MDM2 promoter SNP285 and SNP309; phylogeny and impact on cancer risk

The impact of functional MDM2-polymorphisms on neutrophil counts in breast cancer patients during neoadjuvant chemotherapy

BACKGROUND

Functional polymorphisms in the MDM2 promoters have been linked to cancer risk and several non-malignant conditions. Their potential role in bone marrow function during chemotherapy is largely unknown.

METHODS

We investigated the potential associations between genotypes of MDM2 SNP309 (rs2279744), SNP285 (rs117039649) and del1518 (rs3730485) and neutrophil counts in breast cancer patients receiving neoadjuvant sequential epirubicin and docetaxel, with additional G-CSF, in the DDP-trial (NCT00496795). We applied longitudinal ratios, post vs. pre-treatment, of neutrophil counts as our main measure. Differences by genotypes were tested by Jonckheere-Terpstra test for ranked alternatives, while dominant and recessive models were tested by Mann-Whitney U test, and additional sub-analyses were performed for genotype combinations.

RESULTS

The SNP309 reference T-allele was associated with a better sustained neutrophil count (p = 0.035). A similar association was observed for the alternative del-allele of the del1518 (p = 0.049). Additionally, in combined genotype-analyses, patients with the SNP309 TT genotype and at least one copy of the del1518 del-allele had particularly favorable sustained neutrophil counts during chemotherapy treatment (p = 0.005).

CONCLUSIONS

Our study provides evidence that MDM2 promoter polymorphisms may be associated with neutrophil counts and bone marrow recovery during chemotherapy treatment in breast cancer patients.

TRIAL REGISTRATION

The DDP-trial was registered at ClinicalTrials.gov (NCT00496795; registration date 2007-07-04).

Mechanisms of TP53 Pathway Inactivation in Embryonic and Somatic Cells-Relevance for Understanding (Germ Cell) Tumorigenesis

The P53 pathway is the most important cellular pathway to maintain genomic and cellular integrity, both in embryonic and non-embryonic cells. Stress signals induce its activation, initiating autophagy or cell cycle arrest to enable DNA repair. The persistence of these signals causes either senescence or apoptosis. Over 50% of all solid tumors harbor mutations in TP53 that inactivate the pathway. The remaining cancers are suggested to harbor mutations in genes that regulate the P53 pathway such as its inhibitors Mouse Double Minute 2 and 4 (MDM2 and MDM4, respectively). Many reviews have already been dedicated to P53, MDM2, and MDM4, while this review additionally focuses on the other factors that can deregulate P53 signaling. We discuss that P14^ARF (ARF) functions as a negative regulator of MDM2, explaining the frequent loss of ARF detected in cancers. The long non-coding RNA Antisense Non-coding RNA in the INK4 Locus (ANRIL) is encoded on the same locus as ARF, inhibiting ARF expression, thus contributing to the process of tumorigenesis. Mutations in tripartite motif (TRIM) proteins deregulate P53 signaling through their ubiquitin ligase activity. Several microRNAs (miRNAs) inactivate the P53 pathway through inhibition of translation. CCCTC-binding factor (CTCF) maintains an open chromatin structure at the TP53 locus, explaining its inactivation of CTCF during tumorigenesis. P21, a downstream effector of P53, has been found to be deregulated in different tumor types. This review provides a comprehensive overview of these factors that are known to deregulate the P53 pathway in both somatic and embryonic cells, as well as their malignant counterparts (i.e., somatic and germ cell tumors). It provides insights into which aspects still need to be unraveled to grasp their contribution to tumorigenesis, putatively leading to novel targets for effective cancer therapies.

Impact of MDM2 promoter SNP55 (rs2870820) on risk of endometrial and ovarian cancer

BACKGROUND

While large GWAS analyses have not found convincing associations between MDM2 promoter SNP55 and gynaecological cancers, SNP55 is in linkage disequilibrium with two other functional SNPs in the same promoter, likely to obscure associations between single SNPs and cancer risk. Here, we assessed the impact of SNP55 on risk of endometrial and ovarian cancer, including sub-analyses stratified for other functional SNPs in the region.

MATERIAL AND METHODS

Using a custom LightSNiP assay, we genotyped SNP55 in two large hospital-based cohorts of patients with ovarian (n = 1,332) and endometrial (n = 1,363) cancer and compared genotypes to healthy female controls (n = 1,858).

RESULTS

Among individuals harbouring the SNP309TT genotype, the minor SNP55T-allele was associated with a reduced risk of endometrial (dominant model: OR = 0.63; CI = 0.45-0.88; p = 0.01). Regardless of the genotype in neighbouring SNPs, the SNP55T-allele was also associated with a reduced risk of endometrial cancer before 50 years of age (dominant model: OR = 0.56; CI = 0.34-0.90; p = 0.02). No association between SNP55 status and ovarian cancer risk was observed.

CONCLUSIONS

MDM2 SNP55T-allele may correlate with reduced risk for endometrial cancer in a SNP309T-, but not SNP309G, context.

