Chung Oliver W, Yao Shun, Yang Fu, Wang Ling, Cerda-Smith Christian, Hutchinson Haley M, Wood Kris C, Su Weijia, Khasraw Mustafa, Zou Lee, Ramsden Dale A, Zhang Zz Zhao
Department of Pharmacology & Cancer Biology, Duke University School of Medicine, Durham, USA.
These authors contributed equally.
bioRxiv. 2025 Feb 23:2025.02.18.638901. doi: 10.1101/2025.02.18.638901.
Extrachromosomal circular DNA (ecDNA) are commonly produced within the nucleus to drive genome dynamics and heterogeneity, enabling cancer cell evolution and adaptation. However, the mechanisms underlying ecDNA biogenesis remain poorly understood. Here using genome-wide CRISPR screening in human cells, we identified the BRCA1-A and the LIG4 complexes mediate ecDNA production. Following DNA fragmentation, the upstream BRCA1-A complex protects DNA ends from excessive resection, promoting end-joining for circularization. Conversely, the MRN complex, which mediates end resection and thus antagonizes the BRCA1-A complex, suppresses ecDNA formation. Downstream, LIG4 conservatively catalyzes ecDNA production in and mammals, with patient tumor ecDNA harboring junctions marked by LIG4 activity. Notably, disrupting LIG4 or BRCA1-A in cancer cells impairs ecDNA-mediated adaptation, hindering resistance to both chemotherapy and targeted therapies. Together, our study reveals the roles of the LIG4 and BRCA1-A complexes in ecDNA biogenesis, and uncovers new therapeutic targets to block ecDNA-mediated adaptation for cancer treatment.
染色体外环状DNA（ecDNA）通常在细胞核内产生，以驱动基因组动态变化和异质性，促进癌细胞的进化和适应。然而，ecDNA生物发生的潜在机制仍知之甚少。在这里，我们利用全基因组CRISPR筛选技术在人类细胞中进行研究，发现BRCA1-A和LIG4复合物介导ecDNA的产生。在DNA片段化后，上游的BRCA1-A复合物保护DNA末端免受过度切除，促进末端连接以实现环化。相反，介导末端切除从而拮抗BRCA1-A复合物的MRN复合物则抑制ecDNA的形成。在下游，LIG4在人类和哺乳动物中保守地催化ecDNA的产生，患者肿瘤中的ecDNA含有以LIG4活性为标志的连接点。值得注意的是，破坏癌细胞中的LIG4或BRCA1-A会损害ecDNA介导的适应性，阻碍对化疗和靶向治疗的抗性。总之，我们的研究揭示了LIG4和BRCA1-A复合物在ecDNA生物发生中的作用，并发现了新的治疗靶点，以阻断ecDNA介导的适应性，用于癌症治疗。
