Mitochondrial dysfunction and cancer metastasis

Radiation resistance of cancer cells caused by mitochondrial dysfunction depends on SIRT3-mediated mitophagy

Radiation resistance is the leading cause of radiotherapy failure in patients with cancer. Enhanced DNA damage repair is the main reason for cancer cells to develop resistance to radiation. Autophagy has been widely reported to be linked to increased genome stability and radiation resistance. Mitochondria are highly involved in the cell response to radiotherapy. However, the autophagy subtype mitophagy has not been studied in terms of genome stability. We have previously demonstrated that mitochondrial dysfunction is the cause of radiation resistance in tumour cells. In the present study, we found that SIRT3 was highly expressed in colorectal cancer cells with mitochondrial dysfunction, leading to PINK1/Parkin-mediated mitophagy. Excessive activation of mitophagy enhanced DNA damage repair, therefore promoting the resistance of tumour cells to radiation. Mechanistically, mitophagy resulted in decreased RING1b expression, which led to a reduction in the ubiquitination of histone H2A at K119, thereby enhancing the repair of DNA damage caused by radiation. Additionally, high expression of SIRT3 was related to a poor tumour regression grade in rectal cancer patients treated with neoadjuvant radiotherapy. These findings suggest that restoring mitochondrial function could be an effective method for increasing the radiosensitivity of patients with colorectal cancer.

AML1-ETO-Related Fusion Circular RNAs Contribute to the Proliferation of Leukemia Cells

The AML1-ETO (RUNX1-RUNX1T1) fusion gene created by the chromosome translocation t(8;21) (q21;q22) is one of the essential contributors to leukemogenesis. Only a few studies in the literature have focused on fusion gene-derived circular RNAs (f-circRNAs). Here, we report several AML1-ETO-related fusion circular RNAs (F-CircAEs) in AML1-ETO-positive cell lines and primary patient blasts. Functional studies demonstrate that the over-expression of F-CircAE in NIH3T3 cells promotes cell proliferation in vitro and in vivo. F-CircAE expression enhances the colony formation ability of c-Kit⁺ hematopoietic stem and progenitor cells (HSPCs). Meanwhile, the knockdown of endogenous F-CircAEs can inhibit the proliferation and colony formation ability of AML1-ETO-positive Kasumi-1 cells. Intriguingly, bioinformatic analysis revealed that the glycolysis pathway is down-regulated in F-CircAE-knockdown Kasumi-1 cells and up-regulated in F-CircAE over-expressed NIH3T3 cells. Further studies show that F-CircAE binds to the glycolytic protein ENO-1, up-regulates the expression level of glycolytic enzymes, and enhances lactate production. In summary, our study demonstrates that F-CircAE may exert biological activities on the growth of AML1-ETO leukemia cells by regulating the glycolysis pathway. Determining the role of F-CircAEs in AML1-ETO leukemia can lead to great strides in understanding its pathogenesis, thus providing new diagnostic markers and therapeutic targets.

Comprehensive analysis of tissue proteomics in patients with papillary thyroid microcarcinoma uncovers the underlying mechanism of lymph node metastasis and its significant sex disparities

Background

Lymph node metastasis (LNM) in papillary thyroid microcarcinoma (PTMC) is associated with an increased risk of recurrence and poor prognosis. Sex has been regarded as a critical risk factor for LNM. The present study aimed to investigate the molecular mechanisms underlying LNM and its significant sex disparities in PTMC development.

Methods

A direct data-independent acquisition (DIA) proteomics approach was used to identify differentially expressed proteins (DEPs) in PTMC tumorous tissues with or without LNM and from male and female patients with LNM. The functional annotation of DEPs was performed using bioinformatics methods. Furthermore, The Cancer Genome Atlas Thyroid Carcinoma (TCGA-THCA) dataset and immunohistochemistry (IHC) were used to validate selected DEPs.

Results

The proteomics profile in PTMC with LNM differed from that of PTMC without LNM. The metastasis-related DEPs were primarily enriched in categories associated with mitochondrial dysfunction and may promote tumor progression by activating oxidative phosphorylation and PI3K/AKT signaling pathways. Comparative analyses of these DEPs revealed downregulated expression of specific proteins with well-established links to tumor metastasis, such as SLC25A15, DIRAS2, PLA2R1, and MTARC1. Additionally, the proteomics profiles of male and female PTMC patients with LNM were dramatically distinguishable. An elevated level of ECM-associated proteins might be related to more LNM in male PTMC than in female PTMC patients. The upregulated expression levels of MMRN2 and NID2 correlated with sex disparities and showed a positive relationship with unfavorable variables, such as LNMs and poor prognosis.

Conclusions

The proteomics profiles of PTMC show significant differences associated with LNM and its sex disparities, which further expands our understanding of the functional networks and signaling pathways related to PTMC with LNM.

Insights regarding mitochondrial DNA copy number alterations in human cancer (Review)

Mitochondria are the critical organelles involved in various cellular functions. Mitochondrial biogenesis is activated by multiple cellular mechanisms which require a synchronous regulation between mitochondrial DNA (mtDNA) and nuclear DNA (nDNA). The mitochondrial DNA copy number (mtDNA-CN) is a proxy indicator for mitochondrial activity, and its alteration reflects mitochondrial biogenesis and function. Despite the precise mechanisms that modulate the amount and composition of mtDNA, which have not been fully elucidated, mtDNA-CN is known to influence numerous cellular pathways that are associated with cancer and as well as multiple other diseases. In addition, the utility of current technology in measuring mtDNA-CN contributes to its extensive assessment of diverse traits and tumorigenesis. The present review provides an overview of mtDNA-CN variations across human cancers and an extensive summary of the existing knowledge on the regulation and machinery of mtDNA-CN. The current information on the advanced methods used for mtDNA-CN assessment is also presented.

TMT-Based Quantitative Proteomics Analysis Reveals the Panoramic Pharmacological Molecular Mechanism of β-Elemonic Acid Inhibition of Colorectal Cancer

Colorectal cancer (CRC) is one of the most common cancers worldwide but has limited available therapeutic methods; therefore, there is a need to develop highly efficient prevention and treatment strategies. Here, we investigated the anti-cancer activity of β-elemonic acid (EA) in CRC in vitro and in vivo. Our results showed that EA inhibited cell proliferation and migration in the CRC cell lines SW480 and HCT116. Moreover, EA significantly suppressed the growth of transplanted colorectal tumors in nude mice. Interestingly, high-throughput tandem mass tag (TMT)-based quantitative proteomics indicated that EA mainly targets tumor mitochondria and attenuates the translation of 54 mitochondrial ribosome proteins, many of which are discovered significantly upregulated in clinical CRC patients. More interestingly, EA at a low concentration (lower than 15 μg/ml) repressed the cell cycle by downregulating CDK1, CDK6, and CDC20, whereas at a high concentration (higher than 15 μg/ml), caused a non-apoptotic cell death-ferroptosis via downregulating ferritin (FTL) and upregulating transferrin (TF), ferroxidase (CP), and acyl-CoA synthetase long-chain family member 4 (ACSL4). This is the first report on the panoramic molecular mechanism of EA against CRC, which would make great contributions to developing a novel drug for colorectal cancer therapy.

TFB2M activates aerobic glycolysis in hepatocellular carcinoma cells through the NAD+ /SIRT3/HIF-1α signaling

BACKGROUND AND AIM

Increased aerobic glycolysis has been well-known as a hallmark of cancer, which is closely related to mitochondrial dysfunction. TFB2M (mitochondrial transcription factor B2) is a core mitochondrial transcription factor, which has been shown by us to play an oncogenic role in hepatocellular carcinoma (HCC). However, whether TFB2M contributes to the aerobic glycolysis in HCC cells remains unexplored.

METHODS

The role and underlying molecular mechanisms of TFB2M in the regulation of aerobic glycolysis in HCC cells were systematically investigated by in vitro cell glucose metabolism and metabolomics analyses. Besides, the effects of TFB2M-regulated aerobic glycolysis in the growth and metastasis of HCC cells were also explored.

