Mitochondrial DNA

Overview of Mitochondria and role of mtDNA in Cancer

Image from Wikimedia Commons

Overview of Mitochondria: Mitochondria (plural of mitochondrion) are membrane-bound organelles (the cell's 'mini organs') found in nearly all cells which play a vital role as "cellular power plants" by generating adenosine triphosphate (ATP), used by cells as a source of chemical energy. Mitochondria also play a role in cellular signaling, cellular differentiation, cell death, control of the cell cycle and cell growth, and other roles. Mitochondria are unusual in that they contain their own DNA, whilst the rest of the human genome is concentrated in the nucleus of the cell. Also, Mitochondrial DNA is only inherited from mothers, whist the DNA in the cells nucleus is inherited from both mother and father.

The number of mitochondria in a cell varies according to the type of tissue; many cells have a single mitochondrion, but others can contain hundreds or even thousands of mitochondria. Mitochondrial proteins also vary depending on the type of tissue. Mitochondria are made up of compartments (see diagram) that carry out specialised roles.

Mitochondrial DNA (mtDNA) and Cancer: mtDNA has been linked carcinogenesis because of its high susceptibility to mutations and limited repair mechanisms in comparison to nuclear DNA. mtDNA lacks introns, so mutations tend to occur in coding sequences and it is thought that accumulation of these mutations may lead to tumor formation (Radpour et al, 2009). Research into of role of mtDNA mutations in cancer is advancing understanding of their functional role in carcinogenesis, value in diagnosis and monitoring, and potential therapeutic implications.

Mutations in mitochondrial genes are common in cancer, but they don't tend to inactivate mitochondrial energy metabolism as this would disadvantage the cancer cells ability to divide and proliferate. However, mutations may alter the bioenergetic and biosynthetic state of Mitochondria. "These states communicate with the nucleus through mitochondrial 'retrograde signalling' to modulate signal transduction pathways, transcriptional circuits and chromatin structure to meet the perceived mitochondrial and nuclear requirements of the cancer cell. Cancer cells then reprogramme adjacent stromal cells to optimize the cancer cell environment. These alterations activate out-of-context programmes that are important in development, stress response, wound healing and nutritional status" (Wallace, 2012)

Acknowledgements: Diagram of the structure of a mitochondrion from Wikimedia Commons under a Creative Commons CC0 license.

Recent Research Publications

Shen S, Zhang Y, Zhang R, Gong X
Sarsasapogenin induces apoptosis via the reactive oxygen species-mediated mitochondrial pathway and ER stress pathway in HeLa cells.
Biochem Biophys Res Commun. 2013; 441(2):519-24 [PubMed] Related Publications
Sarsasapogenin is a sapogenin from the Chinese medical herb Anemarrhena asphodeloides Bunge. In the present study, we revealed that sarsasapogenin exhibited antitumor activity by inducing apoptosis in vitro as determined by Hoechst staining analysis and double staining of Annexin V-FITC/PI. In addition, cell cycle arrest in G2/M phase was observed in sarsasapogenin-treated HeLa cells. Moreover, the results revealed that perturbations in the mitochondrial membrane were associated with the deregulation of the Bax/Bcl-2 ratio which led to the upregulation of cytochrome c, followed by activation of caspases. Meanwhile, treatment of sarsasapogenin also activated Unfolded Protein Response (UPR) signaling pathways and these changes were accompanied by increased expression of CHOP. Salubrinal (Sal), a selective inhibitor of endoplasmic reticulum (ER) stress, partially abrogated the sarsasapogenin-related cell death. Furthermore, sarsasapogenin provoked the generation of reactive oxygen species, while the antioxidant N-acetyl cysteine (NAC) effectively blocked the activation of ER stress and apoptosis, suggesting that sarsasapogenin-induced reactive oxygen species is an early event that triggers ER stress mitochondrial apoptotic pathways. Taken together, the results demonstrate that sarsasapogenin exerts its antitumor activity through both reactive oxygen species (ROS)-mediate mitochondrial dysfunction and ER stress cell death.

Related: Cervical Cancer

Ambrus AM, Islam AB, Holmes KB, et al.
Loss of dE2F compromises mitochondrial function.
Dev Cell. 2013; 27(4):438-51 [PubMed] Article available free on PMC after 25/11/2014 Related Publications
E2F/DP transcription factors regulate cell proliferation and apoptosis. Here, we investigated the mechanism of the resistance of Drosophila dDP mutants to irradiation-induced apoptosis. Contrary to the prevailing view, this is not due to an inability to induce the apoptotic transcriptional program, because we show that this program is induced; rather, this is due to a mitochondrial dysfunction of dDP mutants. We attribute this defect to E2F/DP-dependent control of expression of mitochondria-associated genes. Genetic attenuation of several of these E2F/DP targets mimics the dDP mutant mitochondrial phenotype and protects against irradiation-induced apoptosis. Significantly, the role of E2F/DP in the regulation of mitochondrial function is conserved between flies and humans. Thus, our results uncover a role of E2F/DP in the regulation of mitochondrial function and demonstrate that this aspect of E2F regulation is critical for the normal induction of apoptosis in response to irradiation.

Related: Apoptosis Bone Cancers Osteosarcoma

Millard M, Gallagher JD, Olenyuk BZ, Neamati N
A selective mitochondrial-targeted chlorambucil with remarkable cytotoxicity in breast and pancreatic cancers.
J Med Chem. 2013; 56(22):9170-9 [PubMed] Related Publications
Nitrogen mustards, widely used as chemotherapeutics, have limited safety and efficacy. Mitochondria lack a functional nucleotide excision repair mechanism to repair DNA adducts and are sensitive to alkylating agents. Importantly, cancer cells have higher intrinsic mitochondrial membrane potential (Δψmt) than normal cells. Therefore, selectively targeting nitrogen mustards to cancer cell mitochondria based on Δψmt could overcome those limitations. Herein, we describe the design, synthesis, and evaluation of Mito-Chlor, a triphenylphosphonium derivative of the nitrogen mustard chlorambucil. We show that Mito-Chlor localizes to cancer cell mitochondria where it acts on mtDNA to arrest cell cycle and induce cell death, resulting in a 80-fold enhancement of cell kill in a panel of breast and pancreatic cancer cell lines that are insensitive to the parent drug. Significantly, Mito-Chlor delayed tumor progression in a mouse xenograft model of human pancreatic cancer. This is a first example of repurposing chlorambucil, a drug not used in breast and pancreatic cancer treatment, as a novel drug candidate for these diseases.

