Mutation profile of the p53 gene in early mutant p53-positive patches of epidermal cells in SKH-1 mice chronically irradiated with UVB-light and treated orally with caffeine or green tea

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Treatment of SKH-1 hairless mice with UVB (30 mJ/cm2) twice a week for 20 weeks results in a large number of cellular patches visualized in epidermal sheets with an antibody (PAb240) that recognizes mutated p53 protein. These UVB-induced changes in the epidermis occur long before the appearance of tumors. Sequence analysis of the whole coding region of the p53 gene (exons 2 to 11) from patches of control, water treated mice detected all mutation hotspots reported earlier (Dumaz et al., Carcinogenesis 18:897-904, 1997) in UVB-induced mouse squamous cell carcinomas at codons 270 (Arg to Cys), 149 (Pro to Ser), 275 (Pro to Leu and Pro to Ser) and 176 (His to Tyr) with a frequency of 47.7%, 9.1%, 4.5% and 2.3% of the total mutations (N=88), respectively. An additional mutation hotspot at codon 210 (Arg to Cys) was also detected in the patches with a frequency of 8.1%. Treatment of mice with caffeine (0.4 mg/ml) or green tea (6 mg tea solids/ml) as their sole source of drinking fluid simultaneously with the UVB treatment decreased the number of UVB-induced patches by about 40% and increased the proportion of patches with a mutation at codon 238 (Ser to Phe) from 1.2% in the control mice to 13.4% in the caffeine-treated mice and to 10.8% in the tea group. In addition, these treatments eliminated the formation of patches with a mutation at codon 149 (Pro to Ser). One or two p53 mutations were found in 64.4%, 88.0% and 85.3% of the patches from water, caffeine and tea treated animals, respectively. The majority of these mutations were missense substitutions (97.7%, 97.6% and 97.4%, respectively) containing mostly C to T transitions (89.0%, 97.5% and 83.8%, respectively) located at dipyrimidine sites (97.7%, 98.8%, 94.7%, respectively) of the non-transcribed strand (100%, 94% and 86%, respectively). Collectively, these results indicate that (a) major p53 mutation hotspots found in UVB-induced squamous cell carcinomas are also present in PAb240-positive patches of epidermal cells suggesting their formation at a very early stage of tumor development, (b) some mutant p53 positive patches do not have a mutation in the coding region of the p53 gene and (c) treatment of mice with caffeine or green tea during exposure to UVB light decreases the number of UVB-induced patches and changes the mutation profile of the p53 gene in these patches. (Supported in part by NIH Grants CA80759 and CA88961).