4193

MDM2

ACTFS|HDMX|hdm2;Mdm2 p53 binding protein homolog (mouse);MDM2;Mdm2 p53 binding protein homolog (mouse)

E3 ubiquitin-protein ligase Mdm2|MDM2 variant FB28|MDM2 variant FB30|Mdm2, transformed 3T3 cell double minute 2, p53 binding protein|double minute 2, human homolog of; p53-binding protein|oncoprotein Mdm2

12q14.3-q15

protein-coding

Rhabdomyosarcomas are a heterogeneous group of malignant tumors and are the mostcommon soft-tissue sarcoma of childhood. Rhabdomyosarcomas resemble developing skeletal muscle, notably in their expression of the MRF family of transcription factors and the PAX3 and PAX7 genes. These PAX genes are also involved through specific translocations, t(2;13)(q35;q14) and variant t(1;13)(p36;q14) in the alveolar subtype, which result in PAX3-FKHR and PAX7-FKHR fusion genes, respectively. The fusion genes are thought critically to affect downstream targets of PAX3 and PAX7 or possibly have novel targets. Similar downstream changes may also be involved in embryonal and fusion gene negative cases. Genomic amplification of such genes as MYCN, MDM2, CDK4, and PAX7-FKHR is a feature mainly of the alveolar subtype, while specific chromosomal gains, including chromosomes 2, 8, 12, and 13, are associated with the embryonal subtype. Loss ofalleles and imprinting at 11p15.5 and disruption of genes such as IGF2, ATR, PTC, P16, and TP53 have also been implicated in rhabdomyosarcoma development. Whereasthere is now a realistic possibility of cure in the majority of cases, there remains a subset that is resistant to multimodality therapy, including high-dosechemotherapy. Characterization of the defining molecular features of tumors thatare likely to behave aggressively represents a particular challenge. Current research is leading toward a better understanding of rhabdomyosarcoma tumorigenesis, which may ultimately result in novel therapeutic strategies that increase the overall cure. Genes Chromosomes cancer 26:275-285, 1999.#CI- Copyright 1999 Wiley-Liss, Inc.

Although common among adult intracranial neoplasms, pediatric malignant astrocytomas (PMAs) comprise a relatively small proportion of the brain tumors that occur in children. The scarcity of such cases generally requires that molecular analyses of PMAs are based on the utilization of paraffin-embedded material, and here we have used 39 such specimens to examine the incidence and prognostic significance of oncogene and tumor suppressor gene alterations (including amplifications of EGFR, CDK4, and MDM2 as well as inactivating mutations of CDKN2A, TP53, and PTEN) in these tumors. In general, the frequency of alteration for the genes we have studied fell within ranges that have been reported for adult astrocytomas. However, EGFR amplification, which is usually observed in approximately 40% and 15% of adult grade 4 and grade 3 astrocytomas,respectively, was not detected in any member of this series. With regard to prognosis, PTEN mutations were significantly associated with decreased survival among grade 3 and grade 4 PMA patients, a potentially important observation because neither patient age nor tumor malignancy grade was correlated with outcome for these individuals. In total, our data suggest at least one significant distinction between the genetic etiology of pediatric and adult astrocytomas and additionally reveal that analysis of PTEN mutations in PMA patients may be useful in the differential diagnosis of these tumors.

BACKGROUND: Previous studies have suggested that altered expression or dysfunction of the tumor suppressor gene p53 or the oncogene MDM2 could indicatedisease progression in children with leukemia who would fail to achieve completeremission or who would relapse. While these studies mainly have described aberrations of MDM2 and p53 function at the DNA and mRNA-level, we have examinedp53 and MDM2 expression at the protein level. mutation of the p53 tumor suppressor gene may result in cellular accumulation of the p53 protein, due to prolonged half-life of the abnormal protein. The p53 protein can also be rendered nonfunctional by overexpression of proteins that bind to p53, such as MDM2. Bothpathways have been proposed to disrupt cell cycle regulation in humans. Recent studies have shown that increased expressions of MDM2 as well as of p53 can be detected at the protein level in the absence of gene amplification. PROCEDURE: Forty-three bone marrow samples were analyzed immunohistochemically for p53 and MDM2. Twenty-nine bone marrow samples were obtained in children with active, prognostically unfavorable leukemia and MDS. Fourteen bone marrow samples were from children with non-malignant hematological disorders. RESULTS: p53 protein was expressed in 12 patients and MDM2 in 17 patients with leukemia. In the control group MDM2 expression was detected in one child, while p53 was not foundin any of the samples. CONCLUSIONS: Our findings of p53 or MDM2 positive cells in a majority of children with unfavorable prognostic features suggests that dysfunction of the p53-dependent cell growth control have a role in the development of high risk leukemias.#CI- Copyright 2000 Wiley-Liss, Inc.

BACKGROUND: The p53 tumor suppressor gene is the most commonly mutated gene in human cancer, and mutations arise in a wide variety of tumor types. Wild-type p53 functions as a regulator of apoptosis, so mutations in the p53 gene are generally associated with aggressive tumors and a poor prognosis. PROCEDURE: We have investigated the p53 mutation and MDM2 amplification frequencies in biopsies from pediatric rhabdomyosarcoma (RMS) tumors and cell lines by SSCP and Southern analyses. RESULTS: A mutation was detected in only 1 of 20 tumor specimens (5%),whereas the frequency in established RMS cell lines was significantly higher (6/10, 60%). p53 mutations were more common in cell lines derived from tumors previously exposed to chemotherapy compared to those derived from tumors at di-agnosis, and it is likely that these mutations enhanced the probability of successful long-term culture. The frequency of MDM2 gene amplification in patient biopsies was also low (2/20, 10%). Interestingly, complete responses to treatment were obtained in the two patients with tumors that demonstrated amplification ofMDM2. The response to treatment of patients with tumors wild-type for p53 and without MDM2 amplification was quite varied, indicating that expression of a wild-type p53 gene at diagnosis cannot always facilitate a favorable outcome. CONCLUSIONS: p53 mutation and MDM2 gene amplification frequencies are extremely low in RMS tumors, but a wild-type p53 genotype is not always associated with a favorable prognosis.#CI- Copyright 2000 Wiley-Liss, Inc.

