mdm2 gene alterations and mdm2 protein expression in breast carcinomas

MDM2 amplification is rare in gastric cancer

The MDM2 proto-oncogene (MDM2) is a primary negative regulator of p53. The latter is frequently mutated in gastric cancer (GC). In the present study, we aimed to validate gene amplification, protein expression, and the putative tumor biological function of MDM2 in a well-characterized Western GC cohort. MDM2 amplification and protein expression were studied in a cohort of 327 GCs by fluorescence in situ hybridization (FISH) and immunohistochemistry. Gene amplification and protein expression were correlated with diverse clinicopathological patient characteristics including patient outcome. Immunohistochemically, 97 GCs (29.7%) were categorized as MDM2 positive and 230 GCs (70.3%) as negative. An amplification of MDM2 was found in 11 (3.4%) cases without evidence of intratumoral heterogeneity. Nine of these eleven (81.8%) cases showed MDM2 protein expression. MDM2 amplification correlated significantly with MDM2 protein expression (p < 0.001). On a case-by-case analysis, MDM2-amplified cases showed varied histological phenotypes and were most commonly microsatellite stable; EBV, HER2, and MET negative; and FGFR2 positive. A single case harbored both, MDM2 amplification and TP53 mutation. MDM2 amplification and MDM2 expression, respectively, did not correlate with overall or tumor-specific survival. Our targeted analysis of MDM2 in a well-characterized cohort of GC patients showed that MDM2 amplification is rare, of no specific histological phenotype, and may not be always mutually exclusive with TP53 mutations. Given the low number of cases, currently, no diagnostic or therapeutic recommendation related to MDM2 amplification can be given for GC of Western origin.

Novel genomic alteration in superficial esophageal squamous cell neoplasms in non-smoker non-drinker females

Alcohol consumption and smoking pose a significant risk for esophageal squamous cell neoplasia (ESCN) development in males; however, ESCN is often diagnosed in non-drinking and non-smoking females. The mechanisms underlying these differences remain elusive, and understanding them can potentially identify novel pathways involved in ESCN development. We performed short-read sequencing to identify somatic variants on a cancer panel targeting 409 genes using DNA extracted from the superficial squamous cell carcinoma (ESCC) tissues and adjacent non-neoplastic epithelium (NE), and immunohistochemical staining of the protein encoded by the target gene. All male patients (n = 117) were drinkers or smokers, whereas 45% of the female patients (n = 33) were not. Somatic variants were compared among three age-matched groups: 13 female ESCC patients with smoking and drinking habits (known-risk group, F-KR), 13 female ESCC patients without these habits (unknown-risk group, F-UR), and 27 males with ESCC and smoking and drinking habits (M-KR). In the NE, the frequencies of CDKN2A variants were significantly higher in F-UR than in F-KR and M-KR. In both ESCC and NE, p14ARF was significantly overexpressed in F-UR than in the other groups. In conclusion, CDKN2A might be important in ESCC development, independent of known risk factors.

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

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

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

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

MicroRNA-379-5p plays a tumor-suppressive role in human bladder cancer growth and metastasis by directly targeting MDM2

Bladder cancer is the second most common urological malignancy in the US and is the most frequently diagnosed urological malignancy in China. An increasing amount of evidence indicates that microRNAs perform extremely important functions in many biological processes related to the formation and progression of cancers, including bladder cancer. Previous studies have reported that microRNA‑379-5p (miR-379-5p) is involved in tumour initiation and development in human cancers. However, the expression pattern, biological functions and the underlying mechanisms of miR-379-5p in bladder cancer remain unknown. The present study demonstrated that the expression levels of miR‑379-5p in bladder cancer tissues and cell lines were lower than the levels in adjacent normal tissues and the human bladder epithelial immortalized SV-HUC-1 cell line. Restoration of the expression of miR-379-5p inhibited bladder cancer cell proliferation, migration and invasion. Mouse double minute 2 (MDM2) was identified as a direct target gene of miR-379-5p. Furthermore, similar to miR-379-5p overexpression in bladder cancer cells, inhibition of MDM2 exerted tumor-suppressive effects. Rescue experiments showed that upregulation of MDM2 reversed the inhibitory effects of miR-379-5p on bladder cancer cell proliferation, migration and invasion. MDM2 was highly expressed and inversely correlated with miR-379-5p expression in bladder cancer tissues. These findings suggest that the miR-379-5p/MDM2 pathway plays an important role in bladder cancer and could serve as a potential candidate for bladder cancer therapeutics.

mir-660-p53-mir-486 Network: A New Key Regulatory Pathway in Lung Tumorigenesis

Lung cancer is the most frequent cause of cancer-related death worldwide, with limited therapeutic options and rapid development of drug resistance. MicroRNAs, a class of small non-coding RNAs that control different physiological processes, have been associated with cancer development, as either oncomiRNAs or tumor-suppressor miRNAs. In the present study we investigated the interaction between mir-486-5p and mir-660-5p, two independent tumor-suppressor miRNAs, to assess their possible role and synergistic effect in lung cancer treatment. Our data show that mir-660-5p over-expression in A549 lung cancer cells induced a remarkable increase in mir-486-5p expression level and activity, detected as a reduction of its target gene, p85. mir-486-5p expression was confirmed by microRNA in situ hybridization. mir-660-5p modulated mir-486-5p through the silencing of Mouse Double Minute 2 (MDM2), one of its direct target, and then through p53 stimulation. This regulatory pathway was effective in A549, but not in H1299; therefore, only in the context of a functional p53 protein. Our findings support the conclusion that mir-486-5p is positively regulated by mir-660-5p in lung cancer cell lines, through the mir-660-MDM2-p53 pathway, making mir-660-5p even more interesting for its potential successful use in lung cancer therapy.

MDM2 oligomers: antagonizers of the guardian of the genome

Over two decades of MDM2 research has resulted in the accumulation of a wealth of knowledge of many aspects of MDM2 regulation and function, particularly with respect to its most prominent target, p53. For example, recent knock-in mouse studies have shown that MDM2 heterooligomer formation with its homolog, MDMX, is necessary and sufficient in utero to suppress p53 but is dispensable during adulthood. However, despite crucial advances such as these, several aspects regarding basic in vivo functions of MDM2 remain unknown. In one such example, although abundant evidence suggests that MDM2 forms homooligomers and heterooligomers with MDMX, the function and regulation of these homo- and heterooligomers in vivo remain incompletely understood. In this review, we discuss the current state of our knowledge of MDM2 oligomerization as well as current efforts to target the MDM2 oligomer as a broad therapeutic option for cancer treatment.

Estrogen receptor alpha (ERα/ESR1) mediates the p53-independent overexpression of MDM4/MDMX and MDM2 in human breast cancer

MDM2 and MDM4 are heterodimeric, non-redundant oncoproteins that potently inhibit the p53 tumor suppressor protein. MDM2 and MDM4 also enhance the tumorigenicity of breast cancer cells in in vitro and in vivo models and are overexpressed in primary human breast cancers. Prior studies have characterized Estrogen Receptor Alpha (ERα/ESR1) as a regulator of MDM2 expression and an MDM2- and p53-interacting protein. However, similar crosstalk between ERα and MDM4 has not been investigated. Moreover, signaling pathways that mediate the overexpression of MDM4 in human breast cancer remain to be elucidated. Using the Cancer Genome Atlas (TCGA) breast invasive carcinoma patient cohort, we have analyzed correlations between ERα status and MDM4 and MDM2 expression in primary, treatment-naïve, invasive breast carcinoma samples. We report that the expression of MDM4 and MDM2 is elevated in primary human breast cancers of luminal A/B subtypes and associates with ERα-positive disease, independently of p53 mutation status. Furthermore, in cell culture models, ERα positively regulates MDM4 and MDM2 expression via p53-independent mechanisms, and these effects can be blocked by the clinically-relevant endocrine therapies fulvestrant and tamoxifen. Additionally, ERα also positively regulates p53 expression. Lastly, we report that endogenous MDM4 negatively regulates ERα expression and forms a protein complex with ERα in breast cancer cell lines and primary human breast tumor tissue. This suggests direct signaling crosstalk and negative feedback loops between ERα and MDM4 expression in breast cancer cells. Collectively, these novel findings implicate ERα as a central component of the p53-MDM2-MDM4 signaling axis in human breast cancer.