RESULTS

Here, we show that TFB2M markedly enhanced the reprogramming of glucose metabolism from oxidative phosphorylation to aerobic glycolysis mainly through two mechanisms. On the one hand, TFB2M increased the expressions of glycolytic genes GAPDH, LDHA, GLUT1, and HK2. On the other hand, TFB2M decreased the expression of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α), a critical regulator of mitochondrial respiration. Mechanistically, TFB2M regulates the upregulation of glycolytic genes and downregulation of PGC-1α mainly through NAD⁺ /SIRT3/HIF-1α signaling. Additionally, we found that TFBM2 promoted the progression of HCC cells through HIF-1α-regulated reprogramming of glucose metabolism.

CONCLUSIONS

Our findings indicate that TFB2M serves as a critical glucose metabolic reprogramming mechanism in tumorigenesis, which could be used as potential therapeutic target in HCC.

High-throughput microfluidic 3D biomimetic model enabling quantitative description of the human breast tumor microenvironment

Cancer is driven by both genetic aberrations in the tumor cells and fundamental changes in the tumor microenvironment (TME). These changes offer potential targets for novel therapeutics, yet lack of in vitro 3D models recapitulating this complex microenvironment impedes such progress. Here, we generated several tumor-stroma scaffolds reflecting the dynamic in vivo breast TME, using a high throughput microfluidic system. Alginate (Alg) or alginate-alginate sulfate (Alg/Alg-S) hydrogels were used as ECM-mimics, enabling the encapsulation and culture of tumor cells, fibroblasts and immune cells (macrophages and T cells, of the innate and adaptive immune systems, respectively). Specifically, Alg/Alg-S was shown capable of capturing and presenting growth factors and cytokines with binding affinity that is comparable to heparin. Viability and cytotoxicity were shown to strongly correlate with the dynamics of cellular milieu, as well as hydrogel type. Using on-chip immunofluorescence, production of reactive oxygen species and apoptosis were imaged and quantitatively analyzed. We then show how macrophages in our microfluidic system were shifted from a proinflammatory to an immunosuppressive phenotype when encapsulated in Alg/Alg-S, reflecting in vivo TME dynamics. LC-MS proteomic profiling of tumor cells sorted from the TME scaffolds revealed upregulation of proteins involved in cell-cell interactions and immunomodulation in Alg/Alg-S scaffolds, correlating with in vivo findings and demonstrating the appropriateness of Alg/Alg-S as an ECM biomimetic. Finally, we show the formation of large tumor-derived vesicles, formed exclusively in Alg/Alg-S scaffolds. Altogether, our system offers a robust platform for quantitative description of the breast TME that successfully recapitulates in vivo patterns. STATEMENT OF SIGNIFICANCE: Cancer progression is driven by profound changes in both tumor cells and surrounding stroma. Here, we present a high throughput microfluidic system for the generation and analysis of dynamic tumor-stroma scaffolds, that mimic the complex in vivo TME cell proportions and compositions, constructing robust in vitro models for the study of the TME. Utilizing Alg/Alg-S as a bioinspired ECM, mimicking heparin's in vivo capabilities of capturing and presenting signaling molecules, we show how Alg/Alg-S induces complex in vivo-like responses in our models. Alg/Alg-S is shown here to promote dynamic protein expression patterns, that can serve as potential therapeutic targets for breast cancer treatment. Formation of large tumor-derived vesicles, observed exclusively in the Alg/Alg-S scaffolds suggests a mechanism for tumor survival.

Activation of the integrated stress response confers vulnerability to mitoribosome-targeting antibiotics in melanoma

The ability to adapt to environmental stress, including therapeutic insult, contributes to tumor evolution and drug resistance. In suboptimal conditions, the integrated stress response (ISR) promotes survival by dampening cytosolic translation. We show that ISR-dependent survival also relies on a concomitant up-regulation of mitochondrial protein synthesis, a vulnerability that can be exploited using mitoribosome-targeting antibiotics. Accordingly, such agents sensitized to MAPK inhibition, thus preventing the development of resistance in BRAFV600E melanoma models. Additionally, this treatment compromised the growth of melanomas that exhibited elevated ISR activity and resistance to both immunotherapy and targeted therapy. In keeping with this, pharmacological inactivation of ISR, or silencing of ATF4, rescued the antitumoral response to the tetracyclines. Moreover, a melanoma patient exposed to doxycycline experienced complete and long-lasting response of a treatment-resistant lesion. Our study indicates that the repurposing of mitoribosome-targeting antibiotics offers a rational salvage strategy for targeted therapy in BRAF mutant melanoma and a therapeutic option for NRAS-driven and immunotherapy-resistant tumors.

Fueling the cytoskeleton - links between cell metabolism and actin remodeling

Attention has long focused on the actin cytoskeleton as a unit capable of organizing into ensembles that control cell shape, polarity, migration and the establishment of intercellular contacts that support tissue architecture. However, these investigations do not consider observations made over 40 years ago that the actin cytoskeleton directly binds metabolic enzymes, or emerging evidence suggesting that the rearrangement and assembly of the actin cytoskeleton is a major energetic drain. This Review examines recent studies probing how cells adjust their metabolism to provide the energy necessary for cytoskeletal remodeling that occurs during cell migration, epithelial to mesenchymal transitions, and the cellular response to external forces. These studies have revealed that mechanotransduction, cell migration, and epithelial to mesenchymal transitions are accompanied by alterations in glycolysis and oxidative phosphorylation. These metabolic changes provide energy to support the actin cytoskeletal rearrangements necessary to allow cells to assemble the branched actin networks required for cell movement and epithelial to mesenchymal transitions and the large actin bundles necessary for cells to withstand forces. In this Review, we discuss the emerging evidence suggesting that the regulation of these events is highly complex with metabolism affecting the actin cytoskeleton and vice versa.

Mitochondria-Targeted Antioxidants MitoQ and MitoTEMPO Do Not Influence BRAF-Driven Malignant Melanoma and KRAS-Driven Lung Cancer Progression in Mice

Cancer cells produce high levels of mitochondria-associated reactive oxygen species (ROS) that can damage macromolecules, but also promote cell signaling and proliferation. Therefore, mitochondria-targeted antioxidants have been suggested to be useful in anti-cancer therapy, but no studies have convincingly addressed this question. Here, we administered the mitochondria-targeted antioxidants MitoQ and MitoTEMPO to mice with BRAF-induced malignant melanoma and KRAS-induced lung cancer, and found that these compounds had no impact on the number of primary tumors and metastases; and did not influence mitochondrial and nuclear DNA damage levels. Moreover, MitoQ and MitoTEMPO did not influence proliferation of human melanoma and lung cancer cell lines. MitoQ and its control substance dTPP, but not MitoTEMPO, increased glycolytic rates and reduced respiration in melanoma cells; whereas only dTPP produced this effect in lung cancer cells. Our results do not support the use of mitochondria-targeted antioxidants for anti-cancer monotherapy, at least not in malignant melanoma and lung cancer.

miR-145 inhibits mitochondrial function of ovarian cancer by targeting ARL5B

Metabolic reprogramming refers to the transformation of the whole metabolic network including glycolysis and mitochondrial metabolism, mainly manifested in Warburg effect and mitochondrial metabolic reprogramming. The roles of miR-145 in glycolysis have been established in ovarian cancer cells. Howerer, its roles in mitochondrial metabolic reprogramming are still unclear. This study aims to identify whether miR-145 regulates mitochondrial metabolic reprogramming in ovarian cancer cells. First, functional experiment showed that overexpression of miR-145 inhibited mitochondrial function in ovarian cancer cells, evident by the decreased mtDNA copy numbers, ATP level, mitochondrial membrane potential, and the expression levels of mitochondrial markers. Mechanistically, miR-145 inhibited mitochondrial function by targeting ARL5B directly. Futhermore, miR-145 overexpression decreased ARL5B expression in ovarian cancer tissue subcutaneous tumors of nude mice. In conclusion, we have highlighted that miR-145 inhibits mitochondrial function and achieves this by targeting ARL5B directly for the first time. The results provides a more adequate theoretical basis for understanding the molecular pathology of ovarian cancer, and provides the necessary basic data for miR-145 as a potential diagnosis and treatment target for ovarian cancer.

