Soejima Kenzo, Fang Weizhao, Rollins Barrett J
Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115, USA.
Oncogene. 2003 Jul 24;22(30):4723-33. doi: 10.1038/sj.onc.1206510.
Transcriptional silencing of tumor suppressor genes in association with DNA methylation contributes to malignant transformation. However, the specific DNA methyltransferases that initiate this process are unknown. Here we show that a de novo DNA methyltransferase, DNMT3b, substantially contributes to the oncogenic phenotype in a lung cancer model. Normal human bronchial epithelial (NHBE) cells expressing telomerase, SV40 large T antigen, and activated Ras were immortal, formed colonies in soft agar, and expressed DNMT3b. Antisense suppression of DNMT3b prevented soft agar growth. Furthermore, mouse embryo fibroblasts expressing T antigen and Ras formed soft agar colonies and large tumors, but fibroblasts from Dnmt3b(-/-) mice did not grow in soft agar and were much less tumorigenic in vivo. The tumor suppressor genes, FHIT, TSLC1, and RASSF1A were downregulated in transformed NHBE cells, and antisense DNMT3b treatment resulted in re-expression of FHIT and TSLC1. While expression of TSCL1 correlated with methylation of CpG dinucleotides in its promoter region, the expression of FHIT did not, suggesting that DNMT3b may silence genes by several mechanisms including direct DNA methylation or recruitment of proteins that modify chromatin. Regardless of mechanism, our data indicate that DNMT3b plays an important role in transformation.
肿瘤抑制基因的转录沉默与DNA甲基化相关，这有助于恶性转化。然而，启动这一过程的具体DNA甲基转移酶尚不清楚。在此我们表明，一种从头DNA甲基转移酶DNMT3b在肺癌模型中对致癌表型有显著贡献。表达端粒酶、SV40大T抗原和活化Ras的正常人支气管上皮（NHBE）细胞具有永生性，能在软琼脂中形成集落，并表达DNMT3b。对DNMT3b的反义抑制可阻止软琼脂生长。此外，表达T抗原和Ras的小鼠胚胎成纤维细胞能形成软琼脂集落和大肿瘤，但来自Dnmt3b(-/-)小鼠的成纤维细胞在软琼脂中不生长，且在体内的致瘤性要低得多。肿瘤抑制基因FHIT、TSLC1和RASSF1A在转化的NHBE细胞中表达下调，反义DNMT3b处理导致FHIT和TSLC1重新表达。虽然TSCL1的表达与其启动子区域的CpG二核苷酸甲基化相关，但FHIT 的表达却不相关，这表明DNMT3b可能通过多种机制使基因沉默，包括直接DNA甲基化或募集修饰染色质的蛋白质。无论机制如何，我们的数据表明DNMT3b在转化过程中起重要作用。
