MDM2 SNP309 Accelerates Tumor Formation in a Gender-Specific and Hormone-Dependent Manner

Iron-dependent regulation of MDM2 influences p53 activity and hepatic carcinogenesis

Iron overload is a risk factor for hepatocarcinoma, but the pathways involved are poorly characterized. Gene expression analysis in immortalized mouse hepatocytes exposed to iron or the iron chelator deferoxamine revealed that iron downregulated, whereas deferoxamine upregulated, mRNA levels of mouse double minute gene 2 (MDM2), the ubiquitin ligase involved in the degradation of the oncosuppressor p53. Regulation of MDM2 by iron status was observed at protein levels in mouse hepatocytes and rat liver, and was associated with specular changes in p53 expression. Iron dependent regulation of MDM2/p53 was confirmed ex-vivo in human monocytes, by manipulation of iron pool and in a genetic model of iron deficiency, leading to modulation of p53 target genes involved in the antioxidant response and apoptosis. Iron status influenced p53 ubiquitination and degradation rate, and the MDM2 inhibitor nutlin increased p53 levels in iron-depleted cells. Furthermore, nutlin enhanced the antiproliferative activity of deferoxamine in HepG2 hepatoblastoma cells. The MDM2 -309T > G promoter polymorphism, determining increased MDM2 and lower p53 activity, was associated with higher risk of hepatocarcinoma in cirrhotic patients with hemochromatosis, and with HFE mutations in patients with hepatocarcinoma without hemochromatosis, suggesting an interaction between MDM2 and iron in the pathogenesis of hepatocarcinoma. In conclusion, iron status influences p53 activity and antioxidant response by modulating MDM2 expression. MDM2 inhibitors may enhance the antiproliferative activity of iron chelators.

Iron-dependent regulation of MDM2 influences p53 activity and hepatic carcinogenesis

Iron overload is a risk factor for hepatocarcinoma, but the pathways involved are poorly characterized. Gene expression analysis in immortalized mouse hepatocytes exposed to iron or the iron chelator deferoxamine revealed that iron downregulated, whereas deferoxamine upregulated, mRNA levels of mouse double minute gene 2 (MDM2), the ubiquitin ligase involved in the degradation of the oncosuppressor p53. Regulation of MDM2 by iron status was observed at protein levels in mouse hepatocytes and rat liver, and was associated with specular changes in p53 expression. Iron dependent regulation of MDM2/p53 was confirmed ex-vivo in human monocytes, by manipulation of iron pool and in a genetic model of iron deficiency, leading to modulation of p53 target genes involved in the antioxidant response and apoptosis. Iron status influenced p53 ubiquitination and degradation rate, and the MDM2 inhibitor nutlin increased p53 levels in iron-depleted cells. Furthermore, nutlin enhanced the antiproliferative activity of deferoxamine in HepG2 hepatoblastoma cells. The MDM2 -309T > G promoter polymorphism, determining increased MDM2 and lower p53 activity, was associated with higher risk of hepatocarcinoma in cirrhotic patients with hemochromatosis, and with HFE mutations in patients with hepatocarcinoma without hemochromatosis, suggesting an interaction between MDM2 and iron in the pathogenesis of hepatocarcinoma. In conclusion, iron status influences p53 activity and antioxidant response by modulating MDM2 expression. MDM2 inhibitors may enhance the antiproliferative activity of iron chelators.

Association of TP53 and MDM2 polymorphisms with survival in bladder cancer patients treated with chemoradiotherapy

Platinum-based chemoradiotherapy (CRT) as bladder conservation therapy has shown promising results for muscle-invasive bladder cancer. However, CRT might diminish survival as a result of the delay in cystectomy for some patients with non-responding bladder tumors. Because the p53 tumor suppression pathway, including its MDM2 counterpart, is important in chemotherapy- and radiotherapy-associated effects, functional polymorphisms in the TP53 and MDM2 genes could influence the response to treatment and the prognosis following CRT. We investigated associations between two such polymorphisms, and p53 overexpression, and response or survival in bladder cancer patients treated with CRT. The study group comprised 96 patients who underwent CRT for transitional cell carcinoma of the bladder. Single nucleotide polymorphisms (SNPs) in TP53 (codon 72, arginine > proline) and MDM2 (SNP309, T > G) were genotyped using PCR-RFLP, and nuclear expression levels of p53 were examined using immunohistochemistry. None of the genotypes or p53 overexpression was significantly associated with response to CRT. However, patients with MDM2 T / G + G / G genotypes had improved cancer-specific survival rates after CRT (P = 0.009). In multivariate analysis, the MDM2 T / G + G / G genotypes, and more than two of total variant alleles in TP53 and MDM2, were independently associated with improved cancer-specific survival (P = 0.031 and P = 0.015, respectively). In addition, MDM2 genotypes were significantly associated with cystectomy-free survival (P = 0.030). These results suggest that the TP53 and MDM2 genotypes might be useful prognostic factors following CRT in bladder cancer, helping patient selection for bladder conservation therapy.

Germline analysis of thymidine/guanidine polymorphism at position 309 of the Mdm2 promoter in malignant melanoma patients

p53 is a major tumor suppressor gene, frequently mutated in human cancer, but rarely mutated in malignant melanoma (MM). Mdm2, the major negative regulator of p53, is overexpressed in 50-60% of MM patients, by an unknown mechanism. Single nucleotide polymorphism at position 309 of the Mdm2 promoter correlates with increased Mdm2 levels and reduced p53 activation. We speculated that guanine at position 309 (G309) of the Mdm2 promoter might be a cause of Mdm2 overexpression in MM patients, and associated with increased risk of MM. We aimed to estimate the prevalence of G309 in MM patients. Genomic DNA was collected from a cohort of 28 MM patients of various clinical stages. The relevant DNA stretch was sequenced and thymidine/guanidine polymorphism at position 309 of Mdm2 promoter was examined. We compared the resultant frequencies with the frequencies reported in the literature for the general population. The G allele frequency in the cohort of MM patients was 0.518. This frequency is high compared with the reported frequency of 0.351 in Caucasian healthy populations (odds ratio=1.98, P=0.014). It is also higher than a G allele frequency of 0.464 reported for Ashkenazi Jewish women, although this comparison was not statistically significant (odds ratio=1.14, P=0.76). These results suggest that the single nucleotide polymorphism G309 in the Mdm2 promoter might be an important genetic predisposing factor, and possibly indicate a molecular mechanism of disease regarding MM. These results must be confirmed in a larger cohort of MM patients and controls.

