Division of Genomic Stability and DNA Repair, Department of Radiation Oncology, Dana-Farber Cancer Institutes, Harvard Medical School, Boston, Massachusetts, United States of America.
PLoS One. 2011;6(10):e26064. doi: 10.1371/journal.pone.0026064. Epub 2011 Oct 7.
Hypoxia inducible factor 1α (Hif1α) is a stress responsive transcription factor, which regulates the expression of genes required for adaption to hypoxia. Hif1α is normally hydroxylated by an oxygen-dependent prolylhydroxylase, leading to degradation and clearance of Hif1α from the cell. Under hypoxic conditions, the activity of the prolylhydroxylase is reduced and Hif1α accumulates. Hif1α is also constitutively expressed in tumor cells, where it is associated with resistance to ionizing radiation. Activation of the Hif1α transcriptional regulatory pathway may therefore function to protect normal cells from DNA damage caused by ionizing radiation. Here, we utilized the prolylhydroxylase inhibitor dimethyloxalylglycine (DMOG) to elevate Hif1α levels in mouse embryonic fibroblasts (MEFs) to determine if DMOG could function as a radioprotector. The results demonstrate that DMOG increased Hif1α protein levels and decreased the sensitivity of MEFs to ionizing radiation. Further, the ability of DMOG to function as a radioprotector required Hif1α, indicating a key role for Hif1α's transcriptional activity. DMOG also induced the Hif1α -dependent accumulation of several DNA damage response proteins, including CHD4 and MTA3 (sub-units of the NuRD deacetylase complex) and the Suv39h1 histone H3 methyltransferase. Depletion of Suv39h1, but not CHD4 or MTA3, reduced the ability of DMOG to protect cells from radiation damage, implicating increased histone H3 methylation in the radioprotection of cells. Finally, treatment of mice with DMOG prior to total body irradiation resulted in significant radioprotection of the mice, demonstrating the utility of DMOG and related prolylhydroxylase inhibitors to protect whole organisms from ionizing radiation. Activation of Hif1α through prolylhydroxylase inhibition therefore identifies a new pathway for the development of novel radiation protectors.
缺氧诱导因子 1α（Hif1α）是一种应激反应转录因子，可调节适应缺氧所需基因的表达。Hif1α 通常被氧依赖性脯氨酰羟化酶羟化，导致 Hif1α 从细胞中降解和清除。在缺氧条件下，脯氨酰羟化酶的活性降低，Hif1α 积累。Hif1α 在肿瘤细胞中也持续表达，与抵抗电离辐射有关。因此，Hif1α 转录调节途径的激活可能有助于保护正常细胞免受电离辐射引起的 DNA 损伤。在这里，我们利用脯氨酰羟化酶抑制剂二甲基草酰甘氨酸（DMOG）来提高小鼠胚胎成纤维细胞（MEFs）中的 Hif1α 水平，以确定 DMOG 是否可以作为辐射保护剂。结果表明，DMOG 增加了 Hif1α 蛋白水平，并降低了 MEFs 对电离辐射的敏感性。此外，DMOG 作为辐射保护剂的作用需要 Hif1α，表明 Hif1α 的转录活性起着关键作用。DMOG 还诱导了几种 DNA 损伤反应蛋白的 Hif1α 依赖性积累，包括 CHD4 和 MTA3（NuRD 去乙酰化酶复合物的亚单位）和 Suv39h1 组蛋白 H3 甲基转移酶。Suv39h1 的耗尽，但不是 CHD4 或 MTA3 的耗尽，降低了 DMOG 保护细胞免受辐射损伤的能力，表明组蛋白 H3 甲基化的增加在细胞的辐射保护中起作用。最后，在全身照射前用 DMOG 处理小鼠导致小鼠受到显著的辐射保护，证明了 DMOG 和相关脯氨酰羟化酶抑制剂在保护整个生物体免受电离辐射方面的效用。通过脯氨酰羟化酶抑制激活 Hif1α 因此确定了开发新型辐射保护剂的新途径。
