A Single Nucleotide Polymorphism in theMDM2Gene Disrupts the Oscillation of p53 and MDM2 Levels in Cells

Gene variations related to the hepatocellular carcinoma: Results from a field synopsis and Bayesian revaluation

Hepatocellular carcinoma (HCC) is considered as the second cause of cancer-related deaths worldwide. Genetic variations are associated with HCC risk, an issue that has been the subject of several meta-analyses. However, meta-analyses have an important limitation on the likelihood of false positive data. Henceforth, this study aimed to assess the level of noteworthiness in the meta-analyses by means of a Bayesian approach. A systematic search was performed for meta-analyses with associations between gene polymorphisms and HCC. The calculations for the False-Positive Rate Probability (FPRP) and the Bayesian False Discovery Probability (BFDP) were performed to assess the noteworthiness with a statistical power of 1.2 and 1.5 of Odds Ratio at a prior probability of 10^-3 and 10^-5. The quality of studies was evaluated by the Venice criteria. As additional analyses, the gene-gene and protein-protein networks were designed for these genes and products. As results, we found 33 meta-analytic studies on 45 polymorphisms occurring in 35 genes. A total of 1,280 values for FPRP and BFDP were obtained. Seventy-five for FPRP (5.86%) and 95 for BFDP (14.79%) were noteworthy. In conclusion, the polymorphisms in CCND1, CTLA4, EGF, IL6, IL12A, KIF1B, MDM2, MICA, miR-499, MTHFR, PNPLA3, STAT4, TM6SF2, and XPD genes were considered as noteworthy biomarkers for HCC risk.

A common pathway to cancer: Oncogenic mutations abolish p53 oscillations

The tumor suppressor p53 oscillates in response to DNA double-strand breaks, a behavior that has been suggested to be essential to its anti-cancer function. Nearly all human cancers have genetic alterations in the p53 pathway; a number of these alterations have been shown to be oncogenic by experiment. These alterations include somatic mutations and copy number variations as well as germline polymorphisms. Intriguingly, they exhibit a mixed pattern of interactions in tumors, such as co-occurrence, mutual exclusivity, and paradoxically, mutual antagonism. Using a differential equation model of p53-Mdm2 dynamics, we employ Hopf bifurcation analysis to show that these alterations have a common mode of action, to abolish the oscillatory competence of p53, thereby, we suggest, impairing its tumor suppressive function. In this analysis, diverse genetic alterations, widely associated with human cancers clinically, have a unified mechanistic explanation of their role in oncogenesis.

It’s Getting Complicated—A Fresh Look at p53-MDM2-ARF Triangle in Tumorigenesis and Cancer Therapy

Anti-tumorigenic mechanisms mediated by the tumor suppressor p53, upon oncogenic stresses, are our bodies’ greatest weapons to battle against cancer onset and development. Consequently, factors that possess significant p53-regulating activities have been subjects of serious interest from the cancer research community. Among them, MDM2 and ARF are considered the most influential p53 regulators due to their abilities to inhibit and activate p53 functions, respectively. MDM2 inhibits p53 by promoting ubiquitination and proteasome-mediated degradation of p53, while ARF activates p53 by physically interacting with MDM2 to block its access to p53. This conventional understanding of p53-MDM2-ARF functional triangle have guided the direction of p53 research, as well as the development of p53-based therapeutic strategies for the last 30 years. Our increasing knowledge of this triangle during this time, especially through identification of p53-independent functions of MDM2 and ARF, have uncovered many under-appreciated molecular mechanisms connecting these three proteins. Through recognizing both antagonizing and synergizing relationships among them, our consideration for harnessing these relationships to develop effective cancer therapies needs an update accordingly. In this review, we will re-visit the conventional wisdom regarding p53-MDM2-ARF tumor-regulating mechanisms, highlight impactful studies contributing to the modern look of their relationships, and summarize ongoing efforts to target this pathway for effective cancer treatments. A refreshed appreciation of p53-MDM2-ARF network can bring innovative approaches to develop new generations of genetically-informed and clinically-effective cancer therapies.

The roles of mouse double minute 2 (MDM2) oncoprotein in ocular diseases: A review

Mouse double minute 2 (MDM2), an E3 ubiquitin ligase and the primary negative regulator of the tumor suppressor p53, cooperates with its structural homolog MDM4/MDMX to control intracellular p53 level. In turn, overexpression of p53 upregulates and forms an autoregulatory feedback loop with MDM2. The MDM2-p53 axis plays a pivotal role in modulating cell cycle control and apoptosis. MDM2 itself is regulated by the PI3K-AKT and RB-E2F-ARF pathways. While amplification of the MDM2 gene or overexpression of MDM2 (due to MDM2 SNP T309G, for instance) is associated with various malignancies, numerous studies have shown that MDM2/p53 alterations may also play a part in the pathogenetic process of certain ocular disorders (Fig. 1). These include cancers (retinoblastoma, uveal melanoma), fibrocellular proliferative diseases (proliferative vitreoretinopathy, pterygium), neovascular diseases, degenerative diseases (cataract, primary open-angle glaucoma, age-related macular degeneration) and infectious/inflammatory diseases (trachoma, uveitis). In addition, MDM2 is implicated in retinogenesis and regeneration after optic nerve injury. Anti-MDM2 therapy has shown potential as a novel approach to treating these diseases. Despite major safety concerns, there are high expectations for the clinical value of reformative MDM2 inhibitors. This review summarizes important findings about the role of MDM2 in ocular pathologies and provides an overview of recent advances in treating these diseases with anti-MDM2 therapies.

The 40bp Indel Polymorphism rs150550023 in the MDM2 Promoter is Associated with Intriguing Shifts in Gene Expression in the p53-MDM2 Regulatory Hub

Most low-penetrance genetic risk factors for cancer are located in noncoding regions, presumably altering the regulation of neighboring genes. The poorly characterized Indel polymorphism rs150550023 (rs3730485; del1518) in the promoter of MDM2 (human homolog of mouse double minute 2) is a biologically plausible candidate genetic risk factor, which might influence the expression of MDM2, a key negative regulator of the central tumor suppressor p53. Here, we genotyped rs150550023 in a Central European hospital-based case-control study of 407 breast cancer patients and 254 female controls. mRNA levels of MDM2, p53, and the p53 target genes p21, BAX, and PERP were quantified with qRT-PCR, and p53 protein was assessed with immune histochemistry in ≈100 primary breast tumors with ascertained rs150550023 genotype. We found no evidence for an association of rs150550023 with the risk, age at onset, or prognosis of breast cancer. A possible synergism was observed with SNP309 in promoter P2 of MDM2. Mean mRNA levels of MDM2, p53, p21, and BAX were ≈1.5-3 fold elevated in TP53 wildtype tumors with the minor homozygous Del/Del genotype. However, systematic shifts in p53 protein levels or mutation rates were not observed, suggesting that the elevated p53 mRNA levels are due to regulatory feedback loops that compensate for the effects of rs150550023 on MDM2 expression.

