Cancer susceptibility polymorphism of p53 at codon 72 affects phosphorylation and degradation of p53 protein

The common polymorphism of p53 at codon 72, either encoding proline or arginine, has drawn attention as a genetic factor associated with clinical outcome or cancer risk for the last 2 decades. We now show that these two polymorphic variants differ in protein structure, especially within the N-terminal region and, as a consequence, differ in post-translational modification at the N terminus. The arginine form (p53-72R) shows significantly enhanced phosphorylation at Ser-6 and Ser-20 compared with the proline form (p53-72P). We also show diminished Mdm2-mediated degradation of p53-72R compared with p53-72P, which is at least partly brought about by higher levels of phosphorylation at Ser-20 in p53-72R. Furthermore, enhanced p21 expression in p53-72R-expressing cells, which is dependent on phosphorylation at Ser-6, was demonstrated. Differential p21 expression between the variants was also observed upon activation of TGF-β signaling. Collectively, we demonstrate a novel molecular difference and simultaneously suggest a difference in the tumor-suppressing function of the variants.     

p53 codon 72 polymorphism and risk of cervical cancer

Storey et al. (1998) implicated the proline/argine polymorphism of the codon 72 of the tumor-suppressor gene p53 in the development of cervical cancer (CC) with the observation that the p53 protein is more efficiently inactivated by the E6 oncoprotein of human papillomavirus in p53 arginine as compared with its proline isoform. These authors further noted that in the United Kingdom, individuals homozygous for the arginine allele were several times more susceptible to HPV-associated tumorigenesis that proline/arginine heterozygotes. Subsequent studies in different countries failed to unanimously confirm this association. Motivated by the high incidence of CC in Chile, we undertook a case control study obtaining the following frequencies for genotypes PP, AP and AA in 60 ICC cases and 53 carefully selected controls: 0.067, 0.250, 0.683 and 0.075, 0.453, 0.472 respectively. A significant difference (X2 = 3.19 p < 0.02) and an odds ratio of 2.62 supported Storey et al (1998)'s results. In addition, rejecting previous hypotheses about the world distribution of the p53 codon 72 polymorphism, we conclude that this distribution most likely represents ancient human dispersal routes. Several methodological and biological explanations for the results obtained in previous negative association studies are briefly discussed.     

An updated meta-analysis of the p53 codon 72 polymorphism and gastric cancer risk

To investigate the association between p53 codon 72 polymorphisms and gastric cancer risk, a meta-analysis published in 2007 was updated with new data. Relevant literature was retrieved by searching PubMed and statistical analysis conducted using Review Manager software. Twenty-eight case-control studies were included in this meta-analysis, with 6,859 cases and 9,277 controls. The pooled results for all included studies showed that patients with gastric cancer had a borderline lower frequency of the Arg/Arg phenotype (odds ratio (OR) = 0.91, 95 % CI = 0.83-1.00, p = 0.04). When stratified for race, the difference in Arg/Arg frequency was significant among Asians (OR = 0.87, 95 % CI = 0.78-0.97, p = 0.01). On stratifying the various studies we found that, among Asians: (i) patients with cardial gastric cancer had a significantly higher frequency of the Pro/Pro genotype (OR = 1.35, 95 % CI = 1.03-1.77, p = 0.04) than those with non-cardial gastric cancer; (ii) patients with advanced (stage III/IV) gastric cancer had a significantly higher frequency of Arg/Arg (OR = 1.30, 95 % CI = 1.06-1.61, p = 0.01) than those with early (stage I/II) cancer; and (iii) patients with metastasis had a significantly higher frequency of Pro/Pro (OR = 3.31, 95 % CI = 1.31-8.41) than those without metastasis. Our study suggests that, among Asians, the p53 codon 72 Arg/Arg genotype is associated with a modestly decreased risk of gastric cancer, and that this difference in genotype distribution may be associated with cancer stage, location, differentiation and metastasis.     

