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)

Examples of collateral sensitivity, even in experimental tumor systems, remain few. Preliminary data from this laboratory indicated that certain tumor cells expressed increased sensitivity to cisplatin after exposure in vitro to x-irradiation. To further clarify whether the type of fractionated radiation procedure used clinically can induce hypersensitivities to certain antitumor drugs we have pre-exposed the human ovarian carcinoma cell line JA-T/P derived from a tumor from an untreated patient to fractionated x-irradiation (total dose 50 Gy) in vitro. The resultant subline JA-T/DXR-10 expressed collateral sensitivity to cisplatin (CDDP), methotrexate (MTX) and fluorouracil (5-FU), but not to acute x-irradiation. Hypersensitivity to CDDP was associated with decreased activity of DNA polymerase beta (3.5-fold, P less than .01), but unaltered glutathione metabolism. Pre-incubation with cyclosporin A or with 3-aminobenzamide significantly enhanced (twofold, P less than .01) CDDP-induced cytotoxicity in JA-T/P cells, but not in the DXR-10 subline. Consistent with MTX hypersensitivity dihydrofolate reductase activity was significantly decreased (2.9-fold, P less than .01). Despite collateral sensitivity to 5-FU, however, thymidylate synthase activity was increased (twofold, P less than .05) suggesting alternative mechanisms for 5-FU-induced cytotoxicity in these JA-T/DXR-10 cells. These data demonstrate that DNA repair and associated reduced folate metabolism can be modified not only by drugs but also by fractionated x-irradiation.
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PMID:Expression of collateral sensitivity to cisplatin, methotrexate, and fluorouracil in a human ovarian carcinoma cell line following exposure to fractionated x-irradiation in vitro. 155 59

DNA polymerase beta (beta-pol) and its mRNA are maintained at constitutive levels during the cell cycle and during stages of cell growth in culture. To study biological consequences of variations in the level of this DNA repair enzyme and/or its mRNA, we prepared expression vectors in which cDNA for human beta-pol is inserted under the control of a metallothionein promoter (pMT) in the sense and antisense orientation, respectively, and these vectors then were used for stable transformation of mouse 3T3 cells. Vectors also contained the mouse DHFR gene, such that culture of transformants in medium with increasing concentrations of methotrexate resulted in amplification of inserted DNA. The levels of sense and antisense transcripts are strongly increased by culture of transformants in medium with 65 microM Zn2+, although some expression is detected even without Zn2+ induction. After five days of induction, the beta-pol level was about threefold higher in sense cells and about 10-fold lower in antisense cells than in parallel cultures without induction. The antisense line has a threefold increased cell doubling time in the presence of 65 microM Zn2+ compared with the absence of Zn2+. Zn2+ (65 microM) induction for the sense line results in normal growth for the first three days and, thereafter, a complete cessation of growth. Yet, these blocked cells remain fully viable. The results indicate that sudden deregulation of beta-pol expression alters cell growth in mouse 3T3 cells.
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PMID:Deregulation of DNA polymerase beta by sense and antisense RNA expression in mouse 3T3 cells alters cell growth. 169 88

Enhanced DNA repair has been identified as a major mechanism of resistance to the anticancer drug cisplatin in murine leukemia L1210 cells. Studies of other cells have implicated the elevation of a variety of RNA transcripts in cisplatin resistance. This study investigated potential changes in transcription of these genes as well as genes involved in DNA repair. No elevation in any of the following transcripts was observed: thymidylate synthase, dihydrofolate reductase, DNA polymerase alpha, DNA polymerase beta, topoisomerase II, Ha-ras, beta-tubulin, metallothionein and the DNA repair genes ERCC1 and ERCC2. Thymidine kinase was increased no more than 2-fold. None of these RNA were induced by incubation with cisplatin. High levels of cisplatin produced selective decreases in certain RNA. These results demonstrate that the previous observations of elevated RNA can not be universally applied to all cisplatin-resistant cells.
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PMID:Analysis of various mRNA potentially involved in cisplatin resistance of murine leukemia L1210 cells. 197 66

Peritoneal cells were derived from a patient (PK) with adenocarcinoma of the colon during the course of cisplatin/5-fluorouracil (5-FUra) treatment. Resistance to cisplatin and 5-FUra, characterized by a lack of response to chemotherapy and continued growth of the tumor, was concomitantly associated with a 2-4-fold increase in DNA copy number for dTMP synthase and dihydrofolate reductase. There was a corresponding amplification in DNA copy number of the c-myc (2X), H-ras (4X), and c-fos (15X) oncogenes. Cytogenetic studies revealed an iso (13q) chromosome, but failed to show any double minutes or homogeneously staining regions. In addition, drug-resistant tumor cells from PK and another patient (HG) displayed enhanced expression of dTMP synthase, c-fos and DNA polymerase beta when compared to normal colon tissue and the HCT8 human colon carcinoma cell line. These results suggest that elevated oncogene DNA and gene expression may be involved in the development of cisplatin resistance.
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PMID:Differential oncogene amplification in tumor cells from a patient treated with cisplatin and 5-fluorouracil. 214 97

By employing a general biosynthetic method for the elaboration of proteins containing unnatural amino acid analogues, we incorporated (aminooxy)acetic acid into positions 10 and 27 of Escherichia coli dihydrofolate reductase. Introduction of the modified amino acid into DHFR was accomplished in an in vitro protein biosynthesizing system by readthrough of a nonsense (UAG) codon with a suppressor tRNA that had been activated with (aminooxy)acetic acid. Incorporation of the amino acid proceeded with reasonable efficiency at codon position 10 but less well at position 27. (Aminooxy)acetic acid was also incorporated into position 72 of DNA polymerase beta. Peptides containing (aminooxy)acetic acid have been shown to adopt a preferred conformation involving an eight-membered ring that resembles a gamma-turn. Accordingly, the present study may facilitate the elaboration of proteins containing conformationally biased peptidomimetic motifs at predetermined sites. The present results further extend the examples of ribosomally mediated formation of peptide bond analogues of altered connectivity and provide a conformationally biased linkage at a predetermined site. It has also been shown that the elaborated protein can be cleaved chemically at the site containing the modified amino acid.
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PMID:Site-specific incorporation of (aminooxy)acetic acid into proteins. 1223 90