Association of the MDM2 SNP285 and SNP309 Genetic Variants with the Risk, Age at Onset and Prognosis of Breast Cancer in Central European Women: A Hospital-Based Case-Control Study

SNP309T>G (rs2279744) and SNP285G>C (rs117039649) in the MDM2 promoter are thought to have opposite effects on the binding of transcription factor SP1 (specificity protein 1), and consequently on MDM2 expression, p53 levels, cancer risk, age at onset, and prognosis. Here, we genotyped SNP309 and SNP285 in 406 Austrian breast cancer patients and 254 female controls. The SNP309GG genotype was associated with an increased breast cancer risk in p53 negative (OR, 1.82; 95% CI, 1.09–3.03; p = 0.02), but not p53 positive or unselected patients. In contrast, the SNP309TT genotype was associated with an earlier age at onset (TT, 57.0 ± 12.9; TG, 58.6 ± 13.9; GG, 59.7 ± 15.0 years; p = 0.048). 31% of SNP309TT, 26% of TG, and 13% of GG tumors were p53 positive (p = 0.034), indicating a lower selective pressure to mutate TP53 in the presence of the G-allele. Moreover, SNP309TT patients exhibited a shortened metastasis-free survival in multivariable analysis. Censoring carriers of the SNP285C-allele hardly altered the strength of these associations of SNP309, thus challenging the proposed antagonistic function of SNP285C towards SNP309G. The minor SNP285C-allele tended to be non-significantly associated with an increased breast cancer risk and a poor disease-free and metastasis-free survival, which may be bystander effects of its complete linkage disequilibrium with SNP309G. We conclude that the SNP309G-allele attenuates the p53-response and leads to a higher breast cancer risk, but also to a later onset of breast cancer and a trend towards a good prognosis.

MDM2 and P53 polymorphisms contribute together to the risk and survival of prostate cancer

The p53 gene and MDM2 gene play critical roles in cell cycle arrest and apoptosis together. Here, we evaluated the associations of prostate cancer risk and survival with the joint effects of mdm2 and p53 polymorphisms. Totally 1,193 cases and 1,310 age frequency-matched controls were included in the study. Prostate cancer patients were followed to determine the intervals of overall survival and disease-free survival. The Pro⁷²Arg Pro allele (homozygous and heterozygous) were significantly associated with prostate cancer risk with an odds ratio (OR) of 0.77 [95% confidence interval(CI), 0.64-0.93]. SNP309 T alleles were associated with a significantly decreased prostate cancer risk among Pro⁷²Arg Pro alleles carriers (OR=0.79, 95% CI, 0.64-0.98). In addition, comparedwith the Pro⁷²Arg Pro alleles and SNP309 G homozygous, patients carrying both SNP309 T alleles and Pro⁷²Arg Arg homozygous had more favorable disease-free survival (hazard ratio [HR] = 0.59, 95% CI, 0.38-0.93). Our results indicated that SNP309 and Pro⁷²Arg polymorphisms may jointly contributeto the etiology and prognosis of prostate cancer.

The Role of p16 and MDM2 Gene Polymorphisms in Prolactinoma: MDM2 Gene Polymorphisms May Be Associated with Tumor Shrinkage

AIM

Prolactinomas are thought to arise from clonal expansion of a single mutated cell which is subjected to growth stimuli of several permissive factors, although the pathogenetic mechanisms underlying tumorigenesis remain unclear. The present study aimed to investigate the role of p16 (540C→G and 580C→T) and mouse double minute 2 (MDM2) (SNP309T→G) gene polymorphisms in tumorigenesis and characteristics of prolactinoma.

PATIENTS AND METHODS

A total of 74 patients with prolactinoma and 100 age- and gender-matched healthy individuals were enrolled in the study. Serum prolactin levels were measured by enzyme-linked immunosorbent assay (ELISA). p16 and MDM2 polymorphisms were determined by polymerase chain reaction-restriction fragment polymorphism and agarose gel electrophoresis.

RESULTS

p16 540C→G genotype distribution was found to be: CC: 66.2%, CG: 28.4%, GG: 5.4%; p16 580C→T genotype distribution was found to be: CC: 82.4%, CT: 17.6%, TT: 0% and MDM2 genotype distribution was found to be: TT: 31.1%, TG: 47.3%, GG: 21.6% in patients with prolactinoma. Tumor diameter before treatment was correlated with prolactin levels before treatment and percentage of prolactin decrease with treatment (r=0.719, p<0.001, p=0.034 r=0.256, respectively). The number of patients with tumor size decrease of more than 50% in those with homozygous genotype (TT+GG) of MDM2 SNP309T→G was significantly higher than in heterozygous genotype (TG) carriers (odds ratio(OR)=0.18, 95% confidence interval(CI)=0.06-0.58; p=0.003).

CONCLUSION

This study showed that p16 and MDM2 polymorphisms do not play a decisive role in tumorigenesis, but some genotypes of these polymorphisms might be associated with follow-up characteristics of prolactinoma.

