Laboratory of Cancer Biology, Centre for DNA Fingerprinting and Diagnostics, Hyderabad, Telangana, 500001, India.
Laboratory of Cancer Biology, Centre for DNA Fingerprinting and Diagnostics, Hyderabad, Telangana, 500001, India; Laboratory of Cancer Cell Biology, Department of Research, Institute of Liver and Biliary Sciences, Delhi 110070, India.
Exp Cell Res. 2015 Feb 1;331(1):123-141. doi: 10.1016/j.yexcr.2014.11.001. Epub 2014 Nov 12.
Maintaining the genomic integrity is a constant challenge in proliferating cells. Amongst various proteins involved in this process, Sirtuins play a key role in DNA damage repair mechanisms in yeast as well as mammals. In the present work we report the role of one of the least explored Sirtuin viz., SIRT7, under conditions of genomic stress when treated with doxorubicin. Knockdown of SIRT7 sensitized osteosarcoma (U2OS) cells to DNA damage induced cell death by doxorubicin. SIRT7 overexpression in NIH3T3 delayed cell cycle progression by causing delay in G1 to S transition. SIRT7 overexpressing cells when treated with low dose of doxorubicin (0.25 µM) showed delayed onset of senescence, lesser accumulation of DNA damage marker γH2AX and lowered levels of growth arrest markers viz., p53 and p21 when compared to doxorubicin treated control GFP expressing cells. Resistance to DNA damage following SIRT7 overexpression was also evident by EdU incorporation studies where cellular growth arrest was significantly delayed. When treated with higher dose of doxorubicin (>1 µM), SIRT7 conferred resistance to apoptosis by attenuating stress activated kinases (SAPK viz., p38 and JNK) and p53 response thereby shifting the cellular fate towards senescence. Interestingly, relocalization of SIRT7 from nucleolus to nucleoplasm together with its co-localization with SAPK was an important feature associated with DNA damage. SIRT7 mediated resistance to doxorubicin induced apoptosis and senescence was lost when p53 level was restored by nutlin treatment. Overall, we propose SIRT7 attenuates DNA damage, SAPK activation and p53 response thereby promoting cellular survival under conditions of genomic stress.
维持基因组完整性是增殖细胞面临的一项持续挑战。在参与这一过程的各种蛋白质中，Sirtuins 在酵母和哺乳动物的 DNA 损伤修复机制中发挥着关键作用。在本工作中，我们报告了在受到多柔比星处理时，一种研究最少的 Sirtuin 即 SIRT7 在基因组应激条件下的作用。SIRT7 的敲低使骨肉瘤（U2OS）细胞对多柔比星诱导的细胞死亡敏感。SIRT7 在 NIH3T3 中的过表达通过导致 G1 到 S 期转换延迟来延迟细胞周期进程。用低剂量多柔比星（0.25 μM）处理 SIRT7 过表达细胞时，与多柔比星处理的对照 GFP 表达细胞相比，衰老的起始延迟，DNA 损伤标志物 γH2AX 的积累减少，生长停滞标志物 p53 和 p21 的水平降低。SIRT7 过表达后对 DNA 损伤的抗性也通过 EdU 掺入研究得到证明，其中细胞生长停滞明显延迟。用更高剂量的多柔比星（>1 μM）处理时，SIRT7 通过减弱应激激活激酶（SAPK，即 p38 和 JNK）和 p53 反应来抵抗细胞凋亡，从而使细胞命运转向衰老。有趣的是，SIRT7 从核仁到核质的重新定位及其与 SAPK 的共定位是与 DNA 损伤相关的重要特征。当用 nutlin 处理恢复 p53 水平时，SIRT7 介导的对多柔比星诱导的细胞凋亡和衰老的抗性丧失。总的来说，我们提出 SIRT7 通过减弱 DNA 损伤、SAPK 激活和 p53 反应来促进基因组应激条件下的细胞存活。
