Department of Neuro-oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America.
PLoS One. 2011;6(11):e26740. doi: 10.1371/journal.pone.0026740. Epub 2011 Nov 1.
We undertook this study to understand how the transcription factor Sox2 contributes to the malignant phenotype of glioblastoma multiforme (GBM), the most aggressive primary brain tumor. We initially looked for unbalanced genomic rearrangements in the Sox2 locus in 42 GBM samples and found that Sox2 was amplified in 11.5% and overexpressed in all the samples. These results prompted us to further investigate the mechanisms involved in Sox2 overexpression in GBM. We analyzed the methylation status of the Sox2 promoter because high CpG density promoters are associated with key developmental genes. The Sox2 promoter presented a CpG island that was hypomethylated in all the patient samples when compared to normal cell lines. Treatment of Sox2-negative glioma cell lines with 5-azacitidine resulted in the re-expression of Sox2 and in a change in the methylation status of the Sox2 promoter. We further confirmed these results by analyzing data from GBM cases generated by The Cancer Genome Atlas project. We observed Sox2 overexpression (86%; N = 414), Sox2 gene amplification (8.5%; N = 492), and Sox 2 promoter hypomethylation (100%; N = 258), suggesting the relevance of this factor in the malignant phenotype of GBMs. To further explore the role of Sox2, we performed in vitro analysis with brain tumor stem cells (BTSCs) and established glioma cell lines. Downmodulation of Sox2 in BTSCs resulted in the loss of their self-renewal properties. Surprisingly, ectopic expression of Sox2 in established glioma cells was not sufficient to support self-renewal, suggesting that additional factors are required. Furthermore, we observed that ectopic Sox2 expression was sufficient to induce invasion and migration of glioma cells, and knockdown experiments demonstrated that Sox2 was essential for maintaining these properties. Altogether, our data underscore the importance of a pleiotropic role of Sox2 and suggest that it could be used as a therapeutic target in GBM.
我们进行这项研究是为了了解转录因子 Sox2 如何促成胶质母细胞瘤（GBM）的恶性表型，GBM 是最具侵袭性的原发性脑肿瘤。我们最初在 42 个 GBM 样本中寻找 Sox2 基因座的不平衡基因组重排，发现 Sox2 在 11.5%的样本中扩增，并在所有样本中过表达。这些结果促使我们进一步研究 Sox2 在 GBM 中过表达所涉及的机制。我们分析了 Sox2 启动子的甲基化状态，因为高 CpG 密度启动子与关键发育基因相关。与正常细胞系相比，所有患者样本中的 Sox2 启动子都呈现出低甲基化的 CpG 岛。用 5-氮杂胞苷处理 Sox2 阴性神经胶质瘤细胞系，导致 Sox2 重新表达，并导致 Sox2 启动子的甲基化状态发生变化。我们通过分析癌症基因组图谱项目生成的 GBM 病例的数据进一步证实了这些结果。我们观察到 Sox2 过表达（86%；N=414）、Sox2 基因扩增（8.5%；N=492）和 Sox2 启动子低甲基化（100%；N=258），表明该因子与 GBM 的恶性表型相关。为了进一步探讨 Sox2 的作用，我们对脑肿瘤干细胞（BTSCs）进行了体外分析，并建立了神经胶质瘤细胞系。BTSCs 中 Sox2 的下调导致其自我更新特性丧失。令人惊讶的是，外源性 Sox2 在已建立的神经胶质瘤细胞中的表达不足以支持自我更新，这表明需要其他因素。此外，我们观察到外源性 Sox2 表达足以诱导神经胶质瘤细胞的侵袭和迁移，而敲低实验表明 Sox2 对于维持这些特性是必不可少的。总的来说，我们的数据强调了 Sox2 的多效性作用的重要性，并表明它可以作为 GBM 的治疗靶点。
