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.     

Assessment of TP53 Polymorphisms and MDM2 SNP309 in Premenopausal Breast Cancer Risk

Germline polymorphic variants in cancer predisposition genes such as TP53 have been shown to impact the risk of premenopausal cancer. Accordingly, the aim of this study was to assess the spectrum of polymorphisms in TP53 and its negative regulatory gene, MDM2 (SNP309:T>G) in patients with premenopausal breast cancer. Our findings in a cohort of 40 female patients demonstrate no significant correlation between the studied polymorphisms and risk of premenopausal breast cancer. Although one polymorphism is found in high frequency in this cohort (rs1800372:A>G, 9.0%), it was not associated with the risk of developing cancer before the age of 35 years in an extended cohort of 1,420 breast cancer cases. Functional studies of the rs1800372:A>G polymorphic allele reveal that it does not affect p53 transactivation function. Further study of variants or mutations in other cancer susceptibility genes is warranted to refine our understanding of the germline contribution to premenopausal breast cancer susceptibility.     

Association of MDM2 gene SNP 309 polymorphism and human non-small cell lung cancer susceptibility: A meta-analysis

This updated meta-analysis was performed to evaluate the relationship of a common polymorphism (T309 G, rs2279744 T > G) in the murine double minute 2 (MDM2) gene with susceptibility and prognosis of non-small cell lung cancer (NSCLC). The Cochrane Library, PubMed, Embase, CNKI, WanFang and CNKI databases were searched comprehensively for related study. Odds ratios (ORs) with their 95% confidence intervals (95% CI) were calculated. 11 articles with a total 6470 NSCLC patients and 8027 controls met the inclusion criteria were included. MDM2 T309 G polymorphism might be strongly correlated with an increased risk of NSCLC. The overall pooled analysis indicated that MDM2 309 T/G polymorphism was significantly associated with NSCLC susceptibility in the whole population under allelic (OR: 1.22, 95% CI: 1.08–1.38), recessive (OR: 1.37, 95% CI: 1.15–1.63), dominant (OR: 1.23, 95% CI: 1.04–1.45), and homozygous genetic models (OR: 1.49, 95% CI: 1.20–1.86). The subgroup analysis showed a significant association of MDM2 309 T/G polymorphism with NSCLC susceptibility in Asian population, but not in Caucasian population. Besides, a significant association was found again in the female population. The meta-analysis provides convincing evidence that the MDM2 T309 G polymorphism may contribute to NSCLC susceptibility, especially for Asians and women.     

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.     

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.     

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.     

Methionine diet-induced hyperhomocysteinemia accelerates cerebral aneurysm formation in rats

Background and purpose: The pathophysiology of cerebral aneurysms (CA) is linked to chronic inflammation. Endothelial damage is one of the first changes in CA walls resulted from inflammation. It has been shown that increase in plasma homocysteine (Hcy) impairs vascular endothelium and correlates with the development of atherosclerosis. However, the effect of hyperhomocysteinemia (HHcy) on the formation of cerebral aneurysm remains unknown. Methods: Male Sprague–Dawley rats examined for developing cerebral aneurysms after surgical induction in the presence and absence of hypercysteinemia induced by a high l-methionine diet (1 g/kg/d). Aneurysms developed at the anterior cerebral–olfactory artery bifurcation were classified as 4 stages from no abnormality to saccular aneurysm. Plasma homocysteine levels and expression of vascular endothelial growth factor (VEGF), endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), matrix metalloproteinase-2 (MMP-2), and MMP-9 in aneurysmal walls was examined and correlated with CA formation 3 months after surgery. Results: Methionine diet significantly increased plasma homocysteine levels, accelerates CA formation after ligation of the left common carotid artery. Expression of VEGF, iNOS, MMP-2, and MMP-9 in aneurysmal walls was also increased by methionine treatment. Conclusion: Hyperhomocysteinemia accelerates cerebral aneurysm formation, potentially through differential effects on expression of molecules critical for vascular wall modeling in a rat model.     

APC mutation and tumour budding in colorectal cancer

AIM: To determine the frequency of tumour budding and somatic APC mutation in a series of colorectal cancers stratified according to DNA microsatellite instability (MSI) status. Material/Methods: Ninety five colorectal cancers were genotyped for APC mutation in the mutation cluster region (exon 15) and scored for the presence of tumour budding at the invasive margin in haematoxylin and eosin stained sections. A subset was immunostained for beta catenin and p16. RESULTS: The frequency of both somatic APC mutation and tumour budding increased pari passu in cancers stratified as sporadic MSI high (MSI-H), hereditary non-polyposis colorectal cancer (HNPCC), MSI low (MSI-L), and microsatellite stable (MSS). Both budding and APC mutation were significantly less frequent in sporadic MSI-H cancers than in MSI-L or MSS cancers. Tumour buds were characterised by increased immunostaining for both beta catenin and p16. CONCLUSION: Tumour budding is associated with an adverse prognosis. The lack of budding in MSI-H colorectal cancer may account for the improved prognosis of this subset and may be explained by an intact WNT signalling pathway and/or inactivated p16(INK4a).     