Association of p53 codon 72 polymorphism with prostate cancer: a meta-analysis

Relationship of prostate cancer with the polymorphism of p53 codon 72 was reported with inconsistent results. The purpose of this study was to quantitatively evaluate the association between p53 codon 72 polymorphism and prostate cancer susceptibility. We performed an extensive search of relevant studies and made a meta-analysis, including 8 studies with 815 prostate cancer cases and 1047 controls. The combined results showed that there were no significant differences in genotype distribution between prostate cancer cases and control on the basis of all studies, CC/GC versus GG (OR = 1.24, 95% CI: 0.93–1.65), GG/GC versus CC (OR = 0.96, 95% CI: 0.60–1.55), GC versus GG (OR = 1.27, 95% CI: 0.91–1.77), CC versus GG (OR = 1.25, 95% CI:0.74–2.12), GC versus CC (OR = 1.09, 95% CI: 0.63–1.87). When stratifying for the race, there were also no statistically significant differences in genotype distribution between prostate cancer cases and controls. This meta-analysis did not provide an evidence of confirming association between p53 codon 72 polymorphism and prostate cancer.     

The associations of p53 overexpression with p53 codon 72 genetic polymorphism in esophageal cancer

Variations in p53 codon 72 have been identified as significant predisposing factors for various cancers, but molecular mechanisms remain unclear. We investigated associations of p53 overexpression with codon 72 variants and other factors with esophageal cancer. Status of p53 overexpression was determined by immunohistochemical staining. Codon 72 polymorphisms and mutation of p53 was identified by PCR-RFLP and direct sequencing from exons 4 to 9, respectively. We evaluated 126 patients who underwent esophagectomy in the National Taiwan University Hospital, and found that the status of p53 overexpression was significantly influenced by presence of codon 72 polymorphisms. After adjustment for other possible confounders, the incidence of p53 overexpression was significantly decreased in patients with Pro/Pro genotype with an odds ratio (OR) of 0.21 (95% CI: 0.067-0.64) (p = 0.0065) compared with incidence in patients with Arg/Arg genotype. The incidence of p53 overexpression was additively increased with environmental exposure to cigarette smoke, alcohol, and areca quid. When compared with individuals exposed to only one of these environmental risk factors, patients who had exposure to two or three risk factors had ORs of 6.11 (95% CI: 1.80-20.75) and 6.22 (95% CI: 1.81-21.34) for p53 overexpression, respectively. Elderly patients (age >70 years) were also more likely to have p53 overexpression, with an OR of 5.63 (95% CI: 1.53-20.64) compared with overexpression among patients aged less than 55 years. Forty-one patients received further evaluation of p53 mutation. There was also a higher incidence of, but without reaching a statistical significance, p53 mutation in patients with p53 overexpression (OR[95% CI]: 2.18 [0.52-9.6]) and codon 72 Arg/Arg genotype (OR [95% CI] of 0.8 [0.13-4.2], comparing genotypes of Pro/Pro and Arg/Pro with Arg/Arg). Our data provide the first observations that the presence of p53 codon 72 variants can be a significant factor influencing p53 overexpression in esophageal cancer, with overexpression also influenced by combined or prolonged environmental exposures.     

Evaluating the Association between p53 Codon 72 Arg>Pro Polymorphism and Risk of Ovary Cancer: A Meta-Analysis

Aim

Allelic polymorphism in codon 72 of the p53 tumor suppressor gene causes imbalance of p53 protein expression. Earlier studies have shown association between allelic polymorphism in codon 72 of the p53 gene with risk of ovary cancer (OC); however the results are inconclusive and conflicting. Therefore, we performed this meta-analysis to investigate the relation between p53 codon 72 Arg>Pro polymorphism and overall OC susceptibility.

Methods

We searched all eligible published studies based on the association between codon 72 of the p53 Arg>Pro polymorphism and risk of OC. Data were pooled together from individual studies and meta-analysis was performed. Pooled odds ratios (ORs) and 95% CI were calculated for allele contrast, homozygous, heterozygous, dominant and recessive genetic models.

