A Restriction Fragment Length Polymorphism for Human Topoisomerase II: Possible Relationship to Drug-Resistance

Abstract

In previous studies we used Southern blotting to examine the topoisomerase II locus (on chromosome 17) in human leukemia cell lines and noted a difference in the Xmn I restriction endonuclease digestion pattern between an m-AMSA-resistant line and its m-AMSA-sensitive parent line (Zwelling, L. A.; Hinds, M.; Chan, D.; Mayes, J.; Sie, K. L.; Parker, E.; Silberman, L.; Radcliffe, A.; Beran, M.; Blick, M. Characterization of an amsacrine-resistant line o f human leukemia cells. Evidence for a drug-resistant form o f topoisomerase II. Journal of Biological Chemistry 264:16411–16420; 1989). We now demonstrate that the variable Xmn I digestion pattern represents a normal restriction fragment length polymorphism (RFLP) which is observed in subjects without malignant disease and exhibits an autosomal pattern o f inheritance. These data suggest that the previously described deviation in the genomic structure of topoisomerase II in the m-AMSA-resistant cell line did not reflect a new mutation, but rather a reduction to homozygosity at the topoisomerase II locus. This reduction to homozygosity is not due to chromosomal loss, as chromosome 17-specific gene probes clearly identify two chromosome 17’s in the sensitive line and four in the resistant line, using chromosome painting with a chromosome 17-specific library. Some other genetic change must be the cause o f the resistance of HL-60/AMS A and its topoisomerase II to the inhibiting actions of m-AMSA.