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 several aspects of DNA damage formation and repair in human ovarian cancer cell lines which have become resistant to cisplatin through continued exposure to the anticancer drug. The resistant cell lines A2780/cp70 and 2008/c13*5.25 were compared with their respective parental cell lines, A2780 and 2008. Cells in culture were treated with cisplatin, and the two main DNA lesions formed, intrastrand adducts and interstrand cross-links, were quantitated before and after repair incubation. This quantitation was done for total genomic lesions and at the level of individual genes. In the overall genome, the initial frequency of both cisplatin lesions assayed was higher in the parental than in the derivative resistant cell lines. Nonetheless, the total genomic repair of each of these lesions was not increased in the resistant cells. These differences in initial lesion frequency between parental and resistant cell lines were not observed at the gene level. Resistant and parental cells had similar initial frequencies of intrastrand adducts and interstrand cross-links in the dihydrofolate reductase (DHFR) gene and in several other genes after cisplatin treatment of the cells. There was no increase in the repair efficiency of intrastrand adducts in the DHFR gene in resistant cell lines compared with the parental partners. However, a marked and consistent repair difference between parental and resistant cells was observed for the gene-specific repair of cisplatin interstrand cross-links. DNA interstrand cross-links were removed from three genes, the DHFR, multidrug resistance (MDR1), and delta-globin genes, much more efficiently in the resistant cell lines than in the parental cell lines. Our findings suggest that acquired cellular resistance to cisplatin may be associated with increased gene-specific DNA repair efficiency of a specific lesion, the interstrand cross-link.
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PMID:Increased gene-specific repair of cisplatin interstrand cross-links in cisplatin-resistant human ovarian cancer cell lines. 138 Jun 46

We have measured gene specific DNA repair in a normal human fibroblast cell line, and in fibroblast lines from two patients with familial Alzheimer disease (AD). Cells were treated with either ultraviolet radiation (UV) or the chemotherapeutic alkylating agent, nitrogen mustard (HN2). DNA damage formation and repair were studied in the active dihydrofolate reductase (DHFR) gene for the main lesions introduced by each of these two types of DNA damaging agents. The gene specific repair of UV induced cyclobutane pyrimidine dimers in the human DHFR gene was 86% complete in the AD cells after 24 h of repair incubation. This repair efficiency was similar to what we and others have found in normal human fibroblasts. After treatment of the AD cells with HN2, we found the frequency of HN2 induced lesions in the DHFR gene to be similar to the frequency in the transcriptionally inactive delta-globin gene. The gene specific repair of HN2 induced lesions in the DHFR gene was completed within 8-24 h in the normal fibroblast line and in the familial AD line, and the repair kinetics were similar for both cell lines. These results indicate that familial AD fibroblasts have normal gene specific repair of both UV induced and HN2 induced DNA damage in active genes.
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PMID:Gene specific DNA repair of damage induced in familial Alzheimer disease cells by ultraviolet irradiation or by nitrogen mustard. 788 82

A novel assay to detect strand-specific DNA repair after cellular exposure to cisplatin at IC50 levels, is used to measure rapid repair in the divergent upstream gene (DUG), a human MutS homolog, and in the bidirectional promoter for dihydrofolate reductase gene (DHFR) and the contiguous upstream DUG. Single-stranded DNA capable of hybridizing to gene-specific probes is generated enzymatically by the 3'-5' exonuclease activity of T4 DNA polymerase. The presence of cisplatin lesions inhibit the exonucleolytic activity of T4 DNA polymerase and block the formation of single-stranded DNA. This decreases the amount of complementary sequence produced when assayed by gene-specific probe hybridization. With the progression of repair, increasing quantities of single-stranded DNA become available for probe hybridization. This assay was applied to human A2780 ovarian carcinoma cells treated with cisplatin at the beginning of G1 phase. A dose-response experiment showed that the assay was applicable down to cisplatin concentrations of 2.5 microM. To assay for strand-specific gene repair, the synchronized cells were treated with cisplatin and then allowed time to repair in drug-free medium. Extensive removal of cisplatin lesions after 2 hr of cellular repair during early G1 phase in the DUG and the DUG/DHFR promoter was measured, with no evidence of repair in the unexpressed delta-globin gene. The extent of preferential DNA repair was much more distinct than has been observed previously at high-drug dosage in asynchronous cells.
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PMID:Rapid gene-specific repair of cisplatin lesions at the human DUG/DHFR locus comprising the divergent upstream gene and dihydrofolate reductase gene during early G1 phase of the cell cycle assayed by using the exonucleolytic activity of T4 DNA polymerase. 797 95