Oscillatory Dynamics of p53-Mdm2 Circuit in Response to DNA Damage Caused by Ionizing Radiation

Although the dynamical behavior of the p53-Mdm2 loop has been extensively studied, the understanding of the mechanism underlying the regulation of this pathway still remains limited. Herein, we developed an integrated model with five basic components and three ubiquitous time delays for the p53-Mdm2 interaction in response to DNA damage following ionizing radiation (IR). We showed that a sufficient amount of activated ATM level can initiate the p53 oscillations with nearly the same amplitude over a wide range of the ATM level; a proper range of p53 level is also required for generating the oscillations, for too high or too low levels it would fail to generate the oscillations; and increased Mdm2 level leads to decreased amplitude of the p53 oscillation and reduced expression of the p53 activity. Moreover, we found that the negative feedback loop formed between p53 and nuclear Mdm2 plays a dominant role in determining the p53 dynamics, whereas when interaction strength of the negative feedback loop becomes weaker, the positive feedback loop formed between p53 and cytoplasmatic Mdm2 can induce different types of dynamics. Furthermore, we demonstrated that the total time delay required for protein production and nuclear translocation of Mdm2 can induce p53 oscillations even when the p53 level is at a certain stable high steady state or at a certain stable low steady state. In addition, the two important features of the oscillatory dynamics-amplitude and period-can be controlled by such time delay. These results are in agreement with multiple experimental observations and may enrich our understanding of the dynamics of the p53 network.

A cohort study on the association of MDM2 SNP309 with lung cancer risk in Bangladeshi population

BACKGROUND/AIMS

Bangladesh is a densely populated country with an increased incidence of lung cancer, mostly due to smoking. Therefore, elucidating the association of mouse double minute 2 homolog (MDM2) single nucleotide polymorphism (SNP) 309 (rs2279744) with lung cancer risk from smoking in Bangladeshi population has become necessary.

METHODS

DNA was extracted from blood samples of 126 lung cancer patient and 133 healthy controls. The MDM2 SNP309 was genotyped by polymerase chain reaction- restriction fragment length polymorphism (PCR-RFLP), using the restriction enzymes MspA1I. Logistic regression was then carried out to calculate odds ratios (ORs) and 95% confidence intervals (CIs) to estimate the risk of lung cancer. A meta-analysis of SNP309 was also carried out on 12,758 control subjects and 11,638 patient subjects.

RESULTS

In multivariate logistic regression, significantly increased risk of lung cancer was observed for MDM2 SNP309 in the dominant model (TG + GG vs. TT: OR, 2.13; 95% CI, 1.29 to 3.53). Stratification analysis revealed that age, sex, obesity, and smoking also increases the risk of lung cancer when carrying the MDM2 SNP309. Our meta-analysis revealed that MDM2 SNP309 was considerably associated with lung cancer in Asian populations (TG + GG vs. TT: OR, 1.32; 95% CI , 1.12 to 1.56; p = 0.019 for heterogeneity).

CONCLUSION

The MDM2 SNP309 was associated with high risk of lung cancer in Bangladeshi and Asian population, particularly with increased age, smoking, and body mass index.

A comprehensive evaluation of single nucleotide polymorphisms associated with hepatocellular carcinoma risk in Asian populations: A systematic review and network meta-analysis

BACKGROUND

Single nucleotide polymorphisms (SNPs) have been inconsistently associated with hepatocellular carcinoma (HCC) risk. This meta-analysis aimed to synthesize relevant data on SNPs associated with HCC in the Asian population.

METHODS

Databases were searched to identify association studies of SNPs and HCC in Asians published through January 2019. Summary odds ratios (ORs) and 95% confidence intervals (CIs) were calculated based on 41 studies (13,167 patients with HCC and 15,886 noncancer controls). Network meta-analysis and Thakkinstian's algorithm were used to select the most appropriate genetic model, along with false positive report probability (FPRP) for noteworthy associations.

RESULTS

Eleven SNPs meeting the inclusion criteria were tested for association with HCC, including CCND1 rs9344, PTGS2 rs689466, IL18 rs187238 and rs1946518, KIF1B rs17401966, MDM2 rs2279744, MIR146A rs2910164, MIR149 rs2292832, MIR196A2 rs11614913, MIR499A rs3746444, and TGFB1 rs1800469. A significant increase for HCC risk was observed for MDM2 rs2279744, and the dominant (pooled OR = 1.59, 95% CI: 1.26-2.00) and codominant (pooled OR = 1.37, 95% CI: 1.18-1.60) models were determined to be the most appropriate models. MIR499A rs3746444 also showed a significant association with HCC risk under the allele contrast model (pooled OR = 1.36, 95% CI: 1.05-1.77). Only the significance of MDM2 rs2279744 was noteworthy (FPRP < 0.2).

CONCLUSIONS

MDM2 rs2279744 is associated with HCC susceptibility in Asians, and the dominant and codominant models are likely the most appropriate models to estimate HCC risk.

Oscillation induced by Hopf bifurcation in the p53-Mdm2 feedback module

This study develops an integrated model of the p53-Mdm2 interaction composed of five basic components and time delay in the DNA damage response based on the existing research work. Some critical factors, including time delay, system parameters, and their interactions in the p53-Mdm2 system are investigated to examine their effects on the oscillatory behaviour induced by Hopf bifurcation. It is shown that the positive feedback formed between p53 and the activity of Mdm2 in the cytoplasm can cause a slight decrease in the amplitude of the p53 oscillation. The length of the time delay plays an important role in determining the amplitude and period of the oscillation and can significantly extend the parameter range for the system to demonstrate oscillatory behaviour. The numerical simulation results are found to be in good agreement with the published experimental observation. It is expected that the results of this research would be helpful to better understand the biological functions of p53 pathway and provide some clues in the treatment of cancer.

Oscillatory Dynamics of p53 Genetic Network Induced by Feedback Loops and Time Delays

DNA damage caused by γ -irradiation initiates oscillatory expression of the p53 genetic network. Although many studies revealed the effects of the p53-Mdm2 circuit on p53 dynamics, a few studies explored the contribution of upstream kinases to p53 oscillation. In this paper, an integrated mathematical model of the p53 network in response to γ -irradiation is studied, which consists of five basic components, two ubiquitous time delays, and two negative feedback loops. It is found that recurrent p53 pulses are externally initiated by ataxia telangiectasia mutated (ATM), and the negative feedback loop formed between ATM and p53, via Wip1, plays a dominant role in generating p53 oscillation. In addition, p53 oscillation requires not only an appropriate Mdm2 negative strength but also a threshold level of Wip1 negative strength. Furthermore, the time delays required for transcription and translation of Mdm2 and Wip1 proteins are essential for p53 oscillation. In particular, the critical value of time delay for inducing oscillation and the properties of delay-driven Hopf bifurcation are theoretically analyzed. As expected, the results are clearly in consistence with biological experiments and observations.

Roles of cellular heterogeneity, intrinsic and extrinsic noise in variability of p53 oscillation

The p53 protein is a key mediator of the cellular response to various stress signals. In response to DNA damage, the concentration of p53 can temporally oscillate with fluctuations in both the amplitude and period. The underlying mechanism for p53 variability is not fully understood. Here, we construct a core regulatory network of p53 dynamics comprising the ATM-p53-Wip1 and p53-Mdm2 negative feedback loops. We dissect the contributions of cellular heterogeneity, intrinsic noise, and multiple forms of extrinsic noise to p53 variability in terms of the coefficients of variation of four quantities. Cellular heterogeneity greatly determines the fraction of oscillating cells among a population of isogenic cells. Intrinsic noise-fluctuation in biochemical reactions-has little impact on p53 variability given large amounts of molecules, whereas extrinsic colored noise with proper strength and correlation time contributes much to oscillatory variability in individual cells. With the three sources of noise combined, our results reproduce the experimental observations, suggesting that the long correlation time of colored noise is essential to p53 variability. Compared with previous studies, the current work reveals both the individual and integrated effects of distinct noise sources on p53 variability. This study provides a framework for exploring the variability in oscillations in cellular signaling pathways.