Association of the MDM2 SNP285 Polymorphism with Cancer Susceptibility: A Meta-Analysis

The mouse double minute 2 (MDM2) gene encodes a negative regulator for p53, and the polymorphism SNP285 in the promoter region of MDM2 gene has been implicated in cancer risk, but individual published studies had inconclusive results. Therefore, we performed this meta-analysis to obtain a more precise estimation between MDM2 SNP285 polymorphism and risk of cancer. A systematic literature search was performed using the PubMed, Embase, and Chinese Biomedical (CBM) databases. Ultimately, 16 published studies comprising 14,573 cases and 9,115 controls were included. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the strength of associations. Overall, MDM2 SNP285 polymorphism was significantly associated with a decreased overall cancer risk with the heterozygous model (OR = 0.89, 95% CI = 0.79-0.99), and reduced ORs were observed with other genetic models (dominant: OR = 0.90, 95% CI = 0.79-1.01 and allele comparison: OR = 0.91, 95% CI = 0.80-1.03) but not reaching statistical significance. Stratification analysis indicated a decreased risk for ovarian cancer, Caucasians, and studies with relatively large sample size. Despite some limitations, this meta-analysis indicated that the MDM2 SNP285 polymorphism was associated with a decreased cancer risk, which warrants further validation in large and well-designed studies.

A systematic review and meta-analysis of MDM2 polymorphisms in osteosarcoma susceptibility

Two polymorphisms in the murine double minute 2 (MDM2) gene (rs1690916 and rs2279744) have been associated with the risk of osteosarcoma (OS). When we analyzed these two polymorphisms in two new independents cohorts (Spanish and Slovenian), we found no association. In order to clarify this, we conducted a meta-analysis including six populations, with a total of 246 OS patients and 1,760 controls for rs1690916; and 433 OS patients and 1,959 controls for rs2279744. Pooled odds ratio risks and corresponding 95% CI were estimated to assess the possible associations. Our results showed that these two polymorphisms were not associated with the susceptibility of OS under any genetic model studied. In conclusion, the present meta-analysis indicates that MDM2 rs1690916 and rs2279744 cannot be considered as genetic risk factors for OS susceptibility in the different populations. Therefore, the influence of these two polymorphisms on the risk of OS may be less important than previously suggested. Future studies are needed to confirm these results.

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 effects of p21 gene C98A polymorphism on development of uterine leiomyoma in southeast Iranian women

Uterine leiomyoma (UL) is a monoclonal tumor which arises from uninhibited proliferation of a single myometrial cell; therefore, the imbalance in cell cycle regulation could be a key event in its development. In the present study, we aimed to assess the association of p21 gene polymorphisms and UL. Genomic DNA was extracted from blood samples of 154 women with UL and 197 age-, BMI-, and ethnically matched controls. p21 C98A (rs1801270) and C70T (rs1059234) polymorphism genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis. The CA genotype of p21 C98A polymorphism was significantly higher in UL women (28 %) compared to the controls (18 %), and the UL risk was 1.8-fold greater in women with CA genotype compared to CC genotype before and after adjusting for age, BMI, and ethnicity (OR, 1.8 [95 % CI, 1.1 to 3]; P = 0.02). There was no association between the AA genotype of p21 C98A polymorphism and UL. Moreover, the frequency of p21 98A allele was significantly higher in the UL women compared to controls (17 vs. 12 %, p = 0.04). The p21 C70T polymorphism did not correlate with UL before and after adjusting for age, BMI, and ethnicity. There was no difference in haplotype frequency of p21 C70T and C98A polymorphisms between UL patients and the controls. CA genotype of p21 C98A polymorphism may be a risk factor for UL susceptibility; however, p21 C70T polymorphism did not associate with UL.

Prognostic potential of the MDM2 309T>G polymorphism in stage I lung adenocarcinoma

The MDM2 protein plays an important role in the regulation of cell proliferation and apoptosis via ubiquitination and proteasome‐mediated degradation of p53. The genetic polymorphism rs2279744 (c.309T>G) of the MDM2 gene is reportedly associated with susceptibility and/or prognosis in various cancers. In this study, we investigated the risk factors for worse survival in patients with lung adenocarcinoma (AC). We examined the association between c.309T>G and the prognosis of lung cancer by retrospectively reviewing 453 lung cancer patients. We studied both, clinicopathological and genetic characteristics, including the c.309T>G, p53 Arg72Pro, EGFR,KRAS, and p53 mutations. Associations between these factors and survival outcome were analyzed using Cox proportional hazards models. The frequencies of MDM2 polymorphisms were T/T, 20.8%; T/G, 48.6%, and G/G, 30.7%. The overall survival (OS) of AC patients with pathological stage I disease and the MDM2 T/T genotype was significantly shorter than that of those with the T/G or G/G genotypes (P = 0.02). Multivariate analysis revealed that the MDM2 T/T genotype was an independent, significant prognostic factor (hazard ratio [HR] = 2.23; 95% confidence interval [CI]: 1.07–4.65; P = 0.03). The MDM2 T/T genotype was predictive of poorer survival in a Japanese population. Genotyping for this polymorphism might predict the clinical outcomes of stage I AC patients.

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?

