Novel insights into the ecDNA formation mechanism involving MSH3 in methotrexate‑resistant human colorectal cancer cells

作者：Xu Wang, Yanan Qu, Ruonan Xing, Jing Zhou, Yanghe Liu, Huishu Zhang, Jing Zhu, Jinfa Ma, Xiaobo Cui, Tiantian Song, Shukai Xing, Guohua Ji, Peng Liu, Wenjing Sun, Songbin Fu, Xiangning Meng · 发表于：International Journal of Oncology · 年份：2023 · DOI：10.3892/ijo.2023.5582 · 被引用次数：11 · 研究领域：Cancer Genomics and Diagnostics、Genetic factors in colorectal cancer、DNA Repair Mechanisms

Extrachromosomal DNAs (ecDNAs), also known as double minutes (DMs), can induce a fast increase in gene copy numbers and promote the development of cancer, including drug resistance. MutS homolog 3 (MSH3), a key protein in mismatch repair, has been indicated to participate in the regulation of DNA double‑strand break (DSB) repair, which has been reported to be associated with the formation of ecDNAs. However, it remains unclear whether MSH3 can influence drug resistance via ecDNAs in cancer. In the present study, high MSH3 expression was observed in methotrexate (MTX)‑resistant HT29 cells [DM‑ and homogeneously staining region (HSR)‑containing cells] compared with parental HT29 cells. Additionally, decreased amounts of ecDNAs, HSRs and amplified genes locating on ecDNAs and HSRs were detected following depletion of MSH3 and this could be reversed by overexpressing MSH3 in DM‑containing cells. No corresponding changes were found in HSR‑containing cells. The present study further verified the involvement of MSH3‑regulated DNA DSB repair pathways in the formation of ecDNAs by detecting the expression of core proteins and pathway activity. Furthermore, expulsion of ecDNAs/HSRs was detected and increased frequencies of micronuclei/nuclear buds with dihydrofolate reductase ( DHFR ) signals were observed in MSH3‑depleted DM‑containing cells. Finally, changes in MSH3 expression could affect DHFR amplification‑derived DHFR expression and cell sensitivity to MTX, suggesting that MSH3 ...