Zhang Ying, Lim Chang U K, Zhou Junqing, Liber Howard H
Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA.
Toxicol Lett. 2007 Jun 15;171(1-2):50-9. doi: 10.1016/j.toxlet.2007.04.006. Epub 2007 Apr 27.
Mutations of NBS1 are responsible for the human hereditary disease Nijmegen breakage syndrome (NBS), which is characterized by an extremely high cancer rate. In this study, we investigated the influence of NBS1 on ionizing radiation (IR) induced apoptosis. Using small interfering RNA (siRNA) transfection, we knocked down NBS1 protein in three closely related human lymphoblastoid cell lines differing in p53 status: TK6 with a wild-type p53, NH32 with a null mutation of p53, and WTK1 with a mutant p53. We found that up to 48h after 5Gy IR, all three lines showed an obvious induction of apoptosis regardless of the p53 status. The magnitude of apoptosis induction was TK6>NH32>WTK1. This suggested that although p53 is an important modulator of IR-induced apoptosis, other p53-independent apoptosis pathway also exists. Moreover, NBS1 knockdown led to reduction of IR-induced apoptosis in all three lines and both NBS1/ATM/p53/BAX and NBS1/ATM/CHK2/E2F1 apoptosis pathways were partially inactivated. Our results suggest that NBS1 plays an important role in IR-induced apoptosis via both p53-dependent and p53-independent mechanisms. The impaired apoptosis response to DNA damage in NBS1 deficient cells might be one of the important mechanisms of cancer predisposition in NBS patients.
NBS1的突变是导致人类遗传性疾病尼曼-匹克氏综合征（NBS）的原因，该疾病的特征是癌症发病率极高。在本研究中，我们调查了NBS1对电离辐射（IR）诱导的细胞凋亡的影响。通过小干扰RNA（siRNA）转染，我们在三种p53状态不同的密切相关的人类淋巴母细胞系中敲低了NBS1蛋白：具有野生型p53的TK6、p53基因无效突变的NH32和具有突变型p53的WTK1。我们发现，在5Gy IR照射后长达48小时，无论p53状态如何，所有三个细胞系均显示出明显的细胞凋亡诱导。细胞凋亡诱导的程度为TK6>NH32>WTK1。这表明，尽管p53是IR诱导的细胞凋亡的重要调节因子，但其他不依赖p53的细胞凋亡途径也存在。此外，NBS1敲低导致所有三个细胞系中IR诱导的细胞凋亡减少，并且NBS1/ATM/p53/BAX和NBS1/ATM/CHK2/E2F1细胞凋亡途径均部分失活。我们的结果表明，NBS1通过p53依赖性和p53非依赖性机制在IR诱导的细胞凋亡中起重要作用。NBS1缺陷细胞中对DNA损伤的细胞凋亡反应受损可能是NBS患者癌症易感性的重要机制之一。
