title: Altered drug interaction and regulation of topoisomerase IIbeta: potential mechanisms governing sensitivity of HL-60 cells to amsacrine and etoposide.
abstract: Topoisomerase II (topo II), an enzyme essential for cell viability, is present in mammalian cells as the alpha- and beta-isoforms. In human leukemia HL-60/S or HL-60/doxorubicin (DOX)0.05 cells, the levels of topo IIalpha- or beta-protein were similar in either asynchronous exponential or synchronized cultures. Although topo IIalpha was hypophosphorylated in HL-60/DOX0.05 compared with HL-60/S cells, both overall and site-specific hyperphosphorylation of topo IIbeta was apparent in HL-60/DOX0.05 compared with HL-60/S cells. The phosphorylation of topo IIalpha and not beta was enhanced in the S and G(2) + M phases of HL-60/S cells. In contrast, an increase in the phosphorylation of topo IIbeta compared with alpha was apparent in the G(1) and S phases of HL-60/DOX0.05 cells. The cytotoxicity and depletion of topo IIalpha or beta in cells treated with drug for 1 h revealed that mole-for-mole, amsacrine was 2-fold more effective than etoposide in killing HL-60/S or HL-60/DOX0.05 cells and in depleting the beta versus alpha topo II protein. Present results demonstrate that: 1) hyperphosphorylation of topo IIbeta in HL-60/DOX0.05 cells may be a compensatory consequence of the hypophosphorylation of topo IIalpha to maintain normal topo II function during proliferation, and 2) enhanced sensitivity of HL-60/S or HL-60/DOX0.05 cells to amsacrine may be due to the preferential interaction and depletion of topo IIbeta.
authors.affiliation: Experimental Therapeutics Program, Taussig Cancer Center, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
authors.forename: D R
authors.initials: DR
authors.lastname: Grabowski
authors.forename: K A
authors.initials: KA
authors.lastname: Holmes
authors.forename: M
authors.initials: M
authors.lastname: Aoyama
authors.forename: Y
authors.initials: Y
authors.lastname: Ye
authors.forename: L A
authors.initials: LA
authors.lastname: Rybicki
authors.forename: R M
authors.initials: RM
authors.lastname: Bukowski
authors.forename: M K
authors.initials: MK
authors.lastname: Ganapathi
authors.forename: I D
authors.initials: ID
authors.lastname: Hickson
authors.forename: R
authors.initials: R
authors.lastname: Ganapathi
mesh_terms: D000677:Amsacrine / Q000494:pharmacology*; D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D004247:DNA / Q000187:drug effects / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000187:drug effects / Q000378:metabolism*; D004268:DNA-Binding Proteins; D004317:Doxorubicin / Q000494:pharmacology; D004347:Drug Interactions; D019008:Drug Resistance, Neoplasm; D005047:Etoposide / Q000494:pharmacology*; D018922:HL-60 Cells; D006801:Humans; D007527:Isoenzymes / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation
chemical_list: D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D000677:Amsacrine; D005047:Etoposide; D004317:Doxorubicin; D004247:DNA; D004250:DNA Topoisomerases, Type II