Energetic Landscape of MDM2-p53 Interactions by Computational Mutagenesis of the MDM2-p53 Interaction

The ubiquitin ligase MDM2, a principle regulator of the tumor suppressor p53, plays an integral role in regulating cellular levels of p53 and thus a prominent role in current cancer research. Computational analysis used MUMBO to rotamerize the MDM2-p53 crystal structure 1YCR to obtain an exhaustive search of point mutations, resulting in the calculation of the ΔΔG comprehensive energy landscape for the p53-bound regulator. The results herein have revealed a set of residues R65-E69 on MDM2 proximal to the p53 hydrophobic binding pocket that exhibited an energetic profile deviating significantly from similar residues elsewhere in the protein. In light of the continued search for novel competitive inhibitors for MDM2, we discuss possible implications of our findings on the drug discovery field.

Interaction between p53 codon 72 and MDM2 309T>G polymorphisms and the risk of hepatocellular carcinoma

The p53 tumor suppressor and its negative regulator, murine double minute 2 (MDM2), play critical roles in carcinogenesis. P53 codon 72 and MDM2 309T>G polymorphisms could influence p53 and MDM2 function, respectively, and might affect cancer susceptibility. We therefore investigated the association between these two SNPs, alone or in combination, and the risk of hepatocellular carcinoma (HCC) in Chinese. In this case-control study, we genotyped p53 codon 72 and MDM2 309T>G polymorphisms in 985 HCC cases and 992 cancer-free age- and sex-matched controls and evaluated their associations with the risk of HCC. Although no significant main effects were found for these two SNPs in the single-locus analysis and stratified analysis by age, sex, smoking, drinking, and hepatitis B virus (HBV) infection, we found that individuals carrying at least one G allele of the MDM2 309T>G polymorphism had statistically significant increased risk of HCC among those with the p53 Pro/Pro genotype (adjusted odds ratio (OR) = 2.23, 95 % confidence interval (95%CI) = 1.20-4.14 for TG genotype; adjusted OR = 2.67, 95%CI = 1.32-5.42 for GG genotype), and the interaction between p53 codon 72 and MDM2 309T>G was significant (P interaction = 0.017). Our findings suggest that the interaction of p53 codon 72 and MDM2 309T>G may play an important role in the etiology of HCC. More studies with well-designed and large sample sizes are required to validate these observations.

Critical review about MDM2 in cancer: Possible role in malignant mesothelioma and implications for treatment

The tumor suppressor p53 regulates genes involved in DNA repair, metabolism, cell cycle arrest, apoptosis and senescence. p53 is mutated in about 50% of the human cancers, while in tumors with wild-type p53 gene, the protein function may be lost because of overexpression of Murine Double Minute 2 (MDM2). MDM2 targets p53 for ubiquitylation and proteasomal degradation. p53 reactivation through MDM2 inhibitors seems to be a promising strategy to sensitize p53 wild-type cancer cells to apoptosis. Moreover, additional p53-independent molecular functions of MDM2, such as neoangiogenesis promotion, have been suggested. Thus, MDM2 might be a target for anticancer treatment because of its antiapoptotic and proangiogenetic role. Malignant pleural mesothelioma (MPM) is an aggressive asbestos-related tumor where wild-type p53 might be present. The present review gives a complete landscape about the role of MDM2 in cancer pathogenesis, prognosis and treatment, with particular focus on Malignant Pleural Mesothelioma.

Targeting Mdmx to treat breast cancers with wild-type p53

The function of the tumor suppressor p53 is universally compromised in cancers. It is the most frequently mutated gene in human cancers (reviewed). In cases where p53 is not mutated, alternative regulatory pathways inactivate its tumor suppressive functions. This is primarily achieved through elevation in the expression of the key inhibitors of p53: Mdm2 or Mdmx (also called Mdm4) (reviewed). In breast cancer (BrCa), the frequency of p53 mutations varies markedly between the different subtypes, with basal-like BrCas bearing a high frequency of p53 mutations, whereas luminal BrCas generally express wild-type (wt) p53. Here we show that Mdmx is unexpectedly highly expressed in normal breast epithelial cells and its expression is further elevated in most luminal BrCas, whereas p53 expression is generally low, consistent with wt p53 status. Inducible knockdown (KD) of Mdmx in luminal BrCa MCF-7 cells impedes the growth of these cells in culture, in a p53-dependent manner. Importantly, KD of Mdmx in orthotopic xenograft transplants resulted in growth inhibition associated with prolonged survival, both in a preventative model and also in a treatment model. Growth impediment in response to Mdmx KD was associated with cellular senescence. The growth inhibitory capacity of Mdmx KD was recapitulated in an additional luminal BrCa cell line MPE600, which expresses wt p53. Further, the growth inhibitory capacity of Mdmx KD was also demonstrated in the wt p53 basal-like cell line SKBR7 line. These results identify Mdmx growth dependency in wt p53 expressing BrCas, across a range of subtypes. Based on our findings, we propose that Mdmx targeting is an attractive strategy for treating BrCas harboring wt p53.

Verification of gene expression profiles for colorectal cancer using 12 internet public microarray datasets

AIM: To verify gene expression profiles for colorectal cancer using 12 internet public microarray datasets.

METHODS: Logistic regression analysis was performed, and odds ratios for each gene were determined between colorectal cancer (CRC) and controls. Twelve public microarray datasets of GSE 4107, 4183, 8671, 9348, 10961, 13067, 13294, 13471, 14333, 15960, 17538, and 18105, which included 519 cases of adenocarcinoma and 88 normal mucosa controls, were pooled and used to verify 17 selective genes from 3 published studies and estimate the external generality.

RESULTS: We validated the 17 CRC-associated genes from studies by Chang et al (Model 1: 5 genes), Marshall et al (Model 2: 7 genes) and Han et al (Model 3: 5 genes) and performed the multivariate logistic regression analysis using the pooled 12 public microarray datasets as well as the external validation. The goodness-of-fit test of Hosmer-Lemeshow (H-L) showed statistical significance (P = 0.044) for Model 2 of Marshall et al in which observed event rates did not match expected event rates in subgroups of the model population. Expected and observed event rates in subgroups were similar, which are called well calibrated, in Models 1, 3 and 4 with non-significant P values of 0.460, 0.194 and 1.000 for H-L tests, respectively. A 7-gene model of CPEB4, EIF2S3, MGC20553, MS4A1, ANXA3, TNFAIP6 and IL2RB was pairwise selected, which showed the best results in logistic regression analysis (H-L P = 1.000, R² = 0.951, areas under the curve = 0.999, accuracy = 0.968, specificity = 0.966 and sensitivity = 0.994).

CONCLUSION: A novel gene expression profile was associated with CRC and can potentially be applied to blood-based detection assays.

Mir-660 is downregulated in lung cancer patients and its replacement inhibits lung tumorigenesis by targeting MDM2-p53 interaction

Lung cancer represents the leading cause of cancer-related death in developed countries. Despite the advances in diagnostic and therapeutic techniques, the 5-year survival rate remains low. The research for novel therapies directed to biological targets has modified the therapeutic approach, but the frequent engagement of resistance mechanisms and the substantial costs, limit the ability to reduce lung cancer mortality. MicroRNAs (miRNAs) are small noncoding RNAs with known regulatory functions in cancer initiation and progression. In this study we found that mir-660 expression is downregulated in lung tumors compared with adjacent normal tissues and in plasma samples of lung cancer patients with poor prognosis, suggesting a potential functional role of this miRNA in lung tumorigenesis. Transient and stable overexpression of mir-660 using miRNA mimics reduced migration, invasion, and proliferation properties and increased apoptosis in p53 wild-type lung cancer cells (NCI-H460, LT73, and A549). Furthermore, stable overexpression using lentiviral vectors in NCI-H460 and A549 cells inhibited tumor xenograft growth in immunodeficient mice (95 and 50% reduction compared with control, respectively), whereas the effects of mir-660 overexpression were absent in H1299, a lung cancer cell line lacking p53 locus, both in in vitro and in vivo assays. We identified and validated mouse double minute 2 (MDM2) gene, a key regulator of the expression and function of p53, as a new direct target of mir-660. In addition, mir-660 expression reduced both mRNA and protein expression of MDM2 in all cell lines and stabilized p53 protein levels resulting in an upregulation of p21^WAF1/CIP1 in p53 wild-type cells. Our finding supports that mir-660 acts as a tumor suppressor miRNA and we suggest the replacement of mir-660 as a new therapeutic approach for p53 wild-type lung cancer treatment.

