Division of Biochemistry and Molecular Carcinogenesis, Chiba Cancer Center Research Institute, Chiba, Japan.
Oncogene. 2010 May 6;29(18):2681-90. doi: 10.1038/onc.2010.22. Epub 2010 Mar 1.
Recent advances in neuroblastoma (NB) research addressed that epigenetic alterations such as hypermethylation of promoter sequences, with consequent silencing of tumor-suppressor genes, can have significant roles in the tumorigenesis of NB. However, the exact role of epigenetic alterations, except for DNA hypermethylation, remains to be elucidated in NB research. In this paper, we clarified the direct binding of MYCN to Bmi1 promoter and upregulation of Bmi1 transcription by MYCN. Mutation introduction into an MYCN binding site in the Bmi1 promoter suggests that MYCN has more important roles in the transcription of Bmi1 than E2F-related Bmi1 regulation. A correlation between MYCN and polycomb protein Bmi1 expression was observed in primary NB tumors. Expression of Bmi1 resulted in the acceleration of proliferation and colony formation in NB cells. Bmi1-related inhibition of NB cell differentiation was confirmed by neurite extension assay and analysis of differentiation marker molecules. Intriguingly, the above-mentioned Bmi1-related regulation of the NB cell phenotype seems not to be mediated only by p14ARF/p16INK4a in NB cells. Expression profiling analysis using a tumor-specific cDNA microarray addressed the Bmi1-dependent repression of KIF1Bbeta and TSLC1, which have important roles in predicting the prognosis of NB. Chromatin immunoprecipitation assay showed that KIF1Bbeta and TSLC1 are direct targets of Bmi1 in NB cells. These findings suggest that MYCN induces Bmi1 expression, resulting in the repression of tumor suppressors through Polycomb group gene-mediated epigenetic chromosome modification. NB cell proliferation and differentiation seem to be partially dependent on the MYCN/Bmi1/tumor-suppressor pathways.
神经母细胞瘤 (NB) 研究的最新进展表明，表观遗传改变，如启动子序列的高甲基化，导致肿瘤抑制基因沉默，在 NB 的肿瘤发生中可能具有重要作用。然而，除了 DNA 高甲基化之外，表观遗传改变的确切作用在 NB 研究中仍有待阐明。在本文中，我们阐明了 MYCN 与 Bmi1 启动子的直接结合以及 MYCN 对 Bmi1 转录的上调。在 Bmi1 启动子中的 MYCN 结合位点引入突变表明，MYCN 在 Bmi1 转录中的作用比 E2F 相关的 Bmi1 调节更为重要。在原发性 NB 肿瘤中观察到 MYCN 和多梳蛋白 Bmi1 表达之间存在相关性。Bmi1 的表达导致 NB 细胞增殖和集落形成的加速。通过神经突延伸测定和分化标记分子分析证实了 Bmi1 相关的 NB 细胞分化抑制。有趣的是，上述 Bmi1 相关的 NB 细胞表型调节似乎不仅通过 NB 细胞中的 p14ARF/p16INK4a 介导。使用肿瘤特异性 cDNA 微阵列进行的表达谱分析解决了 Bmi1 依赖性抑制 KIF1Bbeta 和 TSLC1 的问题，这在预测 NB 的预后方面具有重要作用。染色质免疫沉淀测定显示 KIF1Bbeta 和 TSLC1 是 NB 细胞中 Bmi1 的直接靶标。这些发现表明，MYCN 诱导 Bmi1 的表达，导致通过 Polycomb 组基因介导的表观遗传染色体修饰抑制肿瘤抑制基因。NB 细胞增殖和分化似乎部分依赖于 MYCN/Bmi1/肿瘤抑制途径。