Mdm2 is an oncogene that binds to and inactivates the tumor suppressor p53. However, the presence of oncogenic splice variants of mdm2 in human tumors that lack the p53 binding site has suggested a p53-independent transforming function for this protein. This report describes expression of 11 different mdm2 splice variants in pediatric rhabdomyosarcoma (RMS) cell lines and tumors at a frequency of 75% and 82%, respectively. Five of these isoforms have previously been described in other tumor histiotypes but six are novel and may be unique to RMS.There was no association between expression of splice variants and mdm2 gene amplification or p53 status. In addition, the frequency of splice variants was much higher than the incidence of mdm2 amplification or p53 mutations. These variants may be important to consider with respect to RMS tumor progression and therapeutic response.

MDM2 protein is thought to exhibit tumorigenic activity by binding to the p53 tumor-suppressor protein and inhibiting its function. Alternatively, MDM2 may have oncogenic roles other than those resulting from p53 interactions. Here we report that MDM2 can induce expression of the p65 subunit of NF-kappaB, which isan anti-apoptotic factor expressed in certain neoplastic cells in response to chemotherapy. Initially, we noted that the overexpression of MDM2 protein in leukemic bone marrow cells of patients with B-cell precursor acute lymphoblasticleukemia (BCP-ALL), and an ALL cell line (EU-4) transfected with the MDM2 gene was associated with elevated expression of p65 and in vitro resistance to doxorubicin (Adriamycin). By cotransfection of the MDM2 gene and p65-promoter-reporter constructs into EU-4 cells, we found that transient and high-level MDM2 expression induced p65 promoter activity. In the presence of wild-type (wt) p53, MDM2 increased p65 promoter activity by reversing p53-mediated suppression of p65. In the absence of p53, MDM2 directly increased p65 promoter activity. Deletion and mutation analysis of the p65 promoter indicated that the region between nt -575 and -178, which contains the first andsecond Sp1-binding sites, was required for activation by MDM2. Further studies using chromatin immunoprecipitation (CHIP) and electrophoretic mobility shift assay (EMSA) showed that MDM2 was able to directly bind to the Sp1 site of the p65 promoter. Our findings suggest that by inducing p65 expression, MDM2 has a p53-independent role in tumorigenesis, which may further elucidate the association between MDM2 overexpression and resistant disease in childhood ALL.

mutation of p53 has been implicated in progression of classical Wilms tumor (WT)into the anaplastic variant (AWT), drug resistance, and poor prognosis. Because of prognostic similarities, clear cell sarcoma of the kidney (CCSK) has been classified with AWT and other aggressive pediatric renal tumors, apart from congenital mesoblastic nephroma (CMN), which is instead a relatively benign tumor of neonates. Initially, CCSK and CMN were assumed to be ontologically related, but the role of p53 in the pathogenesis of either disease has not been sufficiently evaluated as in AWT. We examined the status of p53 in CMN and CCSK in comparison to AWT by immunohistochemistry and mRNA analysis of p53, the downstream effector p21(WAF-1/CIP-1) ( p21), the multidrug resistance gene MDR-1, a putative target of p53, and the p53-antagonist Mdm-2. Surprisingly, strong p53nuclear immunoreactivity was found in cultures from two CMN specimens, but not in frozen or fixed tumor tissue from five other CMN specimens, nor in cell lines ortumor tissue from CCSK. Sequence analysis excluded p53 mutations. The size of the p53 mRNA in CMN and CCSK primary tumors excluded gross deletions or rearrangements. Low levels of Mdm-2 mRNA in CCSK and CMN primary tumors and cultures did not support a role for Mdm-2. Absence of MDR-1 mRNA excluded MDR-1 in the drug-resistant phenotype of CCSK. Cisplatin-induced p21 transactivation assays and G(1) cell cycle arrest analyses showed that p21 transactivation and G(1) arrest occurred in both CCSK and CMN cultures, demonstrating integrity of the p53 signal transduction pathway. Absence of p53 functional abnormalities excluded relationships between CCSK and CMN as in AWT, supporting the association of cellular CMN with congenital fibrosarcomas as more recently proposed.

Rhabdomyosarcoma (RMS) is a family of soft tissue tumors that are associated with the skeletal muscle lineage and generally occur in the pediatric population. Based on histopathologic features, two subtypes, embryonal (ERMS) and alveolar (ARMS), were identified and associated with distinct clinical characteristics and genetic alterations. ARMS is associated with 2;13 or 1;13 chromosomal translocations, which generate PAX3-FKHR and PAX7-FKHR fusion products, respectively. These translocations result in altered expression, function, and subcellular localization of the fusion products relative to the wild-type proteins, and ultimately contribute to oncogenic behavior by modifying growth, differentiation, and apoptosis pathways. In contrast to the specific translocations found in ARMS, most ERMS cases have allelic loss at chromosome 11p15.5. Chromosome fragment transfer studies demonstrated that this region represses tumor cell growth, suggesting the presence of tumor suppressor gene(s)in this region. In both ERMS and ARMS, there is evidence of collaborating alterations that affect common targets, such as the p53 and RB pathways. One mechanism for perturbing these pathways involves amplification of genes such as MDM2 and CDK4; these amplification events occur frequently in ARMS but only rarely in ERMS. Therefore, despite similarities in the downstream targets of these genetic alterations, the striking cytogenetic and molecular differences between ARMS and ERMS indicate distinct molecular etiologies in these two subtypes.