Association of p53Pro72Arg (rs1042522) and MDM2309 (rs2279744) polymorphisms with risk for cervical intraepthelial lesions and cervical cancer development in Macedonian women

High risk Human Papillomavirus (HPV) is an important etiological factor in initiation of squamous intraepithelial lesions (SIL), but not enough for malignant progression to cervical cancer (CCa). Single nucleotide polymorphisms (SNPs): rs1042522 within the codon 72 of p53 and rs2279744 within MDM2 promoter gene are plausible factors for development of SIL or CCa conferring increased attenuation of p53 pathway. We investigated the association of these SNPs with the HPV positive SIL and CCa among women from the Republic of Macedonia. Using a multiplex PCR SNaPShot analysis we genotyped rs1042522 and rs2279744 in 131 HPV positive women with SIL or CCa and 110 HPV and cytologicaly negative controls subject. No significant difference in either genotype or allelic frequencies for rs1042522 and rs2279744 between cases and control was found. The stratification of patients on the basis of the lesion grade revealed lower frequency of CC genotype and C allele of rs1042522 in HSIL and CCa compared to LSIL [GG vs CC; p=0.001, OR=0.4; CG vs CC; p=0.04, OR=0.03 and CG+ GG vs CC; p=0.004, OR=0.2]. Additionally TT genotype and T allele of MDM2 309 showed significantly lower frequency in HSIL and CCa group then in LSIL [G vs T p=0.02, OR=0.52; GG vs TT; p=0.04, OR=0.29; ТТ vs ТG+GG; p=0.007, OR=0.34].The Arg variant of rs1042522 and T allele/TT genotype of rs2279744 are associated with progression to LSIL to HSIL or CCa and may be used as prediction markers in CCa management, but the clinical relevant warrants further validation in large and well-designed studies

SNP55, a new functional polymorphism of MDM2-P2 promoter, contributes to allele-specific expression of MDM2 in endometrial cancers

BACKGROUND

The functional single nucleotide polymorphism (SNP) in the MDM2 promoter region, SNP309, is known to be associated with various diseases, particularly cancer. Although many studies have been performed to demonstrate the mechanism of allele-specific expression (ASE) on SNP309, they have only utilized in vitro techniques. It is unknown whether ASE of MDM2 is ascribed solely to SNP309, in vivo.

METHODS

We attempted to evaluate ASE of MDM2 in vivo using post-labeling followed by automated capillary electrophoresis under single-strand conformation polymorphism conditions. For measuring a quantitative difference, we utilized the SNPs on the exons of MDM2 as markers, the status of which was heterozygous in a large population. To address the cause of ASE beyond 20%, we confirmed sequences of both MDM2-3'UTR and promoter regions. We assessed the SNP which might be the cause of ASE using biomolecular interaction analysis and luciferase assay.

RESULTS

ASE beyond 20% was detected in endometrial cancers, but not in cancer-free endometria samples only when an SNP rs1690916 was used as a marker. We suspected that this ASE in endometrial cancer was caused by the sequence heterogeneity in the MDM2-P2 promoter, and found a new functional polymorphism, which we labelled SNP55. There was no difference between cancer-free endometria and endometrial cancer samples neither for SNP55 genotype frequencies nor allele frequencies, and so, SNP55 alone does not affect endometrial cancer risk. The SNP55 status affected the DNA binding affinity of transcription factor Sp1 and nuclear factor kappa-B (NFκB). Transcriptional activity of the P2 promoter containing SNP55C was suppressed by NFκB p50 homodimers, but that of SNP55T was not. Only ASE-positive endometrial cancer samples displayed nuclear localization of NFκB p50.

CONCLUSIONS

Our findings suggest that both the SNP55 status and the NFκB p50 activity are important in the transcriptional regulation of MDM2 in endometrial cancers.

Deregulation of the EGFR/PI3K/PTEN/Akt/mTORC1 pathway in breast cancer: possibilities for therapeutic intervention

The EGFR/PI3K/PTEN/Akt/mTORC1/GSK-3 pathway plays prominent roles in malignant transformation, prevention of apoptosis, drug resistance and metastasis. The expression of this pathway is frequently altered in breast cancer due to mutations at or aberrant expression of: HER2, ERalpha, BRCA1, BRCA2, EGFR1, PIK3CA, PTEN, TP53, RB as well as other oncogenes and tumor suppressor genes. In some breast cancer cases, mutations at certain components of this pathway (e.g., PIK3CA) are associated with a better prognosis than breast cancers lacking these mutations. The expression of this pathway and upstream HER2 has been associated with breast cancer initiating cells (CICs) and in some cases resistance to treatment. The anti-diabetes drug metformin can suppress the growth of breast CICs and herceptin-resistant HER2+ cells. This review will discuss the importance of the EGFR/PI3K/PTEN/Akt/mTORC1/GSK-3 pathway primarily in breast cancer but will also include relevant examples from other cancer types. The targeting of this pathway will be discussed as well as clinical trials with novel small molecule inhibitors. The targeting of the hormone receptor, HER2 and EGFR1 in breast cancer will be reviewed in association with suppression of the EGFR/PI3K/PTEN/Akt/mTORC1/GSK-3 pathway.

