Delineation of the 6p22 amplification unit in urinary bladder carcinoma cell lines

Eight cell lines from transitional cell carcinoma of the urinary bladder we re analyzed by comparative genomic hybridization. All tumor lines exhibited frequent chromosome gains (11.5/cell line) and losses (8.4/cell line). In six cell lines, gain of chromosome 5p was associated with gains of 6p and 2 0q. In five of these cell lines, amplification of parts of 6p was observed, Cytogenetic investigation combined with fluorescence in situ hybridization analysis revealed typical marker chromosomes with homogeneously staining r egions (RSRs) containing material from 6p, By hybridizing individual yeast artificial chromosome probes from a chromosome 6p contig to these HSRs, a c ontig of three yeast artificial chromosomes common to all 6p HSRs was ident ified that spans less than 2 Mb. The genes SOX4 and PRL were shown to map t o this region and to be coamplified in the cell lines. However, SOX4 was no t overexpressed in any cell line and PRL was not expressed at all. Thus, th e presumptive 6p oncogene remains to be conclusively identified.