A role for sunlight in skin cancer: UV-induced p53 mutations in squamous cell carcinoma

Search for accumulation of p53 protein and detection of human papillomavirus genomes in sebaceous gland carcinoma of the eyelid

Twenty-one Japanese patients with sebaceous carcinoma of the eyelid were investigated for tumour incorporation of human papillomavirus (HPV) types-6, 11, 16, 18, 31, and/or 33 DNA by in situ hybridization with fluorescein isothiocyanate-labelled DNA probes, and for p53 protein accumulation by immunohistochemical analysis with an antibody to p53 protein. Thirteen tumours (61.9%), including 9 cases of multiple infections, were positive for HPV DNA. Positive signal in the nucleus was observed not only in the cancer cells, but also in the cells of surrounding normal sebaceous glands and epidermis. Positive nuclear staining of cancer cells with the antibody to p53 protein was detected in 12 cases (57.1%). p53 protein accumulation was more frequently observed in the clinically advanced cases, occasionally in association with recurrence and/or metastasis. Among the 12 p53-positive cases, 7 were also positive for the presence of HPV DNA. HPV infections exist in a high percentage of sebaceous carcinomas of the eyelid in Japan; the overexpression of p53 protein may be important in both carcinogenesis and progression.

Preferential repair of ultraviolet light-induced DNA damage in the transcribed strand of the human p53 gene

Mutations in the p53 tumor suppressor gene have been found in most human tumors. Analyses of the spectrum of p53 mutations in certain tumor types have shown a bias for mutations originating from lesions presumed to be in the untranscribed strand of the gene. This implies strand specificity for the formation or repair of DNA damage. We measured the induction and repair of ultraviolet light-induced cyclobutane pyrimidine dimers (CPD) in each strand of the human p53 gene in a normal human lung fibroblast cell line using quantitative Southern hybridization. We found that the removal of CPD from the transcribed strand was more rapid than that from the untranscribed strand of this gene, although the frequency of CPD induction was similar in both strands. Preferential repair of the transcribed strand of the p53 gene may account for the mutational spectra of this gene in human tumors.

p53 expression in pseudoepitheliomatous hyperplasia, keratoacanthoma, and squamous cell carcinoma of skin

BACKGROUND

Expression of p53 protein has been described in a variety of human malignant tumors. Recent reports have also demonstrated its presence in benign and reactive lesions. The significance of p53 expression is unclear.

METHODS

This study examines the p53 expression in proliferative lesions of skin, including 6 pseudoepitheliomatous hyperplasia, 33 keratoacanthoma, and 45 squamous cell carcinoma, and to evaluate its significance.

RESULTS

p53 expression was observed in all of the six cases of pseudoepitheliomatous hyperplasia, 78.8% of keratoacanthoma, and 75.5% of squamous cell carcinoma. The staining pattern of pseudoepitheliomatous hyperplasia and keratoacanthoma was generally less intense and extensive compared with that of squamous cell carcinoma. A keratoacanthoma with nuclear atypia that showed strong and extensive p53 staining was also encountered. The perilesional skin in sun-exposed sites often showed the presence of p53-positive keratinocytes. Control skin taken from the buttock was negative for p53 protein. Conversely, p53 was often expressed in carcinomas arising from sun-exposed as well as sun-protected sites. p53 positivity involved mainly the undifferentiated cells at the base of the epidermis or periphery of tumor cords. Differentiated keratinized cells were not stained. p53-positive fibroblasts were also noted in the inflammatory and granulation tissues of pseudoepitheliomatous hyperplasia.

CONCLUSIONS

p53 expression in skin is common and appears to be an early event in a series of genetic alterations reflecting underlying actinic damage, which may lead to but does not necessarily indicate neoplastic or malignant transformation. Because p53 staining is seen in proliferative and undifferentiated cells and ceases to be expressed when the cells differentiate, it appears that the expression of p53 protein, mutant or wild-type, is an indicator of immaturity and proliferative capacity of the cell rather than one of neoplasia or malignancy.

Posttransplant skin cancer: a possible role for p53 gene mutation but not for oncogenic human papillomaviruses

BACKGROUND

Loss of p53 tumor suppressor function is a critical step in the development of diverse malignancies, including skin cancers in nonimmunosuppressed patients where UV-specific p53 gene mutations have been identified. In tumors associated with human papillomavirus (HPV), such as cervical carcinoma, p53 may be inactivated instead by binding to a viral oncoprotein.

OBJECTIVE

Our purpose was to examine the hypothesis that HPV may play an analogous role in the development of posttransplant skin cancer.

METHODS

p53 Immunoreactivity, suggestive of p53 gene mutation, was examined by immunocytochemistry. Oncogenic HPV DNA was detected by polymerase chain reaction.

RESULTS

Comparable p53 immunoreactivity was seen in skin tumors from both transplant and nontransplant patients. HPV DNA was not demonstrated in any tumor specimen.

CONCLUSION

Our data do not implicate oncogenic HPV in posttransplant skin cancer. p53 Gene mutation, rather than HPV-induced p53 degradation, may be more significant in the development of these tumors.

Absence of p53 gene mutations in cutaneous melanoma

Mutations in the p53 tumor suppressor gene are a common finding in many human malignancies. These mutations have been shown to inactivate the p53 protein and sometimes confer an oncogenic potential to the mutated gene. Type and pattern of p53 mutations may give clues to the tumor etiology, for example, ultraviolet-induced CC-->TT and C-->T transitions. Genomic DNA of 16 primary cutaneous melanomas of the superficial and nodular subtype and six melanoma metastases were screened for the presence of mutations in exons 5 to 8 of the p53 tumor suppressor gene, using the polymerase chain reaction and single-strand conformation polymorphism analysis, followed by direct DNA sequencing. We detected no mutations in any of the primary and metastatic melanomas in exons 5 to 8 of the p53 tumor suppressor gene. This indicates that, in contrast to skin carcinomas, p53 mutations are not operative in the evolution of human melanoma.

p53 gene mutations in human skin cancers and precancerous lesions: comparison with immunohistochemical analysis

Mutations of exons 3 through 9 of the p53 gene in skin lesions were screened in 23 cases of squamous cell carcinoma (SCC), 25 cases of basal cell carcinoma (BCC), two cases of Bowen's disease, 10 cases of solar keratosis, and five cases of keratoacanthoma by polymerase chain reaction--single strand conformation polymorphism analysis. Mutations of the p53 gene were detected in seven of 23 SCCs (30%), three of 25 BCCs (12%), and none in all cases of Bowen's disease, solar keratosis, or keratoacanthoma. Of 23 cases of SCC, mutations were detected in four of 15 SCCs (27%) that originated in the sunlight-exposed skin region, in two of three SCCs (67%) that originated in the scar tissue, and in one of three SCCs (33%) that originated in radiation dermatitis. Mutations of C-->T transition predominated in SCC and BCC that originated in the sunlight-exposed skin region. Mutations of C-->A or CC-->AT observed in tumors that originated in the predisposed conditions, presumably unrelated to UV light, are different from those found in UV light-related SCC or BCC. Twelve cases of SCC were comparatively analyzed with the immunohistochemical staining with anti-p53 antibody. Two of four cases with positive staining had missense mutations, and three of eight cases with negative staining had nonsense mutations. Based on these findings, immunohistochemical results do not necessarily mean the presence or absence of p53 gene mutations in skin tumors, and sequence analysis is essential for determining whether the gene is mutated.

