Mitochondrial DNA Copy Research Articles

Effects of chloroplast dysfunction on mitochondria: white sectors in variegated leaves have higher mitochondrial DNA levels and lower dark respiration rates than green sectors.

Co-ordination between plastids and mitochondria is so essential that there should be extensive inter-organellar crosstalk during development of plant cells. Indeed, chloroplast dysfunction in white leaves of plastid ribosome-deficient mutant barley, albostrians, is reportedly accompanied by increases in the levels of mitochondrial DNA and mitochondrial transcripts, suggesting that (i) developmental/physiological status of plastids (or heterotrophic growth condition of albino leaves) can affect the status of mitochondrial genome, and (ii) the function of the affected mitochondria may also be up-regulated accordingly. However, functional aspects of the mitochondria affected by chloroplast dysfunction have not yet been examined in detail. Here, we examined the effects of chloroplast dysfunction on mitochondrial DNA level and dark respiration rate, by comparing white and green sectors within individual variegated leaves, using 12 ornamental plants as experimental materials. The pattern of leaf variegation differed from species to species, suggesting that different mechanisms were involved in the formation of white sectors in different species. Quantitative hybridization analysis revealed that mitochondrial DNA levels were generally higher in white sectors than in green sectors. In spite of the elevated mitochondrial DNA levels, however, dark respiration rates in white sectors were generally lower than those in green sectors. Several possible mechanisms for elevation of mitochondrial DNA level and suppression of dark respiration rates in white sectors are discussed.Electronic supplementary materialThe online version of this article (doi:10.1007/s00709-011-0325-y) contains supplementary material, which is available to authorized users.

The Human Mitochondrial Transcriptome

The human mitochondrial genome comprises a distinct genetic system transcribed as precursor polycistronic transcripts that are subsequently cleaved to generate individual mRNAs, tRNAs, and rRNAs. Here, we provide a comprehensive analysis of the human mitochondrial transcriptome across multiple cell lines and tissues. Using directional deep sequencing and parallel analysis of RNA ends, we demonstrate wide variation in mitochondrial transcript abundance and precisely resolve transcript processing and maturation events. We identify previously undescribed transcripts, including small RNAs, and observe the enrichment of several nuclear RNAs in mitochondria. Using high-throughput in vivo DNaseI footprinting, we establish the global profile of DNA-binding protein occupancy across the mitochondrial genome at single-nucleotide resolution, revealing regulatory features at mitochondrial transcription initiation sites and functional insights into disease-associated variants. This integrated analysis of the mitochondrial transcriptome reveals unexpected complexity in the regulation, expression, and processing of mitochondrial RNA and provides a resource for future studies of mitochondrial function (accessed at http://mitochondria.matticklab.com).

Schwann Cell Mitochondrial Metabolism Supports Long-Term Axonal Survival and Peripheral Nerve Function

Mitochondrial dysfunction is a common cause of peripheral neuropathies. While the role of neuron and axonal mitochondria in peripheral nerve disease is well appreciated, whether Schwann cell (SC) mitochondrial deficits contribute to peripheral neuropathies is unclear. Here, we examine how SC mitochondrial dysfunction affects axonal survival and contributes to the decline of peripheral nerve function by generating mice with SC-specific mitochondrial deficits. These mice (Tfam-SCKOs) were produced through the tissue-specific deletion of the mitochondrial transcription factor A gene (Tfam), which is essential for mitochondrial DNA (mtDNA) transcription and maintenance. Tfam-SCKOs were viable, but as they aged, they developed a progressive peripheral neuropathy characterized by nerve conduction abnormalities as well as extensive muscle denervation. Morphological examination of Tfam-SCKO nerves revealed early preferential loss of small unmyelinated fibers followed by prominent demyelination and degeneration of larger-caliber axons. Tfam-SCKOs displayed sensory and motor deficits consistent with this pathology. Remarkably, the severe mtDNA depletion and respiratory chain abnormalities in Tfam-SCKO mice did not affect SC proliferation or survival. Mitochondrial function in SCs is therefore essential for maintenance of axonal survival and normal peripheral nerve function, suggesting that SC mitochondrial dysfunction contributes to human peripheral neuropathies.

