Cancer Institute, College of Life Science and Bioengineering, Beijing University of Technology, Beijing, China.
Tissue Bank, China-Japan Union Hospital, Jilin University, Changchun, China.
J Cell Physiol. 2019 May;234(5):6286-6297. doi: 10.1002/jcp.27359. Epub 2018 Oct 26.
Ten-eleven translocation 1 (TET1), a widely reported DNA demethylation protein, has been associated with tumorigenesis and metastasis. However, whether TET1 is an oncogene or tumor suppressor gene has been controversial; the mechanism of how TET1 affects cancer progression remains unclear. The current study aims to investigate how TET1 is changed in the tumor microenvironment and to explore the mechanisms of how TET1 affects colon cancer progression. Because hypoxia prevails on solid tumors, we established an important connection between hypoxia and DNA demethylation in tumorigenesis. By qPCR and RNA interference (RNAi) technology, we found that hypoxia increased TET1 expression with a hypoxia-inducible factor-1-alpha (HIF-1α)-dependent manner. By CHIP-qPCR and pyrosequencing technology, we demonstrated that TET1 regulated the target gene expression of HIF-1α through HIF-1α binding to hypoxia-responsive elements (HREs), and HIF-1α binding to HREs depended on CpG methylation levels. By Cell Counting Kit-8 (CCK-8) and transwell assay, we showed that loss of TET1 did not affect cell proliferation but inhibited migration. We also identified two novel gene mutants of TET1 in 120 paired tumor/normal tissue specimens by DNA sequencing and found that TET1 E2082K mutant blocked the TET1-enhanced cell migration. Our results showed that the downregulation of TET1 rescued the abnormally high levels of gene expression resulting from hypoxia in tumors and reduced the migration activity of tumor cells, suggesting a therapeutic role by interference with TET1 in colon cancer treatment. By demonstrating that hypoxia upregulated TET1 and that TET1 drove HIF-1α-responsive genes, we showed that an epigenetic mechanism and tumor microenvironment-driven models coexisted and mutually affected colon cancer.
十号十一号易位蛋白 1（TET1）是一种广泛报道的 DNA 去甲基化蛋白，与肿瘤发生和转移有关。然而，TET1 是癌基因还是抑癌基因一直存在争议；TET1 影响癌症进展的机制尚不清楚。本研究旨在探讨 TET1 在肿瘤微环境中的变化，并探索 TET1 影响结肠癌进展的机制。由于实体瘤中普遍存在缺氧，我们在肿瘤发生中建立了缺氧与 DNA 去甲基化之间的重要联系。通过 qPCR 和 RNA 干扰（RNAi）技术，我们发现缺氧以缺氧诱导因子 1-α（HIF-1α）依赖的方式增加 TET1 的表达。通过 CHIP-qPCR 和焦磷酸测序技术，我们证明 TET1 通过 HIF-1α 与缺氧反应元件（HRE）结合来调节 HIF-1α 的靶基因表达，而 HIF-1α 与 HRE 的结合取决于 CpG 甲基化水平。通过细胞计数试剂盒-8（CCK-8）和 Transwell 测定，我们表明 TET1 的缺失不影响细胞增殖，但抑制迁移。我们还通过 DNA 测序在 120 对肿瘤/正常组织标本中鉴定出两种 TET1 的新基因突变体，并发现 TET1 E2082K 突变体阻断了 TET1 增强的细胞迁移。我们的结果表明，TET1 的下调挽救了肿瘤中因缺氧而导致的异常高基因表达水平，并降低了肿瘤细胞的迁移活性，这表明通过干扰 TET1 在结肠癌治疗中的作用具有治疗作用。通过证明缺氧上调了 TET1，并且 TET1 驱动了 HIF-1α 反应基因，我们表明表观遗传机制和肿瘤微环境驱动的模型共存并相互影响结肠癌。