Infrequent p53 mutations in 7,12-dimethylbenz[a]anthracene-induced mammary tumors in BALB/c and p53 hemizygous mice

We conducted experiments to determine if p53 alterations, which are frequent in human breast cancers, were also common in murine mammary tumors. In 13 mammary tumors from 7,12-dimethylbenz[a]anthracene (DMBA)-treated BALB/c mice were immunohistochemically analyzed for overexpression of p53; p53 protein was not detectable. Three of the tumors were established as cell lines in vitro. p53 protein was rarely detected at passage 4 in these lines but was overexpressed by passage 8 in two of them. The p53 nucleotide sequence was shown to be wild type in one primary mammary tumor and in the two p53-overexpressing cell lines. One cell line that overexpressed p53 in vitro was implanted into BALB/c mice. The resulting tumors retained the wild-type p53 nucleotide sequence but no longer expressed detectable levels of p53 protein, suggesting that the overexpression of wild-type p53 was related to in vitro culture conditions. The effect of DMBA on mammary-tumor development was also tested in mice rendered hemizygous for p53. These mice and wild-type littermate controls had no differences in susceptibility to induction of mammary tumors by oral administration of DMBA. Furthermore, Southern blot hybridization detected no gross alterations in the wild-type p53 allele in mammary tumors from the p53-deficient mice. Point mutation of the wild-type p53 allele was also infrequent in the DMBA-induced mammary tumors from hemizygous p53 mice; it occurred in only one of seven tumors. Thus, the p53 gene is apparently not a primary target for genetic alterations in DMBA-induced mammary tumors. Next, we examined mammary tumors derived from D1 and D2 transplantable hyperplastic alveolar nodule (HAN) outgrowths, which rapidly form tumors containing Ha-ras mutations after DMBA treatment. As ras and p53 mutants can cooperate in transformation, we examined whether D1 and D2 HAN outgrowths have p53 mutations. Unlike in the DMBA-induced primary mammary tumors, nuclear p53 accumulation was observed frequently (10 of 14) in tumors that arose from D1 and D2 HAN outgrowths. Direct sequencing of the entire coding region of the p53 cDNA from six D1 and D2 tumors confirmed that the sequence was wild type. Although wild-type p53 was retained in both DMBA-induced mammary tumors and mammary tumors derived from D1 and D2 preneoplastic outgrowths, wild-type p53 overexpression was detected only in D1 and D2 tumors. Therefore, D1 and D2 tumors appear to arise by a pathway in which p53 expression is altered, whereas DMBA induction affects a different pathway that does not require such alteration.

Ultraviolet irradiation induces c-fos but not c-Ha-ras proto-oncogene expression in human epidermis

The link between sun exposure and skin cancer is well established, but the mechanism of photocarcinogenesis is still incompletely understood. In vitro experimentation has shown that induction of the c-fos proto-oncogene occurs in cultured human keratinocytes after ultraviolet exposure, and c-Ha-ras mutations are commonly present in human skin neoplasms removed from chronically sun-exposed sites. In the present study, the effect of UV irradiation on the expression of these two proto-oncogenes was examined. The sun-protected volar forearm of six subjects was exposed to a standardized erythemogenic dose of solar-simulated light, and punch biopsies were obtained after 1 h and 24 h from the irradiated area and a nearby shielded area. Expression of c-fos, determined by in situ hybridization of histologic cross-sections, was detected in the basal and lower epidermal layers in all biopsies. However, at 1 h there was a marked increase that returned to baseline by 24 h. c-Ha-ras mRNA could not be detected by riboprobe hybridization in any of the biopsy specimens. Our data demonstrate transient induction of c-fos but not c-Ha-ras expression, at least at the timepoints studied, following a modest UV exposure in normal skin. This phenomenon may lead to the subsequent constitutive over-expression and super-inducibility of c-fos observed in cultured keratinocytes derived from photodamaged skin and may facilitate the development of skin cancer.

Chromosome 9 allele loss occurs in both basal and squamous cell carcinomas of the skin

Linkage studies of kindreds with the nevoid basal cell carcinoma syndrome and the high frequency of chromosome 9 allele loss in sporadic basal cell carcinomas indicate that chromosome 9 may contain tumor suppressor genes important in the development of sporadic and familial basal cell carcinomas. The recent mapping of the Ferguson-Smith syndrome, which predisposes affected individuals to the development of multiple lesions histologically indistinguishable from squamous cell carcinomas, suggests that tumor suppressor genes on 9q may also be important in the development of squamous cell neoplasms of the skin. Fifty-four non-melanoma skin cancers (24 basal cell carcinomas, 14 squamous cell carcinomas, and 16 cases of Bowen's disease) were examined for loss of heterozygosity on chromosome 9. Allelic loss at one or more loci on chromosome 9 was observed in 14 of 24 basal cell carcinomas, four of 14 squamous cell carcinomas, and three of 16 cases of Bowen's disease. Allelic deletion of one or more 9q markers was seen in 14 basal cell carcinomas, three squamous cell carcinomas, and three cases of Bowen's disease. Five basal cell carcinomas had interstitial deletions and in one the breakpoint mapped within the nevoid basal cell carcinoma syndrome locus. 9p loss occurred in three of nine informative squamous cell carcinomas. Allelic deletion of 9p markers was not seen in 19 basal cell carcinomas and seven cases of Bowen's disease. These findings suggest that chromosome 9 contains one or more tumor suppressor genes important in the development of both basal and squamous cell carcinomas of the skin.