Results

A total of twelve studies comprising of 993 OC cases and 1264 healthy controls were included in this meta-analysis. Overall, no significant association was detected for Pro allele carrier (Pro vs. Arg: p = 0.916; OR = 0.980, 95% CI = 0.677 to 1.419), homozygous (Pro/Pro vs. Arg/Arg: p = 0.419; OR = 0.731, 95% CI = 0.341 to 1.564), heterozygous (Arg/Pro vs. Arg/Arg: p = 0.248; OR = 1.237, 95% CI = 0.862 to 1.773), dominant (Pro/Pro+Arg/Pro vsArg/Arg: p = 0.699; OR = 1.089, 95% CI = 0.706 to 1.681), and recessive (Pro/Pro vs Arg/Arg+Arg/Pro: p = 0.329; OR = 0.754, 95% CI = 0.428 to 1.329) genetic models, respectively. Also, in the stratified analysis by ethnicity, no significant association of this polymorphism with risk of OC was found in the Caucasian population.

Conclusions

This meta-analysis suggested that codon 72 of the p53 Arg>Pro polymorphism may not significantly contribute in ovary cancer susceptibility. However, future large studies with gene-gene and gene-environment interactions are needed to validate these findings.     

Lack of association between p53 codon 72 polymorphism and endometrial cancer: a meta-analysis

Background: It has been suggested that the p53 tumor suppressor gene Arg72Pro polymorphism is associated with endometrial cancer. However, results have been inconsistent. We performed this meta-analysis to estimate the association between p53 Arg72Pro polymorphism and endometrial cancer. Methods: An electronic search of PubMed was conducted to select studies. Studies containing available genotype frequencies of Arg72Pro were chosen, and the association was assessed by pooled odds ratios (ORs) with 95% confidence intervals (CIs). Results: Nine published studies, including 829 endometrial cancer cases and 1387 controls, were identified. The overall results suggested that the variant genotypes were not associated with the endometrial cancer risk in all genetic models (additive model: OR 1.027, 95% CI 0.893–1.18, P = 0.71; recessive model: OR 1.099, 95% CI 0.802–1.507, P = 0.556; dominant model: OR 1.013, 95% CI 0.842–1.219 P = 0.89). Similarly, the results were negative in subgroup analyses for ethnicity (Caucasian, Asian). Conclusion: This meta-analysis suggests that p53 codon 72 polymorphism is not associated with increased risk of endometrial cancer, especially in Caucasians and Asians. To validate the association between this polymorphism and endometrial cancer, further studies with larger numbers of participants worldwide are needed.     

TP53 codon 72 polymorphism in pigmentary phenotypes

The p53 protein exerts different cellular functions, and recent findings have demonstrated its influence on the cascade of skin pigmentation during UV exposure. Among TP53 gene polymorphisms, the most studied is the G to C transversion in exon 4 at codon 72, which results in three distinct genotypes, Arg/Arg, Pro/Pro and Arg/Pro, each one encoding different p53 isoforms. Therefore, this study aimed to determine the relationship between TP53 codon 72 polymorphism and skin protection against sunburn. Genomic DNA was extracted from peripheral blood samples and genotyping was performed by PCR and confirmed by restriction enzyme digestion. The genotype frequency was 50% for Arg/Arg and 14.6% for Pro/Pro genotype. The frequency of heterozygous subjects was 35.4%. In our population, p53 genotypes were in Hardy-Weinberg (HW) equilibrium (X2 HM less than 3.84), showing a predominance of arginine allele (total Arg allele frequency of 68%). No significant association between p53 genotype and skin colour, hair or eye colour and susceptibility to sun exposure was found. However, further analysis demonstrated a significant association between the genotype Pro/Pro and blue/green eyes among participants who presented redness (P=0.016). Our findings indicate susceptibility to sun exposure when this phenotype (eye colour) occurs simultaneously with Pro/Pro genotype.     

