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

We have studied the effect of some specific enzyme inhibitors on DNA repair and replication after UV damage in Chinese hamster ovary cells. The DNA repair was studied at the level of the average, overall genome and also in the active dihydrofolate reductase gene. Replication was measured in the overall genome. We tested inhibitors of DNA polymerase alpha and delta (aphidicolin), of poly(ADPr) polymerase (3-aminobenzamide), of ribonucleotide reductase (hydroxyurea), of topoisomerase I (camptothecin), and of topoisomerase II (merbarone, VP-16). In addition, we tested the effect of the potential topoisomerase I activator, beta-lapachone. All of these compounds inhibited genome replication and all topoisomerase inhibitors affected the overall genome repair; beta-lapachone stimulated it. None of these compounds had any effect on the gene-specific repair.
Mutat Res 1991 Sep
PMID:Effect of specific enzyme inhibitors on replication, total genome DNA repair and on gene-specific DNA repair after UV irradiation in CHO cells. 165 49

A new gene, dhfrIX, coding for a trimethoprim-resistant dihydrofolate reductase (DHFR), was found in porcine isolates of Escherichia coli. The new enzyme, DHFR IX, containing 178 amino acids, showed an amino acid similarity of about 26% with DHFR I and the chromosomal DHFR of E. coli K-12. The dhfrIX gene was observed to occur on two distinctly different transferable plasmids, although a fragment of about 2.9 kb, including dhfrIX, had an identical restriction enzyme digestion map in each case. The new plasmid-borne dhfrIX gene mediates resistance to a drug level of only about 250 micrograms/ml, as compared with more than 1,000 micrograms/ml for the more frequently encountered dhfrI gene. The new plasmid-borne trimethoprim resistance gene could have been selected and spread as a consequence of the extensive use of trimethoprim in veterinary practice in Sweden. It will be important to try to follow its possible occurrence in human pathogens as well.
Antimicrob Agents Chemother 1991 Sep
PMID:Appearance of a new trimethoprim resistance gene, dhfrIX, in Escherichia coli from swine. 165 8

A major problem in cytostatic treatment of malignant tumors is the development of chemoresistant cell clones. An increased understanding of chemoresistance related mechanisms, improved methods for the detection and localization of resistant cell populations including predictive conclusions on the effectiveness of cytostatic drugs would contribute to the advancement of anti-tumor strategies. This paper reviews current concepts suggested for the development of cellular resistance to natural product drugs (anthracyclines, Vinca alkaloids, epipodophyllotoxines, antibiotics; so-called multidrug resistance substances), alkylating agents (nitrosureas, busulfan and mitomycin C), heavy metal compounds (cisplatin) and antifolates (5-fluorouracil, methotrexate) and describes the role of drug transporting and binding proteins (P-170-glycoprotein), detoxifying enzymes (glutathion-S-transferase, dihydrofolate reductase), DNA repair enzymes (topoisomerase I and II, polymerase alpha and beta), and genomic alterations (amplification, double minutes and homogeneous staining regions) due to resistance. It is focussed on the employment of morphological methods (light microscopy, immunocytochemistry, electron microscopy, fluorescence analysis, in situ hybridization, computer aided morphometric analysis) which will help to detect resistant cell clones in tumor biopsies. First correlations between histological data and clinical course will be reported. In the future, the morphological determination of chemoresistance may play an important role in applied functional tumor pathology.
Pathol Res Pract 1991 Sep
PMID:What's new in cytostatic drug resistance and pathology. 175 14

