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)

Trimetrexate is a lipid soluble dihydrofolate reductase inhibitor which, unlike methotrexate, does not depend upon the membrane folate transport system for cell entry. We investigated the possibility that trimetrexate (but not methotrexate) might permeate intermitotic lymphocytes and, following stimulation, impair only the responding cells, rather than all dividing cells, as is the case with methotrexate. Peripheral blood mononuclear cells from normal individuals were incubated for 1 hr in three moderate to high concentrations (1, 10 and 100 microM) of methotrexate or trimetrexate, washed, and incubated with phytohemagglutinin. Intracellular folate activity, as assessed by the deoxyuridine suppression test, was abnormal at all three concentrations of trimetrexate but only at the highest concentration of methotrexate. Similarly, incorporation of [3H]deoxyuridine was depressed profoundly in trimetrexate-treated cells (2% of control) but unaffected by methotrexate. Analysis of cell cycle distribution by flow cytometry confirmed G0 + G1 arrest in trimetrexate but not methotrexate-treated cells. Neither drug altered morphologic transformation, Tac antigen expression, or incorporation of [3H]thymidine by the "salvage" pathway. Therefore, brief exposure to methotrexate has little effect on intermitotic lymphocytes, whereas trimetrexate very specifically inhibits the conversion of deoxyuridine to thymidine in these cells and leads to the arrest of DNA synthesis in the G0 + G1 phase. This metabolic abnormality markedly reduces in vitro antibody synthesis: a 1-hr treatment of lymphocytes with 10 or 100 microM trimetrexate prior to incubation with pokeweed mitogen on four occasions completely inhibited both IgG and IgM secretion. Similar treatment with methotrexate had no effect until the highest concentration (100 microM) was used. We conclude that brief exposure of peripheral blood mononuclear cells to the nonclassical dihydrofolate reductase inhibitor, trimetrexate, results in inhibition of nucleic acid synthesis and impairment of antibody production. This drug effect may permit more incisive modulation of immune responses.
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PMID:Inhibition of lymphocyte nucleic acid metabolism and antibody production by trimetrexate. 295 54

The human 4F2 cell surface antigen is a 120-kilodalton (kDa) disulfide-linked heterodimer which is composed of an 80- to 90-kDa glycosylated heavy chain (4F2HC) and a 35- to 40-kDa nonglycosylated light chain (4F2LC). 4F2 belongs to a family of inducible cell surface molecules which are involved in T-lymphocyte activation and growth. To better understand the molecular mechanism(s) that controls 4F2HC gene expression in both resting and activated T cells, a 4F2HC human genomic clone was isolated and structurally characterized. The 4F2HC gene spans 8 kilobases of chromosome 11 and is composed of nine exons. The 5' upstream region of the gene displays several properties which are characteristic of housekeeping genes. It is G+C rich and hypomethylated in peripheral blood lymphocyte DNA and contains multiple binding sites for the Sp1 transcription factor while lacking TATA or CCAAT sequences. This region of the gene also displays sequence homologies with several other inducible T-cell genes, including the interleukin-2, interleukin-2 receptor alpha chain, dihydrofolate reductase, thymidine kinase, and transferrin receptor genes. A 255-base-pair fragment of the 4F2HC gene which contains 154 base pairs of the 5' flanking sequence was able to efficiently promote expression of the bacterial chloramphenicol acetyltransferase gene in human Jurkat T cells, indicating that it contains promoter or enhancer (or both) sequences. Analyses of chromatin structure in resting and lectin-activated T cells revealed the presence of stable DNase I-hypersensitive sites within both the 5' flanking and intron 1 regions of the 4F2HC gene. Although the 4F2HC gene displayed many of the structural features characteristic of a constitutively expressed gene, lectin-mediated activation of resting peripheral blood T lymphocytes resulted in a dramatic increase in steady-state levels of 4F2HC mRNA.
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PMID:Isolation and structural characterization of the human 4F2 heavy-chain gene, an inducible gene involved in T-lymphocyte activation. 326 70