Genetic basis of sex-specific resistance to neuro-oncogenesis in (BDIX x BDIV) F(2) rats

The identification of cancer susceptibility- and resistance-mediating genes is an essential prerequisite for prevention and early diagnosis of malignant tumors. Model organisms are helpful to identify variant alleles involved in pathways affecting individual cancer risk. BDIX and BDIV rats of both sexes are highly susceptible and resistant, respectively, to the development of N-ethyl-N-nitrosourea (ENU)-induced malignant peripheral nerve sheath tumors (MPNST), predominantly in the trigeminal nerves. Nevertheless, female (BDIV x BDIX) F(2) intercross rats have a lower MPNST incidence and a longer latency time than males. Six of seven autosomal gene loci (Mss1-Mss7) controlling genetic susceptibility and resistance in (BDIV x BDIX) F(2) hybrids exert allele- and sex-specific effects on tumor incidence and/or latency time of variable strength. Homozygous BDIV alleles at Mss4 or Mss7 located on rat chromosomes 6 and 10, respectively, are sufficient to cause almost complete resistance to ENU-induced MPNST development in female F(2) rats regardless of the genotype of the other locus. Both loci display only weak effects on male cancer risk. Survival curves of ENU-treated F(2) females depleted of animals with homozygous BDIV alleles at Mss4 and Mss7 are not significantly different from those of males, suggesting that these loci account mainly for the excess tumor resistance observed in female F(2) rats. By haplotype analysis Mss4 and Mss7 could be narrowed down to 20 and 12 Mb, respectively, providing a basis for the positional identification of candidate genes.

Recent natural selection identifies a genetic variant in a regulatory subunit of protein phosphatase 2A that associates with altered cancer risk and survival

PURPOSE

A regulated p53-dependent stress response is crucial in suppressing tumor formation and mediating the response to commonly used cancer therapeutics. However, little is known about the human, inherited genetics of this important signaling pathway.

EXPERIMENTAL DESIGN

Studies of human genetic variants in the p53 tumor suppressor gene and MDM2 oncogene have shown that single nucleotide polymorphisms (SNP) can affect p53 signaling, confer cancer risk, and alter outcome, and also suggest that the pathway is under evolutionary selective pressure. Here, we attempt to accelerate the identification of functional p53 pathway SNPs by incorporating these characteristics into an analysis of 142 genes that are known to affect p53 signaling.

RESULTS

We report that a genomic scan for recent natural selection denotes that of the 142 genes studied, the PPP2R5E gene that encodes a regulatory subunit of the tumor suppressing protein phosphatase 2A resides in a naturally selected genomic region. We go on to show that a selected SNP in PPP2R5E (epsilon-SNP2) associates with significant allelic differences in the onset (up to 19.2 years; P = 0.0002) and risk (odds ratio, up to 8.1; P = 0.0009) of soft tissue sarcoma development, as well as overall survival (relative risk, up to 3.04; P = 0.026).

CONCLUSIONS

The PPP2R5E gene is identified as harboring genetic variants that can affect human cancer and are possibly under evolutionary selection pressure.

A polymorphic variant in human MDM4 associates with accelerated age of onset of estrogen receptor negative breast cancer

Murine double minute 4 (MDM4) shares significant structural homology with murine double minute 2 (MDM2) and interacts and regulates transcriptional activity of the tumor suppressor p53. In tumors with wild-type p53, there is often overexpression of MDM2 or MDM4 leading to functional inactivation of p53. A single-nucleotide polymorphism (SNP) in the promoter of human MDM2 (SNP309) was shown to associate with increased MDM2 expression and increased risk of cancer. This study evaluated the association of a SNP in human MDM4 (C>T) with age of onset of breast cancer in two independent cohorts. In cohort 1 of 675 patients, the average age of diagnosis for women with estrogen receptor (ER)-positive and ER-negative breast cancers was 53.2 and 48 years, respectively. In this cohort, homozygous variant (TT) carriers developed ER-negative carcinomas at an earlier age than homozygous wild-type (CC) or heterozygous (TC) such that the age at diagnosis was accelerated by 5.0 years (P = 0.018). This association was validated in a second cohort of breast cancer patients (n = 148), where TT carriers with ER-negative cancer developed the disease 3.8 years earlier than CC carriers (P = 0.006). The effect was more pronounced in Caucasians with ER-negative ductal carcinomas with TT homozygotes developing disease 7.5 years (P = 0.031) and 6.2 years (P = 7 x 10(-5)) earlier than CC carriers in cohorts 1 and 2, respectively. No association was seen in ER-positive ductal cancers suggesting that the SNP in MDM4 only has a functional association in ER-negative breast cancer.

Murine double-minute 2 homolog single nucleotide polymorphism 309 and the risk of gynecologic cancer

A functional T to G germline polymorphism in the promoter region of murine double-minute 2 homolog single nucleotide polymorphism 309 (MDM2-SNP309) has been reported to profoundly accelerate tumor formation, suggesting that it may also represent a powerful cancer predisposing allele. In this study, MDM2-SNP309 was examined in a total of 400 blood samples from 108 normal, 88 cervical, 119 endometrial and 85 ovarian cancer cases using two independent polymerase chain reaction assays for each allele. When the MDM2-SNP309 genotype was classified into two subgroups of TT+TG and GG, the GG genotype was associated with an increased risk for the development of endometrial cancer (odds ratio [OR]= 1.91, 95% confidence interval [CI] = 1.05 to 3.47) compared with the TT+TG genotype (P = 0.0353). The G allele also increased the risk of endometrial cancer (OR = 1.20, 95% CI = 0.83 to 1.74) compared with the T allele, but no statistical difference was found (P = 0.3333). The homozygous GG genotype was also associated with postmenopausal status and type I endometrial cancer (P = 0.0306 and 0.0326, respectively). There was no significant difference in the genotype or allele prevalence between control subjects and cervical or ovarian cancer patients. These results suggest that homozygous GG genotype of MDM2-SNP309 may be a risk factor for postmenopausal and type I endometrial cancer in a Japanese population.

Polymorphisms in p53 and the p53 pathway: roles in cancer susceptibility and response to treatment

The p53 tumour suppressor protein lies at the crossroads of multiple cellular response pathways that control the fate of the cell in response to endogenous or exogenous stresses and inactivation of the p53 tumour suppressor signalling pathway is seen in most human cancers. Such aberrant p53 activity may be caused by mutations in the TP53 gene sequence producing truncated or inactive mutant proteins, or by aberrant production of other proteins that regulate p53 activity, such as gene amplification and overexpression of MDM2 or viral proteins that inhibit or degrade p53. Recent studies have also suggested that inherited genetic polymorphisms in the p53 pathway influence tumour formation, progression and/or response to therapy. In some cases, these variants are clearly associated with clinico-pathological variables or prognosis of cancer, whereas in other cases the evidence is less conclusive. Here, we review the evidence that common polymorphisms in various aspects of p53 biology have important consequences for overall tumour susceptibility, clinico-pathology and prognosis. We also suggest reasons for some of the reported discrepancies in the effects of common polymorphisms on tumourigenesis, which relate to the complexity of effects on tumour formation in combination with other oncogenic changes and other polymorphisms. It is likely that future studies of combinations of polymorphisms in the p53 pathway will be useful for predicting tumour susceptibility in the human population and may serve as predictive biomarkers of tumour response to standard therapies.

Effect of TP53 Arg72Pro and MDM2 SNP309 polymorphisms on the risk of high-grade osteosarcoma development and survival

PURPOSE

The germ-line polymorphisms TP53 Arg72Pro and MDM2 SNP309 T>G are risk factors for tumor development and affect response to chemotherapy and survival in several cancers, but their prognostic and predictive value in patients with high-grade osteosarcomas is not yet defined. The purpose of this study was to investigate the effect of the TP53 Arg72Pro and the MDM2 SNP309 on the risk of osteosarcoma development and survival.