MicroRNA-504 modulates osteosarcoma cell chemoresistance to cisplatin by targeting p53

Chemoresistance implicates the therapeutic value of cisplatin and remains a primary obstacle to its clinical use. MicroRNAs (miRs) negatively modulate the expression of their target genes and are associated with the occurrence and progression of various types of tumor. The abnormal expression of miR-504 has been reported in certain types of human tumor and has been associated with tumor prognosis. However, the association between miR-504 and cisplatin in human osteosarcoma remains unclear. The present study therefore aimed to assess the in vitro effects and possible mechanism of miR-504 in cell proliferation, apoptosis and cisplatin resistance in MG63 osteosarcoma cells. The results demonstrated that miR-504 was overexpressed in osteosarcoma tissues and cells. This overexpression also induced cell proliferation, as determined by MTT and EdU staining assays. Furthermore, miR-504 suppressed cisplatin-induced apoptosis, which was demonstrated via MTT, cell morphology analysis and flow cytometry. Cisplatin-induced G₁ arrest was also suppressed, which was determined by flow cytometry. The potential target genes of miR-504 were predicted using bioinformatics. p53 was confirmed to be a direct target of miR-504 using a luciferase reporter assay and western blot analysis revealed that miR-504 negatively regulated p53 expression at a molecular level. These results indicate that miR-504 contributes to cisplatin resistance in MG63 osteosarcoma cells by suppressing p53. miR-504 may therefore be a potential biomarker for cisplatin resistance in patients with osteosarcoma.

Estrogen-activated MDM2 disrupts mammary tissue architecture through a p53-independent pathway

The Cancer Genome Atlas (TCGA) data indicate that high MDM2 expression correlates with all subtypes of breast cancer. Overexpression of MDM2 drives breast oncogenesis in the presence of wild-type or mutant p53 (mtp53). Importantly, estrogen-receptor positive (ER+) breast cancers overexpress MDM2 and estrogen mediates this expression. We previously demonstrated that this estrogen-MDM2 axis activates the proliferation of breast cancer cell lines T47D (mtp53 L194F) and MCF7 (wild-type p53) in a manner independent of increased degradation of wild-type p53 (ie, p53-independently). Herein we present data supporting the role of the estrogen-MDM2 axis in regulating cell proliferation and mammary tissue architecture of MCF7 and T47D cells in a p53-independent manner. Inducible shRNA mediated MDM2 knockdown inhibited colony formation in soft agar, decreased mass size and induced lumen formation in matrigel and also significantly reduced mitosis as seen by decreased phospho-histone H3 positive cells. The knockdown of MDM2 in both cell lines decreased Rb phosphorylation and the level of E2F1 protein. This signaling was through the estrogen receptor because fulvestrant (a selective estrogen receptor degrader) decreased MDM2 protein levels and decreased phosphorylation of Rb. Taken together these data indicate that in some ER+ breast cancers the estrogen-MDM2-Rb-E2F1 axis is a central hub for estrogen-mediated p53-independent signal transduction. This is the first indication that estrogen signaling utilizes the estrogen-MDM2 axis to provoke phosphorylation of Rb and increase E2F1 while promoting abnormal mammary architecture.

The Role of Oncogenic Tyrosine Kinase NPM-ALK in Genomic Instability

Genomic stability is crucial for cell life and transmitting genetic material is one of the primary tasks of the cell. The cell needs to be able to recognize any possible error and quickly repair it, and thus, cells have developed several mechanisms to detect DNA damage and promote repair during evolution. The DNA damage response (DDR) and DNA repair pathways ensure the control of possible errors that could impair the duplication of genetic information and introduce variants in the DNA. Endogenous and exogenous factors compromise genomic stability and cause dysregulation in the DDR and DNA repair pathways. Cancer cells often impair these mechanisms to overcome cellular barriers (cellular senescence and/or apoptosis), leading to malignancy. NPM (nucleophosmin)-ALK (anaplastic lymphoma kinase) is an oncogenic tyrosine kinase that is involved in the development of anaplastic large cell lymphoma (ALCL). NPM-ALK is known to be involved in the activation of proliferative and anti-apoptotic signaling pathways. New evidence reveals that NPM-ALK translocation also impairs the ability of cells to maintain the genomic stability through both DDR and DNA repair pathways. This review aims to highlight the role of the oncogenic tyrosine kinase NPM-ALK in the cell, and pointing to new possible therapeutic strategies.

Understanding non-linear effects from Hill-type dynamics with application to decoding of p53 signaling

Analytical equations are derived depicting four possible scenarios resulting from pulsed signaling of a system subject to Hill-type dynamics. Pulsed Hill-type dynamics involves the binding of multiple signal molecules to a receptor and occurs e.g., when transcription factor p53 orchestrates cancer prevention, during calcium signaling, and during circadian rhythms. The scenarios involve: (i) enhancement of high-affinity binders compared to low-affinity ones, (ii) slowing reactions involving high-affinity binders, (iii) transfer of the clocking of low-affinity binders from the signal molecule to the products, and (iv) a unique clocking process that produces incremental increases in the activity of high-affinity binders with each signal pulse. In principle, these mostly non-linear effects could control cellular outcomes. An applications to p53 signaling is developed, with binding to most gene promoters identified as category (iii) responses. However, currently unexplained enhancement of high-affinity promoters such as CDKN1a (p21) by pulsed signaling could be an example of (i). In general, provision for all possible scenarios is required in the design of mathematical models incorporating pulsed Hill-type signaling as some aspect.

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.

MDM2 promoter SNP55 (rs2870820) affects risk of colon cancer but not breast-, lung-, or prostate cancer

Two functional SNPs (SNP285G > C; rs117039649 and SNP309T > G; rs2279744) have previously been reported to modulate Sp1 transcription factor binding to the promoter of the proto-oncogene MDM2, and to influence cancer risk. Recently, a third SNP (SNP55C > T; rs2870820) was also reported to affect Sp1 binding and MDM2 transcription. In this large population based case-control study, we genotyped MDM2 SNP55 in 10,779 Caucasian individuals, previously genotyped for SNP309 and SNP285, including cases of colon (n = 1,524), lung (n = 1,323), breast (n = 1,709) and prostate cancer (n = 2,488) and 3,735 non-cancer controls, as well as 299 healthy African-Americans. Applying the dominant model, we found an elevated risk of colon cancer among individuals harbouring SNP55TT/CT genotypes compared to the SNP55CC genotype (OR = 1.15; 95% CI = 1.01-1.30). The risk was found to be highest for left-sided colon cancer (OR = 1.21; 95% CI = 1.00-1.45) and among females (OR = 1.32; 95% CI = 1.01-1.74). Assessing combined genotypes, we found the highest risk of colon cancer among individuals harbouring the SNP55TT or CT together with the SNP309TG genotype (OR = 1.21; 95% CI = 1.00-1.46). Supporting the conclusions from the risk estimates, we found colon cancer cases carrying the SNP55TT/CT genotypes to be diagnosed at younger age as compared to SNP55CC (p = 0.053), in particular among patients carrying the SNP309TG/TT genotypes (p = 0.009).

The Role of MDM2 Amplification and Overexpression in Tumorigenesis

Mouse double minute 2 (MDM2) is a critical negative regulator of the tumor suppressor p53, playing a key role in controlling its transcriptional activity, protein stability, and nuclear localization. MDM2 expression is up-regulated in numerous cancers, resulting in a loss of p53-dependent activities, such as apoptosis and cell-cycle arrest. Genetic amplification and inheritance of MDM2 promoter single-nucleotide polymorphisms (SNPs) are the two best-studied mechanisms for up-regulating MDM2 activity. This article provides an overview of these events in human cancer, highlighting the frequent occurrence of MDM2 amplification in sarcoma and the role of SNP309 and SNP285 in regulating MDM2 expression and cancer risk. The availability of large-scale genomic profiling datasets, like those from The Cancer Genome Atlas Research Network, have provided the opportunity to evaluate the consequences of MDM2 amplification and SNP inheritance across high-quality tumor samples from diverse cancer indications.