Meta-analysis demonstrates no association between p53 codon 72 polymorphism and prostate cancer risk

We examined whether p53 codon 72 polymorphism confers prostate cancer risk by conducting a meta-analysis. Two investigators independently searched the Pubmed, Embase and CBM databases. This meta-analysis was made of seven case-control studies, that included 892 prostate cancer cases and 1020 healthy controls. Meta-analysis results based on all the studies showed no significant association between p53 codon 72 polymorphism and prostate cancer risk in the comparisons of Pro allele vs Arg allele; Pro/Pro + Pro/Arg vs Arg/Arg; Pro/Pro vs Pro/Arg + Arg/Arg; Pro/Pro vs Arg/Arg, and Pro/Arg vs Arg/Arg [odds ratio (OR) = 1.09, 95% confidence interval (CI) = 0.87-1.36, P = 0.47; OR = 1.22, 95%CI = 0.86-1.73, P = 0.27; OR = 1.03, 95%CI = 0.62-1.72, P = 0.91; OR = 1.22, 95%CI = 0.66-2.26, P = 0.52; OR = 1.25, 95%CI = 0.84-1.87, P = 0.27, respectively]. In the subgroup analysis by ethnicity, no association was found between p53 codon 72 polymorphism and prostate cancer risk both in Caucasian and Asian populations. We found no association between p53 codon 72 polymorphism and prostate cancer risk.     

p53 codon 72 polymorphism in cervical cancer patients and healthy women from Poland

A polymorphism at codon 72 of gene p53 results in the presence of either arginine or proline at this position. We investigated the distribution of p53 codon 72 polymorphism in cervical cancer patients and a control group of healthy women from Poland. Our results do not confirm the hypothesis that the p53 codon polymorphism could play a role as a factor for squamous carcinoma of the cervix.     

Tissue-specific apoptotic effects of the p53 codon 72 polymorphism in a mouse model

Currently there are several dozen human polymorphisms that have been loosely associated with cancer risk. Correlating such variants with cancer risk has been challenging, primarily due to factors such as genetic heterogeneity, contributions of diet and environmental factors, and the difficulty in obtaining large sample sizes for analysis. Such difficulties can be circumvented with the establishment of mouse models for human variants. Recently, several groups have modeled human cancer susceptibility polymorphisms in the mouse. Remarkably, in each case these mouse models have accurately reflected human phenotypes, and clarified the contribution of these variants to cancer risk. We recently reported on a mouse model for the codon 72 polymorphism in p53, and found that this polymorphism regulates the ability to cooperate with NFκB and induce apoptosis. Here-in we present evidence that this polymorphism impacts the apoptotic function of p53 in a tissue-specific manner; such tissue-specific effects of polymorphic variants represent an added challenge to human cancer risk association studies. The data presented here support the premise that modeling human polymorphisms in the mouse represents a powerful tool to assess the impact of these variants on cancer risk, progression and therapy.Key words: p53, polymorphism, apoptosis, codon 72, NFκB     

Tissue-specific apoptotic effects of the p53 codon 72 polymorphism in a mouse model

Currently there are several dozen human polymorphisms that have been loosely associated with cancer risk. Correlating such variants with cancer risk has been challenging, primarily due to factors such as genetic heterogeneity, contributions of diet and environmental factors, and the difficulty in obtaining large sample sizes for analysis. Such difficulties can be circumvented with the establishment of mouse models for human variants. Recently, several groups have modeled human cancer susceptibility polymorphisms in the mouse. Remarkably, in each case these mouse models have accurately reflected human phenotypes, and clarified the contribution of these variants to cancer risk. We recently reported on a mouse model for the codon 72 polymorphism in p53, and found that this polymorphism regulates the ability to cooperate with NF-kB and induce apoptosis. Here-in we present evidence that this polymorphism impacts the apoptotic function of p53 in a tissue-specific manner; such tissue-specific effects of polymorphic variants represent an added challenge to human cancer risk association studies. The data presented here support the premise that modeling human polymorphisms in the mouse represents a powerful tool to assess the impact of these variants on cancer risk, progression and therapy.     

