title: Development of multidrug resistance due to multiple factors including P-glycoprotein overexpression under K-selection after MYC and HRAS oncogene activation.
abstract: Multistep tumorigenesis is a form of microevolution consisting of mutation and selection. To clarify the role of selection modalities in tumor development, we examined two alternative evolutionary conditions, r-selection in sparse culture, which allows cells to proliferate rapidly, and K-selection in confluent culture, in which overcrowding constrains cell proliferation. Using MYC- and EJ-RAS-transformed rat embryo fibroblasts, we found that K-selected cells acquired and stably maintained multidrug resistance (MDR) to DOX, VCR, MTX and Ara-C. Then, we examined the involvement of a number of factors potentially causal of the development of MDR, that is, ploidy, Tp53 mutation, doubling time and the expression levels of genes related to drug resistance. Although ploidy status and Tp53 mutations did not correlate with MDR, we found that Abcb1/Mdr1, encoding P-glycoprotein (Pgp), was significantly upregulated after K-selection. Cyclosporin A, a competitive inhibitor of Pgp, increased the intracellular accumulation of DOX and reduced the resistance to it. Indeed, the population of Pgp-transfected cells significantly expanded under K-, but not under r-selection. In addition to Pgp upregulation, altered expression of other genes such as Cda/cytidine deaminase and Slc29a1/equilibrative nucleoside transporter 1 and prolonged doubling times were associated with MDR. This system reproduces events associated with MDR in vivo and would be useful for analysis of MDR development.
authors.affiliation: Department of Hematology and Oncology, Graduate School of Medicine, The University of Tokyo, Tokyo 113-8655, Japan.
authors.forename: Yukari
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sato
authors.forename: Toru
authors.initials: T
authors.lastname: Motokura
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D049109:Cell Proliferation; D018432:Drug Resistance, Multiple; D005347:Fibroblasts; D005786:Gene Expression Regulation; D016259:Genes, myc / Q000235:genetics*; D009369:Neoplasms / Q000188:drug therapy; D011003:Ploidies; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis; D016283:Proto-Oncogene Proteins p21(ras) / Q000096:biosynthesis / Q000235:genetics*; D051381:Rats; D012641:Selection, Genetic; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D016271:Proto-Oncogene Proteins c-myc; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)