p53 codon 72多态性与宫颈癌发生机制的研究

宫颈癌是女性常见的恶性肿瘤，严重影响妇女的生活质量。人乳头状瘤病毒感染是宫颈癌的主要致病因素，近几年的研究发现p53 codon 72多态性与宫颈癌的发生发展密切相关。现主要综述该位点多态性在宫颈癌发生机制中的研究进展。     

The p53 codon 72 proline allele is associated with p53 gene mutations in non-small cell lung cancer.

The p53 gene plays a critical role in cell cycle control, the initiation of apoptosis, and in DNA repair. An Arg/Pro polymorphism at codon 72 of the p53 gene alters the ability of the p53 protein to induce apoptosis, influences the behavior of mutant p53, decreases DNA repair capacity, and may be linked with an increased risk of lung cancer. To further define the role of the p53 codon 72 polymorphism on DNA repair, lung cancer risk, and mutant p53 function, we examined the effect of this polymorphism on mutation of the p53 gene and patient survival in non-small cell lung cancer (NSCLC). Tumor and nonneoplastic (lung or lymphocyte) samples were collected from 182 patients with NSCLC. p53 mutations were detected by direct sequencing and/or the Gene Chip p53 assay in 93 of 182 (51%) tumors. p53 codon 72 polymorphisms were identified by PCR/RFLP analysis. p53 mutations were significantly (P = 0.01) associated with the number of codon 72 Pro alleles: Pro/Pro homozygotes, 17 of 26 (65%); Arg/Pro heterozygotes, 45 of 79 (57%); and Arg/Arg homozygotes, 31 of 77 (40%). The number of codon 72 Pro alleles was independently associated with p53 mutations (odds ratio, 1.97; 95% confidence interval, 1.14-3.40; P = 0.01) in a multiple logistic regression model. The codon 72 polymorphism did not influence patient survival in either the entire patient group or among patients with p53 mutant tumors. In summary, the p53 Pro allele is associated with an increased frequency of p53 mutations in NSCLC.     

p53 codon 72多态性与宫颈癌发生机制的研究

宫颈癌是女性常见的恶性肿瘤,严重影响妇女的生活质量。人乳头状瘤病毒感染是宫颈癌的主要致病因素,近几年的研究发现p53 codon 72多态性与宫颈癌的发生发展密切相关。现主要综述该位点多态性在宫颈癌发生机制中的研究进展。     

UV-induced DNA damage and mutations in Hupki (human p53 knock-in) mice recapitulate p53 hotspot alterations in sun-exposed human skin.

The major etiological agent contributing to human nonmelanoma skin cancer is sunlight. The p53 tumor suppressor gene is usually mutated in these tumors, and the mutations are "UV signature" single or tandem transitions at dipyrimidine sequences in the DNA-binding domain (DBD). Cells that harbor these characteristic mutations are already present in sun-exposed skin areas of healthy individuals, and small epidermal patches that are immunoreactive to anti-p53 antibody accrue as exposure increases. To explore carcinogen-specific human p53 mutation patterns experimentally, we generated a knock-in (Hupki) mouse in which the murine DBD of the p53 gene has been replaced by the homologous human p53 DBD segment; thus, the precise base sequence context frequently targeted by mutagens or endogenous mutagenic processes in human carcinogenesis is present in this strain (J. L. Luo et al., Oncogene, 20: 320-328, 2001). Here we show that when epidermal cells of Hupki mice (p53(ki/ki)) are irradiated in vivo with a single acute dose of UVB light, they accumulate UV photoproducts at the same locations of the p53 gene as human cells. Chronic exposure of Hupki mice (4.5 kJ/m(2) 5x/week for 4 weeks) results in the appearance of cell patches that stain intensely with the anti-p53 antiserum CM1. DNA preparations from 2 cm(2) sections of chronically irradiated Hupki epidermis harbor C to T and CC to TT mutations at two mutation hotspots identified in human skin cancer, one at codons 278-279, and one at codons 247-248; the latter is the most frequent UVB-associated mutation site in humans but not in p53 wild-type mice. Thus, Hupki keratinocytes with these p53 mutations encode an aberrant DBD identical in amino acid sequence to the mutant p53 molecules in human UV-induced tumors. The Hupki mouse model offers a new experimental tool in molecular epidemiology and biomedical research.     