Ras mutations in human melanoma: a marker of malignant progression

In this study we address whether there is an association between ras mutations and disease progression in malignant melanoma. DNA was extracted from 100 paraffin-embedded melanomas and sequences around the 12th, 13th and 61st codons of N-, H-, and K-ras were amplified using the polymerase chain reaction and probed for single base pair mutations using synthetic oligonucleotide probes. Thirty-six melanomas contained mutations, which in 25 cases (69%) occurred at the 61st codon of N-ras. The results from dot blot hybridizations were confirmed by subcloning and sequencing the polymerase chain reaction products from two tumors. No ras mutations were found in Clark's level I melanomas, whereas 19% of level II and 45% of the more advanced primary tumors contained ras mutations (Chi squared test: p < 0.05). The median Breslow thickness of primary melanomas with ras mutations was 0.72 mm, significantly thicker than the 0.42 mm of melanomas without mutations (Mann-Whitney U test, p = 0.042). Ras mutations were found more frequently in primary tumors from continuously exposed skin (56%) than tumors from intermittently or non-sun exposed sites (21%). Fifty percent of locally recurrent and 47% of metastatic melanomas had ras mutations. We conclude that ras mutations occur in a subset of melanomas from sun-exposed skin as a feature of tumor progression.

Analysis of HPV16 E6 and mutant p53-transfected keratinocytes in reconstituted epidermis suggests that wild-type p53 inhibits cytokeratin 19 expression

Using a reconstituted skin culture model we have analysed the effects of oncogenic human papillomavirus (HPV) and mutant TP53 genes on the proliferation and differentiation of human keratinocytes. Immortal cell lines generated by transfection of early passage normal human keratinocytes with HPV16 E7 plus mutant human TP53 (KN #1), HPV16 E7/E6 (KN #2), or HPV16 E7 plus murine p53 (KN #3) were examined. KN #1 and KN #2 behaved identically, reconstructing a tumor-like epidermis characterized by the lack of differentiation and the presence of an aberrant epidermal architecture. In contrast, KN #3 reconstructed an epidermis that was more similar to that obtained with normal keratinocytes. KN #1 and KN #2 were further characterized by the inversion of the proliferative compartment and the abnormal expression of cytokeratin 19 (CK19). Because p53 function is reduced in these cells, either by heterocomplex formation between endogenous wild-type p53 and transfected mutant p53 or by E6-induced degradation of wild-type p53, we hypothesized that CK19 expression may be normally repressed by wild-type p53. This hypothesis was supported by the strict correlation observed between TP53 mutation and CK19 expression in a set of human skin tumors. CK19 was detected in all eight carcinomas containing a mutated TP53 gene but in none of the 16 carcinomas containing only wild-type TP53. These results illustrate the utility of the in vitro reconstituted skin model for investigating the consequences of genetic alterations in human keratinocytes.

p53 mutations in primary human lung tumors and their metastases

In a total of 26 primary human lung tumors and 60 metastases derived from them, exons 5-8 of the p53 tumor suppressor gene were analyzed by single-strand conformation polymorphism and subsequent direct DNA sequencing of amplified DNA. Mutational inactivation of the p53 gene was identified in four of five squamous cell carcinomas, three of nine adenocarcinomas, and two of nine small-cell carcinomas, the overall incidence being 35%. Point mutations occurred at a similar incidence in exons 5-8, with a preference for G-->T transversions. In seven of nine cases (78%), mutations were identical in the primary tumor and all of its metastases, indicating that in lung tumors, p53 mutations usually precede metastasis and that hematogenic and lymphogenic dissemination of tumor cells to other tissues is not associated with a selection against p53 inactivation. In one case, a kidney metastasis had the same mutation as the primary squamous cell carcinoma, whereas a liver metastasis had no mutation, indicating heterogeneity of the primary lung neoplasm and selective metastasis of mutated and nonmutated tumor cells to kidney and liver, respectively. Only in one liver metastasis was a mutation identified that was neither present in the primary lung tumor nor in a kidney metastasis, suggesting that occasionally p53 mutations occur after metastatic spread.

UV and skin cancer: specific p53 gene mutation in normal skin as a biologically relevant exposure measurement

Many human skin tumors contain mutated p53 genes that probably result from UV exposure. To investigate the link between UV exposure and p53 gene mutation, we developed two methods to detect presumptive UV-specific p53 gene mutations in UV-exposed normal skin. The methods are based on mutant allele-specific PCRs and ligase chain reactions and designed to detect CC to TT mutations at codons 245 and 247/248, using 10 micrograms of DNA samples. These specific mutations in the p53 gene have been reported in skin tumors. CC to TT mutations in the p53 gene were detected in cultured human skin cells only after UV irradiation, and the mutation frequency increased with increasing UV dose. Seventeen of 23 samples of normal skin from sun-exposed sites (74%) on Australian skin cancer patients contained CC to TT mutations in one or both of codons 245 and 247/248 of the p53 gene, and only 1 of 20 samples from non-sun-exposed sites (5%) harbored the mutation. None of 15 biopsies of normal skin from non-sun-exposed or intermittently exposed sites on volunteers living in France carried such mutations. Our results suggest that specific p53 gene mutations associated with human skin cancer are induced in normal skin by solar UV radiation. Measurement of these mutations may be useful as a biologically relevant measure of UV exposure in humans and as a possible predictor of risk for skin cancer.

Propylene oxide mutagenesis at template cytosine residues

Propylene oxide (PO) is a widely used industrial reagent which is mutagenic and carcinogenic. We have recently shown that a variety of aliphatic epoxides, including propylene oxide, can react with DNA to form hydroxyalkyl adducts at N-3 of cytosine which rapidly undergo hydrolytic deamination to produce uracil adducts. These 3-hydroxyalkyl uracil adducts are stable in DNA and are postulated to be an important class of potentially mutagenic lesions. Mutagenesis at cytosine residues due to PO modification of single-stranded M13mp2/C141 DNA was studied by transfection of modified DNA into SOS and non-SOS induced E. coli host cells. Mutations of the proline (CCC) codon at C141 which result in reversion of the lacZ phenotype (blue plaques) were scored. It was found that PO treatment of single-stranded DNA results in dose-dependent mutagenesis that is highly SOS dependent. The spectrum of base-substitution mutations found at this site differed when PO-modified DNA was transfected into E. coli with different DNA repair backgrounds. These results indicate that propylene oxide induced DNA adducts at template cytosine residues are mutagenic in E. coli and that this mutagenesis is greatly increased by SOS processing. They also show that these lesions may be repaired by one or more mechanisms.