EXPERIMENTAL DESIGN

The relative risk to develop osteosarcomas and the overall survival associated to TP53 Arg72Pro and MDM2 SNP309 polymorphisms were investigated in 201 patients. Correlations with event-free survival (EFS) were analyzed in a homogeneous subgroup of 130 patients with high-grade osteosarcomas of the limbs, nonmetastatic at diagnosis, which underwent neoadjuvant chemotherapy.

RESULTS

Multivariate analysis showed that the MDM2 polymorphism T309G was associated with an increased risk of developing osteosarcomas [GG versus TT; odds ratio, 2.09; 95% confidence interval (95% CI), 1.15-3.78]. A case/control gender approach evidenced a significant increased risk only for female osteosarcoma patients (GG versus TT; odds ratio, 4.26; 95% CI, 1.61-11.25). Subjects carrying the TP53 Arg72Pro polymorphism were found to have a significantly increased death risk (Pro/Pro versus Arg/Arg; hazard ratio, 2.90; 95% CI, 1.28-6.66). In the subgroup of 130 high-grade osteosarcomas, the TP53 Arg72Pro was an independent marker of EFS (Pro/Pro versus Arg/Arg; hazard ratio, 2.67; 95% CI, 1.17-6.11).

CONCLUSION

The study provides evidence supporting the association of MDM2 SNP309 with high-grade osteosarcoma risk in females and shows that TP53 Arg72Pro has a prognostic value for overall survival and EFS in osteosarcoma patients.

Mutational analysis of TP53, PTEN, PIK3CA and CTNNB1/beta-catenin genes in human herpesvirus 8-associated primary effusion lymphoma

Human herpesvirus 8 (HHV-8)-associated primary effusion lymphoma is a rare non-Hodgkin's lymphoma often associated with Epstein-Barr virus (EBV) infection. Mutations in TP53, PTEN, PIK3CA, CTNNB1/beta-catenin genes and deletion of CDKN2A-ARF (p14(ARF)-p16(NK4a I) ) locus were investigated in sixteen primary primary effusion lymphoma tumors and seven primary effusion lymphoma cell lines using PCR and sequencing. TP53 mutations were detected in one primary primary effusion lymphoma tumor (6.2%) and two primary effusion lymphoma cell lines (28.6%). BC-3 and BCP-1 cell lines showed PTEN gene mutations, associated with a loss of PTEN protein expression in both cases. No mutations were detected in PIK3CA and CTNNB1/beta-catenin hotspot sequences. Only BC-3 contained a homozygous deletion of CDKN2A-ARF locus. Although detected at a higher frequency in primary effusion lymphoma cell lines than in primary primary effusion lymphoma tumors, TP53 and/or PTEN mutations, as well as deletion of CDKN2A-ARF locus are uncommon in primary effusion lymphoma, and are found to correlate with the EBV-negative status of primary effusion lymphoma tumors.

No evidence for association of the MDM2-309 T/G promoter polymorphism with prostate cancer outcomes

OBJECTIVES

Mouse double-minute 2 (MDM2) SNP309 polymorphism (T>G) has been correlated with an increased risk of cancer in multiple tumor types. MDM2 overexpression has shown to be weakly associated with distant tumor metastases, and down-regulation of MDM2 via antisense oligonucleotides in vitro has resulted in the radiosensitization of prostate cancer cell lines. Based on these results, we decided to evaluate the role of MDM2 SNP309 in the context of histopathologic parameters and clinical outcomes in prostate cancer tumors.

MATERIALS AND METHODS

The population consisted of 212 consecutive prostate cancer patients who underwent radical prostatectomy between 1997 and 1999 at Vanderbilt University Medical Center. Two hundred eight of the samples were successfully genotyped for the MDM2 SNP309 polymorphism. Correlations between the polymorphism, recurrence, and survival data were analyzed using univariate and multivariate genetic models.

RESULTS

The only prognostic factor predictive of overall survival in our study was Gleason score (P<0.005). Using χ(2) analysis, we determined that the MDM2 SNP309 polymorphism had no significant association with race (P=0.7512), patient's age at diagnosis (P=0.6820), pre-prostatectomy PSA level (P=0.8606), Gleason's score (P=0.4839), surgical margin status (P=1.0000), extracapsular extension (P=0 .6175), and disease stage (P=0.4945). In addition, there was no significant difference in 3-year recurrence-free survival (P=0.218), or 8-year overall survival (P=0.376).

CONCLUSIONS

Our study finds no evidence for association of the MDM2 SNP309 polymorphism with clinicopathologic variables, recurrence risk, and overall survival outcome in prostate cancer.

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

A large body of evidence strongly suggests that the p53 tumor suppressor pathway is central in reducing cancer frequency in vertebrates. The protein product of the haploinsufficient mouse double minute 2 (MDM2) oncogene binds to and inhibits the p53 protein. Recent studies of human genetic variants in p53 and MDM2 have shown that single nucleotide polymorphisms (SNPs) can affect p53 signaling, confer cancer risk, and suggest that the pathway is under evolutionary selective pressure (1-4). In this report, we analyze the haplotype structure of MDM4, a structural homolog of MDM2, in several different human populations. Unusual patterns of linkage disequilibrium (LD) in the haplotype distribution of MDM4 indicate the presence of candidate SNPs that may also modify the efficacy of the p53 pathway. Association studies in 5 different patient populations reveal that these SNPs in MDM4 confer an increased risk for, or early onset of, human breast and ovarian cancers in Ashkenazi Jewish and European cohorts, respectively. This report not only implicates MDM4 as a key regulator of tumorigenesis in the human breast and ovary, but also exploits for the first time evolutionary driven linkage disequilibrium as a means to select SNPs of p53 pathway genes that might be clinically relevant.

Probing the functional impact of sequence variation on p53-DNA interactions using a novel microsphere assay for protein-DNA binding with human cell extracts

The p53 tumor suppressor regulates its target genes through sequence-specific binding to DNA response elements (REs). Although numerous p53 REs are established, the thousands more identified by bioinformatics are not easily subjected to comparative functional evaluation. To examine the relationship between RE sequence variation -- including polymorphisms -- and p53 binding, we have developed a multiplex format microsphere assay of protein-DNA binding (MAPD) for p53 in nuclear extracts. Using MAPD we measured sequence-specific p53 binding of doxorubicin-activated or transiently expressed p53 to REs from established p53 target genes and p53 consensus REs. To assess the sensitivity and scalability of the assay, we tested 16 variants of the p21 target sequence and a 62-multiplex set of single nucleotide (nt) variants of the p53 consensus sequence and found many changes in p53 binding that are not captured by current computational binding models. A group of eight single nucleotide polymorphisms (SNPs) was examined and binding profiles closely matched transactivation capability tested in luciferase constructs. The in vitro binding characteristics of p53 in nuclear extracts recapitulated the cellular in vivo transactivation capabilities for eight well-established human REs measured by luciferase assay. Using a set of 26 bona fide REs, we observed distinct binding patterns characteristic of transiently expressed wild type and mutant p53s. This microsphere assay system utilizes biologically meaningful cell extracts in a multiplexed, quantitative, in vitro format that provides a powerful experimental tool for elucidating the functional impact of sequence polymorphism and protein variation on protein/DNA binding in transcriptional networks.

