High-Resolution Array-Based Comparative Genomic Hybridization of Bladder Cancers IdentifiesMouse Double Minute 4(MDM4) as an Amplification Target Exclusive ofMDM2andTP53

Abstract

Purpose: Loss of p53 function in urothelial cell carcinoma (UCC) by mutation or inactivation disrupts normal cell cycle checkpoints, generating a favorable milieu for genomic instability, a hallmark of UCC. The aim of this study was to characterize novel DNA copy number changes to identify putative therapeutic targets. Experimental Design:We report our findings using array comparative genomic hybridization on a whole-genome BAC/PAC/cosmid array with a median clone interval of 0.97 Mb to study a series of UCC cases. TP53 status was determined by direct sequencing, and an in-house tissue microarray was constructed to identify protein expression of target genes. Results: Array comparative genomic hybridization allowed identification of novel regions of copy number changes in addition to those already known from previous studies. A novel amplification previously unreported in UCC was identified at 1q32. A chromosome 1tile path array was used to analyze tumors that showed gains and amplification; the mouse double minute 4 (MDM4) homologue was identified as the amplified gene. MDM4 mRNA expression correlated with copy number and tumor grade. Copy number changes of MDM4 and MDM2 occurred exclusively in tumors with wild-type p53. Overexpression of MDM4 corresponded to disruption of p53 transcriptional activity. Immunohistochemistry on an independent series by tissue microarray identified an inverse relationship between Mdm4 and Mdm2, with Mdm4 expression highest in invasive UCC. Conclusion:The data indicate that gain/amplification and overexpression of MDM4 is a novel molecular mechanism by which a subset of UCC escapes p53-dependent growth control, thus providing new avenues for therapeutic intervention.

Genetic and epigenetic alterations of myeloproliferative disorders

“…Interestingly, the 1q locus containing the gene encoding MDM4, a known inhibitor of p53 was repeatedly found to be amplified in post-MPN AML [45,59]. As previously reported in solid tumors [131], gains of 1q were mutually exclusive with p53 mutations, indicating that these two genetic lesions affect the same pathway, which then seems to contribute to 45.5 % of the post-MPN AML cases [130]. The significance of this pathway in leukemic transformation is further supported by the finding that TP53 mutations are the only independent prognostic factor of poor survival in secondary AML [59].…”

Recurrent genomic alterations in benign and malignant pheochromocytomas and paragangliomas revealed by whole-genome array comparative genomic hybridization analysis

“…4) and the other at 1q32, harbouring among others the MDM4 gene. These genes deserve attention as expression of CTSK has been linked with invasiveness in breast cancer (Kleer et al 2008), and the MDM4 locus has recently been found to be amplified in bladder cancer, with associated overexpression of MDM4 and disruption of TP53 activity (Veerakumarasivam et al 2008).…”

The p53 pathway in hematopoiesis: lessons from mouse models, implications for humans

“…49 In this context, 1q gains (ie, MDM4 amplifications) are mutually exclusive with TP53 mutations, a phenomenon also observed in solid tumors. 50 Overexpression of MDM4 has also been reported in CLL, which responds poorly to the MDM2 inhibitor Nutlin, implicating MDM4 as an important p53 inhibitor in CLL. 51 Altogether, these data highlight the importance of dampening p53 levels in transformation of the hematopoietic system.…”