Disease relevance of Dhfr

• A study of chromosomal changes associated with amplified dihydrofolate reductase genes in rat hepatoma cells and their dedifferentiated variants [1].
• The gene was expressed under control of the simian virus 40 (SV40) early promoter in Chinese hamster ovary (CHO) cells deficient in dihydrofolate reductase (DHFR) after co-transformation with a plasmid containing the mouse DHFR gene [2].
• In contrast, the R plasmid R67-specified dihydrofolate reductase (5,6,7,8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) isolated from trimethoprim-resistant Escherichia coli utilized alpha-NADPH and alpha-NADH in addition to the "normal" beta-epimers [3].
• Dihydrofolate reductase in primary brain tumors, cell cultures of central nervous system origin, and normal brain during fetal and neonatal growth [4].
• Rat sarcoma cell extracts contained low levels of dihydrofolate reductase activity, the target enzyme of methotrexate, and inhibition of this enzyme by these three antifolates was similar [5].

High impact information on Dhfr

• A plasmid transfection vector carrying the gene locus that encodes a drug-resistant form of the bifunctional enzyme dihydrofolate reductase-thymidylate synthase from the rodent malaria parasite Plasmodium berghei was constructed [6].
• Methotrexate (MTX) inhibits the enzyme dihydrofolate reductase, which in turn limits the body's ability to perform transmethylation reactions [7].
• A fragment of P4502B1 containing the N-terminal signal and the phosphorylation site could drive the transport of dihydrofolate reductase (DHFR) into mitochondria [8].
• pOMD29 is a hybrid protein containing the NH2-terminal topogenic sequence of a bitopic, integral protein of the outer mitochondrial membrane in yeast, OMM70, fused to dihydrofolate reductase [9].
• In contrast, in the two stably dedifferentiated hepatoma cell lines, amplified dihydrofolate reductase genes are found on large chromosomes of variable size, on ring chromosomes, and on chromosomes containing terminal, median, or multiple centromeres [1].

Chemical compound and disease context of Dhfr

• Exposure of growing cultures of hepatoma cells in vitro to the lipid-soluble dihydrofolate reductase inhibitors metoprine (36 nM) or trimetrexate (2 nM) at subtoxic concentrations causes little change in cell growth rate, colony forming ability, cell cycle distribution, and de novo purine and thymidylate biosynthesis [10].
• A hybrid precursor protein constructed by fusing the mitochondrial matrix-targeting signal of rat preornithine carbamyl transferase to murine cytosolic dihydrofolate reductase (designated pO-DHFR) was expressed in Escherichia coli [11].
• The 3,5-bis(1-propenyl)-4-methoxy derivative 8 was 1 order of magnitude more active against Escherichia coli dihydrofolate reductase than its saturated counterpart, and it was also more active than trimethoprim, 1 [12].
• In a rat model of dual infection, we studied such dihydrofolate reductase (DHFR) inhibitors as PS-15 (25 mg/kg of body weight), epiroprim (100 mg/kg), and pyrimethamine (3 mg/kg) alone or in combination with various doses of dapsone (50, 25, or 5 mg/kg) for the prevention of pneumocystosis and toxoplasmosis [13].
• A series of eight previously undescribed 2,4-diaminothieno[2,3-d]pyrimidine analogues of the potent dihydrofolate reductase (DHFR) inhibitors trimetrexate (TMQ) and piritrexim (PTX) were synthesized as potential drugs against Pneumocystis carinii and Toxoplasma gondii, which are major causes of severe opportunistic infections in AIDS patients [14].

Biological context of Dhfr

• When p53 expression is suppressed by introducing E6, persistent exposure to nicotine enables dihydrofolate reductase gene amplification in the presence of methotrexate (MTX) and the formation of the MTX-resistant colonies [15].
• The rat liver DHFR gene has an open reading frame of 561 bp encoding a protein of 187 amino acids [16].
• Here, we report the isolation of the rat DHFR gene through screening of a rat liver cDNA library [16].
• Cells exposed to antifolates show increased cellular levels of proteins fused to dihydrofolate reductase: a method to modulate gene expression [17].
• We have validated LGS with the rodent malaria parasite Plasmodium chabaudi chabaudi using a phenotype, pyrimethamine resistance, whose controlling gene, that encoding dihydrofolate reductase (dhfr), is known [18].

