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Query: UNIPROT:P04637 (p53)
 77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Extramammary Paget's disease is a particular form of skin cancer of unknown histogenesis. To look for the genetic defects underlying the pathogenesis of this tumour, we have examined loss of heterozygosity (LOH), p53 and human papillomavirus (HPV) status, and the expression of c-erbB-2 and bcl-2 proteins in 14 cases. Unexpectedly, no LOH was detected at several loci commonly lost in other human cancers (namely 3p, 9p, 9q, 13q, 16q, 17p, and 17q) in 12 tumours examined. Altered p53 protein expression was entirely or mostly negative in all 14 cases. Direct sequencing of exons 5-8 of the p53 gene in eight cases revealed no mutation. Polymerase chain reaction amplification of the L1 gene of human papillomavirus (HPV) did not detect the virus that could inactivate p53 and retinoblastoma tumour-suppressor gene products. As expected, c-erbB-2 proto-oncogene protein was overexpressed in six cases. The expression of bcl-2 was negative in all cases. The results presented in this study suggest that molecular events underlying extramammary Paget's disease differ from those of other common epithelial malignancies and that tumour-suppressor genes located in chromosome regions not examined in this study may be important.
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PMID:Tumour cells of extramammary Paget's disease do not show either p53 mutation or allelic loss at several selected loci implicated in other cancers. 932 50

Ultraviolet (UV) radiation is the carcinogenic factor in sunlight; damage to skin cells from repeated exposure can lead to the development of cancer. UV radiation has been mainly implicated as the cause of non-melanoma skin cancer, although some role for UV in malignant melanoma has been suggested. The induction of skin cancer is mainly caused by the accumulation of mutations caused by UV damage. Cellular mechanisms exist to repair the DNA damage, or to induce apoptosis to remove severely damaged cells; however, the additive effects of mutations in genes involved in these mechanisms, or in control of the cell cycle, can lead to abnormal cell proliferation and tumor development. The molecular events in the induction of skin cancer are being actively investigated, and recent research has added to the understanding of the roles of tumor suppressor and oncogenes in skin cancer. UV radiation has been shown to induce the expression of the p53 tumor suppressor gene, and is known to produce "signature" mutations in p53 in human and mouse skin cancers and in the tumor suppressor gene patched in human basal cell carcinoma. The role of UV radiation in suppression of immune surveillance in the skin, which is an important protection against skin tumor development, is also being investigated. The knowledge gained will help to better understand the ways in which skin cancer arises from UV exposure, which will in turn allow development of better methods of treatment and prevention.
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PMID:Mechanisms of induction of skin cancer by UV radiation. 934 91

Mutations in p53 were detected in 11/23 (48%) of non melanoma skin cancers in renal allograft recipients and in 5/8 (63%) of sporadic tumours from immune competent patients. 9/12 (75%) of mutations in transplant patients and all 5 mutations in non transplant tumours were consistent with damage caused by ultraviolet (u.v.) irradiation. DNA sequences, predominantly of the epidermodysplasia verruciformis (EV) subgroup, were detected in 9/23 (39%) of transplant tumours and in 2/8 (25%) of eight non-transplant tumours. There was no relationship between HPV status and p53 mutation, HPV DNA being present in 5/16 (31%) of tumours with p53 mutation and 6/15 (40%) of tumours lacking p53 mutation. These data are consistent with an important role for sunlight in the development of post-transplant skin cancer, and with limited functional data suggesting that E6 proteins of the cutaneous and EV-related papillomaviruses do not target p53 for ubiquitin-mediated degradation.
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PMID:p53 mutations implicate sunlight in post-transplant skin cancer irrespective of human papillomavirus status. 934 8

The most prevalent DNA lesion induced by UV irradiation is the cyclobutane pyrimidine dimer (CPD), which forms at positions of neighboring pyrimidines. Here we show that the rare DNA base 5-methylcytosine is the preferred target for CPD formation when cells are irradiated with natural sunlight. We have mapped the distribution of CPDs formed in normal human keratinocytes along exons of the p53 gene. Codons 196, 245, 248, and 282, which are mutational hot spots in skin cancers, are only weakly to moderately susceptible to formation of CPDs after irradiation with UVC (254 nm) or UVB (320 nm) light sources. However, when cells were exposed to natural sunlight, CPD formation was enhanced up to 15-fold at these codons due to the presence of 5-methylcytosine bases. These results suggest that CPDs containing 5-methylcytosine may play an important role in formation of sunlight-induced skin tumors and that methylation of CpG sequences, besides being involved in spontaneous mutagenesis processes, can also create preferential targets for environmental mutagens and carcinogens.
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PMID:Sunlight induces pyrimidine dimers preferentially at 5-methylcytosine bases. 935 31