Gene expression profile of peripheral blood in colorectal cancer

AIM: Optimal molecular markers for detecting colorectal cancer (CRC) in a blood-based assay were evaluated.

METHODS: A matched (by variables of age and sex) case-control design (111 CRC and 227 non-cancer samples) was applied. Total RNAs isolated from the 338 blood samples were reverse-transcribed, and the relative transcript levels of candidate genes were analyzed. The training set was made of 162 random samples of the total 338 samples. A logistic regression analysis was performed, and odds ratios for each gene were determined between CRC and non-cancer. The samples (n = 176) in the testing set were used to validate the logistic model, and an inferred performance (generality) was verified. By pooling 12 public microarray datasets(GSE 4107, 4183, 8671, 9348, 10961, 13067, 13294, 13471, 14333, 15960, 17538, and 18105), which included 519 cases of adenocarcinoma and 88 controls of normal mucosa, we were able to verify the selected genes from logistic models and estimate their external generality.

RESULTS: The logistic regression analysis resulted in the selection of five significant genes (P < 0.05; MDM2, DUSP6, CPEB4, MMD, and EIF2S3), with odds ratios of 2.978, 6.029, 3.776, 0.538 and 0.138, respectively. The five-gene model performed stably for the discrimination of CRC cases from controls in the training set, with accuracies ranging from 73.9% to 87.0%, a sensitivity of 95% and a specificity of 95%. In addition, a good performance in the test set was obtained using the discrimination model, providing 83.5% accuracy, 66.0% sensitivity, 92.0% specificity, a positive predictive value of 89.2% and a negative predictive value of 73.0%. Multivariate logistic regressions analyzed 12 pooled public microarray data sets as an external validation. Models that provided similar expected and observed event rates in subgroups were termed well calibrated. A model in which MDM2, DUSP6, CPEB4, MMD, and EIF2S3 were selected showed the result in logistic regression analysis (H-L P = 0.460, R2= 0.853, AUC = 0.978, accuracy = 0.949, specificity = 0.818 and sensitivity = 0.971).

CONCLUSION: A novel gene expression profile was associated with CRC and can potentially be applied to blood-based detection assays.

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

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

Subcellular localization of Mdm2 expression and prognosis of breast cancer

BACKGROUND

Mouse double minute 2 (Mdm2) is a negative regulator of the tumor suppressor p53. The p53-Mdm2 pathway may play a role in cancer development and prognosis, although the role of p53-Mdm2 in breast cancer remains unclear.

METHODS

p53 and Mdm2 expressions were determined by immunohistochemistry of tissue microarrays of 865 breast cancer patients who underwent surgery. Clinicopathological characteristics and survival data were analyzed. Mdm2 expression was categorized into four groups: negative, cytoplasm positive, nucleus positive, and concurrent nuclear and cytoplasm positive (N+&C+).

RESULTS

Negative, cytoplasm-positive, nucleus-positive, and N+&C+ expressions of Mdm2 were observed in 59.2, 10.9, 27.8, and 2.1 % of patients, respectively. The N+&C+ group was associated with larger tumor size, higher grade, negativity for estrogen and progesterone receptors, HER2 positivity, high Ki-67 index, p53 positivity, and triple negative breast cancer. p53-positive tumors showed poorer overall survival than p53-negative tumors. The nucleus-positive and N+&C+ groups showed poorer disease-free survival than the negative and cytoplasm-positive groups. In multivariate analysis, nuclear Mdm2 expression including the N+&C+ group was significantly related to poor prognosis.

CONCLUSIONS

Concurrent nuclear and cytoplasmic Mdm2 expression was an independent prognostic factor in patients with breast cancer. Subcellular localization of Mdm2 expression should be considered in the evaluation of Mdm2 in breast cancer.

Prognostic value of the hDMP1-ARF-Hdm2-p53 pathway in breast cancer

Our recent study showed critical roles of Dmp1 as a sensor of oncogenic Ras, HER2/neu signaling and activation of the Arf-p53 pathway. To elucidate the role of human DMP1 (hDMP1) in breast cancer, one hundred and ten pairs of human breast cancer specimen were studied for the alterations of the hDMP1-ARF-Hdm2-p53 pathway with follow up of clinical outcomes. Loss of heterozygosity (LOH) of the hDMP1 locus was found in 42% of human breast carcinomas, while that of INK4a/ARF and p53 were found in 20 and 34%, respectively. Hdm2 amplification was found in 13% of the same sample, which was found independently of LOH for hDMP1. Conversely, LOH for hDMP1 was found in mutually exclusive fashion with that of INK4a/ARF and p53, and was associated with low Ki67 index and diploid karyotype. Consistently, LOH for hDMP1 was associated with luminal A category and longer relapse-free survival, while that of p53 was associated with non-luminal A and shorter survival. Thus, loss of hDMP1 could define a new disease category associated with prognosis of breast cancer patients. Human breast epithelial cells/cancer cells with wild-type p53 were sensitive to growth inhibition by activated Dmp1:ER while those that delete p14(ARF) or p53, and/or Hdm2 amplification showed partial or nearly complete resistance, indicating that p53 is a critical target for hDMP1 to exhibit its biological activity.

Disruption of estrogen receptor alpha-p53 interaction in breast tumors: a novel mechanism underlying the anti-tumor effect of radiation therapy

Inactivation of tumor suppressor p53 is one of the most frequent events in cancer. Unlike many other cancers, however, p53 gene mutations are infrequent in breast cancers, as about 80% of breast tumors contain wild type p53. The mechanisms underlying functional inactivation of wild type p53 in breast cancer have remained elusive. Besides, how p53 gets activated in breast tumors subjected to radiation therapy remains unknown. We recently reported that in MCF-7 breast cancer cells, estrogen receptor alpha (ERalpha) directly binds to p53 and represses its function. Furthermore, the ERalpha-p53 interaction was disrupted by ionizing radiation. These observations have important translational implications especially as there are no reliable cellular or molecular criteria for rational radiotherapy for breast cancer. Here we report our studies towards addressing this important issue, using an MCF-7 breast cancer xenograft model in mice. Radiation effectively inhibits growth of these tumors and stabilizes p53, but has no observable effect on ERalpha protein level. Importantly, chromatin immunoprecipitation (ChIP) assays demonstrated that ERalpha interacts with p53 bound to endogenous target gene promoters in tumors in vivo, and this interaction is considerably reduced in response to radiotherapy although p53 level is increased. Concomitant with its effect on ERalpha-p53 interaction, radiation increases p53-mediated transcriptional activation of several target genes and increases p53-mediated transcriptional repression of survivin. Our studies show that disruption of ERalpha-p53 interaction in vivo resulting in restoration of functional p53 is a cellular response to radiation. Radiation could be affecting ERalpha and/or p53 directly or it could be influencing other proteins associated with the ERalpha-p53 complex. To the best of our knowledge, this is the first report on analysis of DNA-protein-protein interaction occurring on endogenous gene promoters in vivo in breast tumor tissues. These findings suggest that alleviating the inhibitory effect of ERalpha on p53 could be one of the molecular mechanisms underlying activation of p53 by radiation in breast tumors, and therefore, could be exploited to develop more effective ways of combining radiation therapy with systemic therapies such as hormonal therapy and chemotherapy.