Amplification of the EGFR, mdm2, CDK4 and PDGFR A genes has been widely demonstrated in adult malignant gliomas, almost exclusively glioblastomas. To determine the role of these mutational events in pediatric astrocytic gliomas weinvestigated the presence of EGFR, mdm2, CDK4 and PDGFR A gene amplification in 38 childhood brain tumor biopsies, including 24 low-grade astrocytomas and 14 malignant tumors. We used differential PCR assay on DNA extracted either from paraffin embedded or frozen tissues. EGFR gene amplification was detected in 4 out of 14 malignant tumors; no low-grade astrocytoma showed amplification. tumors with EGFR gene amplification were negative for the presence of p53 mutations, asobserved in a previous study. One glioblastoma showed PDGFR A amplification, while no amplifications were observed for mdm2 and CDK4 genes. These data are inline with those obtained from studies on gliomas of adults and suggest the existence of two different subsets of malignant gliomas also in pediatric brain tumors: one carrying EGFR gene amplification, the other showing p53 mutations.

Burkitt's lymphomas (BLs) are characterized by an activated MYC gene that provides a constitutive proliferative signal. However, activated myc can initiate ARF-dependent activation of p53 and apoptosis as well. Data derived from cell culture and animal models suggest that the inactivation of the ARF-MDM-2-p53 apoptotic signaling pathway may be a necessary secondary event for the development of BL. This has not been tested in freshly excised BL tissue. We investigated the ARF-MDM-2-p53 pathway in tumor specimen from 24 children with sporadic BL/B-ALL. Direct sequencing revealed a point mutation in the p53 gene in four BL. Overexpression of MDM-2 was evident in 10 of the BL samples analyzed byreal-time quantitative PCR. Deletion of the CDKN2A locus that encodes ARF or reduced expression of ARF could not be detected in any BL by fluorescence in situ hybridization analysis or real-time quantitative PCR, respectively. Our results indicate that the ARF-MDM-2-p53 apoptotic pathway is disrupted in about 55% of the cases of childhood sporadic BL. We suggest that in addition to the inactivation of the ARF-MDM-2-p53 protective checkpoint function other antiapoptotic mutations may occur in a substantial part of children with sporadic BL.

The prognosis of rhabdomyosarcoma (RMS) in advanced stages is still sobering. Therapy is limited due to local tumor recurrence, development of metastases and multidrug resistance. The aim of this study was to investigate the development of multidrug resistance in cell lines and in xenografts of alveolar and embryonal RMS treated according to the German Soft Tissue Sarcoma Study (CWS). Alveolar and embryonal RMS cell lines were treated with Vincristine, Topotecan, Carboplatin, Actinomycin D, or Ifosfamide. expression levels of resistance-associated genes were assessed using Real time-PCR. Nude mice (NMRI nu/nu, n = 10 per group) underwent xenotransplantation of human embryonal or alveolar RMS. Animals were treated with standard chemotherapeutic drugs Vincristine, Topotecan, Carboplatin, Actinomycin D, or Ifosfamide according to treatment schedules of the CWS-study. tumor sizes were measured and relative tumor volumes were calculated. Animals were sacrificed after 20 days and standard histology, Real-time-PCR for MDR1-, MRP-, LRP- and MDM2-gene as well as immunohistochemistry for MDR1-, LRP-, and MRP-protein were performed. In the cell lines, an up-regulation of MDR-1 gene was found in alveolar rhabdomyosarcoma. In embryonal rhabdomyosarcoma, an up-regulation of LRP and MRP was found. Standard chemotherapy of alveolar rhabdomyosarcoma resulted in a significant reduction of tumor growth (P < 0.05) in ALL groups. In embryonal rhabdomyosarcoma strongest effects were found after treatment with Ifosfamide, Vincristine and Carboplatin (P < 0.05). RT-PCR revealed a MDR1-dependent mechanism in alveolar rhabdomyosarcoma. In embryonal rhabdomyosarcoma, MDR1 occurred to a lower degree. Immunohistochemistry revealedcorrelating expression levels of multidrug resistance-associated proteins. The use of established chemotherapy on human RMS in vivo had strong effects on xenografts compared to their controls. In ALL cases, there was only a reduction of tumor growth, but not a complete eradication of the tumors. Chemotherapy seemed to upregulate the expression of resistance-associated genes in vitro and in vivo. The mechanism of multidrug resistance depends on the tumor subtype. Therefore, further investigations will be required to evaluate multidrug resistance in patients and to investigate new modalities for a reversal of multidrug resistance.

PURPOSE: MDM2 is a key negative regulator of p53 activity, and a single nucleotide polymorphism (SNP309, T>G change; rs 2279744) in its promoter increases the affinity for the transcription factor SP1, enhancing MDM2 expression. We carried out a pilot study to investigate the effect of this polymorphism on development and behavior of neuroblastoma, an extracranial pediatric tumor with unfrequent genetic inactivation of p53. EXPERIMENTAL DESIGN: We genotyped the MDM2-SNP309 alleles of tumor DNA from 239 neuroblastoma patients and peripheral blood DNA from 237 controls. In 40 of 239 neuroblastomas, the MDM2-SNP309 alleles were also genotyped in peripheral blood DNA. Data were analyzed by two-sided Fisher's exact test, log-rank test, and Kaplan-Meier statistics. Where appropriate, data are reported with 95% confidence intervals (CI). RESULTS: The frequency of both the T/G and G/G genotypes or the G/G or T/Ggenotype only was higher in neuroblastoma DNA samples than in controls: 60.3% (95% CI, 54.1-66.5) versus 47.3% (95% CI, 40.9-53.6), 30.4% (95% CI, 22.4-37.8) versus 15.0% (95% CI, 9.2-20.7), and 52.0% (95% CI, 45.0-59.9) versus 41.9% (95%CI, 35.3-48.5), respectively; Two-Sided Fisher's Exact Test P values were 0.006,0.003, and 0.048, respectively; Odds ratios were 1.69 (95% CI, 1.18-2.43), 2.45 (95% CI, 1.37-4.39) and 1.51 (95% CI, 1.02-2.22), respectively. A significant association (P = 0.016) between heterozygous (T/G)/homozygous (G/G) genotypes atSNP309 and advanced clinical stages was also shown. Homozygous/heterozygous SNP309 variant carriers had a shorter 5-year overall survival than patients withthe wild-type allele (P = 0.046; log-rank test). A shorter overall survival in patients with heterozygous/homozygous SNP309 was also observed in the subgroups with age at diagnosis >1 year and adrenal primary tumor (P = 0.024 and P = 0.014, respectively). CONCLUSIONS: Data from this pilot study suggest that the MDM2 G/Gand T/G-SNP309 alleles are markers of increased predisposition to tumor development and disease aggressiveness in neuroblastoma. However, additional studies with larger patient cohorts are required for a definitive assessment of the clinical relevance of these data.