Correlation between human papillomavirus-associated cervical cancer and p53 codon 72 arginine/proline polymorphism

High-risk mucosal human papillomaviruses encode an E6 oncoprotein, which binds the cellular p53 tumor suppressor protein, thereby marking it for degradation through the ubiquitin-mediated pathway. A common p53 polymorphism at codon-72 of exon 4 results in translation to either arginine or proline. Recently reported data suggested an increased susceptibility to E6/ubiquitin-mediated degradation of the Arg72-p53 isoform and an over-representation of the homozygous Arg72-p53 genotype in cervical cancer patients. We have analyzed this polymorphism in a larger series of patients with cervical cancer and in controls in the Czech Republic. We found no statistically significant differences between the codon-72 p53 genotypes of cervical cancer patients and the control women. Based on these results, it is unlikely that Arg72-p53 is associated with an increased risk for human papillomavirus-associated cervical tumor development in Czech women.     

A p53 codon 72 polymorphism associated with prostate cancer development and progression in Japanese

An association between the Pro/Pro genotype of p53 codon 72 and a lower risk of prostate cancer in Caucasians was recently reported. However, the association of this polymorphism with prostate cancer risk in a Japanese population has not been clarified. We performed a case-control study consisting of 114 prostate cancer patients and 105 noncancer controls. Sixty-nine percent (79 of 114) of the patients had a positive family history. The genotypic frequencies in the controls were 39.0% for Arg/Arg, 54.3% for Arg/Pro and 6.7% for Pro/Pro; they were in Hardy-Weinberg equilibrium. When a comparison of the distribution of the p53 codon 72 polymorphism was made between patients with a first-degree family history and all control subjects, the adjusted odds ratios (ORs) for prostate cancer associated with the Arg/Arg, Arg/Pro and Pro/Pro genotypes were 1.00, 0.99 [95% confidence interval (CI) 0.53-1.88] and 2.80 (95% CI 1.04-7.53), respectively. When stratification of cases was performed based on clinical stage (localized or metastatic cancer) and pathological grade (a Gleason score of <7 or > or =7), there tended to be a greater number of patients with localized cancers among those patients with the Arg/Pro genotype than among those with the Arg/Arg genotype (overall cases: age-adjusted OR 0.36, 95% CI 0.13-1.00, p = 0.049; positive family history cases: age-adjusted OR 0.25, 95% CI 0.075-0.84, p = 0.025). In addition, there tended to be a greater number of patients with low-grade cancers among those with the Pro/Pro genotype than among those with other genotypes (overall cases: age-adjusted OR 0.41, 95% CI 0.13-1.30, p = 0.13; positive family history cases: age-adjusted OR 0.20, 95% CI 0.004-0.89, p = 0.035). The present findings suggest that the Pro/Pro genotype of p53 codon 72 played a role in prostate cancer susceptibility in a Japanese population. However, the Pro allele did not appear to worsen such clinical parameters as clinical stage or pathological grade.     

Human papillomavirus genotypes and the p53 codon 72 polymorphism in cervical cancer of Northeastern Thailand

Human papillomavirus (HPV) infection including sub-strain identification was studied in patients with squamous cell cervical cancer (SCCA) in Northeastern Thailand. Subjects were 90 cases of SCCA and 100 healthy controls. Prevalence of high-risk group of HPV infection in the controls and the SCCA patients were 13.0% and 86.7%, respectively. The HPV infection significantly increased the risk for cervical cancer 43.5-fold (95% confidential interval: 17.5-110.6; P <0.00001). Among HPV carrier patients with SCCA (n = 78), HPV-16 was also prominent (70.5%) followed by HPV-18 (23.1%). There was no statistical difference in the subtype distribution between the SCCA and the control groups. There was no significant association between genotype distribution of the p53 codon 72 polymorphism and HPV infection. HPV infection was confirmed as a critical risk factor for cervical cancer development in Northeast Thailand. Since polymorphism of the p53 itself as well as in combination with HPV infection may not be a genetic risk for cervical cancer, much attention should be paid to other risk factors such as sexual behavior and smoking.     