MDM2 promoter polymorphism SNP309 contributes to tumor susceptibility: evidence from 21 case-control studies

Since the identification of a well-characterized functional polymorphism named SNP309 in MDM2, abundant studies were published in the last 2 years to evaluate the association between SNP309 and tumor risk in diverse populations. However, the results remain conflicting rather than conclusive. Because a single study may have been underpowered to detect the effect of low-penetrance genes, a quantitative synthesis to accumulate data from different studies may provide better evidence on the association of genetic variant with tumor susceptibility. We conducted a meta-analysis on 14,770 cases with different tumor types and 14,524 controls from 25 published case-control studies to estimate the effect of SNP309 on tumor risk, as well as to quantify the potential between-study heterogeneity. We found that variant homozygote 309GG was associated with a significantly increased risk of all types of tumors [homozygote comparison: odds ratio (OR), 1.17, 95% confidential interval (95% CI), 1.04-1.33, P = 0.0002 for heterogeneity test; recessive model comparison: OR, 1.15, 95% CI, 1.03-1.28, P = 0.0005 for heterogeneity test]. Tumor type and ethnicity contributed to the substantial heterogeneity (69.5% for homozygote comparison and 77.2% for recessive model comparison). The analyses suggest that MDM2 SNP309 serves as a low-penetrance susceptibility tumor marker. Further large studies incorporate quantitative detection of different p53-responsible environmental stresses, p53 mutation status, and also functional genetic variants in p53-MDM2-related genes are warranted.

A single nucleotide polymorphism in the p53 pathway interacts with gender, environmental stresses and tumor genetics to influence cancer in humans

Cancer biology finds itself in a post-genomic era and the hopes of using inherited genetic variants to improve prevention and treatment strategies are widespread. One of the largest types of inherited genetic variation is the single nucleotide polymorphism (SNP), of which there are at least 4.5 million. The challenge now becomes how to discover which polymorphisms alter cancer in humans and how to begin to understand their mechanism of action. In this report, a series of recent publications will be reviewed that have studied a polymorphism in the p53 tumor suppressor pathway, MDM2 SNP309. These reports have lent insights into how germline genetic variants of the p53 pathway could interact with gender, environmental stresses and tumor genetics to affect cancer in humans. Importantly, these observations have also exposed potential nodes of intervention, which could prove valuable in both the prevention and treatment of this disease in humans.

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

Oscillations of both p53 and MDM2 proteins have been observed in cells after exposure to stress. A mathematical model describing these oscillations predicted that oscillations occur only at selected levels of p53 and MDM2 proteins. This model prediction suggests that oscillations will disappear in cells containing high levels of MDM2 as observed with a single nucleotide polymorphism in the MDM2 gene (SNP309). The effect of SNP309 upon the p53-MDM2 oscillation was examined in various human cell lines and the oscillations were observed in the cells with at least one wild-type allele for SNP309 (T/T or T/G) but not in cells homozygous for SNP309 (G/G). Furthermore, estrogen preferentially stimulated the transcription of MDM2 from SNP309 G allele and increased the levels of MDM2 protein in estrogen-responsive cells homozygous for SNP309 (G/G). These results suggest the possibility that SNP309 G allele may contribute to gender-specific tumorigenesis through further elevating the MDM2 levels and disrupting the p53-MDM2 oscillation. Furthermore, using the H1299-HW24 cells expressing wild-type p53 under a tetracycline-regulated promoter, the p53-MDM2 oscillation was observed only when p53 levels were in a specific range, and DNA damage was found to be necessary for triggering the p53-MDM2 oscillation. This study shows that higher levels of MDM2 in cells homozygous for SNP309 (G/G) do not permit coordinated p53-MDM2 oscillation after stress, which might contribute to decreased efficiency of the p53 pathway and correlates with a clinical phenotype (i.e., the development of cancers at earlier age of onset in female).

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

The importance of the p53 stress response pathway in the suppression of tumor formation is well documented. In a previous report, a single nucleotide polymorphism (SNP309 T/G) was found in the promoter of the MDM2 gene resulting in higher levels of MDM2 RNA and protein and, consequently, in the attenuation of the p53 pathway both in vitro and in vivo. As the SNP309 locus is found in a region of the MDM2 promoter, which is regulated by hormonal signaling pathways, and the G-allele of SNP309 increases the affinity of a well-described cotranscriptional activator of nuclear hormone receptors (i.e., Sp1), the hypothesis that the SNP309 locus could alter the effects of hormones on tumorigenesis was tested in vivo in humans. Data obtained from patients with three different sporadic cancers, from four independent case studies, support this hypothesis, providing an example for the genetic basis of gender differences in cancer and showing that the genotype at a specific locus can affect how hormones, like estrogen, affect tumorigenesis in humans.

Interferon-inducible protein IFIXalpha1 functions as a negative regulator of HDM2

The 200-amino-acid repeat (HIN-200) gene family with the hematopoietic interferon (IFN)-inducible nuclear protein encodes highly homologous proteins involved in cell growth, differentiation, autoimmunity, and tumor suppression. IFIX is the newest member of the human HIN-200 family and is often downregulated in breast tumors and breast cancer cell lines. The expression of the longest isoform of IFIX gene products, IFIXalpha1, is associated with growth inhibition, suppression of transformation, and tumorigenesis. However, the mechanism underlying the tumor suppression activity of IFIXalpha1 is not well understood. Here, we show that IFIXalpha1 downregulates HDM2, a principal negative regulator of p53, at the posttranslational level. IFIXalpha1 destabilizes HDM2 protein and promotes its ubiquitination. The E3 ligase activity of HDM2 appears to be required for this IFIXalpha1 effect. Importantly, HDM2 downregulation is required for the IFIXalpha1-mediated increase of p53 protein levels, transcriptional activity, and nuclear localization, suggesting that IFIXalpha1 positively regulates p53 by acting as a negative regulator of HDM2. We found that IFIXalpha1 interacts with HDM2. Interestingly, the signature motif of the HIN-200 gene family, i.e., the 200-amino-acid HIN domain of IFIXalpha1, is sufficient not only for binding HDM2 but also for downregulating it, leading to p53 activation. Finally, we show that IFIX mediates HDM2 downregulation in an IFN-inducible system. Together, these results suggest that IFIXalpha1 functions as a tumor suppressor by repressing HDM2 function.

Computational studies and peptidomimetic design for the human p53-MDM2 complex

The interaction between human p53 and MDM2 is a key event in controlling cell growth. Many studies have suggested that a p53 mimic would be sufficient to inhibit MDM2 to reduce cell growth in cancerous tissue. In order to design a potent p53 mimic, molecular dynamics (MD) simulations were used to examine the binding interface and the effect of mutating key residues in the human p53-MDM2 complex. The Generalized Born surface area (GBSA) method was used to estimate free energies of binding, and a computational alanine-scanning approach was used to calculate the relative effects in the free energy of binding for key mutations. Our calculations determine the free energy of binding for a model p53-MDM2 complex to be -7.4 kcal/mol, which is in very good agreement with the experimentally determined values (-6.6--8.8 kcal/mol). The alanine-scanning results are in good agreement with experimental data and calculations by other groups. We have used the information from our studies of human p53-MDM2 to design a beta-peptide mimic of p53. MD simulations of the mimic bound to MDM2 estimate a free energy of binding of -8.8 kcal/mol. We have also applied alanine scanning to the mimic-MDM2 complex and reveal which mutations are most likely to alter the binding affinity, possibly giving rise to escape mutants. The mimic was compared to nutlins, a new class of inhibitors that block the formation of the p53-MDM2 complex. There are interesting similarities between the nutlins and our mimic, and the differences point to ways that both inhibitors may be improved. Finally, an additional hydrophobic pocket is noted in the interior of MDM2. It may be possible to design new inhibitors to take advantage of that pocket.

Increased expression of MDM2, cyclin D1, and p27Kip1 in carcinogen-induced rat mammary tumors

It is thought that environmental pollutants, such as polycyclic aromatic hydrocarbons (PAH), contribute to human breast tumorigenesis, yet their roles remain incompletely elucidated. The prototypical PAH 7,12-dimethylbenz(alpha)anthracene (DMBA) specifically and effectively induces mammary tumor formation in rodent models. In an attempt to explore the molecular mechanisms by which PAH initiates and promotes mammary tumorigenesis, we examined the expression of several cell cycle regulators in rat mammary tumors induced by DMBA. Expression of cyclin D1, murine double minute-2 (MDM2), and Akt was up-regulated in tumors in comparison to normal mammary glands, as indicated by RT-PCR, Western blot analysis, and immunohistochemical staining. Expression of p27Kip1 protein was also elevated in the tumors with increased cytoplasmic localization. However, RB protein remained hyperphosphorylated. To directly test the effects of DMBA, the MCF-7 human breast cancer cells were treated. DMBA induced MDM2 expression in a dose- and time-dependent fashion in the MCF-7 cells, and this activation appeared to be p53 dependent. These data suggest that activation of cyclin D1, MDM2, and AKT as well as increased expression and cytoplasmic localization of p27Kip1 may play a role in this model of environmental pollutant-induced mammary tumorigenesis.