The MDM2 oncoprotein is a key negative regulator of the tumor suppressor p53. A functional MDM2 single nucleotide polymorphism (SNP309) in the promoter region increases the affinity of transcription activator Sp1 for the MDM2 gene promoter, resulting in higher expression of MDM2 and thus inhibition of p53 transcriptional activity. UV-induced p53 activation promotes cutaneous transient pigmentation, and the common p53 Arg72Pro polymorphism alters the protein's transcriptional activity. We evaluated the effect of MDM2 SNP309 and its interaction with the p53 Arg72Pro polymorphism on pigmentary phenotypes and skin cancer risk in a nested case-control study within the Nurses' Health Study (NHS) among 219 melanoma cases, 286 squamous cell carcinoma (SCC) cases, 300 basal cell carcinoma (BCC) cases, and 873 controls, and among controls from other studies. We found that the G allele of the MDM2 SNP309 was inversely associated with the presence/absence of moles on the arm among 3,207 women pooled from controls of three nested case-control studies within the NHS. Compared with the MDM2 SNP309 T/T genotype,adjusted odds ratios (ORs) of having moles on the arms for T/G and G/G genotypeswere 0.92 (95% confidence interval (CI), 0.78-1.08) and 0.68 (95% CI, 0.53-0.87), respectively (p, trend, 0.005). We observed suggestive evidence of the association between the carriage of the MDM2 SNP309 G allele and childhood tanning tendency (adjusted OR, 1.30; 95% CI, 1.01-1.68). No significant associations were found between the MDM2 SNP309 and any of the three types of skin cancer. For SCC, the trend of increased risk across the three genotypes of MDM2 was stronger among p53 Pro carriers (p, trend, 0.05) than p53 Arg/Arg wild-type group (p, trend, 0.99; p, interaction, 0.07). These results provide evidence for the potential involvement of MDM2 SNP309 in pigmentary traits.

Alternative splicing plays a fundamental role in generating proteome diversity and is critical in regulation of eukaryotic gene expression. It is estimated that 50% of disease-causing mutations alter splicing efficiency and/or patterns of splicing. An alternatively spliced form of murine double-minute 2, MDM2-ALT1, isassociated with pediatric rhabdomyosarcoma (RMS) at high frequency in primary human tumors and RMS cell lines. We have identified that this isoform can be induced in response to specific types of stress (UV and cisplatin). However, themechanism of alternative splicing of MDM2 in human cancer is unknown. Using UV and cisplatin to model alternative splicing of the MDM2 gene, we have developed a damage-inducible in vitro splicing system. This system employs an MDM2 minigene that mimics the damage-induced alternative splicing observed in vivo. Using thisin vitro splicing system, we have shown that conserved intronic sequences in intron 11 of MDM2 are required for normal splicing. Furthermore, we showed that these intronic elements are also required for the regulated damage-induced alternative splicing of MDM2. The use of this novel damage-inducible system willallow for the systematic identification of regulatory elements and factors involved in the splicing regulation of the MDM2 gene in response to stress. Thisstudy has implications for identification of novel intervention points for development of future therapeutics for rhabdomyosarcoma.

Neuroblastoma is derived from neural crest precursor components of the peripheral sympathetic nervous system and accounts for more than 15% of ALL pediatric cancer deaths. A clearer understanding of the molecular basis of neuroblastoma is required for novel therapeutic approaches to improve morbidity and mortality. Neuroblastoma is uniformly p53 wild type at diagnosis and must overcome p53-mediated tumor suppression during pathogenesis. Amplification of the MYCN oncogene correlates with the most clinically aggressive form of the cancer, and MDM2, a primary inhibitor of the p53 tumor suppressor, is a direct transcriptional target of, and positively regulated by, both MYCN and MYCC. We hypothesize that MDM2 contributes to MYCN-driven tumorigenesis helping to ameliorate p53-dependent apoptotic oncogenic stress during tumor initiation and progression. To study the interaction of MYCN and MDM2, we generated an Mdm2 haploinsufficient transgenic animal model of neuroblastoma. In Mdm2(+/-)MYCN transgenics, tumor latency and animal survival are remarkably extended, whereas tumor incidence and growth are reduced. Analysis of the Mdm2/p53 pathway revealsremarkable p53 stabilization counter-balanced by epigenetic silencing of the p19(Arf) gene in the Mdm2 haploinsufficient tumors. In human neuroblastoma xenograft models, conditional small interfering RNA-mediated knockdown of MDM2 in cells expressing wild-type p53 dramatically suppresses tumor growth in a p53-dependent manner. In summary, we provided evidence for a crucial role for direct inhibition of p53 by MDM2 and suppression of the p19(ARF)/p53 axis in neuroblastoma tumorigenesis, supporting the development of therapies targeting these pathways.

Genomic and immunologic surveillance mechanisms are crucial in protection from cancer. The tumor suppressor protein p53, encoded by TP53, is a major regulator of genome surveillance. Among the natural sequence variants of TP53, rs1042522 (R72P) modifies the risk for solid tumors. To investigate its relevance in childhood acute lymphoblastic leukemia (ALL) susceptibility, we genotyped 114 cases and 414 newborn controls from Wales (UK) for polymorphisms in TP53 (R72P),its negative regulator MDM2 (single-nucleotide polymorphism SNP309, rs2279744), and selected HLA complex genes whose products interact with TP53. TP53 R72P showed a risk association with gene dosage effect (P=0.002) resulting in a strong association of homozygous genotype (OR=2.9, 95% CI=1.5-5.6) and no sex effect. SNP309 did not show any association with primary susceptibility to childhood ALL, even after stratification by sex. However, females with SNP309 minor allele had earlier onset of childhood ALL (median age at diagnosis was 36 months in females, but 60 months in males; P=0.002). The HLA complex genes did not show any statistically significant interaction with R72P. We have therefore identified TP53 R72P as a possible risk modifier for childhood ALL and the association of MDM2 with age at onset with sex effect suggests prenatal hormonal programming ofchildhood ALL susceptibility.

