Altered tumor formation and evolutionary selection of genetic variants in the human MDM4 oncogene

Development and Nanoparticle-Mediated Delivery of Novel MDM2/MDM4 Heterodimer Peptide Inhibitors to Enhance 5-Fluorouracil Nucleolar Stress in Colorectal Cancer Cells

Colorectal cancer (CRC) often involves wild-type p53 inactivation by MDM2 and MDM4 overexpression, promoting tumor progression and resistance to 5-fluoruracil (5-FU). Disrupting the MDM2/4 heterodimer can proficiently reactivate p53, sensitizing cancer cells to 5-FU. Herein, we developed 16 peptides based on Pep3 (1), the only known peptide acting through this mechanism. The new peptides, notably 3 and 9, showed lower IC50 values than 1. When incorporated into tumor-targeted biodegradable nanoparticles, these exhibited cytotoxicity against three different CRC cell lines. Notably, NPs/9 caused a significant increase in p53 levels associated with a strong increment of its main downstream target p21 inducing apoptosis. Also, the combined treatment of 9 with 5-FU caused the activation of nucleolar stress and a synergic apoptotic effect. Hence, the co-delivery of MDM2/4 heterodimer disruptors with 5-FU through nanoparticles might be a promising strategy to overcome drug resistance in CRC.

MDM4: What do we know about the association between its polymorphisms and cancer?

MDM4 is an important p53-negative regulator, consequently, it is involved in cell proliferation, DNA repair, and apoptosis regulation. MDM4 overexpression and amplification are described to lead to cancer formation, metastasis, and poor disease prognosis. Several MDM4 SNPs are in non-coding regions, and some affect the MDM4 regulation by disrupting the micro RNA binding site in 3'UTR (untranslated region). Here, we gathered several association studies with different MDM4 SNPs and populations to understand the relationship between its SNPs and solid tumor risk. Many studies failed to replicate their results regarding different populations, cancer types, and risk genotypes, leading to conflicting conclusions. We suggested that distinct haplotype patterns in different populations might affect the association between MDM4 SNPs and cancer risk. Thus, we propose to investigate some linkage SNPs in specific haplotypes to provide informative MDM4 markers for association studies with cancer.

Role of Sex in the Therapeutic Targeting of p53 Circuitry

Sex profoundly affects cancer incidence and susceptibility to therapy, with sex hormones highly contributing to this disparity. Various studies and omics data suggest a relationship between sex and the oncosuppressor p53 circuitry, including its regulators MDM2 and MDM4. Association of this network with genetic variation underlies sex-related altered cancer risk, age of onset, and cancer sensitivity to therapy. Moreover, sex-related factors, mainly estrogenic hormones, can affect the levels and/or function of the p53 network both in hormone-dependent and independent cancer. Despite this evidence, preclinical and clinical studies aimed to evaluate p53 targeted therapy rarely consider sex and related factors. This review summarizes the studies reporting the relationship between sex and the p53 circuitry, including its associated regulators, MDM2 and MDM4, with particular emphasis on estrogenic hormones. Moreover, we reviewed the evaluation of sex/hormone in preclinical studies and clinical trials employing p53-target therapies, and discuss how patients’ sex and hormonal status could impact these therapeutic approaches.

TP53/miR-129/MDM2/4/TP53 feedback loop modulates cell proliferation and apoptosis in retinoblastoma

Retinoblastoma (RB) is commonly-seen cancer in children. The p53 pathway dysfunction, which can lead to elevated MDM2 or MDM4 (p53 antagonists) protein expression, is frequently observed in almost all human cancers, including RB. The present study attempted to investigate the underlying mechanism from the perspective of non-coding RNA regulation. Here, we demonstrated that p53 and miR-129 were positively correlated with each other in RB. miR-129 directly targeted MDM2/4 to inhibit expression, therefore counteracting MDM2/4-mediated p53 signaling suppression and modulating RB cell proliferation and apoptosis. Moreover, p53 could activate the transcription of miR-129 via binding to the miR-129 promoter region, therefore forming a regulatory loop with MDM2/4 to affect RB progression. Altogether, the p53/miR-129/MDM2/4/p53 regulatory loop can modulate RB cell growth. We provide a solid experimental basis for developing novel therapies for RB.

The p53 Pathway and Metabolism: The Tree That Hides the Forest

Simple Summary

The p53 pathway is a major tumor suppressor pathway that prevents the propagation of abnormal cells by regulating DNA repair, cell cycle progression, cell death, or senescence. The multiple cellular processes regulated by p53 were more recently extended to the control of metabolism, and many studies support the notion that perturbations of p53-associated metabolic activities are linked to cancer development. Converging lines of evidence support the notion that, in addition to p53, other key components of this molecular cascade are also important regulators of metabolism. Here, we illustrate the underestimated complexity of the metabolic network controlled by the p53 pathway and show how its perturbation contributes to human diseases including cancer, aging, and metabolic diseases.

Abstract

The p53 pathway is functionally inactivated in most, if not all, human cancers. The p53 protein is a central effector of numerous stress-related molecular cascades. p53 controls a safeguard mechanism that prevents accumulation of abnormal cells and their transformation by regulating DNA repair, cell cycle progression, cell death, or senescence. The multiple cellular processes regulated by p53 were more recently extended to the control of metabolism and many studies support the notion that perturbations of p53-associated metabolic activities are linked to cancer development, as well as to other pathophysiological conditions including aging, type II diabetes, and liver disease. Although much less documented than p53 metabolic activities, converging lines of evidence indicate that other key components of this tumor suppressor pathway are also involved in cellular metabolism through p53-dependent as well as p53-independent mechanisms. Thus, at least from a metabolic standpoint, the p53 pathway must be considered as a non-linear pathway, but the complex metabolic network controlled by these p53 regulators and the mechanisms by which their activities are coordinated with p53 metabolic functions remain poorly understood. In this review, we highlight some of the metabolic pathways controlled by several central components of the p53 pathway and their role in tissue homeostasis, metabolic diseases, and cancer.

The long and the short of it: the MDM4 tail so far

The mouse double minute 4 (MDM4) is emerging from the shadow of its more famous relative MDM2 and is starting to steal the limelight, largely due to its therapeutic possibilities. MDM4 is a vital regulator of the tumor suppressor p53. It restricts p53 transcriptional activity and also, at least in development, facilitates MDM2's E3 ligase activity toward p53. These functions of MDM4 are critical for normal cell function and a proper response to stress. Their importance for proper cell maintenance and proliferation identifies them as a risk for deregulation associated with the uncontrolled growth of cancer. MDM4 tails are vital for its function, where its N-terminus transactivation domain engages p53 and its C-terminus RING domain binds to MDM2. In this review, we highlight recently identified cellular functions of MDM4 and survey emerging therapies directed to correcting its dysregulation in disease.

The differential diagnoses of uterine leiomyomas and leiomyosarcomas using DNA and RNA sequencing

BACKGROUND

Although uterine leiomyomas and leiomyosarcomas are considered biologically unrelated tumors, they share morphologic and histologic characteristics that complicate their differential diagnosis. The long-term therapeutic option for leiomyoma is laparoscopic myomectomy with morcellation, particularly for patients who wish to preserve their fertility. However, because of the potential dissemination of undiagnosed or hidden leiomyosarcoma from morcellation, there is a need to develop a preoperative assessment of malignancy risk.

OBJECTIVE

Through an integrated comparative genomic and transcriptomic analysis, we aim to identify differential genetic targets in leiomyomas vs leiomyosarcomas using next-generation sequencing as the first step toward preoperative differential diagnosis.