Relationship and prognostic significance of phospho-(serine 166)-murine double minute 2 and Akt activation in node-negative breast cancer with regard to p53 expression

The Akt signalling pathway plays a central role in tumourigenesis. Activation of Akt is related to a more aggressive phenotype in various human cancers, including breast cancer. Its activation contributes to cancer progression via pleiotropic effects, including suppression of apoptosis and modulation of cell cycle regulation. Murine double minute 2 (MDM2) is an oncoprotein that inhibits the function of p53 tumour suppressor protein. Cell culture studies show that Akt-related phosphorylation of MDM2 at serine 166 allows MDM2 to gain nuclear entry and fulfil its p53 regulating function. This study was designed to analyse the relationship of phospho-MDM2 (pMDM2) expression with Akt activation to determine a possible prognostic relevance of pMDM2 in node-negative breast cancer with respect to Akt activation and p53 status. pMDM2, phospho-Akt (pAkt) and p53 protein expression status were analysed immunohistochemically in 121 paraffin-embedded breast cancer cases. Expression of pMDM2 correlated with Akt activation (P<0.001). Univariate analysis identified pMDM2 as a prognostic factor (P=0.0458) in node-negative breast cancers. The unfavourable prognostic significance was even more pronounced in tumours with a pMDM2(+)/pAkt(+) immunophenotype (P=0.0205). Stratification into a p53-negative subgroup further strengthened the adverse prognostic influence. These data confirm that MDM2 phosphorylation at serine 166 is mediated by Akt kinase. Besides the prognostic impact of pMDM2, our findings suggest that Akt-mediated modulation of the MDM2/p53 complex contributes to increased tumour aggressiveness especially in p53-negative breast cancers. However, due to the relatively small number of patients in this cohort, the results obtained need to be confirmed by larger cohorts.

Protein expression of Mdm2 and p53 in hyperplastic and neoplastic lesions of the canine circumanal gland

Hyperplastic and neoplastic lesions of the circumanal gland in dogs were examined immunohistochemically for nuclear expression of Mdm2 and p53 proteins. Mdm2 nuclear labelling was detected in 64.3% of hyperplastic lesions and 70.7% of adenomas, the immunolabelling being stronger in the latter. Mdm2 reactivity in reserve-like cells in adenomas showed wide variation, the immunoreactive cells ranging from 4 to 80%. No reactivity was shown in 81.9% of adenocarcinomas. In contrast to Mdm2 reactivity, each of 14 hyperplastic lesions and 11 adenocarcinomas, and 60 of 65 adenomas (92.3%) failed to show nuclear p53 reactivity. These results suggest that increased expression of Mdm2 is an early event in circumanal gland tumorigenesis, and may be present in the absence of nuclear p53 protein accumulation.

The growth arrest function of the human oncoprotein mouse double minute-2 is disabled by downstream mutation in cancer cells

We have reported earlier that ectopic expression of mouse double minute-2 (MDM2) induces G1 arrest in normal cells. To explain occasional overexpression of MDM2 in cancer cells, we searched for deletion or substitution mutation in the growth suppressor domains of MDM2 in several breast cancer cell lines that overexpress the oncoprotein. Our results suggest the absence of alteration (deletion or substitution) in the open reading frame of MDM2 transcripts in such cells. Because the breast cancer cell line MCF-7 overexpresses MDM2, we isolated the full-length MDM2 transcript from this cell line. The MDM2 cDNA synthesized from transcripts isolated from MCF-7 cells induced inhibition of G1 to S phase transition in normal human diploid cells such as WI38, suggesting that the genetic alterations in breast cancer cells that overexpress MDM2 disable the growth arrest function of the oncoprotein. Consistently, overexpression of full-length MDM2 in MCF-7 cells over its high endogenous level did not inhibit G1-S transition efficiently. Although MDM2 overexpression was accompanied by CDK4 overexpression or absence of cdk4 inhibitor p16 in most breast cancer cells, we found remarkably high levels of cyclin A rather than cyclin E in these cells. Ectopic expression of cyclin A released MDM2-mediated inhibition of G1-S transition in normal human diploid WI38 cells. We propose that cancer cells expressing high levels of cyclin A escape MDM2-mediated G1 arrest, which may account for a selective growth advantage over normal cells.

MEK-ERK signaling controls Hdm2 oncoprotein expression by regulating hdm2 mRNA export to the cytoplasm

The physical and functional interaction between the transcription factor p53 and its negative regulatory partner protein Hdm2 (Mdm2 in mouse) is a key point of convergence of multiple signaling pathways that regulates cell proliferation and survival. hdm2 mRNA transcription is induced by p53, forming the basis of an auto-regulatory feedback loop. Growth and survival factor-activated Ras-Raf-MEK-ERK signaling can also regulate Hdm2 expression independently of p53, contributing to the pro-survival effect of these factors. In murine fibroblasts, this occurs through the regulation of mdm2 mRNA transcription. Here we show that, in human breast cancer epithelial cells, MEK-dependent regulation of Hdm2 expression also occurs at a post-transcriptional level. Pharmacological blockade of MEK activity in T47D cells inhibits Hdm2 protein synthesis by 80-90%. This occurs in the absence of changes in the expression of the major hdm2-P1 mRNA transcript and only an approximately 40% reduction in hdm2-P2 transcript levels. The amounts of both transcripts that are associated with polyribosomes and are, hence, being actively translated are reduced by >80% by the MEK inhibitor, U0126. We show here that this is due to the inhibition of hdm2 mRNA export from the nucleus when MEK activity is inhibited. In MCF-7 breast cancer cells that express wild-type p53, Hdm2 is required to suppress p53-dependent transcription when MEK kinase is active. Regulation of the nuclear export of hdm2 mRNA provides, therefore, a mechanism whereby mitogen-stimulated cells avoid p53-dependent cell cycle arrest or apoptosis by maintaining the dynamic equilibrium of the Hdm2-p53 feedback loop.

Prognostic relevance of gene amplifications and coamplifications in breast cancer

Multiple different oncogenes have been described previously to be amplified in breast cancer including HER2, EGFR, MYC, CCND1, and MDM2. Gene amplification results in oncogene overexpression but may also serve as an indicator of genomic instability. As such, presence of one or several gene amplifications may have prognostic significance. To assess the prognostic importance of amplifications and coamplifications of HER2, EGFR, MYC, CCND1, and MDM2 in breast cancer, we analyzed a breast cancer tissue microarray containing samples from 2197 cancers with follow-up information. Fluorescence in situ hybridizations revealed amplifications of CCND1 in 20.1%, HER2 in 17.3%, MDM2 in 5.7%, MYC in 5.3%, and EGFR in 0.8% of the tumors. All gene amplifications were significantly associated with high grade. HER2 (P < 0.001) and MYC amplification (P < 0.001) were also linked to shortened survival. In case of HER2, this was independent of grade, pT, and pN categories. MYC amplification was almost 3 times more frequent in medullary cancer (15.9%), than in the histologic subtype with the second highest frequency (ductal; 5.6%; P = 0.0046). HER2 and MYC amplification were associated with estrogen receptor/progesterone receptor negativity (P < 0.001) whereas CCND1 amplification was linked to estrogen receptor/progesterone receptor positivity (P < 0.001). Coamplifications were more prevalent than expected based on the individual frequencies. Coamplifications of one or several other oncogenes occurred in 29.6% of CCND1, 43% of HER2, 55.7% of MDM2, 65% of MYC, and 72.8% of EGFR-amplified cancers. HER2/MYC-coamplified cancers had a worse prognosis than tumors with only one of these amplifications. Furthermore, a gradual decrease of survival was observed with increasing number of amplifications. In conclusion, these data support a major prognostic impact of genomic instability as determined by a broad gene amplification survey in breast cancer.