Effect of vasopressin, oxytocin and LHRH (10 and 20 pg/ml medium) on the proliferation and metabolism of cultured rat bone marrow stromal cells was investigated by methyl-3H-thymidine incorporation, cytochemistry and estimation of enzyme activities. Vasopressin did not change of the activity of tetrahydrofolate dehydrogenase (4HFDH), lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G6PD) and the level of reduced glutathione (GSH). However, the higher concentration of vasopressin significantly lowered the activity of acetylcholinesterase (AchE). As compared with the control cultures, stromal cells grown in the presence of oxytocin showed higher (at lower hormone concentration) and lower (at higher concentration) LDH activity as well as lower G6PD activity (only at higher concentration), while the activity of AchE and the level of GSH was not changed. LHRH significantly increased G6PD and AchE activity and decreased LDH activity in the cultured cells. As revealed by cytochemistry, LHRH specifically enhanced 4HFDH activity in reticular cells.
Endocr Regul 1991 Sep
PMID:Effect of vasopressin, oxytocin and LHRH on the proliferation and metabolism of rat bone marrow stromal cells in culture. 176 8

The complete nucleotide and encoded amino acid sequences were determined for the dihydrofolate reductase (DHFR) from the bacteria Enterobacter aerogenes and Citrobacter freundii. These were compared with the closely related Escherichia coli DHFR sequence. The ancestral DHFR sequence common to these three species was reconstructed. Since that ancestor there have been seven, nine, and one amino acid replacements in E. coli, E. aerogenes, and C. freundii, respectively. In E. coli, five of its seven replacements were located in the beta-sheet portion of the protein, and all seven were located in a single restricted region of the protein. In E. aerogenes, all nine of its replacements were located within surface residues, with five clustered in a region topologically distinct from the E. coli cluster. The replaced side chains are sometimes in direct contact but more often are separated by an intervening side chain. It is argued that the temporal clustering of replacements is typical for the evolution of most proteins and that the associated topological clustering gives a picture of how evolutionary change is accommodated by protein structure.
Mol Biol Evol 1991 Sep
PMID:Temporal and topological clustering of diverged residues among enterobacterial dihydrofolate reductases. 176 62

Back propagation neural networks is a new technology useful for modeling nonlinear functions of several variables. This paper explores their applications in the field of quantitative structure-activity relationships. In particular, their ability to fit biological activity surfaces, predict activity, and determine the "functional forms" of its dependence on physical properties is compared to well-established methods in the field. A dataset of 256 5-phenyl-3,4-diamino-6,6-dimethyldihydrotriazines that inhibit dihydrofolate reductase enzyme is used as a basis for comparison. It is found that neural networks lead to enhanced surface fits and predictions relative to standard regression methods. Moreover, they circumvent the need for ad hoc indicator variables, which account for a significant part of the variance in linear regression models. Additionally, they lead to the elucidation of nonlinear and "cross-products" effects that correspond to trade-offs between physical properties in their effect on biological activity. This is the first demonstration of the latter two findings. On the other hand, due to the complexity of the resulting models, an understanding of the local, but not the global, structure-activity relationships is possible. The latter must await further developments. Furthermore, the longer computational time required to train the networks is somewhat inconveniencing, although not restrictive.
J Med Chem 1991 Sep
PMID:Applications of neural networks in quantitative structure-activity relationships of dihydrofolate reductase inhibitors. 189 2

A plasmid containing the K-fgf proto-oncogene linked to the dihydrofolate reductase gene has been constructed, and used in transfection experiments to investigate the effects of K-fgf expression on the tumorigenic and metastatic properties of NIH-3T3 fibroblasts. Analysis of cells transfected with K-fgf revealed that expression of the K-fgf proto-oncogene can, in a single step, induce both tumorigenic and metastatic characteristics, as determined in soft agar cloning experiments, and in tumorigenicity and experimental lung metastasis assays with BALB/c nu/nu mice. Selection for resistance to increasing concentrations of methotrexate lead to the isolation of a series of cell lines containing amplifications of both the dihydrofolate reductase gene and the linked K-fgf gene, which synthesized elevated levels of growth factor message and protein. The most highly resistant and gene amplified cell lines exhibited lower than expected levels of K-fgf mRNA, and also appeared to have down-regulated cell surface growth factor receptors. Further support for the concept that altered K-fgf expression can induce fully malignant and metastatic cells was obtained in experimental metastasis assays, where K-fgf transfected and gene amplified cell lines were highly aggressive.
Biochim Biophys Acta 1991 Sep 23
PMID:Transformation and amplification of the K-fgf proto-oncogene in NIH-3T3 cells, and induction of metastatic potential. 191 83