STUDY DESIGN

Targeted sequencing of DNA and RNA coding regions for solid tumor-associated genes was performed on formalin-fixed paraffin-embedded samples from 13 leiomyomas and 13 leiomyosarcoma cases. DNA sequencing was used to identify copy number variations, single-nucleotide variants, and small insertions/deletions. RNA sequencing was used to identify gene fusions, splice variants, and/or differential gene expression profiles.

RESULTS

In leiomyosarcomas, tumor mutation burden was higher in terms of copy number variations, single nucleotide variants, small insertions/deletions, and gene fusions compared with leiomyomas. For copy number variations, 20 genes were affected by deletions in leiomyosarcomas, compared with 6 observed losses in leiomyomas. Gains (duplications) were identified in 19 genes in leiomyosarcomas, but only 3 genes in leiomyomas. The most common mutations (single-nucleotide variants and insertions/deletions) for leiomyosarcomas were identified in 105 genes of all analyzed leiomyosarcomas; 82 genes were affected in leiomyomas. Of note, 1 tumor previously diagnosed as leiomyosarcoma was established as inflammatory myofibroblastic tumor along this study with a novel ALK-TNS1 fusion. Finally, a differential transcriptomic profile was observed for 11 of 55 genes analyzed in leiomyosarcomas; 8.5% of initially diagnosed leiomyosarcomas showed high-confidence, novel gene fusions that were associated with these tumors.

CONCLUSION

Through integrated comparative genomic and transcriptomic analyses, we identified novel differential genetic targets that potentially differentiate leiomyosarcomas and leiomyomas. This provides a new insight into the differential diagnosis of these myometrial tumors.

Specific allelic variants of SNPs in the MDM2 and MDMX genes are associated with earlier tumor onset and progression in Caucasian breast cancer patients

Background

Genetic factors play a substantial role in breast cancer etiology. Genes encoding proteins that have key functions in the DNA damage response, such as p53 and its inhibitors MDM2 and MDMX, are most likely candidates to harbor allelic variants that influence breast cancer susceptibility. The aim of our study was to comprehensively analyze the impact of SNPs in the TP53, MDM2, and MDMX genes in conjunction with TP53 mutational status regarding the onset and progression of breast cancer.

Methods

In specimen from 815 breast cancer patients, five SNPs within the selected genes were analyzed: TP53 – Arg72Pro (rs1042522), MDM2 – SNP285 (rs2279744), SNP309 (rs117039649); MDMX – SNP31826 (rs1563828), and SNP34091 (rs4245739). Classification of the tumors was evaluated by histomorphology. Subtyping according hormone receptor status, HER2-status and proliferation rate enabled provision of the clinico-pathological surrogate of intrinsic subtypes.

Results

The homozygous C-allele of MDM2 SNP285 was significantly associated with a younger age-at-diagnosis of 44.2 years, in contrast to G/G- and G/C-patients (62.4, 62.7 yrs., respectively; p = 0.0007; log-Rank-test). In contrast, there was no difference regarding the age-at-diagnosis for patients with the respective genotypes of MDM2 SNP309 (p = 0.799; log-Rank-test). In patients with estrogen receptor (ER)-positive and TP53-mutated tumors, however, the T/T-genotype of the MDM2 SNP309 was significantly associated with an earlier average age-at-diagnosis compared with T/G+G/G-patients (53.5 vs. 68.2 yrs; p = 0.002; log-Rank-test). In the triple-negative subgroup, the G/G-patients had an average age-at-diagnosis of 51 years compared with 63 years for SNP309T carriers (p = 0.004; log-Rank-test) indicating a susceptibility of the G/G genotype for the development of triple negative breast cancer. Patients with the A/A-genotype of MDMX SNP31826 with ER-negative tumors were diagnosed 11 years earlier compared with patients and ER-positive tumors (53.2 vs. 64.4 yrs; p = 0.025, log-Rank-test). Furthermore, in luminal B-like patients (HER2-independent) the C/C-genotype of MDMX SNP34091 was significantly correlated with a decreased event-free survival compared with the A/A-genotype (p < 0.001; log-Rank-test).

Conclusions

We showed that SNPs in the MDM2 and MDMX genes affect at least in part the onset and progression of breast cancer dependent on the ER-status. Our findings provide further evidence for the distinct etiological pathways in ER-negative and ER-positive breast cancers.

Bridging the gap by discerning SNPs in linkage disequilibrium and their role in breast cancer

Breast Cancer is the most common cancer among women with several genes involved in disease susceptibility. As majority of genome-wide significant variants fall outside the coding region, it is likely that some of them alter specific gene functions. GWAS database was used to interpret the regulatory functions of these genetic variants. A total of 320 SNPs for breast cancer were selected via GWAS, which were entered into the SNAP web portal tool, to determine the one's found to be in Linkage Disequilibrium (r² < 0.80). The resulting 2024 proxy SNP's were processed in RegulomeDB to predict their regulatory role. Of these, 1440 produced a score ranging from 1-6, whereas the remaining produced no data. Only the variants under score 4 (cut-off value) in RegulomeDB has been studied further. From these variants, 221 had scores of less than 4, indicating a high degree of potential regulatory role associated with them. Further study revealed that 61 of the 221 SNPs were reported to be genome-wide significant for breast cancer, 52 to be associated with other diseases, 99 as unconfirmed for association with breast cancer, leaving only 9 to be novel proxy SNPs linked to breast cancer. Therefore, the study further confirmed postulation of non-coding variants being linked to disease risk thereby, requiring additional validation through genome-wide association studies to substantiate their underlying mechanism.

MDM4 contributes to the increased risk of glioma susceptibility in Han Chinese population

Recently, MDM4 gene has been reported to be a susceptibility gene for glioma in Europeans, but the molecular mechanism of glioma pathogenesis remains unknown. The aim of this study was to investigate whether common variants of MDM4 contribute to the risk of glioma in Han Chinese individuals. A total of 24 single-nucleotide polymorphisms (SNPs) of the MDM4 gene were assessed in a dataset of 562 glioma patients (non-glioblastoma) and 1,192 cancer-free controls. The SNP rs4252707 was found to be strongly associated with the risk of non-GBM (P = 0.000101, adjusted odds ratio (OR) = 1.34, 95% confidence interval (CI) = 1.16–1.55). Further analyses indicated that there was a significant association between A allele of rs4252707 associated with the increased non-GBM risk. Haplotype analysis also confirmed a result similar to that of the single-SNP analysis. Using stratification analyses, we found the association of rs4252707 with an increased non-GBM risk in adults (≥18 years, P = 0.0016) and individuals without IR exposure history (P = 0.0013). Our results provide strong evidence that the MDM4 gene is tightly linked to genetic susceptibility for non-GBM risk in Han Chinese population, indicating a important role for MDM4 gene in the etiology of glioma.

A polymorphism in the tumor suppressor p53 affects aging and longevity in mouse models

Tumor suppressor p53 prevents early death due to cancer development. However, the role of p53 in aging process and longevity has not been well-established. In humans, single nucleotide polymorphism (SNP) with either arginine (R72) or proline (P72) at codon 72 influences p53 activity; the P72 allele has a weaker p53 activity and function in tumor suppression. Here, employing a mouse model with knock-in of human TP53 gene carrying codon 72 SNP, we found that despite increased cancer risk, P72 mice that escape tumor development display a longer lifespan than R72 mice. Further, P72 mice have a delayed development of aging-associated phenotypes compared with R72 mice. Mechanistically, P72 mice can better retain the self-renewal function of stem/progenitor cells compared with R72 mice during aging. This study provides direct genetic evidence demonstrating that p53 codon 72 SNP directly impacts aging and longevity, which supports a role of p53 in regulation of longevity.

How long most animals live depends on the balance between the biological processes that allow them to regenerate their tissues when damaged and those that prevent them from developing cancer. Regeneration relies mostly on cells, in particular stem cells, dividing to make new cells, while cancer occurs when cell division becomes uncontrolled.

