4193

MDM2

MDM2 proto-oncogene, E3 ubiquitin protein ligase;MDM2;MDM2 proto-oncogene, E3 ubiquitin protein ligase

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

12q14.3-q15

protein-coding

The E3 ubiquitin ligase human murine double minute (HDM2) is overexpressed in 40%-80% of late-stage metastatic cancers in the absence of gene amplification. Hdm2 regulates p53 stability via ubiquitination and has also been implicated in altering the sensitivity of cells to TGF-beta1. Whether TGF-beta1 signaling induces Hdm2 expression leading to HDM2-mediated destabilization of p53 has not been investigated. In this study, we report that TGF-beta1-activated SMA- and MAD3 (Smad3/4) transcription factors specifically bound to the second promoter region of HDM2, leading to increased HDM2 protein expression and destabilization of p53 in human cancer cell lines. Additionally, TGF-beta1 expression led to Smad3 activation and murine double minute 2 (Mdm2) expression in murine mammary epithelial cells during epithelial-to-mesenchymal transition (EMT). Furthermore, histological analyses of human breast cancer samples demonstrated that approximately 65% of late-stage carcinomas were positive for activated Smad3 and HDM2, indicating a strong correlation between TGF-beta1-mediated induction of HDM2 and late-stage tumor progression. Identification of Hdm2 as a downstream target of TGF-beta1 represents a critical prosurvival mechanism in cancer progression and provides another point for therapeutic intervention in late-stage cancer.

PURPOSE: The p53/MDM2/p14ARF pathway is one of the major signaling cascades involved in the regulation of apoptosis. Although many tumors have been reported to show disruption of the p53/MDM2/p14ARF pathway, few studies have examined p53, MDM2, and p14ARF simultaneously in colorectal carcinoma. The present study was undertaken to clarify whether correlations exist among MDM2, p53, and p14ARF in colorectal cancer. METHODS: We determined the presence of mutations in the p53 gene, MDM2 expression, and methylation status of the p14ARF in 97 primary colorectal carcinoma specimens. Associations with survival and clinicopathologic factors were investigated. RESULTS: At least one abnormality of these three molecules was found in 82 (84 percent) tumors. We observed a significant inverse association between MDM2 expression and tumor invasion (P = 0.01). Furthermore, the presence of liver metastasis was also significantly associated with low MDM2 expression (P = 0.02). CONCLUSIONS: The results suggest that disruption of the p53/MDM2/p14ARF pathway may frequently participate in colonic carcinogenesis and that MDM2 expression status may be a factor in the prediction of potential invasion and liver metastasis of colorectal carcinomas.

Laryngeal squamous cell carcinoma is one of the most common malignant neoplasms of the head and neck. In Brazil, laryngeal tumors represent 2% of all cancers and are associated with approximately 3,000 deaths annually. Human papillomavirus (HPV) has been reported to play an important role in the etiology of laryngeal cancer. The aim of the present study was to evaluate the expression of p53, p27, and Mdm2 in laryngeal carcinomas. Sixty-three larynx biopsies were selected for the study, including 9 in situ laryngeal carcinomas, 27 laryngeal carcinomas without metastasis and 27 laryngeal carcinomas with metastasis. Twenty-seven cervical lymph nodes from patients with metastatic lesions were also evaluated. The expression levels of p53, p27, and Mdm2 were assessed by immunohistochemistry using a computer-assisted system. HPV detection and typing were performed using PCR, and the HPV types that were evaluated included HPV 6, 11, 16, 18, 31 and 33. Out of 63 patients, 53 (84.1%) were positive for beta-globin (internal control), and 10 (15.9%) were beta-globin negative and therefore excluded from the evaluation. Thus, 7 (13.2%) out of 53 patients were HPV positive, and 46 (86.8%) out of 53 patients were HPV negative. Statistically significant differences (p < 0.05) in Mdm2 expression levels were observed in the in situ laryngeal carcinoma samples compared with the laryngeal carcinoma samples with metastasis. No statistically significant differences (p > 0.05) in either p53 or p27 expression levels were detected. These findings suggest that Mdm2 may be associated with the invasiveness and aggressiveness of laryngeal carcinomas.

Overexpression of vascular endothelial growth factor (VEGF) and the extent of neoangiogenesis are closely correlated with tumor development and cancer metastases. To assess whether VEGF mediated angiogenesis is regulated by HDM2, we treated the GI-101A and HL-60 cells with HDM2 gene specific antisense phosphorothioate oligodeoxynucleotide (AS5). The antisense treatment resulted in a significant reduction of both basal as well as phorbol 12,13-dibutyrate (PDB) and Diethylstilbestrol (DES) induced VEGF mRNA and protein expressions. Furthermore, when the Human Umbilical Vein Endothelial Cells (HUVECs) were exposed to medium obtained from AS5 transfected GI-101A and HL-60 cells, the angiogenesis was significantly reduced compared to the controls in the in vitro angiogenesis assay. On the contrary, the medium obtained from PDB treated cells that expressed HDM2 and VEGF at a higher level showed an increase in the tube formation by HUVEC. Thus, our present study suggests that modulation of HDM2 expression could play an important role in tumor angiogenesis and the metastatic process via transcriptional regulation of VEGF.