Aflatoxin-B exposure does not lead to p53 mutations but results in enhanced liver cancer of Hupki (human p53 knock-in) mice

Hepatocellular carcinoma (HCC) is a common human malignancy that is often associated with risk factors such as aflatoxin-B1 (AFB1) exposure and Hepatitis-B virus infection in developing countries. There is a strong correlation between these risk factors and mutation of the tumor-suppressor gene p53 at codon 249. In vitro experiments have also shown that treatment of human liver cells with AFB1 results in p53 mutations. A tumor-promoting role for mutant p53 was demonstrated using transgenic mice models, in which HCC development was accelerated upon AFB1-exposure. However, wild-type mice in which AFB1 alone was used to induce liver cancers have failed to recapitulate p53 mutations, raising the possibility that mouse DNA context may not be appropriate for the generation of AFB1-induced p53 mutations. We have now tested this hypothesis using the Hupki mice (human p53 knock-in) in which the mouse DNA-binding domain has been replaced by the homologous human p53 segment. Mice were followed for 80 weeks after AFB1 injection for survival and HCC formation. Hupki mice were found to be more susceptible to AFB1 than wild-type mice. Moreover, only 19% of wild-type mice developed HCCs compared to 44% in Hupki mice. However, none of the liver tumors and normal tissues from Hupki mice contained any mutations in the DNA-binding domain of p53. These findings suggest that the human DNA context of the p53 gene alone may not be the sole determinant of AFB1-induced mutagenesis. Furthermore, humanized p53 appears not to be as effective as murine p53 in the mouse cellular environment in preventing malignant transformation.     

p53 mutations cluster at codon 249 in hepatitis B virus-positive hepatocellular carcinomas from China.

DNA samples from 36 hepatocellular carcinoma (HCC) patients from China were screened for a specific mutation affecting codon 249 of the p53 gene, recently identified as a hotspot mutation in some HCCs. We detected the tumor-specific p53 codon 249 mutation in 21 (58%) of 36 HCCs examined. Thirteen patients with the specific codon 249 mutation had lost the remaining allele of p53, whereas the remaining eight patients appeared to have retained both copies of the gene. These results suggest that alterations of p53 may be important events in the genesis of HCCs and that point mutation may precede allele loss.     

Prognostic significance of p53 codon 72 polymorphism in lung carcinomas

Lung cancer is the leading cause of cancer death in Taiwan. Potential molecular markers associated with cancer susceptibility and prognosis are the genes involved in tumorigenesis. Therefore, we investigated the association of p53 codon 72 polymorphism with prognosis in 114 lung cancer patients. The estimated median survival times for patients with proline (Pro)/Pro, arginine (Arg)/Arg, and Arg/Pro genotypes were 25, 26 and 36 months, respectively. We also found that patients with the Pro/Pro genotype had a worse prognosis compared with those with Arg/Pro genotypes, especially for patients with squamous cell lung cancer (P=0.013), male patients (P=0.028) and those aged 60–69 years (P=0.052). In patients with early stage lung cancer, patients with Pro/Pro and Arg/Arg genotypes had a tendency for a worse prognosis than those with the Arg/Pro genotype (P=0.057). Our data suggest that p53 codon 72 polymorphism may be a potential prognostic factor in certain sub groups of lung cancer patients in Taiwan.     

p53 polymorphic variants at codon 72 exert different effects on cell cycle progression

Two common polymorphic forms of the p53 tumor suppressor protein are widely distributed throughout the human population. These encode either proline or arginine at position 72, and this difference results in a marked alteration in the primary structure of the protein. A number of previous studies have shown significant differences in the biochemical properties of the p53 protein, depending on the particular polymorphic form. There is little information, however, on their respective biologic activities. In this study, we have used an inducible switch system for expressing both polymorphic forms of p53 within Saos-2 cells. Cell cycle analysis postinduction of p53 function reveals striking differences in how the 2 forms of p53 bring about a cessation of cell growth. Thus, the Arg72 form of p53 is significantly more efficient than the Pro72 form at inducing apoptosis. In contrast, the Pro72 form appears to induce a higher level of G1 arrest than the Arg72 form. These results demonstrate significant differences in how the codon 72 polymorphism affects the biological activity of p53.     

