Two distinct pathways of cell death triggered by oxidative damage to nuclear and mitochondrial DNAs (original) (raw)
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Mitochondrial DNA damage triggers mitochondrial-superoxide generation and apoptosis
AJP: Cell Physiology, 2007
Recently, it has become apparent that mitochondrial DNA (mtDNA) damage can rapidly initiate apoptosis independent of mutations, although the mechanism involved remains unclear. To elucidate this mechanism, angiotensin II-mediated apoptosis was studied in cells that were transduced with a lentiviral vector to overexpress the DNA repair enzyme 8-oxoguanine glycosylase or were treated with inhibitors known to block angiotensin II-induced mtDNA damage. Cells exhibiting angiotensin II-induced mtDNA damage showed two phases of superoxide generation, the first derived from NAD(P)H oxidase and the second of mitochondrial origin, whereas cells prevented from experiencing mtDNA damage importantly exhibited only the first phase. Furthermore, cells with mtDNA damage demonstrated impairments in mitochondrial protein expression, cellular respiration, and complex 1 activity before the onset of the second phase of oxidation. After the second phase, the mitochondrial membrane potential collapsed, cytochrome c was released, and the cells underwent apoptosis, all of which were prevented by disrupting mtDNA damage. Collectively, these data reveal a novel mechanism of apoptosis that is initiated when mtDNA damage triggers mitochondrial superoxide generation and ultimately the activation of the mitochondrial permeability transition. This novel mechanism may play an important pathological role.
Cancer research, 2001
Mitochondria are not only the major site for generation of reactive oxygen species, but also one of the main targets of oxidative damage. One of the major products of DNA oxidation, 8-oxodeoxyguanosine (8-oxodG), accumulates in mitochondrial DNA (mtDNA) at levels three times higher than in nuclear DNA. The main pathway for the repair of 8-oxodG is the base excision repair pathway initiated by oxoguanine DNA glycosylase (OGG1). We previously demonstrated that mammalian mitochondria from mice efficiently remove 8-oxodG from their genomes and isolated a protein from rat liver mitochondria with 8-oxoguanine (8-oxodG) DNA glycosylase/apurinic DNA lyase activity. In the present study, we demonstrated that the mitochondrial 8-oxodG DNA glycosylase/apurinic DNA lyase activity is the mitochondrial isoform of OGG1. Using mouse liver mitochondria isolated from ogg1(-/-) mice, we showed that the OGG1 gene encodes for the mitochondrial 8-oxodG glycosylase because these extracts have no incision ...
Oncogene, 2008
2-Methoxyestradiol (2-ME), an endogenous estrogen metabolite of 17b-estradiol, is known to induce mitochondria-mediated apoptosis through several mechanisms. We sought to study the effect of mitochondrialy targeted hOGG1 (MTS-hOGG1) on HeLa cells exposed to 2-ME. MTS-hOGG1-expressing cells exposed to 2-ME showed increased cellular survival and had significantly less G 2 /M cell cycle arrest compared to vector-only-transfected cells. In addition, 2-ME exposure resulted in an increase in mitochondrial membrane potential, increased apoptosis, accompanied by higher activation of caspase-3,-9, cleavage of Bid to tBid and protein poly(ADP-ribose) polymerase (PARP) cleavage in HeLa cells lacking MTS-hOGG1. Fas inhibitors cerulenin or C75 inhibited 2-MEinduced caspase activation, PARP cleavage, apoptosis and reversed mitochondrial membrane hyperpolarization, thereby recapitulating the increased expression of MTS-hOGG1. Hence, MTS-hOGG1 plays an important protective role against 2-ME-mediated mitochondrial damage by blocking apoptosis induced through the Fas pathway.
Apoptosis-associated derangement of mitochondrial function in cells lacking mitochondrial DNA
1996
U937 cells lacking mitochondria! DNA (p°cells) are auxotrophic for undine and pyruvate, hypersensitive to hypoglycémie conditions, and resistant to antimycin A-induced apoptosis. In spite of their obvious metabolic defects, p°cells possess a normal mitochondria! transmembrane potential, as well as a near-normal capacity to generate Superoxide anión after menadione treatment. Similarly to p1 controls, p°cells undergo apoptosis in response to tumor necrosis factor-a plus cycloheximide. Detailed comparison of the apoptotic process in p+ and p" cells reveals essentially the same sequence of events. In response to tumor necrosis factor/cycloheximide, cells first lose their mitochondria! transmembrane potential (Ai//ml and then manifest late apoptotic alterations, such as generation of reactive oxygen species and DNA fragmentation. Experi ments involving isolated mitochondria from p* and p°cells confirm that ;< mitochondria can be induced to undergo permeability transition, a process thought to account for the pre-apoptotic Ai//,,, disruption in cells. Like p ' mitochondria, p°mitochondria contain a pre-formed soluble factor that is capable of inducing eliminatili condensation in isolated nuclei in vitro. This factor is released from mitochondria upon induction of permeability transition by calcium or the specific ligand of the adenine nucleotide translocator atractyloside. In conclusion, it appears that all structures involved in the maintenance and pre-apoptotic disruption of the Ai//,,,, as well as a mitochondria! apoptotic factor(s), are present in p°c ells and thus are controlled by the nuclear rather than by the mitochon dria! genome. These findings underline the contribution of mitochondria to the apoptotic process.
