Glioblastoma, a grade IV astrocytoma, has a poor survival rate in part due to ineffective treatment options available. These tumours are heterogeneous with areas of low oxygen levels, termed hypoxic regions. Many intra-cellular signalling pathways, including DNA repair, can be altered by hypoxia. Since DNA damage induction and subsequent activation of DNA repair mechanisms is the cornerstone of glioblastoma treatment, alterations to DNA repair mechanisms could have a direct influence on treatment success. Our aim was to elucidate the impact of chronic hypoxia on DNA repair gene expression in a range of glioblastoma cell lines. We adopted a NanoString transcriptomic approach to examine the expression of 180 DNA repair-related genes in four classical glioblastoma cell lines (U87-MG, U251-MG, D566-MG, T98G) exposed to 5 days of normoxia (21% O2), moderate (1% O2) or severe (0.1% O2) hypoxia. We observed altered gene expression in several DNA repair pathways including homologous recombination repair, non-homologous end-joining and mismatch repair, with hypoxia primarily resulting in downregulation of gene expression. The extent of gene expression changes was dependent on hypoxic severity. Some, but not all, of these downregulations were directly under the control of HIF activity. For example, the downregulation of LIG4, a key component of non-homologous end-joining, was reversed upon inhibition of the hypoxia-inducible factor (HIF). In contrast, the downregulation of the mismatch repair gene, PMS2, was not affected by HIF inhibition. This suggests that numerous molecular mechanisms lead to hypoxia-induced reprogramming of the transcriptional landscape of DNA repair. Whilst the global impact of hypoxia on DNA repair gene expression is likely to lead to genomic instability, tumorigenesis and reduced sensitivity to anti-cancer treatment, treatment re-sensitising might require additional approaches to a simple HIF inhibition.

中文翻译：

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缺氧性脑肿瘤细胞系中错配修复和非同源末端连接途径的下调

胶质母细胞瘤是一种IV级星形细胞瘤，其生存率很低，部分原因是可用的治疗方法无效。这些肿瘤是异质性的，具有低氧水平的区域，称为低氧区域。缺氧可改变许多细胞内信号传导途径，包括DNA修复。由于DNA损伤的诱导和随后DNA修复机制的激活是胶质母细胞瘤治疗的基础，因此DNA修复机制的改变可能直接影响治疗的成功。我们的目的是阐明慢性缺氧对一系列胶质母细胞瘤细胞系中DNA修复基因表达的影响。我们采用了NanoString转录组学方法，研究了暴露于常氧5天（21％O2）的四种经典胶质母细胞瘤细胞系（U87-MG，U251-MG，D566-MG，T98G）中180个与DNA修复相关的基因的表达，中度（1％O2）或严重（0.1％O2）缺氧。我们观察到了几种DNA修复途径中基因表达的改变，包括同源重组修复，非同源末端连接和错配修复，缺氧主要导致基因表达的下调。基因表达变化的程度取决于缺氧严重程度。这些下调中的一些（但不是全部）直接处于HIF活性的控制之下。例如，抑制缺氧诱导因子（HIF）后，可以逆转LIG4（非同源末端连接的关键成分）的下调。相反，错配修复基因PMS2的下调不受HIF抑制的影响。这表明许多分子机制导致缺氧诱导的DNA修复转录景观的重编程。