Xpa Mice Research Articles

Seventh Japanese–German workshop on molecular and cellular aspects of carcinogenesis

Seventh Japanese–German workshop on molecular and cellular aspects of carcinogenesis

Mice deficient in the nucleotide excision repair gene XPA have elevated sensitivity to benzo[ a ]pyrene induction of lung tumors

This study is focused on chemical induction of lung tumors in xeroderma pigmentosum group A gene (XPA)-deficient mice to clarify the role of nucleotide excision repair (NER) in internal organs. Six-week-old female XPA-/-, XPA(+/-) and XPA(+/+) mice were instilled intratracheally with benzo[a] pyrene (B[a]P). A total of 68 surviving XPA mice treated with B[a]P were examined at month 16. The pulmonary adenoma incidence in XPA(-/-) mice was significantly higher than that in XPA(+/+) mice (71 versus 35%). Similarly, tumor multiplicity was elevated and, in addition, only XPA(-/-) mice had lung carcinomas. These results provide the first evidence that a deficiency in the NER gene XPA leads to enhanced tumorigenesis in the lung after exposure to B[a]P.

Seventh Japanese-German workshop on molecular and cellular aspects of carcinogenesis

Seventh Japanese-German workshop on molecular and cellular aspects of carcinogenesis

Nucleotide excision repair modulates the cytotoxic and mutagenic effects of N-n-butyl-N-nitrosourea in cultured mammalian cells as well as in mouse splenocytes in vivo.

The butylating agent N-n-butyl-N-nitrosourea (BNU) was employed to study the role of nucleotide excision repair (NER) in protecting mammalian cells against the genotoxic effects of monofunctional alkylating agents. The direct acting agent BNU was found to be mutagenic in normal and XPA mouse splenocytes after a single i.p. treatment in vivo. After 25 and 35 mg/kg BNU, but not after 75 mg/ kg, 2- to 3-fold more hprt mutants were detected in splenocytes from XPA mice than from normal mice. Using O6-alkylguanine-DNA alkyltransferase (AGT)-deficient hamster cells, it was found that NER-deficient CHO UV5 cells carrying a mutation in the ERCC-2 gene were 40% more mutable towards lesions induced by BNU when compared with parental NER-proficient CHO AA8 cells. UV5 cells were 1.4-fold more sensitive to the cytotoxic effects of BNU compared with AA8 cells. To investigate whether this increased sensitivity of NER-deficient cells is modulated by AGT activity, cell survival studies were performed in human and mouse primary fibroblasts as well. BNU was 2.7-fold more toxic for mouse XPA fibroblasts compared with normal mouse fibroblasts. Comparable results were found for human fibroblasts. Taken together these data indicate that the role of NER in protecting rodent cells against the mutagenic and cytotoxic effects of the alkylating agent BNU depends on AGT.

Effect of heterozygous loss ofp53 on benzo[a]pyrene-induced mutations and tumors in DNA repair-deficientXPA mice

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.

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

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

Defective Global Genome Repair in XPC Mice Is Associated with Skin Cancer Susceptibility But Not with Sensitivity to UVB Induced Erythema and Edema

It is generally presumed that xeroderma pigmentosum (XP) patients are extremely sensitive to developing UV erythema, and that they have a more than 1000-fold increased skin cancer risk. Recently established mouse models for XP can be employed to investigate the mechanism of these increased susceptibilities. In line with human data, both XPA and XPC knockout mice have been shown to have an increased susceptibility to UVB induced squamous cell carcinomas. In XPA knockouts, nucleotide excision repair of UV induced DNA photolesions is completely defective (i.e., both global genome repair and transcription coupled repair are defective). We determined the strand specific removal of cyclobutane pyrimidine dimers and pyrimidine [6-4] pyrimidone photoproducts from the p53 gene in cells from XPC knockout mice and wild-type littermates. Analogous to human XPC cells, embryonic fibroblasts from XPC knockout mice are only capable of performing transcription coupled repair of DNA photolesions. We show that these XPC knockout mice, in striking contrast to XPA knockout mice, do not have a lower minimal erythema/edema dose than their wild-type littermates. Hence, defective global genome repair appears to lead to skin cancer susceptibility, but does not influence the sensitivity to acute effects of UVB radiation, such as erythema and edema. The latter phenomena thus relate to the capacity to perform transcription coupled repair, which suggests that blockage of RNA synthesis is a key event in the development of UV erythema and edema.