Tumor suppressor genes protect against cancer. One such gene encodes a protein called p53 that eliminates damaged cells before they can become cancerous. The p53 protein is also believed to be involved in regulating how quickly an animal ages and how long it lives, but this second role has not yet been clearly established.

Previous studies using different strategies to change the activity of p53 in several mouse models have led to inconsistent results. However, the mouse models used in these earlier studies did not reflect how p53 works under normal conditions.

Zhao et al. have now used mice in which the mouse gene for p53 was replaced with one of two versions of the equivalent human gene to study its impact on lifespan and the aging process. The two versions of p53 only differ slightly; a single building block of the protein, the amino acid at position 72, is a proline in one version but an arginine in the other. This difference makes one version of p53 weaker than the other; in other words, it is less able to eliminate damaged cells. Zhao et al. revealed that the mice with the weaker p53 lived for longer and appeared to age more slowly too. Further experiments showed that the stem cells in the mice with a weaker p53 were able to keep dividing and create new cells for longer. This is important because a decline in this activity – which is known as self-renewal – is a hallmark of aging.

Together these findings show that a small yet common change in p53 impacts both aging and lifespan, possibly by altering how stem cells are regulated. Further work is now needed to better understand why the different versions of p53 have different effects on stem cells.

The associations between MDM4 gene polymorphisms and cancer risk

Considerable studies have investigated the associations between MDM4 gene polymorphisms and cancer risk recently, but with contradictory results. The aim of this meta-analysis was to evaluate the associations between MDM4 gene polymorphisms and cancer risk. Relevant studies were identified by a systematic search of PubMed, Embase, and CNKI databases. Crude odds ratios (ORs) and 95% confidence intervals (CIs) were used to describe the strength of the associations. Fifty-six studies published in 11 publications involving 18,910 cases and 51,609 controls were included in this meta-analysis. Five MDM4 gene polymorphisms were evaluated: rs4245739, rs1563828, rs11801299, rs10900598, and rs1380576. Our analyses suggested that the rs4245739 polymorphism was significantly associated with overall cancer risk. Furthermore, stratification analyses of ethnicity indicated that rs4245739 decreased the risk of cancer among the Asian population, and stratification analyses of smoking status indicated that rs4245739 decreased the risk of cancer among nonsmokers. However, stratification analyses of cancer type and sex suggested that rs4245739 was not related to cancer risk. There were no associations of rs1563828, rs11801299, rs10900598, or rs1380576 with overall cancer risk. In conclusion, our analyses indicated that rs4245739 polymorphism in the MDM4 gene may play an important role in the etiology of cancer.

The role of MDM2 and MDM4 in breast cancer development and prevention

The major cause of death from breast cancer is not the primary tumour, but relapsing, drug-resistant, metastatic disease. Identifying factors that contribute to aggressive cancer offers important leads for therapy. Inherent defence against carcinogens depends on the individual molecular make-up of each person. Important molecular determinants of these responses are under the control of the mouse double minute (MDM) family: comprised of the proteins MDM2 and MDM4. In normal, healthy adult cells, the MDM family functions to critically regulate measured, cellular responses to stress and subsequent recovery. Proper function of the MDM family is vital for normal breast development, but also for preserving genomic fidelity. The MDM family members are best characterized for their negative regulation of the major tumour suppressor p53 to modulate stress responses. Their impact on other cellular regulators is emerging. Inappropriately elevated protein levels of the MDM family are highly associated with an increased risk of cancer incidence. Exploration of the MDM family members as cancer therapeutic targets is relevant for designing tailored anti-cancer treatments, but successful approaches must strategically consider the impact on both the target cancer and adjacent healthy cells and tissues. This review focuses on recent findings pertaining to the role of the MDM family in normal and malignant breast cells.

Variations within 3'-UTR of MDM4 gene contribute to clinical outcomes of advanced non-small cell lung cancer patients following platinum-based chemotherapy

Single-nucleotide polymorphism (SNPs) in microRNA (miRNA)-binding sites may modulate the posttranscriptional regulation of gene expression and explain individual sensitivity to platinum agents. This study aimed to investigate the impact of SNPs located at 3′-untranslated region (UTR) of MDM4 gene, on clinical outcomes of advanced non-small cell lung cancer (NSCLC) patients. Four SNPs were genotyped by using DNA from blood samples of advanced NSCLC patients (642 in the Discovery set and 330 in the Replication set) and were analyzed the relationships with clinical outcomes. Carriers with rs10900598 CC genotype and rs4245739 AC genotype showed increased overall survival (OS) than those with AA genotype (P = 0.017 and P = 0.037, respectively) in the Discovery set and after pooling results from the Replication set. A combined effect on survival of variant alleles was also concluded and validated. Stratification analysis revealed that the effect of MDM4 SNPs was more pronounced in lung adenocarcinoma (LAC) subgroups. A reduced expression of the reporter gene for the C allele of rs4245739 was observed in NSCLC cells using luciferase reporter gene assays. Taken together, our results demonstrate that genetic variations in 3′-UTR of MDM4 gene may influence outcomes of advanced NSCLC by miRNAs-mediated regulation.

Lack of Associations of the MDM4 rs4245739 Polymorphism with Risk of Thyroid Cancer among Iranian-Azeri Patients: a Case-Control Study

Background and Aim:

MDM4, a negative regulator of the p53 tumor suppression pathway, has been demonstrated to be overexpressed in a variety of human cancers. Research has revealed that the rs4245739 A>C polymorphism of MDM4 in the 3’-untranslated region makes it a miR-191 target site, leading to lower MDM4 expression. This study aimed to detect if the rs4245739 single nucleotide polymorphism (SNP) impacts on thyroid cancer (TC) development in Iranian-Azeri patients.

Materials and Method:

Blood samples were taken from 232 healthy controls and 130 TC patients of Iranian-Azeri ethnicity. For genotyping, Tetra-ARMS PCR was performed. SPSS for Windows (version 22.0, IBM SPSS Inc., USA) and the SHEsis online software were used for data analysis.

Results:

Alleles of MDM4 rs4245739 SNP demonstrated no significant different in frequencies between patients and controls (p>0.05). Additionally, genotypes of MDM4 rs4245739 SNP did not increase or decrease TC risk in patients compared with healthy subjects.

Conclusion:

Considering the lack of any observed association between the MDM4 rs4245739 polymorphism and TC, we conclude no significant role in the pathophysiology of the disease.

A PRISMA-compliant meta-analysis of MDM4 genetic variants and cancer susceptibility

Molecular epidemiological research suggests that mouse double minute 4 (MDM4) polymorphisms may be associated with cancer susceptibility, but results remain controversial. To derive a more precise evaluation, we performed a PRISMA compliant meta-analysis focused on five single nucleotide polymorphisms (rs11801299, rs1380576, rs10900598, rs1563828, and rs4245739) of MDM4. Overall, 23 studies involving 22,218 cases and 55,033 controls were analyzed. The results showed that rs4245739 was significantly associated with a decreased cancer risk in the allelic (C vs. A: odds ratio [OR] = 0.848, 95% confidence interval [CI] = 0.765-0.941, P = 0.002), heterozygous (AC vs. AA: OR = 0.831, 95% CI = 0.735-0.939, P = 0.003), and dominant (AC+CC vs. A: OR = 0.823, 95% CI = 0.727-0.932, P = 0.002) models. The association was more prominent in Asians. No significant association was found using any genetic model for the rs11801299, rs1380576, rs10900598, and rs1563828 SNPs. These results indicate that the rs4245739 polymorphism may contribute to a decreased cancer susceptibility and support the hypothesis that genetic variants in the MDM4 genes act as important modifiers of cancer risk.

