Evidence for a mutant allele of the gene for DNA topoisomerase II in adriamycin-resistant P388 murine leukemia cells.
Previous studies have shown that DNA topoisomerase II enzyme activity and protein levels are reduced in cloned lines of Adriamycin-resistant P388 leukemia cells relative to drug-sensitive cells (Deffie et al., Cancer Res., 49: 58-62, 1989). The molecular basis of the reduced topoisomerase II levels in these resistant cells has been investigated. Northern blot analysis of total cellular RNA from drug-sensitive and -resistant cells using a 1.8-kilobase human topoisomerase II complementary DNA revealed the presence of two mRNA species: a 6.6-kilobase transcript that was strongly expressed in drug-sensitive cells but reduced 7- to 8-fold in resistant cells; and a 5.5-kilobase transcript detected only in drug-resistant cells. Southern blot analysis of genomic DNA digested with BamHI, StuI, or PvuII and probed with the 1.8-kilobase complementary DNA for human topoisomerase II showed that, in Adriamycin-resistant cells, there were two different alleles for topoisomerase II, one identical to the native allele but with a lower gene copy number than that found in sensitive cells, and a second allele containing a mutation present only in resistant cells. These findings suggest that the reduced levels of topo II protein in drug-resistant cells may be due to reduced amounts of the native 6.6-kilobase mRNA. The unique 5.5-kilobase mRNA in resistant cells may represent a shortened transcript of the mutated topoisomerase II allele.
Deffie
A M
AM
Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Canada.
Bosman
D J
DJ
Goldenberg
G J
GJ
D000483:Alleles; D000818:Animals; D015152:Blotting, Northern; D015139:Blotting, Southern; D004247:DNA / Q000235:genetics; D015342:DNA Probes; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004273:DNA, Neoplasm / Q000235:genetics; D004317:Doxorubicin / Q000494:pharmacology*; D004351:Drug Resistance; D007941:Leukemia P388 / Q000201:enzymology / Q000235:genetics*; D007942:Leukemia, Experimental / Q000235:genetics*; D051379:Mice; D009154:Mutation; D012334:RNA, Neoplasm / Q000235:genetics; D014407:Tumor Cells, Cultured
D015342:DNA Probes; D004273:DNA, Neoplasm; D012334:RNA, Neoplasm; D004317:Doxorubicin; D004247:DNA; D004250:DNA Topoisomerases, Type II