The distinct roles of NEIL1 and XPA in limiting aflatoxin B₁-induced mutagenesis in mice.

Dietary exposure to aflatoxin B₁ (AFB₁) is a risk factor for the development of hepatocellular carcinomas (HCCs). Following metabolic activation, AFB₁ reacts with guanines to form covalent DNA adducts, which induce high-frequency G > T transversions. The molecular signature associated with these mutational events aligns with the single base substitution signature 24 (SBS24) in the Catalog of Somatic Mutations in Cancer (COSMIC) database. Deficiencies in either base excision repair (BER) due to the absence of Nei-like DNA glycosylase 1 (NEIL1) or nucleotide excision repair (NER) due to the absence of xeroderma complementation group A protein (XPA) contribute to HCCs in murine models. In the current study, ultra-low error duplex sequencing was used to characterize mutational profiles in liver DNAs of NEIL1-deficient, XPA-deficient, and DNA repair-proficient mice following neonatal injection of 1 mg/kg AFB₁. Analyses of AFB₁-induced mutations showed high cosine similarity to SBS24, regardless of repair proficiency status. The absence of NEIL1 resulted in an approximately 30% increase in the frequency of mutations, with distribution suggesting preferential NEIL1-dependent repair of AFB₁ lesions in open chromatin regions. A trend of increased mutagenesis was also observed in the absence of XPA. Consistent with the role of XPA in transcription-coupled repair, mutational profiles in XPA-deficient mice showed disruption of the transcriptional bias in mutations associated with SBS24. Implications: Our findings define the roles of DNA repair pathways in AFB₁-induced mutagenesis and carcinogenesis in murine models, with these findings having implications in human health for those with BER and NER deficiencies.