MDM4 rs4245739 A > C polymorphism correlates with reduced overall cancer risk in a meta-analysis of 69477 subjects

Mouse double minute 4 (MDM4) is a p53-interacting oncoprotein that plays an important role in the p53 tumor suppressor pathway. The common rs4245739 A > C polymorphism creates a miR-191 binding site in the MDM4 gene transcript. Numerous studies have investigated the association between this MDM4 polymorphism and cancer risk, but have failed to reach a definitive conclusion. To address this issue, we conducted a meta-analysis by selecting eligible studies from MEDLINE, EMBASE, and Chinese Biomedical databases. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to assess the strength of the associations. We also performed genotype-based mRNA expression analysis using data from 270 individuals retrieved from public datasets. A total of 15 studies with 19796 cases and 49681 controls were included in the final meta-analysis. The pooled results revealed that the MDM4 rs4245739C allele is associated with a decreased cancer risk in the heterozygous (AC vs. AA: OR = 0.82, 95% CI = 0.73-0.93), dominant (AC/CC vs. AA: OR = 0.82, 95% CI = 0.72-0.93), and allele contrast models (C vs. A: OR = 0.84, 95% CI = 0.76-0.94). The association was more prominent in Asians and population-based studies. We also found that the rs4245739C allele was associated with decreased MDM4 mRNA expression, especially for Caucasians. Thus the MDM4 rs4245739 A > C polymorphism appears to be associated with decreased cancer risk. These findings would be strengthened by new studies with larger sample sizes and encompassing additional ethnicities.

Genetic Modifiers of the p53 Pathway

The tumor suppressor gene TP53 is the most frequently mutated gene in human cancer; this gene is subject to inactivation by mutation or deletion in >50% of sporadic cancers. Genes that encode proteins that regulate p53 function, such as MDM2, MDM4, and CDKN2A (p14(ARF)) are also frequently altered in tumors, and it is generally believed that the p53 pathway is likely to be inactivated by mutation in close to 100% of human tumors. Unlike most other cancer-relevant signaling pathways, some of the genes in the p53 pathway contain functionally significant single nucleotide polymorphisms (SNPs) that alter the amplitude of signaling by this protein. These variants, thus, have the potential to impact cancer risk, progression, and the efficacy of radiation and chemotherapy. In addition, the p53 pathway plays a role in other biological processes, including metabolism and reproductive fitness, so these variants have the potential to modify other diseases as well. Here we have chosen five polymorphisms in three genes in the p53 pathway for review, two in TP53, two in MDM2, and one in MDM4. These five variants were selected based on the quality and reproducibility of functional data associated with them, as well as the convincingness of epidemiological data in support of their association with disease. We also highlight two other polymorphisms that may affect p53 signaling, but for which functional or association data are still forthcoming (KITLG and ANRIL). Finally, we touch on three questions regarding genetic modifiers of the p53 pathway: Why did these variants arise? Were they under selection pressure? And, is there compelling evidence to support genotyping these variants to better predict disease risk and prognosis?

The Roles of MDM2 and MDMX in Cancer

For more than 25 years, MDM2 and its homolog MDMX (also known as MDM4) have been shown to exert oncogenic activity. These two proteins are best understood as negative regulators of the p53 tumor suppressor, although they may have additional p53-independent roles. Understanding the dysregulation of MDM2 and MDMX in human cancers and how they function either together or separately in tumorigenesis may improve methods of diagnosis and for assessing prognosis. Targeting the proteins themselves, or their regulators, may be a promising therapeutic approach to treating some forms of cancer.

The MDM4 SNP34091 (rs4245739) C-allele is associated with increased risk of ovarian-but not endometrial cancer

The MDM4 protein (also known as MDMX or HDMX) is a negative regulator of p53, not only by direct interaction but also through its interaction with MDM2. Further, MDM4 overexpression and amplification have been observed in several cancer forms. Recently, a single nucleotide polymorphism (SNP) in the 3’ untranslated region of the MDM4 gene, SNP34091A > C (rs4245739) was reported to alter MDM4 messenger RNA (mRNA) stability by modulating a microRNA binding site, thereby leading to decreased MDM4 levels. In this case-control study, we aimed to evaluate the possible association between MDM4 SNP34091 status and cancer risk by comparing the genotype frequencies in large hospital-based cohorts of endometrial- (n = 1404) and ovarian (n = 1385) cancer patients with healthy female controls (n = 1870). Genotype frequencies were compared by odds ratio (OR) estimates and Fisher exact tests. We found that individuals harboring the MDM4 SNP34091AC/CC genotypes had a significantly elevated risk for serous ovarian cancer (SOC) in general and high-grade serous ovarian cancer (HGSOC) in particular (SOC: OR = 1.18., 95 % CI = 1.01–1.39; HGSOC: OR = 1.25, CI = 1.02–1.53). No association between SNP34091 genotypes and endometrial cancer risk was observed. Our data indicate the MDM4 SNP34091AC/CC genotypes to be associated with an elevated risk for SOC and in particular the HGSOC type.

Polymorphisms in TP53 are associated with risk and survival of osteosarcoma in a Chinese population

Osteosarcoma (OS) is the most frequent histological form of primary bone cancer in adolescence. TP53 is a tumor suppressor gene which is essential for regulating cell division and preventing tumor formation. The purpose of this study is to examine whether genetic mutations in the TP53 gene are associated with OS risk and survival in a Chinese population. Five polymorphisms in the TP53 gene were selected in a case-control study, including 210 OS patients and 420 cancer-free controls. We found that subjects carrying rs12951053 CC genotype and rs1042522 GG genotype were significantly associated with risk of OS [odds ratio (OR)=1.68, 95% confidence intervals (CI): 1.05-2.68; OR=1.89, 95% CI: 1.16-3.07] compared with subjects carrying the common genotypes. Results of haplotype analysis also showed that A-G-G-A-C haplotype (rs12951053, rs1042522, rs8064946, rs9895829 and rs12602273) conferred significant decreased risk of OS (OR=0.37, 95% CI: 0.19-0.72) compared with A-C-G-A-C haplotype. Besides, rs1042522 was an independent prognostic factor for OS with hazard radio (HR)=1.94 (95% CI: 1.03-3.65) in GG genotype than in CC genotype. Our data suggest that genetic mutations in the TP53 gene are associated with risk and survival of OS in Chinese population.

Genetic and Epigenetic Discoveries in Human Retinoblastoma

Retinoblastoma is a rare pediatric cancer of the retina. Nearly all retinoblastomas are initiated through the biallelic inactivation of the retinoblastoma tumor susceptibility gene (RB1). Whole-genome sequencing has made it possible to identify secondary genetic lesions following RB1 inactivation. One of the major discoveries from retinoblastoma sequencing studies is that some retinoblastoma tumors have stable genomes. Subsequent epigenetic studies showed that changes in the epigenome contribute to the rapid progression of retinoblastoma following RB1 gene inactivation. In addition, gene amplification and elevated expression of p53 antagonists, MDM2 and MDM4, may also play an important role in retinoblastoma tumorigenesis. The knowledge gained from these recent molecular, cellular, genomic, and epigenomic analyses are now being integrated to identify new therapeutic approaches that can help save lives and vision in children with retinoblastoma, with fewer long-term side effects.

