Effect of heterozygous loss of p53 on benzo[a]pyrene‐induced mutations and tumors in DNA repair‐deficient XPA mice

Abstract

XPA-deficient mice have a complete deficiency in nucleotide excision repair, and as such they display a cancer predisposition after exposure to several carcinogens. Besides being sensitive to genotoxic agents applied to the skin, they are also susceptible to human carcinogens given orally, like benzo[a]pyrene (B[a]P). To study the role of the tumor suppressor gene p53 in DNA repair, gene mutation, and tumor induction, we crossed XPA-deficient mice with p53 knockout mice and lacZ (pUR288) gene marker mice. When treated orally (by gavage) with B[a]P, the XPA(-/-)/p53(+/-) double transgenic mice developed tumors much earlier and with higher frequency compared to their single transgenic counterparts. The major tumor type found in all genotypes was generalized lymphoma mainly residing in the spleen; several sarcomas were observed in p53(+/-) and XPA(-/-)/p53(+/-) mice. Next, we determined lacZ mutation frequencies in several (non)target tissues. It appeared that in the spleen (the major tumor target tissue) of XPA(-/-) and XPA(-/-)/p53(+/-) mice the lacZ mutation frequency was significantly elevated (80-100 x 10(-5)), and was two times higher as found in spleens of B[a]P-treated WT and p53(+/-) mice (P = 0.003). In nontumor target tissues like liver and lung, we found a moderate increase in the lacZ gene mutation frequency (30-40 x 10(-5)), which was independent of the genotype. The results obtained with the DNA-repair deficient XPA mice indicate that a significantly increased lacZ mutation frequency in a particular organ/tissue is an early marker for tumor development at later stages at the same site. However, the synergistic effect of a XPA(-/-)- and a p53(+/-)-deficiency in tumor development is not reflected by an absolute increase in the lacZ mutation frequency in the major tumor target tissue of XPA(-/-)/p53(+/-) or p53(+/-) mice compared to that of XPA(-/-) and WT mice, respectively.

Tissue specific mutagenic and carcinogenic responses in NER defective mouse models

“…[65] and [130]. In accordance, in the spleen of Xpa-deficient mice, mutant frequency levels of the non-transcribed lacZ as well as the actively transcribed Hprt gene clearly exceeded those measured in WT mice [130], [131] and [132]. This increase in Hprt gene mutation in Xpa −/− mice was also observed upon exposure to BNU [133].…”

“…However, focusing on urinary bladder tumor development, the mutant frequencies did not predict tumorigenesis as Csb −/− mice showed a mutant frequency comparable with WT and Xpa −/− mice. [65] and [130]. In accordance, in the spleen of Xpa-deficient mice, mutant frequency levels of the non-transcribed lacZ as well as the actively transcribed Hprt gene clearly exceeded those measured in WT mice [130], [131] and [132].…”

Integrating Field Analyses with Laboratory Exposures to Assess Ecosystems Health

“…Administration of benzo [a]pyrene by gavage to mice that lack the nucleotide excision repair gene (XPA -/-) resulted in a high incidence of lymphomas; the tumour response was significantly stronger than that in similarly treated XPA +/-and XPA +/+ mice (de Vries et al, 1997). When treated with benzo [a]pyrene by gavage, XPA -/-/p53 +/-double transgenic mice developed tumours (mainly splenic lymphomas and forestomach tumours) much earlier and at a higher incidence than similarly treated single transgenic (XPA -/-or p53 +/-) and wild-type counterparts (C57/B1/6) (van Oostrom et al, 1999). These cancer-prone…”

Nucleotide Excision Repair and Cancer

“…Other human carcinogens like cyclosporin A (CsA) and diethylstilbestrol (DES), although not directly mutagenic, showed to be carcinogenic in Xpa mice after 39 week exposure, but in contrary the low potent human carcinogen phenacetin did not result in a significant increase in tumors. LacZ and Hprt mutation measurements in Xpa mice after B[a]P and 2-AAF treatment showed a 2-3 fold increase in mutations compared to wild type mice after only 12-13 weeks of exposure (Hoogervorst et al,2005;van Oostrom et al,1999;Bol et al,1998;de Vries et al,1997b). This increase in mutational load in comparison to wild type indicates Xpa mice are more sensitive to mutation accumulation, which consequently corresponds to the increased cancer susceptibility of Xpa mice.…”