title: DNA topoisomerase II isozymes involved in anticancer drug action and resistance.
abstract: DNA topoisomerase II is a major protein of the nuclear matrix. The enzyme appears to have a central role in both DNA organization and replication. The importance of nuclear matrix topoisomerase II alpha as a target for certain anticancer agents was evaluated in CEM human leukemia cells. Studies were done to determine the extent to which the alpha (170 kDa) and beta (180 kDa) isozymes of topoisomerase II form covalent enzyme-DNA complexes in whole cells and in the nuclear matrix and nonmatrix fractions of CEM cells that are either sensitive or resistant to topoisomerase II-active anticancer agents. Topoisomerase II alpha was detected in both the high salt-soluble (nonmatrix) and matrix fractions of nuclei from parental CEM cells. Most of the matrix topoisomerase II alpha was tightly bound to DNA in cells incubated with VM-26. In contrast, topoisomerase II beta was detected only in the high salt-soluble (nonmatrix) fraction of the nucleus. The subnuclear distribution of the alpha and beta topoisomerase II isozymes in CEM/VM-1 cells resistant to topoisomerase-active drugs was similar to that in drug-sensitive CEM cells. However, the amount and activity of topoisomerase II alpha in nuclear matrices of CEM/VM-1 cells were decreased 3- to 6-fold relative to that of CEM cells. The differences observed in the subnuclear distribution and DNA binding pattern of the topoisomerase II isozymes support the hypotheses that each isozyme has a distinct cellular function. Furthermore, these results provide evidence that topoisomerase II alpha is the nuclear matrix target for VM-26, and that depletion of the nuclear matrix isozyme contributes to cellular resistance to this anticancer agent.
authors.affiliation: Department of Experimental Oncology, Hollings Cancer Center, Medical University of South Carolina, Charleston 29425, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Fernandes
authors.forename: J
authors.initials: J
authors.lastname: Qiu
authors.forename: C V
authors.initials: CV
authors.lastname: Catapano
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002467:Cell Nucleus / Q000201:enzymology; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007938:Leukemia / Q000201:enzymology*; D015530:Nuclear Matrix / Q000201:enzymology*; D012965:Sodium Chloride / Q000494:pharmacology; D013713:Teniposide / Q000494:pharmacology*; D059005:Topoisomerase II Inhibitors; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D004273:DNA, Neoplasm; D007527:Isoenzymes; D059005:Topoisomerase II Inhibitors; D012965:Sodium Chloride; D000255:Adenosine Triphosphate; D013713:Teniposide; D004250:DNA Topoisomerases, Type II