Sp1 and the 'hallmarks of cancer'

For many years, transcription factor Sp1 was viewed as a basal transcription factor and relegated to a role in the regulation of so-called housekeeping genes. Identification of Sp1's role in recruiting the general transcription machinery in the absence of a TATA box increased its importance in gene regulation, particularly in light of recent estimates that the majority of mammalian genes lack a TATA box. In this review, we briefly consider the history of Sp1, the founding member of the Sp family of transcription factors. We review the evidence suggesting that Sp1 is highly regulated by post-translational modifications that positively and negatively affect the activity of Sp1 on a wide array of genes. Sp1 is over-expressed in many cancers and is associated with poor prognosis. Targeting Sp1 in cancer treatment has been suggested; however, our review of the literature on the role of Sp1 in the regulation of genes that contribute to the 'hallmarks of cancer' illustrates the extreme complexity of Sp1 functions. Sp1 both activates and suppresses the expression of a number of essential oncogenes and tumor suppressors, as well as genes involved in essential cellular functions, including proliferation, differentiation, the DNA damage response, apoptosis, senescence and angiogenesis. Sp1 is also implicated in inflammation and genomic instability, as well as epigenetic silencing. Given the apparently opposing effects of Sp1, a more complete understanding of the function of Sp1 in cancer is required to validate its potential as a therapeutic target.

The T309G murine double minute 2 gene polymorphism is an independent prognostic factor for patients with renal cell carcinoma

The purpose of this study was to evaluate the association of the T309G MDM2 gene polymorphism with renal cell carcinoma (RCC) risk, pathology, and cancer-specific survival (CSS). T309G MDM2 was genotyped in 449 Caucasians, including 240 with RCC and 209 cancer-free controls. The T309G MDM2 genotype was TT in 174 (38.8%), GT in 214 (47.7%), and GG in 61 (13.6%) subjects, without any significant differences between cases and controls on both univariable (p=0.58) and multivariable logistic regression (each p>0.25). Furthermore, T309G MDM2 was not linked with T stage (p=0.75), N stage (p=0.37), M stage (p=0.94), grade (p=0.21), and subtype (p=0.55). There was, however, a statistically significant association of T309G MDM2 with CSS (p=0.022): patients with TT had significantly worse survival than GG/GT (p=0.009), while those with GT and GG had similar outcomes (p=0.92). The 5-year survival rate for patients with TT, GT, and GG was 69.5%, 84.5%, and 89.7%, respectively. On the multivariable analysis, T309G was identified as an independent prognostic factor. The T309G MDM2 polymorphism is an independent prognostic factor for patients with RCC, with the TT genotype being associated with worse prognosis. In this study, there were no significant associations with RCC risk and pathology.

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).

Population distribution and ancestry of the cancer protective MDM2 SNP285 (rs117039649)

The MDM2 promoter SNP285C is located on the SNP309G allele. While SNP309G enhances Sp1 transcription factor binding and MDM2 transcription, SNP285C antagonizes Sp1 binding and reduces the risk of breast-, ovary- and endometrial cancer. Assessing SNP285 and 309 genotypes across 25 different ethnic populations (>10.000 individuals), the incidence of SNP285C was 6-8% across European populations except for Finns (1.2%) and Saami (0.3%). The incidence decreased towards the Middle-East and Eastern Russia, and SNP285C was absent among Han Chinese, Mongolians and African Americans. Interhaplotype variation analyses estimated SNP285C to have originated about 14,700 years ago (95% CI: 8,300 – 33,300). Both this estimate and the geographical distribution suggest SNP285C to have arisen after the separation between Caucasians and modern day East Asians (17,000 - 40,000 years ago). We observed a strong inverse correlation (r = -0.805; p < 0.001) between the percentage of SNP309G alleles harboring SNP285C and the MAF for SNP309G itself across different populations suggesting selection and environmental adaptation with respect to MDM2 expression in recent human evolution. In conclusion, we found SNP285C to be a pan-Caucasian variant. Ethnic variation regarding distribution of SNP285C needs to be taken into account when assessing the impact of MDM2 SNPs on cancer risk.

MDM2 285G>C and 344T>A gene variants and their association with hepatocellular carcinoma: a Moroccan case-control study

BACKGROUND

MDM2 gene polymorphisms 285G/C and 344 T/A are two single nucleotide polymorphisms (SNPs) recently identified as important variants that could influence the expression of MDM2 gene through the modulation of transcription factors binding on the SNP309T/G. The 285C variant seems to present a geographically distinct distribution in humans and to be associated with a low cancer risk. In the present report, we studied the distribution of the three SNPs in a population with low liver cancer incidence.

METHODS

A group of 119 patients with hepatocellular carcinoma (HCC, 63.45 ± 12.59 year, 26-80) and another of 103 non-HCC controls (56 ± 10.82 year, 22-79) were enrolled to investigate association between MDM2 polymorphisms and susceptibility to develop HCC. The three studied SNPs (285G/C, 309 T/G and 344 T/A) were genotyped using polymerase chain reaction and sequencing techniques.

RESULTS

Genotypes and alleles distributions of the three studied polymorphisms of MDM2 were not significantly different between cases and controls. An increased risk of HCC development was found in case of 309G allele presence albeit without reaching the significance (29.8% vs 22.3%, OR = 1.48, 95% CI, 0.96-2.27, p = 0.073). In addition, neither 285C nor 344A MDM2 variants were significantly associated with an increased risk of HCC (p = 0.688 and p = 1 respectively). Remarkably, we found that the supposedly Caucasian-specific 285C variant was present in 1% of the Moroccan population.