Related: Breast Cancer Chlorambucil Cancer of the Pancreas Pancreatic Cancer

Giang AH, Raymond T, Brookes P, et al.
Mitochondrial dysfunction and permeability transition in osteosarcoma cells showing the Warburg effect.
J Biol Chem. 2013; 288(46):33303-11 [PubMed] Article available free on PMC after 15/11/2014 Related Publications
Metabolic reprogramming in cancer is manifested by persistent aerobic glycolysis and suppression of mitochondrial function and is known as the Warburg effect. The Warburg effect contributes to cancer progression and is considered to be a promising therapeutic target. Understanding the mechanisms used by cancer cells to suppress their mitochondria may lead to development of new approaches to reverse metabolic reprogramming. We have evaluated mitochondrial function and morphology in poorly respiring LM7 and 143B osteosarcoma (OS) cell lines showing the Warburg effect in comparison with actively respiring Saos2 and HOS OS cells and noncancerous osteoblastic hFOB cells. In LM7 and 143B cells, we detected markers of the mitochondrial permeability transition (MPT), such as mitochondrial swelling, depolarization, and membrane permeabilization. In addition, we detected mitochondrial swelling in human OS xenografts in mice and archival human OS specimens using electron microscopy. The MPT inhibitor sanglifehrin A reversed MPT markers and increased respiration in LM7 and 143B cells. Our data suggest that the MPT may play a role in suppression of mitochondrial function, contributing to the Warburg effect in cancer.

Related: Osteosarcoma

Agarwal AR, Yin F, Cadenas E
Metabolic shift in lung alveolar cell mitochondria following acrolein exposure.
Am J Physiol Lung Cell Mol Physiol. 2013; 305(10):L764-73 [PubMed] Related Publications
Acrolein, an α,β unsaturated electrophile, is an environmental pollutant released in ambient air from diesel exhausts and cooking oils. This study examines the role of acrolein in altering mitochondrial function and metabolism in lung-specific cells. RLE-6TN, H441, and primary alveolar type II (pAT2) cells were exposed to acrolein for 4 h, and its effect on mitochondrial oxygen consumption rates was studied by XF Extracellular Flux analysis. Low-dose acrolein exposure decreased mitochondrial respiration in a dose-dependent manner because of alteration in the metabolism of glucose in all the three cell types. Acrolein inhibited glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity, leading to decreased substrate availability for mitochondrial respiration in RLE-6TN, H441, and pAT2 cells; the reduced GAPDH activity was compensated in pAT2 cells by an increase in the activity of glucose-6-phosphate dehydrogenase, the regulatory control of the pentose phosphate pathway. The decrease in pyruvate from glucose metabolism resulted in utilization of alternative sources to support mitochondrial energy production: palmitate-BSA complex increased mitochondrial respiration in RLE-6TN and pAT2 cells. The presence of palmitate in alveolar cells for surfactant biosynthesis may prove to be the alternative fuel source for mitochondrial respiration. Accordingly, a decrease in phosphatidylcholine levels and an increase in phospholipase A2 activity were found in the alveolar cells after acrolein exposure. These findings have implications for understanding the decrease in surfactant levels frequently observed in pathophysiological situations with altered lung function following exposure to environmental toxicants.

Related: Lung Cancer

Qiu JX, He YQ, Wang Y, et al.
Plumbagin induces the apoptosis of human tongue carcinoma cells through the mitochondria-mediated pathway.
Med Sci Monit Basic Res. 2013; 19:228-36 [PubMed] Article available free on PMC after 15/11/2014 Related Publications
BACKGROUND: Plumbagin, a quinonoid constituent isolated from the root of Plumbago zeylanica L., has been proven to possess anti-tumor activity both in vitro and in vivo. However, its anti-tumor properties for human tongue carcinoma have not been reported. This study aimed to investigate the inhibitory effect and the underlying mechanism of plumbagin on the growth of human tongue carcinoma cells.
MATERIAL AND METHODS: Cell proliferation ability was detected by EdU incorporation assay and colony formation assay. Cell-cycle distribution was determined by flow cytometric analysis using propidium iodide (PI) staining. Cellular apoptosis was then evaluated by flow cytometry and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Western blotting was applied to assay the expression of Bax and Bcl-2.
RESULTS: Plumbagin inhibited the growth and proliferation of Tca8113 cells in vitro in a concentration- and time-dependent manner. The cell cycles of plumbagin-treated Tca8113 cells were arrested at the G2/M phase. Cells treated with plumbagin presented the characteristic morphological changes of apoptosis. The ratio of Bax/Bcl-2 was raised by plumbagin in a concentration-dependent manner.
CONCLUSIONS: These results indicate that plumbagin induces the apoptosis of Tca8113 cells through mitochondria-mediated pathway.

Related: Apoptosis Signal Transduction

Sohn YS, Tamir S, Song L, et al.
NAF-1 and mitoNEET are central to human breast cancer proliferation by maintaining mitochondrial homeostasis and promoting tumor growth.
Proc Natl Acad Sci U S A. 2013; 110(36):14676-81 [PubMed] Article available free on PMC after 15/11/2014 Related Publications
Mitochondria are emerging as important players in the transformation process of cells, maintaining the biosynthetic and energetic capacities of cancer cells and serving as one of the primary sites of apoptosis and autophagy regulation. Although several avenues of cancer therapy have focused on mitochondria, progress in developing mitochondria-targeting anticancer drugs nonetheless has been slow, owing to the limited number of known mitochondrial target proteins that link metabolism with autophagy or cell death. Recent studies have demonstrated that two members of the newly discovered family of NEET proteins, NAF-1 (CISD2) and mitoNEET (mNT; CISD1), could play such a role in cancer cells. NAF-1 was shown to be a key player in regulating autophagy, and mNT was proposed to mediate iron and reactive oxygen homeostasis in mitochondria. Here we show that the protein levels of NAF-1 and mNT are elevated in human epithelial breast cancer cells, and that suppressing the level of these proteins using shRNA results in significantly reduced cell proliferation and tumor growth, decreased mitochondrial performance, uncontrolled accumulation of iron and reactive oxygen in mitochondria, and activation of autophagy. Our findings highlight NEET proteins as promising mitochondrial targets for cancer therapy.

Related: Breast Cancer

Ha TK, Kim ME, Yoon JH, et al.
Galangin induces human colon cancer cell death via the mitochondrial dysfunction and caspase-dependent pathway.
Exp Biol Med (Maywood). 2013; 238(9):1047-54 [PubMed] Related Publications
Galangin is a member of flavonols and found in Alpinia officinarum, galangal root, and propolis. Previous studies have demonstrated that galangin has anti-cancer effects on several cancers, including melanoma, hepatoma, and leukaemia cells. However, anti-cancer activity of galangin on human colon cancer has not been established yet. In this study, we investigated the anti-cancer effects of galangin on two types of human colon cancer cells (HCT-15 and HT-29). We found that galangin induced apoptosis and DNA condensation of human colon cancer cells in a dose-dependent manner. We also determined that galangin increased the activation of caspase-3 and -9, and release of apoptosis inducing factor from the mitochondria into the cytoplasm by Western blot analysis. In addition, galangin induced human colon cancer cell death through the alteration of mitochondria membrane potential and dysfunction. These results suggest that galangin induces apoptosis of HCT-15 and HT-29 human colon cancer cells and may prove useful in the development of therapeutic agents for human colon cancer.