Genomic instability in radiation-induced mouse lymphoma from p53 heterozygous mice

Although radiation can directly induce DNA damage and is a known human and animal carcinogen, the number of genetic changes in radiation-induced tumors, and the pathways responsible for generating them, are unknown. We have used high-density BAC arrays covering >95% of the mouse genome for analysis of genomic patterns of aberrations in spontaneous and radiation-induced mouse lymphomas. The majority of radiation-induced tumors exhibit one of three 'signatures' based on gene copy number changes. Some exhibit extensive scrambling of the genome, with very high numbers of recurrent gains and losses. Two other signatures are characterized by excess gains but relatively few losses, or vice versa. Changes in spontaneous tumors often involve whole chromosomes, whereas radiation-induced tumors exhibit a high frequency of localized deletion/amplification events. The number of copy number abnormalities does not correlate with the latency or pathology of the tumors. We propose that specific early events following radiation exposure induce changes in 'caretaker' genes that control specific downstream pathways involved in DNA damage repair. The nature of these early events may determine the overall genomic signature observed in the resulting tumor.     

Distribution of p53 codon 72 polymorphisms in ovarian tumour patients and their prognostic significance in ovarian cancer patients

BACKGROUND: The p53 gene is frequently mutated in various human tumours. In addition, single nucleotide polymorphisms are often observed in exons and introns of the p53 gene in normal tissues and tumours. MATERIALS AND METHODS: The prevalence of a polymorphism involving codon 72 of exon 4 in the p53 gene was studied in peripheral white blood cells and tumour tissues from Danish ovarian tumour patients and in peripheral white blood cells from controls. The analyses were performed by Polymerase Chain Reaction (PCR), Restriction Fragment Length Polymorphism (RFLP) and DNA sequencing. The amino acid residue at this position is either arginine (p53-Arg) or proline (p53-Pro). RESULTS: There was no correlation between the frequency of the three genotypes (Pro/Pro, Arg/Arg and Arg/Pro) and age, stage or histological type of the tumour. A significant difference in survival was observed between ovarian cancer stage III patients with a shift from one genotype in the blood to another genotype in the tissue and patients with no shift (p=0.0216). CONCLUSION: Kaplan-Meier survival analyses and multivariate Cox regression analysis stratified to stage III ovarian cancer patients showed that a shift from one genotype in the blood to another genotype in the tissue is a prognostic factor in Danish ovarian cancer patients.     

p53 Codon 72 and p21 codon 31 polymorphisms in prostate cancer.

The tumor suppressor gene p53 and its downstream effector p21 are thought to play major roles in the development of human malignancy. Polymorphic variants of p53 at codon 72, and p21 at codon 31, have been found to be associated with cancer susceptibility, but few studies have investigated their effect on prostate cancer risk. In this case-control study, we investigated the association of p53 codon 72 and p21 codon 31 polymorphisms with prostate cancer risk in a Taiwanese population. In total, 200 patients with prostate cancer, 247 age-matched male controls, and 181 non-age-matched symptomatic benign prostatic hyperplasia (BPH; American Urological Association symptom score > or = 8 and prostate volume > 20 gm) recruited from two medical centers in southern Taiwan were genotyped. Overall, we found no significant association between p53 polymorphism and risk of prostate cancer. However, for p21 polymorphism, the frequencies of p21 Ser/Ser, Ser/Arg and Arg/Arg were 52 (26.0%), 85 (42.5%), 63 (31.5%) in case patients, 48 (26.5%), 82 (45.3%), 51 (28.2%) in BPH patients, and 76 (30.8%), 119 (48.2%), 52 (21.1%) in controls, respectively. Among the prostate cancer cases and controls, subjects with Arg/Arg genotype were found to have a 1.78-fold increased risk [95% confidence interval (CI), 1.06-3.01] of developing prostate cancer compared with those having the Ser/Ser genotype, after adjusting for other potential covariates. This significant association was slightly stronger [odds ratio (OR), 2.13; 95% CI, 1.16-3.92] in younger men (< or = 72 years; n = 99 and 126 for cases and controls, respectively) and correlated with localized disease stage (OR, 1.96; 95 % CI, 1.15-3.35) and moderately differentiated prostate cancer (OR, 2.04; 95% CI, 1.17-3.53). In addition, the Arg/Arg genotype was associated with BPH risk in those with large prostate volumes (> 50 mL) compared with those having the Ser/Ser genotype [OR, 2.29; 95% CI, 1.07-4.98]. Our findings suggest that the p21 codon 31 polymorphism may be associated with the development of prostate enlargement and cancer.     

