Mitochondrial biosynthesis controls the sensitivity of Chinese hamster cells to hydrogen peroxide

Overexpression of human peroxiredoxin 5 in subcellular compartments of Chinese hamster ovary cells: effects on cytotoxicity and DNA damage caused by peroxides

Peroxiredoxin 5 is a mammalian thioredoxin peroxidase ubiquitously expressed in tissues. Peroxiredoxin 5 can be intracellularly localized to mitochondria, peroxisomes, the cytosol, and, to a lesser extent, the nucleus. This remarkably wide subcellular distribution compared with the five other mammalian peroxiredoxins prompted us to further investigate the antioxidant protective function of peroxiredoxin 5 in mammalian cells according to its subcellular localization. Chinese hamster ovary cells overexpressing human peroxiredoxin 5 in the cytosol, in mitochondria, or in the nucleus were established by stable transfection. Cells overexpressing peroxiredoxin 5 were exposed for 1 h to low or acute oxidative stress with exogenously added hydrogen peroxide or tert-butylhydroperoxide. Cell protection conferred by peroxiredoxin 5 was evaluated by clonogenicity and lactate dehydrogenase assays. Overexpressing peroxiredoxin 5 in either the cytosolic, mitochondrial, or nuclear compartment significantly reduced cell death, with more effective protection with overexpression of peroxiredoxin 5 in mitochondria, confirming that this organelle is a major target of peroxides. Moreover, we evaluated, with the comet assay, nuclear DNA damage induced by hydrogen peroxide or tert-butylhydroperoxide. Overexpression of peroxiredoxin 5 in the nucleus significantly decreased DNA damage induced by both peroxides. In conclusion, the present study suggests that multiple subcellular targeting of peroxiredoxin 5 in mammalian cells can be implicated in antioxidant protective mechanisms under nonpathological conditions but also during acute oxidative stress caused by peroxides occurring in pathophysiological situations.

Calcium associated resistance to H(2)O(2) in Chinese hamster V79 cells

To investigate whether the difference in cellular sensitivity of Chinese hamster V79 and their H(2)O(2)-resistant variant cells (Hpr-4) to H(2)O(2) relates to the difference in intracellular Ca(2+) concentration in these cells, we measured Ca(2+) concentration by calcium ion analysis after loading these cells with Fura-2/AM. Intracellular Ca(2+) concentration increased in both Chinese hamster V79 and Hpr-4 cells as extracellular Ca(2+) concentration increased. However, the increase in intracellular Ca(2+) concentration in response to extracellular H(2)O(2) was more pronounced in Hpr-4 than V79 cells. H(2)O(2) cytotoxicity of Hpr-4 but not V79 cells was also decreased in response to the increase in extracellular Ca(2+) concentration. In parallel with the decrease in cytotoxicity in response to increasing extracellular Ca(2+) concentration, the frequency of mitochondrial DNA single strand breaks (SSB) in Hpr-4 cells also decreased without producing observable nuclear DNA SSB. Use of permeabilized V79 and Hpr-4 cells exposed to H(2)O(2) showed that mitochondrial DNA SSB decreased when extramitochondrial Ca(2+) concentration increased. These findings indicate that elevated intracellular Ca(2+) concentration may protect against H(2)O(2)-induced mitochondrial damage and cytotoxicity in these cells.

Complete repopulation of mouse mitochondrial DNA-less cells with rat mitochondrial DNA restores mitochondrial translation but not mitochondrial respiratory function

By the fusion of mtDNA-less (rho(0)) cells of Mus musculus domesticus with platelets from different species, mtDNA repopulated cybrids were obtained for finding the mtDNA species that could induce mitochondrial abnormalities. Expression of mitochondrial dysfunction might be expected in these cybrids due to incompatibility between nuclear and mitochondrial genomes from different species. The results showed that mouse rho(0) cells could receive mtDNA from a different mouse species, M. spretus, or even mtDNA from the rat, Rattus norvegicus, and that the introduced rat mtDNA, but not M. spretus mtDNA, caused mitochondrial dysfunction, even though rat mtDNA could restore normal mitochondrial translation in the cybrids. Considering that mitochondrial respiratory complexes consist of nuclear DNA- and mtDNA-coded polypeptides, these observations suggest that the nuclear and mitochondrial interactions required for replication, transcription, and translation of introduced rat mtDNA must be less stringently controlled than those required for formation of normal respiratory complexes. As no procedure for introduction of mutagenized mouse mtDNA into living cells has yet been established, these findings provide important insights into generating mtDNA-knockout mice.

The sensitivity to DNA single strand breakage in mitochondria, but not in nuclei, of Chinese hamster V79 and variant cells correlates with their cellular sensitivity to hydrogen peroxide

To investigate whether a relation exists between the level of DNA damage by and cytotoxicity of hydrogen peroxide, we measured the initial level of H2O2-induced nuclear and mitochondrial DNA single strand breaks in Chinese hamster V79 and H2O2-resistant variant cells (Hpr-4) with an alkaline elution technique and a quantitative Southern blot technique, respectively. The frequency of DNA single strand breaks in mitochondrial DNA induced by H2O2 was more than one hundred times that of nuclear DNA in the parent V79 cells. While a similar frequency of nuclear DNA single strand breaks was generated in V79 and Hpr-4 cells at an equidose of H2O2, a lower number of mitochondrial DNA single strand breaks were generated in Hpr-4 cells than in V79 cells by H2O2 in the range of 100 microM to 5 mM. The sensitivity to mitochondrial DNA single strand break-induction correlated with the cellular sensitivity to H2O2 in Chinese hamster V79 and variant cells.

Mitochondrial DNA is required for regulation of glucose-stimulated insulin secretion in a mouse pancreatic beta cell line, MIN6

To determine whether mtDNA and mitochondrial respiratory function in pancreatic beta cells are necessary for the phenotypic expression of glucose-stimulated insulin secretion, we used a cultured mouse pancreatic beta cell line, MIN6, and two derivative lines, mtDNA knockout MIN6 (rho0 MIN6) and mtDNA repopulated cybrid MIN6. The MIN6 cells retain the property of glucose-stimulated insulin secretion, but their mtDNA knockout induced the loss of mitochondrial transcription, translation, and respiration activity, without inhibition of transcription of the insulin gene or loss of succinate dehydrogenase activity, indicating that the observed mitochondrial dysfunction in rho0 MIN6 cells was not due to a cytotoxic side effect derived from the mtDNA knockout. Moreover, the mtDNA depletion also inhibited both the glucose-stimulated increase in the intracellular free Ca2+ content and the elevation of insulin secretion. The possibility of the involvement of nuclear genome-encoded factors in this process was excluded by the observation that the missing sensitivity to extracellular glucose stimulation in rho0 MIN6 cells was restored reversibly by repopulation with foreign mtDNA and isolating cybrid MIN6 clones. Therefore, these findings provide unambiguous evidence for the involvement of the mitochondrial dysfunction induced by mtDNA impairment in developing pathogeneses of some forms of diabetes mellitus.