Accumulation of MDM2 in pleomorphic xanthoastrocytomas

The molecular genetic basis and the tumorigenic mechanism of pleomorphic xanthoastrocytoma (PXA) still remain to be elucidated. The amplification of the mdm2 gene and accumulation of the MDM2 protein, which is considered to be one of the major cellular regulators of p53-mediated cell growth control, were studied in eight specimens of PXA obtained from five patients. All of the PXA samples showed at least focal immunopositivity for MDM2. However, none of the samples showed mdm2 gene amplification. These results suggest that accumulation of MDM2 without gene amplification may be one of the major molecular events occurring in the tumorigenesis of PXA.     

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.     

MDM2 expression in EBV-infected nasopharyngeal carcinoma cells

To understand whether the p53-regulated mdm2 gene expression was altered by the Epstein-Barr virus (EBV) in nasopharyngeal carcinoma (NPC), the NPC-TW01 cell line was infected by EBV through IgA receptor-mediated endocytosis. The mdm2 gene was expressed only in a small fraction of the NPC cell population and could be enhanced in the EBV-infected (EBV+) cells. In the animals bearing EBV+ and EBV- NPC xenografts, the MDM2+ cells only appeared in clusters in both EBV+ and EBV- tumors with stronger expression in EBV+ cells. Cotransfection of pmdm2-Luc plus pSV40-p53 plus pCMV-LMP1 in the NPC-TW06 line that had p53 heterozygous point mutation showed stronger mdm2 promoter activity than cells cotransfected with pmdm2-Luc plus pSV40-p53, but no mdm2 promoter activity was seen in cells cotransfected with pmdm2-Luc plus pCMV-LMP1. Only the EBV-LMP1 but not the EBV-LMP2A gene could enhance p53 to upregulated mdm2 expression. Tumor cells in NPC biopsy specimens revealed similar mdm2 expression as in the animal model. It is concluded that although EBV can indirectly enhance mdm2 gene expression in tumor cells that express this gene, it cannot turn on or directly regulate mdm2 expression in cells that do not express this gene. In other words, EBV plays a role as an enhancer in NPC tumorigenesis.     

Cyclophilin B induces chemoresistance by degrading wild‐type p53 via interaction with MDM2 in colorectal cancer

Colorectal cancer (CRC) is one of the leading causes of cancer‐related deaths worldwide. Chemoresistance is a major problem for effective therapy in CRC. Here, we investigated the mechanism by which peptidylprolyl isomerase B (PPIB; cyclophilin B, CypB) regulates chemoresistance in CRC. We found that CypB is a novel wild‐type p53 (p53WT)‐inducible gene but a negative regulator of p53WT in response to oxaliplatin treatment. Overexpression of CypB shortens the half‐life of p53WT and inhibits oxaliplatin‐induced apoptosis in CRC cells, whereas knockdown of CypB lengthens the half‐life of p53WT and stimulates p53WT‐dependent apoptosis. CypB interacts directly with MDM2, and enhances MDM2‐dependent p53WT ubiquitination and degradation. Furthermore, we firmly validated, using bioinformatics analyses, that overexpression of CypB is associated with poor prognosis in CRC progression and chemoresistance. Hence, we suggest a novel mechanism of chemoresistance caused by overexpressed CypB, which may help to develop new anti‐cancer drugs. We also propose that CypB may be utilized as a predictive biomarker in CRC patients. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

VARS2基因单核苷酸多态性和广东汉族女性散发性乳腺癌相关性研究

目的探讨VARS2(valyl-tRNA synthetase 2)基因中单核苷酸多态性位点(single nucleotide polymorphisms,SNP)rs2249464与广东省汉族女性散发性乳腺癌的相关性。方法采用MassARRAY-IPLEX SNP分型技术,以南方医科大学南方医院的216例广东汉族乳腺癌患者及216例同期健康体检者为研究对象,对rs2249464多态性位点进行基因分型,利用χ2检验统计分析病例组和对照组的基因型频率有无差异,利用非条件Logistic回归计算比数比(odds ratio,OR)和95%可信区间(confidence interval,CI)来评价此位点多态性与乳腺癌的相关性。然后进一步将病例组按雌激素受体(estrogen receptor,ER)和孕激素受体(progesterone receptor,PR)免疫组化结果行分层分析。结果 rs2249464位点C/C,C/T,T/T 3种基因型分布在对照组和病例组之间有统计学差异。根据免疫组化情况进一步分层分析结果表明rs2249464的基因型分布在ER阳性/阴性组之间的差异无统计学意义(P>0.05);但在PR阳性/阴性组之间的差异有统计学意义(P<0.05)。结论 VARS2基因rs2249464位点单核苷酸多态性与广东汉族散发性乳腺癌的易感性具有相关性,且携带T/T基因型的患者更容易罹患PR阴性乳腺癌。