The tumour suppressor p53 is known to prevent cancer progression by inhibiting proliferation and inducing apoptosis of tumour cells. Slug, an invasion promoter, exerts its effects by repressing E-cadherin transcription. Here we show that wild-type p53 (wtp53) suppresses cancer invasion by inducing Slug degradation, whereas mutant p53 may stabilize Slug protein. In non-small-cell lung cancer (NSCLC), mutation of p53 correlates with low MDM2, high Slug and low E-cadherin expression. This expression profile is associated with poor overall survival and short metastasis-free survival in patients with NSCLC. wtp53 upregulates MDM2 and forms a wtp53-MDM2-Slug complex that facilitates MDM2-mediated Slug degradation. Downregulation of Slug by wtp53 or MDM2 enhances E-cadherin expression and represses cancer cell invasiveness. In contrast, mutant p53 inactivates Slug degradation and leads to Slug accumulation and increased cancer cell invasiveness. Our findings indicate that wtp53 and p53 mutants may differentially control cancer invasion and metastasis through the p53-MDM2-Slug pathway.

expression of vascular endothelial growth factor (VEGF) increases in cancer cells during hypoxia. Herein, we report that the MDM2 oncoprotein plays a role in hypoxia-mediated VEGF upregulation. In studying the characteristics of MDM2 and VEGF expression in neuroblastoma cells, we found that hypoxia induced significantly higher upregulation of both VEGF mRNA and protein in MDM2-positive cells than in the MDM2-negative cells, even in cells without wild-type (wt) p53. We found that hypoxia induced translocation of MDM2 from the nucleus to the cytoplasm, which was associated with increased VEGF expression. Enforcing overexpression of cytoplasmic MDM2 by transfection of the mutant MDM2/166A enhanced expression of VEGF mRNA and protein production, even without hypoxia. The results of mechanistic studies demonstrated that the C-terminal RING domain of the MDM2 protein bound to the AU-rich sequence within the 3' untranslated region (3'UTR) of VEGF mRNA; this binding increased VEGF mRNA stability and translation. In addition, knockdown of MDM2 by small interfering RNA (siRNA) in MDM2-overexpressing cancer cells resulted in inhibition of VEGF protein production, cancer cell survival, and angiogenesis. Our results suggest that MDM2 plays a p53-independent role in the regulation of VEGF, which may promote tumor growth and metastasis.

PURPOSE: Mouse double minute 2 (MDM2) is a key negative regulator of the p53 activity. Recently, a polymorphism in the MDM2 intronic promoter, SNP309, was shown to influence MDM2 expression and p53 activity. We examined whether the SNP309 was related to the risk of developing nasopharyngeal carcinoma (NPC) among Chinese populations. EXPERIMENTAL DESIGN: We genotyped the SNP309 in two independent case-control populations in southern China, one is from Guangxi province (including 593 NPC patients and 480 controls) and the other is from Guangdong province (including 239 patients and 286 controls), by PCR direct sequencing. Multivariate logistic regression analysis was used to calculate adjusted odds ratio (OR) and 95% confidence interval (95% CI). RESULTS: We observed that compared with the TT genotype, the genotypes containing G allele (GT + GG genotype) were associated with significant increased susceptibility to NPC in both Guangxi (OR, 1.43; 95% CI, 1.04-1.91) and Guangdong population (OR, 1.53; 95% CI, 1.00-2.36). When these two sample sets were combined, the OR of the GT + GG genotype developing NPC was 1.45 (95% CI, 1.12-1.85) compared with the TT genotype. Furthermore, compared with the TT genotype, the GT + GG genotype was also significantly associated with the advanced lymph node metastasis (OR, 1.84; 95% CI, 1.09-3.05). CONCLUSIONS: Our findings suggest that the MDM2 SNP309 may be a risk factor for the occurrence and advanced neck lymph node metastasis of NPC in Chinese population.

Osteosarcoma is a malignant bone tumor with high metastatic potential. metastasis at diagnosis is the most significant prognostic factor in predicting the clinical outcome of osteosarcoma. We compared the gene expression of metastases that were present at the time of initial diagnosis to those developed later in the course of the disease. We used quantitative real-time polymerase chain reaction to evaluate the gene expression of MDM2, CXCR4, RANKL, RB1, and OSTERIX in 98 samples of osteosarcoma taken from 47 patients (74 metastases and 24 primary tumors) and 30 nonmalignant lung tissues surrounding osteosarcoma metastases. In addition, we investigated the copy number changes of RB1 and MDM2 genes in 12 primary cultures of pulmonary metastases of osteosarcoma, using interphase fluorescence in situ hybridization. Metastases from metastatic patients at diagnosis were characterized by low expression of RB1 and RANKL (P = .0009 and P = .0109, respectively) and overexpression of CXCR4 and MDM2 (P = .0389 and P = .0325, respectively). The loss of RANKL and gain of CXCR4 could also be detected in the primary tumors of metastatic patients at diagnosis (P = .0121 and P = .0264, respectively). Thus, some early genetic events such as the loss of RANKL and the gain of CXCR4 expressions probably facilitate the metastatic progression concomitant with the primary tumor establishment, supporting the role of the CXCR4 receptor in directing osteosarcoma metastases to the lung. On the other hand, late events such as the loss of RB1 and gain of MDM2, crucial regulators of cell cycle, appear to be related to the final mechanisms contributing to the metastatic establishment of osteosarcoma.

In our previous study, the mouse double minute 2 (MDM2) was identified as one of the leading genes that promote the metastasis of pancreatic cancer (PC). However, the mechanism by which MDM2 promotes metastasis of PC is not understood. In this study, we show that down-regulation of MDM2 through lentivirus-mediated RNA interference could also suppress in vitro proliferation and in vivo tumor growth, and led to an obvious inhibition of both in vitro invasion and in vivo live metastases of SW1990HM cells which had an over-expression of MDM2 and a higher metastatic potential. Moreover, we also show that the down-regulation of MDM2 induced a significant decrease in MMP9, Ki-67 and increase in P53, E-Cadherin expression, and results in an altered expression of genes involved in metastasis, apoptosis, and cell proliferation. Our results suggest that MDM2 plays an important role in metastasis as well as tumor growth of PC. MDM2 could be a hopeful target for the control of PC.