AIM: Determination of frequency and prognostic significance of murine double minute protein-2 (MDM-2) over expression and its association with p53 status in children with acute lymphoblastic leukemia (ALL). METHODS: MDM-2 expression by flow cytometry and p53 gene status by PCR were determined in peripheral blood orbone marrow of 46 ALL children (at initial diagnosis) and control group. RESULTS: MDM-2 was significantly overexpressed in 15 patients (32.6%). p53 mutation was detected in six out of 46 patients at initial diagnosis, three of them were out of 29 cases achieving complete remission (CR) and the other three cases were outof 17 of relapsed patients, which is significantly higher than CR group (P<0.05). Positive correlation was found between the MDM-2 overexpression and initial WBCscount, peripheral blast cell count and presence of CNS blasts (P<0.05, <0.05 and<0.05 respectively). CONCLUSION: MDM-2 is overexpressed in a significant number of childhood ALL, and more often observed in the poor outcome group and its frequency is not related to p53 status. Measurement of MDM-2 as a bad prognosticmarker even in cases with non-mutant p53 is very important. Moreover, MDM-2 may be a potential molecular target for production of new cancer therapy.

Myc proteins (c-myc, Mycn and Mycl) target proliferative and apoptotic pathways vital for progression in cancer. Amplification of the MYCN gene has emerged as one of the clearest indicators of aggressive and chemotherapy-refractory diseasein children with neuroblastoma, the most common extracranial solid tumor of childhood. Phosphorylation and ubiquitin-mediated modulation of Myc protein influence stability and represent potential targets for therapeutic intervention. Phosphorylation of Myc proteins is controlled in-part by the receptor tyrosine kinase/phosphatidylinositol 3-kinase/Akt/mTOR signaling, with additional contributions from Aurora A kinase. Myc proteins regulate apoptosis in part through interactions with the p53/Mdm2/Arf signaling pathway. mutation in p53 iscommonly observed in patients with relapsed neuroblastoma, contributing to both biology and therapeutic resistance. This review examines Myc function and regulation in neuroblastoma, and discusses emerging therapies that target Mycn.

The murine double minute protein-2 (MDM-2) oncogene is a determinant of embryogenesis, tumorigenesis, and cell cycle progression. The effects of MDM-2 on these processes depend, in part, on its ability to inactivate the p53 tumor suppressor gene. Our goal was to determine whether MDM-2 protein overexpressionsor p53 gene mutations are a frequent event in poor outcome pediatric acute lymphoblastic leukemia (ALL). This work was conducted on 46 children with ALL (31 males and 15 females) with age range 2-18 years, 18 children with matched age and sex were enrolled in the study as a control group. The MDM-2 expression by flowcytometry and p53 gene status by PCR were determined in peripheral blood or bone marrow of ALL children (at initial diagnosis) and also of control group. The ALL children were treated by the modified BFM 76179 protocol of therapy, 29 patients (63%) achieved complete remission, while 17 patients (37%) were subsequently failed to achieve complete remission or relapsed within 6 months ofachieving complete remission (CR). MDM-2 was significantly overexpressed in 15 ALL patients (32.6%), compared to that of healthy controls, 4 of them (4/15), were out of 29 cases of CR (13.8%), and the other 11 cases were out of 17 relapsed cases (64.7%). In contrast to overexpression of MDM-2, the mutation of p53 was detected in 6 (13%) out of 46 ALL patients at the initial time of diagnosis, 3 of them (10.3%) were out of 29 cases of CR and the other 3 cases (17.6%) were out of 17 of relapsed group, which is significantly higher than CR group (P < 0.05). In relapsed group, 2 patients out of 3 cases with p53 mutationwere MDM-2 negative, also, ALL 3 cases of mutant P53 among patients in CR were negative MDM2. A positive correlation was found between the MDM-2 overexpressionand initial WBCs count, blast cell counts in peripheral blood and presence of CNS blasts (p < 0.05, p < 0.05 and p < 0.05 respectively). These results indicate that MDM-2 is overexpressed in a significant number of childhood ALL, it is morefrequent in relapsed cases and its frequency is not related to p53 status. Thus measuring of MDM-2 as a bad prognostic marker even in cases with non mutant P53 is very important. Moreover, MDM-2 may be a potential molecular target for production of new cancer therapy.

Glioblastoma multiforme (GBM) is one of the deadliest tumors afflicting humans, and the mechanisms of its onset and progression remain largely undefined. Our attempts to elucidate its molecular pathogenesis through DNA copy-number analysis by genome-wide digital karyotyping and single nucleotide polymorphism arrays identified a dramatic focal amplification on chromosome 1q32 in 4 of 57 GBM tumors. Quantitative real-time PCR measurements revealed that HDMX is the most commonly amplified and overexpressed gene in the 1q32 locus. Further genetic screening of 284 low- and high-grade gliomas revealed that HDMX amplifications occur solely in pediatric and adult GBMs and that they are mutually exclusive ofTP53 mutations and MDM2 amplifications. Here, we demonstrate that HDMX regulatesp53 to promote GBM growth and attenuates tumor response to chemotherapy. In GBM cells, HDMX overexpression inhibits p53-mediated transcriptional activation of p21, releases cells from G0 to G1 phase, and enhances cellular proliferation. HDMX overexpression does not affect the expression of PUMA and BAX proapoptotic genes. While in GBM cells treated with the chemotherapeutic agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), HDMX appears to stabilize p53 and promote phosphorylation of the DNA double-stranded break repair protein H2AX, up-regulate the DNA repair gene VPX, stimulate DNA repair, and confer resistanceto BCNU. In summary, HDMX exhibits bona fide oncogenic properties and offers a promising molecular target for GBM therapeutic intervention.