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.

Assessment of functional tag single nucleotide polymorphisms within the DRD2 gene as risk factors for post-traumatic stress disorder in the Han Chinese population

BACKGROUND

Gene variations related to the dopaminergic pathway have been implicated in a number of neuropsychiatric disorders, including post-traumatic stress disorder (PTSD). Dopamine D2 receptor (DRD2) has been shown to significantly contribute to neuropsychiatric disorders and may specifically contribute to predisposition to PTSD. This study aimed to evaluate the association of polymorphisms within the entire DRD2 gene with PTSD in a case-control study.

MATERIALS AND METHODS

A total of 834 unrelated Han Chinese adults, including 497 healthy volunteers and 337 patients with PTSD, were used in this study. Fifteen tag single-nucleotide polymorphisms (tSNPs) were selected spanning the entire DRD2 gene through the construction of haplotype bins. Genotypes were gathered using an improved multiplex ligation detection reaction (iMLDR) technique. Allelic frequencies and clinical characteristics were compared in two independent Han Chinese populations. Moreover, the functionality of the rs2075652 and rs7131056 polymorphisms were assessed by measuring transcriptional enhancer activities.

RESULTS

Fifteen tag SNPs were identified in the Han Chinese population and all were common SNPs. Among 15 tSNPs, two of them (rs2075652 and rs7131056) significantly associated with PTSD. PTSD individuals were more likely to carry the rs2075652A and rs7131056A allele compared to the controls (P<0.05). The haplotype GTGATCGCGCAGGCG, had a risk effect on PTSD occurrence (OR=1.75, 95% CI: 1.24-2.48, P=0.002). Additionally, the rs2075652 polymorphism contained intronic enhancer activities.

CONCLUSIONS

The rs2075652 and rs7131056 polymorphisms, and the haplotype GTGATCGCGCAGGCG within the DRD2 gene, may be potential markers to predict susceptibility to PTSD.

Bifurcation analysis and potential landscapes of the p53-Mdm2 module regulated by the co-activator programmed cell death 5

The dynamics of p53 play important roles in the regulation of cell fate decisions in response to various stresses, and programmed cell death 5 (PDCD5) functions as a co-activator of p53 that modulates p53 dynamics. In the present paper, we investigated how p53 dynamics are modulated by PDCD5 during the deoxyribose nucleic acid damage response using methods of bifurcation analysis and potential landscape. Our results revealed that p53 activities display rich dynamics under different PDCD5 levels, including monostability, bistability with two stable steady states, oscillations, and the coexistence of a stable steady state (or two states) and an oscillatory state. The physical properties of the p53 oscillations were further demonstrated by the potential landscape in which the potential force attracts the system state to the limit cycle attractor, and the curl flux force drives coherent oscillation along the cyclic trajectory. We also investigated the efficiency with which PDCD5 induced p53 oscillations. We show that Hopf bifurcation can be induced by increasing the PDCD5 efficiency and that the system dynamics exhibited clear transition features in both barrier height and energy dissipation when the efficiency was close to the bifurcation point.

The dynamic control of signal transduction networks in cancer cells

Cancer is often considered a genetic disease. However, much of the enormous plasticity of cancer cells to evolve different phenotypes, to adapt to challenging microenvironments and to withstand therapeutic assaults is encoded by the structure and spatiotemporal dynamics of signal transduction networks. In this Review, we discuss recent concepts concerning how the rich signalling dynamics afforded by these networks are regulated and how they impinge on cancer cell proliferation, survival, invasiveness and drug resistance. Understanding this dynamic circuitry by mathematical modelling could pave the way to new therapeutic approaches and personalized treatments.

Impact of the Mdm2(SNP309-G) allele on a murine model of colorectal cancer

A single-nucleotide polymorphism (SNP) in the promoter of the Mdm2 gene (Mdm2(SNP309-G)) results in an increased Mdm2 expression, partial attenuation of the p53 pathway and accelerated tumor development. Clinical case-control studies indicate the Mdm2(SNP309-)(G) allele associates with a significant increase in colorectal cancer (CRC) risk that is heightened in women, but the biological significance of this polymorphism has never been directly evaluated. To examine whether the Mdm2(SNP309-)(G) allele contributes to colorectal cancer, we generated cohorts of mice harboring either the G (minor allelic variant) or T (major allelic variant) allele and treated them with azoxymethane (AOM), a carcinogen that induces sporadic colorectal cancer. Mdm2(SNP309-G/G) mice displayed a significant reduction in survival following AOM treatment with more colonic lesions in a wider distribution throughout the lower and upper colon and an attenuated apoptotic response following exposure. AOM did not significantly induce stabilization of wild-type p53 or activate p53 downstream targets following AOM treatment, regardless of the genotype. Instead, Mdm2(SNP309-G/G) colons had significant changes in the expression of genes that regulate Mdm2 transcription (ERα and Sp1) as well as downstream targets of Mdm2. Together these results suggest the Mdm2(SNP309-)(G) allele significantly impacts CRC through mechanisms outside the p53 pathway.

LIF negatively regulates tumour-suppressor p53 through Stat3/ID1/MDM2 in colorectal cancers

Leukemia inhibitory factor (LIF) has been recently identified as a p53 target gene, which mediates the role of p53 in maternal implantation under normal physiological conditions. Here, we report that LIF is a negative regulator of p53; LIF downregulates p53 protein levels and function in human colorectal cancer (CRC) cells. The downregulation of p53 by LIF is mediated by the activation of Stat3, which transcriptionally induces ID1. ID1 upregulates MDM2, a key negative regulator of p53, and promotes p53 protein degradation. LIF is overexpressed in a large percentage of CRCs. LIF overexpression promotes cellular resistance towards chemotherapeutic agents in cultured CRC cells and colorectal xenograft tumors in a largely p53-dependent manner. Overexpression of LIF is associated with a poor prognosis in CRC patients. Taken together, LIF is a novel negative regulator of p53, overexpression of LIF is an important mechanism for the attenuation of p53, which promotes chemoresistance in CRCs.

TP53 and MDM2 polymorphisms and the risk of endometrial cancer in postmenopausal women

The aim of the study was to determine an association of TP53 codon 72 (Arg72Pro, G>C transversion, rs1042522) and MDM2 SNP309 (T>G change, rs2279744) polymorphisms in endometrial cancer (EC) of postmenopausal women, regarding grading and staging of EC. In the study, endometrial samples from 202 postmenopausal female patients (the study group, n = 152, was women with EC; the control group, n = 50, cancer-free patients) were taken for the evaluation of two gene polymorphisms: TP53 codon 72 and MDM2 SNP309, respectively. Genotypic analyses were performed using the PCR-RFLP technique. There were significant differences in the frequency of TP53 and MDM2 genotypes in EC patients-increased EC occurrence was observed with the presence of MDM2 G/G and TP53 Arg/Arg genotypes, while allele Pro of TP53 decreased cancer risk. Analysis of combined MDM2/TP53 polymorphisms revealed that T/T-Pro/Arg genotype decreased EC risk, whereas G/G-Arg/Arg genotype increased it. Association of these genetic polymorphisms with histological grading showed increased MDM2 G/G homozygote and TP53 Arg/Arg homozygote frequencies in grading 2 as well as allele G overrepresentation in G1 and G3 EC patients. Finally, with clinical FIGO staging under evaluation, an increase in MDM2 G/G and TP53 Arg/Arg homozygote frequencies in staging I and TP53 Arg/Arg homozygote frequencies in staging II were observed. Co-occurrence of some MDM2 SNP309 and TP53 codon 72 polymorphisms seems to influence EC risk, involving grading and staging of this neoplasm at the same time.

