p53 Arg72Pro and MDM2 309 SNPs in hereditary retinoblastoma

The tumor suppressor p53 and its negative regulator MDM2 have crucial roles in a variety of cellular functions such as the control of the cell cycle, senescence, genome stability and apoptosis, and are frequently deregulated in carcinogenesis. Previous studies have highlighted the contribution of the common functional polymorphisms p53 p.Arg72Pro and MDM2 309SNP to the risk of both common cancers and Li-Fraumeni syndrome. Their possible role in retinoblastoma has recently been addressed by Castéra et al, who however only studied the MDM2 309SNP. Here, for the first time, we analyzed both single nucleotide polymorphisms (SNPs) in a case-control study of 111 Italian hereditary retinoblastoma patients. We found a significant association of the p53 Pro/Pro genotype with the disease (odds ratio=3.58, P=0.002). The MDM2 309SNP showed a weak negative association of allele G that deserves further investigation. These findings further support the hypothesis that genetic variability of the p53 pathway contributes to the individual susceptibility to retinoblastoma, as shown for Li-Fraumeni syndrome and a variety of non-hereditary cancers.     

Common polymorphisms in the MDM2 and TP53 genes and the relationship between TP53 mutations and patient outcomes in glioblastomas

MDM2 SNP309 is associated with younger age of tumor onset in patients with Li-Fraumeni syndrome, and TP53 codon 72 polymorphism decreases its apoptotic potential. Glioblastomas frequently show genetic alterations in the TP53 pathway. In the present study, we assessed MDM2 SNP309 in 360 glioblastomas, and correlated these with patient age and survival, as well as other alterations in the TP53 pathway. Frequencies of the MDM2 SNP309 T/T, T/G and G/G genotypes in glioblastomas were 40%, 46% and 14%, respectively. Multivariate analysis showed that MDM2 SNP309 G/G allele was significantly associated with favorable outcome in female glioblastoma patients (hazard ratio 0.54; 95% CI = 0.32–0.92). There was a significant association between MDM2 SNP309 G alleles and TP53 codon 72 Pro/Pro in glioblastomas. Glioblastoma patients with TP53 codon 72 Pro/Pro genotype were significantly younger than Arg/Arg carriers (mean 50.2 vs. 56.1 years; P  = 0.018). Multivariate analysis showed that those with TP53 codon 72 Arg/Pro allele had significantly shorter survival than those with Arg/Arg allele (hazard ratio 1.35; 95% CI = 1.07–1.71). Detailed analyses revealed that TP53 codon 72 Pro allele was significantly associated with shorter survival among patients with glioblastomas carrying a TP53 mutation, and among those treated with surgery plus radiotherapy.     

The single-nucleotide polymorphism 309 in the MDM2 gene contributes to the Li-Fraumeni syndrome and related phenotypes

Li-Fraumeni syndrome (LFS) is an autosomal-dominant cancer predisposition syndrome of which the majority is caused by TP53 germline mutations and is characterised by different tumour types occurring at relatively young age. Recently, it was shown that a single-nucleotide polymorphism (SNP) in the MDM2 gene, SNP309 (T>G variation), was associated with accelerated tumour formation in LFS patients who carry a TP53 germline mutation. To confirm this finding in different populations, we screened 25 Dutch and 11 Finnish TP53 mutation carriers for the presence of the SNP309 G allele in the MDM2 gene. Additionally, we investigated whether the SNP309 G allele plays a role in 72 Dutch TP53-negative LFS and LFS-related patients. In the TP53 germline mutation carriers, a significant difference was seen in the mean age of tumour onset for the SNP309 G allele group, that is, 29.7 years as compared to the SNP309 homozygous T group 45.5 years (P=0.005). In patients of LFS and LFS-related TP53-negative families, no difference was seen in the mean age of tumour onset. However, this TP53-negative group did show a significantly higher percentage of SNP309 homozygotes (G/G) compared to the general population (P=0.02). In conclusion, TP53 germline mutation carriers who have an SNP309 G allele have an earlier onset of tumour formation. The higher prevalence of MDM2 SNP309 homozygous G/G carriers in the TP53-negative group suggests that this allele contributes to cancer susceptibility in LFS and LFS-related families.     