BACKGROUND: The variant polymorphism in the gene MDM2, SNP309, leads to increased level of mdm2 protein and subsequent downregulation of p53 tumor suppressor pathway. Presence of this single nucleotide polymorphism (SNP) has been associated with earlier tumorigenesis in patients with Li-Fraumeni syndrome, as well as decreased survival in patients with CLL. In addition, cells homozygous (G/G) for SNP 309 were found to have 10-fold increase resistance to topoisomerase II inhibitors in vitro. PROCEDURE: We genotyped children (n = 575) with de novo acute myeloid leukemia (AML) treated on three children's Oncology Group protocols (CCG 2941/2961/AAML 03P1) for the presence of SNP309. Healthy blood donors were genotyped as control population. RESULTS: The variant G/G genotype was associated with an increased susceptibility to AML (OR 1.5; P = 0.049). However, the presence of the variant allele at SNP309 did not modify disease response or toxicity in children treated on CCG protocols 2941/2961. CONCLUSIONS: The variant SNP 309 influences susceptibility to pediatric AML, but does not impact overall response to therapy.#CI- (c) 2010 Wiley-Liss, Inc.

Neuroblastoma is the most common childhood solid tumor, yet current treatment approaches have not been able to effectively control this cancer. Amplification and overexpression of MYCN have been shown to be closely related with high risk and poor prognosis in neuroblastoma. This suggests that MYCN is an important target for the antitumor therapy. Recently, vector-based RNA interference (RNAi)systems have been successfully used to eliminate gene expression, but knockdown of MYCN by vector-based RNAi as a therapeutic model for neuroblastoma has not been fully established. In this study, we used a lentivirus vector-based RNAi approach which expresses short hairpin RNA (shRNA) to knockdown MYCN in neuroblastoma cell lines IMR-32 and LAN-1. Western blotting analysis showed thatexpressions of MYCN were efficiently downregulated after infection with MYCN shRNA expression vector. The stable suppression of MYCN expression induced differentiation and apoptosis in neuroblastoma cell lines. Furthermore, we demonstrated that these changes were associated with caspase-3 activation, p27 upregulation as well as Bcl-2 and MDM2 downregulation. Finally, we demonstrated that downregulation of MYCN expression significantly reduced colony formation invitro and tumor growth in nude mice. Our data indicate that lentivirus vector-mediated silencing of MYCN in neuroblastoma cells could efficiently and significantly inhibit tumor growth both in vitro and in vivo. Therefore we demonstrate the therapeutic potential of lentivirus-delivered shRNA as a novel approach for treatment of neuroblastoma and other malignant tumors with MYCN overexpression.#CI- Copyright (c) 2011 Elsevier Inc. ALL rights reserved.

The tumor suppressor gene TP53 is the most commonly mutated gene in human cancer. The reported prevalence of mutations in rhabdomyosarcoma (RMS) varies widely, with recent larger studies suggesting that TP53 mutations in pediatric RMS may be extremely rare. Overexpression of MDM2 also attenuates p53 function. We have performed TP53 mutation/MDM2 amplification analyses in the largest series analyzed thus far, including DNA isolated from 37 alveolar and 38 embryonal RMS tumor samples obtained from the Cooperative Human Tissue Network (CHTN). Available samples were frozen tumor tissues (N = 48) and histopathology slides. TP53 mutations in exons 4-9 were analyzed by direct sequencing in ALL samples, and MDM2 amplification analysis was performed by differential PCR on a subset of22 samples. We found only one sample (1/75, 1.3%) carrying a TP53 mutation at codon 259 (p.D259Y) and no MDM2 amplification. Two SNPs in the TP53 pathway, associated with accelerated tumor onset in germline TP53 mutation carriers, (TP53 SNP72 (rs no. 1042522) and MDM2 SNP309 (rs no. 2279744)), were not found to confer earlier tumor onset. In conclusion, we confirm the extremely low prevalence of TP53 mutations/MDM2 amplifications in pediatric RMS (1.33% and 0%,respectively). The possible inactivation of p53 function by other mechanisms thus remains to be elucidated.

Medulloblastomas account for 20% of pediatric brain tumors. With an overall survival of 40%-70%, their treatment is still a challenge. The majority of medulloblastomas lack p53 mutations, but even in cancers retaining wild-type p53, the tumor surveillance function of p53 is inhibited by the oncoprotein MDM2. Deregulation of the MDM2/p53 balance leads to malignant transformation. Here, weanalyzed MDM2 mRNA and protein expression in primary medulloblastomas and normalcerebellum and assessed the mutational status of p53 and MDM2 expression in 6 medulloblastoma cell lines. MDM2 expression was elevated in medulloblastomas, compared with cerebellum. Four of 6 medulloblastoma cell lines expressed wild-type p53 and high levels of MDM2. The tumor-promoting p53-MDM2 interaction can be inhibited by the small molecule, nutlin-3, restoring p53 function. Targeting the p53-MDM2 axis using nutlin-3 significantly reduced cell viability and induced either cell cycle arrest or apoptosis and expression of the p53 target gene p21 in these 4 cell lines. In contrast, DAOY and UW-228 cells harboring TP53 mutations were almost unaffected by nutlin-3 treatment. MDM2 knockdown in medulloblastoma cells by siRNA mimicked nutlin-3 treatment, whereasexpression of dominant negative p53 abrogated nutlin-3 effects. Oral nutlin-3 treatment of mice with established medulloblastoma xenografts inhibited tumor growth and significantly increased survival. Thus, nutlin-3 reduced medulloblastoma cell viability in vitro and in vivo by re-activating p53 function. We suggest that inhibition of the MDM2-p53 interaction with nutlin-3 is a promising therapeutic option for medulloblastomas with functional p53 that should be further evaluated in clinical trials.