Radiosensitization by antisense anti-MDM2 mixed-backbone oligonucleotide in in vitro and in vivo human cancer models

PURPOSE

The MDM2 oncogene, amplified or overexpressed in many human cancers, has been suggested to be a novel target for cancer therapy. We have demonstrated a second-generation antisense antihuman-MDM2 oligonucleotide to have antitumor activity when administered alone or in combination with cancer chemotherapeutic agents. In the present study, we investigated the effect of the antisense oligonucleotide on radiation therapy.

EXPERIMENTAL DESIGN

The in vitro radiosensitization activity was determined in cell lines of human cancers of prostate (LNCaP and PC3), breast (MCF-7 and MDA-MB-468), pancreas (PANC-1), and glioma (U87-MG and A172) and its in vivo radiosensitization activity in xenograft models of LNCaP, PC3, MCF-7, MDA-MB-468, and PANC-1.

RESULTS

In cells containing at least one functional p53 allele (LNCaP, U87-MG, and A172), after specific inhibition of MDM2 expression, p53 and p21 levels were elevated. In LNCaP cells, the Bax level was increased, and Bcl-2 and E2F1 levels were decreased. In PC3 cells that are p53 null, after inhibition of MDM2 expression, Bax and p21 levels were elevated, and E2F1 levels were decreased. On the basis of in vitro clonogenic assay, the antisense oligonucleotide, in a sequence-specific manner, significantly increased radiation-induced antiproliferation effects. It also increased radiation-induced inhibitory effects on tumor growth in SCID or nude mice bearing LNCaP, PC3, MCF-7, MDA-MB-468, and PANC-1 xenografts.

CONCLUSIONS

These results suggest that MDM2 has a role in radiation therapy of human cancers, regardless of p53 status, providing a basis for future development of MDM2 inhibitors, such as antisense oligonucleotides, as radiosensitizers.

Use of High-Throughput Protein Array for Profiling of Differentially Expressed Proteins in Normal and Malignant Breast Tissue

cDNA arrays provide a powerful tool to identify gene expression pattern that are potentially associated with tumor invasion and metastasis. However, genes work at the protein level and, since the transcriptional activity of a gene does not necessarily reflect cellular protein expression, the identification and quantification of proteins is essential for the understanding of molecular events leading to malignant transformation. We have therefore employed a high-throughput protein microarray system which contains 378 well-characterized monoclonal antibodies in order to compare the gene expression pattern of malignant and adjacent normal breast tissue in a patient with primary breast cancer. Using this technique, we have identified a number of proteins that show increased expression levels in malignant breast tissues such as casein kinase Ie, p53, annexin XI, CDC25C, eIF-4E and MAP kinase 7. The expression of other proteins, such as the multifunctional regulator 14-3-3e was found to be decreased in malignant breast tissue, whereas the majority of proteins remained unchanged when compared to the corresponding non-malignant samples. The protein expression pattern was confirmed by immunohistochemistry, in which antibodies against 8 representative proteins known to be involved in carcinogenesis were employed in paraffin-embedded normal and malignant tissue sections deriving from the same patient. In each case, the results obtained by IHC matched the data obtained by antibody microarray system. Taken together, we have described for the first time a tumor cell specificity protein expression pattern by use of a novel commercially available antibody microarray system. We have thus demonstrated the feasibility of high-throughput protein arrays in the proteomic analysis of human breast tissue. We hypothesize that the use of protein arrays will not only increase our understanding of the molecular events, but could prove useful in evaluating prognosis and in determining optimal antineoplastic therapy.

p14ARF expression in invasive breast cancers and ductal carcinoma in situ--relationships to p53 and Hdm2

Introduction

p14^ARF stabilises nuclear p53, with a variable expression of p14^ARF mRNA in breast cancers. In vitro, nuclear p14^ARF binds Hdm2 to block Hdm2-dependent nucleocytoplasmic shuttling of p53, which is required before cytoplasmic degradation of p53. p14^ARF is negatively regulated by p53 and through p53-independent pathways. No studies have yet examined levels of p14^ARF protein expression in breast cancer and their relationship to Hdm2/p53 immunoreactivity or subcellular localisation. Previously, immunohistochemical expression of cytoplasmic p14^ARF, p53 and Hdm2 has been described. HER-2 (c-erbB2/neu) predicts prognosis and interacts with the p14^ARF/Hdm2 pathway to inactivate p14^ARF and to influence Hdm2 activity and localisation. This study examined p14^ARF and p53/Hdm2 expression and subcellular localisation by using immunohistochemistry in a series of invasive ductal breast cancers (IDCs) with concomitant ductal carcinoma in situ (DCIS), to evaluate whether findings in vitro were related to clinicopathological parameters such as HER-2 and their effect on patient outcome.

Methods

The 4C6 anti-p14^ARF monoclonal antibody and Dako Envision Plus system were used to evaluate p14^ARF expression in 103 patients; p53/Hdm2 staining was performed.

Results

p14^ARF was evaluable in 96 patients, with nuclear p14^ARF expression (modified Quick-score ≥ 3) in 79% (n = 76) of IDCs and in associated DCIS in 74 patients. Cytoplasmic p14^ARF was detectable in 23 breast cancers. Nuclear and cytoplasmic p14^ARF showed no correlation with p53 subcellular immunoreactivity. Increasing levels of cytoplasmic p14^ARF were associated with nuclear and cytoplasmic Hdm2 expression (P < 0.001). Subcellular ARF expression was not associated with clinicopathological parameters, and although not an independent prognosticator, these preliminary findings suggest that cytoplasmic p14^ARF might be associated with a better overall survival (P = 0.09; log rank). The association between HER-2 positivity and nuclear p14^ARF (P = 0.038), as well as nuclear Hdm2 (P = 0.019), reflects the in vitro findings of HER-2 interaction with the ARF/Hdm2 pathway. Cytoplasmic p53 and Hdm2 expression might have biological implications, through an association of cytoplasmic p53 with increased tumour proliferation (P = 0.005), and an improved overall survival (P = 0.002, log rank) in cytoplasmic Hdm2-expressing tumours, that independently predict favourable overall survival (P = 0.02) and disease-free survival (P = 0.03).

Conclusions

Nuclear p14^ARF expression is similar in IDCs and DCIS and is associated with Hdm2 immunoreactivity. Nuclear p14^ARF and Hdm2 might be regulated by HER-2. Clearly, our findings in vivo suggest a complexity of p14^ARF/Hdm2 and p53 pathways in which consideration of cytoplasmic p14^ARF and Hdm2 might have tumorigenic implications.

Chemosensitization and radiosensitization of human cancer by antisense anti-MDM2 oligonucleotides: in vitro and in vivo activities and mechanisms

MDM2 oncogene is overexpressed in many human cancers including breast, colon, and prostate cancer, and MDM2 levels are associated with poor prognosis in patients with cancer. Here, we summarize the investigation of the functions of MDM2 oncogene in human cancer growth and the value of MDM2 as a drug target for prostate cancer therapy by using antisense to inhibit MDM2 expression. Antisense anti-human-MDM2 oligonucleotides and mismatch controls were tested in in vitro and in vivo human cancer models for antitumor activity. Targeted gene products and related proteins were analyzed and the antitumor activity was determined when the oligonucleotides were used alone or in combination with cancer chemotherapeutics and radiation therapy. The antisense oligonucleotide specifically inhibited MDM2 expression in a dose- and time-dependent manner, resulting in significant antitumor activity in vitro and in vivo. The antisense oligonucleotides also potentiated the effects of p53 activation and p21 induction by chemotherapeutic agents 10-hydroxycamptothecin, adriamycin, 5-fluorouracil, and paclitaxel. In a dose-dependent manner, the antisense oligonucleotide showed antitumor activity in nude mice bearing human cancer xenografts and increased therapeutic effectiveness of the chemotherapeutic agents irinotecan, paclitaxel, and Rituxan and radiation therapy. These results indicate that MDM2 has a role in various tumor growth through both p53-dependent and p53-independent mechanisms, indicating that MDM2 inhibitors have a broad spectrum of antitumor activities in human cancers regardless of p53 status. These results provide a basis for clinical evaluation of antisense anti-MDM2 oligonucleotides as chemosensitizer and radiosensitizer.