Ultraviolet light has been identified as the major carcinogen in skin cancer and the p53 tumor suppressor gene is a major target for UV-induced mutations. The mutations are probably caused by unrepaired UV-induced cyclobutane pyrimidine dimers (CPD) and possibly by the less frequent pyrimidine (6-4) pyrimidone photoproducts. While hot spots for p53 mutations in human nonmelanoma skin tumors correspond quite well to slow spots for CPD repair in cultured cells irradiated with the model mutagen 254 nm UVC (which is not present in terrestrial sunlight), they do not all coincide with sequences that are initially frequently damaged by 254 nm UVC. Using LMPCR (ligation-mediated polymerase chain reaction), we show that environmentally relevant UVB light induces CPD at CC and Pyr(m)C positions much more frequently than does UVC light, and that all eight skin cancer hot spots in p53 are also hot spots for UVB-induced CPD. Our results show that methylation of dipyrimidine sites (Pyr(m)CpG) is associated with an increase rate of CPD formation upon UVB irradiation. Consequently, DNA methylation may increase the mutagenic potential of UVB and explains that several p53 mutation hot spots are found at Pyr(m)CpG. The distribution patterns of CPD formation and the photofootprint patterns found along exons 5 and 6 of p53 gene are suggestive of DNA folding into nucleosomes.
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PMID:UVB-induced cyclobutane pyrimidine dimer frequency correlates with skin cancer mutational hotspots in p53. 938 97

Mutations of the p53 gene have been implicated as an important factor in the pathogenesis of ultraviolet light induced skin cancers. To examine the role of p53 in skin carcinogenesis, we observed the development of skin cancers in homozygous p53-deficient (-/-) mice and wild-type p53 (+/+) mice, after chronic ultraviolet B (290-320 nm) exposure. At a dose of 2 J per m2 per s of ultraviolet B for 30 min three times per week, all p53-/- mice developed skin tumors by week 12. All the p53-/- mice developed multiple tumors by week 16. The majority of the tumors occurred on the ears. None of the p53+/+ mice developed skin tumors after 17 wk of UV exposure. Ten p53-/- tumors were examined histologically: five invasive squamous cell carcinomas, four squamous cell carcinomas in situ, and one actinic keratosis. p53-/- mice have a short life-span due to internal tumors or a deficiency in the immune system; however, ultraviolet B exposure did not significantly reduce the life-span of p53-/- mice. These results demonstrate that loss of wild-type p53 function shortens the latent period and predisposes the animals to the development of squamous cell carcinomas after ultraviolet irradiation.
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PMID:Induction of squamous cell carcinoma in p53-deficient mice after ultraviolet irradiation. 942 91

Because most non-melanocytic human skin cancers have p53 mutations, it is unclear whether the aberrant growth of these cancers is simply a result of the abrogation of a p53 downstream mediator, the universal cyclin-dependent kinase inhibitor p21WAF1. To investigate the role of p21WAF1 in human skin carcinogenesis, we studied its regulation in normal and p53-mutated immortalized human keratinocytes. In proliferating human normal keratinocytes (HNK), more wild-type p53 protein (wt p53) was expressed than in growth-arrested differentiating keratinocytes. However, the function of wt p53 as a transcriptional activator of the p21WAF1 gene was suppressed in proliferating keratinocytes. In response to ultraviolet B irradiation, expression of wt p53 increased in proliferating keratinocytes, but p21WAF1 transcriptional activation was not induced. Two isoforms of mdm2 (p57 and p90), which can bind to wt p53 and negatively regulate wt p53 function, were expressed in proliferating HNK, suggesting that mdm2 may play a role in the suppression of wt p53's function in proliferating HNK. Increased expression of p21WAF1 was detected in both Ca(2+)-induced growth-arrested and differentiating HNK, in which the wt p53 expression was down regulated. This reflects the complexity of the p53/p21WAF1 pathways of cell-cycle regulation and differentiation in keratinocytes. No p21WAF1 expression was detected in human immortalized keratinocytes (HaCaT) or in two ras-transformed variants, HaCaT ras I/7 and HaCaT ras II/3, which have two p53 mutations. Retrovirus-mediated expression of p21WAF1 stopped the growth of all these cell types, but expression of wt p53 did not affect the cells' growth properties. p21WAF1 also downregulated human telomerase RNA component mRNA expression in HaCaT cells. This novel function of p21WAF1 partly explains the suppression of telomerase activity by p21WAF1 expression in HaCaT. Taken together, these results are consistent with the idea that p21WAF1 successfully inhibits the growth of non-melanocytic skin cancers, even those with alterations in p53, p21ras, retinoblastoma gene product, and telomerase activity.
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PMID:Growth arrest of immortalized human keratinocytes and suppression of telomerase activity by p21WAF1 gene expression. 947 69

