Open AccessPhenotypic evolution of cells resistant to bromodeoxyuridine.
Author(s) -
Morgan Harris,
Kathleen Collier
Publication year - 1980
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.77.7.4206
Subject(s) - thymidine , aminopterin , bromodeoxyuridine , thymidine kinase , hypoxanthine , biology , chinese hamster , phenotype , biochemistry , microbiology and biotechnology , genetics , cell culture , dna , cell growth , immunology , enzyme , gene , virus , methotrexate , herpes simplex virus
Variants resistant to bromodeoxyuridine (BrdUrd) and deficient in thymidine kinase (ATP:thymidine 5'-phosphotransferase; EC 2.7.1.21) have been obtained from V79 Chinese hamster cells by a combination of spontaneous and drug-induced change. Initial mutations take place in wild-type populations as a facilitating step to give partially resistant clones that can be isolated by one-step selection in BrdUrd. When these tolerant populations are maintained for extended periods in BrdUrd-containing medium, a gradual phenotypic transition occurs in which BrdUrd appears to act as an inductive as well as selective agent. Thymidine kinase activity declines logarithmically over an interval of 8-10 weeks as the growth rate rises and the cells become completely resistant to BrdUrd. Relative plating efficiency in hypoxanthine/aminopterin/thymidine medium also decreases, but the decrease is not coordinate with shifts in thymidine kinase activity. The potential for colony formation in hypoxanthine/aminopterin/thymidine continues to decrease exponentially for at least 18 weeks after thymidine kinase deficiency and complete resistance to BrdUrd have been established. These phenotypic modifications are continuous or multistep in character; by clonal analysis they are found to occur in most, if not all, cells maintained in the presence of BrdUrd. Populations in transition thus come to be complex mosaics of different phenotypes that are comparatively stable if isolated in drug-free medium. The progressive evolution of cells resistant to BrdUrd will require new models for an underlying explanation.