Targeted inhibition of ATP5B gene prevents bone erosion in collagen-induced arthritis by inhibiting osteoclastogenesis.

Bone resorption by osteoclasts is an energy consuming activity, which depends on mitochondrial ATP. ATP5B, a mitochondrial ATP synthase beta subunit, is a catalytic core involved in producing ATP. Here, we investigated the contribution of ATP5B in osteoclast differentiation and joint destruction. ATP5B (LV-ATP5B) targeting or non-targeting (LV-NC) siRNA containing lentivirus particles were transduced into bone marrow macrophage derived osteoclasts or locally administered to arthritic mouse joints. Inhibition of ATP5B reduced the expression of osteoclast related genes and proteins, suppressed bone resorption by significantly impairing F-actin formation and decreased the levels of adhesion-associated proteins. In addition, ATP5B deficiency caused osteoclast mitochondrial dysfunction and, impaired the secretion of vacuole protons and MMP9. Importantly, inhibition of ATP5B expression, protected arthritis mice from joint destructions although serum levels of inflammatory mediators (TNF-α, IL-1ß) and IgG2α antibodies were unaffected. These results demonstrate an essential function of ATP5B in osteoclast differentiation and bone resorption, and suggest it as a potential therapeutic target for protecting bones in RA.

Current understanding of structure, function and biogenesis of yeast mitochondrial ATP synthase.

The yeast mitochondrial ATP synthase is a rotary molecular machine primarily responsible for the production of energy used to drive cellular processes. The enzyme complex is composed of 17 different subunits grouped into a soluble F1 sector and a membrane-embedded F0 sector. The catalytic head of the F1 sector and the membrane integrated motor module in the F0 sector are connected by two stalks, the F1 central stalk and the F0 peripheral stalk. Proton translocation through the F0 motor module drives the rotation of the subunit 910-ring that generates torque which is transmitted to the calaytic head through the γ subunit of the central stalk. The rotation of the γ subunit causes changes in conformation of the catalytic head which leads to the synthesis of ATP. Biogenesis of the enzyme involves modular assembly of polypeptides of dual genetic origin, the nuclear and the mitochondrial genomes. Most of the yeast ATP synthase subunits are encoded by the genome of the nucleus, translated on cytosolic ribosomes and imported into mitochondria. In the mitochondria, the enzyme forms a dimer which contributes to the formation of cristae, a characteristic of mitochondrial morphology. Substantial progress has recently been made on the elucidation of detailed stucture, function and biogenesis of yeast mitochondrial ATP synthase. The recent availability of high-resolution structure of the complete monomeric form, as well as the atomic model for the dimeric F0 sector, has advanced the understanding of the enzyme complex. This review is intended to provide an overview of current understanding of the molecular structure, catalytic mechanism, subunit import into mitochondria, and the subunit assembly into the enzyme complex. This is important as the yeast mitochondrial ATP synthase may be used as a model for understanding the corresponding enzyme complexes from human and other eukaryotic cells in physiological and diseased states.

Knockout of Tmem70 alters biogenesis of ATP synthase and leads to embryonal lethality in mice.