Risk of MDM2 SNP309 alone or in combination with the p53 codon 72 polymorphism in acute myeloid leukemia

A single nucleotide polymorphism (SNP) in the promoter of MDM2 gene, SNP309 T>G (a T-G exchange at nucleotide 309 in the first intron), can increase the expression level of MDM2, thereby causing an impairment of p53 tumor suppressor activity. A G-C exchange at p53 codon 72 polymorphism results in a substitution of proline (Pro) for arginine (Arg) in the transactivation domain, which was shown to alter the primary structure of the p53 protein. Both polymorphisms have been implicated in cancer. To investigate whether that MDM2 SNP309 and p53 codon 72 polymorphism should be at least partially responsible for genetic susceptibility to acute myeloid leukemia (AML), both polymorphisms were determined in a case-control study consisting of 231 AML patients and 128 normal individuals. The MDM2 SNP309G allele was associated with increased risk of AML. Furthermore, the p53 codon 72 and MDM2 SNP309 polymorphisms did not associate with age of onset and any other clinical parameters studied. When the p53 and MDM2 polymorphisms were combined, no multiplicative joint effect between the MDM2 GG and p53 Pro/Pro genotypes exists in the risk of developing AML. These results suggest that the MDM2 SNP309 homozygous GG genotype may be a genetic susceptibility factor in the pathogenesis of AML.

The ups and downs of p53: understanding protein dynamics in single cells

Cells living in a complex environment must constantly detect, process and appropriately respond to changing signals. Therefore, all cellular information processing is dynamic in nature. As a consequence, understanding the process of signal transduction often requires detailed quantitative analysis of dynamic behaviours. Here, we focus on the oscillatory dynamics of the tumour suppressor protein p53 as a model for studying protein dynamics in single cells to better understand its regulation and function.

Association of MDM2 SNP309, age of onset, and gender in cutaneous melanoma

PURPOSE

In certain cancers, MDM2 SNP309 has been associated with early tumor onset in women. In melanoma, incidence rates are higher in women than in men among individuals less than 40 years of age, but among those older than 50 years of age, melanoma is more frequent in men than in women. To investigate this difference, we examined the association among MDM2 SNP309, age at diagnosis, and gender among melanoma patients.

EXPERIMENTAL DESIGN

Prospectively enrolled melanoma patients (N = 227) were evaluated for MDM2 SNP309 and the related polymorphism, p53 Arg72Pro. DNA was isolated from patient blood samples, and genotypes were analyzed by PCR-restriction fragment length polymorphism. Associations among MDM2 SNP309, p53 Arg72Pro, age at diagnosis, and clinicopathologic features of melanoma were analyzed.

RESULTS

The median age at diagnosis was 13 years earlier among women with a SNP309 GG genotype (46 years) compared with women with TG+TT genotypes (59 years; P = 0.19). Analyses using age dichotomized at each decade indicated that women with a GG genotype had significantly higher risks of being diagnosed with melanoma at ages <50 years compared with women >or=50 years, but not when the comparison was made between women <60 and >or=60 years. At ages <50 years, women with a GG genotype had a 3.89 times greater chance of being diagnosed compared with women with TG+TT genotypes (P = 0.01). Similar observations were not seen among men.

CONCLUSIONS

Our data suggest that MDM2 may play an important role in the development of melanoma in women. The MDM2 SNP309 genotype may help identify women at risk of developing melanoma at a young age.

Lack of association of the TP53 Arg72Pro SNP and the MDM2 SNP309 with systemic lupus erythematosus in Caucasian, African American, and Asian children and adults

The p53 tumour suppressor is the central regulator of apoptosis. Previously, the functional TP53 Arg72Pro polymorphism was found to be associated with systemic lupus erythematosus (SLE) in Koreans but not Spaniards. MDM2 is the major negative regulator of p53. An intronic polymorphism in MDM2, the SNP309, attenuates p53 activity and is associated with accelerated tumour development in premenopausal women. Polymorphic variation in MDM2 has never been studied in SLE. The aim of this study is to further assess the contribution of p53-pathway genetic variation to SLE by testing the association of the TP53 Arg72Pro polymorphism and the MDM2 SNP309 with SLE in a well-characterised and ethnically diverse cohort of patients with both childhood- and adult-onset SLE (n = 314). No association was found between the TP53 Arg72Pro polymorphism and SLE in patients of European descent, Asian descent or in African Americans, nor was an association found between the MDM2 SNP309 and SLE in patients of European descent or in African Americans. In addition, there was no correlation between either variant and early-onset disease or nephritis, an index of severe disease. It is concluded that neither the TP53 Arg72Pro polymorphism nor the MDM2 SNP309 contributes significantly to either susceptibility or disease severity in SLE.

Potential of Advexin: a p53 gene-replacement therapy in Li-Fraumeni syndrome

Li-Fraumeni syndrome is a rare autosomal dominant cancer predisposition syndrome. The majority of families fulfilling definition of Li-Fraumeni syndrome demonstrate inherited abnormalities involving the p53 gene. Cells with dysfunctional p53 are predisposed to the development of cancer phenotype. Advexin (Introgen Therapeutics Inc., TX, USA) is an adenoviral-based experimental therapeutic that provides delivery of wild-type p53 to cancer cells and demonstrates anticancer activity following adequate expression of p53. Theoretically, correction of p53 function in cancer developing in patients with Li-Fraumeni syndrome through treatment with Advexin will provide anti-tumor activity. One patient with Li-Fraumeni syndrome has been reported to have responded to Advexin. This review will summarize background knowledge of Li-Fraumeni syndrome, mechanisms of Advexin and clinical response of cancer to Advexin with a focus on Li-Fraumeni syndrome.

Targeting Mdm2 and Mdmx in cancer therapy: better living through medicinal chemistry?

Genomic and proteomic profiling of human tumor samples and tumor-derived cell lines are essential for the realization of personalized therapy in oncology. Identification of the changes required for tumor initiation or maintenance will likely provide new targets for small-molecule and biological therapeutics. For example, inactivation of the p53 tumor suppressor pathway occurs in most human cancers. Although this can be due to frank p53 gene mutation, almost half of all cancers retain the wild-type p53 allele, indicating that the pathway is disabled by other means. Alternate mechanisms include deletion or epigenetic inactivation of the p53-positive regulator arf, methylation of the p53 promoter, or elevated expression of the p53 regulators Mdm2 and Mdmx. This review discusses current models of p53 regulation by Mdm2 and Mdmx and presents the rationale for design of future Mdmx-specific therapeutics based on our knowledge of its structure and biological functions.

MDM2 SNP309T>G polymorphism and risk of hepatocellular carcinoma: a case-control analysis in a Moroccan population

BACKGROUND

The Murine double minute 2 (MDM2) gene encodes a negative regulator of the p53 tumor suppressor protein. A single nucleotide polymorphism (SNP) in the MDM2 promoter (a T to G exchange at nucleotide 309) has been reported to produce accelerated tumor formation. The aim of this study was to investigate whether this functional SNP is associated with an enhanced risk of liver tumorigenesis in Moroccan patients.

