Elevated frequencies of benzo(a)pyrene-induced Hprt mutations in internal tissue of XPA-deficient mice

Area of Science:

• Genetics and Molecular Biology
• Toxicology
• Cancer Research

Background:

• Xeroderma pigmentosum (XP) is a genetic disorder characterized by extreme sun sensitivity and a high predisposition to skin cancer.
• XP patients exhibit cellular defects in nucleotide excision repair (NER), a critical DNA repair pathway.
• Genetically engineered mice deficient in the XPA gene, a key component of NER, have been developed to model XP.

Purpose of the Study:

• To investigate the consequences of defective NER on mutagenesis in mice exposed to environmental mutagens.
• To assess the role of NER in repairing DNA damage induced by benzo(a)pyrene and 2-acetylaminofluorene.
• To provide direct evidence in mammals linking deficient NER to enhanced mutagenesis in internal tissues.

Main Methods:

• Mature T lymphocytes were isolated from normal and XPA-deficient mice.
• Cells were stimulated to proliferate in vitro to select for mutants at the endogenous Hprt locus.
• Mice were exposed to benzo(a)pyrene and 2-acetylaminofluorene, and Hprt mutant frequencies were analyzed.

Main Results:

• Benzo(a)pyrene exposure caused a dose-dependent increase in Hprt mutant frequency in normal mice.
• XPA mice showed an earlier onset of Hprt mutations after chronic benzo(a)pyrene exposure compared to normal mice.
• 2-acetylaminofluorene did not significantly increase Hprt mutant frequency in either normal or XPA mice, attributed to low DNA adduct formation.

Conclusions:

• Deficient NER in mammals leads to enhanced mutagenesis in endogenous genes upon exposure to environmental mutagens like benzo(a)pyrene.
• This study provides the first direct evidence in mammals supporting the link between defective NER and increased mutation susceptibility.
• The findings underscore the importance of NER in protecting against chemically induced mutations in internal tissues.