The mechanisms were examined that underlie the extreme resistance to methotrexate (MTX) by near diploid leukemic T-cells (LALW-2) exposed to the drug only during the course of therapy administered to the patient of origin. Despite the LALW-2 cells being highly resistant to MTX (inhibitory dose for 50% of cells, more than 10(-3) mol/l), southern blot analysis did not show any amplification of the dihydrofolate reductase gene, nor was there any evidence, by comparison with drug-sensitive CCRF-CEM cells, that the gene was overexpressed. Kinetic analysis of dihydrofolate reductase activity in the presence of MTX provided no basis for attributing resistance in LALW-2 cells to a change in enzyme structure. By contrast, studies of MTX accumulation revealed that the LALW-2 cells accumulated significantly less drug than either CCRF-CEM cells or a MTX-resistant CCRF-CEM subline with a characterized transport defect. These data suggest that extreme MTX resistance in LALW-2 cells is mediated by reduced drug accumulation in the absence of any effect on the target enzyme.
Cancer 1991 Sep 01
PMID:Reduced drug accumulation as the mechanism of extreme clinical resistance to methotrexate in the human T-cell leukemia xenograft, LALW-2. 191 92

We have employed 15N NMR to characterize the conformations of Escherichia coli dihydrofolate reductase (ECDHFR) in complex with [5-15N]folate or [5-15N]methotrexate (MTX). Two 15N resonances were observed for DHFR/MTX binary complex. The relative population of these two conformations is pH dependent. Addition of NADP+ or NADPH results in the disappearance of the low field resonance. In contrast, only one conformation was observed for both the DHFR/folate and DHFR/folate/NADP+ complexes. However, the 15N chemical shift of [5-15N]folate in the binary DHFR/folate complex is 7.28 ppm upfield from that of the ternary complex, suggesting the possible loss of a hydrogen bonding to N5 of folate in the ternary complex.
FEBS Lett 1991 Sep 09
PMID:15N NMR studies of the conformation of E. coli dihydrofolate reductase in complex with folate or methotrexate. 191 51

We examined removal of cyclobutane pyrimidine dimers (CPDs) from the dihydrofolate reductase (DHFR) gene in ultraviolet-irradiated Chinese hamster ovary (CHO) UV61 and UV5 cells. The sensitivity of UV61 cells to UV-irradiation is intermediate between that of the parental CHO cells and that of mutants such as UV5 that are highly defective in excision repair. UV61 cells have been characterized as having normal repair of pyrimidine(6-4)pyrimidone photoproducts (6-4 PPs) but no detectable removal of CPDs from the genome overall. We find that the extent of removal of CPDs from the DHFR gene in UV61 cells is intermediate between that of the parental CHO cells and that of the UV5 mutant, and the observed repair appears to be confined to the transcribed strand. We detected no removal of CPDs from the DHFR gene in UV5 cells. Our findings in UV61 cells demonstrate a correlation between survival after UV-irradiation and CPD repair in an expressed gene in a cell line with moderate UV-sensitivity and yet no apparent removal of CPDs from the genome as a whole. We have thus demonstrated that overall repair measurements can be misleading. Our results have implications for the determination of the relative biological importance of the CPD and the 6-4 PP, and they further support the hypothesis that removal of CPDs from transcriptionally active DNA is crucial for UV-resistance.
Mutat Res 1991 Sep
PMID:The genetic defect in the Chinese hamster ovary cell mutant UV61 permits moderate selective repair of cyclobutane pyrimidine dimers in an expressed gene. 192 50


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