We have examined the gene- and strand-specific DNA repair of UV-induced cyclobutane pyrimidine dimers in fibroblasts from normal individuals and from patients with the DNA repair-deficient disorder xeroderma pigmentosum (XP). Cells were studied from XP complementation groups A, C, D, and F. DNA repair was assessed in the essential, active gene, dihydrofolate reductase (DHFR), in the active c-myc protooncogene, and in the transcriptionally inactive delta-globin gene. In addition, repair was studied in the individual strands of the DHFR gene in normal and group C cells. In the two strains of group C cells, we find preferential DNA repair of the DHFR gene and a strand bias of the repair with more repair in the transcribed strand. This is in general accordance with previously published reports (Venema, J., van Hoffen, A., Natarajan, A.T., van Zeeland, A.A., and Mullenders, L.H.F. (1990) Nucleic Acids Res. 18, 443-448; Venema, J., van Hoffen, A., and Mullenders, L.H.F. (1991) Mol. Cell. Biol. 11, 4128-4134), but we now find that there is more repair in the nontranscribed strand and less in the transcribed strand than what has been observed previously. In XP group A and D strains, we find little or no gene-specific DNA repair. In cells from an individual in XP complementation group F, we find less repair of dimers in the active gene than what has been observed for the overall genome. We have also measured the colony-forming ability of the strains after treatment with UV and find that this measure of survival does not correlate with the level of gene-specific repair of dimers. Thus, XP group F represents a novel repair phenotype with little or no gene-specific repair of dimers, but with relatively high UV resistance. We also evaluate the XP patients' clinical features in relation to gene-specific repair of dimers.
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PMID:Gene-specific DNA repair in xeroderma pigmentosum complementation groups A, C, D, and F. Relation to cellular survival and clinical features. 844 62

We have measured the gene-specific repair of ultraviolet irradiation (UV)-induced cyclobutane pyrimidine dimers (CPD) in freshly isolated human peripheral blood CD4+ T-lymphocytes. Two populations of CD4+ lymphocytes were assayed: resting and proliferating cells. DNA repair was assessed in the essential gene dihydrofolate reductase (DHFR) as well as in each of its strands, in the proliferation inducible c-myc gene and in the inactive delta-globin gene. Transcription rates in these genes were determined by nuclear run-on assay in the two cell populations. The rate of DHFR transcription increased 10-fold from resting to proliferating lymphocytes. Transcripts from c-myc were present only in proliferating cells, and we detected no delta-globin transcripts in either cell population. During the 24-h period after UV irradiation, there was little or no repair in any of the genes in the resting cells; there was some repair in the transcribed strand of the DHFR gene, but no repair in its nontranscribed strand. In the proliferating cells where the transcription of DHFR was much increased, the repair was efficient. The delta-globin gene was not expressed in either cell population, but it was more efficiently repaired in the proliferating than in the resting cells. We suggest that the gene-specific repair activity in CD4+ lymphocytes can reflect the proliferative state of the cells as well as the transcriptional state of the gene.
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PMID:Gene-specific repair in human CD4+ lymphocytes reflects transcription and proliferation. 876 60

G0 cells in a tumor are insensitive to the chemotherapeutical agents. The nature of this resistance is not completely understood. One of the factors modulating sensitivity of cells may be DNA repair of drug induced DNA damage. In this study we have compared gene-specific formation and repair of cisplatin-induced interstrand cross-links (ICL) in human G0 and proliferating CD4+ lymphocytes. Cisplatin killing of G0 CD4+ lymphocytes is inefficient, and these cells resemble those in a tumor. After exposure to cisplatin under similar conditions, the frequency of ICL introduced is twice as high in the proliferating compared to the resting lymphocytes. Repair of ICL was measured in the housekeeping gene, dihydrofolate reductase (DHFR), in the proliferation inducible c-myc gene, and in the inactive delta-globin gene. We observed similar relative rates and extent of ICL repair in all three genes studied, in G0 or proliferating CD4+ lymphocytes. The mechanisms responsible for the resistance of G0 CD4+ lymphocytes towards cisplatin are discussed.
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PMID:Lack of correlation between repair of DNA interstrand cross-links and differential sensitivity of G0 and proliferating CD4+ lymphocytes towards cisplatin. 1073 62