The development and validation of a single SNaPshot multiplex for tiger species and subspecies identification—Implications for forensic purposes

The tiger (Panthera tigris) is currently listed on Appendix I of the Convention on the International Trade in Endangered Species of Wild Fauna and Flora; this affords it the highest level of international protection. To aid in the investigation of alleged illegal trade in tiger body parts and derivatives, molecular approaches have been developed to identify biological material as being of tiger in origin. Some countries also require knowledge of the exact tiger subspecies present in order to prosecute anyone alleged to be trading in tiger products. In this study we aimed to develop and validate a reliable single assay to identify tiger species and subspecies simultaneously; this test is based on identification of single nucleotide polymorphisms (SNPs) within the tiger mitochondrial genome. The mitochondrial DNA sequence from four of the five extant putative tiger subspecies that currently exist in the wild were obtained and combined with DNA sequence data from 492 tiger and 349 other mammalian species available on GenBank. From the sequence data a total of 11 SNP loci were identified as suitable for further analyses. Five SNPs were species-specific for tiger and six amplify one of the tiger subspecies-specific SNPs, three of which were specific to P. t. sumatrae and the other three were specific to P. t. tigris. The multiplex assay was able to reliably identify 15 voucher tiger samples. The sensitivity of the test was 15,000 mitochondrial DNA copies (approximately 0.26pg), indicating that it will work on trace amounts of tissue, bone or hair samples. This simple test will add to the DNA-based methods currently being used to identify the presence of tiger within mixed samples.

Mitochondrial DNA transcription regulation and nucleoid organization

Mitochondrial biogenesis is a complex process depending on both nuclear and mitochondrial DNA (mtDNA) transcription regulation to tightly coordinate mitochondrial levels and the cell's energy demand. The energy requirements for a cell to support its metabolic function can change in response to varying physiological conditions, such as, proliferation and differentiation. Therefore, mitochondrial transcription regulation is constantly being modulated in order to establish efficient mitochondrial oxidative metabolism and proper cellular function. The aim of this article is to review the function of major protein factors that are directly involved in the process of mtDNA transcription regulation, as well as, the importance of mitochondrial nucleoid structure and its influence on mtDNA segregation and transcription regulation. Here, we discuss the current knowledge on the molecular mode of action of transcription factors comprising the mitochondrial transcriptional machinery, as well as the action of nuclear receptors on regulatory regions of the mtDNA.

Frequent Truncating Mutation of TFAM Induces Mitochondrial DNA Depletion and Apoptotic Resistance in Microsatellite-Unstable Colorectal Cancer

The mitochondrial transcription factor A (TFAM) is required for mitochondrial DNA (mtDNA) replication and transcription. Disruption of TFAM results in heart failure and premature aging in mice. But very little is known about the role of TFAM in cancer development. Here, we report the identification of frequent frameshift mutations in the coding mononucleotide repeat of TFAM in sporadic colorectal cancer (CRC) cell lines and in primary tumors with microsatellite instability (MSI), but not in microsatellite stable (MSS) CRC cell lines and tumors. The presence of the TFAM truncating mutation, in CRC cells with MSI, reduced the TFAM protein level in vivo and in vitro and correlated with mtDNA depletion. Furthermore, forced overexpression of wild-type TFAM in RKO cells carrying a TFAM truncating mutation suppressed cell proliferation and inhibited RKO cell-induced xenograft tumor growth. Moreover, these cells showed more susceptibility to cisplatin-induced apoptosis due to an increase of cytochrome b (Cyt b) expression and its release from mitochondria. An interaction assay between TFAM and the heavy-strand promoter (HSP) of mitochondria revealed that mutant TFAM exhibited reduced binding to HSP, leading to reduction in Cyt b transcription. Collectively, these data provide evidence that a high incidence of TFAM truncating mutations leads to mitochondrial copy number reduction and mitochondrial instability, distinguishing most CRC with MSI from MSS CRC. These mutations may play an important role in tumorigenesis and cisplatin-induced apoptotic resistance of most microsatellite-unstable CRCs.

