Transcriptional down-regulation of c-myc expression in an erythroleukemic cell line, K562, and its doxorubicin-resistant variant by two topoisomerase II inhibitors, doxorubicin and amsacrine.
We have evaluated the effect of two topoisomerase II (Topo II) poisons, amsacrine and doxorubicin, on the expression of the c-myc oncogene, both at the mRNA and protein levels, in the leukemia cell line, K562, and its doxorubicin-resistant counterpart, K562 DoxR. We report in this study a concentration-dependent decrease in c-myc mRNA levels upon exposure of both cell lines to amsacrine and doxorubicin, with a more pronounced effect for amsacrine in the resistant line. In either case, c-myc down-regulation closely paralleled the drug-induced growth inhibition. We have also used the technique of PCR stop-assay to detect the occurrence of DNA breaks within the P2 promoter of the c-myc gene. We have shown that Topo II-mediated breaks induced by amsacrine are probably responsible for the down-regulation of c-myc in the resistant line. In addition, amsacrine induced apoptosis only in the resistant line while doxorubicin did not induce apoptosis in any cell line. These results suggest that c-myc is not involved in the resistance of K562 DoxR cells, but can induce the apoptosis pathway in these cells, while no drug-induced apoptosis could be detected in the sensitive line.
Clary
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Department of Medical Biochemistry and Molecular Biology, Université Victor Segalen Bordeaux 2, France.
Larrue
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Pourquier
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Robert
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D000677:Amsacrine / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002467:Cell Nucleus / Q000378:metabolism; D053938:DNA Fragmentation; D015342:DNA Probes; D004317:Doxorubicin / Q000494:pharmacology*; D018432:Drug Resistance, Multiple; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D016259:Genes, myc; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute; D016133:Polymerase Chain Reaction; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000096:biosynthesis; D059005:Topoisomerase II Inhibitors; D014158:Transcription, Genetic / Q000187:drug effects*; D014407:Tumor Cells, Cultured
D015342:DNA Probes; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D059005:Topoisomerase II Inhibitors; D000677:Amsacrine; D004317:Doxorubicin