TMEM70, a 21-kDa protein localized in the inner mitochondrial membrane, has been shown to facilitate the biogenesis of mammalian F1Fo ATP synthase. Mutations of the TMEM70 gene represent the most frequent cause of isolated ATP synthase deficiency resulting in a severe mitochondrial disease presenting as neonatal encephalo-cardiomyopathy (OMIM 604273). To better understand the biological role of this factor, we generated Tmem70-deficient mice and found that the homozygous Tmem70-/- knockouts exhibited profound growth retardation and embryonic lethality at ∼9.5 days post coitum. Blue-Native electrophoresis demonstrated an isolated deficiency in fully assembled ATP synthase in the Tmem70-/- embryos (80% decrease) and a marked accumulation of F1 complexes indicative of impairment in ATP synthase biogenesis that was stalled at the early stage, following the formation of F1 oligomer. Consequently, a decrease in ADP-stimulated State 3 respiration, respiratory control ratio and ATP/ADP ratios, indicated compromised mitochondrial ATP production. Tmem70-/- embryos exhibited delayed development of the cardiovascular system and a disturbed heart mitochondrial ultrastructure, with concentric or irregular cristae structures. Tmem70+/- heterozygous mice were fully viable and displayed normal postnatal growth and development of the mitochondrial oxidative phosphorylation system. Nevertheless, they presented with mild deterioration of heart function. Our results demonstrated that Tmem70 knockout in the mouse results in embryonic lethality due to the lack of ATP synthase and impairment of mitochondrial energy provision. This is analogous to TMEM70 dysfunction in humans and verifies the crucial role of this factor in the biosynthesis and assembly of mammalian ATP synthase.

All trans retinoic acid depresses the content and activity of the mitochondrial ATP synthase in human keratinocytes.

Proteomic analysis shows that treatment of keratinocytes cultures with all trans retinoic acid (ATRA), under condition in which it inhibits cell growth, results in marked decrease of the level of the F1-ß subunit of the catalytic sector of the mitochondrial FoF1 ATP synthase complex. Enzymatic analysis shows in ATRA-treated keratinocytes a consistent depression of the ATPase activity, with decreased olygomycin sensitivity, indicating an overall alteration of the ATP synthase complex. These findings, together with the previously reported inhibition of respiratory complex I, show that depression of the activity of oxidative phosphorylation enzymes is involved in the cell growth inhibitory action of ATRA.

Developmental defect of cytochrome oxidase mutants of Streptomyces coelicolor A3(2).

To study the link between energy metabolism and secondary metabolism/morphological development in Streptomyces, knockout mutants were generated with regard to the subunits of the cytochrome oxidase supercomplex (CcO) in Streptomyces coelicolor A3(2). All mutants exhibited an identical phenotype: viable but defective in antibiotic production and cell differentiation when grown in both complex and minimal media. The growth yield of the CcO mutant was about half of that of the WT strain on glucose medium while both strains grew similarly on maltose medium. Intracellular ATP measurement demonstrated that the CcO mutant exhibited high intracellular ATP level. A similar elevation of intracellular ATP level was observed with regard to the WT strain cultured in the presence of BCDA, a copper-chelating agent. Reverse transcriptase PCR analysis demonstrated that the transcription of ATP synthase operon is upregulated in the CcO mutant. Addition of carbonylcyanide m-chlorophenylhydrazone, an inhibitor of ATP synthesis, promoted antibiotic production and aerial mycelia formation in the CcO mutant and BCDA-treated WT cells. We hypothesize that the deficiency of CcO causes accumulation of intracellular ATP, and that the high ATP level inhibits the onset of development in S. coelicolor.

Humanin Derivatives Inhibit Necrotic Cell Death in Neurons.

Humanin and its derivatives are peptides known for their protective antiapoptotic effects against Alzheimer's disease. Herein, we identify a novel function of the humanin-derivative AGA(C8R)-HNG17 (namely, protection against cellular necrosis). Necrosis is one of the main modes of cell death, which was until recently considered an unmoderated process. However, recent findings suggest the opposite. We have found that AGA(C8R)-HNG17 confers protection against necrosis in the neuronal cell lines PC-12 and NSC-34, where necrosis is induced in a glucose-free medium by either chemohypoxia or by a shift from apoptosis to necrosis. Our studies in traumatic brain injury models in mice, where necrosis is the main mode of neuronal cell death, have shown that AGA(C8R)-HNG17 has a protective effect. This result is demonstrated by a decrease in a neuronal severity score and by a reduction in brain edema, as measured by magnetic resonance imaging (MRI). An insight into the peptide's antinecrotic mechanism was attained through measurements of cellular ATP levels in PC-12 cells under necrotic conditions, showing that the peptide mitigates a necrosis-associated decrease in ATP levels. Further, we demonstrate the peptide's direct enhancement of the activity of ATP synthase activity, isolated from rat-liver mitochondria, suggesting that AGA(C8R)-HNG17 targets the mitochondria and regulates cellular ATP levels. Thus, AGA(C8R)-HNG17 has potential use for the development of drug therapies for necrosis-related diseases, for example, traumatic brain injury, stroke, myocardial infarction, and other conditions for which no efficient drug-based treatment is currently available. Finally, this study provides new insight into the mechanisms underlying the antinecrotic mode of action of AGA(C8R)-HNG17.