CONCLUSIONS

This is the first study of the MDM2 SNP285G/C and SNP344T/A polymorphisms in association with HCC development. In contrast with previous studies, showing that females carrying SNP285C variant have a significantly reduced risk of developing breast, ovarian and endometrial cancer, no significant modulation of HCC risk was found in a North-African population.

Inhibition of GSK-3β activity can result in drug and hormonal resistance and alter sensitivity to targeted therapy in MCF-7 breast cancer cells

The PI3K/Akt/mTORC1 pathway plays prominent roles in malignant transformation, prevention of apoptosis, drug resistance, and metastasis. One molecule regulated by this pathway is GSK-3β. GSK-3β is phosphorylated by Akt on S9, which leads to its inactivation; however, GSK-3β also can regulate the activity of the PI3K/Akt/mTORC1 pathway by phosphorylating molecules such as PTEN, TSC2, p70S6K, and 4E-BP1. To further elucidate the roles of GSK-3β in chemotherapeutic drug and hormonal resistance of MCF-7 breast cancer cells, we transfected MCF-7 breast cancer cells with wild-type (WT), kinase-dead (KD), and constitutively activated (A9) forms of GSK-3β. MCF-7/GSK-3β(KD) cells were more resistant to doxorubicin and tamoxifen compared with either MCF-7/GSK-3β(WT) or MCF-7/GSK-3β(A9) cells. In the presence and absence of doxorubicin, the MCF-7/GSK-3β(KD) cells formed more colonies in soft agar compared with MCF-7/GSK-3β(WT) or MCF-7/GSK-3β(A9) cells. In contrast, MCF-7/GSK-3β(KD) cells displayed an elevated sensitivity to the mTORC1 blocker rapamycin compared with MCF-7/GSK-3β(WT) or MCF-7/GSK-3β(A9) cells, while no differences between the 3 cell types were observed upon treatment with a MEK inhibitor by itself. However, resistance to doxorubicin and tamoxifen were alleviated in MCF-7/GSK-3β(KD) cells upon co-treatment with an MEK inhibitor, indicating regulation of this resistance by the Raf/MEK/ERK pathway. Treatment of MCF-7 and MCF-7/GSK-3β(WT) cells with doxorubicin eliminated the detection of S9-phosphorylated GSK-3β, while total GSK-3β was still detected. In contrast, S9-phosphorylated GSK-3β was still detected in MCF-7/GSK-3β(KD) and MCF-7/GSK-3β(A9) cells, indicating that one of the effects of doxorubicin on MCF-7 cells was suppression of S9-phosphorylated GSK-3β, which could result in increased GSK-3β activity. Taken together, these results demonstrate that introduction of GSK-3β(KD) into MCF-7 breast cancer cells promotes resistance to doxorubicin and tamoxifen, but sensitizes the cells to mTORC1 blockade by rapamycin. Therefore GSK-3β is a key regulatory molecule in sensitivity of breast cancer cells to chemo-, hormonal, and targeted therapy.

Recent discoveries in the cycling, growing and aging of the p53 field

The P53 gene and it product p53 protein is the most studied tumor suppressor, which was considered as oncogene for two decades until 1990. More than 60 thousand papers on the topic of p53 has been abstracted in Pubmed. What yet could be discovered about its role in cell death, growth arrest and apoptosis, as well as a mediator of the therapeutic effect of anticancer drugs. Still during recent few years even more amazing discoveries have been done. Here we review such topics as suppression of epigenetic silencing of a large number of non-coding RNAs, role of p53 in suppression of the senescence phenotype, inhibition of oncogenic metabolism, protection of normal cells from chemotherapy and even tumor suppression without apoptosis and cell cycle arrest.

Do CDKN2 p16 540 C>G, CDKN2 p16 580 C>T, and MDM2 SNP309 T>G gene variants act on colorectal cancer development or progression?

CDNK2 p16 plays a pivotal role in G1/S transition by regulating the p53 pathway, which was regulated by a nuclear oncoprotein, mouse double minute 2 (MDM2). Overexpression of the MDM2 gene has been shown in a number of tumor types, its gene amplification is found to associate with accelerated tumor development and failure to treatment in both hereditary and sporadic cancers. Although genetic association studies have revealed the relationship between certain genetic polymorphisms and genes that play important roles in the development and progression of colorectal cancer (CRC), it is still unknown. Therefore, the polymorphisms of p16 540 C>G, 580 C>T, and MDM2 SNP309 T>G designed to investigate the risk of CRC development and progression in a Turkish population. We enrolled 87 patients with CRC and 75 healthy controls into the study. Genotypings were determined using polymerase chain reaction-restriction fragment length polymorphism techniques. Genotype distributions of p16 540 C>G and 580 C>T were found in agreement with the Hardy-Weinberg equilibrium in patients and controls. MDM2 SNP309 T>G was found in agreement with the Hardy-Weinberg equilibrium in controls, but not in patients. The results of our study, the G allele of p16 540 C>G and GG genotype of MDM2 SNP309 T>G were found significantly lower in patients compared with controls (p<0.001, p<0.05, respectively). Haplotype analyses have shown that the C allele of both the CDKN2 p16 540 C>G and 580 C>T variants together indicate a risk haplotype for the patient group; besides, carrying the G allele of p16 540 and G allele of MDM2 also seems a risk haplotype for the patient group. Our study is the first study that investigates the relationship among variants of CDKN2 p16 540 C>G, 580 C>T, and MDM2 SNP309 T>G risk of CRC and the development and progression in the Turkish population.

