Patches of Mutant p53-Immunoreactive Epidermal Cells Induced by Chronic UVB Irradiation Harbor the Same p53 Mutations as Squamous Cell Carcinomas in the Skin of Hairless SKH-1 Mice

Abstract

Treatment of SKH-1 hairless mice with UVB (30 mJ/cm 2 ) twice a week for 20 weeks results in the formation of cellular patches, long before the appearance of tumors, that are visualized in epidermal sheets with an antibody (PAb240) recognizing mutated p53 protein. Direct sequencing analysis of the whole coding region of the p53 gene (exons 2-11) detected one or two mutations in 64.4% of 104 analyzed patches and no mutations in nonstained adjacent normal controls. Homozygous mutation was detected in 22.4% of the mutant patches. Except for two nonsense mutations, all others were missense (exons 4-9) and mostly (95.5%) at the DNA-binding domain. Primer extension analysis of cloned PCR fragments found three of four double-mutated patches harboring different mutations in separate alleles. All mutation hotspots reported earlier in UVB-induced mouse squamous cell carcinomas (SCC) at codons 270 (Arg ! Cys), 149 (Pro ! Ser), 275 (Pro ! Leu and Pro ! Ser), and 176 (His ! Tyr) with a frequency of 32.1%, 7.1%, 14.7%, and 3.2% were detected in epidermal patches at a frequency 47.7%, 9.1%, 4.5%, and 2.3%, respectively. Mutations at codons 210 and 191 found in patches at respective frequencies of 8.0% and 4.5% were not previously detected in UVB-induced mouse SCC. In summary, (a) the p53 mutation profile of UVB-induced skin patches and SCC was very similar suggesting that patches are precursor lesions for SCC, (b) a small number of patches harbored mutations that were not before observed in SCC from UVB-treated mice, and (c) about 36% of the patches did not harbor a p53 mutation. (Cancer Res 2005; 65(9): 3577-85)

Dietary Immunosuppressants Do Not Enhance UV-Induced Skin Carcinogenesis, and Reveal Discordance between p53-Mutant Early Clones and Carcinomas

“…As the hotspot mutations at codons 270 or 275 comprise about half of the mutations in the p53 gene, the mutational frequency suggests that maximally 20% of the cells in the skin would harbor mutated p53 (if cells harbored more than one mutation in similar percentages as mut-p53 cell clusters, the fraction would come down to about 14%; refs. 29,35). These results are in agreement with a recent deep sequencing study of human skin from middle-aged individuals revealing that persistent p53 mutations had accumulated in 14% of the epidermal cells (36).…”

Protection against UVR Involves MC1R-Mediated Non-Pigmentary and Pigmentary Mechanisms In Vivo

“…Similar p53 mutations have been identified in non-melanoma skin cancers, consistent with the view that UVR-induced p53 gene damage, if inadequately repaired, allows proliferation of abnormal keratinocytes to form p53 clones, some of which subsequently develop into cancer (Bäckvall et al, 2004;Kramata et al, 2005;Rebel et al, 2005). The development of p53 clones therefore serves as a sensitive assay to measure inadequate repair of UVR-induced DNA damage in single epidermal cells and for effects on clonal proliferation in skin.…”

“…Chronic exposure of skin to UVR results in development of clones of keratinocytes immunopositive for p53, with many of these containing p53 mutations (varying from 29 to 64% in individual studies), especially in exons 5-8 (Jonason et al, 1996;Tabata et al, 1999;Bäckvall et al, 2004;Kramata et al, 2005;Rebel et al, 2005). Similar p53 mutations have been identified in non-melanoma skin cancers, consistent with the view that UVR-induced p53 gene damage, if inadequately repaired, allows proliferation of abnormal keratinocytes to form p53 clones, some of which subsequently develop into cancer (Bäckvall et al, 2004;Kramata et al, 2005;Rebel et al, 2005).…”

Bioavailability and stability issues in understanding the cancer preventive effects of tea polyphenols

“…Treatment of mice with orally administered EGCG or topical caffeine as the sole source of drinking fluid, following discontinuation of UVB treatment, enhanced the disappearance of p53 mutant patches, but had no effect on surrounding normal tissues. 17,18 These data suggest that the cancer preventive effect of caffeine or EGCG occurs via a pro-apoptotic effect in early precancerous lesions. Numerous mechanisms have been suggested based on cell line studies (Fig.…”