Related: Apoptosis Signal Transduction

Valenti D, de Bari L, Manente GA, et al.
Negative modulation of mitochondrial oxidative phosphorylation by epigallocatechin-3 gallate leads to growth arrest and apoptosis in human malignant pleural mesothelioma cells.
Biochim Biophys Acta. 2013; 1832(12):2085-96 [PubMed] Related Publications
Increasing evidence reveals a large dependency of epithelial cancer cells on oxidative phosphorylation (OXPHOS) for energy production. In this study we tested the potential of epigallocatechin-3-gallate (EGCG), a natural polyphenol known to target mitochondria, in inducing OXPHOS impairment and cell energy deficit in human epitheliod (REN cells) and biphasic (MSTO-211H cells) malignant pleural mesothelioma (MMe), a rare but highly aggressive tumor with high unmet need for treatment. Due to EGCG instability that causes H2O2 formation in culture medium, the drug was added to MMe cells in the presence of exogenous superoxide dismutase and catalase, already proved to stabilize the EGCG molecule and prevent EGCG-dependent reactive oxygen species formation. We show that under these experimental conditions, EGCG causes the selective arrest of MMe cell growth with respect to normal mesothelial cells and the induction of mitochondria-mediated apoptosis, as revealed by early mitochondrial ultrastructure modification, swelling and cytochrome c release. We disclose a novel mechanism by which EGCG induces apoptosis through the impairment of mitochondrial respiratory chain complexes, particularly of complex I, II and ATP synthase. This induces a strong reduction in ATP production by OXPHOS, that is not adequately counterbalanced by glycolytic shift, resulting in cell energy deficit, cell cycle arrest and apoptosis. The EGCG-dependent negative modulation of mitochondrial energy metabolism, selective for cancer cells, gives an important input for the development of novel pharmacological strategies for MMe.

Related: Apoptosis Lung Cancer Mesothelioma

Kim MJ, Yun HS, Hong EH, et al.
Depletion of end-binding protein 1 (EB1) promotes apoptosis of human non-small-cell lung cancer cells via reactive oxygen species and Bax-mediated mitochondrial dysfunction.
Cancer Lett. 2013; 339(1):15-24 [PubMed] Related Publications
Although end-binding protein 1 (EB1) is well known to regulate microtubule dynamics, the role of EB1 in apoptosis of non-small cell lung cancer (NSCLC) is poorly understood. Here, we investigated the molecular mechanism by which EB1 regulates apoptosis in H460, A549, and H1299 cells. Depletion of EB1 in A549 and H1299 cells, which express high levels of EB1, induced cell death in a p53-independent manner through over-production of reactive oxygen species (ROS) and Bax induction. This phenomenon was potentiated in radiation-treated EB1-knockdown cells and was largely blocked by N-acetyl-L-cysteine, a scavenger of ROS. ROS accelerated the activation of nuclear factor-kappa B (NF-κB) to promote transcriptional activity of Bax, an action that was accompanied by cytochrome c translocation and apoptosis-inducing factor (AIF) release. The NF-κB inhibitor, BAY 11-7082, potently inhibited the apoptosis induced by EB1 knockdown and radiation treatment, in association with diminished activity of the mitochondrial death pathway. Conversely, ectopic overexpression of EB1 in H460 cells, which express low levels of EB1, remarkably abrogated radiation-induced apoptosis and NF-κB-mediated mitochondrial dysfunction. Our data provide the first demonstration that down-regulation of EB1 promotes NSCLC cell death by inducing ROS-mediated, NF-κB-dependent Bax signaling cascades, a process in which cytochrome c and AIF play important roles, indicating a potential therapeutic benefit of EB1 in lung cancer.

Related: Apoptosis Non-Small Cell Lung Cancer Lung Cancer TP53

Zhdanov AV, Waters AH, Golubeva AV, et al.
Availability of the key metabolic substrates dictates the respiratory response of cancer cells to the mitochondrial uncoupling.
Biochim Biophys Acta. 2014; 1837(1):51-62 [PubMed] Related Publications
Active glycolysis and glutaminolysis provide bioenergetic stability of cancer cells in physiological conditions. Under hypoxia, metabolic and mitochondrial disorders, or pharmacological treatment, a deficit of key metabolic substrates may become life-threatening to cancer cells. We analysed the effects of mitochondrial uncoupling by FCCP on the respiration of cells fed by different combinations of Glc, Gal, Gln and Pyr. In cancer PC12 and HCT116 cells, a large increase in O2 consumption rate (OCR) upon uncoupling was only seen when Gln was combined with either Glc or Pyr. Inhibition of glutaminolysis with BPTES abolished this effect. Despite the key role of Gln, addition of FCCP inhibited respiration and induced apoptosis in cells supplied with Gln alone or Gal/Gln. For all substrate combinations, amplitude of respiratory responses to FCCP did not correlate with Akt, Erk and AMPK phosphorylation, cellular ATP, and resting OCR, mitochondrial Ca(2+) or membrane potential. However, we propose that proton motive force could modulate respiratory response to FCCP by regulating mitochondrial transport of Gln and Pyr, which decreases upon mitochondrial depolarisation. As a result, an increase in respiration upon uncoupling is abolished in cells, deprived of Gln or Pyr (Glc). Unlike PC12 or HCT116 cells, mouse embryonic fibroblasts were capable of generating pronounced response to FCCP when deprived of Gln, thus exhibiting lower dependence on glutaminolysis. Overall, the differential regulation of the respiratory response to FCCP by metabolic environment suggests that mitochondrial uncoupling has a potential for substrate-specific inhibition of cell function, and can be explored for selective cancer treatment.

Related: Apoptosis Cancer Prevention and Risk Reduction

Zheng H, Li S, Hsu P, Qu CK
Induction of a tumor-associated activating mutation in protein tyrosine phosphatase Ptpn11 (Shp2) enhances mitochondrial metabolism, leading to oxidative stress and senescence.
J Biol Chem. 2013; 288(36):25727-38 [PubMed] Article available free on PMC after 06/09/2014 Related Publications
Activating mutations in Ptpn11 (Shp2), a protein tyrosine phosphatase involved in diverse cell signaling pathways, are associated with pediatric leukemias and solid tumors. However, the pathogenic effects of these mutations have not been fully characterized. Here, we report that induction of the Ptpn11(E76K/+) mutation, the most common and active Ptpn11 mutation found in leukemias and solid tumors, in primary mouse embryonic fibroblasts resulted in proliferative arrest and premature senescence. As a result, apoptosis was markedly increased. These cellular responses were accompanied and mediated by up-regulation of p53 and p21. Moreover, intracellular levels of reactive oxygen species (ROS), byproducts of mitochondrial oxidative phosphorylation, were elevated in Ptpn11(E76K/+) cells. Since Shp2 is also distributed to the mitochondria (in addition to the cytosol), the impact of the Ptpn11(E76K/+) mutation on mitochondrial function was analyzed. These analyses revealed that oxygen consumption of Ptpn11(E76K/+) cells and the respiratory function of Ptpn11(E76K/+) mitochondria were significantly increased. Furthermore, we found that phosphorylation of mitochondrial Stat3, one of the substrates of Shp2 phosphatase, was greatly decreased in the mutant cells with the activating mutation Ptpn11(E76K/+). This study provides novel insights into the initial effects of tumor-associated Ptpn11 mutations.