Mitochondrial Respiratory Defect Enhances Hepatoma Cell Invasiveness via STAT3/NFE2L1/STX12 Axis

Simple Summary

Mitochondria are essential organelles responsible for aerobic ATP production in eukaryotes. However, many solid tumor cells harbor an impaired mitochondrial ATP production system: oxidative phosphorylation (OXPHOS). The aim of this study was to elucidate the involvement of the mitochondrial OXPHOS defect in cancer cell activity, especially focusing on hepatoma cell invasiveness. We demonstrated that NADH:Ubiquinone Oxidoreductase Subunit A9 (NDUFA9) depletion was an upstream driver of the OXPHOS defect and nuclear factor-erythroid 2 like 1 (NFE2L1) upregulation in HCC tumors. NFE2L1 is the key transcription factor to enhance hepatoma cell invasiveness via STX12 expression. Our study presents a novel mitochondrial dysfunction-mediated retrograde signaling pathway and the resulting transcriptomic reprogramming in liver cancer progression, providing the NDUFA9/NFE2L1/STX12 axis as a key prognostic marker of aggressive liver cancer with mitochondrial defects.

Abstract

Mitochondrial respiratory defects have been implicated in cancer progression and metastasis, but how they control tumor cell aggressiveness remains unclear. Here, we demonstrate that a mitochondrial respiratory defect induces nuclear factor-erythroid 2 like 1 (NFE2L1) expression at the transcriptional level via reactive oxygen species (ROS)-mediated STAT3 activation. We identified syntaxin 12 (STX12) as an effective downstream target of NFE2L1 by performing cDNA microarray analysis after the overexpression and depletion of NFE2L1 in hepatoma cells. Bioinformatics analysis of The Cancer Genome Atlas Liver Hepatocellular carcinoma (TCGA-LIHC) open database (n = 371) also revealed a significant positive association (r = 0.3, p = 2.49 × 10⁻⁹) between NFE2L1 and STX12 expression. We further demonstrated that STX12 is upregulated through the ROS/STAT3/NFE2L1 axis and is a key downstream effector of NFE2L1 in modulating hepatoma cell invasiveness. In addition, gene enrichment analysis of TCGA-LIHC also showed that epithelial–mesenchymal transition (EMT)-related core genes are significantly upregulated in tumors co-expressing NFE2L1 and STX12. The positive association between NFE2L1 and STX12 expression was validated by immunohistochemistry of the hepatocellular carcinoma tissue array. Finally, higher EMT gene enrichment and worse overall survival (p = 0.043) were observed in the NFE2L1 and STX12 co-expression group with mitochondrial defect, as indicated by low NDUFA9 expression. Collectively, our results indicate that NFE2L1 is a key mitochondrial retrograde signaling-mediated primary gene product enhancing hepatoma cell invasiveness via STX12 expression and promoting liver cancer progression.

Exosomal Circ-ZNF652 Promotes Cell Proliferation, Migration, Invasion and Glycolysis in Hepatocellular Carcinoma via miR-29a-3p/GUCD1 Axis

BACKGROUND

Circular RNAs (circRNAs) play a crucial role in hepatocellular carcinoma (HCC) progression. However, the role of exosomal circRNAs in HCC is still largely unknown. We aimed to explore the function of exosomal circ-ZNF652 in HCC.

METHODS

The morphology and size of exosomes were examined by transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA). The expression of circ-ZNF652, ZNF652 mRNA, microRNA-29a-3p (miR-29a-3p) and guanylyl cyclase domain containing 1 (GUCD1) mRNA was determined by quantitative real-time polymerase chain reaction (qRT-PCR). The protein levels of CD63, CD81, hexokinase 2 (HK2) and GUCD1 were examined via Western blot assay. The stability of circ-ZNF652 was examined by RNase R digestion assay. Cell proliferation was analyzed by 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) assay. Cell migration and invasion were assessed by transwell assay. The glycolysis level was detected via specific kits. The association between miR-29a-3p and circ-ZNF652 or GUCD1 was analyzed by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. A murine xenograft model was constructed to explore the effect of circ-ZNF652 in vivo.

RESULTS

Exosomal circ-ZNF652 was upregulated in HCC patients' serums and HCC cells. Exosomal circ-ZNF652 could transfer to HCC cells, and circ-ZNF652 silencing suppressed HCC cell proliferation, migration, invasion and glycolysis. Circ-ZNF652 was a sponge of miR-29a-3p, and the inhibitory effect of circ-ZNF652 silencing on HCC cell progression was weakened by miR-29a-3p inhibitor. GUCD1 was a target gene of miR-29a-3p, and GUCD1 overexpression restored the effect of miR-29a-3p on HCC cell development. Moreover, circ-ZNF652 knockdown repressed tumor growth in vivo.

CONCLUSION

Exosomal circ-ZNF652 contributes to HCC cell proliferation, migration, invasion and glycolysis by miR-29a-3p/GUCD1 axis.

Over-expression of TFB2M facilitates cell growth and metastasis via activating ROS-Akt-NF-κB signalling in hepatocellular carcinoma

BACKGROUND & AIMS

Human TFB2M (mitochondrial transcription factor B2) is a key regulator of mitochondria transcription. Our bioinformatic analysis based on the cancer genome atlas (TCGA) data revealed an aberrant over-expression of TFB2M in hepatocellular carcinoma (HCC). However, the functional roles of TFB2M in tumourigenesis remains unexplored, including HCC.

METHODS

The expression and clinical significance of TFB2M were evaluated by qRT-PCR and western blot analysis. The biological effects and underlying mechanisms of TFB2M in HCC were determined by cell proliferation, colony formation, cell cycle, apoptosis, migration and invasion assays.

RESULTS

TFB2M was commonly up-regulated in HCC mainly because of the down-regulation of miR101-3p, which significantly correlated with poor survival of HCC patients. Functional experiments revealed that TFB2M significantly promoted HCC cell proliferation, migration and invasion, while inhibited apoptosis in vitro and promoted xenograft tumourigenesis and lung metastasis in nude mice models in vivo. Mechanistically, increased production of reactive oxygen species (ROS) and subsequently activated Akt/NF-κB signalling was found to be involved in the promotion of growth and metastasis by TFB2M in HCC cells.

CONCLUSIONS

These findings suggest that TFB2M plays a pivotal oncogenic role in HCC cells through activating ROS-Akt-NF-κB signalling pathway.

Blood-based bioenergetics: An emerging translational and clinical tool

Accumulating studies demonstrate that mitochondrial genetics and function are central to determining the susceptibility to, and prognosis of numerous diseases across all organ systems. Despite this recognition, mitochondrial function remains poorly characterized in humans primarily due to the invasiveness of obtaining viable tissue for mitochondrial studies. Recent studies have begun to test the hypothesis that circulating blood cells, which can be obtained by minimally invasive methodology, can be utilized as a biomarker of systemic bioenergetic function in human populations. Here we present the available methodologies for assessing blood cell bioenergetics and review studies that have applied these techniques to healthy and disease populations. We focus on the validation of this methodology in healthy subjects, as well as studies testing whether blood cell bioenergetics are altered in disease, correlate with clinical parameters, and compare with other methodology for assessing human mitochondrial function. Finally, we present the challenges and goals for the development of this emerging approach into a tool for translational research and personalized medicine.

