Mutation spectra of epidermal p53 clones adjacent to basal cell carcinoma and squamous cell carcinoma

Loss of EphA7 Expression in Basal Cell Carcinoma by Hypermethylation of CpG Islands in the Promoter Region

Basal cell carcinoma (BCC) is the most common malignancy worldwide, with increasing incidence. BCCs present low mortality but high morbidity, and its pathogenesis remains unclear. Eph receptors have been implicated in tumorigenesis. EphA7 plays a role as a tumor suppressor in certain cancers. We checked EphA7 expression levels and methylation status in a set of BCCs, benign skin diseases, and compound nevus tissue samples using immunohistochemistry. EphA7 protein was positively expressed in normal basal cells, benign skin diseases, and compound nevus cells, but lost in areas of BCC tissues. We detected hypermethylation in BCC tissue samples with reduced expression of EphA7. There is a significant relationship between the expression level of EphA7 receptor protein and the methylation status of CpG islands in the EphA7 promoter region (P < 0.001). To our knowledge, this is the first study to report the EphA7 expression profile and hypermethylation of EphA7 in BCC. The role of the EphA7 gene and the status of hypermethylation in tumorigenesis and treatment of BCC warrant further investigation.

Genital basal cell carcinoma, a different pathogenesis from sun-exposed basal cell carcinoma? A case-control study of 30 cases

BACKGROUND

Genital basal cell carcinoma (BCC) accounts for <1% of all BCCs. We aimed to elucidate the pathogenesis of genital BCC.

METHODS

We retrospectively evaluated cases of pathologically diagnosed genital BCC between 1990 and 2016 in an Asian tertiary referral center. The control group was composed of consecutive cases, from 2016, of BCCs occurring in sun-exposed areas. Presence of human papillomavirus (HPV) was evaluated by polymerase chain reaction (PCR). Immunohistochemical p16 and p53 staining was performed and analyzed.

RESULTS

We found 33 genital BCCs (33/1837, 1.8%) over 26 years. The mean follow-up duration was 30.0 ± 33.2 months. Genital BCCs had a larger size (14.05 vs 8.92 mm, P = 0.014), more common presence of ulcers (61.3% vs 32.0%, P = 0.035), shorter epidermal p53 clone (0.33 vs 1.20 mm, P = 0.007), and high p53 expression levels. Most cases (29/30, 96.7%) showed negative or faint spotty p16 staining. Patient age, tumor depth, presence of pigment, or histology subtype did not differ significantly. Thirty genital BCCs were negative for HPV.

CONCLUSIONS

HPV infection is mostly likely not involved in genital BCC pathogenesis. A greater level of p53 expression in genital BCCs implicates pathways other than ultraviolet (UV)-specific p53 mutations in their pathogenesis.

Occurrence of metachronous basal cell carcinomas: a prognostic model

BACKGROUND

A third of patients with a first basal cell carcinoma (BCC) will develop subsequent (metachronous) BCCs.

OBJECTIVES

To study the prognostic effect of the number of previous BCC diagnosis dates a patient has experienced to derive a prediction model to assess the risk of metachronous BCCs that may inform individualized decision making on surveillance.

METHODS

We considered participants of north-western European ancestry from a prospective population-based cohort study (Rotterdam Study). After linkage with the Dutch Pathology Registry, 1077 patients with a first BCC were included. Candidate predictors for metachronous BCCs included patient, lifestyle and tumour characteristics. The prognostic model was developed with Fine and Gray regression analysis to account for competing risk of death. We used bootstrapping to correct for within-patient correlation and statistical optimism in predictive performance.

RESULTS

Second to fifth BCCs occurred in 293, 122, 58 and 36 patients, with median follow-up times of 3·0, 2·1, 1·7 and 1·8 years after the previous BCC, respectively. The risk of a new BCC was higher for patients with more metachronous BCCs. Having more than one BCC at diagnosis was another strong predictor of metachronous BCCs. Discriminative ability of the model was reasonable with an optimism-corrected c-index of 0·70 at 3 years.

CONCLUSIONS

The number of previous BCC diagnosis dates was a strong prognostic factor and should be considered when predicting the risk of metachronous BCCs. When the number of previous BCC diagnosis dates is combined with other readily available characteristics into a prognostic model, patients at high risk of a new BCC can be identified.