MTOR pathway activation in age-related retinal disease

Vision loss degrades the quality of life of aged individuals. The major cause in industrialized countries is age-related macular degeneration (AMD), a blinding eye disease due to death of photoreceptors in the macula, a specialized retinal region responsible for high acuity vision. Photoreceptor death in AMD is thought to follow damage to the retinal pigment epithelium (RPE) [1], a monolayer of polarized, post-mitotic cells located between the photoreceptors and the choroidal blood supply that performs a variety of crucial tasks [2]. One proposed mechanism of RPE dysfunction in AMD posits a lifetime of oxidative damage leading to deposits (termed drusen) between the RPE and choroid, inflammation [3], and diminished RPE mitochondrial function [4, 5]. Macular RPE mitochondrial DNA from AMD eyes is more damaged than corresponding macular nuclear DNA [6], and macular RPE mitochondrial DNA damage correlates positively with AMD severity [7]. To model RPE mitochondrial DNA damage in AMD, we selectively ablated mitochondrial DNA replication and transcription in the RPE of postnatal mice [8]. The resulting deficit in RPE oxidative phosphorylation (OXPHOS) caused a slowly progressive photoreceptor degeneration, as well as a number of RPE morphological changes similar to those seen in AMD. The most prominent early RPE changes were hypertrophy and dedifferentiation, which coincided with activation of the mTOR pathway in OXPHOS-deficient RPE cells. Robust mTOR activation in the context of OXPHOS deficiency is counterintuitive because mTOR integrates trophic factor and nutrient availability signals to regulate cell growth and proliferation [9], and poisoning of mitochondrial energy production inhibits mTOR [10]. The fact that ATP levels in OXPHOS-deficient RPE cells were not substantially different from controls helps to resolve this apparent paradox. Levels of selected glycolytic metabolites were increased by several orders of magnitude, indicating a large glycolytic flux capable of generating ATP at a high rate. However, dependence on aerobic glycolysis is not a requirement for mTOR activation; acute treatment of wild-type mice with a strong oxidant that the targets the RPE also activated mTOR and triggered dedifferentiation, with profound negative consequences for adjacent photoreceptors [8]. Features suggestive of RPE hypertrophy and/or dedifferentiation have been reported for a number of other mouse retinal degeneration models [11-13], suggesting that a mTOR-associated RPE stress response may be quite general. OXPHOS deficiency leads eventually to RPE atrophy, which is seen more commonly in AMD than RPE hypertrophy. Our findings suggest that RPE hypertrophy may be present at earlier stages of AMD. Indeed, ocular coherence tomography imaging demonstrated thickened macular RPE more frequently in early AMD eyes than in advanced AMD or control eyes (C. Zhao, unpublished). RPE hypertrophy may be less prominent in advanced AMD because drusen and diminished transport through aged Bruch's basement membrane [14] may restrict access of RPE cells to nutrients from the choroidal blood supply. RPE cells in most mouse models are presumably not limited in this regard, facilitating mTOR activation. Hence, the stress response we have identified may shed light on RPE-related disease processes in which nutrients are readily available. Intriguingly, pharmacological inhibition of mTORC1 with rapamycin blunted RPE dedifferentiation and hypertrophy and preserved photoreceptor numbers and function for both the metabolic and oxidative stress models [8]. Rapamycin has recently been shown to have the remarkable ability to increase the longevity of mice, even when administered late in life [15]. Our results thus connect age-dependent retinal degeneration with a pathway known to be critical for the determination of lifespan. An in depth understanding is needed of the requirements for mTOR activation in the RPE and the mechanism by which the pathway mediates RPE dedifferentiation, with the goal of combating age-related retinal disease and extending human healthspan.

Exercise Increases Mitochondrial PGC-1α Content and Promotes Nuclear-Mitochondrial Cross-talk to Coordinate Mitochondrial Biogenesis