Natural selection and functional genetic variation in the p53 pathway

The allele frequencies of two functional single-nucleotide polymorphisms (SNPs) in the p53 pathway, the MDM2 SNP309 and TP53 Arg72Pro, vary dramatically among populations. That the frequencies of the TP53 SNP follow a clinal distribution may suggest that selective pressure from environmental variables correlated with latitude contributed to these observed population differences. Recently, winter temperature and UV radiation were found to be significantly correlated with the TP53 and the MDM2 SNPs, respectively, in East Asians; whether these correlations are more extreme than expected based upon nonselective factors such as patterns of human migration remains unclear. Here, we genotyped these two SNPs in 971 unrelated individuals from 52 unique populations worldwide and tested for correlations with both latitude and a number of climate-related environmental variables on a global scale, controlling for these neutral processes. The TP53 SNP was associated with a significant selection signal for a few climate variables, such as short-wave radiation flux in the winter, but these signals were no longer significant after correction for multiple tests. The MDM2 SNP did not exhibit a significant signal with any climate variable. Therefore, these SNPs are unlikely to be under selective pressure driven by these variables. Thus, these data underscore the need to incorporate population history when assessing signatures of selection.     

Impact of the MDM2 SNP309 and p53 Arg72Pro polymorphism on age of tumour onset in Li-Fraumeni syndrome

Li-Fraumeni syndrome, resulting from p53 (TP53) germline mutations, represents one of the most devastating genetic predispositions to cancer. Recently, the MDM2 SNP309 (T-->G variation) was shown to be associated with accelerated tumour formation in p53 mutation carriers. The impact of the common p53 codon 72 polymorphism on cancer risk remains controversial. We therefore investigated the effect of these two polymorphisms in 61 French carriers of the p53 germline mutation. The mean age of tumour onset in MDMD2 SNP309 G allele carriers (19.6 years) was significantly different from that observed in patients homozygous for the T allele (29.9 years, p<0.05). For the p53 codon 72 polymorphism, the mean age of tumour onset in Arg allele carriers (21.8 years) was also different from that of Pro/Pro patients (34.4 years, p<0.05). We observed a cumulative effect of both polymorphisms because the mean ages of tumour onset in carriers of the MDM2G and p53Arg alleles (16.9 years) and those with the MDM2T/T and p53Pro/Pro genotypes (43 years) were clearly different (p<0.02). Therefore, our results confirm the impact of the MDM2 SNP309 G allele on the age of tumour onset in germline p53 mutation carriers, and suggest that this effect may be amplified by the p53 72Arg allele. Polymorphisms affecting p53 degradation therefore represent one of the rare examples of modifier genetic factors identified to date in mendelian predispositions to cancer.     

The MDM2 promoter polymorphism SNP309T-->G and the risk of uterine leiomyosarcoma, colorectal cancer, and squamous cell carcinoma of the head and neck

Background: MDM2 acts as a principal regulator of the tumour suppressor p53 by targeting its destruction through the ubiquitin pathway. A polymorphism in the MDM2 promoter (SNP309) was recently identified. SNP309 was shown to result, via Sp1, in higher levels of MDM2 RNA and protein, and subsequent attenuation of the p53 pathway. Furthermore, SNP309 was proposed to be associated with accelerated soft tissue sarcoma formation in both hereditary (Li-Fraumeni) and sporadic cases in humans. Methods: We evaluated the possible contribution of SNP309 to three tumour types known to be linked with the MDM2/p53 pathway, using genomic sequencing or restriction fragment length polymorphism as screening methods. Three separate Finnish tumour materials (population based sets of 68 patients with early onset uterine leiomyosarcomas and 1042 patients with colorectal cancer, and a series of 162 patients with squamous cell carcinoma of the head and neck) and a set of 185 healthy Finnish controls were analysed for SNP309. Results: Frequencies of SNP309 were similar in all four cohorts. In the colorectal cancer series, SNP309 was somewhat more frequent in women and in patients with microsatellite stable tumours. Female SNP309 carriers were diagnosed with colorectal cancer approximately 2.7 years earlier than those carrying the wild type gene. However, no statistically significant association of SNP309 with patients'' age at disease onset or to any other clinicopathological parameter was found in these three tumour materials. Conclusion: SNP309 had no significant contribution to tumour formation in our materials. Possible associations of SNP309 with microsatellite stable colorectal cancer and with earlier disease onset in female carriers need to be examined in subsequent studies.     