Does Notch play a tumor suppressor role across diverse squamous cell carcinomas?

The role of Notch pathway in tumorigenesis is highly variable. It can be tumor suppressive or pro‐oncogenic, typically depending on the cellular context. Squamous cell carcinoma (SCC) is a cancer of the squamous cell, which can occur in diverse human tissues. SCCs are one of the most frequent human malignancies for which the pathologic mechanisms remain elusive. Recent genomic analysis of diverse SCCs identified marked levels of mutations in NOTCH1, implicating Notch signaling pathways in the pathogenesis of SCCs. In this review, evidences highlighting NOTCH's role in different types of SCCs are summarized. Moreover, based on accumulating structural information of the NOTCH receptor, the functional consequences of NOTCH1 gene mutations identified from diverse SCCs are analyzed, emphasizing loss of function of Notch in these cancers. Finally, we discuss the convergent view on an intriguing possibility that Notch may function as tumor suppressor in SCCs across different tissues. These mechanistic insights into Notch signaling pathways will help to guide the research of SCCs and development of therapeutic strategies for these cancers.

p53 staining correlates with tumor type and location in sebaceous neoplasms

Sebaceous neoplasms are commonly considered in their relationship to the Muir-Torre syndrome and the now well-documented loss of DNA mismatch repair proteins leading to microsatellite instability. However, sebaceous neoplasms showing microsatellite instability comprise only a subset of this group of tumors, and thus, alternative tumorigenic mechanisms must exist. This article explores the relationship of p53, a tumor suppressor implicated in other cutaneous malignancies, and sebaceous neoplasia. We examined 94 sebaceous tumors from 92 patients. Tumors with strong nuclear p53 staining were significantly associated with the diagnosis of sebaceous carcinoma compared with benign sebaceous lesions, most notably for periocular carcinomas. Importantly, nuclear mismatch repair protein expression was intact in all lesions showing p53 alterations, suggesting that p53 dysfunction may represent a divergent pathway in the molecular pathogenesis of these tumors.

Infrequent p53 gene mutation but UV gradient-like p53 protein positivity in keloids

Keloids are characterized by extreme fibroblastic overgrowth of unknown pathogenesis after skin injury. Previous studies, mostly in non-Caucasian populations, suggest that p53 mutations may be involved. To substantiate this, we performed DNA sequence analysis of exons 4-8 of the p53 gene and immunohistochemical staining of p53 protein in archived keloidal tissue samples from 23 Caucasian patients. In contrast to previous reports, we found mutated p53 in keloidal tissue in a minority of cases (2/23; 12%). The G allele frequency and C allele frequency at the p53 polymorphic codon 72 were 0.72 (33/46) and 0.28 (13/46), respectively, in our study, a finding that was similar to the 0.77 (184/240) vs. 0.23 (56/240) (P = 0.4580; chi-squared test) observed in the Hap Map data of a European population but statistically significantly different from the 0.43 (547/1258) vs. 0.57 (711/1258) (P = 0.0002; chi-squared test) observed in the 1000 Genome project [Database of Single Nucleotide Polymorphisms (dbSNP). Bethesda (MD): National Center for Biotechnology Information, National Library of Medicine. dbSNP accession:rs1042522, (dbSNP Build ID: 132). Available from: (http://www.ncbi.nlm.nih.gov/SNP/] a difference most likely due to the different genetic background of the populations enrolled. However, one-third of the keloidal samples showed lesional nuclear p53 staining with a UV penetration gradient-like positivity (P ≤ 0.0084). Staining with an anti-cyclobutane pyrimidine dimer antibody revealed the total absence of short-term photoproducts in the epidermis as well as keloidal tissue. Furthermore, all fibroblasts expressing p53 stained negative for Ki-67, indicating that these cells were in a quiescent stage and p53 upregulation did not contribute to keloidal proliferation. We conclude that p53 plays no major role in the pathogenesis of keloids in the Caucasian population.

Relation between expression pattern of p53 and survivin in cutaneous basal cell carcinomas

Background

The tumor suppressor gene p53 is a key regulator of cell division and/or apoptosis. Survivin is a multifunctional member of the inhibitor of apoptosis family. Survivin and p53 represent diametrically opposed signals that influence the apoptotic pathway.

