放疗利用高能量的放射线，破坏肿瘤细胞的遗传物质DNA，使其失去增殖能力而死亡，是肿瘤治疗的主要手段之一。我们前期研究发现，放疗诱导的Caspase-3激活及细胞凋亡对于肿瘤治疗为双刃剑，凋亡细胞并非被动死亡，而是积极抗争求生，激活的Caspase-3可激活iPLA2/AA/PGE2信号通路产生生长因子，通过旁分泌形式促进残存的肿瘤细胞再增殖，在Nature Medicine发表。后续研究发现Caspase-3还可激活PKCδ/Akt/VEGF-A信号通路等参与肿瘤再增殖。更有意义的是，我们发现放疗后可产生多倍体巨核细胞，巨核细胞可重新产生二倍体小细胞，新产生的小细胞可继续增殖分裂，引发肿瘤再增殖。本研究拟通过单细胞RNA测序，筛查启动“去多倍体化”的关键基因，并通过CRISPR/Cas9技术敲除关键基因，体内外实验验证其作用与作用机制，为临床靶向阻断肿瘤再增殖、提升放疗效果提供实验依据。

Radiotherapy uses high-energy radiation to destroy the genetic material DNA of tumor cells and kill tumor cells by making it lose the ability to regenerate. This is also one of the main means treat tumor. Our previous studies have found that radiotherapy induced Caspase-3 activation and apoptosis is a double-edged sword. We propose that apoptotic cells are not passive death, but will actively fight for survival. The radiotherapy induced apoptotic cells with activated Caspase-3 can produce cytokines through the iPLA2/AA/PGE2 signaling pathway, and promote the repopulation of residual tumor cells through paracrine method. Caspase-3 can also participate in tumor repopulation through PKCδ/Akt/VEGF-A signaling pathways. More interestedly, we found that polyploid nuclei giant cells can be produced after radiotherapy, and some giant nuclear cells can re-produce small cells, and newly produced small cells can continue to proliferate and divide, triggering tumor re-growth or recurrence. This study is intended to focus on the mechanism of "de-polyploid" of giant nuclear cells to produce small cells. We plan to do single-cell RNA sequencing, to screen the key genes which regulate "de-polyploid" process. In order to verify the role or function of the found key genes we plan to knockout the key genes through CRISPR/Cas9 technology, and investigate the possible underline mechanism for "de-polyploid" by in vitro and in vivo experiments. The goal of this study is to better understand the mechanism of tumor repopulation and find the targets for improving the effect of radiotherapy.