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.

MDM2 SNP285 does not antagonize the effect of SNP309 in lung cancer

Conflicting reports exist regarding the contribution of SNP309 in MDM2 to cancer risk. Recently, SNP285 was shown to act as an antagonist to SNP309 by overriding the effect of SNP309 on SP1-mediated transcription. Moreover, SNP285 modified the relationship between SNP309 and risk of breast, ovarian and endometrial cancer. We assessed whether SNP285 confounded the effect of SNP309 in lung cancer in a cohort of 720 controls and 556 cases. Our cohort included both Caucasians and African Americans. Neither SNP309 nor SNP285 was associated with lung cancer risk or survival. In addition, removal of individuals who carried the variant C allele of SNP285 did not modify the association between SNP309 with either lung cancer risk or survival. Although an effect of SNP285 has been demonstrated in breast, ovarian and endometrial cancer, our findings do not support a role for this SNP in lung cancer and raise the possibility that the effect of SNP285 is restricted to cancers in women.

Effect of the MDM2 promoter polymorphisms SNP309T>G and SNP285G>C on the risk of ovarian cancer in BRCA1 mutation carriers

Background

While BRCA mutation carriers possess a 20-40% lifetime risk of developing ovarian cancer, knowledge about genetic modifying factors influencing the phenotypic expression remains obscure. We explored the distribution of the MDM2 polymorphisms SNP309T>G and the recently discovered SNP285G>C in Norwegian patients with BRCA related ovarian cancer.

Methods

221 BRCA related ovarian cancer cases (BRCA1; n = 161 and BRCA2; n = 60) were tested for the MDM2 polymorphisms. Results were compared to healthy controls (n = 2,465).

Results

The SNP309G allele was associated with elevated OR for ovarian cancer in BRCA1 mutation carriers (SNP309TG: OR 1.53; CI 1.07-2.19; p = 0.020; SNP309GG: OR 1.92; CI 1.19-3.10; p = 0.009; SNP309TG+GG combined: OR 1.61; CI 1.15-2.27; p = 0.005). In contrast, the SNP285C allele reduced risk of BRCA1 related ovarian cancer in carriers of the SNP309G allele (OR 0.50; CI 0.24-1.04; p = 0.057). Censoring individuals carrying the SNP285C/309G haplotype from the analysis elevated the OR related to the SNP309G allele (OR 1.73; CI 1.23-2.45; p = 0.002). The mean age at disease onset was 3.1 years earlier in carriers of SNP309TG+GG as compared to carriers of SNP309TT (p = 0.068). No such associations were found in BRCA2 related ovarian cancer.

Conclusions

Our results indicate the SNP309G allele to increase and the SNP285C allele to reduce the risk of BRCA1 related ovarian cancer. If confirmed in independent studies, this finding may have implications to counseling and decision-making regarding risk reducing measures in BRCA1 mutation carriers.

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.

Effects of the MDM2 promoter SNP285 and SNP309 on Sp1 transcription factor binding and cancer risk

The proto-oncogene MDM2 inhibits p53 and plays a key role in cell growth control and apoptosis. Identification of two antagonizing MDM2 polymorphisms, SNP285 and SNP309, affecting cancer risk through modulation of Sp1 transcription factor binding, shed new light on the biological activity and phylogeny of this gene.

Induction of ASAP (MAP9) contributes to p53 stabilization in response to DNA damage

p53 is a key tumor suppressor that controls DNA damage response and genomic integrity. In response to genotoxic stress, p53 is stabilized and activated, resulting in controlled activation of genes involved in cell cycle arrest, DNA repair and/or apoptosis. ASAP is a centrosome- and spindle-associated protein, the deregulation of which induces severe mitotic defects. We show here that following double-strand break DNA formation, ASAP directly interacts with and stabilizes p53 by enhancing its p300-mediated acetylation and blocking its MDM2-mediated ubiquitination and degradation, leading to an increase of p53 transcriptional activity. Upon DNA damage, ASAP is transiently accumulated before being degraded upon persistent damage. This work links the p53 response with the cytoskeleton and confirms that the DNA-damaging signaling pathway is coordinated by centrosomal proteins. We reveal the existence of a new pathway through which ASAP signals the DNA damage response by regulating the p300-MDM2-p53 loop. These results point out ASAP as a possible target for the design of drugs to sensitize radio-resistant tumors.

