Safina Alfiya, Cheney Peter, Pal Mahadeb, Brodsky Leonid, Ivanov Alexander, Kirsanov Kirill, Lesovaya Ekaterina, Naberezhnov Denis, Nesher Elimelech, Koman Igor, Wang Dan, Wang Jianming, Yakubovskaya Marianna, Winkler Duane, Gurova Katerina
Department of Cell Stress Biology, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14127, USA.
Department of Evolutionary & Environmental Biology, Tauber Bioinformatics Research Center, University of Haifa, Mount Carmel, Haifa 31905, Israel.
Nucleic Acids Res. 2017 Feb 28;45(4):1925-1945. doi: 10.1093/nar/gkw1366.
Transitions of B-DNA to alternative DNA structures (ADS) can be triggered by negative torsional strain, which occurs during replication and transcription, and may lead to genomic instability. However, how ADS are recognized in cells is unclear. We found that the binding of candidate anticancer drug, curaxin, to cellular DNA results in uncoiling of nucleosomal DNA, accumulation of negative supercoiling and conversion of multiple regions of genomic DNA into left-handed Z-form. Histone chaperone FACT binds rapidly to the same regions via the SSRP1 subunit in curaxin-treated cells. In vitro binding of purified SSRP1 or its isolated CID domain to a methylated DNA fragment containing alternating purine/pyrimidines, which is prone to Z-DNA transition, is much stronger than to other types of DNA. We propose that FACT can recognize and bind Z-DNA or DNA in transition from a B to Z form. Binding of FACT to these genomic regions triggers a p53 response. Furthermore, FACT has been shown to bind to other types of ADS through a different structural domain, which also leads to p53 activation. Thus, we propose that FACT acts as a sensor of ADS formation in cells. Recognition of ADS by FACT followed by a p53 response may explain the role of FACT in DNA damage prevention.
B-DNA向替代DNA结构（ADS）的转变可由负扭转应变引发，这种应变在复制和转录过程中出现，并可能导致基因组不稳定。然而，ADS在细胞中是如何被识别的尚不清楚。我们发现，候选抗癌药物curaxin与细胞DNA的结合会导致核小体DNA解旋、负超螺旋积累以及基因组DNA的多个区域转化为左手Z型。在curaxin处理的细胞中，组蛋白伴侣FACT通过SSRP1亚基迅速结合到相同区域。纯化的SSRP1或其分离的CID结构域与含有交替嘌呤/嘧啶的甲基化DNA片段（易于发生Z-DNA转变）的体外结合，比与其他类型的DNA的结合要强得多。我们提出，FACT可以识别并结合Z-DNA或从B型向Z型转变过程中的DNA。FACT与这些基因组区域的结合会触发p53反应。此外，已证明FACT通过不同的结构域与其他类型的ADS结合，这也会导致p53激活。因此，我们提出FACT在细胞中充当ADS形成的传感器。FACT对ADS的识别随后引发p53反应，这可能解释了FACT在预防DNA损伤中的作用。