Prevention of photocarcinogenesis and UV‐induced immunosuppression in mice by topical tannic acid

Topical application of tannic acid, a phenolic antioxidant derived from plants, was found to inhibit the cutaneous carcinogenesis and the immunosuppression induced by ultraviolet B (UVB) irradiation with no visible toxicity. BALB/cAnNTacfBR mice were treated with 200 micrograms of tannic acid three times weekly for two weeks before UV treatments began and throughout the experiment. UVB irradiation consisted of five 30-minute exposures per week to banks of six FS40 Westinghouse sunlamps. In the photocarcinogenesis study, mice received a total dose of approximately 1.09 x 10(6) J/m2. Skin cancer incidence in UV-irradiated mice was 75% at 26 weeks after the first UV exposure; tannic acid reduced this to 42%. Immunosuppression induced by UVB irradiation normally prevents the host from rejecting antigenic syngeneic UV-induced tumors. Immunosuppression in these experiments was measured by a passive transfer assay. Tumor challenges grew to an average of 88 +/- 20, 36 +/- 11, and 20 +/- 8 mm2 in naive recipients of splenocytes from UVB-irradiated mice, nonirradiated control mice, and UVB-irradiated mice treated with tannic acid, respectively. Thus topical tannic acid treatment prevented the transfer of enhanced tumor susceptibility with splenocytes from UVB-irradiated mice.

Active oxygen mechanisms of UV inflammation

Active oxygen radicals are important in the pathogenesis of UV irradiation injury. The initiating mechanisms involve the generation of hydroxyl radicals, superoxide, and organic hydroperoxides due to photochemical reactions. These active oxygen species lead to DNA strand breakage, mutation and the generation of inflammatory mediators such as cytokines and arachidonic acid metabolites which amplify the irradiation-induced inflammation. Several compounds have recently been utilized to successfully decrease these effects. Improved understanding of the mechanisms by which active oxygen species induce injury in skin now promises improved treatment.

Historical origins of current concepts of carcinogenesis

The first attempts to understand the causes of cancer were based on generalizations of what might now be termed a "holistic" nature, and hereditary influences were recognized at an early stage; these views survive principally through a supposed positive connection between psychological factors such as stress and diminished ability to combat the progressive development of tumors through some form of immunologically mediated rejection of potentially cancerous cells. While evidence for immunosurveillance is generally accepted, it is now widely regarded as almost wholly confined to instances where tumor viruses are involved as causative agents. The earliest theorists drew an analogy between the processes of carcinogenesis and of evolution; the cancer cells acquired the ability to outstrip their normal counterparts in their capacity for proliferation. This was even before evolution had been interpreted as involving a continuous succession of mutations. Evidence was already to hand before the end of the 18th century that exogenous agents, notably soot, a product of the "industrial revolution," could cause skin cancer. Somewhat over 100 years later, another industrial innovation, the manufacture of synthetic dyestuffs, implicated specific chemical compounds that could act systemically to cause bladder cancer. Meanwhile, the 19th century saw the establishment of the fundamentals of modern medical science; of particular relevance to cancer was the demonstration that it involved abnormalities in the process of cell division. The commencement of the 20th century was marked by a rediscovery of the concept of mutation; and it was proposed that cancer originated through uncontrolled division of somatically mutated cells. At around this time, two further important exogenous causative agents were discovered: X-rays and tumor viruses. In the late 1920s, x-radiation became the first established exogenous cause of mutagenesis. The discoverer of this phenomenon, H. J. Muller, suggested that while mutation in a single cell was the primary causative mechanism in carcinogenesis, its generally observed logarithmic increase in incidence with age reflected a "multihit" process, and that multiple successive mutations were required in the progeny of the original mutants. He also recognized that the rate of proliferation of potentially cancerous cells would markedly influence the probability of their subsequent mutation. These considerations are essentially the foundation of the generally accepted view of carcinogenesis that now seems unlikely to be superseded. However, this acceptance did not come about unopposed. The analogy between carcinogenesis and evolution was disliked by many biologists because it embodied the concept that cancer was an inevitable consequence of our evolutionary origins.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular mechanisms of radiation oncogenesis

Resolving the molecular mechanisms of radiation oncogenesis represents an important but daunting challenge in radiation research. This brief review outlines the principal oncogenic mechanisms that need to be considered in the context of radiation effects on the genome, how these might relate to specific gene and chromosomal changes relevant to neoplasia and the possible implications of such knowledge for the modelling of cancer risk. The long-term application of this mechanistic knowledge to the determination of tumour causality and for the assessment of individual cancer risk is also briefly discussed.

p53 mutations in human bladder cancer

Mutations in the tumor suppressor gene p53 play an important role in carcinogenesis and tumor progression. To assess the status of p53 from genomic DNA from bladder cancer samples a two stage polymerase chain reaction was employed. The technique provided material for subsequent detection of mutations by Single Strand Conformation Polymorphism (SSCP) analysis followed by DNA sequence analysis. SSCP analysis of exons 5 to 9 of p53 was performed using fragments from PCR end-labeled with 32P followed by autoradiography using an electrophoresis system with temperature control. This SSCP method improved resolution of mutations in exons 5, 7, and 8 and the sharpness of bands in exons 6 and 9. Bands with altered migration patterns were excised from the dried SSCP gels, reamplified by PCR, and sequenced. Mutations in conserved exons 5, 6, 7, 8, and 9 of the p53 gene were analyzed from bladder tumor biopsies. Our results are consistent with the literature in that mutations in p53 are predominantly found in high grade bladder cancer (Odds Ratio = 4.05, Fisher Exact P = 0.104); however, the results were not statistically significant due to small numbers. Eight of 35 (23%) tumor samples examined showed mutations in p53 (including two double mutations). Six of 13 (46%) grade III and IV tumors had p53 mutations vs. 2 of 17 (12%) grade I and II tumors. Normal individuals carried no p53 mutations. We found no correlation between pack years of smoking and mutation in p53. The spectrum of mutations confirmed a high proportion of G:C C:G transversions as well as the occurrence of double mutations.

G-->A mutations in p53 and Ha-ras genes in esophageal papillomas induced by N-nitrosomethylbenzylamine in two strains of rats

In human esophageal cancers, no ras gene mutations but a relatively high prevalence of p53 gene mutations have been reported. We found a high prevalence of point mutations in Ha-ras and p53 genes in N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumors in two strains of rats (BD VI and F344). Our analysis showed the point mutation GGA-->GAA (expected from the known mechanisms of action of NMBA) at Ha-ras codon 12 in 22 of 46 (48%) and 22 of 38 (58%) papillomas from BD VI and F344 rats, respectively. There was no significant difference in the prevalence of ras mutations in tumors induced by high doses (5.0 mg/kg) and low doses (2.5 mg/kg) of NMBA. Eleven papillomas from each strain were analyzed for p53 mutations. The prevalent mutations found were G-->A and C-->T transitions. The frequency of p53 mutation was 36% (four of 11) for each strain. No apparent hot-spot codon or exon was found in the p53 gene, and two papillomas contained double mutations in this gene. The high prevalence of G-->A mutations in the rat Ha-ras gene contrasts with that in the human gene, in which no ras mutations have been found in primary tumors, and suggests either that the biology of esophageal carcinogenesis differs in humans and rats or that nitrosamines are not the major etiological risk factor for human esophageal cancers.