EGFL9 promotes breast cancer metastasis by inducing cMET activation and metabolic reprogramming

The molecular mechanisms driving metastatic progression in triple-negative breast cancer (TNBC) patients are poorly understood. In this study, we demonstrate that epidermal growth factor-like 9 (EGFL9) is significantly upregulated in basal-like breast cancer cells and associated with metastatic progression in breast tumor samples. Functionally, EGFL9 is both necessary and sufficient to enhance cancer cell migration and invasion, as well as distant metastasis. Mechanistically, we demonstrate that EGFL9 binds cMET, activating cMET-mediated downstream signaling. EGFL9 and cMET co-localize at both the cell membrane and within the mitochondria. We further identify an interaction between EGFL9 and the cytochrome c oxidase (COX) assembly factor COA3. Consequently, EGFL9 regulates COX activity and modulates cell metabolism, promoting a Warburg-like metabolic phenotype. Finally, we show that combined pharmacological inhibition of cMET and glycolysis reverses EGFL9-driven stemness. Our results identify EGFL9 as a therapeutic target for combating metastatic progression in TNBC.

Triple-negative breast cancer is an aggressive form of the disease. Here, the authors identify EGFL9 as a mediator of metastasis in TNBC through interactions with cMET.

Mitochondrion: I am more than a fuel server

Apart from reliable management of the "powerhouse" of the cell, mitochondria faithfully orchestrate a diverse array of important and critical functions in governing cellular signaling, apoptosis, autophagy, mitophagy and innate and adaptive immune system. Introduction of instability and imbalance in the mitochondrial own genome or the nuclear encoded mitochondrial proteome would result in the manifestation of various diseases through alterations in the oxidative phosphorylation system (OXPHOS) and nuclear-mitochondria retrograde signaling. Understanding mitochondrial biology and dynamism are thus of paramount importance to develop strategies to prevent or treat various diseases caused due to mitochondrial alterations.

5-Aminolevulinic acid induced apoptosis via oxidative stress in normal gastric epithelial cells

5-Aminolevulinic acid, a precursor of heme, is utilized in a variety of applications including cancer treatment, surgery, and plant nutrition. However, 5-aminolevulinic acid itself induces oxidative stress and subsequent lipid peroxidation. Reactive oxygen species are factors in oxidative stress, not only causing cellular injury but also inducing several signal transduction pathways. Especially in cancer cells, a significant amount of signalling activation and subsequent activation of protein is caused by the enhancement of reactive oxygen species production. Reactive oxygen species levels in normal cells are low and an oxidative condition is harmful; hence, administration of 5-aminolevulinic acid to normal cells may induce oxidative stress, resulting in cell death. In this study, we investigated the effect of 5-aminolevulinic acid on normal and cancer cells with regard to oxidative stress. We used the rat normal gastric cell line RGM and its cancer-like mutant cell line RGK. 5-Aminolevulinic acid treatment of RGM cells enhanced reactive oxygen species generation and induced apoptosis associated with p53, whereas RGK cells were unaffected. In addition, RGM cell viability was recovered by application of N-acetyl-l-cysteine or p53 inhibitor. These results suggest that 5-aminolevulinic acid causes oxidative stress in normal gastric cells and induces apoptosis via the p53-dependent pathway.

Mutations in the ND2 Subunit of Mitochondrial Complex I Are Sufficient to Confer Increased Tumorigenic and Metastatic Potential to Cancer Cells

Multiprotein complexes of the mitochondrial electron transport chain form associations to generate supercomplexes. The relationship between tumor cell ability to assemble mitochondrial supercomplexes, tumorigenesis and metastasis has not been studied thoroughly. The mitochondrial and metabolic differences between L929dt cells, which lost matrix attachment and MHC-I expression, and their parental cell line L929, were analyzed. L929dt cells have lower capacity to generate energy through OXPHOS and lower respiratory capacity than parental L929 cells. Most importantly, L929dt cells show defects in mitochondrial supercomplex assembly, especially in those that contain complex I. These defects correlate with mtDNA mutations in L929dt cells at the ND2 subunit of complex I and are accompanied by a glycolytic shift. In addition, L929dt cells show higher in vivo tumorigenic and metastatic potential than the parental cell line. Cybrids with L929dt mitochondria in L929 nuclear background reproduce all L929dt properties, demonstrating that mitochondrial mutations are responsible for the aggressive tumor phenotype. In spite of their higher tumorigenic potential, L929dt or mitochondrial L929dt cybrid cells are sensitive both in vitro and in vivo to the PDK1 inhibitor dichloroacetate, which favors OXPHOS, suggesting benefits for the use of metabolic inhibitors in the treatment of especially aggressive tumors.

Lactic acidosis caused by repressed lactate dehydrogenase subunit B expression down-regulates mitochondrial oxidative phosphorylation via the pyruvate dehydrogenase (PDH)-PDH kinase axis

Aerobic glycolysis and mitochondrial dysfunction are key metabolic features of cancer cells, but their interplay during cancer development remains unclear. We previously reported that human hepatoma cells with mitochondrial defects exhibit down-regulated lactate dehydrogenase subunit B (LDHB) expression. Here, using several molecular and biochemical assays and informatics analyses, we investigated how LDHB suppression regulates mitochondrial respiratory activity and contributes to liver cancer progression. We found that transcriptional LDHB down-regulation is an upstream event during suppressed oxidative phosphorylation. We also observed that LDHB knockdown increases inhibitory phosphorylation of pyruvate dehydrogenase (PDH) via lactate-mediated PDH kinase (PDK) activation and thereby attenuates oxidative phosphorylation activity. Interestingly, monocarboxylate transporter 1 was the major lactate transporter in hepatoma cells, and its expression was essential for PDH phosphorylation by modulating intracellular lactate levels. Finally, bioinformatics analysis of the hepatocellular carcinoma cohort from The Cancer Genome Atlas revealed that a low LDHB/LDHA ratio is statistically significantly associated with poor prognostic outcomes. A low ratio was also associated with a significant enrichment in glycolysis genes and negatively correlated with PDK1 and 2 expression, supporting a close link between LDHB suppression and the PDK-PDH axis. These results suggest that LDHB suppression is a key mechanism that enhances glycolysis and is critically involved in the maintenance and propagation of mitochondrial dysfunction via lactate release in liver cancer progression.

Oncogenic Metabolism Acts as a Prerequisite Step for Induction of Cancer Metastasis and Cancer Stem Cell Phenotype

Metastasis is a major obstacle to the efficient and successful treatment of cancer. Initiation of metastasis requires epithelial-mesenchymal transition (EMT) that is regulated by several transcription factors, including Snail and ZEB1/2. EMT is closely linked to the acquisition of cancer stem cell (CSC) properties and chemoresistance, which contribute to tumor malignancy. Tumor suppressor p53 inhibits EMT and metastasis by negatively regulating several EMT-inducing transcription factors and regulatory molecules; thus, its inhibition is crucial in EMT, invasion, metastasis, and stemness. Metabolic alterations are another hallmark of cancer. Most cancer cells are more dependent on glycolysis than on mitochondrial oxidative phosphorylation for their energy production, even in the presence of oxygen. Cancer cells enhance other oncogenic metabolic pathways, such as glutamine metabolism, pentose phosphate pathway, and the synthesis of fatty acids and cholesterol. Metabolic reprogramming in cancer is regulated by the activation of oncogenes or loss of tumor suppressors that contribute to tumor progression. Oncogenic metabolism has been recently linked closely with the induction of EMT or CSC phenotypes by the induction of several metabolic enzyme genes. In addition, several transcription factors and molecules involved in EMT or CSCs, including Snail, Dlx-2, HIF-1α, STAT3, TGF-β, Wnt, and Akt, regulate oncogenic metabolism. Moreover, p53 induces metabolic change by directly regulating several metabolic enzymes. The collective data indicate the importance of oncogenic metabolism in the regulation of EMT, cell invasion and metastasis, and adoption of the CSC phenotype, which all contribute to malignant transformation and tumor development. In this review, we highlight the oncogenic metabolism as a key regulator of EMT and CSC, which is related with tumor progression involving metastasis and chemoresistance. Targeting oncometabolism might be a promising strategy for the development of effective anticancer therapy.