Effects of MDM2 promoter polymorphisms on the development of cervical neoplasia in a Southeastern Brazilian population

We investigated the importance of two adjacent functional polymorphisms in the Murine Double Minute 2 (MDM2) gene, SNP285 G > C and SNP309 T > G, for the development of cervical lesions in a Southeastern Brazilian population (293 cases and 184 controls). MDM2 genotyping was performed by PCR-RFLP (Polymerase Chain Reaction-Restriction Fragment Length Polymorphism) and/or DNA sequencing. MDM2 SNP309 has potential as a biomarker of cervical neoplasia in non-smokers, patients with family history of cancer, or those who had late sexual debut (>16 years). Besides, this polymorphism may help identify women at risk of developing severe cervical lesion at a young age (<30 years).

ESR1 rs9340799 is associated with endometriosis-related infertility and in vitro fertilization failure

Estrogen receptor alpha has a central role in human fertility by regulating estrogen action in all human reproductive tissues. Leukemia inhibitory factor (LIF) expression, a cytokine critical for blastocyst implantation, is mediated by estrogen signaling, so we hypothesized that ESR1 gene polymorphisms might be candidate risk markers for endometriosis-related infertility and in vitro fertilization (IVF) failure. We included 98 infertile women with endometriosis, 115 infertile women with at least one IVF failure and also 134 fertile women as controls. TaqMan SNP assays were used for genotyping LIF (rs929271), MDM2 (rs2279744), MDM4 (rs1563828), USP7 (rs1529916), and ESR1 (rs9340799 and rs2234693) polymorphisms. The SNP ESR1 rs9340799 was associated with endometriosis-related infertility (P < 0.001) and also with IVF failure (P = 0.018). After controlling for age, infertile women with ESR1 rs9340799 GG genotype presented 4-fold increased risk of endometriosis (OR 4.67, 95% CI 1.84–11.83, P = 0.001) and 3-fold increased risk of IVF failure (OR 3.33, 95% CI 1.38–8.03, P = 0.007). Our results demonstrate an association between ESR1 rs9340799 polymorphism and infertile women with endometriosis and also with women who were submitted to IVF procedures and had no blastocyst implantation.

The identification of an ESCC susceptibility SNP rs920778 that regulates the expression of lncRNA HOTAIR via a novel intronic enhancer

Long noncoding RNA (lncRNA) HOX transcript antisense RNA (HOTAIR), which could induce genome-wide retargeting of polycomb-repressive complex 2, trimethylates histone H3 lysine-27 (H3K27me3) and deregulation of multiple downstream genes, is involved in development and progression of esophageal squamous cell carcinoma (ESCC). We hypothesized that the functional single nucleotide polymorphisms (SNP) in HOTAIR may affect HOTAIR expression and/or its function and, thus, ESCC risk. Therefore, we examined the association between three haplotype-tagging SNPs (htSNP) across the whole HOTAIR locus and ESCC risk as well as the functional relevance of an ESCC susceptibility SNP rs920778. Genotypes were determined in three independent case-control sets consisted of 2098 ESCC patients and 2150 controls. The allele-specific regulation on HOTAIR expression by the rs920778 SNP was investigated in vitro and in vivo. We found that the HOTAIR rs920778 TT carriers had a 1.37-fold, 1.78-fold and 2.08-fold increased ESCC risk in Jinan, Shijiazhuang and Huaian populations, respectively, compared with the CC carriers (P = 0.003, 7.7 × 10(-4) and 5.9 × 10(-4)). During inspecting functional relevance of the rs920778 SNP, we identified a novel intronic HOTAIR enhancer locating between +1719bp and +2353bp from the transcriptional start site through reporter assays. Moreover, there is an allelic regulation of rs920778 on HOTAIR expression via this enhancer in both ESCC cell lines and normal esophageal tissue specimens, with higher HOTAIR expression among T allele carriers. These results demonstrate that functional genetic variants influencing lncRNA regulation may explain a fraction of ESCC genetic basis.

Fulvestrant treatment alters MDM2 protein turnover and sensitivity of human breast carcinoma cells to chemotherapeutic drugs

The human homologue of mouse double minute 2 (MDM2) is overexpressed in tumors and contributes to tumorigenesis through inhibition of p53 activity. We investigated the effect of the anti-estrogen fulvestrant on MDM2 expression and sensitivity of estrogen receptor positive human breast cancer cell lines to chemotherapeutics. Fulvestrant down-regulated MDM2 through increased protein turnover. Fulvestrant blocked estrogen-dependent up-regulation of MDM2 and decreased basal expression of MDM2 in the absence of estradiol. As combinations of fulvestrant with doxorubicin, etoposide or paclitaxel were synergistic, altering cell cycle distribution and increasing cell death, this provides rationale for testing combinatorial chemotherapy with fulvestrant as a novel therapeutic strategy for patients with advanced breast cancer.

Correlation between oncogenic mutations and parameter sensitivity of the apoptosis pathway model

One of the major breakthroughs in oncogenesis research in recent years is the discovery that, in most patients, oncogenic mutations are concentrated in a few core biological functional pathways. This discovery indicates that oncogenic mechanisms are highly related to the dynamics of biologic regulatory networks, which govern the behaviour of functional pathways. Here, we propose that oncogenic mutations found in different biological functional pathways are closely related to parameter sensitivity of the corresponding networks. To test this hypothesis, we focus on the DNA damage-induced apoptotic pathway—the most important safeguard against oncogenesis. We first built the regulatory network that governs the apoptosis pathway, and then translated the network into dynamics equations. Using sensitivity analysis of the network parameters and comparing the results with cancer gene mutation spectra, we found that parameters that significantly affect the bifurcation point correspond to high-frequency oncogenic mutations. This result shows that the position of the bifurcation point is a better measure of the functionality of a biological network than gene expression levels of certain key proteins. It further demonstrates the suitability of applying systems-level analysis to biological networks as opposed to studying genes or proteins in isolation.

Among complex genetic diseases affecting humans, cancer is a major cause of death. In 2008, a genome-wide analysis of hundreds of tumour samples showed that oncogenic mutations are concentrated in a few core functional pathways, revealing a new conceptual framework for cancer biology research, where the role of oncogenic mutations and oncogenic mechanisms are addressed from a network perspective. We therefore propose a new way of identifying high-frequency gene mutations in cancer: gene mutations may affect their corresponding proteins' activity in the biological regulatory network and can be considered as perturbations of the dynamical system. Therefore, mutations that induce qualitative changes in biological networks should correspond to high-frequency mutations in cancer. This concept can help us identify and understand the function of genes that play an important role in oncogenesis, thereby allowing targeted and effective design of gene-based therapy in cancer.

