Acids Res. 2006 Mar 20;34(5):1620-32. Print
Dimerization and opposite base-dependent catalytic impairment of polymorphic S326C OGG1 glycosylase.
Hill JW, Evans MK.
Laboratory of Cellular and Molecular Biology, National Institute on Aging, National Institutes of Health,
Human 8-oxoguanine-DNA glycosylase (OGG1) is the major enzyme for repairing 8-oxoguanine (8-oxoG), a mutagenic guanine base lesion produced by reactive oxygen species (ROS). A frequently occurring OGG1 polymorphism in human populations results in the substitution of serine 326 for cysteine (S326C). The 326 C/C genotype is linked to numerous cancers, although the mechanism of carcinogenesis associated with the variant is unclear. We performed detailed enzymatic studies of polymorphic OGG1 and found functional defects in the enzyme. S326C OGG1 excised 8-oxoG from duplex DNA and cleaved abasic sites at rates 2- to 6-fold lower than the wild-type enzyme, depending upon the base opposite the lesion. Binding experiments showed that the polymorphic OGG1 binds DNA damage with significantly less affinity than the wild-type enzyme. Remarkably, gel shift, chemical cross-linking and gel filtration experiments showed that S326C both exists in solution and binds damaged DNA as a dimer. S326C OGG1 enzyme expressed in human cells was also found to have reduced activity and a dimeric conformation. The glycosylase activity of S326C OGG1 was not significantly stimulated by the presence of AP-endonuclease. The altered substrate specificity, lack of stimulation by AP-endonuclease 1 (APE1) and anomalous DNA binding conformation of S326C OGG1 may contribute to its linkage to cancer incidence.
PMID: 16549874 [PubMed - indexed for MEDLINE]
Protection of INS-1 cells from free fatty acid-induced apoptosis by targeting hOGG1 to mitochondria.
Rachek LI, Thornley NP, Grishko VI, LeDoux SP, Wilson GL.
Department of Cell Biology and Neuroscience, College of Medicine, University of South Alabama, Mobile, AL 36688, USA. email@example.com
Chronic exposure to elevated levels of free fatty acids (FFAs) impairs pancreatic beta-cell function and contributes to the decline of insulin secretion in type 2 diabetes. Previously, we reported that FFAs caused increased nitric oxide (NO) production, which damaged mitochondrial DNA (mtDNA) and ultimately led to apoptosis in INS-1 cells. To firmly establish the link between FFA-generated mtDNA damage and apoptosis, we stably transfected INS-1 cells with an expression vector containing the gene for the DNA repair enzyme human 8-oxoguanine DNA glycosylase/apurinic lyase (hOGG1) downstream of the mitochondrial targeting sequence (MTS) from manganese superoxide dismutase. Successful integration of MTS-OGG1 into the INS-1 cellular genome was confirmed by Southern blot analysis. Western blots and enzyme activity assays revealed that hOGG1 was targeted to mitochondria and the recombinant enzyme was active. MTS-OGG1 cells showed a significant decrease in FFA-induced mtDNA damage compared with vector-only transfectants. Additionally, hOGG1 overexpression in mitochondria decreased FFA-induced inhibition of ATP production and protected INS-1 cells from apoptosis. These results indicate that mtDNA damage plays a pivotal role in FFA-induced beta-cell dysfunction and apoptosis. Therefore, targeting DNA repair enzymes into beta-cell mitochondria could be a potential therapeutic strategy for preventing or delaying the onset of type 2 diabetes symptoms.
PMID: 16567524 [PubMed - in process]
Nucleic Acids Res. 2006 Mar 20;34(5):1620-32. Print 2006.
Diabetes. 2006 Apr;55(4):1022-8.