Related: Cancer Prevention and Risk Reduction TP53

Whitaker HC, Patel D, Howat WJ, et al.
Peroxiredoxin-3 is overexpressed in prostate cancer and promotes cancer cell survival by protecting cells from oxidative stress.
Br J Cancer. 2013; 109(4):983-93 [PubMed] Article available free on PMC after 20/08/2014 Related Publications
OBJECTIVE: We have previously identified peroxiredoxin-3 (PRDX-3) as a cell-surface protein that is androgen regulated in the LNCaP prostate cancer (PCa) cell line. PRDX-3 is a member of the peroxiredoxin family that are responsible for neutralising reactive oxygen species.
EXPERIMENTAL DESIGN: PRDX-3 expression was examined in tissue from 32 patients using immunohistochemistry. Subcellular distribution was determined using confocal microscopy. PRDX-3 expression was determined in antiandrogen-resistant cell lines by western blotting and quantitative RT-PCR. The pathways of PRDX-3 overexpression and knockdown on apoptosis and response to oxidative stress were investigated using protein arrays.
RESULTS: PRDX-3 is upregulated in a number of endocrine-regulated tumours; in particular in PCa and prostatic intraepithelial neoplasia. Although the majority of PRDX-3 is localised to the mitochondria, we have confirmed that PRDX-3 at the cell membrane is androgen regulated. In antiandrogen-resistant LNCaP cell lines, PRDX-3 is upregulated at the protein but not RNA level. Resistant cells also possess an upregulation of the tricarboxylic acid (TCA) pathway and resistance to H₂O₂-induced apoptosis through a failure to activate pro-apoptotic pathways. Knockdown of PRDX-3 restored H₂O₂ sensitivity.
CONCLUSION: Our results suggest that PRDX-3 has an essential role in regulating oxidation-induced apoptosis in antiandrogen-resistant cells. PRDX-3 may have potential as a therapeutic target in castrate-independent PCa.

Related: Apoptosis Prostate Cancer

Jiang Y, Yang J, Yang C, et al.
Vitamin K4 induces tumor cytotoxicity in human prostate carcinoma PC-3 cells via the mitochondria-related apoptotic pathway.
Pharmazie. 2013; 68(6):442-8 [PubMed] Related Publications
Vitamin K4 (VK4) is a synthetic hydrophilic menadione compound, which is clinically used as hemostasis medicine. It has been reported that several vitamin Ks had inhibitory effects on various cancer cells. However, there is no report about VK4s anticancer activity. The goal of this study was to investigate the inhibitory effect of VK4 on human prostate PC-3 cells and the mechanisms involved. We found that VK4 dose-dependently inhibited cell proliferation in PC-3 cells with an IC50 value of about 20.94 microM. Hoechst 33258 Staining results showed that VK4 caused DNA fragmentation in PC-3 cells. PI staining results indicated that VK4-induced PC-3 cell cycle arrest at the S phase. Further mechanistic studies revealed that VK4-mediated induction of apoptosis in PC-3 cell is associated with disruption of mitochondrial membrane potential, down-regulation of Bcl-2, and up-regulation of Bax, release of cytochrome c from mitochondria, and activation of caspase-3 and PARR Thus, VK4 might be useful in prostate cancer chemotherapy.

Related: Apoptosis Prostate Cancer

Wang X, Peralta S, Moraes CT
Mitochondrial alterations during carcinogenesis: a review of metabolic transformation and targets for anticancer treatments.
Adv Cancer Res. 2013; 119:127-60 [PubMed] Related Publications
Mitochondria play important roles in multiple cellular processes including energy metabolism, cell death, and aging. Regulated energy production and utilization are critical in maintaining energy homeostasis in normal cells and functional organs. However, mitochondria go through a series of morphological and functional alterations during carcinogenesis. The metabolic profile in transformed cells is altered to accommodate their fast proliferation, confer resistance to cell death, or facilitate metastasis. These transformations also provide targets for anticancer treatment at different levels. In this review, we discuss the major modifications in cell metabolism during carcinogenesis, including energy metabolism, apoptotic and autophagic cell death, adaptation of tumor microenvironment, and metastasis. We also summarize some of the main metabolic targets for treatments.

Related: Apoptosis Cancer Prevention and Risk Reduction

Yu JH, Zheng GB, Liu CY, et al.
Dracorhodin perchlorate induced human breast cancer MCF-7 apoptosis through mitochondrial pathways.
Int J Med Sci. 2013; 10(9):1149-56 [PubMed] Article available free on PMC after 20/08/2014 Related Publications
OBJECTIVE: Dracorhodin perchlorate (DP) was a synthetic analogue of the antimicrobial anthocyanin red pigment dracorhodin. It was reported that DP could induce apoptosis in human prostate cancer, human gastric tumor cells and human melanoma, but the cytotoxic effect of DP on human breast cancer was not investigated. This study would investigate whether DP was a candidate chemical of anti-human breast cancer.
METHODS: The MTT assay reflected the number of viable cells through measuring the activity of cellular enzymes. Phase contrast microscopy visualized cell morphology. Fluorescence microscopy detected nuclear fragmentation after Hoechst 33258 staining. Flowcytometric analysis of Annexin V-PI staining and Rodamine 123 staining was used to detect cell apoptosis and mitochondrial membrane potential (MMP). Real time PCR detected mRNA level. Western blot examined protein expression.
RESULTS: DP dose and time-dependently inhibited the growth of MCF-7 cells. DP inhibited MCF-7 cell growth through apoptosis. DP regulated the expression of Bcl-2 and Bax, which were mitochondrial pathway proteins, to decrease MMP, and DP promoted the transcription of Bax and inhibited Bcl-2. Apoptosis-inducing factor (AIF) and cytochrome c which localized in mitochondrial in physiological condition were released into cytoplasm when MMP was decreased. DP activated caspase-9, which was the downstream of mitochondrial pathway. Therefore DP decreased MMP to release AIF and cytochrome c into cytoplasm, further activating caspase 9, lastly led to apoptosis.
CONCLUSION: Therefore DP was a candidate for anti-breast cancer, DP induced apoptosis of MCF-7 through mitochondrial pathway.