Identification of SNPs associated with response of breast cancer patients to neoadjuvant chemotherapy in the EORTC-10994 randomized phase III trial

Using cell line panels we identified associations between single-nucleotide polymorphisms (SNPs) and chemosensitivity. To validate these findings in clinics, we genotyped a subset of patients included in a neoadjuvant breast cancer trial to explore the relationship between genotypes and clinical outcome according to treatment received and p53 status. We genotyped 384 selected SNPs in the germline DNA extracted from formalin-fixed paraffin-embedded non-invaded lymph nodes of 243 patients. The polymorphisms of five selected genes were first studied, and then all 384 SNPs were considered. Correction for multiple testing was applied. CYP1B1 polymorphism was significantly associated with pathological complete response (pCR) in patients who had received DNA-damaging agents. MDM2, MDM4 and TP53BP1 polymorphisms were significantly associated with pCR in patients harboring a p53-positive tumor. In the complete SNP panel, there was a significant association between overall survival (OS) and a SNP of ADH1C, R272Q (P=0.0023). By multivariate analysis, only ADH1C genotype and p53 status were significantly associated with OS.

Separate enrichment analysis of pathways for up- and downregulated genes

Two strategies are often adopted for enrichment analysis of pathways: the analysis of all differentially expressed (DE) genes together or the analysis of up- and downregulated genes separately. However, few studies have examined the rationales of these enrichment analysis strategies. Using both microarray and RNA-seq data, we show that gene pairs with functional links in pathways tended to have positively correlated expression levels, which could result in an imbalance between the up- and downregulated genes in particular pathways. We then show that the imbalance could greatly reduce the statistical power for finding disease-associated pathways through the analysis of all-DE genes. Further, using gene expression profiles from five types of tumours, we illustrate that the separate analysis of up- and downregulated genes could identify more pathways that are really pertinent to phenotypic difference. In conclusion, analysing up- and downregulated genes separately is more powerful than analysing all of the DE genes together.

A genetic variant in p63 (rs17506395) is associated with breast cancer susceptibility and prognosis

BACKGROUND

p63, homologous to p53, has been investigated to be involved in various aspects of tumorigenesis and cancer progression. Recently, we have identified a functional single nucleotide polymorphism (SNP) rs17506395 (T>G) in p63 which was associated with female reproduction and ovarian cancer development. The present study aimed to evaluate the association of rs17506395 genotypes with breast cancer susceptibility, clinicopathological characteristics and prognosis.

PATIENTS AND METHODS

TaqMan assay was used to genotype the rs17506395 polymorphism. The expression of p63 mRNA was determined by quantitative reverse-transcription PCR (qRT-PCR). Unconditional logistic regression and univariate Cox hazard regression analyses were performed to evaluate the association of rs17506395 with breast cancer susceptibility and prognosis respectively.

RESULTS

First, we found that breast tumors with TT genotype exhibited higher level of p63 mRNA compared with other genotypes in breast cancer tissues, indicating that rs17506395 may be a functional single nucleotide polymorphism in breast cancer. Further investigation revealed that the presence of TT genotype was statistically correlated with increased risk for breast cancer, compared with genotypes containing the G allele (GG and GT). Moreover, a significant association between rs17506395 polymorphism and age at diagnosis and status of hormone receptor was observed. Consistently, prognostic analysis showed that patients carrying TT genotype represent unfavorable survival, suggesting that TT genotype may be a biomarker for poor prognosis in breast cancer.

CONCLUSION

Our data suggest that rs17506395 polymorphism can function as a risk factor and prognostic indicator for breast cancer, whereas precise mechanism underlying the function of this polymorphism needs further investigation.

A polymorphic p53 response element in KIT ligand influences cancer risk and has undergone natural selection

The ability of p53 to regulate transcription is crucial for tumor suppression and implies that inherited polymorphisms in functional p53-binding sites could influence cancer. Here, we identify a polymorphic p53 responsive element and demonstrate its influence on cancer risk using genome-wide data sets of cancer susceptibility loci, genetic variation, p53 occupancy, and p53-binding sites. We uncover a single-nucleotide polymorphism (SNP) in a functional p53-binding site and establish its influence on the ability of p53 to bind to and regulate transcription of the KITLG gene. The SNP resides in KITLG and associates with one of the largest risks identified among cancer genome-wide association studies. We establish that the SNP has undergone positive selection throughout evolution, signifying a selective benefit, but go on to show that similar SNPs are rare in the genome due to negative selection, indicating that polymorphisms in p53-binding sites are primarily detrimental to humans.

Genome-wide association studies identify four ER negative-specific breast cancer risk loci

Estrogen receptor (ER)-negative tumors represent 20-30% of all breast cancers, with a higher proportion occurring in younger women and women of African ancestry. The etiology and clinical behavior of ER-negative tumors are different from those of tumors expressing ER (ER positive), including differences in genetic predisposition. To identify susceptibility loci specific to ER-negative disease, we combined in a meta-analysis 3 genome-wide association studies of 4,193 ER-negative breast cancer cases and 35,194 controls with a series of 40 follow-up studies (6,514 cases and 41,455 controls), genotyped using a custom Illumina array, iCOGS, developed by the Collaborative Oncological Gene-environment Study (COGS). SNPs at four loci, 1q32.1 (MDM4, P = 2.1 × 10(-12) and LGR6, P = 1.4 × 10(-8)), 2p24.1 (P = 4.6 × 10(-8)) and 16q12.2 (FTO, P = 4.0 × 10(-8)), were associated with ER-negative but not ER-positive breast cancer (P > 0.05). These findings provide further evidence for distinct etiological pathways associated with invasive ER-positive and ER-negative breast cancers.

Genome-wide association study in BRCA1 mutation carriers identifies novel loci associated with breast and ovarian cancer risk

BRCA1-associated breast and ovarian cancer risks can be modified by common genetic variants. To identify further cancer risk-modifying loci, we performed a multi-stage GWAS of 11,705 BRCA1 carriers (of whom 5,920 were diagnosed with breast and 1,839 were diagnosed with ovarian cancer), with a further replication in an additional sample of 2,646 BRCA1 carriers. We identified a novel breast cancer risk modifier locus at 1q32 for BRCA1 carriers (rs2290854, P = 2.7 × 10(-8), HR = 1.14, 95% CI: 1.09-1.20). In addition, we identified two novel ovarian cancer risk modifier loci: 17q21.31 (rs17631303, P = 1.4 × 10(-8), HR = 1.27, 95% CI: 1.17-1.38) and 4q32.3 (rs4691139, P = 3.4 × 10(-8), HR = 1.20, 95% CI: 1.17-1.38). The 4q32.3 locus was not associated with ovarian cancer risk in the general population or BRCA2 carriers, suggesting a BRCA1-specific association. The 17q21.31 locus was also associated with ovarian cancer risk in 8,211 BRCA2 carriers (P = 2×10(-4)). These loci may lead to an improved understanding of the etiology of breast and ovarian tumors in BRCA1 carriers. Based on the joint distribution of the known BRCA1 breast cancer risk-modifying loci, we estimated that the breast cancer lifetime risks for the 5% of BRCA1 carriers at lowest risk are 28%-50% compared to 81%-100% for the 5% at highest risk. Similarly, based on the known ovarian cancer risk-modifying loci, the 5% of BRCA1 carriers at lowest risk have an estimated lifetime risk of developing ovarian cancer of 28% or lower, whereas the 5% at highest risk will have a risk of 63% or higher. Such differences in risk may have important implications for risk prediction and clinical management for BRCA1 carriers.

Mapping genetic alterations causing chemoresistance in cancer: identifying the roads by tracking the drivers

Although new agents are implemented to cancer therapy, we lack fundamental understandings of the mechanisms of chemoresistance, the main obstacle to cure in cancer. Here we review clinical evidence linking molecular defects to drug resistance across different tumour forms and discuss contemporary experimental evidence exploring these mechanisms. Although evidence, in general, is sparse and fragmentary, merging knowledge links drug resistance, and also sensitivity, to defects in functional pathways having a key role in cell growth arrest or death and DNA repair. As these pathways may act in concert, there is a need to explore multiple mechanisms in parallel. Taking advantage of massive parallel sequencing and other novel high-throughput technologies and base research on biological hypotheses, we now have the possibility to characterize functional defects related to these key pathways and to design a new generation of studies identifying the mechanisms controlling resistance to different treatment regimens in different tumour forms.

