Changes in the cyclin D1 gene copy number in melanoma cell lines detected by double-target fluorescence in situ hybridization

The cyclin D1 gene is often amplified in solid tumors. Six human melanoma c ell lines derived from tumors at various stages of progression were analyze d by double-target fluorescence in situ hybridization (FISH) and dot blot h ybridization to detect cyclin D1 gene amplification and deletion. FISH was performed using a probe for cyclin D1 and an alpha satellite of the chromos ome 11 probe, to analyze the cyclin D1 copy number relative to the numbers of chromosome 11 in individual cells. Copies of both the cyclin D1 gene and chromosome 11 were observed in the nuclei of all cell lines. However, the copy numbers of the cyclin D1 gene and of chromosome 11 were closely associ ated and the copy number ratio of cyclin D1 to chromosome 11 (cyclin D1/chr omosome 11) was almost one in all cell lines. This finding indicated that t he extra copies of cyclin D1 were always accompanied by extra copies of chr omosome 11. At the cellular level, cyclin D1 amplification was detected in fewer than 5% of interphase nuclei in only two cell lines, and the gene was deleted in all cell lines to various degrees. Dot blot hybridization revea led no amplification of cyclin D1 in any of the cell lines. We concluded th at amplification of the cyclin D1 gene is rare in these melanoma cell lines .