TP53 R72P and MDM2 SNP309 polymorphisms in modification of childhood acute lymphoblastic leukemia susceptibility

Genomic and immunologic surveillance mechanisms are crucial in protection from cancer. The tumor suppressor protein p53, encoded by TP53, is a major regulator of genome surveillance. Among the natural sequence variants of TP53, rs1042522 (R72P) modifies the risk for solid tumors. To investigate its relevance in childhood acute lymphoblastic leukemia (ALL) susceptibility, we genotyped 114 cases and 414 newborn controls from Wales (UK) for polymorphisms in TP53 (R72P), its negative regulator MDM2 (single-nucleotide polymorphism SNP309, rs2279744), and selected HLA complex genes whose products interact with TP53. TP53 R72P showed a risk association with gene dosage effect (P=0.002) resulting in a strong association of homozygous genotype (OR=2.9, 95% CI=1.5–5.6) and no sex effect. SNP309 did not show any association with primary susceptibility to childhood ALL, even after stratification by sex. However, females with SNP309 minor allele had earlier onset of childhood ALL (median age at diagnosis was 36 months in females, but 60 months in males; P=0.002). The HLA complex genes did not show any statistically significant interaction with R72P. We have therefore identified TP53 R72P as a possible risk modifier for childhood ALL and the association of MDM2 with age at onset with sex effect suggests prenatal hormonal programming of childhood ALL susceptibility.     

Association between polymorphisms of TP53 and MDM2 and prostate cancer risk in southern Chinese

Alterations in the TP53 and MDM2 genes appear to be important in the development of many human tumors, but evidence is conflicting on associations between polymorphisms in these genes and risk of prostate cancer (PCa). The influence of TP53 codon 72, MDM2 SNP309, and MDM2 C1797G polymorphisms in southern Chinese PCa patients was investigated. In the comparison of genotype distributions of TP53 codon 72 between cases and controls, the adjusted odds ratios for PCa associated with the Pro/Pro, Arg/Pro, and Arg/Arg genotypes were 1.00, 1.89 (95% CI = 1.20-2.97), and 2.01 (95% CI = 1.11-3.64), respectively; however, MDM2 SNP309 and C1797G did not show any significant difference between cases and controls. When TP53 and MDM2 polymorphisms were combined based on the numbers of variant risk alleles (i.e., G-allele of TP53 codon 72, G-allele of MDM2 SNP309, and G-allele of MDM2 C1797G), individuals with 3-5 variants had a 1.56-fold greater risk of PCa than those with 0-2 variants (95% CI = 1.07-2.26). Moreover, subjects with 0-2 variants had 33.3% positive p53 expression, whereas subjects with 3-5 variants had 23.3% p53 expression (P = 0.39). These findings suggest that TP53 and MDM2 polymorphisms play a role in PCa susceptibility in southern Chinese Han population.     

Common polymorphisms in TP53 and MDM2 and the relationship to TP53 mutations and clinical outcomes in women with ovarian and peritoneal carcinomas

The importance of somatic TP53 mutations and germline TP53 codon 72 genotype in the survival of women with epithelial ovarian cancer is controversial. Recent data suggest that a promoter polymorphism in the MDM2 gene may influence age of cancer onset in a gender-specific fashion. We sought to determine the relationship between somatic TP53 mutations, germline genotypes at TP53 codon 72 and MDM2 SNP309, and overall survival and response to chemotherapy in a large series of patients with ovarian and peritoneal carcinomas. Of the 188 cancers, 103 (54.8%) had a TP53 mutation, of which 71% were missense mutations and 29% were null mutations. TP53 mutation status and mutation type (null vs. missense) did not influence response to therapy or overall survival. Women with the codon 72 Pro/Pro had a decreased overall survival (median, 29 months) compared with women with one or two arginine alleles (median, 49 months; P=0.04). Somatic mutation or deletion was equally common for either codon 72 allele. Age of diagnosis was not influenced by codon 72 but showed a trend for younger age in women with somatic TP53 mutations and the MDM2 G/G genotype.     

