Mitogenic hormones and tumor promoters greatly increase the incidence of colony-forming cells bearing amplified dihydrofolate reductase genes.
- 1 September 1983
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 80 (17), 5330-5334
- https://doi.org/10.1073/pnas.80.17.5330
Abstract
The presence of a phorbol ester tumor promoter, phorbol 12-myristate 13-acetate (PMA), during a single-step selection for methotrexate (MTX)-resistant mouse 3T6 cells results in an up to 100-fold increase in the incidence of MTX-resistant, colony-forming cells. MTX resistance of most of these cells is due to amplification of the gene for dihydrofolate reductase (DHFR), the target enzyme for MTX. Other active, noncytotoxic phorbol ester tumor promoters, such as phorbol 12, 13-didecanoate and 20-phorbol 12,13-butyrate, at their optimal concentrations (.apprxeq. 0.1 .mu.M), are approximately equal to PMA in increasing the incidence of MTX-resistant 3T6 colonies. Mezerein, a potent 2nd-stage tumor promoter, but a weak complete promoter, increases the incidence of MTX resistance up to 350-fold, the strongest effect for any of the agents so far tested. PMA analogs that are inactive as tumor promoters, such as phorbol or phorbol 12,13,20-triacetate, have no effect on the incidence of MTX-resistant 3T6 colonies. Anthralin, a nonphorbol tumor promoter, is .apprxeq. 40% as active as PMA in the MTX selection assay. The hormones insulin, arginine vasopressin and epidermal growth factor, all of which are mitogenic for 3T6 cells, also exert a strong PMA-like effect on the incidence of MTX-resistant 3T6 colonies under conditions of MTX selection. The effect of insulin at its optimal concentration (.apprxeq. 1 .mu.g/ml) is .apprxeq. 70% that of PMA. Although the effect of PMA on the incidence of MTX-resistant 3T6 colonies does not significantly depend on the initial density of seeded cells or volume of the medium added, the analogous effect of insulin is strongly influenced by these parameters. Mevalonic acid, arachidonic acid, thymidine, caffeine and nicotine, all of which are known to influence patterns of DNA synthesis in mammalian cells, were tested at their highest noncytotoxic concentrations and failed to produce any significant effect on the incidence of MTX-resistant 3T6 colonies. Possible mechanisms of hormone and tumor promoter-facilitated gene amplification in mammalian cells, relationship of mitogenic hormones to tumor promoters, and also implications of the findings for the problem of drug resistance in cancer chemotherapy are discussed.This publication has 40 references indexed in Scilit:
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