The MDM2 309T>G polymorphism and ovarian cancer risk: a meta-analysis of 1534 cases and 2211 controls

Background

Recently, there have been a number of studies on the association between MDM2 (Murine Double Minute 2) 309 polymorphism and ovarian cancer risk. However, the results of previous reports remain controversial and ambiguous. Thus, we performed a meta-analysis to explore more precisely the association between MDM2 309 polymorphism and the risk of ovarian cancer.

Methods

A meta-analysis was performed to examine the association between MDM2 309T>G polymorphism and ovarian cancer risk. Odds ratio (OR) and its 95% confidence interval (CI) were used for statistical analysis.

Results

Our publication search identified a total of 6 studies with 1534 cases and 2211 controls. No significant association was found between MDM2 309T>G polymorphism and ovarian cancer risk in total population analysis. In the subgroup meta-analysis by ethnicity, a negative association was shown in Asian subgroup (G vs. T OR = 0.774, 95% CI = 0.628–0.955, P = 0.017, P_het = 0.327; GG vs. TT: OR = 0.601, 95% CI = 0.395–0.914, P = 0.017, P_het = 0.417; dominant model TG+GG vs. TT: OR = 0.661, 95% CI = 0.468–0.934, P = 0.019, P_het = 0.880), and no significant association in any genetic models among Caucasians was observed.

Conclusions

This meta-analysis provides evidence for the association between MDM2 309 polymorphism and ovarian cancer risk, supporting the hypothesis that MDM2 SNP309 G allele acts as an important ovarian cancer protective factor in Asians but not in Caucasians.

Polymorphism of genes and implantation failure

Implantation failure is the most frequent cause of pregnancy loss in couples who try to conceive, either in a natural way or using assisted reproductive techniques (ART). Identify the precise mechanisms of implantation failure can lead to identify couples at risk and also providing appropriate therapeutic options to affected couples. Despite the high prevalence of this disorder, a few causing factors are demonstrated so far. Recent studies indicate that genetic factors play an important role in the occurrence of recurrent implantation failure. Although some of these factors, such as numerical chromosomal aneuploidy are known to be causative factors, there are some other factors that solely increase susceptibility to this event. In the present review we try to list the genetic polymorphisms that are known as susceptibility factors in implantation failure.

The TP53 fertility network

The TP53 gene, first described in 1979, was identified as a tumor suppressor gene in 1989, when it became clear that its product, the p53 nuclear phosphoprotein, was frequently inactivated in many different forms of cancers. Nicknamed "guardian of the genome", TP53 occupies a central node in stress response networks. The p53 protein has a key role as transcription factor in limiting oncogenesis through several growth suppressive functions, such as initiating apoptosis, senescence, or cell cycle arrest. The p53 protein is directly inactivated in about 50% of all tumors as a result of somatic gene mutations or deletions, and over 80% of tumors demonstrate dysfunctional p53 signaling. Beyond the undeniable importance of p53 as a tumor suppressor, an increasing number of new functions for p53 have been reported, including its ability to regulate energy metabolism, to control autophagy, and to participate in various aspects of differentiation and development. Recently, studies on genetic variations in TP53 among different populations have led to the notion that the p53 protein might play an important role in regulating fertility. This review summarizes current knowledge on the basic functions of different genes of the TP53 family and TP53 pathway with respect to fertility. We also provide original analyses based on genomic and genotype databases, providing further insights into the possible roles of the TP53 pathway in human reproduction.

Polymorphisms in the p63 and p73 genes are associated with ovarian cancer risk and clinicopathological variables

Objective

p73 and p63 are two structural and functional homologs of p53, and their biological functions in cancer progression have attracted attention due to the presence of variants generated by genetic polymorphisms. Recently, three single nucleotide polymorphisms (SNPs) in the p63 and p73 genes have been associated with female reproduction. In the present study, we aimed to evaluate the relationship between these SNPs and ovarian cancer susceptibility and clinical pathology.

Methods

We genotyped the p63 (rs873330 [Genbank, refSNP ID] T > C [T: original base, C: mutant base]) and p73 (rs4648551 G > A and rs6695978 G > A) SNPs in ovarian cancers and healthy controls and analyzed the distributions of genotype frequencies to evaluate the association of the genotypes with the risk of ovarian cancer and the clinicopathological characteristics. Logistic regression models were applied in statistical analyses.

Results

Our research revealed that p73 rs6695978 G > A was significantly associated with ovarian cancer patients. Women with the A allele were at increased risk of ovarian cancer compared to carriers of the G allele (OR = 1.55; 95% CI:1.07–2.19; P = 0.003). Meanwhile, the at-risk A allele was positively related with the occurrence of mucinous ovarian cancer (OR = 3.48; 95% CI:1.15-6.83; P = 0.001), low degree of differentiation (OR = 1.87; 95% CI:1.03-3.47; P = 0.003), lymph node metastasis (OR = 1.69; 95% CI: 1.14-2.75; P = 0.010) and estrogen receptor positive (OR = 2.72; 95% CI: 1.38-4.81; P = 0.002). However, we were unable to find any associations of the polymorphisms in another two SNPs (rs4648551 G > A, rs873330 T > C) with ovarian cancer risk and clinicopathological parameters.

Conclusions

The p73 rs6695978 G > A polymorphism will serve as a modifier of ovarian cancer susceptibility and prognosis. Further investigations with large sample sizes and of the mechanistic relevance of p73 polymorphism will be warranted

TP53 PIN3 and PEX4 polymorphisms and infertility associated with endometriosis or with post-in vitro fertilization implantation failure

p53 has a crucial role in human fertility by regulating the expression of leukemia inhibitory factor (LIF), a secreted cytokine critical for blastocyst implantation. To examine whether TP53 polymorphisms may be involved with in vitro fertilization (IVF) failure and endometriosis (END), we have assessed the associations between TP53 polymorphism in intron 2 (PIN2; G/C, intron 2), PIN3 (one (N, non-duplicated) or two (D, duplicated) repeats of a 16-bp motif, intron 3) and polymorphism in exon 4 (PEX4; C/G, p.P72R, exon 4) in 98 women with END and 115 women with post-IVF failure. In addition, 134 fertile women and 300 women unselected with respect to fertility-related features were assessed. TP53 polymorphisms and haplotypes were identified by amplification refractory mutation system polymerase chain reaction. TP53 PIN3 and PEX4 were associated with both END (P=0.042 and P=0.007, respectively) and IVF (P=0.004 and P=0.009, respectively) when compared with women both selected and unselected for fertility-related features. Haplotypes D-C and N-C were related to higher risk for END (P=0.002, P=0.001, respectively) and failure of IVF (P=0.018 and P=0.002, respectively) when compared with the Fertile group. These results support that specific TP53 haplotypes are associated with an increased risk of END-associated infertility and with post-IVF failure.

