Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P00492 (hypoxanthine-guanine phosphoribosyltransferase)
 2,385 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Chinese hamster cell mutant EM-C11, which is hypersensitive to the cell killing effects of alkylating agents compared to its parental line CHO9, has been used to study the impact of base excision repair on the mutagenic effects of DNA methylation damage. This cell line has a defect in the xrcc1 gene. XRCC1 can interact with DNA polymerase-beta, thereby suppressing strand displacement, and DNA ligase III, both of which have been implicated in base excision repair. XRCC1 may, therefore, allow efficient ligation of single-strand breaks generated during base excision repair. Both EM-C11 and CHO9 cells were treated with methyl methanesulfonate (MMS), a DNA-methylating agent reacting predominantly with nitrogen atoms generating adducts which are substrates for the base excision repair pathway. EM-C11 cells are much more sensitive to the cytotoxic effects of MMS than CHO9: for EM-C11, the dose of MMS inducing 10% survival is 6-fold lower than that for CHO9. In contrast, mutation induction at the hprt locus following MMS is similar in EM-C11 and CHO9. Molecular analysis of hprt gene mutations showed that although the largest class of hprt mutations, both in EM-C11 and CHO9 cells, consisted of GC > AT transitions, most likely caused by O6-methylguanine, the size of this class was smaller in EM-C11. The fraction of deletion mutants in EM-C11, however, was twice as large as that found in CHO9 cells. These results suggest that reduced ligation efficiency of single-strand breaks generated during base excision repair, as result of a defect in XRCC1, may lead to the formation of deletions.
 ...
PMID:Methyl methanesulfonate-induced hprt mutation spectra in the Chinese hamster cell line CHO9 and its xrcc1-deficient derivative EM-C11. 962 68

Questions about possible adverse health effects from exposures to uranium have arisen as a result of uranium mining, residual mine tailings and use of depleted uranium in the military. The purpose of the current study was to measure the toxicity of depleted uranium as uranyl acetate (UA) in mammalian cells. The activity of UA in the parental CHO AA8 line was compared with that in the XRCC1-deficient CHO EM9 line. Cytotoxicity was measured by clonogenic survival. A dose of 200 microM UA over 24 h produced 3.1-fold greater cell death in the CHO EM9 than the CHO AA8 line, and a dose of 300 microM was 1.7-fold more cytotoxic. Mutagenicity at the hypoxanthine (guanine) phosphoribosyltransferase (hprt) locus was measured by selection with 6-thioguanine. A dose of 200 microM UA produced approximately 5-fold higher averaged induced mutant frequency in the CHO EM9 line relative to the CHO AA8 line. The generation of DNA strand breaks was measured by the alkaline comet assay at 40 min and 24 h exposures. DNA strand breaks were detected in both lines; however a dose response may have been masked by U-DNA adducts or crosslinks. Uranium-DNA adducts were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) at 24 and 48 h exposures. A maximum adduct level of 8 U atoms/10(3) DNA-P for the 300 microM dose was found in the EM9 line after 48 h. This is the first report of the formation of uranium-DNA adducts and mutations in mammalian cells after direct exposure to a depleted uranium compound. Data suggest that uranium could be chemically genotoxic and mutagenic through the formation of strand breaks and covalent U-DNA adducts. Thus the health risks for uranium exposure could go beyond those for radiation exposure.
 ...
PMID:Uranyl acetate induces hprt mutations and uranium-DNA adducts in Chinese hamster ovary EM9 cells. 1619 14

Naturally occurring uranium and depleted uranium (DU) are believed to be health hazards by virtue of both their chemical and radiological properties. The mechanism(s) behind uranium's chemotoxic effects has yet to be elucidated. Previous work has shown that DU, as uranyl acetate (UA), was mutagenic at the hypoxanthine (guanine) phosphoribosyltransferase (hprt) locus in XRCC1-deficient CHO EM9 cells. The purpose of the current study was to characterize the mutations induced by UA at the hprt locus of CHO EM9 cells and compare the mutation spectrum of UA with those of hydrogen peroxide and spontaneous mutations in the same line. The hypothesis being tested was that if DU as UA is chemically genotoxic then the mutation spectrum induced by the heavy metal should be distinct from that produced spontaneously or by H2O2. A total of 59 UA-induced, 38 spontaneous, and 45 H2O2-induced mutations were identified. Base substitutions comprised 29%, 42%, and 16% of UA, spontaneous, and H2O2 mutants, respectively. The frequency of G --> T or C --> A substitutions was not significantly different in spontaneous or H2O2-induced mutants than in UA-induced mutants, suggesting a possible role for 8-oxodG damage in UA mutagenesis. However, the observation that UA produced significantly more major genomic rearrangements (multiexon insertions and deletions) than occurred spontaneously suggests the possibility that DNA strand breaks or crosslinks could also be UA-induced mutagenic lesions. The unique mutation spectrum elicited by exposure to UA suggests that UA generates mutations in ways that are different from spontaneous and free radical as well as radiological mechanisms.
 ...
PMID:Molecular analysis of hprt mutations generated in Chinese hamster ovary EM9 cells by uranyl acetate, by hydrogen peroxide, and spontaneously. 1629 11

UVA generates low levels of cyclobutane pyrimidine dimers (CPDs). Here we asked the question whether CPDs could fully explain the level of mutations induced by UVA. Relative mutagenicities of UVA and UVC were calculated at equal levels of CPDs in cell lines, deficient in different aspects of repair. Survival and gene mutations in the hprt locus were analyzed in a set of Chinese hamster ovary (CHO) cell lines, i.e., wild-type, Cockayne syndrome B protein-deficient (CSB), XRCC3-deficient and XRCC1-deficient adjusted to the same level of CPDs which was analyzed as strand breaks as a result of DNA cleavage by T4 endonuclease V at CPD sites. Induced mutagenicity of UVA was approximately 2 times higher than the mutagenicity of UVC in both wild-type and XRCC1-deficient cells when calculated at equal level of CPDs. Since this discrepancy could be explained by the fact that the TT-dimers, induced by UVA, might be more mutagenic than C-containing CPDs induced by UVC, we applied acetophenone, a photosensitizer previously shown to generate enhanced levels of TT-CPDs upon UVB exposure. The results suggested that the TT-CPDs were actually less mutagenic than the C-containing CPDs. We also found that the mutagenic effect of UVA was not significantly enhanced in a cell line deficient in the repair of CPDs. Altogether this suggests that neither base excision- nor nucleotide excision-repair was involved. We further challenge the possibility that the lesion responsible for the mutations induced by UVA was of a more complex nature and which possibly is repaired by homologous recombination (HR). The results indicated that UVA was more recombinogenic than UVC at equal levels of CPDs. We therefore suggest that UVA induces a complex type of lesion, which might be an obstruction during replication fork progression that requires HR repair to be further processed.
 ...
PMID:Cyclobutane pyrimidine dimers do not fully explain the mutagenicity induced by UVA in Chinese hamster cells. 1895 Jun 48