Low incidence of c-Ha-ras gene mutations in benign and malignant cutaneous lesions from transplant recipients

Transplant recipients successively develop benign, premalignant and malignant skin lesions on sun-exposed areas. It has been suggested that UV radiations might induce mutations in ras oncogenes and p53 tumour-suppressor gene, responsible for skin cancers. With PCR and oligoprobe hybridization, we investigated c-Ha-ras gene mutations at codons 12 and 61 in 120 cutaneous lesions from grafted patients, since they could represent a marker of the evolution of benign skin lesions towards malignancy in this population; 29 similar skin biopsies from non-immunosuppressed patients were also analyzed. In transplant recipients, we detected mutations at codon 12 only in 1/42 non-melanoma skin cancers and 2/29 pre-cancerous keratoses. No mutation was detected in 11 cases of cutaneous Bowen's disease from grafted patients and in pre-malignant and malignant skin samples from control patients. Benign warts exhibited an overall incidence of 18% and 15% of mutations at codon 12 of c-Ha-ras gene in grafted and control patients respectively. We detected only one mutation at codon 61 in a plantar wart. Human papillomaviruses (HPV) are thought to be involved in the malignant evolution of cutaneous disorders in transplant recipients and cooperate with a ras oncogene to induce malignancy in vitro. The presence of HPV DNA in our series of skin samples from grafted patients showed no correlation with the occurrence of c-Ha-ras mutations. Our findings indicate that c-Ha-ras-gene activation by mutations is rare in cutaneous lesions from transplant recipients, and is unlikely to play a crucial role in transformation towards malignancy in skin carcinogenesis among grafted patients.

Specific UV-induced mutation spectrum in the p53 gene of skin tumors from DNA-repair-deficient xeroderma pigmentosum patients

The UV component of sunlight is the major carcinogen involved in the etiology of skin cancers. We have studied the rare, hereditary syndrome xeroderma pigmentosum (XP), which is characterized by a very high incidence of cutaneous tumors on exposed skin at an early age, probably due to a deficiency in excision repair of UV-induced lesions. It is interesting to determine the UV mutation spectrum in XP skin tumors in order to correlate the absence of repair of specific DNA lesions and the initiation of skin tumors. The p53 gene is frequently mutated in human cancers and represents a good target for studying mutation spectra since there are > 100 potential sites for phenotypic mutations. Using reverse transcription-PCR and single-strand conformation polymorphism to analyze > 40 XP skin tumors (mainly basal and squamous cell carcinomas), we have found that 40% (17 out of 43) contained at least one point mutation on the p53 gene. All the mutations were located at dipyrimidine sites, essentially at CC sequences, which are hot spots for UV-induced DNA lesions. Sixty-one percent of these mutations were tandem CC-->TT mutations considered to be unique to UV-induced lesions; these mutations are not observed in internal human tumors. All the mutations, except two, must be due to translesion synthesis of unrepaired dipyrimidine lesions left on the nontranscribed strand. These results show the existence of preferential repair of UV lesions [either pyrimidine dimers or pyrimidine-pyrimidone (6-4) photoproducts] on the transcribed strand in human tissues.

Relative probability of mutagenic translesion synthesis on the leading and lagging strands during replication of UV-irradiated DNA in a human cell extract

We have previously demonstrated mutagenic bypass of pyrimidine dimers during SV40 origin-dependent replication of UV-irradiated DNA in human cell extracts [Thomas, D. C., & Kunkel, T. A. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 7744-7748]. Here we use two vectors having the origin of replication on opposite sides of a lacZ alpha reporter gene to examine the relative probability of mutagenic translesion synthesis on the leading and lagging strands. Although replication of both vectors is inhibited by UVB irradiation in a dose-dependent manner, the covalently closed DNA products of replication contain T4 endonuclease sensitive sites, indicating that bypass of cyclobutane pyrimidine dimers occurred. At fluences of 70 and 100 J/m2, the mutant frequencies obtained with both vectors are substantially higher than with control DNAs. Sequence analysis of mutants obtained with both vectors reveal three types of mutations at frequencies significantly above those obtained from replication of undamaged DNA. These are C-->T transitions, accounting for about two-thirds of the mutants, a small number of CC-->TT substitutions, and complex mutations. Comparing the distribution of C-->T substitutions in the two spectra permits an estimation of the probability of mutagenic translesion replication of the same sequence when replicated as the leading or lagging strand. The data suggest that the overall average UV-independent C-->T substitution probability per phenotypically detectable dipyrimidine site is the same during leading and lagging strand replication. However, statistically significant differences are observed when the distribution of C-->T substitutions is considered.(ABSTRACT TRUNCATED AT 250 WORDS)

p53 immunoreactivity in cutaneous PUVA tumors is similar to that in other non-melanoma skin neoplasms

Expression of the p53 tumor suppressor gene product was determined in keratoses and skin cancers associated with psoralen photochemotherapy (PUVA). An immunocytochemical study was employed using CM-1 (polyclonal) and Do-1 (monoclonal) antibodies to human wild-type p53. Thirty-two cutaneous lesions and 20 perilesional PUVA-irradiated skin biopsies were examined from 7 patients, all of whom had received more than 200 PUVA treatments and/or a cumulative UVA dose of greater than 1000J/cm2 as treatment for widespread plaque psoriasis. p53 immunoreactivity was seen in 7 of 15 squamous cell carcinomas (46.7%), 5 of 8 dysplastic keratoses (62.5%) and in no basal cell carcinomas or benign keratoses. The overall prevalence of p53 immunoreactivity in 46.2% of malignant or dysplastic PUVA-associated skin tumors is similar to that previously found by our group in comparable skin tumors from the general population. Most patients with lesions showing positive p53 immunoreactivity had, however, been exposed to additional risk factors before receiving PUVA therapy. p53 gene sequencing of PUVA-associated non-melanoma skin cancer (NMSC) may clarify whether p53 mutation contributes to the development of these tumors and whether this relates to PUVA therapy or prior carcinogen exposure.

Association of skin malignancies with various and multiple carcinogenic and noncarcinogenic human papillomaviruses in renal transplant recipients

BACKGROUND

Organ transplant recipients receiving immunosuppressive treatment are prone to skin carcinomas on sun-exposed areas, and the frequency of such carcinomas in the long term reaches 40%. These carcinomas primarily are squamous cell carcinomas (SCC), which often are preceded by viral warts and premalignant keratoses. Human papillomaviruses (HPV) with other cocarcinogenic factors have been reported to play a role in the development of carcinomas in these patients.