Related: Apoptosis Breast Cancer Signal Transduction

Nie H, Shu H, Vartak R, et al.
Mitochondrial common deletion, a potential biomarker for cancer occurrence, is selected against in cancer background: a meta-analysis of 38 studies.
PLoS One. 2013; 8(7):e67953 [PubMed] Article available free on PMC after 20/08/2014 Related Publications
Mitochondrial dysfunction has been long proposed to play a major role in tumorigenesis. Mitochondrial DNA (mtDNA) mutations, especially the mtDNA 4,977 bp deletion has been found in patients of various types of cancer. In order to comprehend the mtDNA 4,977 bp deletion status in various cancer types, we performed a meta-analysis composed of 33 publications, in which a total of 1613 cancer cases, 1516 adjacent normals and 638 healthy controls were included. When all studies were pooled, we found that cancerous tissue carried a lower mtDNA 4,977 bp deletion frequency than adjacent non-cancerous tissue (OR = 0.43, 95% CI = 0.20-0.92, P = 0.03 for heterogeneity test, I(2) = 91.5%) among various types of cancer. In the stratified analysis by cancer type the deletion frequency was even lower in tumor tissue than in adjacent normal tissue of breast cancer (OR = 0.19, 95% CI = 0.06-0.61, P = 0.005 for heterogeneity test, I(2)= 82.7%). Interestingly, this observation became more significant in the stratified studies with larger sample sizes (OR = 0.70, 95% CI = 0.58-0.86, P = 0.0005 for heterogeneity test, I(2) = 95.1%). Furthermore, when compared with the normal tissue from the matched healthy controls, increased deletion frequencies were observed in both adjacent non-cancerous tissue (OR = 3.02, 95% CI = 2.13-4.28, P<0.00001 for heterogeneity test, I(2)= 53.7%), and cancerous tissue (OR = 1.36, 95% CI = 1.04-1.77, P = 0.02 for heterogeneity test, I(2)= 83.5%). This meta-analysis suggests that the mtDNA 4,977 bp deletion is often found in cancerous tissue and thus has the potential to be a biomarker for cancer occurrence in the tissue, but at the same time being selected against in various types of carcinoma tissues. Larger and better-designed studies are still warranted to confirm these findings.

Related: Cancer Prevention and Risk Reduction

Zhang L, Ren X, Cheng Y, et al.
Identification of Sirtuin 3, a mitochondrial protein deacetylase, as a new contributor to tamoxifen resistance in breast cancer cells.
Biochem Pharmacol. 2013; 86(6):726-33 [PubMed] Related Publications
The current study reports a previously unappreciated role of Sirtuin 3 (SIRT3), a mitochondrial protein deacetylase, in altering sensitivity of breast cancer cells to tamoxifen (Tam), a commonly used anti-estrogen agent. We showed that SIRT3 was significantly up-regulated at both mRNA and protein levels in the Tam-resistance human breast cancer cell line MTR-3, which was derived from MCF-7 line by continuous selective culture in the presence of 1μM of Tam for two years. We further demonstrated that SIRT3 was rapidly up-regulated in the sensitive MCF-7 cells following exposure to Tam. Transfection of MCF-7 cells with a SIRT3 expression plasmid decreased cellular sensitivity to Tam and blocked the Tam-induced apoptosis. Furthermore, silencing of SIRT3 expression in MTR-3 cells sensitized the resistant cells to Tam and enhanced apoptotic cell death. MTR-3 cells with silencing of SIRT3 expression showed increases in the mitochondrial content of ERβ, ROS level and apoptosis. These results not only uncovered a new role for SIRT3 in cancer but also identified this mitochondrial protein deacetylase as a previously unrecognized factor that participates in regulation of Tam sensitivity in breast cancer cells. Thus, SIRT3 might be considered as a potential target for overcoming Tam resistance in treatment of breast cancer.

Related: Apoptosis Breast Cancer Signal Transduction

Ussakli CH, Ebaee A, Binkley J, et al.
Mitochondria and tumor progression in ulcerative colitis.
J Natl Cancer Inst. 2013; 105(16):1239-48 [PubMed] Article available free on PMC after 21/08/2014 Related Publications
BACKGROUND: The role of mitochondria in cancer is poorly understood. Ulcerative colitis (UC) is an inflammatory bowel disease that predisposes to colorectal cancer and is an excellent model to study tumor progression. Our goal was to characterize mitochondrial alterations in UC tumorigenesis.
METHODS: Nondysplastic colon biopsies from UC patients with high-grade dysplasia or cancer (progressors; n = 9) and UC patients dysplasia free (nonprogressors; n = 9) were immunostained for cytochrome C oxidase (COX), a component of the electron transport chain, and were quantified by multispectral imaging. For six additional progressors, nondysplastic and dysplastic biopsies were stained for COX and additional mitochondrial proteins including PGC1α, the master regulator of mitochondrial biogenesis. Mitochondrial DNA (mtDNA) copy number was determined by quantitative polymerase chain reaction. Generalized estimating equations with two-sided tests were used to account for correlation of measurements within individuals.
RESULTS: Nondysplastic biopsies of UC progressors showed statistically significant COX loss compared with UC nonprogressors by generalized estimating equation (-18.5 units, 95% confidence interval = -12.1 to -24.9; P < .001). COX intensity progressively decreased with proximity to dysplasia and was the lowest in adjacent to dysplasia and dysplastic epithelium. Surprisingly, COX intensity was statistically significantly increased in cancers. This bimodal pattern was observed for other mitochondrial proteins, including PGC1α, and was confirmed by mtDNA copy number.
CONCLUSIONS: Mitochondrial loss precedes the development of dysplasia, and it could be used to detect and potentially predict cancer. Cancer cells restore mitochondria, suggesting that mitochondria are needed for further proliferation. This bimodal pattern might be driven by transcriptional regulation of mitochondrial biogenesis by PGC1α.

Related: Colorectal (Bowel) Cancer FISH

Hall A, Larsen AK, Parhamifar L, et al.
High resolution respirometry analysis of polyethylenimine-mediated mitochondrial energy crisis and cellular stress: Mitochondrial proton leak and inhibition of the electron transport system.
Biochim Biophys Acta. 2013; 1827(10):1213-25 [PubMed] Related Publications
Polyethylenimines (PEIs) are highly efficient non-viral transfectants, but can induce cell death through poorly understood necrotic and apoptotic processes as well as autophagy. Through high resolution respirometry studies in H1299 cells we demonstrate that the 25kDa branched polyethylenimine (25k-PEI-B), in a concentration and time-dependent manner, facilitates mitochondrial proton leak and inhibits the electron transport system. These events were associated with gradual reduction of the mitochondrial membrane potential and mitochondrial ATP synthesis. The intracellular ATP levels further declined as a consequence of PEI-mediated plasma membrane damage and subsequent ATP leakage to the extracellular medium. Studies with freshly isolated mouse liver mitochondria corroborated with bioenergetic findings and demonstrated parallel polycation concentration- and time-dependent changes in state 2 and state 4o oxygen flux as well as lowered ADP phosphorylation (state 3) and mitochondrial ATP synthesis. Polycation-mediated reduction of electron transport system activity was further demonstrated in 'broken mitochondria' (freeze-thawed mitochondrial preparations). Moreover, by using both high-resolution respirometry and spectrophotometry analysis of cytochrome c oxidase activity we were able to identify complex IV (cytochrome c oxidase) as a likely specific site of PEI mediated inhibition within the electron transport system. Unraveling the mechanisms of PEI-mediated mitochondrial energy crisis is central for combinatorial design of safer polymeric non-viral gene delivery systems.