Material/Methods

To determine the role of p53 and survivin in basal cell carcinoma (BCC), we evaluated the expression pattern of both proteins with regard to the percentage of positively immunostained tumor cells, the intensity of staining, and subcellular localization among 31 subjects with BCC.

Results

Overexpression of p53 protein was found in 28 of 31 cases (90.3%), whereas survivin accumulation was seen in 27 (87.1%). For p53, moderate and/or strong immunoreactivity was seen in 20 of 28 cases (71.4%), and 26 of 28 cases (92.9%) showed more than 25% reactive tumor cells. Nuclear p53 staining was detected in 23 of 28 cases (82.1%), whereas combined nuclear and cytoplasmic localization was found in only 5 of 28 cases (17.9%). Survivin revealed mild intensity of immuno-reaction in 22 of 27 cases (71%), and 25 of 27 cases (92.6%) showed less than 25% labeled tumor cells. Combined nuclear and cytoplasmic survivin localization was present in 26 of 27 cases (96.3%). Statistically significant differences were detected in the assessed expression parameters between those proteins.

Conclusions

Our results suggest that overexpression of wild type p53 protein may suppress the expression of survivin and its antiapoptotic activity in BCC cells.

Basal cell carcinomas arise from hair follicle stem cells in Ptch1(+/-) mice

Basal cell carcinomas (BCCs) are hedgehog-driven tumors that resemble follicular and interfollicular epidermal basal keratinocytes and hence long have been thought to arise from these cells. However, the actual cell of origin is unknown. Using cell fate tracking of X-ray induced BCCs in Ptch1(+/-) mice, we found their essentially exclusive origin to be keratin 15-expressing stem cells of the follicular bulge. However, conditional loss of p53 not only enhanced BCC carcinogenesis from the bulge but also produced BCCs from the interfollicular epidermis, at least in part by enhancing Smo expression. This latter finding is consistent with the lack of visible tumors on ears and tail, sites lacking Smo expression, in Ptch1(+/-) mice.

Do nonmelanoma skin cancers develop from extra-cutaneous stem cells?

A hypothesis is presented that nonmelanoma skin cancers can develop from extra-cutaneous stem cells, and not exclusively from skin keratinocytes. This idea is supported by recent findings regarding the initiation of cancers in the digestive tract, and by a cancer stem cell model of a neoplasia. It is known that multipotent adult progenitor cells can trans-differentiate into very diverse cellular lineages and can be recruited to areas of profound tissue injury. In these settings, they might also initiate malignant transformation. Some epidemiological data and recent findings regarding mechanisms of wound healing indicate that skin cancers could also originate from bone marrow-derived or other extra-cutaneous stem cells in addition to local stem cells. It can therefore be speculated that the biology of keratinocyte stem cells derived from these sources differs from that of local epidermal stem cells, and consequently, these cells might be poorly controlled within their niches. Furthermore, in chronically inflamed skin, or in an immunodeficient patient, malignant transformation of extra-cutaneous stem cells is more likely to occur. There is one well-documented case of basal cell cancer which has arisen from donor cells in a kidney transplant recipient, but it remains unclear if this cancer developed directly from a donor-derived cell, or via fusion of such cells with premalignant keratinocytes. Hopefully, combining animal models of skin cancer initiation with experiments exploring the role of bone marrow-derived cells in skin healing will bring to light the exact mechanism of carcinogenesis of nonmelanoma skin cancers.

Low prevalence of p53, p16(INK4a) and Ha-ras tumour-specific mutations in low-graded actinic keratosis

BACKGROUND

Ultraviolet radiation induces DNA damage and is the major risk factor for the development of non-melanoma skin cancer (NMSC). Different mutation rates of p53, p16(INK4a) and Ha-ras in cutaneous squamous cell carcinoma (SCC) and the earlier stage actinic keratosis (AK) have been reported.

OBJECTIVES

To assess the presence of missense mutations in hotspot exons of p53, p16(INK4a) and Ha-ras in low-graded AK.

PATIENTS/METHODS

Cryo-biopsies of 75 sun-exposed AK lesions and 75 sun-shielded areas of normal skin from 75 AK patients were analysed to identify mutations in p53 (exons 7 and 8), p16(INK4a) (exon 2) and Ha-ras (exon 1) using polymerase chain reaction (PCR) followed by direct sequencing. As a representative subset of the specimens, ten mutation-negative AK were also micro-dissected in order to exclude the possibility that additional mutations were undetected.