Molecular Analysis by Gene Expression of Mitochondrial ATPase Subunits in Papillary Thyroid Cancer: Is ATP5E Transcript a Possible Early Tumor Marker?

BACKGROUND: Cancer development involves an "injury" to the respiratory machinery (Warburg effect) due to decreased or impaired mitochondrial function. This circumstance results in a down regulation of some of the ATPase subunits of the malignant tissue. The objective of this work was to assess and compare the relative expression of mRNA of mitochondrial ATPase subunits between samples of thyroid cancer and benign nodules. MATERIAL AND METHODS: Samples from 31 patients who had an operation for PTC at the General Hospital of Mexico were snap-frozen and stored at -70°C. Thirty-five patients who had an operation for benign tumors were also included in the study. mRNA expression levels of alpha, beta, gamma, and epsilon subunits of F1 and "c12" of subunit Fo were determined by real-time RT-PCR (by duplicate), in order to determine if abnormal expression of these genes could partially explain the Warburg effect in papillary thyroid cancer (PTC). RESULTS: ATP5E transcript alteration (down-expression) was highly associated to PTC diagnosis OR=11.76 (95% confidence interval, 1.245-237.98; p=0.04). CONCLUSIONS: Relative down-expression of ATP5E transcript was highly associated with PTC diagnosis. This transcript alteration may be used as a tumoral marker in papillary thyroid cancer.

Deletion of the transcriptional regulator opi1p decreases cardiolipin content and disrupts mitochondrial metabolism in Saccharomyces cerevisiae.

Cardiolipin, the main anionic phospholipid in the inner mitochondrial membrane, provides shape, charge and osmotic support to this membrane due to its biophysical properties. In addition, it helps form respiratory supercomplexes and provides functionality to mitochondrial proteins. Defects in the biosynthesis or remodeling of cardiolipin have been related to severe diseases, such as Barth syndrome. Opi1p, a transcriptional repressor for most enzymes in phospholipid biosynthesis found in Saccharomyces cerevisiae, has been demonstrated not to affect the biosynthesis of this mitochondrial phospholipid. However, we found that opi1 deletion compromises mitochondrial metabolism producing severe respiratory defects. The mechanism producing this phenotype was explored and found to be a mitochondrial cardiolipin depletion of almost 50%, resulting in low cytochrome content and high mitochondrial DNA instability. The origin of this low cardiolipin content strongly correlated with the overproduction of inositol, an intrinsic phenotype of this mutation. Overall, our results show that adequate regulation of phospholipid synthesis is essential for the maintenance of mitochondrial function.

Glucocorticoid receptor is involved in the breed-dependent transcriptional regulation of mtDNA- and nuclear-encoded mitochondria genes in the liver of newborn piglets.

