Laverty Daniel J, Tomar Rachana, Erlich Sophie, Stone Michael P, Nagel Zachary D
Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA 02115, United States.
Department of Chemistry, Vanderbilt Ingram Cancer Center, and Vanderbilt Center for Structural Biology, Vanderbilt University, Nashville, TN 37235, United States.
NAR Cancer. 2025 Sep 3;7(3):zcaf030. doi: 10.1093/narcan/zcaf030. eCollection 2025 Sep.
The mycotoxin, aflatoxin B (AFB), is a potent mutagen that contaminates agricultural food supplies. After ingestion, AFB is oxidized into a reactive electrophile that alkylates DNA, forming bulky lesions such as the genotoxic formamidopyrimidine lesion, AFB-Fapy dG. This lesion is mainly repaired by nucleotide excision repair (NER) in bacteria; however, in humans the picture is less clear. We report a plasmid-based host cell reactivation assay containing a site-specific AFB-Fapy dG lesion and present evidence that this lesion is mainly repaired by transcription-coupled NER (TC-NER) in human cells. Using a combination of isogenic knockout cell lines and immortalized fibroblasts from xeroderma pigmentosum and Cockayne syndrome patients, we show that the TC-NER factors CSA, CSB, and UVSSA are required for efficient AFB-Fapy dG repair, while the global-genome NER protein, XPC, is dispensable. Furthermore, knockout of CSB or UVSSA impairs AFB-Fapy dG repair to a similar degree as knockout of the core NER nuclease, XPF. Our data indicate that TC-NER is the major repair pathway for AFB-Fapy dG adducts in human cells.
霉菌毒素黄曲霉毒素B（AFB）是一种污染农产品供应的强效诱变剂。摄入后，AFB被氧化成一种活性亲电试剂，使DNA烷基化，形成诸如基因毒性甲酰胺嘧啶损伤AFB-Fapy dG等大的损伤。这种损伤在细菌中主要通过核苷酸切除修复（NER）进行修复；然而，在人类中情况尚不清楚。我们报告了一种基于质粒的宿主细胞再激活试验，该试验含有位点特异性的AFB-Fapy dG损伤，并提供证据表明这种损伤在人类细胞中主要通过转录偶联NER（TC-NER）进行修复。使用来自着色性干皮病和科凯恩综合征患者的同基因敲除细胞系和永生化成纤维细胞的组合，我们表明高效修复AFB-Fapy dG需要TC-NER因子CSA、CSB和UVSSA，而全基因组NER蛋白XPC则是可有可无的。此外，敲除CSB或UVSSA对AFB-Fapy dG修复的损害程度与敲除核心NER核酸酶XPF相似。我们的数据表明，TC-NER是人类细胞中AFB-Fapy dG加合物的主要修复途径。