Retinoblastoma is a childhood cancer of the developing retina that begins in utero and is diagnosed in the first years of life. Biallelic RB1 gene inactivation is the initiating genetic lesion in retinoblastoma. The p53 gene isintact in human retinoblastoma but the pathway is believed to be suppressed by increased expression of MDM4 (MDMX) and MDM2. Here we quantify the expression ofMDM4 and MDM2 mRNA and protein in human fetal retinae, primary retinoblastomas, retinoblastoma cell lines and several independent orthotopic retinoblastoma xenografts. We found that MDM4 is the major p53 antagonist expressed in retinoblastoma and in the developing human retina. We also discovered that MDM4 protein steady state levels are much higher in retinoblastoma than in human fetal retinae. This increase would not have been predicted based on the mRNA levels. We explored several possible post-transcriptional mechanisms that may contribute tothe elevated levels of MDM4 protein. A proportion of MDM4 transcripts are alternatively spliced to produce protein products that are reported to be more stable and oncogenic. We also discovered that a microRNA predicted to target MDM4 (miR191) was downregulated in retinoblastoma relative to human fetal retinae anda subset of samples had somatic mutations that eliminated the miR-191 binding site in the MDM4 mRNA. Taken together, these data suggest that post-transcriptional mechanisms may contribute to stabilization of the MDM4 protein in retinoblastoma.

Osteosarcoma (OS) is the most common pediatric bone malignancy worldwide. The MDM2 gene is an important candidate gene for influencing the susceptibility to OS. The objective of this study aimed to detect the potential association between MDM2 genetic variants and OS susceptibility in Chinese Han population. We recruited 415 OS patients and 431 cancer-free controls in this case-control study. The c.44C>T and c.1002T>C genetic variants in MDM2 gene were investigatedusing created restriction site-polymerase chain reaction (CRS-PCR) and PCR-restriction fragment length polymorphism (PCR-RFLP), respectively. We found that the genotypes/alleles of c.44C>T and c.1002T>C were statistically associated with the increased risk of OS (for c.44C>T, TT versus (vs.) CC: OR = 2.43, 95% CI 1.49-3.95, p < 0.001; T vs. C: OR = 1.36, 95% CI 1.11-1.67, p = 0.003; for c.1002T>C, CC vs. TT: OR = 2.38, 95% CI 1.37-4.13, p = 0.002; C vs. T: OR = 1.27, 95% CI 1.02-1.56, p = 0.030). The T allele and TT genotype of c.44C>T and C allele and CC genotype of c.1002T>C could be increased risk factors for the susceptibility to OS. Results from this study suggest that MDM2 genetic variantsare potentially related to OS susceptibility in Chinese Han population, and might be used as molecular markers for assessing OS susceptibility.

In adults, loss of heterozygosity for DNA on 17p has been shown in high-grade anaplastic astrocytomas (AAs) and glioblastomas multiforme (GMs), and mutation of the TP53 tumor suppressor gene has been reported in ALL grades of astrocytomas. Little is known, however, about 17p deletion and TP53 mutation in juvenile pilocytic astrocytomas (JPAs), the most common low-grade tumors seen in children. To elucidate the genetic characteristics of pediatric high-grade astrocytomas and JPAs, we performed restriction fragment length polymorphism analysis with probesderived from 17p and TP53 mutational studies in 28 tumor specimens. Telomeric chromosome arm 17p markers 144-D6 and ABR were lost in 6 (75%) of 8 informative tumors classified as high-grade (7 AAs, 1 GM) and in 2 (10%) of 20 informative JPAs. Loss of 17p probes centromeric to the TP53 gene were also detected in 3 AAs and 5 JPAs. Four of the 6 (66%) JPAs with losses of 17p DNA sequences recurred rapidly despite aggressive therapy, whereas only 5 of the other 14 (36%) recurred. mutation of the TP53 gene was detected by polymerase chain reaction and denaturing gradient gel electrophoresis in only 1 JPA and 1 AA. These tumors were also examined for MDM2 gene amplification as an alternate inactivation mechanismfor TP53 gene function: no instances of alteration were identified. These results suggest that a gene or genes in addition to TP53 on 17p may be involved in the etiology or progression of high-grade astrocytomas and aggressive JPAs in children.(ABSTRACT TRUNCATED AT 250 WORDS)

The wild-type (wt) p53 tumor suppressor gene is commonly inactivated in human malignancies, either by mutations or by loss of expression. An additional proposed mechanism for inactivation of wt-p53 is amplification of the murine double minute 2 (MDM2) gene and overexpression of the MDM2 protein, which binds to p53 and eliminates its tumor suppressor function. To investigate a potential role for MDM2 in the inactivation of wt-p53 in pediatric acute lymphoblastic leukemia (ALL), we examined the expression of MDM2 and p53, as well as the occurrence of p53 mutations and possible amplification of the MDM2 gene, in 19 pediatric ALL cell lines and one pediatric acute myelogenous leukemia (AML) line. Although we did not find significant amplification of the MDM2 gene in any of the leukemic lines, we detected overexpression of MDM2 in ALL 10 lines that expressed wt-p53. Of the 10 lines without overexpression of the MDM2 gene, six (including the AML line) did not express p53, and four expressed mutant p53 with single point mutations in exons 7 and 8. To determine whether primary leukemic cells showed a similar correlation, we analyzed the original cryopreserved leukemic bone marrow cells from seven patients from whom cell lines were established. We obtained similar results from both the primary leukemic cells and the corresponding cell lines: overexpression of MDM2 was present in primary cells that expressed wt-p53 but not in cells that lacked expression of wt-p53. These findings suggest an important role for MDM2 in the pathogenesis of pediatric ALLin which leukemic cells express wt-p53.