Association of genetic polymorphisms in MDM2, PTEN and P53 with risk of esophageal squamous cell carcinoma

Genetic variations in MDM2, PTEN and P53 might be involved in cancer susceptibility. To assess the contribution of polymorphisms in these three genes to the risk of esophageal squamous cell carcinoma (ESCC) in a Chinese population, we genotyped MDM2 T309G, Del1518, PTEN rs701848, rs2735343 and P53 Arg72Pro polymorphisms using PCR-restriction fragment length polymorphism analysis in 226 ESCC cases and 226 cancer-free controls. Here we showed that the risk of ESCC was elevated in subjects with any of the variant genotypes of PTEN rs2735343 and P53 Arg72Pro polymorphisms, but not any genotype of MDM2 or PTEN rs701848. Moreover, multiplicative interactions were observed between PTEN rs2735343 and P53 Arg72Pro or smoking status on risk of ESCC. Our study firstly indicated that PTEN rs2735343 might be a susceptibility factor for ESCC and reaffirmed the role of P53 Arg72Pro in ESCC in this Chinese population, but did not replicate the positive association between MDM2 T309G and ESCC found previously.     

MDM2 SNP309 accelerates colorectal tumour formation in women

Recent studies have shown that the G-allele of MDM2 SNP309 (T/G) in the p53 tumour suppressor pathway can accelerate tumorigenesis and alter the risk of various cancers in women and not in men. In this report, data are presented from two independent groups of patients that suggest that the G-allele of SNP309 accelerates colorectal tumour formation only in women, and that lend further support to the model that primarily female-specific hormones, such as oestrogen, could either directly or indirectly allow for the G-allele of SNP309 to accelerate tumour formation in women.     

Molecular detection of the G(-248)A BAX promoter nucleotide change in B cell chronic lymphocytic leukaemia.

BACKGROUND: A novel single nucleotide polymorphism (SNP), G(-248)A, in the 5' untranslated region of the BAX promoter and its association with reduced protein expression, progression beyond Rai stage 0, and treatment resistance in chronic lymphocytic leukaemia (CLL) has been reported previously. AIM: To develop a restriction enzyme analysis (REA) based method for routine detection of BAX promoter SNP in a clinical laboratory. METHODS: The BAX promoter was analysed in duplicate by REA and sequencing in 90 samples (from 45 patients with CLL, 43 controls, and two cell lines). The promoter region was amplified, digested with restriction endonucleases (Aci I and Tau I), and separated by gel electrophoresis. RESULTS: After digestion, the normal GG genotype samples produced three distinct bands. The homozygous AA replacement abolished the cleavage site, resulting in a single band. Although the heterozygous samples produced three bands, the two smaller visible bands were reduced in intensity (> 50%). The test characteristics of Aci I REA were better than those of Tau I REA, in terms of sensitivity (100% v 77.8%), specificity (98.6% v 92.3%), positive predictive value (95.03% v 87.4%), and negative predictive value (100% v 85.83%). CONCLUSIONS: REA using Aci I is a highly sensitive and specific method for detecting the BAX G(-248)A SNP in CLL.     

P53、P21WAFI、MDM2及BAX在食管鳞癌中的表达和相关性分析

目的：检测P53、MDM2、P21^WAFI、BAX在食管鳞癌中的表达,探讨它们与食管鳞癌临床病理特征之间的关系。方法：采用免疫组化检测食管鳞癌、正常食管粘膜和不典型增生组织中上述基因蛋白的表达。结果：各指标在上述组织中的表达有显著性差异。MDM2在淋巴结转移组中的阳性表达率为80％,未转移组中为35．7％,两者之间有显著性差异。随着食管鳞癌组织学分级的增高,P53、MDM2的表达逐渐增高,P21^WAFI、BAX的表达逐渐降低。结论：P53、P21、MDM2、BAX多个基因的异常在食管癌的发生、发展过程中共同发挥作用;MDM2过表达与肿瘤的侵袭性和转移有关。P53、P21^WAFI、MDM2在食管鳞癌中的表达无相关性,P53与BAX的表达呈负相关。     

Genetic polymorphisms in cell cycle regulatory genes MDM2 and TP53 are associated with susceptibility to lung cancer

