Abstract
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. 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. 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 1 tile 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. 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.
Highlights
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 level of expression of the p53 target gene in these tumors was comparable with expression levels in mutant p53 tumors (Fig. 2D). These results suggest that, in addition to p53 mutation and MDM2, mouse double minute 4 (MDM4) plays an important role in the p53 pathway in UCC
We carried out a genome-wide survey to identify DNA copy number alterations using 1-Mb array comparative genomic hybridization
Summary
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. 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, providing new avenues for therapeutic intervention. Genomic instability assessed by DNA copy number changes is a hallmark of aggressive UCC; losses of 2q, 3p, 4p, 5q, CDKN2A/p16 (8p), 10q, 11p, and RB1 (13q) and gains of 5p, EGFR (7p), 8q21, 11q13, ERBB2 (17q), 20q, and E2F3 (6p) are commonly reported (4 – 6). DNA copy number has been shown to consistently correlate with gene expression level of a significant fraction of genes, with 44% to 62% of genes within a region of amplification being overexpressed (7 – 9), for example, gains of 11q13 and 17q21 harboring CCND1 and ERBB2 oncogenes in UCC (10, 11). Conventional cytogenetic methods do not provide a global view of the myriad of genetic events within a single tumor
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
