STRUCTURE AND METHYLATION-BASED SILENCING OF A GENE (DBCCR1) WITHIN ACANDIDATE BLADDER-CANCER TUMOR-SUPPRESSOR REGION AT 9Q32-Q33

Loss of heterozygosity (LOH) on chromosome 9q is the most frequent gen etic alteration in transitional cell carcinoma (TCC) of the bladder, i ndicating the presence of one or more relevant tumor suppressor genes. We previously mapped one of these putative tumor suppressor loci to 9 q32-q33 and localized the candidate region within a single YAC 840 kb in size. This locus has been designated DBC1 (for deleted in bladder c ancer gene 1). We have identified a novel gene, DBCCR1, in this candid ate region by searching for expressed sequence tags (ESTs) that map to YACs spanning the region. Database searching using the entire DBCCR1 cDNA sequence identified several human ESTs and a few homologous mouse ESTs. However, the predicted 761-amino-acid sequence had no significa nt homology to known protein sequences. Mutation analysis of the codin g region and Southern blot analysis detected neither somatic mutations nor gross genetic alterations in primary TCCs. Although DBCCR1 was ex pressed in multiple normal human tissues including urothelium, mRNA ex pression was absent in 5 of 10 (50%) bladder cancer cell lines. Methyl ation analysis of the CpG island at the 5' region of the gene and the induction of de novo expression by a demethylating agent indicated tha t this island might be a frequent target for hypermethylation and that hypermethylation-based silencing of the gene occurs in TCC. These fin dings make DBCCR1 a good candidate for DBC1. (C) 1998 Academic Press.