RESULTS

Eight missense and one nonsense point mutations were found in the 75 AK lesions examined (12%), of which seven (9%) were tumour-specific (i.e. present in AK lesions only) and two (3%) were p16(INK4a) mutations (i.e. also detected in normal skin). Three of the tumour-specific mutations (42%) were cytosine (C) to thymine (T) transitions at pyrimidine-rich sequences. Tumour-specific mutations were identified in 1% of p16(INK4a) (exon 2), 1% of Ha-ras (exon 1) and at a higher rate of 7% in p53 (exons 7 and 8), including one nonsense mutation.

CONCLUSIONS

The evaluation of a large number of AK specimens in this study have found a low gene mutation rate in low-graded AK lesions. p53 mutations rather than p16(INK4a) and/or Ha-ras mutations may be an early event in the development of AK to cutaneous SCC.

More epidermal p53 patches adjacent to skin carcinomas in renal transplant recipients than in immunocompetent patients: the role of azathioprine

Immunosuppressive medication in renal transplant recipients (RTR) strongly increases the risk of cancers on sun-exposed skin. This increased risk was considered an inevitable collateral effect of immunosuppression, because UV-induced carcinomas in mice were found to be highly antigenic. Here, we posed the question whether immunosuppression also increases the frequency of p53-mutant foci ('p53 patches'), putative microscopic precursors of squamous cell carcinomas. As the majority of RTR was kept on azathioprine for most of the time, we investigated whether this drug could increase UV-induced p53 patches by immunosuppression. As azathioprine can impair UV-damaged DNA repair under certain conditions, we also investigated whether DNA repair was affected. Archive material of RTR and immunocompetent patients (ICP), as well as azathioprine-administered hairless mice were examined for p53 patches. DNA repair was investigated by ascertaining the effect of azathioprine on unscheduled DNA synthesis (UDS) in UV-irradiated human keratinocytes. P53 patches were more prevalent in RTR than in ICP in normal skin adjacent to carcinomas (P = 0.02), in spite of a lower mean age in the RTR (52 vs 63 years, P = 0.001), but we found no increase in UV-induced p53 patches in mice that were immunosuppressed by azathioprine. We found a significant reduction in DNA repair activity in keratinocytes treated with azathioprine (P = 0.011). UV-induced UDS in humans is dominated by repair of cyclobutane pyrimidine dimers, and these DNA lesions can lead to 'UV-signature' mutations in the P53 gene, giving rise to p53 patches.

Single base instability is promoted in vulvar lichen sclerosus

Single base substitution mutations in codons 248 and 273 of TP53 and codon 12 Kirsten-ras (KRAS) are commonly found in human carcinomas. To determine whether these mutations also occur in normal and inflamed tissues from which carcinomas arise, we utilized the ultra-sensitive polymerase chain reaction/restriction endonuclease/ligase chain reaction mutation assay. Ninety samples of genital skin, including lichen sclerosus (LS) affected skin, adjacent normal and non-adjacent normal, were assayed. Mutations were detected in 103 of 349 assays and consisted of KRAS G34A, G34T, G35A, and TP53 C742T, G818C, C817T, and G818A mutations. Mutant prevalence varied from 1 to 20 per 10(6) wild-type cells. Mutations occurred significantly more frequently in LS (78/224 (35%)) than adjacent normal (20/88 (23%)) and non-adjacent normal genital skin (5/38 (13%)). KRAS G34A mutation was relatively common to all classes of specimen, whereas TP53 gene C742T and G818C mutations were significantly more frequent in LS than normal genital skin. In matched samples, immunohistochemistry evaluation of p53 protein expression revealed the presence of epidermal p53 clones in LS whose presence and number significantly correlated with the presence of TP53 C742T and G818C mutations. Based on these results, it appears oncogenic point mutations occur in normal genital skin, and are selected for in LS.

