p53 mutations in cutaneous lesions induced in the hairless mouse by a solar ultraviolet light simulator

Abstract

We investigated skin lesions induced in hairless SKH:HR1 mice by chronic exposure to a solar ultraviolet light (UV) simulator for alterations of the p53 gene in conserved domains. Mutations of exons 5-8 of the p53 gene in skin lesions were screened in 31 benign skin lesions (hyperplasias), 25 precancerous skin lesions (keratoacanthomas), and 25 malignant skin lesions (squamous cell carcinomas; SCC) by polymerase chain reaction-single-strand conformation polymorphism analysis. Most of the mutations occurred at dipyrimidine sequences located on the nontranscribed strand; the most frequent modifications were C-->T transitions (77%) and CC-->TT tandem mutations (5%); the latter are considered the UV fingerprint. p53 mutations were detected in 3% of the hyperplasias, 12% of the keratoacanthomas, and 52% of the SCCs. Hence, the high frequency of p53 mutations in SCCs compared with keratoacanthomas induced by a solar UV simulator suggested that, in our study, p53 mutations probably occurred as a late event in the skin carcinogenesis progression of SCC. Interestingly, the level of CC-->TT tandem mutations in the SCCs (5%) was similar to that found in SCCs induced in hairless mice by UVB alone. p53 protein was also detected in the different types of skin lesions by immunohistochemical analysis. Thus, our data from hairless mouse skin tumors induced by a solar UV simulator confirmed the major role of UVB-induced DNA damage in skin carcinogenesis and suggested that UVA plays a minor role in bringing about p53 alterations.

INK4a‐ARF mutations in skin carcinomas from UV irradiated hairless mice

“…The mutational spectrum of the INK4a‐ARF mutations clearly indicated a role for UVB in mice photocarcinogenesis, as all mutations were C:G > T:A transitions occurring at dipyrimidic sites almost exclusively at CC sequences that were also very prone to mutagenesis in human skin cancers, therefore confirming data from previous mutational analysis of the p53 gene [6]. A hot spot at codon 71 of the murine p16 INK4a gene was observed in three tumors.…”

“…In this work, we have shown for the first time the presence of UV‐induced INK4a‐ARF mutations in 5 of 57 (9%) of mouse‐invasive SCCs. This mutational frequency of INK4a‐ARF was lower than that seen for the p53 gene (52–73%) [6,7]. Yet, to our knowledge, INK4a‐ARF mutations are extremely rare in mice tumors [15], as they only have been described once in liver tumors of mice exposed in utero to 3‐methylcholanthrene [16], further emphasizing the importance of our results.…”

“…Abbreviations: SCC, squamous cell carcinoma, KA, keratoacanthoma. P53 mutations were identified in a previous work [6]. A total of 52 skin specimens (five normal skin samples, 10 skin hyperplasias, 12 keratoacanthomas, and 25 SCCs) were analysed in the model irradiated with the solar simulator.…”

Relationship between UV-induced mutant p53 patches and skin tumours, analysed by mutation spectra and by induction kinetics in various DNA-repair-deficient mice

“…Although the same hotspot mutations in murine SCCs were described in other studies, the percentages tended to be lower: Analysis of relationship between UV-induced mutant p53 patches and skin tumours we found that 53% of the SCCs carried C!T transitions in codon 267, whereas Dumaz et al (8) found 39% and Queille (36) 46%. This slight difference may be attributable to the fact that we only included SCCs that are positive for Pab240 antibody in order to have a properly matched comparison with the Pab240-positive patches.…”

E6/E7 Expression of Human Papillomavirus Type 20 (HPV-20) and HPV-27 Influences Proliferation and Differentiation of the Skin in UV-Irradiated SKH-hr1 Transgenic Mice

“…UV-B irradiation increases the number of cells and prolonged the period of immunoreactivity to p53 in SKH-1 mice (4,5). The induction of p53 mutations by chronic UV-B exposure and its association with the development of malignant tumors have been demonstrated in these mice (4,42,46). In our study, p53 expression measured under chronic UV exposure in transgenic skin was reflected not only in the number of expressing cells but also in the distribution of these cells.…”