Mitochondrial genome and functional defects in osteosarcoma are associated with their aggressive phenotype

Osteosarcoma (OSA) is an aggressive mesenchymal tumor of the bone that affects children and occurs spontaneously in dogs. Human and canine OSA share similar clinical, biological and genetic features, which make dogs an excellent comparative model to investigate the etiology and pathogenesis of OSA. Mitochondrial (mt) defects have been reported in many different cancers including OSA, although it is not known whether these defects contribute to OSA progression and metastasis. Taking a comparative approach using canine OSA cell lines and tumor tissues we investigated the effects of mtDNA content and dysfunction on OSA biology. OSA tumor tissues had low mtDNA contents compared to the matched non-tumor tissues. We observed mitochondrial heterogeneity among the OSA cell lines and the most invasive cells expressing increased levels of OSA metastasis genes contained the highest amount of mitochondrial defects (reduced mtDNA copies, mt respiration, and expression of electron transport chain proteins). While mitochondria maintain a filamentous network in healthy cells, the mitochondrial morphology in OSA cells were mostly "donut shaped", typical of "stressed" mitochondria. Moreover the expression levels of mitochondrial retrograde signaling proteins Akt1, IGF1R, hnRNPA2 and NFkB correlated with the invasiveness of the OSA cells. Furthermore, we demonstrate the causal role of mitochondrial defects in inducing the invasive phenotype by Ethidium Bromide induced-mtDNA depletion in OSA cells. Our data suggest that defects in mitochondrial genome and function are prevalent in OSA and that lower mtDNA content is associated with higher tumor cell invasiveness. We propose that mt defects in OSA might serve as a prognostic biomarker and a target for therapeutic intervention in OSA patients.

Mitochondrial inheritance and cancer

Mitochondria are essential intracellular organelles that are responsible for energy metabolism, cell growth, and differentiation, redox homeostasis, oncogenic signaling, and apoptosis. These multifunctional organelles have been implicated in cancer initiation, progression, and metastasis, relapse, and acquired drug resistance due to metabolic alterations in transformed cells. Maternally inherited mitochondrial DNA (mtDNA) is thought to contribute to cancer development and prognosis and proposed as a therapeutic target for cancer treatment. In this review, we summarize the current knowledge of mtDNA alterations, with a specific focus on somatic changes, germline variants, haplogroups, large deletions, and mtDNA content changes associated with cancer susceptibility and prognosis. We also discuss the potential of mtDNA as biomarkers of cancer detection and targets of cancer treatment. Deeper understanding of the mechanisms underlying these associations requires further investigation.

Mitochondrial dysfunction suppresses p53 expression via calcium-mediated nuclear factor-kB signaling in HCT116 human colorectal carcinoma cells

Mitochondrial DNA (mtDNA) mutations are often observed in various cancer types. Although the correlation between mitochondrial dysfunction and cancer malignancy has been demonstrated by several studies, further research is required to elucidate the molecular mechanisms underlying accelerated tumor development and progression due to mitochondrial mutations. We generated an mtDNA-depleted cell line, ρ⁰, via long-term ethidium bromide treatment to define the molecular mechanisms of tumor malignancy induced by mitochondrial dysfunction. Mitochondrial dysfunction in ρ⁰ cells reduced drug-induced cell death and decreased the expression of pro-apoptotic proteins including p53. The p53 expression was reduced by activation of nuclear factor-κB that depended on elevated levels of free calcium in HCT116/ρ⁰ cells. Overall, these data provide a novel mechanism for tumor development and drug resistance due to mitochondrial dysfunction.

Histone deacetylase HDAC4 promotes the proliferation and invasion of glioma cells

Glioma is the most lethal type of primary brain tumor characterized by aggressiveness and a poor prognosis. Histone deacetylase 4 (HDAC4) is frequently dysregulated in human malignancies. However, its biological functions in the development of glioma are not fully understood. The present study aimed to evaluate HDAC4 expression in human glioma and to elucidate the mechanistic role of HDAC4 in glioma. The results suggested that HDAC4 was significantly upregulated in glioma tissues and a number of glioma cell lines compared with adjacent non-tumor tissues and the non-cancerous human glial cell line SVG p12, respectively (P<0.05). The proliferation, adenosine triphosphate (ATP) levels and invasion ability were substantially enhanced in U251 cells with HDAC4 overexpression, and suppressed in U251 cells with a knockdown of HDAC4 compared with that in U251 cells transfected with the negative control. Knockdown of HDAC4 resulted in cell cycle arrest at the G0/G1 phase and induced the increase of reactive oxygen species level in U251 cells. Furthermore, HDAC4 overexpression was revealed to substantially inhibit the expression of cyclin-dependent kinase (CDK) inhibitors p21 and p27, and the expression of E-cadherin and β‑catenin in glioma U251 cells. Knockdown of HDAC4 substantially promoted the expression of CDK1 and CDK2 and vimentin in glioma U251 cells. Mechanistically, the results of the present study demonstrated that HDAC4 displayed a significant upregulation in glioma, and promoted glioma cell proliferation and invasion mediated through the repression of p21, p27, E-cadherin and β‑catenin, and the potentiation of CDK1, CDK2 and vimentin. Altogether, the present study revealed that HDAC4 overexpression was central for the tumorigenesis of glioma, which may serve as a useful prognostic biomarker and potential therapeutic target for glioma.

Vnn1 pantetheinase limits the Warburg effect and sarcoma growth by rescuing mitochondrial activity

Expression of the Vnn1 pantetheinase by sarcomas is tumor suppressive by limiting the use of aerobic glycolysis for growth and rescuing mitochondrial activity through CoA regeneration.

Like other tumors, aggressive soft tissue sarcomas (STS) use glycolysis rather than mitochondrial oxidative phosphorylation (OXPHOS) for growth. Given the importance of the cofactor coenzyme A (CoA) in energy metabolism, we investigated the impact of Vnn1 pantetheinase—an enzyme that degrades pantetheine into pantothenate (vitamin B5, the CoA biosynthetic precursor) and cysyteamine—on tumor growth. Using two models, we show that Vnn1⁺ STS remain differentiated and grow slowly, and that in patients a detectable level of VNN1 expression in STS is associated with an improved prognosis. Increasing pantetheinase activity in aggressive tumors limits their growth. Using combined approaches, we demonstrate that Vnn1 permits restoration of CoA pools, thereby maintaining OXPHOS. The simultaneous production of cysteamine limits glycolysis and release of lactate, resulting in a partial inhibition of STS growth in vitro and in vivo. We propose that the Warburg effect observed in aggressive STS is reversed by induction of Vnn1 pantetheinase and the rewiring of cellular energy metabolism by its products.

Deep sequencing reveals the mitochondrial DNA variation landscapes of breast-to-brain metastasis blood samples

Breast-to-brain metastasis (BBM) often represents a terminal event, due to the inability of many systemic treatments to cross the blood-brain barrier (BBB), rendering the brain a sanctuary site for tumour cells. Identifying genetic variations that can predict the patients who will develop BBM would allow targeting of adjuvant treatments to reduce risk while disease bulk is minimal. Germ-line genetic variations may contribute to whether a BBM forms by influencing the primary tumour subtype that presents, or by influencing the host response to the tumour or treatment regimen, or by facilitating transition of tumour cells across the BBB and establish a viable brain metastasis. The role of mitochondrial DNA (mtDNA) variants specifically in BBM is underexplored. Consequently, using a sensitive deep sequencing approach, we characterized the mtDNA variation landscapes of blood samples derived from 13 females who were diagnosed with early-onset breast cancer and later went on to develop BBM. We also predicted the potential pathogenic significance of variations identified in all mtDNA-encoded oxidative phosphorylation (OXPHOS) proteins using 3D protein structural mapping and analysis, to identify variations worthy of follow-up. From the 70 variations found in protein coding regions, we reveal novel links between three specific mtDNA variations and altered OXPHOS structure and function in 23% of the BBM samples. Further studies are required to confirm the origin of mtDNA variations, and whether they correlate with (1) the predicted alterations in mitochondrial function and (2) increased risk of developing breast-to-brain metastasis using a much larger cohort of samples.