Notch1 is a p53 target gene involved in human keratinocyte tumor suppression through negative regulation of ROCK1/2 and MRCKalpha kinases

Little is known about the regulation and function of the Notch1 gene in negative control of human tumors. Here we show that Notch1 gene expression and activity are substantially down-modulated in keratinocyte cancer cell lines and tumors, with expression of this gene being under p53 control in these cells. Genetic suppression of Notch signaling in primary human keratinocytes is sufficient, together with activated ras, to cause aggressive squamous cell carcinoma formation. Similar tumor-promoting effects are also caused by in vivo treatment of mice, grafted with keratinocytes expressing oncogenic ras alone, with a pharmacological inhibitor of endogenous Notch signaling. These effects are linked with a lesser commitment of keratinocytes to differentiation, an expansion of stem cell populations, and a mechanism involving up-regulation of ROCK1/2 and MRCKalpha kinases, two key effectors of small Rho GTPases previously implicated in neoplastic progression. Thus, the Notch1 gene is a p53 target with a role in human tumor suppression through negative regulation of Rho effectors.

The effects on human health from stratospheric ozone depletion and its interactions with climate change

Ozone depletion leads to an increase in the ultraviolet-B (UV-B) component (280-315 nm) of solar ultraviolet radiation (UVR) reaching the surface of the Earth with important consequences for human health. Solar UVR has many harmful and some beneficial effects on individuals and, in this review, information mainly published since the previous report in 2003 (F. R. de Gruijl, J. Longstreth, M. Norval, A. P. Cullen, H. Slaper, M. L. Kripke, Y. Takizawa and J. C. van der Leun, Photochem. Photobiol. Sci., 2003, 2, pp. 16-28) is discussed. The eye is exposed directly to sunlight and this can result in acute or long-term damage. Studying how UV-B interacts with the surface and internal structures of the eye has led to a further understanding of the location and pathogenesis of a number of ocular diseases, including pterygium and cataract. The skin is also exposed directly to solar UVR, and the development of skin cancer is the main adverse health outcome of excessive UVR exposure. Skin cancer is the most common form of malignancy amongst fair-skinned people, and its incidence has increased markedly in recent decades. Projections consistently indicate a further doubling in the next ten years. It is recognised that genetic factors in addition to those controlling pigment variation can modulate the response of an individual to UVR. Several of the genetic factors affecting susceptibility to the development of squamous cell carcinoma, basal cell carcinoma and melanoma have been identified. Exposure to solar UVR down-regulates immune responses, in the skin and systemically, by a combination of mechanisms including the generation of particularly potent subsets of T regulatory cells. Such immunosuppression is known to be a crucial factor in the generation of skin cancers. Apart from a detrimental effect on infections caused by some members of the herpesvirus and papillomavirus families, the impact of UV-induced immunosuppression on other microbial diseases and vaccination efficacy is not clear. One important beneficial effect of solar UV-B is its contribution to the cutaneous synthesis of vitamin D, recognised to be a crucial hormone for bone health and for other aspects of general health. There is accumulating evidence that UVR exposure, either directly or via stimulation of vitamin D production, has protective effects on the development of some autoimmune diseases, including multiple sclerosis and type 1 diabetes. Adequate vitamin D may also be protective for the development of several internal cancers and infections. Difficulties associated with balancing the positive effects of vitamin D with the negative effects of too much exposure to solar UV-B are considered. Various strategies that can be adopted by the individual to protect against excessive exposure of the eye or the skin to sunlight are suggested. Finally, possible interactions between ozone depletion and climate warming are outlined briefly, as well as how these might influence human behaviour with regard to sun exposure.

Radiation-induced cutaneous carcinoma of the head and neck: is there an early role for p53 mutations?

BACKGROUND

Little is known about the molecular mechanisms underlying ionizing radiation-induced carcinogenesis of the skin.

AIMS

To investigate the possible role of p53 in radiodermatitis and in the development of radiation-induced cutaneous carcinomas.

METHODS

The study group comprised six patients affected by cutaneous carcinomas arising in radiodermatitis (one squamous cell carcinoma and five basal cell carcinomas), and seven patients presenting only chronic radiodermatitis. Skin specimens were evaluated for p53 immunohistochemical expression. Using laser-assisted microdissection, areas with different p53 immunoreactivity were separately submitted to DNA isolation and p53 gene analysis.