MDM2 promoter SNP344T>A (rs1196333) status does not affect cancer risk

The MDM2 proto-oncogene plays a key role in central cellular processes like growth control and apoptosis, and the gene locus is frequently amplified in sarcomas. Two polymorphisms located in the MDM2 promoter P2 have been shown to affect cancer risk. One of these polymorphisms (SNP309T>G; rs2279744) facilitates Sp1 transcription factor binding to the promoter and is associated with increased cancer risk. In contrast, SNP285G>C (rs117039649), located 24 bp upstream of rs2279744, and in complete linkage disequilibrium with the SNP309G allele, reduces Sp1 recruitment and lowers cancer risk. Thus, fine tuning of MDM2 expression has proven to be of significant importance with respect to tumorigenesis. We assessed the potential functional effects of a third MDM2 promoter P2 polymorphism (SNP344T>A; rs1196333) located on the SNP309T allele. While in silico analyses indicated SNP344A to modulate TFAP2A, SPIB and AP1 transcription factor binding, we found no effect of SNP344 status on MDM2 expression levels. Assessing the frequency of SNP344A in healthy Caucasians (n = 2,954) and patients suffering from ovarian (n = 1,927), breast (n = 1,271), endometrial (n = 895) or prostatic cancer (n = 641), we detected no significant difference in the distribution of this polymorphism between any of these cancer forms and healthy controls (6.1% in healthy controls, and 4.9%, 5.0%, 5.4% and 7.2% in the cancer groups, respectively). In conclusion, our findings provide no evidence indicating that SNP344A may affect MDM2 transcription or cancer risk.

Downregulation of Mdm2 and Mdm4 enhances viral gene expression during adenovirus infection

Successful viral replication entails elimination or bypass of host antiviral mechanisms. Here, we show that shRNA-mediated knockdown of murine double minute (Mdm2) and its paralog Mdm4 enhanced the expression of early and late viral gene products during adenovirus (HAdV) infection. Remarkably, whereas the expression of HAdV genes was low in p53-deficient mouse embryonic fibroblasts (p53KO MEFs), the HAdV early gene products were efficiently expressed in Mdm2/p53 double-knockout (DKO) and Mdm4/p53 DKO MEFs, and viral capsid proteins were produced in Mdm2/p53 DKO MEFs. Thus, Mdm2 and Mdm4 seem to have potent antiviral property. In cells infected with wt HAdV or a mutant virus lacking the E1B-55K gene (dl 1520), both Mdm2 and Mdm4 were rapidly depleted, whereas replication-deficient mutant viruses (Ad-GFP) or ΔpTP with deletions within the coding sequence of preterminal binding protein failed to induce their downregulation. Reduced expression of Mdm2 and Mdm4 was not due to general shutoff of host protein synthesis. Additionally, expression of a dominant-negative mutant of Cul5 did not affect Mdm2/Mdm4 downregulation. Thus, viral replication but not the presence of E1B-55K is required for Mdm2/Mdm4 degradation. Surprisingly, treatment of HAdV-infected cells with proteasome inhibitor MG132 only partially restored the protein levels of Mdm2 and Mdm4, suggesting that they may also be downregulated through an additional mechanism independent of proteasome. Interestingly, cyclin D1 and p21 appear to be downregulated similarly during HAdV infection. Collectively, our work provides the first biochemical evidence for antiviral function of Mdm2 and Mdm4 and that viruses employ efficient countermeasure to ensure viral replication.

SNP285C modulates oestrogen receptor/Sp1 binding to the MDM2 promoter and reduces the risk of endometrial but not prostatic cancer

INTRODUCTION

The MDM2 promoter polymorphism (SNP309T > G) extends a binding site for the transcription factor Sp1 and has been linked to elevated cancer risk and/or young age at cancer diagnosis, especially in females. Recently, we reported an adjacent polymorphism (SNP285G > C). SNP285C antagonises the effect of SNP309G by reducing Sp1 binding and lowers the risk of breast and ovarian cancer.

METHODS

We assessed the potential gender specificity in the effect of this polymorphism. We performed in silico predictions of transcription factor binding sites in the MDM2 promoter and analysed MDM2 SNP285 and SNP309 status in two independent cohorts of endometrial (n = 438 and 472) and 666 prostatic cancer patients, and compared to 3.140 healthy controls.

RESULTS

We identified three oestrogen-receptor binding elements (EREs) within the MDM2 intronic promoter, one of which overlapping the Sp1 binding-site harbouring SNP285. The SNP285C/309G haplotype was associated with a reduced Odds Ratio (OR) for endometrial cancer (OR1: 0.55; Confidence Interval (CI) 0.32-0.97; OR2: 0.65; CI 0.40-1.08, especially for ER+ tumours; OR: 0.48; CI 0.28-0.87) but not for prostatic cancer among SNP309TG heterozygotes. SNP309G (SNP309TG or SNP309GG genotype) was associated with a moderately increased risk of endometrial cancer (OR: 1.17; CI 1.00-1.37) compared to SNP309TT homozygotes. Removing individuals harbouring the SNP309G-counteracting SNP285C polymorphism from the analysis strengthened this association (OR: 1.20; CI 1.02-1.41).

CONCLUSION

The finding of an ERE overlapping with the Sp1-binding site affected by SNP285, taken together with the significant impact of SNP285 on the risk of breast, ovarian and now endometrial cancer but not prostatic cancer, suggests a gender specific effect of SNP285C on cancer risk.