Negative regulation of G1/S transition by the candidate bladder tumour suppressor gene DBCCR1

Deletion of all or part of chromosome 9q is the most common genetic alteration in all stages and grades of bladder cancer. DBCCR1 (deleted in bladder cancer chromosome region candidate 1) maps to the chromosome region 9q32-33, a candidate tumour suppressor locus for bladder cancer. Although no mutations of DBCCR1 have been detected in bladder tumours, expression of DBCCR1 is silenced by promoter hypermethylation in 50% of bladder cancer cell lines analysed. Here we sought to provide functional evidence to authenticate DBCCR1 as a tumour suppressor using gene-transfer methods. Exogenous expression of DBCCR1 protein or an HA epitope-tagged fusion protein, HA-DBCCR1 in NIH3T3 cells and human bladder tumour cell lines resulted in suppression of proliferation. Cell cycle analyses in NIH3T3 cells revealed that DBCCR1-mediated growth inhibition was due to an increase in the number of cells in the G1 phase of the cell cycle. The levels of apoptosis were not altered. These results demonstrate a role for DBCCR1 in cell cycle control, thereby supporting the hypothesis that this is the tumour suppressor gene targeted by 9q32-33 deletion in bladder cancer.