Estradiol stabilizes p53 protein in breast cancer cell line, MCF-7

Overexpression of the oncoprotein MDM2, an important regulator of the p53 tumor suppressor protein, is often observed in breast cancer tissues and cell lines, particularly in those which express estrogen receptor alpha (ERalpha). In MCF-7 breast cancer cell line possessing wild-type p53, ERalpha, and overexpressing MDM2, p53 accumulation was stimulated by 17beta-estradiol (E2) in a concentration-dependent manner. On the other hand, E2 caused no change of the expression of p53 mRNA, indicating that E2 affects p53 at the post-transcriptional level. To analyze the mechanism of p53 accumulation by E2, the stability of p53, ERalpha and MDM2 proteins was analyzed in the presence of cycloheximide under an E2-supplemented or -depleted condition. E2 significantly extended the half-life of p53 protein, but shortened that of ERalpha in MCF-7 cells. E2 significantly decreased the stability of p90(MDM2) and p60(MDM2) in MCF-7. Interestingly, E2 increased the ratio p60(MDM2)/p90(MDM2) inversely proportionally to the degradation of p53. These results suggest that the ratio of the two MDM2 proteins, p90(MDM2) and p60(MDM2), may affect the accumulation of wild-type p53 protein in response to E2.

The expression of murine double minute 2 is a favorable prognostic marker in esophageal squamous cell carcinoma without p53 protein accumulation

BACKGROUND

Murine double minute 2 (MDM2) is an oncoprotein that inhibits the function of p53 tumor-suppressor protein. Although there have been a few reports on MDM2 gene abnormalities, there has been no investigation into expression of the product of this gene in esophageal squamous cell carcinoma. Thus, the clinicopathological and prognostic significance of the product of the MDM2 gene is as yet unknown.

METHODS

MDM2 protein expression status was analyzed in surgically resected materials by immunohistochemical procedures.

RESULTS

The expression of MDM2 significantly correlated inversely with tumor size, depth of invasion, lymph node metastasis, lymphatic vessel invasion, and stage of disease. However, the expression of MDM2 correlated with neither p53 protein accumulation status nor Ki-67 labeling index. The prognosis with MDM2-positive status was significantly better than that with MDM2-negative status for patients with p53-negative tumors, but not in those with p53-positive tumors. Moreover, multivariate analysis showed that the expression of MDM2 was an independent prognostic factor in patients with p53-negative tumors.

CONCLUSIONS

These findings indicate that MDM2 immunohistochemical analysis may provide useful information concerning the prognosis in esophageal squamous cell carcinoma patients with p53-negative tumors.

Loss of p19ARF enhances the defects of Mdm2 overexpression in the mammary gland

The protein encoded by the murine double minute 2 (Mdm2) gene inactivates the function of the tumor suppressor p53. The targeted expression of the mdm2 transgene (BLGmdm2) to the mammary epithelium disrupts the cell cycle, causing multiple rounds of DNA synthesis without proper cell division and consequently poor mammary gland development. These phenotypes in the mammary epithelia of the transgenic mice are not dependent on either p53 or the transcription factor E2F1, as mice null for these genes carrying the BLGmdm2 transgene exhibit similar defects to mice carrying the BLGmdm2 transgene alone. p19ARF, an alternative splice product of the INK4a/ARF locus, has been shown to interact directly with MDM2. Therefore, BLGmdm2 transgenic mice null for p19ARF were created to gain insight into the mechanism by which mdm2 overexpression disrupts the cell cycle. The BLGmdm2 phenotype in the absence of p19ARF was worse than BLGmdm2 mice and visible as early as day 15 of pregnancy. By day 5 of lactation the phenotype was very pronounced. Histological analysis of the mammary gland showed a decrease in ductal branching, smaller and fewer lobuloalveolar structures, and a decrease in luminal secretions. Multinucleated and enlarged cells were present due to continued replication in the absence of cytokinesis. Thus, the absence of p19ARF in this in vivo system enhanced the defect caused by mdm2 overexpression.

Proliferation- and apoptosis-related proteins in intracranial ependymomas: an immunohistochemical analysis

As the value of grading of ependymomas is currently debated we studied the expression of proliferation- and apoptosis-related proteins in these tumors as these mechanisms both are suggested to be important in tumor growth. We characterized the immunohistochemical expression of p53, Mdm2, Bcl-2, and Bax in 51 intracranial ependymomas. We also assessed the apoptosis- and proliferation-index, measured by MIB-1, PCNA-immunohistochemistry, and analyzed the clinical parameters. Of all used antibodies, the correlation with survival and the correlation among ordered categories was assessed. None of the analyzed immunohistochemical variables were significantly correlated with tumor grade. On the other hand, PCNA, MIB-1, and p53 were significantly related to the survival of the patient. In multivariate analysis, p53 was the only independent predictive variable (p = 0.0132).

CONCLUSION

The strongest predictors of survival in univariate analysis were the expression of PCNA, MIB-1 and p53. In multivariate analysis a p53 expression > 1% showed to be significantly related with a worse survival. The predicting value of p53 expression has to be confirmed by others before solid conclusions can be made. Apoptosis seems not to be an important mechanism in tumor growth in ependymomas. The expression of Mdm2, Bcl-2, and Bax were not related to survival.

Overexpression of MDM2 oncoprotein correlates with possession of estrogen receptor alpha and lack of MDM2 mRNA splice variants in human breast cancer

To evaluate the significance of murine double minute 2 (MDM2) oncoprotein in human breast cancer as a nuclear-cytoplasmic shuttling protein, an estrogen receptor (ER) alpha regulator, and a prognostic marker and to study how MDM2 is overexpressed, we investigated its status in tissue samples and examined the correlation between overexpression and MDM2 gene abnormalities, status, and clinicopathological parameters. We detected MDM2 oncoprotein in both nucleus and cytoplasm by frozen-section immunohistochemistry. There was a significant correlation between MDM2 overexpression and low-grade nuclear atypia, absence of lymph node involvement, and increased levels of ER alpha protein. Our molecular assays found no point mutations in Ser17, but there was a correlation between MDM2 overexpression and the lack of splice variant mRNAs. These results suggest that the distribution of MDM2 reflects its nuclear-cytoplasmic shuttling ability; that interaction between p53 and MDM2 for tumor progression is not enhanced by point mutations at codon 17; and that the expression of MDM2 splice variants is a reason for the lack of its overexpression. MDM2 overexpression correlates with favorable prognostic parameters. A decreased level of MDM2 will lead to a deviation from the ER alpha signaling pathway.

MDM2 enhances the function of estrogen receptor alpha in human breast cancer cells

Overexpression of the oncoprotein MDM2, a negative feedback regulator of p53, is often observed in breast cancer tissue and cell lines, particularly in those which express estrogen receptor alpha (ERalpha). In this study, we report a novel function of MDM2, i.e., as a positive regulator of ERalpha. This function does not involve p53. MDM2 overexpressing clones derived from the breast cancer cell line, MCF-7 cells, showed a remarkable growth advantage only in estradiol supplemented conditions, and this profile coincided with increased transcriptional activity of ERalpha in these cells. Though p53 has been reported to be an inhibitor of ERalpha function, p53 protein in MDM2 overexpressing clones was more abundant than in the parental cells. When ERalpha was exogenously expressed in p53-null cells, its activity was enhanced by coexpression of MDM2. Mammalian two-hybrid assays and GST pull-down assays indicated that MDM2 could interact with ERalpha. These results indicate that MDM2 is a direct activator of ERalpha function, and suggest such a role for MDM2 in ERalpha-positive breast cancer.