The p53 response in single cells is linearly correlated to the number of DNA breaks without a distinct threshold

BACKGROUND

The tumor suppressor protein p53 is activated by cellular stress. DNA double strand breaks (DSBs) induce the activation of the kinase ATM, which stabilizes p53 and activates its transcriptional activity. Single cell analysis revealed that DSBs induced by gamma irradiation trigger p53 accumulation in a series of pulses that vary in number from cell to cell. Higher levels of irradiation increase the number of p53 pulses suggesting that they arise from periodic examination of the damage by ATM. If damage persists, additional pulses of p53 are triggered. The threshold of damage required for activating a p53 pulse is unclear. Previous studies that averaged the response across cell populations suggested that one or two DNA breaks are sufficient for activating ATM and p53. However, it is possible that by averaging over a population of cells important features of the dependency between DNA breaks and p53 dynamics are missed.

RESULTS

Using fluorescent reporters we developed a system for following in individual cells the number of DSBs, the kinetics of repair and the p53 response. We found a large variation in the initial number of DSBs and the rate of repair between individual cells. Cells with higher number of DSBs had higher probability of showing a p53 pulse. However, there was no distinct threshold number of breaks for inducing a p53 pulse. We present evidence that the decision to activate p53 given a specific number of breaks is not entirely stochastic, but instead is influenced by both cell-intrinsic factors and previous exposure to DNA damage. We also show that the natural variations in the initial amount of p53, rate of DSB repair and cell cycle phase do not affect the probability of activating p53 in response to DNA damage.

CONCLUSIONS

The use of fluorescent reporters to quantify DNA damage and p53 levels in live cells provided a quantitative analysis of the complex interrelationships between both processes. Our study shows that p53 activation differs even between cells that have a similar number of DNA breaks. Understanding the origin and consequences of such variability in normal and cancerous cells is crucial for developing efficient and selective therapeutic interventions.

An updated meta-analysis on the association of MDM2 SNP309 polymorphism with colorectal cancer risk

BACKGROUND

The mouse double minute 2 (MDM2) gene encodes a phosphoprotein that interacts with P53 and negatively regulates its activity. The SNP309 polymorphism (T-G) in the promoter of MDM2 gene has been reported to be associated with enhanced MDM2 expression and tumor development. Studies investigating the association between MDM2 SNP309 polymorphism and colorectal cancer (CRC) risk reported conflicting results. We performed a meta-analysis of all available studies to explore the association of this polymorphism with CRC risk.

METHODS

All studies published up to July 2013 on the association between MDM2 SNP309 polymorphism and CRC risk were identified by searching electronic databases PubMed, EMBASE, and Chinese Biomedical Literature database (CBM) databases. The association between the MDM2 SNP309 polymorphism and CRC risk was assessed by odds ratios (ORs) together with their 95% confidence intervals (CIs).

RESULTS

A total of 14 case-control studies including 4460 CRC cases and 4828 controls were identified. We did not find a significant association between the MDM2 SNP309 polymorphism and CRC risk in all genetic models in overall population. However, in subgroup analysis by ethnicity, significant associations were found in Asians (TG vs. TT: OR = 1.197, 95% CI = 1.055-1.358, P=0.005; GG+TG vs. TT: OR = 1.246, 95% CI = 1.106-1.404, P=0.000) and Africans. When stratified by HWE in controls, significantly increased risk was also found among the studies consistent with HWE (TG vs. TT: OR = 1.166, 95% CI = 1.037-1.311, P= 0.010). In subgroup analysis according to p53 mutation status, and gender, no any significant association was detected.

CONCLUSIONS

The present meta-analysis suggests that the MDM2 is a candidate gene for CRC susceptibility. The MDM2 SNP309 polymorphism may be a risk factor for CRC in Asians.

MDM2 phenotypic and genotypic profiling, respective to TP53 genetic status, in diffuse large B-cell lymphoma patients treated with rituximab-CHOP immunochemotherapy: a report from the International DLBCL Rituximab-CHOP Consortium Program

MDM2 is a key negative regulator of the tumor suppressor p53, however, the prognostic significance of MDM2 overexpression in diffuse large B-cell lymphoma (DLBCL) has not been defined convincingly. In a p53 genetically-defined large cohort of de novo DLBCL patients treated with rituximab, cyclophosphamide, hydroxydaunorubicin, vincristine, and prednisone (R-CHOP) chemotherapy, we assessed MDM2 and p53 expression by immunohistochemistry (n = 478), MDM2 gene amplification by fluorescence in situ hybridization (n = 364), and a single nucleotide polymorphism in the MDM2 promoter, SNP309, by SNP genotyping assay (n = 108). Our results show that MDM2 overexpression, unlike p53 overexpression, is not a significant prognostic factor in overall DLBCL. Both MDM2 and p53 overexpression do not predict for an adverse clinical outcome in patients with wild-type p53 but predicts for significantly poorer survival in patients with mutated p53. Variable p53 activities may ultimately determine the survival differences, as suggested by the gene expression profiling analysis. MDM2 amplification was observed in 3 of 364 (0.8%) patients with high MDM2 expression. The presence of SNP309 did not correlate with MDM2 expression and survival. This study indicates that evaluation of MDM2 and p53 expression correlating with TP53 genetic status is essential to assess their prognostic significance and is important for designing therapeutic strategies that target the MDM2-p53 interaction.

Mechanisms that enhance sustainability of p53 pulses

The tumor suppressor p53 protein shows various dynamic responses depending on the types and extent of cellular stresses. In particular, in response to DNA damage induced by γ-irradiation, cells generate a series of p53 pulses. Recent research has shown the importance of sustaining repeated p53 pulses for recovery from DNA damage. However, far too little attention has been paid to understanding how cells can sustain p53 pulses given the complexities of genetic heterogeneity and intrinsic noise. Here, we explore potential molecular mechanisms that enhance the sustainability of p53 pulses by developing a new mathematical model of the p53 regulatory system. This model can reproduce many experimental results that describe the dynamics of p53 pulses. By simulating the model both deterministically and stochastically, we found three potential mechanisms that improve the sustainability of p53 pulses: 1) the recently identified positive feedback loop between p53 and Rorα allows cells to sustain p53 pulses with high amplitude over a wide range of conditions, 2) intrinsic noise can often prevent the dampening of p53 pulses even after mutations, and 3) coupling of p53 pulses in neighboring cells via cytochrome-c significantly reduces the chance of failure in sustaining p53 pulses in the presence of heterogeneity among cells. Finally, in light of these results, we propose testable experiments that can reveal important mechanisms underlying p53 dynamics.

Stochastic and Deterministic Models of Cellular p53 Regulation

The protein p53 is a key regulator of cellular response to a wide variety of stressors. In cancer cells inhibitory regulators of p53 such as MDM2 and MDMX proteins are often overexpressed. We apply in silico techniques to better understand the role and interactions of these proteins in a cell cycle process. Furthermore we investigate the role of stochasticity in determining system behavior. We have found that stochasticity is able to affect system behavior profoundly. We also derive a general result for the way in which initially synchronized oscillating stochastic systems will fall out of synchronization with each other.

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.

TP53*P72 allele influences negatively female life expectancy in a population of central Italy: cross-sectional study and genetic-demographic approach analysis

The association of TP53 P72R (rs1042522) with longevity remains uncertain and varies with ethnicity. Here, we tested its association with longevity in a cross-sectional population of Central Italy (18-106 years, N = 1,072), by integrating demographic information and frequency data to account for the different survival rates between sexes through the application of a genetic-demographic approach. rs1042522 affects females longevity, showing significant associations in Comparison 2 (Age Class 3 [>91 years] vs Age Class 2 [73-91 years]) under both additive (odds ratio [OR] 0.574; p = .006) and dominant (OR 0.513; p = .006) models. The TP53*P72 allele is significantly underrepresented in Age Class 3 only in women (OR 0.575; p = .008). The genetic-demographic approach demonstrated that the frequency of female TP53*P72 carriers underwent a significant reduction after 82 years (OR 0.586; p = .002). The same analyses gave nonsignificant results in men. The discrepancies among the results obtained on rs1042522 for longevity could result from the pleiotropic effects of p53 and the potential ethnic variation of its functional variants.