METHODS

Five hundred renal-graft recipients referred to our department were examined for the presence of warts, precancerous keratoses, Bowen disease, keratoacanthomas, and basal and squamous cell carcinomas. Adequate material for histologic and virologic examination was obtained from 24 patients. An in situ molecular hybridization technique was performed using biotinylated DNA probes for HPV types 1a, 2a, 5, 16, and 18 under stringent conditions.

RESULTS

HPV DNA was detected in 44 of 86 specimens, including 14 of 17 warts, 4 of 17 premalignant keratoses, 1 of 4 Bowen disease lesions, 8 of 12 keratoacanthomas, 3 of 4 tumors in which distinction between keratoacanthomas and SCC was difficult, and 14 of 30 SCC. Twenty-six of 44 positive specimens contained several HPV types, whereas 30 specimens contained oncogenic types. Benign types 1 or 2 were detected alone in five SCC. HPV types 16 and 18 (usually detected in genital lesions) were found in 26 samples from sun-exposed areas.

CONCLUSIONS

Our results show that oncogenic and benign HPV often are detected within premalignant keratoses and SCC in organ transplant recipients, which suggests that HPV may play a role in the development of cutaneous malignancies.

p53 protein in aggressive and non-aggressive basal cell carcinoma

Basal cell carcinoma (BCC) is the most frequent cutaneous neoplasm, with a generally favorable clinical behavior. Sometimes, indeed, it recurs after therapy and/or metastasizes. As point mutations in the coding sequence of the p53 tumor suppressor gene have been implicated in the progression of many human tumors, we studied the expression of p53 protein on this neoplasia. We tested immunohistochemically the positivity for p53 protein (NCL-p53-CM1, YLEM) on 19 cases of morphologically "non aggressive" BCC (BCC1) and on 19 "aggressive" BCC (BCC2), all with one or more relapses and 3 with distant metastases also. Results were related to clinico-pathological and follow-up data. All but one BCC2 were found positive for p53 protein. Conversely, only 2 cases of BCC1 exhibited low immunoreactivity for p53 protein, with high statistical differences between the two groups. No correlation was found between the immunoreactivity, age of patients, and site of the lesions. The availability of immunohistochemistry and the relatively easy interpretation of the results make screening for p53 protein a possibly useful tool in the prognostic evaluation of BCC.

Tumourigenesis associated with the p53 tumour suppressor gene

The p53 gene is contained within 16-20 kb of cellular DNA located on the short arm of human chromosome 17 at position 17p13.1. This gene encodes a 393-amino-acid nuclear phosphoprotein involved in the regulation of cell proliferation. Current evidence suggests that loss of normal p53 function is associated with cell transformation in vitro and development of neoplasms in vivo. More than 50% of human malignancies of epithelial, mesenchymal, haematopoietic, lymphoid, and central nervous system origin analysed thus far, were shown to contain an altered p53 gene. The oncoproteins derived from several tumour viruses, including the SV40 large T antigen, the adenovirus E1B protein and papillomavirus E6 protein, as well as specific cellular gene products, e.g. murine double minute-2 (MDM2), were found to bind to the wild-type p53 protein and presumably lead to inactivation of this gene product. Therefore, the inactivation of p53 tumour suppressor gene is currently regarded as an almost universal step in the development of human cancers. The current data on p53-associated tumourigenesis are briefly discussed in this minireview.

The relation between p53 mutation and p53 immunostaining in non-melanoma skin cancer

Extensive study of the p53 gene has established its role as a tumour-suppressor gene, and the involvement of mutant p53 in a wide spectrum of human malignancy. Many mutations of p53 result in a protein product that is abnormally stable, so that it becomes readily detectable by immunocytochemistry. In contrast, under normal conditions, it has been considered that levels of wild-type p53 were too low to be detectable. Although positive immunocytochemistry has been used as a marker of mutation, recent evidence suggests that this assumption may not always be valid. We have carried out both PCR-sequencing of exons 5-8 of the p53 gene in 20 basal cell carcinomas (BCC), and immunocytochemistry of these tumours with the anti-p53 antibody DO7. Twenty cases of Bowen's disease, in which we had previously documented mutations, were also immunostained. We report a low rate of p53 mutation in the BCCs we examined (2/20), and a discrepancy between tumours with positive immunostaining and those with mutation in both Bowen's disease and BCC. Of eight tumours in which we detected mutation, only four were immunopositive: of 19 immunopositive samples, only four showed detectable mutation. We discuss the implications of our results for the use of positive immunostaining in clinical diagnosis, and the involvement of p53 in skin carcinogenesis.

A 127 kDa component of a UV-damaged DNA-binding complex, which is defective in some xeroderma pigmentosum group E patients, is homologous to a slime mold protein

A cDNA which encodes a approximately 127 kDa UV-damaged DNA-binding (UV-DDB) protein with high affinity for (6-4)pyrimidine dimers [Abramic', M., Levine, A.S. & Protic', M., J. Biol. Chem. 266: 22493-22500, 1991] has been isolated from a monkey cell cDNA library. The presence of this protein in complexes bound to UV-damaged DNA was confirmed by immunoblotting. The human cognate of the UV-DDB gene was localized to chromosome 11. UV-DDB mRNA was expressed in all human tissues examined, including cells from two patients with xeroderma pigmentosum (group E) that are deficient in UV-DDB activity, which suggests that the binding defect in these cells may reside in a dysfunctional UV-DDB protein. Database searches have revealed significant homology of the UV-DDB protein sequence with partial sequences of yet uncharacterized proteins from Dictyostelium discoideum (44% identity over 529 amino acids) and Oryza sativa (54% identity over 74 residues). According to our results, the UV-DDB polypeptide belongs to a highly conserved, structurally novel family of proteins that may be involved in the early steps of the UV response, e.g., DNA damage recognition.

