Jeff W Hill1, Michele K Evans. 1. Laboratory of Cellular and Molecular Biology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224-6825, United States.
Abstract
BACKGROUND: Mutations and polymorphisms of OGG1, the major mammalian 8-oxoguanine repair activity, are associated with increased risk for several cancers. Decreased 8-oxoguanine repair capacity due to variant forms of the OGG1 gene is a common feature of numerous cancer cell lines. One such cell line, human KG-1 leukemia cells, has previously been demonstrated to be deficient in the excision of 8-oxoguanine from oxidatively damaged DNA. KG-1 cells have a homozygous R229Q amino acid substitution in OGG1 that has been presumed to alter the function of OGG1 and result in elevated levels of genomic 8-oxoG and hypersensitivity to 8-hydroxydeoxyguanosine nucleoside and ionizing radiation observed in KG-1 cells. METHODS: We characterized the enzymatic activity of R229Q OGG1 and the effect of the enzyme on cell survival following treatment with DNA damaging agents. RESULTS: R229Q OGG1 had activity similar to the wild-type enzyme, yet was easily heat inactivated at physiological temperature. R229Q OGG1 expressed in human cells had significantly lower activity than wild-type OGG1 and was also highly thermolabile. Expression of R229Q OGG1 sensitized KG-1 cells to killing by menadione and 8-hydroxydeoxyguanosine, but not ionizing radiation. CONCLUSIONS: These results suggest that decreased 8-oxoguanine repair in KG-1 is due to thermolability of R229Q OGG1 and that the enzyme variant increases cellular susceptibility to killing resulting from oxidative DNA damage. The R229Q OGG1 variant is a validated polymorphism prevalent in world populations and not an isolated mutation in KG-1 cells, thus the R229Q OGG1 allele may be a novel marker for cancer susceptibility.
BACKGROUND: Mutations and polymorphisms of OGG1, the major mammalian8-oxoguanine repair activity, are associated with increased risk for several cancers. Decreased 8-oxoguanine repair capacity due to variant forms of the OGG1 gene is a common feature of numerous cancer cell lines. One such cell line, human KG-1 leukemia cells, has previously been demonstrated to be deficient in the excision of 8-oxoguanine from oxidatively damaged DNA. KG-1 cells have a homozygous R229Q amino acid substitution in OGG1 that has been presumed to alter the function of OGG1 and result in elevated levels of genomic 8-oxoG and hypersensitivity to 8-hydroxydeoxyguanosine nucleoside and ionizing radiation observed in KG-1 cells. METHODS: We characterized the enzymatic activity of R229QOGG1 and the effect of the enzyme on cell survival following treatment with DNA damaging agents. RESULTS:R229QOGG1 had activity similar to the wild-type enzyme, yet was easily heat inactivated at physiological temperature. R229QOGG1 expressed in human cells had significantly lower activity than wild-type OGG1 and was also highly thermolabile. Expression of R229QOGG1 sensitized KG-1 cells to killing by menadione and 8-hydroxydeoxyguanosine, but not ionizing radiation. CONCLUSIONS: These results suggest that decreased 8-oxoguanine repair in KG-1 is due to thermolability of R229QOGG1 and that the enzyme variant increases cellular susceptibility to killing resulting from oxidative DNA damage. The R229QOGG1 variant is a validated polymorphism prevalent in world populations and not an isolated mutation in KG-1 cells, thus the R229QOGG1 allele may be a novel marker for cancer susceptibility.
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