Knockdown of LncRNA-UCA1 suppresses chemoresistance of pediatric AML by inhibiting glycolysis through the microRNA-125a/hexokinase 2 pathway

Dysregulation of lncRNAs is implicated in chemoresistance in varieties of tumor including acute myeloid leukemia (AML). LncRNA urothelial carcinoma-associated 1 (UCA1) was reported to play an oncogenic role in AML. However, whether UCA1 was involved in chemoresistance in pediatric AML remains unclear. UCA1 expression in AML patients after adriamycin (ADR)-based chemotherapy and ADR-resistant AML cells was examined by qRT-PCR. The effects of UCA1 on the cytotoxicity of ADR and glycolysis were evaluated by MTT assay and measuring the glucose consumption and lactate production in HL60 and HL60/ADR cells, repectively. The protein levels of hypoxia-inducible factor 1α (HIF-1α) and hexokinase 2 (HK2) were determined by Western blot. Luciferase reporter assay and RNA immunoprecipitation (RIP) assay were used to confirm the relationships between UCA1, HK2, and miR-125a. We found that UCA1 expression was upregulated following ADR-based chemotherapy. Knockdown of UCA1 increased the cytotoxic effect of ADR and inhibited HIF-1α-dependent glycolysis in ADR-resistant AML cells. Additionally, UCA1 functioned as a ceRNA of miR-125a by directly binding to miR-125a. HK2, a target of miR-125a, was positively regulated by UCA1 in HL60 and HL60/ADR cells. More notably, UCA1 overexpression overturned miR-125-mediated inhibition on HIF-1α-dependent glycolysis in HL60 and HL60/ADR cells. Furthermore, 2-deoxy-glucose (2-DG) exposure inhibited HIF-1α-dependent glycolysis, and attenuated UCA1-induced increase of chemoresistance in HL60 and HL60/ADR cells. We conclude that knockdown of UCA1 plays a positive role in overcoming the chemoresistance of pediatric AML, through suppressing glycolysis by the miR-125a/HK2 pathway, contributing to a better understanding of the molecular mechanism of chemoresistance in AML.

How the Warburg effect supports aggressiveness and drug resistance of cancer cells?

Cancer cells employ both conventional oxidative metabolism and glycolytic anaerobic metabolism. However, their proliferation is marked by a shift towards increasing glycolytic metabolism even in the presence of O₂ (Warburg effect). HIF1, a major hypoxia induced transcription factor, promotes a dissociation between glycolysis and the tricarboxylic acid cycle, a process limiting the efficient production of ATP and citrate which otherwise would arrest glycolysis. The Warburg effect also favors an intracellular alkaline pH which is a driving force in many aspects of cancer cell proliferation (enhancement of glycolysis and cell cycle progression) and of cancer aggressiveness (resistance to various processes including hypoxia, apoptosis, cytotoxic drugs and immune response). This metabolism leads to epigenetic and genetic alterations with the occurrence of multiple new cell phenotypes which enhance cancer cell growth and aggressiveness. In depth understanding of these metabolic changes in cancer cells may lead to the development of novel therapeutic strategies, which when combined with existing cancer treatments, might improve their effectiveness and/or overcome chemoresistance.

Primary tumor and pre-metastatic niches co-targeting “peptides-lego” hybrid hydroxyapatite nanoparticles for metastatic breast cancer treatment

Hybrid hydroxyapatite nanoparticles orchestrating tumor metastasis resisting therapy (TMRT) and tumor metastasis targeting therapy (TMTT).

Association of mitochondrial copy number variation and T16189C polymorphism with colorectal cancer in North Indian population

Globally, colorectal cancer is the third most common type of cancer. Genetic instability leading to cancer development is one of the major causes for development of cancer. Alterations in mitochondrial genome, that is, mutations, single-nucleotide polymorphisms, and copy number variations are known to contribute in cancer development. The aim of our study was to investigate association of mitochondrial T16189C polymorphism and copy number variation with colorectal cancer in North Indian population. DNA isolated from peripheral blood of 126 colorectal cancer patients and 114 healthy North Indian subjects was analyzed for T16189C polymorphism and half of them for mitochondrial copy number variation. Genotyping was done using polymerase chain reaction-restriction fragment length polymorphism, and copy number variation was estimated using real-time polymerase chain reaction, numbers of mitochondrial copies and found to be significantly higher in colorectal cancer patients than healthy controls (88 (58-154), p = 0.001). In the regression analysis, increased mitochondrial copy number variation was associated with risk of colorectal cancer (odds ratio = 2.885, 95% confidence interval = 1.3-6.358). However, T16189C polymorphism was found to be significantly associated with the risk of rectal cancer (odds ratio = 5.213, p = 0.001) and non-significantly with colon cancer (odds ratio = 0.867, p = 0.791). Also, false-positive report probability analysis was done to validate the significant findings. Our results here indicate that mitochondrial copy number variation may be playing an important role in the development of colorectal cancer, and detection of mitochondrial copy number variation can be used as a biomarker for predicting the risk of colorectal cancer in North Indian subjects.

Mitochondrial Dysfunction: A Novel Potential Driver of Epithelial-to-Mesenchymal Transition in Cancer

Epithelial-to-mesenchymal transition (EMT) allows epithelial cancer cells to assume mesenchymal features, endowing them with enhanced motility and invasiveness, thus enabling cancer dissemination and metastatic spread. The induction of EMT is orchestrated by EMT-inducing transcription factors that switch on the expression of “mesenchymal” genes and switch off the expression of “epithelial” genes. Mitochondrial dysfunction is a hallmark of cancer and has been associated with progression to a metastatic and drug-resistant phenotype. The mechanistic link between metastasis and mitochondrial dysfunction is gradually emerging. The discovery that mitochondrial dysfunction owing to deregulated mitophagy, depletion of the mitochondrial genome (mitochondrial DNA) or mutations in Krebs’ cycle enzymes, such as succinate dehydrogenase, fumarate hydratase, and isocitrate dehydrogenase, activate the EMT gene signature has provided evidence that mitochondrial dysfunction and EMT are interconnected. In this review, we provide an overview of the current knowledge on the role of different types of mitochondrial dysfunction in inducing EMT in cancer cells. We place emphasis on recent advances in the identification of signaling components in the mito-nuclear communication network initiated by dysfunctional mitochondria that promote cellular remodeling and EMT activation in cancer cells.

TOP1MT deficiency promotes GC invasion and migration via the enhancements of LDHA expression and aerobic glycolysis

Aerobic glycolysis plays an important role in cancer progression. New target genes regulating cancer aerobic glycolysis must be explored to improve patient prognosis. Mitochondrial topoisomerase I (TOP1MT) deficiency suppresses glucose oxidative metabolism but enhances glycolysis in normal cells. Here, we examined the role of TOP1MT in gastric cancer (GC) and attempted to determine the underlying mechanism. Using in vitro and in vivo experiments and analyzing the clinicopathological characteristics of patients with GC, we found that TOP1MT expression was lower in GC samples than in adjacent nonmalignant tissues. TOP1MT knockdown significantly promoted GC migration and invasion in vitro and in vivo Importantly, TOP1MT silencing increased glucose consumption, lactate production, glucose transporter 1 expression and the epithelial-mesenchymal transition (EMT) in GC. Additionally, regulation of glucose metabolism induced by TOP1MT was significantly associated with lactate dehydrogenase A (LDHA) expression. A retrospective analysis of clinical data from 295 patients with GC demonstrated that low TOP1MT expression was associated with lymph node metastasis, recurrence and high mortality rates. TOP1MT deficiency enhanced glucose aerobic glycolysis by stimulating LDHA to promote GC progression.