Replication of UV-irradiated DNA in human cell extracts: evidence for mutagenic bypass of pyrimidine dimers

We have examined the efficiency and fidelity of simian virus 40-origin-dependent replication of UV-irradiated double-stranded DNA in extracts of human cells. Using as a mutational target the alpha-complementation domain of the Escherichia coli lacZ gene in bacteriophage M13mp2 DNA, replication of undamaged DNA in HeLa cell extracts was highly accurate, whereas replication of DNA irradiated with UV light (280-320 nm) was both less efficient and less accurate. Replication was inhibited by irradiation in a dose-dependent manner. Nonetheless, covalently closed, monomer-length circular products were generated that were resistant to digestion by Dpn I, showing that they resulted from semiconservative replication. These products were incised by T4 endonuclease V, whereas the undamaged replication products were not, suggesting that pyrimidine dimers were bypassed during replication. When replicated, UV-irradiated DNA was used to transfect an E. coli alpha-complementation host strain to score mutant M13mp2 plaques, the mutant plaque frequency was substantially higher than that obtained with either unirradiated, replicated DNA, or unreplicated, UV-irradiated DNA. Both the increased mutagenicity and the inhibition of replication associated with UV irradiation were reversed by treatment of the irradiated DNA with photolyase before replication. Sequence analysis of mutants resulting from replication of UV-irradiated DNA demonstrated that most mutants contained C-->T transition errors at dipyrimidine sites. A few mutants contained 1-nt frameshift errors or tandem double CC-->TT substitutions. The data are consistent with the interpretation that pyrimidine dimers are bypassed during replication by the multiprotein replication apparatus in human cell extracts and that this bypass is mutagenic primarily via misincorporation of dAMP opposite a cytosine (or uracil) in the dimer.

In vivo repair of cytosine hydrates in DNA of cultured human lymphoblasts

Ultraviolet irradiation of DNA in vitro results in the production of a wide variety of pyrimidine base alterations, including cytosine hydrates. Enzymes that initiate the repair of monomeric pyrimidine damage have been identified in both bacterial and mammalian systems; however, the in vivo formation and repair of cytosine photohydrates has not been demonstrated in cellular DNA. Using Escherichia coli endonuclease III as a damage-specific probe, we have shown that ring-saturated pyrimidines are formed in cultured human cells by irradiation with broad-spectrum UV light. In addition, these types of base damage are removed from the DNA of human lymphoblasts within 5 h following the irradiation. Analysis of the action spectrum for the formation of cytosine hydrates in DNA reveals that these photoproducts are formed most efficiently by irradiation in the range of 255-265 nm light, coinciding with the wavelengths that are maximally absorbed by the DNA bases.

Cell death by apoptosis in epidermal biology

Homeostasis in continually renewing tissues is maintained by a tightly regulated balance between cell proliferation, cell differentiation, and cell death. Until recently, proliferation was thought to be the primary point of control in the regulation of normal tissue kinetic homeostasis and as such has been the major focus of both understanding the etiology of disease and developing therapeutic strategies. Now, physiologic cell death, known as apoptosis (ă-pŏp-to' sĭs, ă-po-to' sĭs [Thomas CL (ed.): Taber's Cyclopedic Medical Dictionary. F.A. Davis, Co., Philadelphia, 1989)] has gained scientific recognition as an active regulatory mechanism, complementary, but functionally opposite, to proliferation with important roles in shaping and maintaining tissue size and prevention of disease. In this review we will describe the concept of apoptosis and discuss possible molecular mechanisms of its regulation that may have implications for skin biology.

A correlative study of p53 protein alteration and p53 gene mutation in glioblastoma multiforme

The p53 tumor suppressor gene is frequently mutated in glioblastomas. Mutations within the p53 gene often result in aberrant expression of the p53 protein leading to protein accumulation within the nucleus of the cells which can be detected by immunochemistry. Many studies have correlated alterations of p53 protein expression with p53 gene mutations. Positive staining of tumor cells for p53 protein has been widely assumed, perhaps incorrectly, to signify the presence of p53 gene mutations. This study compared the immunostaining patterns for p53 protein in 37 glioblastomas with the molecular genetic data obtained by the single strand conformation polymorphism assay. p53 gene mutations were detected in 46% (17 of 37) of glioblastomas, while 65% (24 of 37) of glioblastomas were positive for protein accumulation by immunohistochemistry. Although 30 of 37 glioblastomas analyzed showed concordance for p53 protein expression and p53 gene mutations, a subset of seven glioblastomas showed discordant accumulation of the p53 protein in the absence of any detectable p53 gene mutations. The mdm-2 gene was assessed in 17 glioblastomas for gene rearrangements or amplification, but none were found. This result suggests that a mechanism other than p53 gene mutation can result in altered p53 protein expression.

Mutation of the tumor suppressor gene TP53 is not detected in psoriatic skin

We investigated the tumor-suppressor gene, TP53, in psoriatic skin at gene (GP53) and protein (p53) levels. No mutation was detected in the seven exons analyzed using a combination of polymerase chain reaction and single-strand conformation polymorphism techniques. In addition, by immunohistochemistry using three different anti-p53 antibodies, no positive staining, reported to be associated with mutations and/or abnormal expression of the TP53 gene, was observed in psoriatic skin biopsies, in contrast to recent reports. These results suggest that the proliferative status of psoriatic keratinocytes does not implicate the TP53 gene.

Mutation and expression of the p53 gene in malignant melanoma cell lines

Three monoclonal antibodies (MAbs) against p53 protein (PAb 24o, DO-I and PAb1801) were used to define the immunophenotype of 13 melanoma cell lines. Immunoreactions could be detected in 12 out of 13 cell lines by using the indirect immunofluorescence technique. In 7 of these the majority of cells displayed cytoplasmic staining whereas positive nuclei were detected in only a few cells. Two cell lines had predominantly nuclear reactivity, while the remaining 3 cell lines showed signals in both locations. Despite identical nuclear staining patterns, the 3 MAbs produced qualitatively distinct cytoplasmic immunoreactions. PAb240 and DO-1, which showed similar staining frequencies, appeared more sensitive in the detection of p53 protein than did PAb1801. Immunoprecipitations of lysates from each of the cell lines, with MAbs DO-1 and 1801 (which bind to both wild-type and mutant p53 species) detected 53-kDa proteins, whereas PAb240 (which recognizes the mutant conformation of the protein in this type of assay) detected 53-kDa proteins in only 4 cell lines. Nucleotide sequencing of exons 5 to 9 of TP53 in these latter cell lines showed that each has homozygous point mutations in the locus, whereas in the others no TP53 alterations were found. Three of the 4 mutations were C-to-T transversions, alterations possibly caused by damage from UV-light. Our findings indicate that immunostaining with p53 antibodies, although common in malignant melanoma, results from the presence of mutant p53 protein in about 30% of the cases tested. Neither immunostaining with PAb240 nor the patterns of intracellular distributions of the signals are sufficient to detect TP53 mutations.