METHODS

The study consisted in the comparison of 96 hepatocellular carcinomas (HCC) cases and 222 controls without HCC matched for age, gender and ethnicity. PCR-RFLP and sequencing methods were used to determine the genotype at the MDM2 SNP309T>G locus.

RESULTS

Overall, our results indicate that the GG genotype of SNP309 is significantly associated with an increased risk of HCC (odds ratio, OR=2.60, 95% CI, 1.08-6.28). Interestingly, despite a wide range of confidence interval, there is a trend associating the GG genotype with a high risk of HCC in males (OR=3.31; 95% CI, 0.93-11.82) and in HCV-infected patients (OR=3.7; 95% CI, 0.82-16.45). By contrast, no association between age at diagnosis and MDM2 SNP309 genotypes was observed in HCC patients (P=0.610).

CONCLUSION

Our findings suggest that the MDM2 309T>G polymorphism is an important modulator of hepatocellular carcinoma development in Moroccan patients.

Effects of the single nucleotide polymorphism at MDM2 309 on breast cancer patients with/without BRCA1/2 mutations

BACKGROUND

A germ line single nucleotide polymorphism (SNP) in the first intron of the gene encoding MDM2 at position 309, an important modulator of p53, has been described. BRCA1/2 mutation have been associated with increased rates of breast cancers with mutated P53. It was shown that the presence of MDM2 309 SNP correlated with younger cancer onset age in individuals with a p53 mutations. The differential effects of this SNP were also linked to estrogen receptor activation. Here we report on our study of 453 Ashkenazi breast cancer patients of whom 180 were positive for the known Ashkenazi BRCA1/2 mutations

METHODS

DNA from breast cancer patients was obtained for analysis of one of the three common BRCA1/2 mutations and MDM2 SNP309. Data regarding cancer onset and death ages was obtained from our database and Statistical analysis was performed using the SPSS statistical package (SPCC Inc., Chicago, IL), and JMP software (SAS Institute, Cary, NC).

RESULTS

The percentage of MDM2 SNP309 in control and BRCA 1/2 population which is similar to that reported for other Jewish Ashkenazi populations at 52.2% for the heterozygotes and 25.0% for MDM2SNP309G/G and 22.8% for MDM2SNP309T/T.There was not a statistical significant difference in median age of disease onset in the different MDM2 SNP309 subgroups of the BRCA1/2 carriers. When we further divided the group into under and above 51 years old ( presumed menopause age) in the BRCA1 positive subset we found that there were less patients of the MDM2SNP309 G/G versus the MDM2SNP309 T/T in the over 51 patient group (p = 0.049). This result has been obtained in a relatively small subgroup and is of borderline statistical significance. Interestingly, in the BRCA1/2 mutation carriers, we found a survival advantage for patients harboring the SNP309 G/G genotype (p = 0.0086) but not for the 272 patients not harbouring this mutations.

CONCLUSION

MDM2SNP309G/G main effect on BRCA1/2 positive mutation carriers is linked to its effect on patients survival. Further research is needed in order to understand the reason for this difference.

p53 polymorphisms: cancer implications

The normal functioning of p53 is a potent barrier to cancer. Tumour-associated mutations in TP53, typically single nucleotide substitutions in the coding sequence, are a hallmark of most human cancers and cause dramatic defects in p53 function. By contrast, only a small fraction, if any, of the >200 naturally occurring sequence variations (single nucleotide polymorphisms, SNPs) of TP53 in human populations are expected to cause measurable perturbation of p53 function. Polymorphisms in the TP53 locus that might have cancer-related phenotypical manifestations are the subject of this Review. Polymorphic variants of other genes in the p53 pathway, such as MDM2, which might have biological consequences either individually or in combination with p53 variants are also discussed.

Results based on 124 cases of breast cancer and 97 controls from Taiwan suggest that the single nucleotide polymorphism (SNP309) in the MDM2 gene promoter is associated with earlier onset and increased risk of breast cancer

Background

It has been suggested that the single nucleotide polymorphism 309 (SNP309, T -> G) in the promoter region of the MDM2 gene is important for tumor development; however, with regards to breast cancer, inconsistent associations have been reported worldwide. It is speculated that these conflicting results may have arisen due to different patient subgroups and ethnicities studied. For the first time, this study explores the effect of the MDM2 SNP309 genotype on Taiwanese breast cancer patients.

Methods

Genomic DNA was obtained from the whole blood of 124 breast cancer patients and 97 cancer-free healthy women living in Taiwan. MDM2 SNP309 genotyping was carried out by restriction fragment length polymorphism (RFLP) assay. The multivariate logistic regression and the Kaplan-Meier method were used for analyzing the risk association and significance of age at diagnosis among different MDM2 SNP309 genotypes, respectively.

Results

Compared to the TT genotype, an increased risk association with breast cancer was apparent for the GG genotype (OR = 3.05, 95% CI = 1.04 to 8.95), and for the TG genotype (OR = 2.12, 95% CI = 0.90 to 5.00) after adjusting for age, cardiovascular disease/diabetes, oral contraceptive usage, and body mass index, which exhibits significant difference between cases and controls. Furthermore, the average ages at diagnosis for breast cancer patients were 53.6, 52 and 47 years for those harboring TT, TG and GG genotypes, respectively. A significant difference in median age of onset for breast cancer between GG and TT+TG genotypes was obtained by the log-rank test (p = 0.0067).

Conclusion

Findings based on the current sample size suggest that the MDM2 SNP309 GG genotype may be associated with both the risk of breast cancer and an earlier age of onset in Taiwanese women.

A single nucleotide polymorphism in the Mdm2 promoter and risk of sepsis

BACKGROUND

The Mdm2-SNP309(T/G) polymorphism has been shown to upregulate transcription of Mdm2 and subsequently attenuate the p53 pathway. Its role in regulating the human response to acute illness has not been reported.

METHODS

Patients from the surgical intensive care unit were prospectively enrolled. SNP309 genotype was determined, and a genotype-based comparison of clinical outcomes was performed.

RESULTS

Of the 85 enrolled patients, 41 had wild type (T/T) and 44 had mutant (32 T/G and 12 G/G) genotypes. The mutant-genotype group tended to have a longer LOS in both the surgical intensive care unit (P = .40) and the hospital (P = .08), but these trends did not reach significance. No observable genotype-based differences were noted in any other measured parameters.

CONCLUSIONS

The Mdm2-SNP309(G) allele may be associated with longer LOS. However, it does not appear to influence any other clinical characteristics, nor can it be used to predict clinical outcome.

The genetics of the p53 pathway, apoptosis and cancer therapy

The p53 pathway has been shown to mediate cellular stress responses; p53 can initiate DNA repair, cell-cycle arrest, senescence and, importantly, apoptosis. These responses have been implicated in an individual's ability to suppress tumour formation and to respond to many types of cancer therapy. Here we focus on how best to use knowledge of this pathway to tailor current therapies and develop novel ones. Studies of the genetics of p53 pathway components - in particular p53 itself and its negative regulator MDM2 - in cancer cells has proven useful in the development of targeted therapies. Furthermore, inherited single nucleotide polymorphisms in p53 pathway genes could serve a similar purpose.

