Fan Ming, Ahmed Kazi Mokim, Coleman Mitchell C, Spitz Douglas R, Li Jian Jian
Division of Molecular Radiobiology, School of Health Sciences and Purdue Cancer Center, Purdue University, West Lafayette, Indiana, USA.
Cancer Res. 2007 Apr 1;67(7):3220-8. doi: 10.1158/0008-5472.CAN-06-2728.
Mechanisms governing inducible resistance to ionizing radiation in untransformed epithelial cells pre-exposed to low-dose ionizing radiation (LDIR; </=10 cGy) are not well understood. The present study provides evidence that pre-exposure to 10 cGy X-rays increases clonogenic survival of mouse skin JB6P+ epithelial cells subsequently exposed to 2 Gy doses of gamma-rays. To elucidate the molecular pathways of LDIR-induced adaptive radioresistance, the transcription factor nuclear factor-kappaB (NF-kappaB) and a group of NF-kappaB-related proteins [i.e., p65, manganese superoxide dismutase (MnSOD), phosphorylated extracellular signal-regulated kinase, cyclin B1, and 14-3-3zeta] were identified to be activated as early as 15 min after LDIR. Further analysis revealed that a substantial amount of both 14-3-3zeta and cyclin B1 accumulated in the cytoplasm at 4 to 8 h when cell survival was enhanced. The nuclear 14-3-3zeta and cyclin B1 were reduced and increased at 4 and 24 h, respectively, after LDIR. Using YFP-fusion gene expression vectors, interaction between 14-3-3zeta and cyclin B1 was visualized in living cells, and LDIR enhanced the nuclear translocation of the 14-3-3zeta/cyclin B1 complex. Treatment of JB6P+ cells with the NF-kappaB inhibitor IMD-0354 suppressed LDIR-induced expression of MnSOD, 14-3-3zeta, and cyclin B1 and diminished the adaptive radioresistance. In addition, treatment with small interfering RNA against mouse MnSOD was shown to inhibit the development of LDIR-induced radioresistance. Together, these results show that NF-kappaB, MnSOD, 14-3-3zeta, and cyclin B1 contribute to LDIR-induced adaptive radioresistance in mouse skin epithelial cells.
低剂量电离辐射（LDIR；≤10 cGy）预照射的未转化上皮细胞中诱导性抗电离辐射的机制尚未完全明确。本研究提供的证据表明，预先暴露于10 cGy X射线可提高随后暴露于2 Gy剂量γ射线的小鼠皮肤JB6P +上皮细胞的克隆形成存活率。为阐明LDIR诱导的适应性放射抗性的分子途径，转录因子核因子-κB（NF-κB）和一组NF-κB相关蛋白[即p65、锰超氧化物歧化酶（MnSOD）、磷酸化细胞外信号调节激酶、细胞周期蛋白B1和14-3-3ζ]被确定在LDIR后15分钟就被激活。进一步分析表明，当细胞存活率提高时，在4至8小时时，大量的14-3-3ζ和细胞周期蛋白B1在细胞质中积累。LDIR后，核内14-3-3ζ和细胞周期蛋白B1分别在4小时和24小时减少和增加。使用YFP融合基因表达载体，在活细胞中观察到14-3-3ζ和细胞周期蛋白B1之间的相互作用，并且LDIR增强了14-3-3ζ/细胞周期蛋白B1复合物的核转位。用NF-κB抑制剂IMD-0354处理JB6P +细胞可抑制LDIR诱导的MnSOD、14-3-3ζ和细胞周期蛋白B1的表达，并降低适应性放射抗性。此外，用针对小鼠MnSOD的小干扰RNA处理可抑制LDIR诱导的放射抗性的发展。总之，这些结果表明NF-κB、MnSOD、14-3-3ζ和细胞周期蛋白B1有助于小鼠皮肤上皮细胞中LDIR诱导的适应性放射抗性。