Endurance exercise is known to induce metabolic adaptations in skeletal muscle via activation of the transcriptional co-activator peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α). PGC-1α regulates mitochondrial biogenesis via regulating transcription of nuclear-encoded mitochondrial genes. Recently, PGC-1α has been shown to reside in mitochondria; however, the physiological consequences of mitochondrial PGC-1α remain unknown. We sought to delineate if an acute bout of endurance exercise can mediate an increase in mitochondrial PGC-1α content where it may co-activate mitochondrial transcription factor A to promote mtDNA transcription. C57Bl/6J mice (n = 12/group; ♀ = ♂) were randomly assigned to sedentary (SED), forced-endurance (END) exercise (15 m/min for 90 min), or forced endurance +3 h of recovery (END+3h) group. The END group was sacrificed immediately after exercise, whereas the SED and END+3h groups were euthanized 3 h after acute exercise. Acute exercise coordinately increased the mRNA expression of nuclear and mitochondrial DNA-encoded mitochondrial transcripts. Nuclear and mitochondrial abundance of PGC-1α in END and END+3h groups was significantly higher versus SED mice. In mitochondria, PGC-1α is in a complex with mitochondrial transcription factor A at mtDNA D-loop, and this interaction was positively modulated by exercise, similar to the increased binding of PGC-1α at the NRF-1 promoter. We conclude that in response to acute altered energy demands, PGC-1α re-localizes into nuclear and mitochondrial compartments where it functions as a transcriptional co-activator for both nuclear and mitochondrial DNA transcription factors. These results suggest that PGC-1α may dynamically facilitate nuclear-mitochondrial DNA cross-talk to promote net mitochondrial biogenesis.

Shot-gun proteomic analysis of mitochondrial D-loop DNA binding proteins: identification of mitochondrial histones

Transcription and replication of mitochondrial DNA (mtDNA) are regulated by nuclear DNA-encoded proteins that are targeted into mitochondria. A decrease in mtDNA copy number results in mitochondrial dysfunction, which may lead to insulin resistance and metabolic syndromes. We analyzed mitochondrial proteins that physically bind to human mitochondrial D-loop DNA using a shot-gun proteomics approach following protein enrichment by D-loop DNA-linked affinity chromatography. A total of 152 D-loop DNA binding proteins were identified by peptide sequencing using ultra high pressure capillary reverse-phase liquid chromatography/tandem mass spectrometry. Bioinformatic analysis showed that 68 were mitochondrial proteins, 96 were DNA/RNA/protein binding proteins and 114 proteins might form a complex via protein-protein interactions. Histone family members of H1, H2A, H2B, H3, and H4, were detected in abundance among them. In particular, histones H2A and H2B were present in the mitochondrial membrane as integral membrane proteins and not bound directly to mtDNA inside the organelle. Histones H1.2, H3 and H4 were associated with the outer mitochondrial membrane. Silencing of H2AX expression inhibited mitochondrial protein transport. Our data suggests that many mitochondrial proteins may reside in multiple subcellular compartments like H2AX and exert multiple functions.

Ooplast-mediated developmental rescue of bovine oocytes exposed to ethidium bromide

Ooplasm transfer has been used successfully to treat infertility in women with ooplasmic insufficiency and has culminated in the birth of healthy babies. To investigate whether mitochondrial dysfunction is a factor in ooplasmic insufficiency, bovine oocytes were exposed to ethidium bromide, an inhibitor of mitochondrial DNA replication and transcription, during in-vitro maturation (IVM). Exposure of immature oocytes to ethidium bromide for 24h during IVM hampered meiotic resumption and the migration of cortical granules. However, a briefer treatment with ethidium bromide during the last 4h of IVM led to partial arrest of preimplantation development without affecting oocyte maturation. Ooplasm transfer was then performed to rescue the oocytes with impaired development. In spite of this developmental hindrance, transfer of normal ooplasm into ethidium bromide-treated oocytes resulted in a complete rescue of embryonic development and the birth of heteroplasmic calves. Although this study unable to determine whether developmental rescue occurred exclusively through introduction of unaffected mitochondria into ethidium bromide-damaged oocytes, e.g. ethidium bromide may also affect other ooplasm components, these results clearly demonstrate that ooplasm transfer can completely rescue developmentally compromised oocytes, supporting the potential use of ooplasm transfer in therapeutic applications.