MDM2 SNP309 rs2279744 Polymorphism and Gastric Cancer Risk: A Meta-Analysis

Background

MDM2 is a major negative regulator of p53, and a single nucleotide polymorphism (SNP) in the MDM2 promoter region SNP309 has been demonstrated to be associated with an increased MDM2 expression and a significantly earlier age of onset of several tumors, including gastric cancer. Several studies were published to evaluate the association between SNP309 and gastric cancer risk. However, the results remain conflicting rather than conclusive.

Objective

The aim of this study was to assess the association between the MDM2 SNP309 polymorphism and gastric risk.

Methods

We performed a meta-analysis to investigate this relationship. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to assess the strength of the association. The pooled ORs were performed for codominant model, dominant model, and recessive model, respectively.

Results

Five published case-control studies, including 1,621 gastric cancer cases and 2,639 controls were identified. We found that the MDM2 SNP309 polymorphism was associated with a significantly increased risk of gastric cancer risk when all studies were pooled into the meta-analysis (GG versus TT, OR = 1.54; 95%CI = 1.04–2.29, and GG versus GT/TT, OR = 1.49, 95%CI = 1.30–1.72). Furthermore, Egger''s test did not show any evidence of publication bias (P = 0.799 for GG versus TT).

Conclusion

Our results suggest that the MDM2 SNP309 polymorphism may be a low-penetrant risk factor for the development of gastric cancer.     

p53 codon 72 polymorphism, DNA damage and repair, and risk of non-melanoma skin cancer

A very common polymorphism of p53, that of codon 72, codes either for a proline (P72) or an arginine (R72). The two alleles differ in their biological properties: P72 is a stronger inducer of p21, while R72 induces 5-10 times more apoptosis. It is not known, however, whether this polymorphism influences genome stability. The influence of p53 codon 72 polymorphism on cancer risk has been studied for different types of cancer with mixed and inconsistent results. With respect to sporadic non-melanoma skin cancer (NMSC), there are few studies, with small sample sizes, and none in a Latinoamerican population. These studies have found no association between p53 genotype at codon 72 and NMSC. We analyzed whether p53 codon 72 genotype influences genomic stability and the sensitivity of cells to UVB. We also carried out a case-control study of NMSC in a Mexican population which included 204 BCC cases, 42 SCC cases, and 238 controls. There was no association between p53 genotype and basal levels of DNA damage, oxidative DNA damage sensitivity, or DNA repair capacity. R72 dominantly increased the in vitro sensitivity of cells to UVB-induced apoptosis. There was no significant association either between p53 genotype and basal cell carcinoma (BCC), squamous cell carcinoma (SCC) or both combined.     

DAPK1 Promoter Methylation and Cervical Cancer Risk: A Systematic Review and a Meta-Analysis

Objective

The Death-Associated Protein Kinase 1 (DAPK1) gene has been frequently investigated in cervical cancer (CC). The aim of the present study was to carry out a systematic review and a meta-analysis in order to evaluate DAPK1 promoter methylation as an epigenetic marker for CC risk.

Methods

A systematic literature search was carried out. The Cochrane software package Review Manager 5.2 was used. The fixed-effects or random-effects models, according to heterogeneity across studies, were used to calculate odds ratios (ORs) and 95% Confidence Intervals (CIs). Furthermore, subgroup analyses were conducted by histological type, assays used to evaluate DAPK1 promoter methylation, and control sample source.

Results

A total of 20 papers, published between 2001 and 2014, on 1929 samples, were included in the meta-analysis. DAPK1 promoter methylation was associated with an increased CC risk based on the random effects model (OR: 21.20; 95%CI = 11.14–40.35). Omitting the most heterogeneous study, the between study heterogeneity decreased and the association increased (OR: 24.13; 95% CI = 15.83–36.78). The association was also confirmed in all the subgroups analyses.

Conclusions

A significant strong association between DAPK1 promoter methylation and CC was shown and confirmed independently by histological tumor type, method used to evaluate methylation and source of control samples. Methylation markers may have value in early detection of CC precursor lesions, provide added reassurances of safety for women who are candidates for less frequent screens, and predict outcomes of women infected with human papilloma virus.