Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520, USA.
Nucleic Acids Res. 2013 Oct;41(19):8979-94. doi: 10.1093/nar/gkt670. Epub 2013 Aug 2.
DNA sequences capable of forming triplexes are prevalent in the human genome and have been found to be intrinsically mutagenic. Consequently, a balance between DNA repair and apoptosis is critical to counteract their effect on genomic integrity. Using triplex-forming oligonucleotides to synthetically create altered helical distortions, we have determined that pro-apoptotic pathways are activated by the formation of triplex structures. Moreover, the TFIIH factor, XPD, occupies a central role in triggering apoptosis in response to triplex-induced DNA strand breaks. Here, we show that triplexes are capable of inducing XPD-independent double strand breaks, which result in the formation of γH2AX foci. XPD was subsequently recruited to the triplex-induced double strand breaks and co-localized with γH2AX at the damage site. Furthermore, phosphorylation of H2AX tyrosine 142 was found to stimulate the signaling pathway of XPD-dependent apoptosis. We suggest that this mechanism may play an active role in minimizing genomic instability induced by naturally occurring noncanonical structures, perhaps protecting against cancer initiation.
能够形成三链体的 DNA 序列在人类基因组中很普遍，并且已被发现具有内在的诱变作用。因此，DNA 修复和细胞凋亡之间的平衡对于抵消它们对基因组完整性的影响至关重要。我们使用形成三链体的寡核苷酸来人为地制造改变的螺旋扭曲，从而确定了促凋亡途径是通过三链体结构的形成而被激活的。此外，TFIIH 因子 XPD 在响应三链体诱导的 DNA 链断裂而引发细胞凋亡中起着核心作用。在这里，我们表明三链体能够诱导 XPD 非依赖性双链断裂，从而导致 γH2AX 焦点的形成。随后，XPD 被招募到三链体诱导的双链断裂处，并与 γH2AX 在损伤部位共定位。此外，还发现 H2AX 酪氨酸 142 的磷酸化能够刺激 XPD 依赖性凋亡的信号通路。我们认为，这种机制可能在最小化由自然发生的非canonical 结构引起的基因组不稳定性方面发挥积极作用，也许可以预防癌症的发生。