The tumor suppressor TP53 pathway plays a crucial role in preventing carcinogenesis through its ability to impose cell cycle arrest and apoptosis following DNA damage and oncogene activation. MDM2 is a key negative regulator of the TP53 pathway and is overexpressed in many cancers as oncoprotein. We investigated the association between genetic variation in the promoter region of MDM2 (c.-5+309G>T, rs2279744:g.G>T) and the coding region of TP53 (c.215G>C, rs1042522:g.G>C, designated Arg72Pro) and the risk of developing lung cancer. The genotypes of 1,106 patients and 1,420 controls were determined by tetra-primer amplification refractory mutation system (ARMS)-PCR or PCR-based restriction fragment length polymorphism (RFLP). Associations with risk of lung cancer were estimated by logistic regression. We observed an increased lung cancer risk associated with the MDM2 GG (odds ratio [OR] = 1.83, 95% confidence interval [CI] = 1.45-2.32) and TG (OR = 1.33, 95% CI = 1.09-1.63) genotypes. An increased risk was also associated with the TP53 Pro/Pro genotype (OR = 1.47, 95% CI = 1.17-1.85, P = 0.003) compared to the Arg/Arg genotype. The gene-gene interaction of MDM2 and TP53 polymorphisms increased lung cancer risk in a supermultiplicative manner (OR for the presence of both MDM2 GG and TP53 Pro/Pro genotypes = 4.56, 95% CI = 2.76-7.54). Significant interactions were observed between these polymorphisms (respectively and jointly) and smoking (OR = 10.41, 95% CI = 5.26-20.58) for smokers with both the MDM2 GG and TP53 Pro/Pro genotypes. In conclusion, genetic polymorphisms in cell cycle regulatory genes MDM2 and TP53 contribute to the risk of developing lung cancer.     

High twinning rate in Candido Godoi: a new role for p53 in human fertility

BACKGROUND Candido Godói (CG) is a small town in South Brazil, which has the highest prevalence of twin births in Brazil. Recently, a number of studies have shown that p53 plays an important role in reproduction through blastocyst implantation and intra utero embryo survival. Thus, gene polymorphisms in the p53 pathway were investigated in this population. METHODS Single nucleotide polymorphisms from five genes in the p53 pathway were investigated, as well as background characteristics of 42 mothers of twins (cases) and 101 mothers of singletons (controls), all residents from CG. RESULTS Mothers of twins have higher number of pregnancies and higher frequencies of P72 allele at TP53 and T allele at MDM4 genes compared with controls. Logistic regression shows that both TP53 and number of pregnancies maintained their association with twinning (P =0.004 and P =0.002, respectively), with TP53 having a higher odds ratio than number of pregnancies (2.73 versus 1.70, respectively). No interactive effect between TP53 and MDM4 (P =0.966) is observed. As expected, mothers of twins have three times more cases of cancer in their first-degree relatives than control mothers (P =0.011). CONCLUSIONS Our results suggest that the P72 allele of TP53 is a strong risk factor for twinning in CG, while the number of pregnancies and the T allele at MDM4 may represent weaker risk factors. These two alleles are associated with infertility, but the anti-apoptotic effect of low levels of p53 in general, and of the P72 allele in particular, may play a role after implantation, enhancing the chance for a double pregnancy to succeed to term.     

p53基因第72密码子多态性与中国人肝细胞癌遗传易感性的相关性

目的探讨在有无慢性乙型肝炎的不同背景下郦基因第72密码子多态性（R72P）与中国人肝细胞癌（hepatocellular carcinoma，HCC）遗传易感性的关系。方法采用聚合酶链反应-限制性片段长度多态方法，检测469例HCC（HBsAg阴性110例、HBsAg阳性359例）与567名对照（HBsAg阴性430例、HBsAg阳性137例）的郦R72P基因型分布及差异。结果全样本以及HBsAg阳性样本的HCC与对照问的基因型分布差异均无统计学意义。但在HBsAg阴性人群中，72P是HCC发生的危险因素（OR=1，69，95％CI=1，25～2．27）。与R／R基因型相比，R／P的HCC风险增加至1．73倍（95％CI=0．96～3．11），P／P的HCC风险显著增加至3．29倍（95％CI=1．58～6．86）。携带72P的男性个体、HCC家族史阳性个体的HCC风险分别进一步增加至9．39倍（95％CI=3，08～28．62）和11，14倍（95％CI=1，62～76．67）。结论皿形72P增加HBsAg阴性中国人的HCC风险，并与男性、HCC家族史在增加HCC风险中有协同作用。