Chen Dexi, Yu Zhiyong, Zhu Zhiyi, Lopez Charles D
Department of Medicine, Division of Hematology and Medical Oncology, Oregon Health and Science University, 3181 S.W. Sam Jackson Park Road, Portland, OR 97239, USA.
J Biol Chem. 2008 May 30;283(22):15381-9. doi: 10.1074/jbc.M710296200. Epub 2008 Mar 17.
The E2F1 transcription factor activates S-phase-promoting genes, mediates apoptosis, and stimulates DNA repair through incompletely understood mechanisms. XRCC1 (x-ray repair cross-complementing group 1) protein is important for efficient single strand break/base excision repair. Although both damage and proliferative signals increase XRCC1 levels, the mechanisms regulating XRCC1 transcription remain unclear. To study these upstream mechanisms, the XRCC1 promoter was cloned into a luciferase reporter. Ectopic expression of wild-type E2F1, but not an inactive mutant E2F1(132E), activated the XRCC1 promoter-luciferase reporter, and deletion of predicted E2F1 binding sites in the promoter attenuated E2F1-induced activation. Endogenous XRCC1 expression increased in cells conditionally expressing wild-type, but not mutant E2F1, and methyl methanesulfonate-induced DNA damage stimulated XRCC1 expression in E2F1(+/+) but not E2F1(-/-) mouse embryo fibroblasts (MEFs). Additionally, E2F1(-/-) MEFs displayed attenuated DNA repair after methyl methanesulfonate-induced damage compared with E2F1(+/+) MEFs. Moreover, Chinese hamster ovary cells with mutant XRCC1 (EM9) were more sensitive to E2F1-induced apoptosis compared with Chinese hamster ovary cells with wild-type XRCC1 (AA8). These results provide new mechanistic insight into the role of the E2F pathway in maintaining genomic stability.
E2F1转录因子可激活促进S期的基因，介导细胞凋亡，并通过尚不完全清楚的机制刺激DNA修复。XRCC1（X射线修复交叉互补基因1）蛋白对于高效的单链断裂/碱基切除修复至关重要。尽管损伤信号和增殖信号均可提高XRCC1水平，但调节XRCC1转录的机制仍不清楚。为了研究这些上游机制，将XRCC1启动子克隆到荧光素酶报告基因中。野生型E2F1的异位表达可激活XRCC1启动子-荧光素酶报告基因，而无活性的突变型E2F1（132E）则不能，并且启动子中预测的E2F1结合位点的缺失会减弱E2F1诱导的激活作用。在条件性表达野生型而非突变型E2F1的细胞中，内源性XRCC1表达增加，甲磺酸甲酯诱导的DNA损伤可刺激E2F1（+/+）而非E2F1（-/-）小鼠胚胎成纤维细胞（MEF）中的XRCC1表达。此外，与E2F1（+/+）MEF相比，E2F1（-/-）MEF在甲磺酸甲酯诱导的损伤后显示出减弱的DNA修复能力。此外，与具有野生型XRCC1（AA8）的中国仓鼠卵巢细胞相比，具有突变型XRCC1（EM9）的中国仓鼠卵巢细胞对E2F1诱导的细胞凋亡更敏感。这些结果为E2F途径在维持基因组稳定性中的作用提供了新的机制性见解。
