calpain and 8-hydroxyguanine

8-Oxoguanine (8-oxoG), a common DNA lesion caused by reactive oxygen species, is associated with carcinogenesis and neurodegeneration. Although the mechanism by which 8-oxoG causes carcinogenesis is well understood, the mechanism by which it causes neurodegeneration is unknown. Here, we report that neurodegeneration is triggered by MUTYH-mediated excision repair of 8-oxoG-paired adenine. Mutant mice lacking 8-oxo-2'-deoxyguanosine triphosphate-depleting (8-oxo-dGTP-depleting) MTH1 and/or 8-oxoG-excising OGG1 exhibited severe striatal neurodegeneration, whereas mutant mice lacking MUTYH or OGG1/MUTYH were resistant to neurodegeneration under conditions of oxidative stress. These results indicate that OGG1 and MTH1 are protective, while MUTYH promotes neurodegeneration. We observed that 8-oxoG accumulated in the mitochondrial DNA of neurons and caused calpain-dependent neuronal loss, while delayed nuclear accumulation of 8-oxoG in microglia resulted in PARP-dependent activation of apoptosis-inducing factor and exacerbated microgliosis. These results revealed that neurodegeneration is a complex process caused by 8-oxoG accumulation in the genomes of neurons and microglia. Different signaling pathways were triggered by the accumulation of single-strand breaks in each type of DNA generated during base excision repair initiated by MUTYH, suggesting that suppression of MUTYH may protect the brain under conditions of oxidative stress.

Topics: Animals; Apoptosis Inducing Factor; Benzamides; Calpain; Cell Nucleus; Corpus Striatum; Dipeptides; DNA Breaks, Single-Stranded; DNA Glycosylases; DNA Repair; DNA, Mitochondrial; Guanine; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Microglia; Mitochondria; Motor Activity; Neurodegenerative Diseases; Nitro Compounds; Oxidative Stress; Phosphoric Monoester Hydrolases; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerase Inhibitors; Poly(ADP-ribose) Polymerases; Propionates

Oxidative base lesions, such as 8-oxoguanine, accumulate in nuclear and mitochondrial DNAs under oxidative stress, resulting in cell death. However, it is not known whether only oxidative lesion accumulated in mitochondrial DNA is involved in such cell death. By introducing human cDNA encoding a nuclear form of 8-oxoG DNA glycosylase (hOGG1-1a) into immortalized mouse embryo fibroblasts lacking Ogg1 gene, we established a cell line which selectively accumulates 8-oxoguanine in mitochondrial DNA under oxidative stress. Selective accumulation of 8-oxoguanine in mitochondrial DNA in this cell line causes degradation of mitochondrial DNA followed by ATP depletion, mitochondrial membrane permeability transition, and Ca(2+) efflux, which in turn activates calpains to execute cell death. Knockdown of MUTYH which excises adenine opposite 8-oxoG in DNA prevents degradation of mitochondrial DNA and activation of calpain, thus suppressing the cell death induced by menadione.

Topics: Adenosine Triphosphate; Animals; Blotting, Southern; Calcium; Calpain; Cell Nucleus; Cell Survival; Cells, Cultured; DNA Damage; DNA Glycosylases; DNA Repair; DNA, Mitochondrial; Embryo, Mammalian; Fibroblasts; Guanine; Humans; Membrane Potential, Mitochondrial; Mice; Mice, Knockout; Mitochondria; Oxidation-Reduction; Oxidative Stress

Deficient repair activity for 8-hydroxy-2'-deoxyguanine (8-oxoguanine), a premutagenic oxidative DNA damage, has been observed in affected tissues in neurodegenerative diseases of aging, such as Alzheimer's disease, and in ischemia/reperfusion injury, type 2 diabetes mellitus, and cancer. These conditions have in common the accumulation of oxidative DNA damage, which is believed to play a role in disease progression, and loss of intracellular calcium regulation. These observations suggest that oxidative DNA damage repair capacity may be influenced by fluctuations in cellular calcium. We have identified human 8-oxoguanine-DNA glycosylase 1 (OGG1), the major 8-oxoguanine repair activity, as a specific target of the Ca(2+)-dependent protease Calpain I. Protein sequencing of a truncated partially calpain-digested OGG1 revealed that calpain recognizes OGG1 for degradation at a putative PEST (proline, glutamic acid, serine, threonine) sequence in the C-terminus of the enzyme. Co-immunoprecipitation experiments showed that OGG1 and Calpain I are associated in human cells. Exposure of HeLa cells to hydrogen peroxide or cisplatin resulted in the degradation of OGG1. Pretreatment of cells with the calpain inhibitor calpeptin resulted in inhibition of OGG1 proteolysis and suggests that OGG1 is a target for calpain-mediated degradation in vivo during oxidative stress- and cisplatin-induced apoptosis. Polymorphic OGG1 S326C was comparatively resistant to calpain digestion in vitro, yet was also degraded by a calpain-dependent pathway in vivo following DNA damaging agent exposure. The degradation of OGG1 by calpain may contribute to decreased 8-oxoguanine repair activity and elevated levels of 8-oxoguanine reported in tissues undergoing chronic oxidative stress, ischemia/reperfusion, and other cellular stressors known to produce perturbations of intracellular calcium homeostasis which activate calpain.

Topics: Amino Acid Motifs; Amino Acid Sequence; Antineoplastic Agents; Apoptosis; Calpain; Cisplatin; Dipeptides; DNA Glycosylases; Enzyme Inhibitors; Guanine; HeLa Cells; Humans; Hydrogen Peroxide; Molecular Sequence Data; Oxidative Stress; Proteolysis