Anatomical context of Dhfr

• Persistent nicotine treatment potentiates amplification of the dihydrofolate reductase gene in rat lung epithelial cells as a consequence of Ras activation [15].
• We conclude that the nature of the chromosomal changes associated with dihydrofolate reductase gene amplification are the result of differences in cell lines rather than in the protocols employed for selection [1].
• KB cells, which do not contain detectable levels of GTP cyclohydrolase or BH4 but do contain dihydrofolate reductase, readily convert sepiapterin to BH4 and this conversion is completely prevented by methotrexate [19].
• DHFR was taken up by freshly isolated rat liver lysosomes and methotrexate reduced this uptake by about 80% [20].
• The susceptibility toward proteases of mouse dihydrofolate reductase (DHFR), synthesized in a coupled transcription-translation system with rabbit reticulocytes, decreased in the presence of its substrate analogue, methotrexate [20].

Associations of Dhfr with chemical compounds

• Altering the activity of phosphoinositide 3-OH-kinase has no effect on dihydrofolate reductase amplification [15].
• However 13 was no more potent than PTX against M. avium DHFR, and its SI was no better than that of TMP [21].
• Design, synthesis, and antifolate activity of new analogues of piritrexim and other diaminopyrimidine dihydrofolate reductase inhibitors with omega-carboxyalkoxy or omega-carboxy-1-alkynyl substitution in the side chain [21].
• In a Chinese hamster ovary cell mutant lacking dihydrofolate reductase (DUKX-B11), endogenous formation of BH4 proceeds normally but, unlike the parent cells, these cells or extracts of them do not convert sepiapterin or 7,8-dihydrobiopterin to BH4 [19].
• Addition of dexamethasone, a synthetic glucocorticoid agonist, decreased the activity of the chimeric protein, as measured by colony formation in selective medium, binding of fluoresceinated methotrexate, and direct enzymatic assay for DHFR [22].

Physical interactions of Dhfr

• Analysis of the transcription factor E2F complexes formed in the promoter regions of cdc2 and dihydrofolate reductase genes showed that the amount of complexes formed is maximal at the G1/S boundary, but decreases in S phase when these genes are transcribed extensively [23].

Other interactions of Dhfr

• Dexamethasone negatively regulates the activity of a chimeric dihydrofolate reductase/glucocorticoid receptor protein [22].
• Stimulation of methotrexate resistance and dihydrofolate reductase gene amplification by c-myc [24].
• Correlation analysis of Baker's studies on enzyme inhibition. 1. Guanine deaminase, xanthine oxidase, dihydrofolate reductase, and complement [25].
• The activities of sepiapterin reductase and dihydrofolate reductase, putative enzymes in the biosynthetic pathway from GTP to BH4, were not increased by reserpine [26].
• Rat proenkephalin was overexpressed in Chinese hamster ovary cells using the dihydrofolate reductase-coupled genetic amplification method [27].

Analytical, diagnostic and therapeutic context of Dhfr

• In the present study, this was proven by immunoelectron microscopy of the cultured Chinese hamster ovary cells stably expressing fusion proteins of the amino-terminal sequences of the thiolase precursor and Escherichia coli dihydrofolate reductase [28].
• Seven days after treatment (PD 17), the dihydrofolate reductase reaction showed weakly positive cells with small grains of formazan in the perinuclear regions and dipeptidylaminopeptidase II activity, which had appeared at this time in some cells of the controls, was not observed [29].
• We developed a method to determine dihydrofolate reductase (DHFR) activity at pH 7.4 (37 degrees C) by monitoring its product, tetrahydrofolate (H(4)folate), using HPLC with electrochemical detection [30].
• 1. Methotrexate was administered immediately after partial (70%) hepatectomy, resulting in complete inhibition of dihydrofolate reductase in 24 h-regenerating liver [31].
• Assay of dihydrofolate reductase activity by monitoring tetrahydrofolate using high-performance liquid chromatography with electrochemical detection [30].

References