Association of HDM2 transcript levels with age of onset and prognosis in soft tissue sarcomas

The p53 stress response is crucial for the prevention of tumor formation. The oncogene HDM2 is one of the key negative regulators of p53 and is a central node in the p53 pathway. P53 and HDM2 form an oscillating feedback loop. HDM2 expression is regulated by different promoters. To evaluate its clinical relevance, we determined the levels of HDM2 transcripts originating from the constitutive P1 and p53-sensitive P2 promoter in 133 soft tissue sarcomas and correlated the results with the age of diagnosis and the patients' outcome. We show that only high levels of the HDM2-P1 transcript but not the P2 transcript are associated with an 11-year earlier age of onset (50.5 years) compared with low P1 levels (61.5 years; P < 0.0001, t test). In addition, low P1 and P2 mRNA expression levels were independent predictors of poor outcome for patients with soft tissue sarcomas (low P1: relative risk, 3.7; P < 0.0001; low P2: relative risk, 2.5; P = 0.001). A change in the expression levels of the HDM2 transcripts originating from the two HDM2 promoters could disrupt the oscillating P53-HDM2 feedback loop in a way that elevated levels of HDM2-P1 transcript are associated with an earlier age of tumor onset and that reduced levels of HDM2-P1 or HDM2-P2 transcripts are correlated with poor prognosis of patients with soft tissue sarcomas.

Therapeutic considerations for Mdm2: not just a one trick pony

BACKGROUND: The mdm2 proto-oncogene is elevated in numerous late stage cancers. The Mdm2 protein manifests its oncogenic properties in part through inactivation of the tumor suppressor protein p53. Recent efforts in anti-cancer drug design have focused on the identification of small molecules that disrupt the Mdm2-p53 interaction, in hopes of re-engaging the p53 pathway. OBJECTIVE: In addition to binding p53, Mdm2 complexes with numerous proteins involved in DNA repair, translation, metabolic activities, tumor growth and apoptosis. Additional biochemical analysis is required to understand how Mdm2 integrates into all of these cellular processes. Post-translational modifications to Mdm2 can alter its ability to associate with numerous proteins. Changes in protein structure may also affect the ability of small molecule inhibitors to effectively antagonize Mdm2. CONCLUSION: The complexity of Mdm2 modification has been largely neglected during the development of previous Mdm2 inhibitors. Future high-throughput or in silico screening efforts will need to recognize the importance of post-translational modifications to Mdm2. Furthermore, the identification of molecules that target other domains in Mdm2 may provide a tool to prevent other pivotal p53-independent functions of Mdm2. These aims provide a useful roadmap for the discovery of new Mdm2 binding compounds with therapeutic potency that may exceed its predecessors.

Genotyping of single nucleotide polymorphism in MDM2 genes by universal fluorescence primer PCR and capillary electrophoresis

Single nucleotide polymorphism (SNP) 309 in the promoter region of the murine double minute 2 (MDM2) gene plays an important role in human tumorigenesis. We established a simple and effective CE method for SNP detection in the MDM2 gene. We designed one universal fluorescence-based nonhuman-sequence primer and one fragment-oriented primer, which were combined in one tube, and proceeded with the polymerase chain reaction (PCR). The amplicons were analyzed by capillary electrophoresis using single-strand conformation polymorphism method. PCR fragments generated from this two-in-one PCR displayed either T/T or G/G homozygosity or T/G heterozygosity. A total of 304 samples were blindly genotyped using this developed method, which included the DNA from 138 healthy volunteers, 43 chronic myeloid leukemia (CML) patients, and 123 colorectal cancer (CRC) patients. The results were confirmed by DNA sequencing and showed good agreement. The SSCP-CE method was feasible for SNP screening of MDM2 in large populations.

Transcriptional responses to estrogen and progesterone in mammary gland identify networks regulating p53 activity

Estrogen and progestins are essential for mammary growth and differentiation but also enhance the activity of the p53 tumor suppressor protein in the mammary epithelium. However, the pathways by which these hormones regulate p53 activity are unknown. Microarrays were used to profile the transcriptional changes within the mammary gland after administration of either vehicle, 17beta-estradiol (E), or progesterone (P) individually and combined (EP). Treatment with EP yielded 1182 unique genes that were differentially expressed compared to the vehicle-treated group. Although 30% of genes were responsive to either E or P individually, combined treatment with both EP had a synergistic effect accounting for 60% of the differentially regulated genes. Analysis of protein-protein interactions identified p53, RelA, Snw1, and Igfals as common targets of genes regulated by EP. RelA and p53 form hubs within a network connected by genes that are regulated by EP and that may coordinate the competing functions of RelA and p53 in proliferation and survival of cells. Induction of early growth response 1 (Egr1) and Stratifin (Sfn) (also known as 14-3-3sigma) by EP was confirmed by reverse transcription-quantitative PCR and shown to be p53 independent. In luciferase reporter assays, Egr1 was shown to enhance transcriptional activation by p53 and inhibit nuclear factor kappaB activity. These results identify a gene expression network that provides redundant activation of RelA to support proliferation as well as sensitize p53 to ensure proper surveillance and integration of their competing functions through factors such as Egr1, which both enhance p53 and inhibit RelA.

MDM2 SNP309 is associated with high grade node positive breast tumours and is in linkage disequilibrium with a novel MDM2 intron 1 polymorphism

INTRODUCTION

A functional polymorphism within MDM2, SNP309 T>G, has been linked to early onset cancer. This study examined clinical associations of breast cancer with SNP309 in a Scottish Caucasian population and investigated additional MDM2 intron 1 polymorphisms.

METHODS

Intron 1 of MDM2 was PCR amplified and directly sequenced from 299 breast cancer patients and 275 cancer free controls and compared with clinical and pathological parameters.

RESULTS

SNP309 was observed, for the control and breast cancer cohorts respectively, at frequencies of: T/T = 44.7% and 39.5%; G/T = 42.2% and 47.2%; G/G = 13.1% and 13.4%, indicating that SNP309 is not a predisposing factor for breast cancer. The 309G/G genotype was associated with high grade tumours (OR = 1.64, 95%CI = 1.06-2.53, p = 0.025) and greater nodal involvement (OR = 2.51, 95%CI = 1.26-4.98, p = 0.009). SNP309 was not associated with an earlier age of cancer diagnosis. No association was observed between genotype and age of breast cancer diagnosis when patients were stratified by menopausal status and estrogen receptor status. Three additional low frequency SNPs were identified: 344T>A, 285G>C and 443G>T, the latter two novel. SNP285 was in complete linkage disequilibrium with SNP309 (D' = 1.0) with the minor alleles being in phase with each other. Moreover, the 285C/C, 309G/G double homozygous genotype was only observed in the breast cancer cohort.

CONCLUSION

SNP309G/G is associated with poor prognostic breast cancer features in the Scottish population. Additionally, a novel SNP, SNP285, that is in linkage disequilibrium with SNP309, may also have a role in breast tumorigenesis.