The p53 codon 72 polymorphism and lung cancer risk.

The p53 tumor suppressor gene frequently is mutated in many forms of human carcinomas. A common polymorphism occurs at codon 72 of exon 4, with two alleles encoding either arginine (CGC) or proline (CCC). This p53 polymorphism reportedly is associated with lung cancer susceptibility. However, not all investigations have been consistent, and this hypothesized association remains controversial. We tested the hypothesis that the Pro/Pro genotype is associated with increased lung cancer risk in a large case-control study of lung cancer that included 482 cases and 510 controls from the Massachusetts General Hospital in Boston, Massachusetts. DNA from peripheral blood samples was examined by PCR-RFLP. Pro/Pro homozygotes were found more frequently in adenocarcinomas (cases, 16.4%; controls, 12.0%; P = 0.03). The prevalence of the Pro/Pro homozygous genotype increased in frequency with increasing pack-years of smoking. The combined susceptible genotype homozygous Pro/Pro and heterozygous Arg/Pro was associated with a 1.45-fold higher risk of adenocarcinoma compared with Arg/Arg genotype (95% confidence interval = 1.01-2.06; P = 0.04) after adjustment for relevant variables. Lung adenocarcinoma risk increased with the presence of one or both variant alleles across smoking strata. In addition, at each level of smoking (except nonsmoker and light smoker), the risk associated with smoking was higher for the population with the combined variant (Arg/Pro + Pro/Pro) genotype. The risk for the combined genotype was associated with tobacco exposure status. In conclusion, the codon 72 germ-line polymorphism (Arg/Pro) of the common tumor suppressor gene p53 contributes to heritable susceptibility for smoke-induced lung adenocarcinoma. The modifications by p53 polymorphism and pack-years resulted in an increased risk of the susceptible genotype to lung adenocarcinoma. The p53 gene may modulate the response to environment carcinogens and thereby affect the risk of developing lung adenocarcinoma.     

Homozygous arginine at codon 72 of p53 has no prognostic significance in cervical cancer.

Mutation of p53, a tumour suppressor gene, is uncommon in cervical cancer but the detection of human papillomavirus (HPV) DNA in cervical cancer is common. The findings of increased susceptibility to degradation of p53 by E6 protein of HPV16/18 in cervical cancer with homozygous arginine at codon 72 (HA72) of p53 led to this study on whether cervical cancers with HA72 were more aggressive with the increase in the rate of loss of p53 function. In 102 cervical cancers, 76.5% were HPV16/18 positive and 30% had HA72. No survival difference was detected between HA72 and non-HA72 tumours irrespective of HPV16/18 status. Furthermore, the detection of HPV16/18 in cervical cancer was found not to be of prognostic significance in this study.     

p53 codon 72 polymorphism in basal cell carcinoma of the skin

Basal cell carcinoma (BCC) is the most prevalent cancer in Iran. A common polymorphism at codon 72 of exon 4 of p53 tumor suppressor gene has been reported to be associated with increased inheritable susceptibility to several cancers. In the present study the frequency of p53 codon 72 polymorphism in 91 patients with BCC of skin, compared to 465 healthy normal individuals, was investigated. In total, there was no significant difference in the p53 genotypes between patients and controls. However, there was an apparent increase in theArgl Arg genotype among those BCC patients who had a history of occupational sun exposure, compared to non-exposed patients (46.3% vs. 23.1%, P=0.11). A trend of increase in the frequency ofArg allele among sun-exposed patients was also observed (69.4% vs. 53.8%, P=0.07). Comparison of the genotype frequencies between sunexposed patients and normal controls confirmed the accumulation ofArgl Arg genotype in these patients (46.3% vs. 34.8%, P = 0.07). In addition, the frequency ofArg allele was significantly higher in sunexposed patients compared to controls (69.4% vs. 58.2%, P=0.03). Our results suggest thatArg allele at codon 72 of p53 gene might affect the risk of ultraviolet-induced basal cell carcinoma.     