Murine double minute 2 promoter SNP309 polymorphism and prostate cancer risk: a meta-analysis

OBJECTIVE

The murine double minute 2 gene encodes a negative regulator of the tumor protein p53. A single nucleotide polymorphism in murine double minute 2 promoter, SNP309 T>G, has been reported to alter murine double minute 2 protein expression and to accelerate tumor formation in humans. We carried out a meta-analysis to explore the association between this polymorphism and prostate cancer risk.

METHODS

All eligible studies were searched in PubMed. Crude odds ratios, with 95% confidence intervals, were assessed for the association using fixed- and random-effects models.

RESULTS

Overall, five case-control studies (872 cases, 1005 controls) were included in the meta-analysis. A significant association between murine double minute 2 SNP309 and prostate cancer risk was observed for homozygote genetic model GG versus TT (odds ratio 0.72, 95% confidence interval 0.55-0.95, P < 0.05, P = 0.130 for heterogeneity), and for dominant model TG + GG versus TT (odds ratio 0.79, 95% confidence interval 0.65-0.96, P < 0.05, P = 0.119 for heterogeneity). The stratified analysis based on ethnicity showed a significant effect of the polymorphism on prostate cancer risk in Caucasians for GG versus TT.

CONCLUSIONS

Findings of the present meta-analysis suggest that the murine double minute 2 309 G allele might be associated with a reduced risk of prostate cancer. The effect of murine double minute 2 309 G allele on tumorigenesis might be influenced by sex and hormonal status.

p53 dynamics control cell fate

Cells transmit information through molecular signals that often show complex dynamical patterns. The dynamic behavior of the tumor suppressor p53 varies depending on the stimulus; in response to double-strand DNA breaks, it shows a series of repeated pulses. Using a computational model, we identified a sequence of precisely timed drug additions that alter p53 pulses to instead produce a sustained p53 response. This leads to the expression of a different set of downstream genes and also alters cell fate: Cells that experience p53 pulses recover from DNA damage, whereas cells exposed to sustained p53 signaling frequently undergo senescence. Our results show that protein dynamics can be an important part of a signal, directly influencing cellular fate decisions.

The MDM2 SNP309 G allele is not preferentially amplified in bone and soft tissue tumors

The transcriptional enhancer region in intron 1 of the proto-oncogene MDM2 contains a polymorphic site (SNP309) that may harbor a G or a T nucleotide. Previous studies have shown that the G allele confers a higher affinity for the Sp1 transcription factor, resulting in an increased transcriptional activity of MDM2. A constitutional G allele has also been associated with earlier onset of various cancer types, and studies of sarcomas have shown an enrichment of the G allele in tumors with MDM2 amplification, notably atypical lipomatous tumor (also known as well-differentiated liposarcoma). In the present study, we analyzed the SNP309 genotype in blood samples and tumor tissue from 57 patients with bone or soft tissue tumors showing amplification of MDM2. We did not observe any constitutional enrichment of the G allele. More importantly, there was no preferential amplification of the G allele in tumor tissue from TG heterozygotes. The expression levels of MDM2 messenger RNA were not higher in tumors with amplification of the G allele than in tumors with amplification of the T allele. Thus, we could not find any evidence for a selective advantage of the SNP309 G allele in bone and soft tissue tumors with MDM2 amplification.

Identification of functional DNA variants in the constitutive promoter region of MDM2

Although mutations in the oncoprotein murine double minute 2 (MDM2) are rare, MDM2 gene overexpression has been observed in several human tumors. Given that even modest changes in MDM2 levels might influence the p53 tumor suppressor signaling pathway, we postulated that sequence variation in the promoter region of MDM2 could lead to disregulated expression and variation in gene dosage. Two promoters have been reported for MDM2; an internal promoter (P2), which is located near the end of intron 1 and is p53-responsive, and an upstream constitutive promoter (P1), which is p53-independent. Both promoter regions contain DNA variants that could influence the expression levels of MDM2, including the well-studied single nucleotide polymorphism (SNP) SNP309, which is located in the promoter P2; i.e., upstream of exon 2. In this report, we screened the promoter P1 for DNA variants and assessed the functional impact of the corresponding SNPs. Using the dbSNP database and genotyping validation in individuals of European descent, we identified three common SNPs (-1494 G > A; indel 40 bp; and -182 C > G). Three major promoter haplotypes were inferred by using these three promoter SNPs together with rs2279744 (SNP309). Following subcloning into a gene reporter system, we found that two of the haplotypes significantly influenced MDM2 promoter activity in a haplotype-specific manner. Site-directed mutagenesis experiments indicated that the 40 bp insertion/deletion variation is causing the observed allelic promoter activity. This study suggests that part of the variability in the MDM2 expression levels could be explained by allelic p53-independent P1 promoter activity.

The risks, degree of malignancy and clinical progression of prostate cancer associated with the MDM2 T309G polymorphism: a meta-analysis

To determine the risk, malignant degree and clinical progression of prostate cancer (PCa) associated with mouse double-minute 2 protein (MDM2) T309G variants, a meta-analysis was performed on all eligible published studies. Odds ratios (ORs) with 95% confidence intervals (CIs) were estimated to assess these associations in seven studies that included 5151 cases and 1003 controls. In the overall analysis, the 309G allele was significantly associated with a decreased PCa risk (OR=0.85, 95% CI: 0.74-0.97); this was also the case for the homozygous comparison (OR=0.72, 95% CI: 0.55-0.95) and the dominant genetic model (OR=0.79, 95% CI: 0.65-0.96). The 309G allele was also found to be significantly associated with lower degrees of PCa malignancy (OR=0.85, 95% CI: 0.75-0.96) in the overall analysis, as well as in the heterozygous comparison (OR=0.79, 95% CI: 0.65-0.96), homozygous comparison (OR=0.76, 95% CI: 0.58-0.98) and dominant genetic model (OR=0.81, 95% CI: 0.68-0.96). Furthermore, grouping analysis showed that the 309G allele in Caucasians was significantly correlated with a decreased PCa risk (OR=0.77, 95% CI: 0.61-0.96); this was also the case in the homozygous comparison (OR=0.51, 95% CI: 0.31-0.86). The grouping analysis also showed that the 309G variant in Caucasians was significantly associated with a lower degree of PCa malignancy in all of the genetic models. In addition, we found that the 309G variant in Caucasians was significantly associated with a slower PCa clinical progression in all of the genetic models. In summary, our meta-analysis showed that the MDM2 309G variant was significantly associated with a decreased PCa risk, lower malignant degree and slower clinical progression in Caucasians, but there was no obvious association in the Asian population.

Interaction of OKL38 and p53 in regulating mitochondrial structure and function

The tumor suppressor p53 is a well-known transcription factor controlling the expression of its target genes involved in cell cycle and apoptosis. In addition, p53 also plays a direct proapoptotic role in mitochondria by regulating cytochrome c release. Recently, we identified a novel downstream target of p53, OKL38, which relocalizes from nucleus to mitochondria upon forced expression to induce apoptosis. However, the mechanism underlying OKL38 targeting to mitochondria and apoptosis induction remains unclear. Here, we found that OKL38 interacts with p53 to regulate mitochondria function. After DNA damage, OKL38 colocalizes with p53 to mitochondria in U2OS cells. Further, p53 and OKL38 are targeted to mitochondria in synergy: forced expression of OKL38 leads to p53 localization to mitochondria while the expression of a mitochondria enriched p53 polymorphic variant, p53^R72, leads to OKL38 enrichment in mitochondria. Biochemical analyses found that OKL38 and p53 interact in vivo and in vitro via multiple domains. In cell biological assays, multiple regions of OKL38 mediate its mitochondria localization and induce mitochondria morphology changes. OKL38 induces formation of megamitochondria and increases cellular levels of reactive oxygen species. Furthermore, OKL38 induces cytochrome c release upon incubation with mitochondria. Taken together, our studies suggest that OKL38 regulates mitochondria morphology and functions during apoptosis together with p53.

