Drug-sensitivity and DNA-binding of a subform of topoisomerase II alpha in resistant human HL-60 cells.
Topoisomerase II alpha (170 kDa) expressed in human HL-60 cells is heterogeneous in charge. By two-dimensional electrophoresis and chromatofocussing two major subforms with pI of 6.5 and 6.7 can be resolved. By preparative anion-exchange chromatography we separated the known topoisomerase II isoenzymes (170/180 kDa) and in addition a late-eluting 170 kDa form, which has not been described before. The catalytic optimum of this late-eluting form is shifted to pH 9.4. It is more than 100-fold resistant to orthovanadate, amsacrine or etoposide, and has an increased salt stability. SDS-treatment induces covalent attachment of this enzyme fraction to calf thymus DNA in the absence of drug. The latter observations indicate an increase in DNA-binding. In the tightly DNA-bound state the late-eluting enzyme is not targeted by cleavable complex forming drugs. Accordingly, cells may become drug-resistant by expressing this form predominantly.
Boege
F
F
Medizinische Poliklinik, University of Würzburg, Germany.
Biersack
H
H
Meyer
P
P
D000677:Amsacrine / Q000494:pharmacology; D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents / Q000494:pharmacology*; D004250:DNA Topoisomerases, Type II / Q000187:drug effects* / Q000378:metabolism; D004273:DNA, Neoplasm / Q000187:drug effects; D004268:DNA-Binding Proteins; D004351:Drug Resistance / Q000235:genetics*; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D007527:Isoenzymes / Q000187:drug effects* / Q000378:metabolism; D007938:Leukemia / Q000188:drug therapy* / Q000201:enzymology; D014407:Tumor Cells, Cultured; D014638:Vanadates / Q000494:pharmacology
D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D000677:Amsacrine; D014638:Vanadates; D005047:Etoposide; D004250:DNA Topoisomerases, Type II