Analysis of MDM2 and MDM4 single nucleotide polymorphisms, mRNA splicing and protein expression in retinoblastoma

Retinoblastoma is a childhood cancer of the developing retina that begins in utero and is diagnosed in the first years of life. Biallelic RB1 gene inactivation is the initiating genetic lesion in retinoblastoma. The p53 gene is intact in human retinoblastoma but the pathway is believed to be suppressed by increased expression of MDM4 (MDMX) and MDM2. Here we quantify the expression of MDM4 and MDM2 mRNA and protein in human fetal retinae, primary retinoblastomas, retinoblastoma cell lines and several independent orthotopic retinoblastoma xenografts. We found that MDM4 is the major p53 antagonist expressed in retinoblastoma and in the developing human retina. We also discovered that MDM4 protein steady state levels are much higher in retinoblastoma than in human fetal retinae. This increase would not have been predicted based on the mRNA levels. We explored several possible post-transcriptional mechanisms that may contribute to the elevated levels of MDM4 protein. A proportion of MDM4 transcripts are alternatively spliced to produce protein products that are reported to be more stable and oncogenic. We also discovered that a microRNA predicted to target MDM4 (miR191) was downregulated in retinoblastoma relative to human fetal retinae and a subset of samples had somatic mutations that eliminated the miR-191 binding site in the MDM4 mRNA. Taken together, these data suggest that post-transcriptional mechanisms may contribute to stabilization of the MDM4 protein in retinoblastoma.

Role of an MDM4 polymorphism in the early age of onset of nasopharyngeal carcinoma

Mouse double minute 4 (MDM4) is a critical negative regulator of the tumor suppressor p53. The results of studies have revealed that an MDM4 polymorphism (rs1563828) may contribute to the earlier onset of several malignant diseases. However, the correlation between this polymorphism and nasopharyngeal carcinoma (NPC) susceptibility has not been explored. We performed a case-control study with 210 NPC patients and 200 healthy controls. Significant associations were found when comparing the age of onset of NPC according to the rs1563828 genotype (P=0.01). The average age of onset of NPC in patients with the TT, CC and CT genotypes was 39.3, 48.2 and 45.5 years, respectively. Homozygous variant (TT) carriers developed NPC at an earlier age than homozygous (CC) carriers, such that the age of onset was accelerated by 8.9 years (P=0.002). Our data suggest that rs1563828 is a modifier of the age of onset of NPC in the population studied. The age of onset for NPC with TT homozygotes was earlier than CC carriers.

High twinning rate in Cândido Godói: a new role for p53 in human fertility

BACKGROUND

Cândido 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.

Regulation of Fertility by the p53 Family Members

The p53 family members, which consist of 3 transcription factors-p53, p63, and p73-are conserved during evolution. The p53 family proteins are involved in many important cellular functions, including tumor suppression (p53 and p73), the development of epithelial cell layers (p63), and the development of central nervous system and immune system (p73). Studies on p53-like proteins in low organisms have demonstrated that their primordial functions are to maintain the genomic integrity of germ cells and ensure faithful development and reproduction. In vertebrates, the p53 family proteins retain these functions in reproduction and at the same time have developed additional important functions in reproduction, such as the regulation of embryonic implantation (p53). p53 regulates embryonic implantation through transcriptional regulation of leukemia inhibitory factor (LIF). p63, in particular TAp63, is a main regulator to protect the fidelity of female germ cells during meiotic arrest. p73, in particular TAp73, regulates the ovary function and the quality of oocytes. Loss of p53, p63, or p73 genes in female mice leads to a significant decrease in fertility. These functions of the p53 family proteins in reproduction provide a plausible explanation for positive evolutionary selection observed in a group of single nucleotide polymorphisms and haplotypes in the p53 family genes. A better understanding of the functions of the p53 family proteins in reproduction may lead to new strategies for fertility treatment.

Polymorphisms of MDM4 and risk of squamous cell carcinoma of the head and neck

PURPOSE

Mouse double minute 4 (MDM4), a homolog of MDM2, is one of the key negative regulators of p53, and its amplification or overexpression contributes to carcinogenesis by inhibiting the p53 tumor suppressor activity. We investigated the association between MDM4 polymorphisms and the risk of squamous cell carcinoma of the head and neck (SCCHN).

METHODS

We genotyped three MDM4 tagging polymorphisms, two in the 3' untranslated region (rs11801299G>A and rs10900598G>T) and one in intron 1 (rs1380576C>G), in a case-control study of 1075 non-Hispanic white SCCHN patients and 1079 cancer-free controls, and evaluated their associations with SCCHN risk.

RESULTS

Although none of these three polymorphisms individually had a statistically significant effect on the risk of SCCHN, nor did their combined number of putative risk genotypes (i.e. rs11801299GG, rs1380576CG+GG, and rs10900598GG) [odds ratio (OR)=1.16; 95% confidence interval (95% CI) =0.93-1.45], we found that individuals with 1-3 risk genotypes had statistically significant increased risk of oropharyngeal cancer (OR=1.32; 95% CI=1.00-1.73), particularly for those with T1-2 stage (OR=1.40; 95% CI=1.02-1.94), those with regional lymph node metastases (N1-3) (OR=1.44; 95% CI=1.07-1.95), and those with late stages (III and IV) (OR=1.34; 95% CI=1.01-1.77).

CONCLUSION

These results suggest that the joint effect of MDM4 variants may contribute to the risk of oropharyngeal cancer in non-Hispanic whites. Additional studies are warranted to unravel whether the particular stage distribution of oropharyngeal cancer with the strongest association (T1-2, N1-3, and III-IV) is a possible link with human papillomavirus-related oropharyngeal cancers.

Modifying effect of MDM4 variants on risk of HPV16-associated squamous cell carcinoma of oropharynx

BACKGROUND

The p53 pathway plays a critical role in maintaining genomic stability and preventing tumor formation. Given the roles of both MDM4 and HPV16 E6 oncoproteins in inhibition of p53 activity, we tested the hypothesis that MDM4 polymorphisms are associated with the risk of HPV16-associated squamous cell carcinoma of head and neck (SCCHN).

METHODS

Genotyping was conducted on 3 tagging single nucleotide polymorphisms (rs11801299 G>A, rs10900598 G>T, and rs1380576 C>G) in MDM4, and serology was used to determine HPV 16 exposure in 380 cases and 335 cancer-free controls that were frequency-matched by age, sex, smoking, and drinking status.

RESULTS

None of 3 MDM4 polymorphisms alone was significantly associated with risk of overall SCCHN. With further analysis stratified by HPV16 serology and tumor site, we found that each polymorphism individually modified the risk of HPV16-associated squamous cell carcinoma of the oropharynx (SCCOP), and such effect modification was particularly pronounced in never smokers and never drinkers.

CONCLUSION

The risk of HPV16-associated SCCOP could be modified by MDM4 polymorphisms. Large and prospective studies are needed to validate our findings.

Regulation of female reproduction by p53 and its family members

Tumor suppressor p53 is crucial for embryonic implantation through transcriptional up-regulation of uterine leukemia inhibitory factor (LIF). This article reports that p53 and estrogen receptor α were activated in endometrial tissues during implantation to coordinately regulate LIF production. By using human p53 knockin (Hupki) mice carrying a single nucleotide polymorphism (SNP) at codon 72 (arginine/proline), the arginine allele was demonstrated to produce higher uterine LIF levels during implantation than the proline allele. In humans, the diversity of haplotypes of the p53 gene has decreased during evolution, because the arginine allele, existing in only a subset of haplotypes, is under positive selection. This observation is consistent with previous results showing that the proline allele is enriched in patients undergoing in vitro fertilization (IVF). Studies with p63- and p73-knockout mice have demonstrated the involvement of p63 and p73 in female reproduction and their roles in egg formation and apoptosis (p63) and spindle checkpoint (p73) in female mice. Here, the role of p63 and p73 in human reproduction was investigated. Selected alleles of SNPs in p63 and p73 genes were enriched in IVF patients. These findings demonstrate that the p53 family members are involved in several steps to regulate female reproduction in mice and humans.