BACKGROUND: Mitochondria, which are essential for the functionality of eukaryotic cells, are particularly important in metabolically active tissues such as liver. Different breeds of pigs demonstrate distinct metabolic profiles in the liver, yet little is known whether the expression and transcriptional regulation of mitochondrial genes differ between breeds. RESULTS: Here we used male newborn Large White (LW) and Erhualian (EHL) piglets to delineate the difference in hepatic mitochondrial gene regulation between breeds. The hepatic content of ATP was significantly higher (p < 0.01) in EHL piglets, which was associated with lower mtDNA copy number (p < 0.05). Most of the mtDNA-encoded genes (10 of 13), however, were more abundantly expressed in EHL compared to LW piglets. We also detected 3 differentially expressed nuclear-encoded mitochondrial genes, among which isocitrate dehydrogenase 2 (IDH2) and ATP synthase, H+ transporting, mitochondrial Fo complex, subunit d (ATP5H) were expressed significantly lower, while adenylate kinase 1 (AK1) was significantly over expressed in EHL piglets. Compared to LW, the over expression of mtDNA-encoded genes in EHL was associated with significantly higher (p < 0.01) glucocorticoid receptor (GR) binding to the control region of mtDNA with no alterations in the methylation status. For nuclear-encoded genes, however, a negative correlation was observed between GR binding and mRNA expression of AK1 and ATP5H. Moreover, higher expression of AK1 in EHL piglets was also associated with lower cytosine methylation (p < 0.05) and hydroxymethylation (p < 0.05). In the promoter region. CONCLUSIONS: These results indicate a role of the GR in the breed-dependent regulation of mitochondrial genes in the liver of newborn piglets.

Nuclear expression of a mitochondrial DNA gene: mitochondrial targeting of allotopically expressed mutant ATP6 in transgenic mice.

Nuclear encoding of mitochondrial DNA transgenes followed by mitochondrial targeting of the expressed proteins (allotopic expression; AE) represents a potentially powerful strategy for creating animal models of mtDNA disease. Mice were created that allotopically express either a mutant (A6M) or wildtype (A6W) mt-Atp6 transgene. Compared to non-transgenic controls, A6M mice displayed neuromuscular and motor deficiencies (wire hang, pole, and balance beam analyses; P < 0.05), no locomotor differences (gait analysis; P < 0.05) and enhanced endurance in Rota-Rod evaluations (P < 0.05). A6W mice exhibited inferior muscle strength (wire hang test; P < 0.05), no difference in balance beam footsteps, accelerating Rota-Rod, pole test and gait analyses; (P < 0.05) and superior performance in balance beam time-to-cross and constant velocity Rota-Rod analyses (P < 0.05) in comparison to non-transgenic control mice. Mice of both transgenic lines did not differ from non-transgenic controls in a number of bioenergetic and biochemical tests including measurements of serum lactate and mitochondrial MnSOD protein levels, ATP synthesis rate, and oxygen consumption (P > 0.05). This study illustrates a mouse model capable of circumventing in vivo mitochondrial mutations. Moreover, it provides evidence supporting AE as a tool for mtDNA disease research with implications in development of DNA-based therapeutics.

Purification, characterization and reconstitution into membranes of the oligomeric c-subunit ring of thermophilic F(o)F(1)-ATP synthase expressed in Escherichia coli.

F(o)F(1)-ATP synthase catalyzes ATP synthesis coupled with proton-translocation across the membrane. The membrane-embedded F(o) portion is responsible for the H(+) translocation coupled with rotation of the oligomeric c-subunit ring, which induces rotation of the γ subunit of F(1). For solid-state NMR measurements, F(o)F(1) of thermophilic Bacillus PS3 (TF(o)F(1)) was overexpressed in Escherichia coli and the intact c-subunit ring (TF(o)c-ring) was isolated by new procedures. One of the key improvement in this purification was the introduction of a His residue to each c-subunit that acts as a virtual His(10)-tag of the c-ring. After solubilization from membranes by sodium deoxycholate, the c-ring was purified by Ni-NTA affinity chromatography, followed by anion-exchange chromatography. The intactness of the isolated c-ring was confirmed by high-resolution clear native PAGE, sedimentation analysis, and H(+)-translocation activity. The isotope-labeled intact TF(o)c-ring was successfully purified in such an amount as enough for solid-state NMR measurements. The isolated TF(o)c-rings were reconstituted into lipid membranes. A solid-state NMR spectrum at a high quality was obtained with this membrane sample, revealing that this purification procedure was suitable for the investigation by solid-state NMR. The purification method developed here can also be used for other physicochemical investigations.

