Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.5.1.3 (dihydrofolate reductase)
 5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous work has shown that 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. We show here that other active, noncytotoxic phorbol ester tumor promoters, such as phorbol 12, 13-didecanoate and 20-phorbol 12,13-butyrate, at their optimal concentrations (approximately equal to 0.1 microM) are approximately equal to PMA in increasing the incidence of MTX-resistant 3T6 colonies. Mezerein, a potent second-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 approximately equal to 40% as active as PMA in the MTX selection assay. Remarkably, 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 (approximately equal to 1 microgram/ml) is approximately equal to 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. We discuss possible mechanisms of hormone- and tumor promoter-facilitated gene amplification in mammalian cells, relationship of mitogenic hormones to tumor promoters, and also implications of our findings for the problem of drug resistance in cancer chemotherapy.
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PMID:Mitogenic hormones and tumor promoters greatly increase the incidence of colony-forming cells bearing amplified dihydrofolate reductase genes. 635 Oct 57

We discuss our recent findings in three related areas of the gene amplification field. 1) We have found that tumor-promoting phorbol esters, nonphorbol tumor promoters, and most significantly, mitogenic hormones, such as insulin, vasopressin, and epidermal growth factor (EGF), greatly increase the incidence of methotrexate (MTX) resistance in 3T6 cells under condition of MTX selection. Most of these MTX-resistant cells bear amplified dihydrofolate reductase (DHFR) genes. 2) We have discovered that when mouse cells bearing unstably amplified DHFR genes are grown in the presence of nonlethal concentrations of hydroxyurea (HU), the rate of loss of the DHFR genes from these cells is greatly increased. 3) We have developed a new method for detection and mapping of homologous, repeated and amplified DNA sequences, and have used this method to detect and clone amplified DNA fragments in mammalian cells resistant simultaneously to a number of different drugs.
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PMID:Acquisition and loss of amplified genes: dramatic effects of hormones, tumor promoters and cytotoxic drugs. 639 91

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.
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PMID:[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]. 668 74