Identification of differentially expressed genes in human bladder cancer through genome-wide gene expression profiling

Large-scale gene expression profiling is an effective strategy for understanding the progression of bladder cancer (BC). The aim of this study was to identify genes that are expressed differently in the course of BC progression and to establish new biomarkers for BC. Specimens from 21 patients with pathologically confirmed superficial (n=10) or invasive (n=11) BC and 4 normal bladder samples were studied; samples from 14 of the 21 BC samples were subjected to microarray analysis. The validity of the microarray results was verified by real-time RT-PCR. Of the 136 up-regulated genes we detected, 21 were present in all 14 BCs examined (100%), 44 in 13 (92.9%), and the other 71 in 12 BCs (85.7%). Of 69 down-regulated genes, 25 were found in all 14 BCs (100%), 22 in 13 (92.9%), and the other 22 in 12 BCs (85.7%). Functional annotation revealed that of the up-regulated genes, 36% were involved in metabolism and 14% in transcription and processing; 25% of the down-regulated genes were linked to cell adhesion/surface and 21% to cytoskeleton/cell membrane. Real-time RT-PCR confirmed the microarray results obtained for the 6 most highly up- and the 2 most highly down-regulated genes. Among the 6 most highly up-regulated genes, CKS2 was the only gene with a significantly greater level of up-regulation in invasive than in superficial BC (p=0.04). To confirm this result, we subjected all 21 BC samples to real-time PCR assay for CKS2. We found a considerable difference between superficial and invasive BC (p=0.001). Interestingly, there was a considerable difference between the normal bladder and invasive BC (p=0.001) and less difference between the normal bladder and superficial BC (p=0.005). We identified several genes as promising candidates for diagnostic biomarkers of human BC and the CKS2 gene not only as a potential biomarker for diagnosing, but also for staging human BC. This is the first report demonstrating that CKS2 expression is strongly correlated with the progression of human BC.