Related: Non-Small Cell Lung Cancer Lung Cancer

Chen B, Xu M, Zhang H, et al.
Cisplatin-induced non-apoptotic death of pancreatic cancer cells requires mitochondrial cyclophilin-D-p53 signaling.
Biochem Biophys Res Commun. 2013; 437(4):526-31 [PubMed] Related Publications
The pancreatic cancer remains a fatal disease for the majority of patients. Cisplatin has displayed significant cytotoxic effects against the pancreatic cancer cells, however the underlying mechanisms remain inconclusive. Here, we found that cisplatin mainly induced non-apoptotic death of the pancreatic cancer cells (AsPC-1 and Capan-2), which was associated with a significant p53 activation (phosphorylation and accumulation). Further, activated p53 was found to translocate to mitochondria where it formed a complex with cyclophilin D (Cyp-D). We provided evidences to support that mitochondrial Cyp-D/p53 complexation might be critical for cisplatin-induced non-apoptotic death of pancreatic cancer cells. Inhibition of Cyp-D by its inhibitor cyclosporine A (CsA), or by shRNA-mediated knockdown suppressed cisplatin-induced pancreatic cancer cell death. Both CsA and Cyp-D knockdown also disrupted the Cyp-D/p53 complex formation in mitochondria. Meanwhile, the pancreatic cancer cells with p53 knockdown were resistant to cisplatin. On the other hand, HEK-293 over-expressing Cyp-D were hyper-sensitive to cisplatin. Interestingly, camptothecin (CMT)-induced pancreatic cancer cell apoptotic death was not affected CsA or Cyp-D knockdown. Together, these data suggested that cisplatin-induced non-apoptotic death requires mitochondria Cyp-D-p53 signaling in pancreatic cancer cells.

Related: Apoptosis Cisplatin Cancer of the Pancreas Pancreatic Cancer Signal Transduction TP53

Mathieu V, Van Den Berge E, Ceusters J, et al.
New 5-Aryl-1H-imidazoles display in vitro antitumor activity against apoptosis-resistant cancer models, including melanomas, through mitochondrial targeting.
J Med Chem. 2013; 56(17):6626-37 [PubMed] Related Publications
We designed and synthesized 48 aryl-1H-imidazole derivatives and investigated their in vitro growth inhibitory activity in cancer cell lines known to present various levels of resistance to proapoptotic stimuli. The IC50 in vitro growth inhibitory concentration of these compounds ranged from >100 μM to single digit μM. Among the most active compounds, 2i displayed similar in vitro growth inhibition in cancer cells independent of the cells' levels of resistance to proapoptotic stimuli and was found to be cytostatic in melanoma cell lines. Compound 2i was then tested by the National Cancer Institute Human Tumor Cell Line Anti-Cancer Drug Screen, and the NCI COMPARE algorithm did not reveal any correlation between its growth inhibition profiles with the NCI database compound profiles. The use of transcriptomically characterized melanoma models then enabled us to highlight mitochondrial targeting by 2i. This hypothesis was further confirmed by reactive oxygen production measurement and oxygen consumption analysis.

Related: Apoptosis Melanoma Cancer Prevention and Risk Reduction

Pokorný J, Foletti A, Kobilková J, et al.
Biophysical insights into cancer transformation and treatment.
ScientificWorldJournal. 2013; 2013:195028 [PubMed] Article available free on PMC after 21/08/2014 Related Publications
Biological systems are hierarchically self-organized complex structures characterized by nonlinear interactions. Biochemical energy is transformed into work of physical forces required for various biological functions. We postulate that energy transduction depends on endogenous electrodynamic fields generated by microtubules. Microtubules and mitochondria colocalize in cells with microtubules providing tracks for mitochondrial movement. Besides energy transformation, mitochondria form a spatially distributed proton charge layer and a resultant strong static electric field, which causes water ordering in the surrounding cytosol. These effects create conditions for generation of coherent electrodynamic field. The metabolic energy transduction pathways are strongly affected in cancers. Mitochondrial dysfunction in cancer cells (Warburg effect) or in fibroblasts associated with cancer cells (reverse Warburg effect) results in decreased or increased power of the generated electromagnetic field, respectively, and shifted and rebuilt frequency spectra. Disturbed electrodynamic interaction forces between cancer and healthy cells may favor local invasion and metastasis. A therapeutic strategy of targeting dysfunctional mitochondria for restoration of their physiological functions makes it possible to switch on the natural apoptotic pathway blocked in cancer transformed cells. Experience with dichloroacetate in cancer treatment and reestablishment of the healthy state may help in the development of novel effective drugs aimed at the mitochondrial function.

Related: Cancer Prevention and Risk Reduction

Looi CY, Moharram B, Paydar M, et al.
Induction of apoptosis in melanoma A375 cells by a chloroform fraction of Centratherum anthelminticum (L.) seeds involves NF-kappaB, p53 and Bcl-2-controlled mitochondrial signaling pathways.
BMC Complement Altern Med. 2013; 13:166 [PubMed] Article available free on PMC after 21/08/2014 Related Publications
BACKGROUND: Centratherum anthelminticum (L.) Kuntze (scientific synonyms: Vernonia anthelmintica; black cumin) is one of the ingredients of an Ayurvedic preparation, called "Kayakalp", commonly applied to treat skin disorders in India and Southeast Asia. Despite its well known anti-inflammatory property on skin diseases, the anti-cancer effect of C. anthelminticum seeds on skin cancer is less documented. The present study aims to investigate the anti-cancer effect of Centratherum anthelminticum (L.) seeds chloroform fraction (CACF) on human melanoma cells and to elucidate the molecular mechanism involved.
METHODS: A chloroform fraction was extracted from C. anthelminticum (CACF). Bioactive compounds of the CACF were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Human melanoma cell line A375 was treated with CACF in vitro. Effects of CACF on growth inhibition, morphology, stress and survival of the cell were examined with MTT, high content screening (HSC) array scan and flow cytometry analyses. Involvement of intrinsic or extrinsic pathways in the CACF-induced A375 cell death mechanism was examined using a caspase luminescence assay. The results were further verified with different caspase inhibitors. In addition, Western blot analysis was performed to elucidate the changes in apoptosis-associated molecules. Finally, the effect of CACF on the NF-κB nuclear translocation ability was assayed.
RESULTS: The MTT assay showed that CACF dose-dependently inhibited cell growth of A375, while exerted less cytotoxic effect on normal primary epithelial melanocytes. We demonstrated that CACF induced cell growth inhibition through apoptosis, as evidenced by cell shrinkage, increased annexin V staining and formation of membrane blebs. CACF treatment also resulted in higher reactive oxygen species (ROS) production and lower Bcl-2 expression, leading to decrease mitochondrial membrane potential (MMP). Disruption of the MMP facilitated the release of mitochondrial cytochrome c, which activates caspase-9 and downstream caspase-3/7, resulting in DNA fragmentation and up-regulation of p53 in melanoma cells. Moreover, CACF prevented TNF-α-induced NF-κB nuclear translocation, which further committed A375 cells toward apoptosis.
CONCLUSIONS: Together, our findings suggest CACF as a potential therapeutic agent against human melanoma malignancy.

