Molecular genetic analysis of chromosome 9 candidate tumor-suppressor loci in bladder cancer cell lines.

Underrepresentation of chromosome 9 is a common finding in bladder cancer. Frequent loss of the whole chromosome suggests the presence of at least one relevant tumor suppressor gene on each arm. Candidate regions identified by loss of heterozygosity (LOH) analysis include a region at 9p21 containing CDKN2A, which encodes p16 and p14(ARF), a large region at 9q12-31 including PTCH and many other genes, a small region at 9q32-33, which includes the DBCCR1 gene, and a region at 9q34 including the TSC1 gene. Experimental replacement of genes or chromosomes into tumor cells with appropriate deletions or mutations represents an important approach to test the functional significance of candidate tumor suppressor genes. Loss of an entire copy of chromosome 9 in many bladder tumor cell lines provides no indication of which gene or genes are affected, and selection of appropriate recipient cells for gene replacement is difficult. We have investigated three candidate tumor suppressor genes on chromosome 9 (CDKN2A, DBCCR1, and TSC1), at the DNA level and by expression analysis in a panel of bladder tumor cell lines, many of which have probable LOH along the length of the chromosome, as indicated by homozygosity for multiple polymorphic markers. Cytogenetically, we found no reduction in the numbers of chromosomes 9 relative to total chromosome count. Homozygous deletion of the CDKN2A locus was frequent but homozygous deletion of TSC1 was not found. A new cell line, DSH1, derived from a pT1G2 transitional cell carcinoma with known homozygous deletion of DBCCR1, is described. This study identifies suitable cell lines for future functional analysis of both CDKN2A and DBCCR1.