Efficacy in Treating Lung Metastasis of Invasive Breast Cancer with Functional Vincristine Plus Dasatinib Liposomes

Background: The metastasis of breast cancer is the leading cause of death, while lung metastasis is a major clinical phenomenon in patients with invasive breast cancer. The current treatment option comprising surgery, radiation, and standard chemotherapy cannot achieve a satisfactory effect on the treatment of lung metastasis of breast cancer. In this study, we report the potential of preventing lung metastasis of invasive breast cancer using the newly developed functional vincristine plus dasatinib liposomes. Methods: The investigations were performed on invasive breast cancer MDA-MB-231 cells in vitro and in lung metastatic model of invasive breast cancer MDA-MB-231 cells in nude mice. Results: The functional drug liposomes were able to induce cell cycle arrest at G2/M phase, induce apoptosis, inhibit adhesion, migration, and invasion of breast cancer cells in vitro, and prevent lung metastasis of breast cancer in nude mice. Conclusion: These findings indicate a potential clinical use of functional vincristine plus dasatinib liposomes for treating metastatic breast cancer.

Tri-allelic heteroplasmies, DNA-RNA differences and their polynucleotide tract associations in the mitochondrial genome

The human mitochondrial genome has been extensively studied for its function and disease associations. Utilizing five types of high-throughput sequencing data on ten breast cancer patients (total N=50), we examined several aspects of the mitochondrial genome that have not been thoroughly studied, including the occurrence of tri-allelic heteroplasmy, the difference between DNA and RNA, and the variants association with polynucleotide tracts. We validated four previously reported and identified 23 additional tri-allelic positions. Furthermore, we detected 18 single nucleotide and seven InDel differences between DNA and RNA. Previous studies have suggested that some of these differences are caused by post transcriptional methylation. The rest can be accredited to RNA editing, polyadenylation or sequencing errors. Most importantly, we found that the tri-allelic positions, and differences between DNA and RNA, are strongly associated with polynucleotide tracts in the mitochondrial genome, suggesting DNA instability or difficulty sequencing around the polynucleotide tract regions.

Current and upcoming mitochondrial targets for cancer therapy

Mitochondria are essential intracellular organelles that regulate energy metabolism, cell death, and signaling pathways that are important for cell proliferation and differentiation. Therefore, mitochondria are fundamentally implicated in cancer biology, including initiation, growth, metastasis, relapse, and acquired drug resistance. Based on these implications, mitochondria have been proposed as a major therapeutic target for cancer treatment. In addition to classical view of mitochondria in cancer biology, recent studies found novel pathophysiological roles of mitochondria in cancer. In this review, we introduce recent concepts of mitochondrial roles in cancer biology including mitochondrial DNA mutation and epigenetic modulation, energy metabolism reprogramming, mitochondrial channels, involvement in metastasis and drug resistance, and cancer stem cells. We also discuss the role of mitochondria in emerging cancer therapeutic strategies, especially cancer immunotherapy and CRISPR-Cas9 system gene therapy.

Metabolic reprogramming and epithelial-to-mesenchymal transition in cancer

Several lines of evidence indicate that during transformation epithelial cancer cells can acquire mesenchymal features via a process called epithelial-to-mesenchymal transition (EMT). This process endows cancer cells with increased invasive and migratory capacity, enabling tumour dissemination and metastasis. EMT is associated with a complex metabolic reprogramming, orchestrated by EMT transcription factors, which support the energy requirements of increased motility and growth in harsh environmental conditions. The discovery that mutations in metabolic genes such as FH, SDH and IDH activate EMT provided further evidence that EMT and metabolism are intertwined. In this review, we discuss the role of EMT in cancer and the underpinning metabolic reprogramming. We also put forward the hypothesis that, by altering chromatin structure and function, metabolic pathways engaged by EMT are necessary for its full activation.

Uncoupling protein 2 and metabolic diseases

Mitochondria are fascinating organelles involved in various cellular-metabolic activities that are integral for mammalian development. Although they perform diverse, yet interconnected functions, mitochondria are remarkably regulated by complex signaling networks. Therefore, it is not surprising that mitochondrial dysfunction is involved in plethora of diseases, including neurodegenerative and metabolic disorders. One of the many factors that lead to mitochondrial-associated metabolic diseases is the uncoupling protein-2, a family of mitochondrial anion proteins present in the inner mitochondrial membrane. Since their discovery, uncoupling proteins have attracted considerable attention due to their involvement in mitochondrial-mediated oxidative stress and energy metabolism. This review attempts to provide a summary of recent developments in the field of uncoupling protein 2 relating to mitochondrial associated metabolic diseases.

Glycolysis inhibition improves photodynamic therapy response rates for equine sarcoids

Photodynamic therapy (PDT) holds great promise in treating veterinary and human dermatological neoplasms, including equine sarcoids, but is currently hindered by the amount of photosensitiser and light that can be delivered to lesions thicker than around 2 mm, and by the intrinsic antioxidant defences of tumour cells. We have developed a new PDT technique that combines an efficient transdermal penetration enhancer solution, for topical delivery of 5-aminolevulinic acid (ALA) photosensitiser, with acute topical post-PDT application of the glycolysis inhibitor lonidamine. We show that the new PDT combination treatment selectively kills sarcoid cells in vitro, with repeated rounds of treatment increasing sarcoid sensitisation to PDT. In vivo, ALA PDT followed by 600 μM lonidamine substantially improves treatment outcomes for occult, verrucous, nodular and fibroblastic sarcoids after 1 month (93% treatment response in 27 sarcoids), compared with PDT using only ALA (14% treatment response in 7 sarcoids).

Changes in mitochondrial function during EMT induced by TGFβ-1 in pancreatic cancer

Mitochondrial dysfunction is linked to cancer. Differences in the number, morphology and function of mitochondria have been observed between normal cells and cancer cells. However, changes in mitochondrial function during epithelial-mesenchymal transition (EMT) in pancreatic cancer are less known. In the present study, the cultured human pancreatic cancer cell line Panc-1 was treated with transforming growth factor (TGF)β-1. Mitochondrial functions following TGFβ-1 exposure in pancreatic cancer were investigated. It was noticed that TGFβ-1 treatment induces morphologic changes and a shift from epithelial to mesenchymal phenotype in pancreatic cancer. Furthermore, increased mitochondrial mass was detected in pancreatic cancer following TGFβ-1 treatment. Besides, the production of reactive oxygen species in TGFβ-1-treated pancreatic cancer cells significantly increased compared with the control cells. Our results indicate that the phenomenon of EMT in pancreatic cancer has an association with mitochondrial dysfunction. Mitochondrial dysfunction may be a cause of EMT in pancreatic cancer, which leads to heterogeneity in pancreatic cancer, and may be a potential therapeutic target in the future.

Altered mitochondrial DNA copy number contributes to human cancer risk: evidence from an updated meta-analysis

Accumulating epidemiological evidence indicates that the quantitative changes in human mitochondrial DNA (mtDNA) copy number could affect the genetic susceptibility of malignancies in a tumor-specific manner, but the results are still elusive. To provide a more precise estimation on the association between mtDNA copy number and risk of diverse malignancies, a meta-analysis was conducted by calculating the pooled odds ratios (OR) and the 95% confidence intervals (95% CI). A total of 36 case-control studies involving 11,847 cases and 15,438 controls were finally included in the meta-analysis. Overall analysis of all studies suggested no significant association between mtDNA content and cancer risk (OR = 1.044, 95% CI = 0.866–1.260, P = 0.651). Subgroup analyses by cancer types showed an obvious positive association between mtDNA content and lymphoma and breast cancer (OR = 1.645, 95% CI = 1.117–2.421, P = 0.012; OR = 1.721, 95% CI = 1.130–2.622, P = 0.011, respectively), and a negative association for hepatic carcinoma. Stratified analyses by other confounding factors also found increased cancer risk in people with drinking addiction. Further analysis using studies of quartiles found that populations with the highest mtDNA content may be under more obvious risk of melanoma and that Western populations were more susceptible than Asians.

