overexpression was detected in 81.25% of clinical HCC specimens and was negatively associated with MTSS1 in HCC cells and clinical samples. The underlying mechanism by which DNMT3B silences MTSS1 was studied using a combination of methylation-specific polymerase chain reaction (PCR) and bisulfite genome sequencing, chromatin immunoprecipitation-PCR and luciferase reporter assays. We found that the MTSS1 promoter region was sparsely methylated, and the methylation inhibitors failed to abolish DNMT3B-mediated MTSS1 silencing. DNMT3B protein bound directly to the 5'-flanking region (-865/-645) of the MTSS1 gene to inhibit its transcription. The functional role of MTSS1 was investigated using in vitro and in vivo tumorigenicity assays. As a result, MTSS1 exerted tumor suppressor effects and arrested cells in the G2/M phase, but not the G1/S phase of the cell cycle when it was depleted or overexpressed in HCC cells. Taken together, MTSS1, a novel target of DNMT3B, is repressed by DNMT3B via a DNA methylation-independent mechanism. MTSS1 was further characterized as a novel tumor suppressor gene in HCC. These findings highlight how DNMT3B regulates MTSS1, and such data may be useful for the development of new treatment options for HCC.
DNA 甲基转移酶 3B（DNMT3B）通过表观遗传机制在肝细胞癌（HCC）进展过程中介导基因沉默。我们旨在鉴定 DNMT3B 的新靶标及其在 HCC 中的潜在调节机制。转移抑制因子 1（MTSS1）是 DNMT3B 的靶标之一，被选为进一步研究的对象。在 81.25%的临床 HCC 标本中检测到 DNMT3B 过表达，并且在 HCC 细胞和临床样本中与 MTSS1 呈负相关。使用甲基化特异性聚合酶链反应（PCR）和亚硫酸氢盐基因组测序、染色质免疫沉淀-PCR 和荧光素酶报告基因检测的组合研究了 DNMT3B 沉默 MTSS1 的潜在机制。我们发现 MTSS1 启动子区域稀疏甲基化，并且甲基化抑制剂未能消除 DNMT3B 介导的 MTSS1 沉默。DNMT3B 蛋白直接结合 MTSS1 基因的 5'-侧翼区（-865/-645）以抑制其转录。使用体外和体内致瘤性测定研究了 MTSS1 的功能作用。结果表明，当 MTSS1 在 HCC 细胞中耗尽或过表达时，MTSS1 发挥肿瘤抑制作用并使细胞停滞在 G2/M 期，而不是细胞周期的 G1/S 期。总之，MTSS1 是 DNMT3B 的一个新靶标，通过非 DNA 甲基化机制被 DNMT3B 抑制。MTSS1 进一步被表征为 HCC 中的一种新的肿瘤抑制基因。这些发现强调了 DNMT3B 如何调节 MTSS1，并且此类数据可能对开发 HCC 的新治疗选择有用。