EF-1α and mitochondrial ATP synthase ß chain: alteration of their expression in encystment-induced Colpoda cucullus.

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the total proteins contained in encystment-induced Colpoda cucullus showed that a 50-kDa protein (p50) disappeared, whereas the expression of a 49-kDa protein (p49) was enhanced in early phase of morphogenetic transformation into the resting cyst (i.e. 2-5 h after the onset of encystment induction). Puromycin or actinomycin D inhibited the alteration in the expression of p50 and p49 by the induction of encystment. These results suggest that the encystment-specific alteration in expression of these proteins is performed by a transcriptional regulation. Liquid chromatography tandem mass spectrometry analysis revealed that p50 is mitochondrial ATP synthase ß chains, and that p49 is elongation factor 1α.

Shrimp ATP synthase genes complement yeast null mutants for ATP hydrolysis but not synthesis activity.

The aim of this study was to examine the feasibility of employing a yeast functional complementation assay for shrimp genes by using the shrimp mitochondrial F(1)F(0)-ATP synthase enzyme complex as a model. Yeast mutants defective in this complex are typically respiratory-deficient and cannot grow on non-fermentable carbon sources such as glycerol, allowing easy verification of functional complementation by yeast growth on media with them as the only carbon source. We cloned the previous published sequence of ATP2 (coding for ATP synthase ß subunit) from the Pacific white shrimp Penaeus vannamei (Pv) and also successfully amplified a novel PvATP3 (coding for the ATP synthase γ subunit). Analysis of the putative amino acid sequence of PvATP3 revealed a significant homology with the ATP synthase γ subunit of crustaceans and insects. Complementation assays were performed using full-length ATP2 and ATP3 as well as a chimeric form of ATP2 containing a leader peptide sequence from yeast and a mature sequence from shrimp. However, the shrimp genes were unable to complement the growth of respective yeast mutants on glycerol medium, even though transcriptional expression of the shrimp genes from plasmid-borne constructs in the transformed yeast cells was confirmed by RT-PCR. Interestingly, both PvATP2 and PvATP3 suppressed the lethality of the yeast F(1) mutants after the elimination of mitochondrial DNA, which suggests the assembly of a functional F(1) complex necessary for the maintenance of membrane potential in the ρ(0) state. These data suggest an incompatibility of the shrimp/yeast chimeric F(1)-ATPase with the stalk and probably also the F(0) sectors of the ATP synthase, which is essential for coupled energy transduction and ATP synthesis.

The effect of oral melatonin supplementation on MT-ATP6 gene expression and IVF outcomes in Iranian infertile couples: a nonrandomized controlled trial.

This study aims to evaluate the effect of melatonin supplementation on the outcomes of in vitro fertilization (IVF) and mitochondrial adenosine triphosphate production (MT-ATP6) gene expression in Iranian infertile couples. A single-blind nonrandomized controlled trial was conducted, recruiting 90 infertile couples who underwent IVF at an infertility center in Tehran, Iran. Patients who were assigned to the intervention group received melatonin as a supplementation to the standard controlled ovarian stimulation (COS). The control group received a COS protocol only. Primary outcome was the mRNA level of the MT-ATP6 gene in cumulus cells of ovarian follicles. Secondary outcomes were the mean number of mature oocytes retrieved, the embryo quality, and biochemical and clinical pregnancy rates. The mRNA level of the MT-ATP6 gene in cumulus cells between intervention and control groups was not statistically different (0.931 vs.1; P Ëƒ 0.05). The mean number of poor-quality embryos was significantly lower in the intervention group than that in the control group (0.27 vs. 0.80; P = 0.028). The biochemical and clinical pregnancy rates were higher in the intervention group (24% vs. 14%, P = 0.089, and 14% vs. 7%, P = 0.302, respectively); however, the difference was not significant. Melatonin supplementation did not increase the odds of clinical pregnancy and the number of mature oocytes retrieved, but significantly reduced the number of low-quality embryos. More extensive studies focusing on the level of MT-ATP6 gene expression in the oocyte or blastomere cells may further elucidate the effect of supplementation with melatonin in infertile couples who have poor clinical outcomes. Trial registration: Current Controlled Trials: IRCT2015042912307N4.

