The antioxidative response mediated by transcription factor NRF2 is thought to be a pivotal cellular defense system against various extrinsic stresses. It has been reported that activation of the NRF2 pathway confers cells with resistance to ionizing radiation-induced damage. However, the underlying mechanism remains largely unknown. In the current research, it was found that alpha-particle radiation has the ability to stimulate NRF2 expression in human osteosarcoma U-2 OS cells. Knockdown of cellular NRF2 level by shRNA-mediated gene silencing decreased the survival rate, increased the micronucleus formation rate and apoptosis rate in irradiated cells. Consistently, knockdown of NRF2 resulted in decreased expression of p65 and Bcl-2, and increased expression of p53 and Bax. Besides, it was observed that increased expression of NRF2 was partially dependent on radiation induced phosphorylation of ERK 1/2. Further results showed that radiation promoted autophagy flux which leads to the enhanced phosphorylation of ERK 1/2, as evidenced by the resultls that knockdown of ATG5 (Autophagy protein 5) gene by shRNA suppressed both radiation induced ERK 1/2 phosphorylation and NRF2 upregulation. Based on these results, it is proposed that attenuation of NRF2 antioxidative pathway can sensitize U-2 OS cells to radiation, where NRF2 antioxidative response is regulated by autophagy mediated activation of ERK 1/2 kinases.

中文翻译：

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通过自噬/ERK 1/2 上调 NRF2 可改善电离辐射诱导的人骨肉瘤 U-2 OS 细胞死亡。

转录因子 NRF2 介导的抗氧化反应被认为是抵御各种外在压力的关键细胞防御系统。据报道，NRF2 通路的激活赋予细胞对电离辐射诱导的损伤的抵抗力。然而，潜在的机制在很大程度上仍然未知。在目前的研究中，发现α粒子辐射具有刺激人骨肉瘤U-2 OS细胞中NRF2表达的能力。shRNA 介导的基因沉默对细胞 NRF2 水平的敲低降低了受照射细胞的存活率，增加了微核形成率和凋亡率。一致地，NRF2 的敲低导致 p65 和 Bcl-2 的表达降低，而 p53 和 Bax 的表达增加。除了，据观察，NRF2 表达的增加部分依赖于辐射诱导的 ERK 1/2 磷酸化。进一步的结果表明，辐射促进了自噬通量，导致 ERK 1/2 的磷酸化增强，正如通过 shRNA 敲低 ATG5（自噬蛋白 5）基因抑制辐射诱导的 ERK 1/2 磷酸化和 NRF2 上调的结果所证明的那样。基于这些结果，提出 NRF2 抗氧化途径的减弱可以使 U-2 OS 细胞对辐射敏感，其中 NRF2 抗氧化反应受自噬介导的 ERK 1/2 激酶激活的调节。结果表明，shRNA 对 ATG5（自噬蛋白 5）基因的敲低抑制了辐射诱导的 ERK 1/2 磷酸化和 NRF2 上调。基于这些结果，提出 NRF2 抗氧化途径的减弱可以使 U-2 OS 细胞对辐射敏感，其中 NRF2 抗氧化反应受自噬介导的 ERK 1/2 激酶激活的调节。结果表明，shRNA 对 ATG5（自噬蛋白 5）基因的敲低抑制了辐射诱导的 ERK 1/2 磷酸化和 NRF2 上调。基于这些结果，提出 NRF2 抗氧化途径的减弱可以使 U-2 OS 细胞对辐射敏感，其中 NRF2 抗氧化反应受自噬介导的 ERK 1/2 激酶激活的调节。