[Amplification of portions of the genome in the somatic cells of mammals resistant to colchicine. V. The induction of gene amplification in the cells of the Djungarian hamster and the mouse].

The influence of some agents on gene amplification in Djungarian hamster and mouse cells was studied. The tumor promotor 12-O-tetradecanoylphorbol-13-acetate (TPA), the epidermal growth factor (EGF), insulin, and 5-bromodeoxyuridine (BUdR) increase the incidence of colchicine-resistance, connected with amplification of the genes, which probably encode the polypeptide p22. The highest frequency of gene amplification was observed after the pretreatment of cells with TPA, which enhanced the number of colchicine-resistant colonies 44-200-fold. Mitostatic agents colchicine and colcemid increased the number of methotrexate-resistant cells, 2.0-6.5 times. These cells usually arise as the result of amplification of dihydrofolate reductase genes. Dexamethasone and ethidium bromide did not change the portion of cells resistant to colchicine. Ethylmethane sulfonate (EMS) decreased the number of colchicine-resistant cells. The cells of two Djungarian hamster colchicine-resistant clones obtained after treatment with TPA did not differ from those of spontaneously derived colchicine-resistant clones. Both have similar survival patterns in the medium with different colchicine concentrations, unstable inheritance of the drug resistance, the additional chromosome 4 and small chromatin bodies-the structures containing the amplified genes. Possible mechanisms of the induction of gene amplification by the agents used are discussed.