The emergence of human-evolutionary medical genomics

In this review, I describe how evolutionary genomics is uniquely suited to spearhead advances in understanding human disease risk, owing to the privileged position of genes as fundamental causes of phenotypic variation, and the ability of population genetic and phylogenetic methods to robustly infer processes of natural selection, drift, and mutation from genetic variation at the levels of family, population, species, and clade. I first provide an overview of models for the origins and maintenance of genetically based disease risk in humans. I then discuss how analyses of genetic disease risk can be dovetailed with studies of positive and balancing selection, to evaluate the degree to which the 'genes that make us human' also represent the genes that mediate risk of polygenic disease. Finally, I present four basic principles for the nascent field of human evolutionary medical genomics, each of which represents a process that is nonintuitive from a proximate perspective. Joint consideration of these principles compels novel forms of interdisciplinary analyses, most notably studies that (i) analyze tradeoffs at the level of molecular genetics, and (ii) identify genetic variants that are derived in the human lineage or in specific populations, and then compare individuals with derived versus ancestral alleles.

An illegitimate microRNA target site within the 3' UTR of MDM4 affects ovarian cancer progression and chemosensitivity

Overexpression of MDM4 (also known as MDMX or HDMX) is thought to promote tumorigenesis by decreasing p53 tumor suppressor function. Even modest decrease in Mdm4 levels affects tumorigenesis in mice, suggesting that genetic variants of MDM4 might have similar effects in humans. We sequenced the MDM4 gene in a series of ovarian cancer cell lines and carcinomas to identify mutations and/or single nucleotide polymorphisms (SNPs). We identified an SNP (SNP34091) in the 3'-UTR of MDM4 that creates a putative target site for hsa-miR-191, a microRNA that is highly expressed in normal and tumor tissues. Biochemical evidence supports specific miR-191-dependent regulation of the MDM4-C, but not MDM4-A, variant. Consistently, the A-allele was associated with statistically significant increased expression of MDM4 mRNA and protein levels in ovarian carcinomas. Importantly, the wild-type genotype (A/A) is more frequent (57.8% vs. 42.2% for A/C and C/C, respectively) in patients with high-grade carcinomas than in patients with low-grade carcinomas (47.2% vs. 52.5% for A/A and A/C + C/C, respectively). Moreover, A/A patients who do not express the estrogen receptor had a 4.2-fold [95% confidence interval (CI) = 1.2-13.5; P = 0.02] increased risk of recurrence and 5.5-fold (95% CI = 1.5-20.5; P = 0.01) increased risk of tumor-related death. Unexpectedly, the frequency of p53 mutations was not significantly lower in A/A patients. We conclude that acquisition of an illegitimate miR-191 target site causes downregulation of MDM4 expression, thereby significantly delaying ovarian carcinoma progression and tumor-related death. Importantly, these effects appear to be, at least partly, independent of p53.

The origins and evolution of genetic disease risk in modern humans

Patterns and risks of human disease have evolved. In this article, I review evidence regarding the importance of recent adaptive evolution, positive selection, and genomic conflicts in shaping the genetic and phenotypic architectures of polygenic human diseases. Strong recent selection in human populations can create and maintain genetically based disease risk primarily through three processes: increased scope for dysregulation from recent human adaptations, divergent optima generated by intraspecific genomic conflicts, and transient or stable deleterious by-products of positive selection caused by antagonistic pleiotropy, ultimately due to trade-offs at the levels of molecular genetics, development, and physiology. Human disease due to these processes appears to be concentrated in three sets of phenotypes: cognition and emotion, reproductive traits, and life-history traits related to long life-span. Diverse, convergent lines of evidence suggest that a small set of tissues whose pleiotropic patterns of gene function and expression are under especially strong selection-brain, placenta, testis, prostate, breast, and ovary-has mediated a considerable proportion of disease risk in modern humans.

The regulation of the p53-mediated stress response by MDM2 and MDM4

Exquisite control of the activity of p53 is necessary for mammalian survival. Too much p53 is lethal, whereas too little permits tumorigenesis. MDM2 and MDM4 are structurally related proteins critical for the control of p53 activity during development, homeostasis, and the response to stress. These two essential proteins regulate both the activation of p53 in response to stress and the recovery of cells following resolution of the damage, yet both are oncogenic when overexpressed. Thus, multiple regulatory circuits ensure that their activities are fine-tuned to promote tumor-free survival. Numerous diverse stressors activate p53, and much research has gone into trying to find commonalities between them that would explain the mechanism by which p53 becomes active. It is now clear that although these diverse stressors activate p53 by different biochemical pathways, one common feature is the effort they direct, through a variety of means, toward disrupting the functions of both MDM2 and MDM4. This article provides an overview of the relationship between MDM2 and MDM4, features the various biochemical mechanisms by which p53 is activated through inhibition of their functions, and proposes some emerging areas for investigation of the p53-mediated stress response.

Single-nucleotide polymorphisms in p53 pathway and aggressiveness of prostate cancer in a Caucasian population

PURPOSE

The tumor suppressor p53 plays a crucial role in maintaining genomic stability and tumor prevention. Mdm2, Mdm4, and Hausp are all critical regulators of the p53 protein. Despite the importance of the p53 pathway in prostate cancer development and progression, little is known about the association of functional single-nucleotide polymorphisms (SNP) in the p53 pathway genes and prostate cancer aggressiveness.

EXPERIMENTAL DESIGN

In this study, we analyze the association of SNPs in p53, Mdm2, Mdm4, and Hausp genes with prostate cancer clinicopathologic variables in a large hospital-based Caucasian prostate cancer cohort (N = 4,073).

RESULTS

We found that the Mdm2 SNP309 T allele was associated with earlier onset prostate cancer (P = 0.004), higher Gleason scores (P = 0.004), and higher stages in men undergoing a radical prostatectomy (P = 0.011). Both the Mdm4 and Hausp SNPs (rs1380576 and rs1529916) were found to be associated with higher D'Amico risk prostate cancer category at the time of diagnosis (P = 0.023 and P = 0.046, respectively). Mdm4 SNP was also found to be associated with higher Gleason score at radical prostatectomy (P = 0.047). We did not observe any statistically significant association between the p53 Arg72Pro polymorphism and prostate cancer aggressiveness or pathologic variables.

CONCLUSIONS

These results suggested the importance of these p53 regulators in prostate cancer development and progression.

Effects of MDM2, MDM4 and TP53 codon 72 polymorphisms on cancer risk in a cohort study of carriers of TP53 germline mutations

Background

Previous studies have shown that MDM2 SNP309 and p53 codon 72 have modifier effects on germline P53 mutations, but those studies relied on case-only studies with small sample sizes. The impact of MDM4 polymorphism on tumor onset in germline mutation carriers has not previously been studied.

Methodology/Principal Findings

We analyzed 213 p53 germline mutation carriers including 168(78.9%) affected with cancer and 174 who had genotypic data. We analyzed time to first cancer using Kaplan-Meier and Cox proportional hazards methods, comparing risks according to polymorphism genotypes. For MDM2 SNP309, a significant difference of 9.0 years in the average age of cancer diagnosis was observed between GG/GT and TT carriers (18.6 versus 27.6 years, P = 0.0087). The hazards ratio was 1.58 (P = 0.03) comparing risks among individuals with GG/GT to risk among TT, but this effect was only significant in females (HR = 1.60, P = 0.02). Compared to other genotypes, P53 codon 72 PP homozygotes had a 2.24 times (P = 0.03) higher rate for time to develop cancer. We observed a multiplicative joint effect of MDM2 and p53 codon72 polymorphism on risk. The MDM4 polymorphism had no significant effects.

Conclusions/Significance

Our results suggest that the MDM2 SNP309 G allele is associated with cancer risk in p53 germline mutation carriers and accelerates time to cancer onset with a pronounced effect in females. A multiplicative joint effect exists between the MDM2 SNP309 G allele and the p53 codon 72 G allele in the risk of cancer development. Our results further define cancer risk in carriers of germline p53 mutations.