Amplification of Dihydrofolate Reductase Genes in Methotrexate-resistant Cultured Mouse Cells

1. R. T. Schimke,
2. F. W. Alt,
3. R. E. Kellems,
4. R. J. Kaufman, and
5. J. R. Bertino

1. Department of Biological Sciences, Stanford University, Stanford, California 94305

Excerpt

Our laboratory has been investigating the mechanism whereby cultured cells acquire resistance to the four amino analogs of folic acid, a phenomenon often associated both in cultured cells and in human neoplasms (Bertino et al. 1963) with elevated levels of dihydrofolate reductase activity. Resistant cell variants containing up to a 300-fold increase in dihydrofolate reductase activity can be obtained by growth of cells in progressively increasing concentrations of methotrexate (Hakala et al. 1961; Fisher 1961; Friedkin et al. 1962). Previous reports from this laboratory, using a resistant cell line (AT-3000) and several clones (R-1 to R-4) obtained from the AT-3000 line, all of which have been derived from a mouse sarcoma S-180 cell line, have demonstrated that the increase in dihydrofolate reductase activity results solely from an increased rate of enzyme synthesis (Alt et al. 1976), and that there is a proportionality between the rate of enzyme synthesis and the...

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  ↵* Permanent address: Departments of Pharmacology and Medicine, Yale University, New Haven, Connecticut 06510.