LY6K is a novel molecular target in bladder cancer on basis of integrate genome-wide profiling

BACKGROUND: The aim of this study is to find a novel molecular target based on chromosomal alteration and array-based gene expression analyses in bladder cancer (BC). We investigated a cancer testis antigen, LY6K, which is located on chromosome 8q24.3. METHODS: Five BC cell lines were subjected to high-resolution array-comparative genomic hybridisation with 244 000 probes. The expression levels of LY6K mRNA were evaluated in BC cell lines and clinical BC specimens by real-time reverse transcription–PCR. The cell lines were subjected to fluorescence in situ hybridisation of LY6K. Cell viability was evaluated by cell growth, wound healing, and matrigel invasion assays. RESULTS: Typical gained loci (P<0.0001) at 6p21.33-p21.32, 8q24.3, 9q34.13, 11q13.1-q14.1, 12q13.12-q13.13, 16p13.3, and 20q11.21-q13.33 were observed in all of the cell lines. We focused on 8q24.3 locus where LY6K gene harbours, and it was the top upregulated one in the gene profile from the BC cell line. LY6K mRNA expression was significantly higher in 91 BCs than in 37 normal bladder epitheliums (P<0.0001). Fluorescence in situ hybridisation validated that the high LY6K mRNA expression was due to gene amplification in the region where the gene harbours. Cell viability assays demonstrated that significant inhibitions of cell growth, migration, and invasion occured in LY6K knock down BC cell lines; converse phenomena were observed in a stable LY6K transfectant; and LY6K knockdown of the transfectant retrieved the original phenotype from the LY6K transfectant. CONCLUSION: Upregulation of the oncogenic LY6K gene located on the gained locus at 8q24.3 may contribute BC development.