title: Chromosome breakage at a major fragile site associated with P-glycoprotein gene amplification in multidrug-resistant CHO cells.
abstract: Recent studies of several drug-resistant Chinese hamster cell lines suggested that a breakage-fusion-bridge mechanism is frequently involved in the amplification of drug resistance genes. These observations underscore the importance of chromosome breakage in the initiation of DNA amplification in mammalian cells. However, the mechanism of this breakage is unknown. Here, we propose that the site of chromosome breakage consistent with the initial event of P-glycoprotein (P-gp) gene amplification via the breakage-fusion-bridge cycle in three independently established multidrug-resistant CHO cells was located at 1q31. This site is a major chromosome fragile site that can be induced by methotrexate and aphidicolin treatments. Pretreatments of CHO cells with methotrexate or aphidicolin enhanced the frequencies of resistance to vinca alkaloid and amplification of the P-gp gene. These observations suggest that chromosome fragile sites play a pivotal role in DNA amplification in mammalian cells. Our data are also consistent with the hypothesis that gene amplification can be initiated by stress-induced chromosome breakage that is independent of modes of action of cytotoxic agents. Drug-resistant variants may arise by their growth advantage due to overproduction of cellular target molecules via gene amplification.
authors.affiliation: Department of Molecular Pathology, University of Texas M. D. Anderson Cancer Center, Houston 77030.
authors.forename: M T
authors.initials: MT
authors.lastname: Kuo
authors.forename: R C
authors.initials: RC
authors.lastname: Vyas
authors.forename: L X
authors.initials: LX
authors.lastname: Jiang
authors.forename: W N
authors.initials: WN
authors.lastname: Hittelman
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000818:Animals; D016590:Aphidicolin / Q000494:pharmacology; D016466:CHO Cells; D002352:Carrier Proteins / Q000235:genetics*; D043283:Chromosome Fragile Sites; D002873:Chromosome Fragility; D006224:Cricetinae; D004249:DNA Damage; D004351:Drug Resistance; D005784:Gene Amplification; D017404:In Situ Hybridization, Fluorescence; D008562:Membrane Glycoproteins / Q000235:genetics*; D008727:Methotrexate / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D016590:Aphidicolin; D008727:Methotrexate