Extensive amplification of bcr/abl fusion genes clustered on three marker chromosomes in human leukemic cell line K-562.

Using fluorescence in situ hybridization (FISH), we were able to demonstrate 22-24-fold amplification of the bcr/abl fusion gene in the human leukemic cell line K-562. About 60% of the amplified sequences are localized to a large acrocentric marker chromosome, with another 30% clustered on a small acrocentric chromosome. In addition to these two masked Ph chromosomes, the remaining bcr/abl fusion genes are located on a der(2) distal to band q33. G- and C-banding analysis revealed similar unique banding patterns in both masked Ph chromosomes and suggests that amplification occurred by tandem duplication of the bcr/abl fusion site. Because the number of bcr/abl fusion genes may be increasing over time, it is critical that researchers using K-562 cells should be aware of this extensive amplification.