Loss of heterozygosity is common for the short arm of chromosome 17 in medulloblastomas, and putative medulloblastoma suppressor loci have been localized to 17p13. The colocalization of the p53 tumor suppressor gene to 17p13raises the possibility that its mutant alleles may play a role in the malignant transformation of "medulloblasts." mutations and deletions of the p53 gene have been described in many tumor types and in the germline of some individuals with the Li-Fraumeni syndrome, but reports on the status of the p53 and mdm2 (a gene coding for a p53-associated protein reportedly amplified in human sarcomas) genes in medulloblastomas are few and an indication of their roles, if any, in the etiology of this important childhood tumor has yet to emerge. Here we have analyzed polymerase chain reaction-amplified products of exons 4-9 (95% of reported p53 mutations occur within this region) of the p53 gene in 9 medulloblastomas for potential mutations using the technique of single strand conformation polymorphism analysis and DNA sequencing. We found only one mutation, an A-T to T-A transversion involving the second base of codon 285 and resulting in the substitution of valine for glutamic acid, amplification of the mdm2 gene could be detected in zero of eight of these tumors. These findings suggest that genetic events associated with the inactivation of p53 gene occur in only a minor subset of medulloblastomas.

Loss of function of the p53 tumor suppressor gene by point mutation is the most commonly detected genetic alteration in human cancer. There is growing evidence that amplification and overexpression of the MDM2 gene are alternative mechanisms that also lead to functional inactivation of p53. While p53 mutations and MDM2 amplification have been reported to occur in rhabdomyosarcoma and osteogenic sarcoma, the incidence of MDM2 in other pediatric solid tumors is not known. We therefore tested a series of other pediatric solid tumors for MDM2 gene amplification. MDM2 amplification could not be detected in specimens from 40 Wilms' tumors, 15 neuroblastomas, 12 sarcomas, or 4 hepatoblastomas tested. To determine whether MDM2 amplification was an alternative mechanism of p53 inactivation in adult carcinomas that frequently possess p53 mutations, 68 samples of squamous cell carcinomas of the upper aerodigestive tract, 24% of which were previously shown to contain p53 mutations, were also tested for MDM2 amplification. MDM2 amplification did not occur in any of the tumor specimens tested. These findings suggest that MDM2 amplification may only occur in a limited subset of human tumors. Loss of function of p53 may be an essential event in human tumorigenesis. If so, then other mechanisms of p53 inactivation must occur in those tumors that exhibit neither p53 mutation nor MDM2 amplification.

MDM2 gene overexpression has been implicated in the pathogenesis of human neoplasia via inhibition of the p53 tumor-suppressor function. To investigate the potential involvement of the MDM2 oncogene in the pathogenesis of childhood rhabdomyosarcoma (RMS) we studied MDM2 abnormalities in six RMS cell lines in correlation with the p53 status. Three showed overexpression of MDM2 mRNA and protein, one with concomitant MDM2 gene amplification. ALL three lacked p53 mutation and expressed low levels of p53 mRNA but exhibited elevated p53 proteins. Double immunostaining revealed that the overexpressed MDM2 and p53 proteins were co-localized to the same cell nuclei. Furthermore, the two proteins were physically associated, as shown by co-immunoprecipitation and Western blot analysis. The half-life of the p53 protein was prolonged in the MDM2-expressing RMS cells. The extended half-life wildtype p53 protein and its complex formationwith the elevated MDM2 suggest that the underlying mechanism for p53 protein accumulation in these cell lines is p53 stabilization by an overabundant MDM2 protein. The overexpressed MDM2 protein had a short half-life. The three remaining RMS cell lines exhibited low MDM2 mRNA and protein levels and carried p53 mutations. This study suggest that MDM2 overexpression represents an alternative mechanism for p53 inactivation in a subset of childhood RMS without p53 mutations. The results further indicate that the elevated MDM2 protein is responsible for wildtype p53 protein accumulation via stabilization.

Cytogenetic and molecular genetic studies were performed on a pleomorphic sarcoma removed from the left atrium of a 15-year-old girl. Histologic analysis was consistent with a storiform-pleomorphic malignant fibrous histiocytoma (MFH). Although MFH is the most common soft-tissue sarcoma of late adulthood. It is extremely rare in childhood and its existence in the pediatric population remains controversial. Cytogenetic analysis revealed several alterations previously associated with adult MFH, including abnormalities of chromosomal bands 11p11 and 19p13. Moreover, the tumor demonstrated homogeneously staining regions (HSR) anddouble minute chromosomes (dmin) suggestive of gene amplification. We therefore screened the case for amplification of genes localized to chromosomal bands 12q13-14, including the putative protooncogenes MDM2, CDK4, SAS, CHOP, and CLI, which are frequently amplified and overexpressed in adult MFH. Southern and Northern blot analysis confirmed the coamplification of MDM2, CDK4, SAS, and CHOP. To our knowledge, such coamplification studies of the 12q13-14 amplicon have not been previously detected in pediatric MFH. Our results provide cytogenetic and molecular genetic evidence that pediatric and adult MFH are histogenetically related entities.

The role of tumor suppressor genes and oncogenes in the development of Ewing's sarcoma has not yet been fully clarified. In this study, we analyzed the frequency of p53 tumor suppressor gene mutation in exons 4-8 by PCR-SSCP and direct sequencing, and the expression of p53-protein in Ewing's sarcoma (ES) by using immunohistochemistry. The overexpression of MDM2, which acts as a functional inactivator of p53, was studied by immunohistochemistry. In addition,a screening for point mutations in the hot spot regions codon 12 and 13 of exon 1 and codon 61 of exon 2 of ras-genes (H-ras, N-ras, K-ras) was performed. In one case, a p53 gene mutation could be confirmed in codon 238 of exon 7 (1/24). Overexpression of MDM2 was found in five cases; in ras-genes, no mutations were detected. Compared with other highly malignant mesenchymal pediatric tumors suchas osteosarcomas, mutations of p53 and ras in Ewing's sarcomas are an extraordinarily rare event. However, their frequency is comparable to that of PNET, suggesting that the low incidence of these mutations in ES and PNET could be group-specific for tumors of neuroectodermal genesis.