RESULTS

In the majority of cases (9/12, 75%), p53 immunoreactivity was detected in radiation-damaged epidermis. In carcinomas p53 oncoprotein was expressed by several neoplastic cells in one case (16.7%%), or by nearly all neoplastic cells in four (66.7%). SSCP band shifts were detected in 9/25 samples (36%) microdissected from irradiated epidermis and in 3/6 (50%) carcinomas. DNA sequencing demonstrated two repeatedly found mutations: a G deletion at codon 244 and an A-->G transition at codon 205, as well as hallmarks of ultraviolet mutagenic action, including a C-->T transition occurring at a dipyrimidine site and a CC-->TT tandem double-base transition.

CONCLUSION

Our data indicate that irradiation induces significant p53 alterations that may be relevant in the modification of epithelial maturation processes and may be responsible for the high risk for development of carcinomas in radiodermatitis.

Expression of p53 tumor suppressor protein in sun-exposed skin and associations with sunscreen use and time spent outdoors: a community-based study

The p53 gene is a tumor suppressor gene that is commonly mutated in skin cancer and sun-exposed skin, and this can be detected through immunohistochemical expression of the p53 protein. The authors hypothesized that time spent outdoors is associated with p53 protein expression in human skin and that sunscreen use counteracts the association. In 1996, they investigated this in a community-based cross-sectional study in Australia. Detailed information about skin type, time spent outdoors, and sunscreen use was collected from 139 residents of a subtropical township who also provided a skin biopsy from the back of the hand for measurement of p53 expression. Increasing time spent outdoors was positively associated with immunoreactivity in the whole epidermis and in the basal layer of the epidermis. After adjustment for confounders, p53 immunoreactivity was twice as high for people who used sunscreen 1 or 2 days per week as for those who used sunscreen daily (whole epidermis: ratio estimate=2.0, 95% confidence interval: 1.1, 3.6; basal layer: ratio estimate=1.7, 95% confidence interval: 0.9, 3.1). The authors conclude that p53 immunoreactivity in the skin is a marker of exposure to ultraviolet light in the past 6 months, but this may be mitigated by regular application of sunscreen.

Infrared radiation induces the p53 signaling pathway: role in infrared prevention of ultraviolet B toxicity

We have previously observed that preirradiation with naturally occurring doses of near-infrared (IR) protects normal human dermal fibroblasts from ultraviolet (UV) cytotoxicity in vitro. This effect was observed in temperature-controlled conditions, without heat shock protein (Hsp72-70) induction. Moreover, IR inhibited UVB-induced apoptosis by modulating the Bcl2/Bax balance, pointing to a role of p53. Here, we show for the first time that p53-deficient SaOs cells are not protected from UVB cytotoxicity by IR preirradiation, suggesting that the response to IR is p53-dependent. Thus, we investigated the effect of IR on the p53 signaling pathway. Normal human dermal fibroblasts exposed in vitro to IR accumulated p53 protein, involving p53 stabilization and phosphorylation of serine 15 (Ser15) and Ser20. IR-induced p53 accumulation correlated with increased expression of p21 and GADD45, showing that IR also stimulates p53 transcriptional activity. By modulating UVB-induced targets of the p53 signaling pathway, IR irradiation appears to anticipate the UVB response and to prepare cells to better resist subsequent UV-induced stress. This is reinforced by the fact that IR preirradiation reduces the formation of UVB-induced thymine dimers.

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

Clusters of p53 immunopositive epidermal keratinocytes (so-called p53 patches, clones or foci) are found in sun or ultraviolet (UV) light-exposed skin. We investigated to what extent these p53 patches are genuine precursors of skin carcinomas in chronically irradiated hairless (SKH1) mice. The mutation spectra of exons 5-8 of the p53 gene of laser-micro-dissected mutant p53 patches and carcinomas were therefore compared. The mutations we found were mainly UV-signature mutations (C-->T and CC-->TT at dipyrimidine sites) located at known hotspots. No significant differences were found between both spectra, indicating that all p53 patches harbour mutations with which they could progress to carcinomas. To examine whether these p53 patches can be used as tumour risk indicators, we made an extensive comparison of the induction kinetics of these patches and carcinomas in genetically modified mice with various defects in nucleotide excision repair (NER), i.e. xeroderma pigmentosum A (Xpa), Xpc and Cockayne syndrome B (Csb) and wild-type mice. In this aforementioned order, the mouse strains developed both p53 patches and carcinomas in the course of daily exposure to 40 J/m(2) UV. Hence, the order in which the NER-deficient mice developed patches was predictive of the order in which they developed tumours. The induction kinetics of the patches in Xpc-deficient mice differed notably from the others: there was a stationary phase (days 13-41) where the numbers were limited to 5-10 patches per mouse before an explosive increase which ran parallel to the other groups. The chance that a p53 patch progresses to carcinoma is relatively small (estimated at 1 out of 8300-40,000/individual when the first tumour appears), but our results are strongly indicative of a causal relationship between p53 patches and carcinomas.

