Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9039, USA.
Proc Natl Acad Sci U S A. 2012 Oct 23;109(43):E2949-55. doi: 10.1073/pnas.1207718109. Epub 2012 Oct 8.
Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a key transcriptional regulator for antioxidant and anti-inflammation enzymes that binds to its endogenous inhibitor protein, Kelch-like ECH (erythroid cell-derived protein with CNC homology)-associated protein 1, in the cytoplasm under normal conditions. Various endogenous or environmental oxidative stresses, such as ionizing radiation (IR), can disrupt the Nrf2-Kelch-like ECH-associated protein 1 complex. This allows Nrf2 to translocate from the cytoplasm into the nucleus to induce transcription of heme oxygenase-1 and other cytoprotective enzymes through binding to antioxidant responsive elements. However, how Nrf2 protects cells from IR-induced damage remains unclear. Here, we report that Nrf2 activation by the synthetic triterpenoids, bardoxolone methyl (BARD) and 2-cyano-3,12-dioxooleana-1,9 (11)-dien-28-oic acid-ethyl amide, protects colonic epithelial cells against IR-induced damage, in part, by enhancing signaling of the DNA damage response. Pretreatment with BARD reduced the frequency of both G1 and S/G2 chromosome aberrations and enhanced the disappearance of repairosomes (C-terminal binding protein interacting protein, Rad51, and p53 binding protein-1 foci) after IR. BARD protected cells from IR toxicity in a Nrf2-dependent manner. The p53 binding protein-1 promoter contains three antioxidant responsive elements in which Nrf2 directly binds following BARD treatment. In addition, 2-cyano-3,12-dioxooleana-1,9 (11)-dien-28-oic acid-ethyl amide provided before exposure to a lethal dose of whole-body irradiation protected WT mice from DNA damage and acute gastrointestinal toxicity, which resulted in improved overall survival. These results demonstrate that Nrf2 activation by synthetic triterpenoids is a promising candidate target to protect the gastrointestinal tract against acute IR in vitro and in vivo.
核因子红细胞 2 相关因子 2（Nrf2）是一种关键的转录调节因子，可调节抗氧化和抗炎酶，在正常情况下，它与细胞内源性抑制剂蛋白 Kelch 样 ECH（红细胞衍生蛋白与 CNC 同源）相关蛋白 1 结合在细胞质中。各种内源性或环境氧化应激，如电离辐射（IR），可以破坏 Nrf2-Kelch 样 ECH 相关蛋白 1 复合物。这使得 Nrf2 从细胞质易位到细胞核，通过与抗氧化反应元件结合，诱导血红素加氧酶-1 和其他细胞保护酶的转录。然而，Nrf2 如何保护细胞免受 IR 诱导的损伤仍不清楚。在这里，我们报告合成三萜类化合物 bardoxolone 甲基（BARD）和 2-氰基-3,12-二氧代齐墩果酸-1,9（11）-二烯-28-酸乙酯激活 Nrf2，部分通过增强 DNA 损伤反应信号来保护结肠上皮细胞免受 IR 损伤。BARD 预处理可降低 G1 和 S/G2 染色体畸变的频率，并增强 IR 后修复体（C 端结合蛋白相互作用蛋白、Rad51 和 p53 结合蛋白-1 焦点）的消失。BARD 以 Nrf2 依赖的方式保护细胞免受 IR 毒性。p53 结合蛋白-1 启动子包含三个抗氧化反应元件，BARD 处理后 Nrf2 直接结合。此外，在全身照射致死剂量照射前给予 2-氰基-3,12-二氧代齐墩果酸-1,9（11）-二烯-28-酸乙酯可保护 WT 小鼠免受 DNA 损伤和急性胃肠道毒性，从而提高整体存活率。这些结果表明，合成三萜类化合物激活 Nrf2 是一种有前途的候选靶点，可在体外和体内保护胃肠道免受急性 IR。
