Oncogene&JBC：解析DNA修复蛋白与癌症复发

就像机体会对抗生素产生抵抗一样，肿瘤细胞也会对特定的抗癌药物产生抵抗。中佛罗里达大学UCF的研究人员发现，在乳腺癌和卵巢癌等数种癌症中出现的KLF8蛋白，是癌细胞抗性和癌症复发的关键。KLF8是一种DNA修复蛋白，研究显示它既能帮助肿瘤细胞抵抗抗癌药物，也能够帮助肿瘤细胞再生。

“所有细胞都有DNA修复机制，”领导这项研究的UCF医学院副教授赵季和（音译：Jihe Zhao）解释道，短短几个月间他已经连续在Journal of Biological Chemistry和Oncogene等杂志上发表了数篇有关KLF8蛋白的文章。“这也是我们在不断的DNA损伤威胁下得以存活的原因。KLF8在乳腺癌和卵巢癌等多种癌症中均存在过表达现象。如果我们能够在癌症治疗中阻止这一基因的启动，就有望阻止肿瘤复发。当然这还需要进一步深入研究，不过前景是非常乐观的。”

据美国癌症协会统计，全美有两百五十万至两百七十万女性患有乳腺癌，其中10-20%的患者会经历癌症复发。现有的治疗方式取决于癌症发展的阶段，包括手术切除和一系列抗癌的化疗药物。每年约有22,200名女性也被诊断出卵巢癌。

以破坏DNA为目的的化疗方法，依赖于癌细胞修复失败，并由此促使癌细胞死亡。不过细胞中DNA修复功能的水平过高，不但可能增加癌细胞对这类化疗的抗性，也可能会因DNA修复不当使基因组/染色体不稳定从而增加恶性细胞。

赵副教授的团队利用一种治疗乳腺癌的抗癌药物，来确定KLF8蛋白的作用。“确实，研究显示促进DNA修复的KLF8与癌细胞对阿霉素产生抗性有着明显的关联，” 赵副教授说。“在其他类型基因毒性剂（DNA烷化剂和电离辐射等）引起的DNA损伤修复过程中，KLF8蛋白是否也起到同样的作用，这一点还需要进一步研究来验证。

此外，研究还指出KLF8蛋白除了增强癌细胞的抗药性以外，还可能因DNA异常修复干扰基因组的完整性，并最终引发癌症的侵袭进程。

doi:10.1038/onc.2012.545
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Transformation of human ovarian surface epithelial cells by Krüppel-like factor 8

H Lu, X Wang, A M Urvalek, T Li, H Xie, L Yu and J Zhao

We have previously demonstrated that Krüppel-like factor 8 (KLF8) participates in oncogenic transformation of mouse fibroblasts and is highly overexpressed in human ovarian cancer. In this work, we first correlated KLF8 overexpression with the aggressiveness of ovarian patient tumors and then tested if KLF8 could transform human ovarian epithelial cells. Using the immortalized non-tumorigenic human ovarian surface epithelial cell line T80 and retroviral infection, we generated cell lines that constitutively overexpress KLF8 alone or its combination with the known ovarian oncogenes c-Myc, Stat3c and/or Akt and examined the cell lines for anchorage-independent growth and tumorigenesis. The soft agar clonogenic assay showed that T80/KLF8 cells formed significantly more colonies than the mock cells. Interestingly, the cells expressing both KLF8 and c-Myc formed the largest amounts of colonies, greater than the sum of colonies formed by the cells expressing KLF8 and c-Myc alone. These results suggested that KLF8 might be a weak oncogene that works cooperatively with c-Myc to transform ovarian cells. Surprisingly, overexpression of KLF8 alone was sufficient to induce tumorigenesis in nude mice resulting in short lifespan irrespective of whether the T80/KLF8 cells were injected subcutaneously, intraperitoneally or orthotopically into the ovarian bursa. Histopathological studies confirmed that the T80/KLF8 tumors were characteristic of human serous ovarian carcinomas. Comparative expression profiling and functional studies identified the cell cycle regulators cyclin D1 and USP44 as primary KLF8 targets and effectors for the T80 transformation. Overall, we identified KLF8 overexpression as an important factor in human ovarian carcinoma pathogenesis.

doi: 10.1074/jbc.M112.418053
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A Novel Role of Krüppel-like Factor 8 in DNA Repair in Breast Cancer Cells

Heng Lu‡, Liu Hu‡, Tianshu Li‡, Satadru Lahiri‡, Chao Shen‡, Melissa S. Wason‡, Debarati Mukherjee‡, Hui Xie§, Lin Yu‡ and Jihe Zhao‡

Krüppel-like factor 8 (KLF8) regulates critical gene transcription and cellular events associated with cancer. However, the role of KLF8 in cancer remains largely unknown. Here, we report a surprisingly novel role for KLF8 in DNA repair in breast cancer cells. Comet, clonogenic, and WST-1 assays showed that KLF8 expression is required for protecting human breast cancer cells from doxorubicin-induced DNA damage and cell death. Western blotting indicated that overexpression of ectopic KLF8 attenuated the levels of the DNA damage marker γH2A.X in doxorubicin-treated PARP-1+/+ but not PARP-1−/− mouse embryonic fibroblasts, whereas the PARP-1-binding-defective KLF8 mutant failed to do so. Interestingly, in response to the DNA damage, KLF8 was phosphorylated by the DNA-dependent protein kinase catalytic subunit and, subsequently, SUMOylated by SUMO E3 ligases protein inhibitors of activated STAT (PIASs), which depends upon the interaction of KLF8 with DNA-dependent protein kinase catalytic subunit, PIASs, and PARP-1 as well as their enzymatic activities. Lastly, we show evidence that KLF8 was recruited to the DNA damage site. These results suggest a novel role and mechanism for KLF8 in the regulation of DNA repair and therapeutic resistance in breast cancer cells.