A novel R229Q OGG1 polymorphism results in a thermolabile enzyme that sensitizes KG-1 leukemia cells to DNA damaging agents.
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.
Hill
Jeff W
JW
Laboratory of Cellular and Molecular Biology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224-6825, United States.
Evans
Michele K
MK
D000080242:8-Hydroxy-2'-Deoxyguanosine; D000483:Alleles; D019943:Amino Acid Substitution; D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects; D045647:DNA Glycosylases / Q000235:genetics* / Q000378:metabolism; D003849:Deoxyguanosine / Q000031:analogs & derivatives / Q000494:pharmacology; D015870:Gene Expression; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D006358:Hot Temperature; D006801:Humans; D007938:Leukemia / Q000201:enzymology / Q000235:genetics / Q000628:therapy*; D011110:Polymorphism, Genetic; D011839:Radiation, Ionizing; D024483:Vitamin K 3 / Q000494:pharmacology; D014815:Vitamins / Q000494:pharmacology
D000970:Antineoplastic Agents; D014815:Vitamins; C024829:8-hydroxyguanine; D006147:Guanine; D024483:Vitamin K 3; D000080242:8-Hydroxy-2'-Deoxyguanosine; D045647:DNA Glycosylases; C479058:oxoguanine glycosylase 1, human; D003849:Deoxyguanosine