Comparative proteomic analysis of human placenta derived from assisted reproductive technology.

The aim of this study was to use proteomics-based approach to examine differences in protein expression in placenta derived from assisted reproductive technology (ART) and normal pregnancy. Using 2-DE we found that, compared with the control group, 12 spots in standard in vitro fertilization group and 18 spots in intracytoplasmic sperm injection group were identified as significantly differentially expressed proteins. Among them, six spots were differentially expressed in both standard IVF and ICSI groups with the same change tendency. Totally, 20 proteins were successfully identified by MALDI TOF/TOF MS, including proteins involved in the membrane traffic, metabolism, nucleic acid processing, stress response and cytoskeleton. Notably, five proteins detected to be differentially expressed in both ART groups were identified as annexin A3, hnRNP C1/C2, alpha-SNAP, FTL and ATP5A. Some of the proteins were confirmed by Western blot and immunohistochemistry analysis. Our study allowed for the initial identification of these proteins related to various functions in placentation with significantly altered abundance in ART groups. The present results reveal that abnormal protein profiles are involved in ART placenta and these differentially expressed proteins may be valuable for the evaluation of potential association between ART treatment and offspring outcome.

Mitochondrial diseases and genetic defects of ATP synthase.

ATP synthase is a key enzyme of mitochondrial energy conversion. In mammals, it produces most of cellular ATP. Alteration of ATP synthase biogenesis may cause two types of isolated defects: qualitative when the enzyme is structurally modified and does not function properly, and quantitative when it is present in insufficient amounts. In both cases the cellular energy provision is impaired, and diminished use of mitochondrial DeltamuH+ promotes ROS production by the mitochondrial respiratory chain. The primary genetic defects have so far been localized in mtDNA ATP6 gene and nuclear ATP12 gene, however, involvement of other nuclear genes is highly probable.

Lithium increases PGC-1alpha expression and mitochondrial biogenesis in primary bovine aortic endothelial cells.

Lithium is a therapeutic agent commonly used to treat bipolar disorder and its beneficial effects are thought to be due to a combination of activation of the Wnt/beta-catenin pathway via inhibition of glycogen synthase kinase-3beta and depletion of the inositol pool via inhibition of the inositol monophosphatase-1. We demonstrated that lithium in primary endothelial cells induced an increase in mitochondrial mass leading to an increase in ATP production without any significant change in mitochondrial efficiency. This increase in mitochondrial mass was associated with an increase in the mRNA levels of mitochondrial biogenesis transcription factors: nuclear respiratory factor-1 and -2beta, as well as mitochondrial transcription factors A and B2, which lead to the coordinated upregulation of oxidative phosphorylation components encoded by either the nuclear or mitochondrial genome. These effects of lithium on mitochondrial biogenesis were independent of the inhibition of glycogen synthase kinase-3beta and independent of inositol depletion. Also, expression of the coactivator PGC-1alpha was increased, whereas expression of the coactivator PRC was not affected. Lithium treatment rapidly induced a decrease in activating Akt-Ser473 phosphorylation and inhibitory Forkhead box class O (FOXO1)-Thr24 phosphorylation, as well as an increase in activating c-AMP responsive element binding (CREB)-Ser133 phosphorylation, two mechanisms known to control PGC-1alpha expression. Together, our results show that lithium induces mitochondrial biogenesis via CREB/PGC-1alpha and FOXO1/PGC-1alpha cascades, which highlight the pleiotropic effects of lithium and reveal also novel beneficial effects via preservation of mitochondrial functions.