MDM2 SNP309 does not confer an increased risk to oral squamous cell carcinoma but may modulate the age of disease onset

The MDM2 SNP309 has been associated with increased expression of the protein which could suppress p53 function, and has been shown to modulate risk to cancer. We have previously shown that overexpression of MDM2 is a common event in oral cancers. In the present study, we determined the association between the MDM2 SNP309 polymorphism and oral cancer in 207 oral cancer patients and 116 normal subjects. We genotyped the MDM2 SNP309 by PCR-RFLP. Logistic regression was adapted to calculate odds ratios for MDM2 SNP309 polymorphism from univariate and multivariable adjusted models. Our results suggest that MDM2 SNP309 does not confer increased risk to oral cancer (OR=1.55, 95% CI=0.77-3.11). However, the GG/TG genotype was associated with later disease onset in women above 55 years of age. Collectively, our data suggests that MDM2 SNP309 may modulate the risk to oral cancer and is a modifier of the age at oral cancer onset in women above the age of 55 years.

Liver-specific expression of p53-negative regulator mdm2 leads to growth retardation and fragile liver in zebrafish

Tumorigenesis requires inactivation of the p53 tumor suppressor pathway, likely involving the negative regulator Mdm2 protein. To analyze the possible roles of Mdm2 in oncogenesis and other functions during zebrafish hepatogenesis, we generated transgenic zebrafish by liver-specific Mdm2 over-expression utilizing a fusion between genes encoding GFP and mdm2, GFP::Mdm2. Over-expression of GFP::Mdm2 in the zebrafish liver did not interrupt normal liver development in the larval stages but approximately 30% of the adult fish raised from the same larvae displayed obvious growth retardation at 16 weeks of age. Most growth-retarded adults displayed liver atrophy, contraction, or hypoplasia, which proved lethal within 4 to 8 months. Histologically, over-expression of GFP::Mdm2 in Gmdm2-liver leading to liver degeneration may in some way have been due to an increased cell apoptosis accompanied by a slightly interrupted cell cycle or hepatocyte proliferation. Liver degeneration or other transgenic phenotypes were not associated with liver cancer; however, liver-degenerated phenotypes could be passed to wild-type zebrafish. In this study, we generated transgenic zebrafish lines with a "fragile liver." The "fragile liver" zebrafish can provide a model for molecular pathology of liver diseases and for screening small molecules that affect mdm2-related pathways.

Association between polymorphisms in cell cycle genes and advanced prostate carcinoma

BACKGROUND

Single nucleotide polymorphisms (SNPs) have been associated with a variety of malignancies including prostate carcinoma (PCa). Since a high percentage of PCa patients have low risk disease, of particular interest is not whether SNPs are associated with localized PCa, but whether they are associated with aggressive, potentially lethal disease. Herein, we explored the role of SNPs in cell cycle genes to determine if they were associated with advanced PCa.

METHODS

Nine previously implicated SNPs in six cell cycle genes were evaluated in a European-American cohort of 186 patients with advanced PCa and 222 cancer-free controls. All patients received hormone ablation and had either a PSA>50 ng/ml or documented metastatic disease. Controls were all 75 years of age or older, had a negative DRE and had a PSA<4.0 ng/ml. All genotypes were determined using Pyrosequencing assays.

RESULTS

One of nine (CDKN1A c10791t) was statistically different (P<0.05) and an additional two of nine (CCND1 a870g and MDM2 tSNP309g) approached significance (P<0.1). Analysis of genotypes revealed that presence of at least one copy of the t allele of MDM2 tSNP309g was associated with an increased risk of advanced PCa (OR 2.26: 95% CI=1.15-4.46) which was particularly strong in androgen-independent disease (OR 2.28: 95% CI=1.01-5.12) and younger age of diagnosis (OR 2.61: 95% CI=1.05-6.46).

CONCLUSION

These results suggest that in a European-American population, SNPs within cell cycle genes are promising markers for aggressive PCa. Larger studies will be needed to confirm these findings.

MDM2 SNP309 is associated with endometrial cancer risk

Mouse double-minute 2 homologue (MDM2) is a key negative regulator of p53, a tumor suppressor gene that initiates cell cycle arrest and apoptosis in response to DNA damage and other cellular stresses. A T > G polymorphism found in the promoter region of MDM2 (SNP309) increases MDM2 expression and thereby attenuates p53 activity. We genotyped the MDM2 polymorphism SNP309 in endometrial cancer case-control studies nested within the Nurses' Health Study (454 cases and 1,132 controls) and the Women's Health Study (137 cases and 411 controls). Due to a significant difference in genotype distribution by ethnicity, we restricted our analyses to Caucasians. We calculated odds ratios and 95% confidence intervals using conditional and unconditional logistic regression adjusted for age at menarche, parity and age at first birth, postmenopausal hormone use at diagnosis, age at menopause and menopausal status at diagnosis, first-degree family history of colon cancer, body mass index at diagnosis, and cigarette smoking status at diagnosis. Women with a heterozygous genotype had no greater risk whereas those with a homozygous variant genotype had a greater risk than women with a wild-type genotype for the MDM2 SNP309 (covariate-adjusted odds ratio, 1.87; 95% confidence interval, 1.29-2.73) for endometrial cancer. We observed no association between age at diagnosis and genotype. Women carrying two copies of the MDM2 SNP309 variant may be at greater risk of endometrial cancer.

Genetic variants in germline TP53 and MDM2 SNP309 are not associated with early onset colorectal cancer

BACKGROUND AND OBJECTIVES

Colorectal cancer (CRC) arising in patients under age 30 is a rare disease, and few cases have been reported within Li-Fraumeni kindreds. To determine how often alterations in the p53 pathway genes contribute to disease susceptibility, we have evaluated patients with early onset CRC for the presence of germline variants in the p53 gene and MDM2 SNP309.

METHODS

Thirty-five patients with CRC diagnosed before age 30 were included in this study-based on tissue availability. DNA samples from peripheral blood leukocytes were analyzed for constitutional mutations and polymorphisms in p53 as well as polymorphisms in MDM2 SNP309.

RESULTS

No mutations were found in exons 4-10 of the p53 gene. The frequencies of polymorphisms in p53 and in MDM2 SNP309 did not differ from rates previously reported for normal control populations, and no polymorphism in either gene could be associated with early onset CRC.

CONCLUSIONS

Neither germline variants in p53 nor MDM2 SNP309 play an underlying role in the development of very early onset CRC. For the large majority of cases, the genetic basis of this disease remains unknown.

CRHR1 polymorphisms predict bone density in survivors of acute lymphoblastic leukemia

PURPOSE

Corticosteroids are a critical component of therapy for acute lymphoblastic leukemia (ALL) but are associated with late effects, such as osteoporosis. Risk factors remain poorly defined. Because CRHR1 polymorphisms have been associated with other corticosteroid effects, our goal was to define whether CRHR1 polymorphisms predict which patients with ALL are likely to develop bone mineral deficits.