p53基因多态性与乳腺癌的相关性研究进展

 【摘要】　乳腺癌为危害妇女生命健康的恶性肿瘤之一,肿瘤抑制基因p53是迄今发现的与人类恶性肿瘤关系最密切的基因之一。位于p53基因第4外显子上的第72位密码子多态性与多种肿瘤密切相关,是近年来研究的热点。国内关于p53基因多态性的研究多为肺癌、子宫颈癌、食管癌、卵巢癌等方面,乳腺癌方面的报道少见。现就其与乳腺癌相关性的生物学功能作一总结。     

p53 codon 72 polymorphism in vulval cancer and vulval intraepithelial neoplasia

p53 codon 72 polymorphism was analysed in UK women with human papillomavirus (HPV)-associated vulval intraepithelial neoplasia and vulval squamous cell carcinoma. Arginine homozygotes were significantly less common in either group compared with controls. We conclude that the arginine polymorphism may confer protection against the development of HPV-associated vulval neoplasia.     

p53 codon 72 polymorphism and its association with bladder cancer

p53 codon 72 Arg homozygosity has been associated with increased risk of developing cervical cancer. This association has been tested in various human cancers with controversial results. In the present study we investigated the impact of this polymorphism in a population-based case-control study of bladder cancer. Using allele-specific polymerase chain reaction to detect the p53 codon 72 polymorphism, we tested peripheral blood samples from 50 patients with bladder cancer and 99 healthy individuals of similar age and from the same geographical region. Tumor specimens from all bladder cancer patients were examined for the presence of human papilloma virus (HPV). The distribution of p53 alleles in bladder cancer patients and in controls was statistically significant (P<0.002; odds ratio, 2.67; 95% confidence interval, 1.38-5.20), and homozygosity for arginine at residue 72 was associated with an increased risk for bladder cancer (P<0.00002; odds ratio, 4.69; 95% confidence interval, 2.13-10.41). The presence of HPV was found in six of the 50 patients (12%). This is the first study correlating p53 codon 72 polymorphism with bladder cancer. Our results provide evidence that this p53 polymorphism is implicated in bladder carcinogenesis and that individuals harboring the Arg/Arg genotype have an increased risk of developing bladder cancer.     

High prevalence of mutations at codon 249 of the p53 gene in hepatocellular carcinomas from Senegal.

In hepatocellular carcinoma, mutation within the p53 gene occurs mainly at codon 249 and its frequency has been associated with exposure to aflatoxin. As Senegal is a country where liver cancer incidence is one of the highest in the world and where people are highly exposed to aflatoxin, we screened 15 liver cancer samples from this country for mutation at codon 249 of the p53 gene. Non-tumoral DNA from the patients showed a wild type genotype. Mutation at codon 249 of the p53 gene was detected in 10 of the 15 tumour tissues tested (67%). This frequency of mutation in codon 249 of the p53 gene is the highest described. These results confirmed that there is an association between countries of high aflatoxin intake and a high frequency of mutation in codon 249 of p53 gene, and that HBV alone does not contribute to these base changes.     

Effect of p53 codon 72 genotype on breast cancer survival depends on p53 gene status

In vitro studies suggest that p53 codon 72 genotype alters the apoptotic capacity of p53 protein, with the 72 arginine (R) form of wild-type p53 harboring a greater apoptosis-inducing potential than the 72 proline (P) variant. The aim of this study was to investigate whether the association between the p53 codon 72 genotype and breast cancer survival was modified by p53 gene status. In our study, we examined the p53 codon 72 genotype and p53 mutations (through exons 4-9) in paraffin-embedded specimens from 414 breast cancer patients with a median follow-up of 8.2 years. We report that the p53 codon 72 genotype was significantly associated with disease-free survival (DFS, p = 0.02) but not with disease-specific survival (DSS, p = 0.24) in the entire study population (n = 414). In contrast, the codon 72 genotype was strongly associated with both DFS (p = 0.001) and DSS (p = 0.04) among patients with a wild-type p53 tumor (n = 346), patients with the P/P variant had worse DFS and DSS than did those with the P/R or R/R variant in this subgroup of patients. More importantly, as compared with the P/R or R/R variant, the P/P variant remained an independent prognostic factor of DFS among patients with a wild-type p53 tumor (HR = 2.5; 95%CI = 1.4-4.4; p = 0.003). We conclude that the effect of p53 codon 72 genotype on breast cancer survival is dependent on p53 gene status, the P/P variant is strongly associated with poor prognosis among patients with a wild-type p53 tumor.