Free Radical Biology and Medicine, 2011
Emerging evidence suggests that mitochondrial (mt) DNA damage may be a trigger for apoptosis in oxidant challenged pulmonary artery endothelial cells (PAECs). Understanding the rate-limiting determinants of mtDNA repair may point to new targets for intervention in acute lung injury. The base excision repair (BER) pathway is the only pathway for oxidative damage repair in mtDNA. One of the key BER enzymes is Ogg1, which excises the base oxidation product, 8-oxoguanine. Previously we demonstrated that over-expression of mitochondrially-targeted Ogg1 in PAECs attenuated apoptosis induced by xanthine oxidase (XO) treatment. To test the idea that Ogg1 is a potentially rate-limiting BER determinant protecting cells from oxidant-mediated death, PAECs transfected with siRNA to Ogg1 were challenged with XO and the extent of mitochondrial and nuclear DNA damage was determined along with indices of apoptosis. Transfected cells demonstrated significantly reduced Ogg1 activity, which was accompanied by delayed repair of XO-induced mtDNA damage and linked to increased XO-mediated apoptosis. The nuclear genome was undamaged by XO in either control PAECs or cells depleted of Ogg1. These observations suggest that Ogg1 plays a critical and possibly rate-limiting role in defending PAECs from oxidant-induced apoptosis by limiting the persistence of oxidative damage in the mitochondrial genome.
Role of mitochondrial hOGG1 and aconitase in oxidant-induced lung epithelial cell apoptosis
Free Radical Biology and Medicine, 2009
8-Oxoguanine DNA glycosylase (Ogg1) repairs 8-oxo-7,8-dihydroxyguanine (8-oxoG), one of the most abundant DNA adducts caused by oxidative stress. In the mitochondria, Ogg1 is thought to prevent activation of the intrinsic apoptotic pathway in response to oxidative stress by augmenting DNA repair. However, the predominance of the beta-Ogg1 isoform, which lacks 8-oxoG DNA glycosylase activity, suggests that mitochondrial Ogg1 functions in a role independent of DNA repair. We report here that overexpression of mitochondria-targeted human alpha-hOgg1 (mt-hOgg1) in human lung adenocarcinoma cells with some alveolar epithelial cell characteristics (A549 cells) prevents oxidant-induced mitochondrial dysfunction and apoptosis by preserving mitochondrial aconitase. Importantly, mitochondrial alpha-hOgg1 mutants lacking 8-oxoG DNA repair activity were as effective as wild-type mt-hOgg1 in preventing oxidant-induced caspase-9 activation, reductions in mitochondrial aconitase, and apoptosis, su...
Mutation Research/Genetic Toxicology and Environmental Mutagenesis, 2010
Accumulation of oxidized bases such as 8-oxoguanine in either nuclear or mitochondrial DNA triggers various cellular dysfunctions including mutagenesis, and programmed cell death or senescence. Recent studies have revealed that oxidized nucleoside triphosphates such as 8-oxo-dGTP in the nucleotide pool are the main source of oxidized bases accumulating in the DNA of cells under oxidative stress. To counteract such deleterious effects of nucleotide pool damage, mammalian cells possess MutT homolog-1 (MTH1) with oxidized purine nucleoside triphosphatase and related enzymes, thus minimizing the accumulation of oxidized bases in cellular DNA. Depletion or increased expression of the MTH1 protein have revealed its significant roles in avoiding programmed cell death or senescence as well as mutagenesis, and accumulating evidences indicate that MTH1 is involved in suppression of degenerative disorders such as neurodegeneration.
Cell Death and Differentiation, 2001
A hallmark of apoptosis is the fragmentation of nuclear DNA. Although this activity involves the caspase-3-dependent DNAse CAD (caspase-activated DNAse), evidence exists that DNA fragmentation can occur independently of caspase activity. Here we report on the ability of truncated Bid (tBid) to induce the release of a DNAse activity from mitochondria. This DNAse activity was identified by mass spectrometry as endonuclease G, an abundant 30 kDa protein released from mitochondria under apoptotic conditions. No tBid-induced endonuclease G release could be observed in mitochondria from Bcl-2-transgenic mice. The in vivo occurrence of endonuclease G release from mitochondria during apoptosis was confirmed in the liver from mice injected with agonistic anti-Fas antibody and is completely prevented in Bcl-2 transgenic mice. These data indicate that endonuclease G may be involved in CAD-independent DNA fragmentation during cell death pathways in which truncated Bid is