High glucose promotes the release and expression of novel vasoactive peptide, coupling factor 6, in human umbilical vein endothelial cells.

As a novel vasoactive peptide, plasma coupling factor 6 (CF6) was shown to be elevated in patients with diabetes mellitus, yet the mechanism involved is unknown. We studied CF6 protein release and its potential mechanism in human umbilical vein endothelial cells (HUVECs) incubated with high glucose levels. High glucose level enhanced CF6 expression and peptide secretion in HUVECs in a time- and concentration-dependent manner, which was independent of increased osmolarity. PKC or p38 MAPK inhibition significantly suppressed high glucose-mediated CF6 release in HUVECs, and the inhibition rate was -45% and -30%, respectively. Also, high glucose-induced CF6 production was antagonized by insulin treatment. Hence, high glucose increases the expression and secretion of CF6 in endothelial cells and appears to be mediated by PKC and p38 MAPK activity.

Down-regulation of mitochondrial F1F0-ATP synthase in human colon cancer cells with induced 5-fluorouracil resistance.

5-Fluorouracil (5-FU) is widely used for treatment of advanced colorectal cancer. However, it is common for such patients to develop resistance to 5-FU, and this drug resistance becomes a critical problem for chemotherapy. The mechanisms underlying this resistance are largely unknown. To screen for proteins possibly responsible for 5-FU resistance, cells resistant to 5-FU were derived from human colon cancer cell lines and two-dimensional gel electrophoresis-based comparative proteomics was done. Two-dimensional gel electrophoresis data showed there was lower expression of the alpha subunit of mitochondrial F(1)F(0)-ATP synthase (ATP synthase) in 5-FU-resistant cells compared with parent cells. Western blotting showed that expression of other ATP synthase complex subunits was also lower in 5-FU-resistant cell lines and that these resistant cells also showed decreased ATP synthase activity and reduced intracellular ATP content. The ATP synthase inhibitor, oligomycin A, strongly antagonized 5-FU-induced suppression of cell proliferation. When 5-FU sensitivity was compared with ATP synthase activity in six different human colon cancer cell lines, a positive correlation has been found. Furthermore, suppressed ATP synthase d-subunit expression by siRNA transfection increased cell viability in the presence of 5-FU. Bioenergetic dysfunction of mitochondria has been reported as a hallmark of many types of cancers (i.e., down-regulation of ATP synthase beta-subunit expression in liver, kidney, colon, squamous oesophageal, and lung carcinomas, as well as in breast and gastric adenocarcinomas). Our findings show that ATP synthase down-regulation may not only be a bioenergetic signature of colorectal carcinomas but may also lead to cellular events responsible for 5-FU resistance.

Nuclear-encoded mitochondrial complex I gene expression is restored to normal levels by inhibition of unedited ATP9 transgene expression in Arabidopsis thaliana.

Mitochondria play an important role during sporogenesis in plants. The steady state levels of the nuclear-encoded mitochondrial complex I (nCI), PSST, TYKY and NADHBP transcripts increase in flowers of male-sterile plants with impairment of mitochondrial function generated by the expression of the unedited version of ATP9 (u-ATP9). This suggests a nuclear control of nCI genes in response to the mitochondrial flaw. To evaluate this hypothesis, transgenic plants carrying the GUS reporter gene, under the control of the PSST, TYKY and NADHBP promoters, were constructed. We present evidence that suppression by antisense strategy of the expression of u-ATP9 restores the normal levels of three nCI transcripts, indicating that the increase in PSST, TYKY and NADHBP in plants with a mitochondrial flaw occurs at the transcriptional level. The data presented here support the hypothesis that a mitochondrial dysfunction triggers a retrograde signaling which induce some nuclear-encoded mitochondrial genes. Moreover, these results demonstrate that this is a valuable experimental model for studying nucleus-mitochondria cross-talk events.