Mitochondrial Lon protease regulates mitochondrial DNA copy number and transcription by selective degradation of mitochondrial transcription factor A (TFAM)

Lon is the major protease in the mitochondrial matrix in eukaryotes, and is well conserved among species. Although a role for Lon in mitochondrial biogenesis has been proposed, the mechanistic basis is unclear. Here, we demonstrate a role for Lon in mtDNA metabolism. An RNA interference (RNAi) construct was designed that reduces Lon to less than 10% of its normal level in Drosophila Schneider cells. RNAi knockdown of Lon results in increased abundance of mitochondrial transcription factor A (TFAM) and mtDNA copy number. In a corollary manner, overexpression of Lon reduces TFAM levels and mtDNA copy number. Notably, induction of mtDNA depletion in Lon knockdown cells does not result in degradation of TFAM, thereby causing a dramatic increase in the TFAMmtDNA ratio. The increased TFAMmtDNA ratio in turn causes inhibition of mitochondrial transcription. We conclude that Lon regulates mitochondrial transcription by stabilizing the mitochondrial TFAMmtDNA ratio via selective degradation of TFAM.

HYPOXIA-INDUCED ALTERATION OF MITOCHONDRIAL GENES IN CARDIOMYOCYTES

The hypoxic conditions induced by reduced blood flow decreases oxygen availability in target tissues. Cellular hypoxia leads to mitochondrial dysfunction, decreased energy production, and increased production of reactive oxygen species. To determine the alteration in expression of mitochondrial genes after hypoxia in cardiomyocytes, we developed a rodent mitochondrial gene chip (RoMitoChip). The chip had 1088 probe sets including 46 probe sets representing 37 mouse mitochondrial DNA transcripts and the remaining probe sets representing mouse nuclear genes contributing to the mitochondrial structure and function. Mouse cardiomyocytes isolated from neonatal C57BL/6 mice that were subjected to hypoxia (1% oxygen) for different time intervals demonstrated a dichotomy in the expression profile of tRNA and mRNA transcripts. We report a total of 483 signature genes that were altered by hypoxia in the cardiac myocytes and related to mitochondrial structure and function. This includes 23 transcripts on mitochondrial DNA. Pathway analysis demonstrated predominant changes in the expression of genes involved in oxidative phosphorylation, glucose and fatty acid metabolism, and apoptosis. The most upregulated genes after 24 h of hypoxia included hypoxia-inducible factor 1, alpha subunit, inducible genes Bnip3, Pdk1, and Aldoc. Whereas Bnip3 is important in the cardiomyocyte death pathway, Pdk1 enzyme is critical in conserving mitochondrial function by diverting metabolic intermediates to glycolysis. This study identifies the participation of two important pathways, cell death and glycolytic, and two key proteins, Bnip3 and Pdk1, playing critical roles in these pathways in cardiomyocytes after severe hypoxia.

Unraveling Environmental Effects on Mitochondria

Look into any cell today, and you’ll see remnants of ancient bacteria by the thousands. These mitochondria—tiny organelles in the cell that each possess their own DNA—have come under a growing scientific spotlight; scientists increasingly believe they play a central role in many, if not most, human illnesses. Exquisitely sensitive to environmental threats, mitochondria convert dietary sugars into a high-energy molecule—adenosine triphosphate (ATP)—that cells use as fuel. And when mitochondria falter, cells lose power, just as a flashlight dims when its batteries weaken. Now scientists are linking environmental interactions with the mitochondria to an array of metabolic and age-related maladies, including cancer, autism, type 2 diabetes, Alzheimer disease, Parkinson disease, and cardiovascular illness.

Regulation of mitochondrial biogenesis

Although it is well established that physical activity increases mitochondrial content in muscle, the molecular mechanisms underlying this process have only recently been elucidated. Mitochondrial dysfunction is an important component of different diseases associated with aging, such as Type 2 diabetes and Alzheimer's disease. PGC-1alpha (peroxisome-proliferator-activated receptor gamma co-activator-1alpha) is a co-transcriptional regulation factor that induces mitochondrial biogenesis by activating different transcription factors, including nuclear respiratory factor 1 and nuclear respiratory factor 2, which activate mitochondrial transcription factor A. The latter drives transcription and replication of mitochondrial DNA. PGC-1alpha itself is regulated by several different key factors involved in mitochondrial biogenesis, which will be reviewed in this chapter. Of those, AMPK (AMP-activated protein kinase) is of major importance. AMPK acts as an energy sensor of the cell and works as a key regulator of mitochondrial biogenesis. AMPK activity has been shown to decrease with age, which may contribute to decreased mitochondrial biogenesis and function with aging. Given the potentially important role of mitochondrial dysfunction in the pathogenesis of numerous diseases and in the process of aging, understanding the molecular mechanisms regulating mitochondrial biogenesis and function may provide potentially important novel therapeutic targets.