Association of MDM2 SNP309 variation with lung cancer risk: evidence from 7196 cases and 8456 controls

Background

Evidence suggests that MDM2 T309G polymorphism may be a risk factor for several cancers. Increasing investigations have been conducted on the association of MDM2 T309G polymorphisms with lung cancer risk and have yielded conflicting results. Previous meta-analyses on this issue have reported inconclusive data. The aim of the present study was to derive a more precise estimation of the relationship.

Methods and Findings

Updated meta-analyses examining the association between MDM2 T309G polymorphism and lung cancer risk were performed. Separate analyses on ethnicity, smoking status, histological types and gender as well as source of controls were also implemented. Eligible studies were identified for the period up to Feb 2012. Lastly, ten publications including eleven case-control studies were selected for analysis. The overall data failed to indicate a significant association between MDM2 T309G polymorphism and lung cancer risk (GG vs TT OR = 1.14; 95%CI = 0.95−1.37; dominant model: OR = 1.05; 95%CI = 0.92−1.19; recessive model: OR = 1.12; 95%CI = 0.99−1.27). In a subgroup analysis by smoking status, increased lung cancer risk was shown among never-smokers (GG vs TT: OR = 1.76; 95%CI = 1.36−2.29; dominant model: OR = 1.48; 95%CI = 1.22−1.81; recessive model: OR = 1.37; 95%CI = 1.11−1.69). In subgroup analysis by gender, elevated risk was presented among women under a recessive model (OR = 1.29; 95%CI = 1.04−1.59). In the subgroup analysis by ethnicity, histological types and source of controls, no marked associations were observed.

Conclusions

Compared to the previous meta-analyses, the results of this study confirmed that MDM2 T309G polymorphism might be a risk factor for lung cancer among never-smokers. However, the data failed to suggest a marked association between the G allele of MDM2 T309G and lung cancer risk among Asians. More interestingly, subgroup analysis by gender indicated that homozygous GG alleles might raise lung cancer risk among females.

Susceptibility to cervical cancer: an overview

Cervical cancer is the second most common cancer in females worldwide. It is well-established that Human Papillomavirus (HPV) infections play a critical role in the development of cervical cancer. However, a large number of women infected with oncogenic HPV types will never develop cervical cancer. Thus, there are several external environment and genetic factors involved in the progression of a precancerous lesion to invasive cancer. In this review article, we addressed possible susceptible phenotypes to cervical cancer, focusing on host genome and HPV DNA variability, multiple HPV infections, co-infection with other agents, circulating HPV DNA and lifestyle.

TAp63γ enhances nucleotide excision repair through transcriptional regulation of DNA repair genes

p63 and p73, two p53 family members, play crucial roles in development and tumor suppression. p63 and p73 have multiple isoforms, which have similar or distinct biological functions. Transactivation (TA) isoforms of p63 and p73 have high similarity with p53 and often have biological functions similar to p53. p53 plays an important role in nucleotide excision repair (NER) through transcriptional regulation of target genes involved in NER, including DDB2, XPC and GADD45. To investigate whether TAp63 and TAp73 play a similar role in NER, Saos2 cells with inducible expression of specific isoforms of TAp63 and TAp73, including TAp63α/β/γ and TAp73α/β/γ isoforms, were employed. Overexpression of TAp63γ significantly enhances NER of ultraviolet (UV)-induced DNA damage, including cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts, and enhances cell survival after UV irradiation in Soas2 cells. The enhancement of NER of UV-induced DNA damage by TAp63γ was also confirmed in H1299 cells with overexpression of TAp63γ. Consistently, knockdown of endogenous TAp63 decreases NER of UV-induced DNA damage in H1299 cells. TAp63α/β and TAp73α/β/γ isoforms do not have a clear effect on NER in Saos2 or H1299 cells. TAp63γ overexpression clearly induces the expression of DDB2, XPC and GADD45 at both RNA and protein levels. Furthermore, luciferase reporter assays show that TAp63γ transcriptionally activates DDB2, XPC and GADD45 genes through the regulation of the p53 binding elements in these genes. These results demonstrate that TAp63γ enhances NER to remove UV-induced DNA damage and maintain genomic stability through transcriptional induction of a set of NER proteins, which provides an additional important mechanism that contributes to the function of TAp63 in tumor suppression.

The Regulation of Aging and Longevity: A New and Complex Role of p53

p53 plays a critical role in tumor suppression. As a transcription factor, in response to stress signals, p53 regulates its target genes and initiates stress responses, including cell cycle arrest, apoptosis, and/or senescence, to exert its function in tumor suppression. Emerging evidence has suggested that p53 is also an important but complex player in the regulation of aging and longevity in worms, flies, mice, and humans. Whereas p53 accelerates the aging process and shortens life span in some contexts, p53 can also extend life span in some other contexts. Thus, p53 appears to regulate aging and longevity in a context-dependent manner. Here, the authors review some recent advances in the study of the role of p53 in the regulation of aging and longevity in both invertebrate and vertebrate models. Furthermore, they discuss the potential mechanisms by which p53 regulates aging and longevity, including the p53 regulation of insulin/TOR signaling, stem/progenitor cells, and reactive oxygen species.

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.

Effects of MDM2 promoter polymorphisms and p53 codon 72 polymorphism on risk and age at onset of squamous cell carcinoma of the head and neck

Both p53 tumor suppressor and murine double minute 2 (MDM2) oncoprotein are crucial in carcinogenesis. We hypothesized that MDM2 promoter single nucleotide polymorphisms (SNPs) SNP309 T > G, A2164G, and p53 codon 72 are associated with risk and age at onset of squamous cell carcinoma of head and neck (SCCHN). We genotyped these SNPs in a study of 1,083 Caucasian SCCHN cases and 1,090 cancer-free controls. Although none of these SNPs individually had a significant effect on risk of SCCHN, nor did their combined putative risk genotypes (i.e., MDM2 SNP309 GT + GG, 2164 AA, and p53 codon 72 CC), we found that individuals with two to three risk genotypes had significantly increased risk of non-oropharyngeal cancer (OR = 1.42; 95% CI = 1.07-1.88). This increased risk was more pronounced among young subjects, men, smokers, and drinkers. In addition, female patients carrying the MDM2 SNP309 GT and GG genotypes showed a 3-yr (56.7 yr) and 9-yr (51.2 yr) earlier age at onset of non-oropharyngeal cancer (P(trend) = 0.007), respectively, compared with those carrying the TT genotype (60.1 yr). The youngest age (42.5 yr) at onset of non-oropharyngeal cancer was observed in female patients with the combined MDM2 SNP309 GG and p53 codon 72 CC genotypes. The findings suggest that MDM2 SNP309, A2164G, and p53 codon 72 SNPs may collectively contribute to non-oropharyngeal cancer risk and that MDM2 SNP309 individually or in combination with p53 codon 72 may accelerate the development of non-oropharyngeal cancer in women. Further studies with large sample sizes are warranted to validate these results.