title: Mutation P732L in human DNA topoisomerase IIbeta abolishes DNA cleavage in the presence of calcium and confers drug resistance.
abstract: The anti cancer drug methyl N-(4'-(9-acridinylamino)-3-methoxy-phenyl) methane sulfonamide (mAMSA) targets human DNA topoisomerase IIbeta. We report here the first selection with mAMSA of resistant human topoisomerase IIbeta. Random mutagenesis of human DNA topoisomerase IIbeta cDNA, followed by selection in yeast for resistance to mAMSA, identified betaP732L. This mutant was 10-fold less sensitive to mAMSA and cross-resistant to other chemotherapeutic agents such as etoposide, ellipticine, methyl N-(4'-(9-acridinylamino)-2-methoxy-phenyl) carbamate hydrochloride (mAMCA), methyl N-(4'-(9-acridinylamino)-phenyl) carbamate hydrochloride (AMCA), and doxorubicin. betaP732L is functional but has reduced strand passage activities and altered DNA binding compared with the wild-type protein. It has drastically altered cleavage properties compared with the wild-type enzyme. It cleaved a 40-base pair (bp) DNA substrate in the presence of magnesium but at positions different from that of the wild-type protein. More striking is that betaP732L was unable to cleave the 40-bp DNA substrate, a 500-bp linear substrate, or a 4.3-kilobase supercoiled substrate in the presence of calcium ions. This is the first report of a topoisomerase II mutation abolishing the ability of calcium to support DNA cleavage. This provides evidence for metal ion requirement for the phosphoryltransfer reaction of topoisomerase II and a possible mechanism for drug resistance.
authors.affiliation: Institute for Cell and Molecular Bioscience, The Medical School, University of Newcastle, Newcastle upon Tyne, NE2 4HH, UK.
authors.forename: Chrysoula
authors.initials: C
authors.lastname: Leontiou
authors.forename: Jeremy H
authors.initials: JH
authors.lastname: Lakey
authors.forename: Robert
authors.initials: R
authors.lastname: Lightowlers
authors.forename: Rozalind M
authors.initials: RM
authors.lastname: Turnbull
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Austin
mesh_terms: D000595:Amino Acid Sequence; D000677:Amsacrine / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004250:DNA Topoisomerases, Type II / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D006801:Humans; D008274:Magnesium / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids; D017386:Sequence Homology, Amino Acid; D020349:Surface Plasmon Resonance
chemical_list: D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; D000677:Amsacrine; D004247:DNA; D004250:DNA Topoisomerases, Type II; D008274:Magnesium; D002118:Calcium