INFLUENCE OF NUCLEOTIDE EXCISION-REPAIR ON N-HYDROXY-2-ACETYLAMINOFLUORENE-INDUCED MUTAGENESIS STUDIED IN LAMBDA-LACZ-TRANSGENIC MICE

To study the influence of nucleotide excision repair (NER) on mutagene sis in vivo, ERCC1+/-, XPA-/-, and wild-type (ERCC1+/+ and XPA+/+, res pectively) lambda lacZ-transgenic mice were treated i.p. with N-hydrox y-2-acetylaminofluorene (N-OH-AAF) and lacZ mutant frequencies were de termined in liver. No significant effect of the treatment on the mutan t frequency in wild-type or ERCC 1-heterozygous mice was observed. The liver mutant frequency appeared to be significantly increased in trea ted XPA-/- mice only. To distinguish N-OH-AAF-induced from spontaneous mutations, lacZ mutants derived from treated XPA-/- mice were subject ed to DNA-sequence analysis and the spectrum obtained was compared to that established for lacZ mutants in liver of PBS-treated lambda lacZ- transgenic mice of the parent strain 40.6. The N-OH-AAF-induced mutati on spectrum appeared to be significantly different from the spontaneou s mutation spectrum: the former consisted of mainly (19/22) single bp substitutions targeted at G, of which the majority (12/19) were G:C -- > T:A transversions, suggesting that N-(deoxy-guanosin-8-yl)-2-aminofl uorene [dG-CB-AF], the major DNA adduct in N-OH-AAF-treated mice, is t he premutagenic lesion. After analysis of 21 spontaneous mutants, only ten single bp substitutions targeted at G were found, of which five w ere G:C --> T:A transversions. This study with XPA-/- lambda lacZ-tran sgenic mice shows that one of the components of NER, that is, the XPA protein, suppresses mutagenesis in vivo. (C) 1998 Wiley-Liss, Inc.