Deoxynucleoside Salvage Enzymes and Tissue Specific Mitochondrial DNA Depletion

Adequate mitochondrial DNA (mtDNA) copies are required for normal mitochondria function and reductions in mtDNA copy number due to genetic alterations cause tissue-specific mtDNA depletion syndrome (MDS). There are eight nuclear genes, directly or indirectly involved in mtDNA replication and mtDNA precursor synthesis, which have been identified as the cause of MDS. However, the tissue specific pathology of these nuclear gene mutations is not well understood. Here, mtDNA synthesis, mtDNA copy number control, and mtDNA turnover, as well as the synthesis of mtDNA precursors in relation to the levels of salvage enzymes are discussed. The question why MDS caused by TK2 and p53R2 mutations are predominantly muscle specific while dGK deficiency affected mainly liver will be addressed.

Mitochondrial DNA transcription in mouse liver, skeletal muscle, and brain following lethal X-ray irradiation

Using quantitative real-time PCR, the levels of mitochondrial DNA transcripts in murine tissues (skeletal muscle, liver, and brain) were determined at different time points (1, 5, and 24 h) following X-ray irradiation at the dose of 10 Gy. One hour after irradiation the levels of mitochondrial transcripts ND2, ND4, CYTB, and ATP6 dramatically decreased by 85-95% and remained at the same minimum level for 24 h in all analyzed tissues. This decrease was not associated with depletion of mtDNA as a matrix for transcription, since mtDNA copy number increased after irradiation in all tissues. The decrease in mitochondrial transcription in liver, brain, and skeletal muscle did not generally result from the damage of cell transcription apparatus, because the transcription level of nuclear housekeeping gene BETA-ACTIN remained virtually unchanged after irradiation. The mitochondrial gene transcription decreased after irradiation in the same manner as that of the nuclear gene TFB2M encoding mitochondrial transcription factor, whose regulatory role under normal conditions is well understood.

Abstract 122: Mitochondrial dysregulation and cellular death resistance in response to genotoxic stress

Abstract Cellular death resistance is at the foundation of neoplastic progression. Our objective is to identify mechanisms by which genotoxin exposure of normal human cells may lead to intrinsic alterations allowing for selection of survivors with a growth-advantaged phenotype. Certain forms of hexavalent chromium [(Cr(VI)] are human respiratory carcinogens/oxidizing agents. We have generated populations of BJ-hTERT fibroblasts (stably transfected with the telomerase gene), which have acquired resistance to Cr(VI)-induced death, that was not related to DNA adduct formation. In the present study, subclones were derived from clonogenic survivors of BJ-hTERT cells treated with either 0 µM (CC) or a single exposure to 5 µM (DR1 and DR2) Cr(VI). We investigated caspase 3 cleavage in these lines after 24 h exposure to Cr(VI). CC cells exhibited a >70 fold increase in cleaved caspase 3 expression after Cr(VI) treatment, accompanied by substantial release of mitochondrial cytochrome c, consistent with induction of the mitochondrial apoptosis pathway. In sharp contrast, DR1 and DR2 cells showed significant resistance to Cr(VI)-induced caspase 3 cleavage, which was ∼10 fold increase as compared to control, and Cr(VI)-induced cytochrome c release was negligible. Apoptotic resistance was not related to differences in either hTERT or p53 protein levels, which were similar among the cell lines before and after Cr(VI) treatment. We next investigated potential intrinsic mitochondrial alterations that may contribute to the observed apoptosis resistant phenotype. We measured mitochondrial (mt) DNA copy number by RT-PCR of the mtND1 gene, and found no difference among the cell lines, before or after Cr(VI) treatment. Notably, mtDNA is highly susceptible to oxidative damage. Amplification of an 8.9 kb mtDNA product has been shown to be inversely proportional to mtDNA damage. Intriguingly, our data show that the CC cells display 10-20% less amplifiable mtDNA, as compared to the DR cells (reaching statistical significance in DR1), with no effect of Cr(VI) treatment. Mitochondrial spare respiratory capacity (SRC) has been associated with maintenance of a cellular energy reserve in the face of oxidative stress. We measured basal SRC in the CC and DR cells after injection of 1.5 µM FCCP, a respiratory chain uncoupler. Of note, DR1 and DR2 cells showed a significant, ∼2-fold increase in oxygen consumption rate (OCR) as compared to CC cells, with no difference in basal OCR. Taken together, these data indicate that DR cells have both decreased mtDNA damage and increased SRC, which may be related to their intrinsic death resistance. In conclusion, our data suggest that cell survival after a single genotoxic insult involves the selection of cells with intrinsic mitochondrial dysregulation, leading to death resistance, which may play a role in neoplastic progression. Supported by NIH grants CA107972 to SC and supplement to KW, ES05304 and ES09961 to SRP. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 122.

