Spotlight on Differentially Expressed Genes in Urinary Bladder Cancer

INTRODUCTION: We previously identified common differentially expressed (DE) genes in bladder cancer (BC). In the present study we analyzed in depth, the expression of several groups of these DE genes. MATERIALS AND METHODS: Samples from 30 human BCs and their adjacent normal tissues were analyzed by whole genome cDNA microarrays, qRT-PCR and Western blotting. Our attention was focused on cell-cycle control and DNA damage repair genes, genes related to apoptosis, signal transduction, angiogenesis, as well as cellular proliferation, invasion and metastasis. Four publicly available GEO Datasets were further analyzed, and the expression data of the genes of interest (GOIs) were compared to those of the present study. The relationship among the GOI was also investigated. GO and KEGG molecular pathway analysis was performed to identify possible enrichment of genes with specific biological themes. RESULTS: Unsupervised cluster analysis of DNA microarray data revealed a clear distinction in BC vs. control samples and low vs. high grade tumors. Genes with at least 2-fold differential expression in BC vs. controls, as well as in non-muscle invasive vs. muscle invasive tumors and in low vs. high grade tumors, were identified and ranked. Specific attention was paid to the changes in osteopontin (OPN, SPP1) expression, due to its multiple biological functions. Similarly, genes exhibiting equal or low expression in BC vs. the controls were scored. Significant pair-wise correlations in gene expression were scored. GO analysis revealed the multi-facet character of the GOIs, since they participate in a variety of mechanisms, including cell proliferation, cell death, metabolism, cell shape, and cytoskeletal re-organization. KEGG analysis revealed that the most significant pathway was that of Bladder Cancer (p = 1.5×10(-31)). CONCLUSIONS: The present work adds to the current knowledge on molecular signature identification of BC. Such works should progress in order to gain more insight into disease molecular mechanisms

MDM2 promotes p21(waf1/cip1) proteasomal turnover independently of ubiquitylation

The CDK inhibitor p21(waf1/cip1) is degraded by a ubiquitin-independent proteolytic pathway. Here, we show that MDM2 mediates this degradation process. Overexpression of wild-type or ring finger-deleted, but not nuclear localization signal (NLS)-deleted, MDM2 decreased p21(waf1/cip1) levels without ubiquitylating this protein and affecting its mRNA level in p53(–/–) cells. This decrease was reversed by the proteasome inhibitors MG132 and lactacystin, by p19(arf), and by small interfering RNA (siRNA) against MDM2. p21(waf1/cip1) bound to MDM2 in vitro and in cells. The p21(waf1/cip1)-binding-defective mutant of MDM2 was unable to degrade p21(waf1/cip1). MDM2 shortened the half-life of both exogenous and endogenous p21(waf1/cip1) by 50% and led to the degradation of its lysine-free mutant. Consequently, MDM2 suppressed p21(waf1/cip1)-induced cell growth arrest of human p53(–/–) and p53(–/–)/Rb(–/–)cells. These results demonstrate that MDM2 directly inhibits p21(waf1/cip1) function by reducing p21(waf1/cip1) stability in a ubiquitin-independent fashion