Genetic alterations of the p14ARF -hdm2-p53 regulatory pathway in breast carcinoma

TP53 is the most commonly mutated tumor suppressor gene in human cancers. The amplification and overexpression of HDM2 plays a role in tumorigenesis via inactivation of p53-dependent cell cycle arrest. p14ARF, an alternate transcript of the INK4A tumor suppressor locus, prevents hdm2-induced transcriptional silencing of p53 by binding hdm2. The role of this p14ARF-hdm2-p53 regulatory pathway in breast carcinoma is unknown. We hypothesized that p14ARF mutations and HDM2 gene amplification may be alternative mechanisms of p53 inactivation in breast cancer. Mutational analysis of TP53 (exons 5-9) and exon 1beta of pl4ARF was performed by PCR-SSCP and putative mutations were confirmed by sequencing. p14ARF mRNA expression was evaluated by RT-PCR and the presence of HDM2 gene amplification by differential PCR. Among the cell lines, 7/14 (50%) harbored TP53 mutations and 2/14 (14%) had a deletion ofp14ARF exon 1beta with no detectable p14ARF mRNA. None demonstrated HDM2 gene amplification. TP53 mutations were identified in 7/36 (19%) breast tumors and HDM2 amplification in 2/30 (7%) tumors. All the tumors contained an intact p14ARF exon 1beta with corresponding expression of the mRNA. Alterations in the various components of this regulatory pathway were identified in nine (64%) cell lines and 25% of the 36 breast cancers with TP53 mutation being the predominant aberration. Although p14ARF mutations and HDM2 gene amplification appear to be uncommon events in breast carcinoma, deregulation of this pathway may occur via alternative mechanisms in breast carcinogenesis.

Alterations in MDM2 expression in esophageal squamous cell carcinoma: relationship with p53 status

In view of the significance of MDM2 as a regulator as well as critical target of wild type p53, this study was undertaken to determine the alteration in MDM2 expression in esophageal squamons cell carcinoma (ESCC) and its relationship to clinicopathological parameters as well as p53gene and protein status. Immunohistochemical analysis of MDM2 and p53 proteins on paraffin embedded sections from 64 surgically resected ESCCs and matched histologically normal tissues showed overexpression of MDM2 protein in 23/64 (36%) ESCCs, while the histopathologically normal esophageal tissues did not show detectable level of MDM2 immunoreactivity. Interestingly, MDM2 /p53 + phenotype was observed in 37/64 (58%) cases. None of the cases with p53 mis-sense mutations (12/30, 40%) showed detectable level of MDM2 protein. Missense p53 mutations were significantly associated with discordant p53 + /MDM2 immunophenotype (p= 0.004). The most intriguing feature of the study was accumulation of MDM2 in the absence of detectable p53 in 11% of and overexpression of MDM2 and p53 in 25% of ESCCs, suggesting a p53-independent role for MDM2 in a subset of tumors. These results underscore the involvement of MDM2 in p53-dependent and -independent pathways in the pathogenesis of esophageal cancer in the Indian population.

Overexpression of p53 protein and MDM2 in papillary carcinomas of the thyroid: Correlations with clinicopathologic features

Expression of p53 protein and MDM2 was evaluated in paraffin-embedded tissue from 78 patients with papillary carcinomas of the thyroid (PCT), in order to elucidate the relationship between them and their correlations with some clinicopathologic features implicated in tumor progression. These proteins were expressed in nuclei of tumor cells, but not in non-tumor cells. Staining was defined as positive when 10% or more of tumor cells expressed these proteins. The number of cases positive for p53 protein was 21/78 (27%), and that positive for MDM2 was 26/78 (33%). Co-overexpression of p53 protein and MDM2 was observed in 12/78 cases (15%). A significant positive relationship was found between them (P < 0.01); p53-positive cases tended to be also positive for MDM2 and vice versa. Statistical analysis revealed that overexpression of p53 protein significantly correlated with large tumor size (P = 0.0271) and the presence of capsular invasion (P = 0.04). There were significant positive correlations between tumor size and intrathyroidal invasion and between tumor size and capsular invasion in PCT, suggesting that p53 protein overexpression is associated only with tumor progression (tumor size). However, we could not find any significant correlations between MDM2 expression and clinicopathologic features. Our findings suggest that overexpression of p53 protein and MDM2 in papillary carcinoma of the thyroid is associated with the progression of the tumors, and that p53 may be a marker of the progression of PCT.

Telomerase activity in primary and secondary glioblastomas multiforme as a novel molecular tumor marker

OBJECT

Telomerase activity is responsible for cell immortality. To examine the role of telomerase in the carcinogenesis of human glioblastomas multiforme (GBMs), the authors studied telomerase activity, telomerase component expression, and telomere lengths in 42 GBM samples.

METHODS

In all samples, EGFR and MDM2 amplifications and overexpressions were examined using Southern and Northern blot analyses. The p53 mutation was analyzed using polymerase chain reaction-single strand conformational polymorphism and by direct sequence analysis. Specimens of tissues were immunostained with p53, EGFR, and MDM2 antibodies. Allelic loss on chromosomes 17p and 10 was assessed by loss of heterozygosity (LOH) assays. Telomerase activity, expression of its components (human telomerase reverse transcriptase [hTERT], human telomerase RNA component [hTERC], and telomerase-associated protein [TEP1]), and telomere lengths were analyzed using the telomeric repeat amplification protocol (TRAP)-hybridization protection assay, reverse transcription-polymerase chain reaction, and Southern blot analysis. According to the results of assessments of EGFR and MDM2 amplifications, p53 mutation, LOHs in chromosomes 17p and 10, and the clinical course of the disease, the 42 samples were classified into 22 primary and 20 secondary glioblastomas. Twenty-six (61.9%) of all 42 samples demonstrated detectable telomerase activity during the TRAP assay. Secondary GBMs displayed significantly higher levels of telomerase activity and hTERT expression than primary GBMs. Tumors with a p53 gene mutation demonstrated significantly higher telomerase activity than those without a p53 mutation. Four samples with a codon 175 mutation demonstrated an exceptionally high amount of telomerase activity. In secondary GBMs, the increase in telomerase activity and the hTERT expression level correlated with the increased frequency of p53 mutations. There was no significant difference in telomere length between primary and secondary GBMs.

CONCLUSIONS

These results suggest that telomerase activity and p53 mutations both play important roles in the multistep carcinogenesis of GBMs. Telomerase activity and hTERT expression may be considered as novel distinctive factors in human GBMs.

Mdm2 gene amplification in gastric cancer correlation with expression of Mdm2 protein and p53 alterations

Mdm2, localized on chromosome 12, is considered a negative regulator of p53 function and seems to play a role in the pathogenesis of a variety of tumors. The mdm2 amplification in advanced-stage gastric carcinoma has not yet been investigated. Mdm2 amplification was determined in 43 gastric carcinomas, and the genetic results were correlated with mdm2 protein expression, p53 alterations, and clinicopathologic data. The tumors were classified according to Lauren: 20 intestinal-type tumors, 19 tumors of diffuse growth inclusive of a primary small cell carcinoma, and 4 carcinomas with mixed differentiation. Staging was based on the pTNM classification system. Mdm2 and p53 were demonstrated by immunohistology on formalin-fixed and paraffin-embedded tumor tissue. The mdm2 oncogene was amplified by nonradioactive hybridization of tumor DNA with an mdm2 cDNA probe. The Southern blots were evaluated densitometrically. For p53 mutation screening, we analyzed the highly conservative regions of the p53 gene (exons 4 to 8) with the use of the polymerase chain reaction-single-strand conformation polymorphism technique. Polymerase chain reaction products with band shifting were directly sequenced. Mdm2 amplification was demonstrated in 18 tumors (41.8%). The mdm2 gene was amplified more frequently in carcinomas with a diffuse growth pattern. Gastric carcinomas of the intestinal type, however, showed a higher frequency of p53 alterations. There was no statistical significance of the molecular genetic and immunohistologic results of the mdm2/p53 status to staging as well as to age and sex of the patients. The mdm2/p53 pathway is a part of the carcinogenesis of gastric carcinoma. Only approximately 20% of gastric carcinomas failed to show mdm2 and/or p53 alterations. The upregulation of the mdm2 oncogene and the accompanying inactivation of the tumor suppressor gene 53 seem to play a role above all in carcinomas of the diffuse type.