Mitochondrial metabolic remodeling in response to genetic and environmental perturbations

Mitochondria are metabolic hubs within mammalian cells and demonstrate significant metabolic plasticity. In oxygenated environments with ample carbohydrate, amino acid, and lipid sources, they are able to use the tricarboxylic acid cycle for the production of anabolic metabolites and ATP. However, in conditions where oxygen becomes limiting for oxidative phosphorylation, they can rapidly signal to increase cytosolic glycolytic ATP production, while awaiting hypoxia‐induced changes in the proteome mediated by the activity of transcription factors such as hypoxia‐inducible factor 1. Hypoxia is a well‐described phenotype of most cancers, driving many aspects of malignancy. Improving our understanding of how mitochondria change their metabolism in response to this stimulus may therefore elicit the design of new selective therapies. Many of the recent advances in our understanding of mitochondrial metabolic plasticity have been acquired through investigations of cancer‐associated mutations in metabolic enzymes, including succinate dehydrogenase, fumarate hydratase, and isocitrate dehydrogenase. This review will describe how metabolic perturbations induced by hypoxia and mutations in these enzymes have informed our knowledge in the control of mitochondrial metabolism, and will examine what this may mean for the biology of the cancers in which these mutations are observed. WIREs Syst Biol Med 2016, 8:272–285. doi: 10.1002/wsbm.1334

For further resources related to this article, please visit the WIREs website.

Mitochondria single nucleotide variation across six blood cell types

It has been shown that heteroplasmic mitochondrial DNA variants can be tissue specific. However, whether mitochondrial DNA variants are specific by blood cell types has not been investigated. Motivated by this question and using mitochondria sequences extracted from RNAseq data from six distinct blood cell types (neutrophil, monocyte, myeloid dendritic, natural killer, T and B), we thoroughly compared SNPs and heteroplasmies among these cell types. Each cell type from each subject was sequenced at four time points used as biological replicates. We found that mitochondria content is low in neutrophil compared to the other five blood cell types. Subsequent analysis on the other five blood cell types showed that at the SNP level, there was no discrepancy. At the heteroplasmy level, we observed good concordances among all blood cell types. However, the allele frequencies of the heteroplasmy differed between blood cell types for certain heteroplasmic sites. Furthermore, we identified five tri-allelic sites (1610, 2617, 8303, 12146, 13710) that are likely caused by RNA editing. Three out of these five sites are located at the ninth position of tRNA genes, and are likely resulting from post-transcriptional methylation.

Evaluating the Effects of Tetrachloro-1,4-benzoquinone, an Active Metabolite of Pentachlorophenol, on the Growth of Human Breast Cancer Cells

Tetrachloro-1,4-benzoquinone (TCBQ), an active metabolite of pentachlorophenol (PCP), is genotoxic and potentially carcinogenic. As an electrophilic and oxidative molecule, TCBQ can conjugate with deoxyguanosine in DNA molecules and/or impose oxidative stress in cells. In the current study, we investigated the effects of TCBQ on intracellular ROS production, apoptosis, and cytotoxicity against three different subtypes of human breast cancer cells. Luminal A subtype MCF7 (ER⁺, PR⁺, HER2⁻) cells maintained the highest intracellular ROS level and were subjected to TCBQ-induced ROS reduction, apoptosis, and cytotoxicity. HER2 subtype Sk-Br-3 (ER⁻, PR⁻, HER2⁺) cells possessed the lowest intracellular ROS level. TCBQ promoted ROS production, inhibited apoptosis, and elevated cytotoxicity (due to necrosis) against Sk-Br-3 cells. Triple-negative/basal-like subtype MDA-MB-231 cells were less sensitive towards TCBQ treatment. Therefore, the effect of prolonged exposure to PCP and its active metabolites on cancer growth is highly cancer-cell-type specific.

Mitochondrial DNA copy number in whole blood and glioma risk: A case control study

Alterations in mitochondrial DNA (mtDNA) copy number are observed in human gliomas. However, whether variations in mtDNA copy number in whole blood play any role in glioma carcinogenesis is still largely unknown. In current study with 395 glioma patients and 425 healthy controls, we intended to investigate the association between mtDNA copy number in whole blood and glioma risk. Overall, we found that levels of mtDNA copy number were significantly higher in glioma cases than healthy controls (mean: 1.48 vs. 1.32, P < 0.01). In both cases and controls, levels of mtDNA copy number were inversely correlated with age (P < 0.01, respectively). And in cases, newly diagnosed, glioblastoma (GBM), and high grade glioma patients had significantly lower mtDNA copy number than their counterparts (P = 0.02, P < 0.01, and P = 0.04, respectively). In the multivariate analysis, elevated mtDNA copy number levels were associated with a 1.63-fold increased risk of glioma (adjusted odds ratio (OR) = 1.63, 95% confidence interval (CI) = 1.23-2.14). In further quartile analysis, study subjects who had highest levels of mtNDA copy number had 1.75-fold increased risk of gliomas (adjOR = 1.75, 95%CI = 1.18-2.61). In brief, our findings support the role of mtDNA copy number in the glioma carcinogenesis. © 2016 Wiley Periodicals, Inc.

Melatonin Cytotoxicity Is Associated to Warburg Effect Inhibition in Ewing Sarcoma Cells

Melatonin kills or inhibits the proliferation of different cancer cell types, and this is associated with an increase or a decrease in reactive oxygen species, respectively. Intracellular oxidants originate mainly from oxidative metabolism, and cancer cells frequently show alterations in this metabolic pathway, such as the Warburg effect (aerobic glycolysis). Thus, we hypothesized that melatonin could also regulate differentially oxidative metabolism in cells where it is cytotoxic (Ewing sarcoma cells) and in cells where it inhibits proliferation (chondrosarcoma cells). Ewing sarcoma cells but not chondrosarcoma cells showed a metabolic profile consistent with aerobic glycolysis, i.e. increased glucose uptake, LDH activity, lactate production and HIF-1α activation. Melatonin reversed Ewing sarcoma metabolic profile and this effect was associated with its cytotoxicity. The differential regulation of metabolism by melatonin could explain why the hormone is harmless for a wide spectrum of normal and only a few tumoral cells, while it kills specific tumor cell types.

Eight proteins play critical roles in RCC with bone metastasis via mitochondrial dysfunction

Most kidney cancers are renal cell carcinomas (RCC). RCC lacks early warning signs and 70 % of patients with RCC develop metastases. Among them, 50 % of patients having skeletal metastases developed a dismal survival of less than 10 % at 5 years. Therefore, exploring the key driving proteins and pathways involved in RCC bone metastasis could benefit patients’ therapy and prolong their survival. We examined the difference between the OS-RC-2 cells and the OS-RC-2-BM5 cells (subpopulation from OS-RC-2) of RCC with proteomics. Then we employed Western-blot, immunohistochemistry and the clinical database (oncomine) to screen and verify the key proteins and then we analyzed the functions and the related pathways of selected key proteins with system biology approaches. Our proteomic data revealed 26 significant changed spots (fold change <0.5 and >1.9, P < 0.05) between two cells. The Western blotting results validated for these identified spots were consistent with the proteomics’. From the public clinical database, 23 out of 26 proteins were connected with RCC metastases and 9 out of 23 with survival time directly (P < 0.05). Finally, only 8 out of 9 proteins had significantly positive results in tissues of RCC patients with bone metastasis compared with primary tumor (P < 0.05). System biology analyzing results showed these eight proteins mainly distributed in oxidative phosphorylation which indicates that mitochondria dysfunction played the critical role to regulate cells metastasis. Our article used a variety of experimental techniques to find eight proteins which abnormally regulated mitochondrial function to achieve a successful induction for RCC metastasis to bone.