Gene mutations and increased levels of p53 protein in human squamous cell carcinomas and their cell lines

Using immunocytochemical and Western blotting techniques we have demonstrated the presence of abnormally high levels of p53 protein in 8/24 (33%) of human squamous cell carcinomas (SCC) and 9/18 (50%) of SCC cell lines. There was a correlation between the immunocytochemical results obtained with eight SCC samples and their corresponding cell lines. Direct sequencing of PCR-amplified, reverse transcribed, p53 mRNA confirmed the expression of point mutations in six of the positive cell lines and detected in-frame deletions in two others. We also detected two stop mutations and three out-of-frame deletions in five lines which did not express elevated levels of p53 protein. Several of the mutations found in SCC of the tongue (3/7) were in a region (codons 144-166) previously identified as being a p53 mutational hot spot in non-small cell lung tumours (Mitsudomi et al., 1992). In 11/13 cases only the mutant alleles were expressed suggesting loss or reduced expression of the wild type alleles in these cases. Six of the mutations were also detected in the SCCs from which the lines were derived, strongly suggesting that the mutations occurred, and were selected, in vivo. The 12th mutation GTG-->GGG (valine-->glycine) at codon 216 was expressed in line SCC-12 clone B along with an apparently normal p53 allele and is to our knowledge a novel mutation. Line BICR-19 also expressed a normal p53 allele in addition to one where exon 10 was deleted. Additionally 15 of the SCC lines (including all of those which did not show elevated p53 protein levels) were screened for the presence of human papillomavirus types 16 and 18 and were found to be negative. These results are discussed in relation to the pathogenesis of SCC and the immortalisation of human keratinocytes in vitro.

Detection of thymine dimers in suprabasal and basal cells of chronically UV-B exposed hairless mice

An immunocytochemical method was developed to study induction and removal of DNA damage in specific cell populations in the epidermis of hairless mice during chronic ultraviolet (UV) exposure. Identification of mouse suprabasal cells was performed with an immunoperoxidase stain. This stain was shown not to affect the fluorescent nuclear stains, used to reveal DNA and DNA damage. In skin cells from hairless mice irradiated daily with 1500 J/m2 UV-B for 11 consecutive days, cyclobutane thymine dimers accumulated in epidermal cells and reached a maximum level after 3 d. Thereafter dimer levels dropped to a lower, more constant level. So epidermal cells in vivo, both suprabasal and basal cells, remove dimers effectively, in contrast to cultured rodent cells, which display hardly any repair in genomic DNA. Dimer content in suprabasal cells was higher than that in basal cells, but initially the patterns of induction and removal of dimers in both cell types were rather similar. At days 4-11, however, after the drop in dimer content, the amount of dimers in basal cells prior to UV exposure was almost as low as that in non-exposed cells. The results presented here suggest important roles for both UV-induced DNA repair and cell proliferation in protecting epidermal cells against the mutagenic and carcinogenic effects of UV.

TP53 tumor-suppressor gene and human carcinogenesis

The wild-type tumor-suppressor TP53 gene encodes for a nuclear protein which has been shown to act as a transcriptional modulator. The cellular role of the p53 protein is the control of cell proliferation, particularly important in stressed cells. The TP53 gene is frequently mutated in sporadic and familial human cancers. Most transforming mutations localize in highly conserved domains of the gene and define hot-spot regions that have a certain degree of tissue specificity. Moreover, most mutations are point mutations and the type and localization of the nucleotide substitution may sometimes help in recognizing the carcinogenic agent. This is the case for C to T transitions at dipyrimidine sites induced by UV radiation in cutaneous epitheliomas. Inactivation of p53 protein can also occur through mechanisms other than genetic alteration, such as binding to viral or cellular proteins. Loss of wild-type TP53 function seems therefore to play a crucial role in cell transformation in human cancers, either during carcinogenesis or later in tumor progression.

p53 mutations are common and early events that precede tumor invasion in squamous cell neoplasia of the skin

Mutations of the p53 gene are the most common genetic abnormality described in human cancer; p53 mutations have recently been reported in more than half of the cases of squamous cell carcinomas of the skin. We have previously reported positive p53 immunostaining in Bowen's disease and actinic keratosis. To determine if this abnormal immunostaining reflects p53 mutation or alternative pathways of p53 protein inactivation we have performed direct sequencing of p53 in 20 further cases of Bowen's disease. We found eight mutations in 20 cases, seven of which would produce alterations in the p53 protein product. Our results suggest that p53 mutation is an early event in malignant conversion, frequently preceding invasion in squamous cell neoplasia of the skin. The type and site of the observed mutations reflect known mutational hotspots and support the role of ultraviolet radiation in the pathogenesis of these tumors.

p53 gene mutations and protein accumulation in human ovarian cancer

Mutations of the p53 gene on chromosome 17p are a common genetic change in the malignant progression of many cancers. We have analyzed 38 malignant tumors of ovarian or peritoneal müllerian type for evidence of p53 variations at either the DNA or protein levels. Genetic studies were based on single-strand conformation polymorphism analysis and DNA sequencing of exons 2 through 11 of the p53 gene; mutations were detected in 79% of the tumors. These data show a statistically significant association between mutations at C.G pairs and a history of estrogen therapy. Two of 20 patients whose normal tissue could be studied carried germ-line mutations of p53. Immunohistochemical analysis of the p53 protein was carried out using monoclonal antibody PAb1801. Ninety-six percent of the missense mutations were associated with abnormal accumulation of p53 protein, but nonsense mutations, a splicing mutation, and most deletions did not result in p53 protein accumulation. A statistically significant association between p53 protein accumulation in poorly differentiated stage III serous carcinomas and small primary tumor size at diagnosis was found, perhaps suggesting that p53 protein accumulation accelerates the metastatic spread from a primary tumor. Overall, our findings indicate that alterations of p53 play a major role in ovarian cancer, including predisposition to the disease in some patients, and suggest a possible mechanism for somatic mutations leading to this cancer.

Tandem double CC-->TT mutations are produced by reactive oxygen species

Oxidative damage to DNA is mutagenic and thus may play a role in carcinogenesis. Because of the large number of different DNA lesions formed by oxidative species, no genetic alteration so far identified is exclusively associated with oxygen damage. Tandem double CC-->TT mutations are known to occur via UV damage to DNA and are thought to be a specific indicator of UV exposure. Using a sensitive reversion assay that can detect both single and double mutations within the same codon of the M13-encoded lacZ alpha gene, we show that treatments that produce reactive oxygen species can also produce tandem double CC-->TT mutations. The frequency at which these mutations occur is less than that for single base mutations by a factor of approximately 30. The induction of these mutations is inhibited by treatment that scavenges hydroxyl radicals. This unique mutation provides a marker of oxygen free radical-induced mutagenesis in cells that are not exposed to UV-irradiation and an indicator for assessing the involvement of oxidative damage to DNA in aging and tumor progression.