Related: Apoptosis Melanoma Signal Transduction Skin Cancer TP53

Li Y, He L, Zeng N, et al.
Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) signaling regulates mitochondrial biogenesis and respiration via estrogen-related receptor α (ERRα).
J Biol Chem. 2013; 288(35):25007-24 [PubMed] Article available free on PMC after 30/08/2014 Related Publications
Mitochondrial abnormalities are associated with cancer development, yet how oncogenic signals affect mitochondrial functions has not been fully understood. In this study, we investigate the relationship between mitochondrial alterations and PI3K/protein kinase B (AKT) signaling activation using hepatocytes and liver tissues as our experimental models. We show here that liver-specific deletion of Pten, which leads to activation of PI3K/AKT, is associated with elevated oxidative stress, increased mitochondrial mass, and augmented respiration accompanied by enhanced glycolysis. Consistent with these observations, estrogen-related receptor α (ERRα), an orphan nuclear receptor known for its role in mitochondrial biogenesis, is up-regulated in the absence of phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Our pharmacological and genetic studies show that PI3K/AKT activity regulates the expression of ERRα and mitochondrial biogenesis/respiration. Furthermore, cAMP-response element-binding protein, as a downstream target of AKT, plays a role in the regulation of ERRα, independent of PKA signaling. ERRα regulates reactive oxygen species production, and ERRα knockdown attenuates proliferation and colony-forming potential in Pten-null hepatocytes. Finally, analysis of clinical datasets from liver tissues showed a negative correlation between expressions of ERRα and PTEN in patients with liver cancer. Therefore, this study has established a previously unrecognized link between a growth signal and mitochondrial metabolism.

Related: Liver Cancer PTEN v-akt murine thymoma viral oncogene homolog 1 (14q32.3) Signal Transduction

Guo Y, Zhang W, Yan YY, et al.
Triterpenoid pristimerin induced HepG2 cells apoptosis through ROS-mediated mitochondrial dysfunction.
J BUON. 2013 Apr-Jun; 18(2):477-85 [PubMed] Related Publications
PURPOSE: To investigate the anticancer properties implicated in a natural triterpenoid (pristimerin)-induced apoptosis and inhibited proliferation in human hepatocellular carcinoma (HCC) HepG2 cell line.
METHODS: The cytotoxic activity of pristimerin in HepG2 cells was determined by MTT assay. Apoptotic morphology was observed by fluorescence microscope with Hoechst 33258 staining and percent apoptosis was measured by annexin V/PI double staining. DiOC6 for mitochondrial potential (ΔΨm) and DCFH-DA for reactive oxygen species (ROS) were determined by flow cytometry. Changes of apoptotic- related proteins were analysed by Western blot.
RESULTS: Pristimerin exerted a potent cytotoxic effect on HepG2 cells. After HepG2 cells were treated with pristimerin, typical apoptotic bodies, increasing the proportion of apoptotic annexin V-positive cells and activation of caspase-3 were detected in a dose-dependent manner. It was intriguing that pristimerin increased the generation of ROS with a collapse of the mitochondrial membrane potential in the cells. In addition, there was significant change in other mitochondrial membrane proteins triggered by pristimerin, such as Bcl-2 and Bax. Pristimerin also effectively induced subsequent release of cytochrome C from mitochondria into the cytosol, downregulated EGFR protein expression and inhibited downstream signaling pathways in HepG2 cells. Pretreatment with N-acetylcysteine (NAC) blocked ROS generation and resulted in loss of mitochondrial membrane potential, release of cytochrome C and apoptosis induced by pristimerin.
CONCLUSION: These data indicate that ROS play an essential role in the induction of apoptosis by pristimerin in HepG2 cells.

Related: Apoptosis Liver Cancer

Su CM, Wang SW, Lee TH, et al.
Trichodermin induces cell apoptosis through mitochondrial dysfunction and endoplasmic reticulum stress in human chondrosarcoma cells.
Toxicol Appl Pharmacol. 2013; 272(2):335-44 [PubMed] Related Publications
Chondrosarcoma is the second most common primary bone tumor, and it responds poorly to both chemotherapy and radiation treatment. Nalanthamala psidii was described originally as Myxosporium in 1926. This is the first study to investigate the anti-tumor activity of trichodermin (trichothec-9-en-4-ol, 12,13-epoxy-, acetate), an endophytic fungal metabolite from N. psidii against human chondrosarcoma cells. We demonstrated that trichodermin induced cell apoptosis in human chondrosarcoma cell lines (JJ012 and SW1353 cells) instead of primary chondrocytes. In addition, trichodermin triggered endoplasmic reticulum (ER) stress protein levels of IRE1, p-PERK, GRP78, and GRP94, which were characterized by changes in cytosolic calcium levels. Furthermore, trichodermin induced the upregulation of Bax and Bid, the downregulation of Bcl-2, and the dysfunction of mitochondria, which released cytochrome c and activated caspase-3 in human chondrosarcoma. In addition, animal experiments illustrated reduced tumor volume, which led to an increased number of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive cells and an increased level of cleaved PARP protein following trichodermin treatment. Together, this study demonstrates that trichodermin is a novel anti-tumor agent against human chondrosarcoma cells both in vitro and in vivo via mitochondrial dysfunction and ER stress.

Related: Apoptosis Bone Cancers Chondrosarcoma

Xu E, Sun W, Gu J, et al.
Association of mitochondrial DNA copy number in peripheral blood leukocytes with risk of esophageal adenocarcinoma.
Carcinogenesis. 2013; 34(11):2521-4 [PubMed] Article available free on PMC after 01/11/2014 Related Publications
Alterations of mitochondrial DNA (mtDNA) have been associated with the risk of a number of human cancers; however, the relationship between mtDNA copy number in peripheral blood leukocytes and the risk of esophageal adenocarcinoma (EAC) has not been reported. In this study, we determined relative mtDNA copy number in peripheral blood leukocytes of 218 EAC cases and 218 frequency-matched controls. We calculated odds ratios and 95% confidence intervals using unconditional logistic regression, adjusting for age, sex and smoking status. MtDNA copy number was significantly lower in cases than in controls (mean ± SD, 1.16 ± 0.30 versus 1.27 ± 0.43, P = 0.002). Dichotomized at the median value of mtDNA copy number in the controls, low mtDNA copy number was significantly associated with an increased risk of EAC (odds ratio: 1.55, 95% confidence interval: 1.05-2.29). A significant dose-response relationship was observed between mtDNA copy number and risk of EAC in quartile analysis. Our results suggest that low mtDNA copy number in peripheral blood leukocytes is associated with increased susceptibility to EAC.