Nonmelanoma skin cancers (NMSC) are among the most common malignancies in the world. Typically, these neoplasms grow slowly and are comparatively indolent in their clinical behavior. The most frequent molecular alterations implicated in the pathogenesis of these neoplasms involve genes known to be regulators of cell death including p53, Ha-ras and bcl-2. In order to evaluate the significance cell death deregulation during skin carcinogenesis, we generated a transgenic mouse model (HK1.bcl-2) using the human keratin 1 promoter to target the expression of a human bcl-2 minigene to the epidermis. Transgenic HK1.bcl-2 protein was expressed at high levels specifically in the epidermis extending from the stratum basale through the stratum granulosum. The epidermis of HK1.bcl-2 mice exhibited multifocal hyperplasia without associated hyperkeratosis and aberrant expression of keratin 6. The rate of proliferation was similar in HK1.bcl-2 and control epidermis although suprabasal BrdUrd incorporating cells were present only in HK1.bcl-2 skin. Keratinocytes from the HK1.bcl-2 mice were significantly more resistant to cell death induction by U.V.-B, DMBA, and TPA, compared to control keratinocytes. Furthermore, papillomas developed at a significantly greater frequency and shorter latency in the HK1.bcl-2 mice compared to control littermates following initiation with DMBA and promotion with TPA. Together these results support a role for bcl-2 in the pathogenesis of NMSC.
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PMID:Human keratin-1.bcl-2 transgenic mice aberrantly express keratin 6, exhibit reduced sensitivity to keratinocyte cell death induction, and are susceptible to skin tumor formation. 948 76

We examined the spectrum of p53 mutations found in 40 UV-induced skin tumors of xeroderma pigmentosum group A gene (XPA)-deficient mice. p53 mutations were detected in 48% of the tumors. Nearly all of the mutations were induced at dipyrimidine sites. Ninety-three % of the mutations were G.C-->A.T transitions at dipyrimidine sites, including tandem transitions (CC-->TT), which are the hallmark of the UVB-induced mutation. Seventy-two % of the mutations at dipyrimidine sites could be ascribed to damage on the transcribed strand. In addition, no evident mutational hot spots were detected. This is in contrast to the UVB-induced skin tumors of normal mice, in which 92% of p53 mutations occurred as a result of DNA damage on the nontranscribed strand, and clear hot spots were observed. Thus, XPA-deficient mice showed significant mutation features that might be characteristic of the absence of nucleotide excision repair and may provide a good animal model for the analysis of the high incidence of skin cancer in xeroderma pigmentosum group A patients.
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PMID:Strand specificity and absence of hot spots for p53 mutations in ultraviolet B-induced skin tumors of XPA-deficient mice. 948 15

In this study, we investigated whether the spectrum of p53 mutations in skin tumors induced in hairless SKH-hr1 mice by a solar simulator (290-400 nm) are similar to those found in skin tumors induced in C3H mice by UV radiation from unfiltered (250-400 nm) and Kodacel-filtered (290-400 nm) FS40 sunlamps. Analysis of tumor DNA for p53 mutations revealed that 14 of 16 (87.5%) SkH-hr1 skin tumors induced by the solar simulator contained mutations. Single C-->T transitions at dipyrimidine sequences located on the nontranscribed DNA strand were the most predominant type of p53 mutation. Remarkably, 52% of all p53 mutations in solar simulator-induced SKH-hr1 skin tumors occurred at codon 270, which is also a hotspot in C3H skin tumors induced by unfiltered and Kodacel-filtered FS40 sunlamps. However, T-->G transversions, which are hallmarks of UVA-induced mutations, were not detected in any of the solar simulator-induced skin tumors analyzed. These results demonstrate that the p53 mutation spectra seen in solar simulator-induced SKH-hr1 skin tumors are similar to those present in -unfiltered and Kodacel-filtered FS40 sunlamp-induced C3H skin tumors. In addition, our data indicate that the UVA present in solar simulator radiation does not play a role in the induction of p53 mutations that contribute to skin cancer development.
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PMID:p53 Mutations in hairless SKH-hr1 mouse skin tumors induced by a solar simulator. 948


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