Effect of administration of caffeine or green tea on the mutation profile in the p53 gene in early mutant p53-positive patches of epidermal cells induced by chronic UVB-irradiation of hairless SKH-1 mice

Irradiation of SKH-1 mice with UVB light for 20 weeks resulted in a large number of patches of epidermal cells, which was visualized with an antibody that recognizes mutated p53 protein. Oral treatment of mice with caffeine (0.4 mg/ml) or green tea (6 mg tea solids/ml) as the drinking fluid during UVB irradiation decreased the number of patches by approximately 40%. Sequencing analysis of the p53 gene (exons 3 to 9) detected 88, 82 or 39 point mutations in 67, 70 or 29 patches from water, caffeine or tea treated mice, respectively. A major hotspot at codon 270 (Arg-->Cys) accounted for 47.7% (water), 70.7% (caffeine) or 46.2% (tea) of all mutations. Patches from caffeine treated mice had fewer types of mutations than patches from mice treated with water or tea. Administration of caffeine or tea during 20 weeks of UVB irradiation eliminated mutations at codons 149 (Pro-->Ser) and 210 (Arg-->Cys) but increased the frequency of mutations at codon 238 (Ser-->Phe). Topical applications of caffeine (1.2 mg in 100 microl acetone) once a day, five times a week for 6 weeks after stopping UVB decreased the number of patches by 63% when compared with mice treated with acetone. DNA sequencing analysis detected 63 and 68 mutations in 48 and 57 patches from acetone or caffeine treated mice, respectively. Although no differences in the frequency, position or types of mutations were observed, the caffeine group harbored less homozygous mutations (12.3% of the total) than the acetone group (31.3% of the total, P = 0.029). In summary, oral treatment of mice with caffeine or green tea during chronic UVB irradiation changed the mutation profile of the p53 gene in early mutant p53 positive epidermal patches, and topical applications of caffeine after discontinuation of chronic UVB irradiation specifically eliminated patches harboring homozygous p53 mutations.

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

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.

Administration of green tea or caffeine enhances the disappearance of UVB-induced patches of mutant p53 positive epidermal cells in SKH-1 mice

Irradiation of female SKH-1 hairless mice with UVB (30 mJ/cm2) twice a week for 10-20 weeks resulted in the formation of a large number of cellular patches (>8 adjacent cells/patch) that are recognized with an antibody (Pab240) which recognizes mutated but not wild-type p53 protein. These patches are not recognized by an antibody (Pab1620) to wild-type p53 protein. The patches, which are considered putative early cellular markers of the beginning of tumor formation, started appearing after 4-6 weeks of UVB treatment, and multiple patches were observed after treatment for 10 weeks. The number and size of the patches increased progressively with continued UVB treatment. Discontinuation of UVB for 4 weeks resulted in an 80-90% decrease in the number of these patches. The number of the remaining patches did not decrease any further but remained relatively constant for at least 4-9 weeks. Oral administration of green tea (6 mg tea solids/ml) or caffeine (0.4 mg/ml) as the sole source of drinking fluid during irradiation with UVB, twice a week for 20 weeks, inhibited UVB-induced formation of mutant p53 positive patches by approximately 40%. Oral administration of green tea (6 mg tea solids/ml) as the sole source of drinking fluid or topical applications of caffeine (6.2 micromol) once a day 5 days a week starting immediately after discontinuation of UVB treatment enhanced the rate and extent of disappearance of the mutant p53-positive patches. Topical applications of caffeine to the dorsal skin of mice pretreated with UVB for 20 weeks resulted in enhanced apoptosis selectively in focal basal cell hyperplastic areas of the epidermis (putative precancerous lesions), but not in areas of the epidermis that only had diffuse hyperplasia. Our studies indicate that the chemopreventive effect of caffeine or green tea may occur by a proapoptotic effect preferentially in early precancerous lesions.