Related: Cancer of the Esophagus Esophageal Cancer

Lai CH, Huang SF, Liao CT, et al.
Clinical significance in oral cavity squamous cell carcinoma of pathogenic somatic mitochondrial mutations.
PLoS One. 2013; 8(6):e65578 [PubMed] Article available free on PMC after 01/11/2014 Related Publications
Somatic mutations affecting the mitochondrial DNA (mtDNA) have been frequently observed in human cancers and proposed as important oncological biomarkers. However, the clinical significance of mtDNA mutations in cancer remains unclear. This study was therefore performed to explore the possible clinical use in assessing oral squamous cell carcinoma (OSCC) of pathogenic mtDNA mutations. The entire mitochondrial genome of 300 OSCC with their matched control DNAs was screened by direct sequencing and criteria were set to define a pathogenic somatic mutation. The patients' TP53 R72P genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism. The relationships between pathogenic somatic mutations, clinicopathogical features, TP53 R72P genotype and clinical prognosis were analyzed. Overall, 645 somatic mtDNA mutations were identified and 91 of these mutations were defined as pathogenic. About one quarter (74/300) of the OSCC tumor samples contained pathogenic mutations. Individuals with the TP53 R allele had a higher frequency of pathogenic somatic mutation than those with the PP genotype. Kaplan-Meier analysis indicated that TP53 R allele patients with pathogenic somatic mutations demonstrated a significant association with a poorer disease-free survival than other individuals (HR = 1.71; 95% CI, 1.15-2.57; p = 0.009) and this phenomenon still existed after adjusting for mtDNA haplogroup, tumor stage with treatment regimens, differentiation and age at diagnosis (HR = 1.59; 95% CI, 1.06-2.40; p = 0.03). Subgroup analyses showed that this phenomenon was limited to patients who received adjuvant radiotherapy/chemo-radiotherapy after surgery. The results strongly indicated that pathogenic mtDNA mutations are a potential prognostic marker for OSCCs. Furthermore, functional mitochondria may play an active role in cancer development and the patient's response to radiotherapy/chemo-radiotherapy.

Related: Oral Cancer TP53

Hsu CC, Wang CH, Wu LC, et al.
Mitochondrial dysfunction represses HIF-1α protein synthesis through AMPK activation in human hepatoma HepG2 cells.
Biochim Biophys Acta. 2013; 1830(10):4743-51 [PubMed] Related Publications
BACKGROUND: Hypoxia-inducible factor-1α (HIF-1α) is an important transcription factor that modulates cellular responses to hypoxia and also plays critical roles in cancer progression. Recently, somatic mutations and decreased copy number of mitochondrial DNA (mtDNA) were detected in hepatocellular carcinoma (HCC). These mutations were shown to have the potential to cause mitochondrial dysfunction. However, the effects and mechanisms of mitochondrial dysfunction on HIF-1α function are not fully understood. This study aims to explore the underlying mechanism by which mitochondrial dysfunction regulates HIF-1α expression.
METHODS: Human hepatoma HepG2 cells were treated with various mitochondrial respiration inhibitors and an uncoupler, respectively, and the mRNA and protein expressions as well as transactivation activity of HIF-1α were determined. The role of AMP-activated protein kinase (AMPK) was further analyzed by compound C and AMPK knock-down.
RESULTS: Treatments of mitochondrial inhibitors and an uncoupler respectively reduced both the protein level and transactivation activity of HIF-1α in HepG2 cells under normoxia or hypoxia. The mitochondrial dysfunction-repressed HIF-1α protein synthesis was associated with decreased phosphorylations of p70(S6K) and 4E-BP-1. Moreover, mitochondrial dysfunction decreased intracellular ATP content and elevated the phosphorylation of AMPK. Treatments with compound C, an AMPK inhibitor, and knock-down of AMPK partially rescued the mitochondrial dysfunction-repressed HIF-1α expression.
CONCLUSIONS: Mitochondrial dysfunctions resulted in reduced HIF-1α protein synthesis through AMPK-dependent manner in HepG2 cells.
GENERAL SIGNIFICANCE: Our results provided a mechanism for communication from mitochondria to the nucleus through AMPK-HIF-1α. Mitochondrial function is important for HIF-1α expression in cancer progression.

Related: Liver Cancer

mtDNA Databases and Resources (3 links)

Further References

Radpour R, Fan AX, Kohler C, et al.
Current understanding of mitochondrial DNA in breast cancer.
Breast J. 2009 Sep-Oct; 15(5):505-9 [PubMed] Related Publications
The recent surge in mitochondrial research has been driven by the identification of mitochondria-associated diseases and the role of mitochondria in apoptosis and aging. Mitochondrial DNA (mtDNA) has been proposed to be involved in carcinogenesis because of its high susceptibility to mutations and limited repair mechanisms in comparison to nuclear DNA. As mtDNA lacks introns, it has been suggested that most mutations will occur in coding sequences. The subsequent accumulation of mutations may lead to tumor formation. By virtue of their clonal nature, high copy number and high frequent mutations may provide a powerful molecular biomarker for the detection of cancer. It has been suggested that the extent of mtDNA mutations might be useful in the prognosis of cancer outcome and/or the response to certain therapies. In this review article, we aim to provide a brief summary of our current understanding of mitochondrial genetics and biology, review the mtDNA alterations reported in breast cancer, and offer some perspectives as to the emergence of mtDNA mutations, including their functional consequences in cancer development, diagnostic criteria, and therapeutic implications.

Related: Breast Cancer Kidney Cancer Stomach Cancer Gastric Cancer

Wallace DC
Mitochondria and cancer.
Nat Rev Cancer. 2012; 12(10):685-98 [PubMed] Related Publications
Contrary to conventional wisdom, functional mitochondria are essential for the cancer cell. Although mutations in mitochondrial genes are common in cancer cells, they do not inactivate mitochondrial energy metabolism but rather alter the mitochondrial bioenergetic and biosynthetic state. These states communicate with the nucleus through mitochondrial 'retrograde signalling' to modulate signal transduction pathways, transcriptional circuits and chromatin structure to meet the perceived mitochondrial and nuclear requirements of the cancer cell. Cancer cells then reprogramme adjacent stromal cells to optimize the cancer cell environment. These alterations activate out-of-context programmes that are important in development, stress response, wound healing and nutritional status.

Related: Cancer Prevention and Risk Reduction Signal Transduction


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