title: The cytoplasmic trafficking of DNA topoisomerase IIalpha correlates with etoposide resistance in human myeloma cells.
abstract: In this study we have investigated the role of topoisomerase (topo) IIalpha trafficking in cellular drug resistance. To accomplish this, it was necessary to separate the influence of cell cycle, drug uptake, topo protein levels, and enzyme trafficking on drug sensitivity. Thus, we developed a cell model (called accelerated plateau) using human myeloma H929 cells that reproducibly translocates topo IIalpha to the cytoplasm. Compared to log-phase cells, the cytoplasmic redistribution of topo IIalpha in plateau-phase cells correlated with a 10-fold resistance to VP-16 and a 40-60% reduction in the number of drug-induced double-strand DNA breaks. In addition, 7-fold more VP-16 was necessary to achieve 50% topo IIalpha band depletion, suggesting that there are fewer drug-induced topo-DNA complexes formed in quiescent cells than in log-phase cells. The total cellular amount of topo IIalpha and topo IIbeta protein in log- and plateau-phase cells was similar as determined by Western blot analysis. There was a 25% reduction in S-phase cell number in plateau cells (determined by bromodeoxyuridine (BrdU) incorporation), while there was no significant difference in the equilibrium concentrations of [(3)H]-VP-16 when log cells were compared with plateau cells. Furthermore, the nuclear/cytoplasmic ratio of topo IIalpha is increased 58-fold in accelerated-plateau H929 cells treated with leptomycin B (LMB) when compared to untreated cells. It appears that the nuclear-cytoplasmic shuttling of topo IIalpha, which decreases the amount of nuclear target enzyme, is a major mechanism of drug resistance to topo II inhibitors in plateau-phase myeloma cells.
authors.affiliation: Experimental Therapeutics Program, Departments of Interdisciplinary Oncology and Biochemistry and Molecular Biology, H. Lee Moffitt Cancer Center and Research Institute, University of South Florida, Tampa, FL 33612, USA.
authors.forename: Roxane
authors.initials: R
authors.lastname: Engel
authors.forename: Nikola I
authors.initials: NI
authors.lastname: Valkov
authors.forename: Jana L
authors.initials: JL
authors.lastname: Gump
authors.forename: Lori
authors.initials: L
authors.lastname: Hazlehurst
authors.forename: William S
authors.initials: WS
authors.lastname: Dalton
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Sullivan
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000493:pharmacokinetics / Q000627:therapeutic use; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000627:therapeutic use; D000972:Antineoplastic Agents, Phytogenic / Q000493:pharmacokinetics / Q000627:therapeutic use*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000201:enzymology; D020552:Comet Assay; D003593:Cytoplasm / Q000201:enzymology*; D004250:DNA Topoisomerases, Type II / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D015180:Electrophoresis, Gel, Two-Dimensional; D005047:Etoposide / Q000493:pharmacokinetics / Q000627:therapeutic use*; D005231:Fatty Acids, Unsaturated / Q000493:pharmacokinetics / Q000627:therapeutic use; D005434:Flow Cytometry; D018922:HL-60 Cells; D006801:Humans; D008856:Microscopy, Fluorescence; D008942:Mitoxantrone / Q000493:pharmacokinetics / Q000627:therapeutic use; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000201:enzymology; D010954:Plasmacytoma / Q000188:drug therapy / Q000201:enzymology; D021381:Protein Transport; D013347:Subcellular Fractions
chemical_list: D000903:Antibiotics, Antineoplastic; D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D005231:Fatty Acids, Unsaturated; D005047:Etoposide; D008942:Mitoxantrone; D004250:DNA Topoisomerases, Type II; C038753:leptomycin B