PATIENTS AND METHODS

The mean bone mineral density z scores of 309 long-term survivors of ALL were determined by quantitative computed tomography of the trabecular lumbar spine. We analyzed whether CRHR1 genotypes, adjusted for sex, ALL treatment regimen, and weight, could predict bone density.

RESULTS

We found that three single nucleotide polymorphisms (SNPs), all in linkage disequilibrium, were associated with bone density in a sex-specific manner. Bone density was lower in males (P = .001), in nonblack patients (P < .08), in those who were not overweight (P < .001), and in those who received intensive antimetabolites and glucocorticoids (P < .001). After adjustment for these features, the G allele at the rs1876828 SNP was associated with lower z scores (P = .02) in males but tended to have the opposite association in females (P = .09).

CONCLUSION

CRHR1 polymorphisms may impact the risk of bone density deficits in patients treated with corticosteroids and antimetabolites in a sex-specific manner.

Impact of MDM2 single nucleotide polymorphism on tumor onset in head and neck squamous cell carcinoma

CONCLUSIONS

The GG genotype of MDM2 SNP309 is associated with an earlier onset of head and neck squamous cell carcinoma (HNSCC) in the Japanese population. SNP309 may be a key factor in the tumorigenesis of HNSCC as well as other hereditary or sporadic tumors.

OBJECTIVE

This study was designed to evaluate the association between the single nucleotide polymorphism (SNP) 309 in the MDM2 gene with HNSCC. An MDM2 protein down-regulates the p53 pathway. Recently, an important SNP was discovered in the MDM2 promoter region, which could affect the tumorigenesis of HNSCC by attenuation of the p53 pathway.

PATIENTS AND METHODS

Patients with 103 HNSCCs were genotyped using direct sequencing and real-time PCR. The relationship between the SNP309 genotypes and the clinicopathological features was statistically analyzed.

RESULTS

The number of patients genotyped to TT, TG, and GG was 29 (28%), 46 (44.7%), and 28 (27.2%), respectively. The average age at tumor onset was 65.6 years for TT, 62.9 years for TG, and 56.7 years for GG. The patients with the GG genotype had a significantly earlier tumor onset in comparison to those with the TT genotype (p=0.032).

Mdm2-SNP309 polymorphism in prostate cancer: no evidence for association with increased risk or histopathological tumour characteristics

The search for inherited cancer susceptibility factors is a major focus of epidemiologic cancer studies. Analyses of single-nucleotide polymorphisms (SNP) in a variety of genes revealed a correlation between a specific allele variant and cancer predisposition. Human mouse double-minute 2 protein (Mdm2) is a cellular E3 ligase capable of ubiquitination and degradation of p53. Therefore, Mdm2 is a crucial factor of cell cycle control and cell survival. The Mdm2 promoter SNP309 was shown to increase Mdm2 expression and can, thereby, inhibit the p53 pathway. This SNP was found to be associated with increased risk and early onset of various malignancies. For prostate cancer no studies are reported to date. In a case-control study we determined the distribution of the Mdm2 SNP309 in 145 male subjects with prostate cancer and in 124 male controls without any malignancy using RFLP analysis. Cases and controls showed a similar distribution of the SNP (P=0.299). Genotype distribution showed neither an association with histopathological characteristics of the tumours nor with prognosis. Age at disease onset was also not modified by the SNP. This first study of the Mdm2 SNP309 in prostate cancer patients suggests no correlation between a certain allelic variant and an increased cancer risk.

Recurrent initiation: a mechanism for triggering p53 pulses in response to DNA damage

DNA damage initiates a series of p53 pulses. Although much is known about the interactions surrounding p53, little is known about which interactions contribute to p53's dynamical behavior. The simplest explanation is that these pulses are oscillations intrinsic to the p53/Mdm2 negative feedback loop. Here we present evidence that this simple mechanism is insufficient to explain p53 pulses; we show that p53 pulses are externally driven by pulses in the upstream signaling kinases, ATM and Chk2, and that the negative feedback between p53 and ATM, via Wip1, is essential for maintaining the uniform shape of p53 pulses. We propose that p53 pulses result from repeated initiation by ATM, which is reactivated by persistent DNA damage. Our study emphasizes the importance of collecting quantitative dynamic information at high temporal resolution for understanding the regulation of signaling pathways and opens new ways to manipulate p53 pulses to ask questions about their function in response to DNA damage.

Combined effects of MDM2 SNP 309 and p53 mutation on oral squamous cell carcinomas associated with areca quid chewing

The recently identified single nucleotide polymorphism in the MDM2 promoter (SNP 309) may contribute to the early onset of both sporadic and hereditary malignancies in patients with defective p53. We tested this hypothesis by examining the effects of combined MDM2 polymorphisms and somatic p53 mutations on 351 oral squamous cell carcinomas (OSCCs) associated with areca quid chewing. We found that the G allele of MDM2 SNP 309 was associated with early age of onset (p=0.02) and poor differentiation of OSCC tumors (p=0.01). The frequency of lymph node extracapsular spread (LNECS) was increased in individuals having both the MDM2 SNP 309 GG genotype and p53 mutation (chi(2) for trend p=0.04). MDM2 GG genotype and p53 mutations were associated with poor disease-free survival in both early and lymph node positive advanced stage OSCC patients (Hazard ratio=2.77 and 1.93, respectively). Taken together, an interaction between MDM2 SNP 309 and p53 with respect to tumor behaviors (including disease onset, tumor differentiation, LNECS and disease-free survival) was observed in sporadic Taiwanese OSCCs.

MDM2 SNP309 Is Associated With Poor Outcome in B-Cell Chronic Lymphocytic Leukemia

Purpose

A single nucleotide polymorphism (SNP) at position 309 in the promoter region of MDM2 leading to increased expression of MDM2 and attenuated function of p53 has been negatively associated with onset and outcome of disease in solid tumors. Because inactivation of p53 by deletion and/or mutations also impacts on the clinical course of B-cell chronic lymphocytic leukemia (B-CLL), we assessed the role of the SNP309 genotype in B-CLL.

Patients and Methods

The frequency of SNP309 T/T, T/G, or G/G genotypes and the p53 status (wild type, mutated, or deleted) were assessed and correlated with clinical outcome in 140 B-CLL patients and a second independent cohort. In addition, the correlation of the MDM2 SNP309 genotype with the MDM2 protein expression level in B-CLL cells was evaluated by immunoblotting.

Results

A significant negative association of the SNP309 T/G and G/G genotypes with overall survival was seen (T/G genotype, relative risk = 3.7; 95% CI, 1.2 to 11.5; P = .02; G/G genotype, relative risk = 9.1; 95% CI, 2.4 to 35.1; P = .001), but no correlation with incidence or onset of B-CLL was observed. The influence of the heterozygous SNP309 T/G genotype on treatment-free survival depended on the p53 status but not on the CD38, Zap-70, or IgVH mutational status or Rai stage of B-CLL patients. The unfavorable SNP309 T/G and G/G genotypes were associated with a gene-dosage–dependent increase of MDM2 expression.

Conclusion

The MDM2 SNP309 genotype influencing MDM2 expression levels was identified as an additional independent risk factor in B-CLL. Targeting MDM2-p53 interactions might emerge as a successful treatment strategy for B-CLL.