Mitochondrial DNA alterations and reduced mitochondrial function in aging

Oxidative damage to mitochondrial DNA increases with aging. This damage has the potential to affect mitochondrial DNA replication and transcription which could alter the abundance or functionality of mitochondrial proteins. This review describes mitochondrial DNA alterations and changes in mitochondrial function that occur with aging. Age-related alterations in mitochondrial DNA as a possible contributor to the reduction in mitochondrial function are discussed.

Expression of mitochondrial transcription factor A in endometrial carcinomas: clinicopathologic correlations and prognostic significance

Mitochondrial transcription factor A (mtTFA) is necessary for both transcription and maintenance of mitochondrial DNA. This study was conducted to elucidate the clinicopathologic and prognostic significance of mtTFA in patients with endometrial carcinoma. This study investigated the relationship between the immunohistochemical expression of mtTFA and various clinicopathological variables in 276 endometrial carcinomas, including 245 endometrioid adenocarcinomas and 31 nonendometrioid carcinomas (21 serous carcinomas and 10 clear cell adenocarcinomas). Both uni- and multivariate regression analyses were performed. The mtTFA labeling index of endometrioid adenocarcinomas ranged from 0% to 98%, with a median value of 32%, which was selected as the cut-off point for mtTFA expression. The mtTFA expression in endometrioid adenocarcinomas was significantly associated with the surgical stage, myometrial invasion, lymphovascular space invasion, cervical invasion, and lymph node metastasis. In contrast, no correlation between clinicopathologic variables and mtTFA expression was found in nonendometrioid carcinomas. Correlation analysis between mtTFA and p53 expression by using the Pearson test showed significant correlation in endometrioid adenocarcinomas (P = 0.007), but no significant correlation in nonendometrioid carcinomas (P = 0.947). A univariate survival analysis showed that the 10-year overall survival rate of the patients with mtTFA-positive endometrioid adenocarcinoma was significantly worse than that of patients with mtTFA-negative endometrioid adenocarcinoma (80.8% vs. 93.8%, P = 0.012). However, the multivariate analysis revealed that mtTFA expression in endometrioid adenocarcinomas was no independent prognostic factor. The positive mtTFA expression is a useful maker for progression of the tumors and the poor prognosis of the patients in endometrioid adenocarcinomas.

Cytonuclear conflict in interpopulation hybrids: the role of RNA polymerase in mtDNA transcription and replication

Organismal fitness requires functional integration of nuclear and mitochondrial genomes. Structural and regulatory elements coevolve within lineages and several studies have found that interpopulation hybridization disrupts mitonuclear interactions. Because mitochondrial RNA polymerase (mtRPOL) plays key roles in both mitochondrial DNA (mtDNA) replication and transcription, the interaction between mtRPOL and coevolved regulatory sites in the mtDNA may be central to mitonuclear integration. Here, we generate interpopulation hybrids between divergent populations of the copepod Tigriopus californicus to obtain lines having different combinations of mtRPOL and mtDNA. Lines were scored for mtDNA copy number and ATP6 (mtDNA) gene expression. We find that there is a genotype-dependent negative association between mitochondrial transcriptional response and mtDNA copy number. We argue that an observed increase in mtDNA copy number and reduced mtDNA transcription in hybrids reflects the regulatory role of mtRPOL; depending on the mitonuclear genotype, hybridization may disrupt the normal balance between transcription and replication of the mitochondrial genome.