Frequency and phenotypic implications of mitochondrial DNA mutations in human squamous cell cancers of the head and neck

Profiling mitochondrial DNA mutations in tumors and circulating extracellular vesicles of triple-negative breast cancer patients for potential biomarker development

Early detection and recurrence prediction are challenging in triple-negative breast cancer (TNBC) patients. We aimed to develop mitochondrial DNA (mtDNA)-based liquid biomarkers to improve TNBC management. Mitochondrial genome (MG) enrichment and next-generation sequencing mapped the entire MG in 73 samples (64 tissues and 9 extracellular vesicles [EV] samples) from 32 metastatic TNBCs. We measured mtDNA and cardiolipin (CL) contents, NDUFB8, and SDHB protein expression in tumors and in corresponding circulating EVs. We identified 168 nonsynonymous mtDNA mutations, with 73% (123/186) coding and 27% (45/168) noncoding in nature. Twenty percent of mutations were nucleotide transversions. Respiratory complex I (RCI) was the key target, which harbored 44% (74/168) of the overall mtDNA mutations. A panel of 11 hotspot mtDNA mutations was identified among 19%-38% TNBCs, which were detectable in the serum-derived EVs with 82% specificity. Overall, 38% of the metastatic tumor-signature mtDNA mutations were traceable in the EVs. An appreciable number of mtDNA mutations were homoplasmic (18%, 31/168), novel (14%, 23/168), and potentially pathogenic (9%, 15/168). The overall and RCI-specific mtDNA mutational load was higher in women with African compared to European ancestry accompanied by an exclusive abundance of respiratory complex (RC) protein NDUFB8 (RCI) and SDHB (RCII) therein. Increased mtDNA (p < 0.0001) content was recorded in both tumors and EVs along with an abundance of CL (p = 0.0001) content in the EVs. Aggressive tumor-signature mtDNA mutation detection and measurement of mtDNA and CL contents in the EVs bear the potential to formulate noninvasive early detection and recurrence prediction strategies.

Prognostic Value of Circulating Mitochondrial DNA in Prostate Cancer and Underlying Mechanism

Circulating DNAs are considered as degraded DNA fragments of approximately 50-200 bp, found in blood plasma, consisting of cell-free mitochondrial and nuclear DNA. Such cell-free DNAs in the blood are found to be altered in different pathological conditions including lupus, heart disease, and malignancies. While nuclear DNAs are being used and being developed as a powerful clinical biomarker in liquid biopsies, mitochondrial DNAs (mtDNAs) are associated with inflammatory conditions including cancer progression. Patients with cancer including prostate cancer are found to have measurable concentrations of mitochondrial DNA in circulation in comparison with healthy controls. The plasma content of mitochondrial DNA is dramatically elevated in both prostate cancer patients and mouse models treated with the chemotherapeutic drug. Cell-free mtDNA, in its oxidized form, induced a pro-inflammatory condition and activates NLRP3-mediated inflammasome formation which causes IL-1β-mediated activation of growth factors. On the other hand, interacting with TLR9, mtDNAs trigger NF-κB-mediated complement C3a positive feedback paracrine loop and activate pro-proliferating signaling through upregulating AKT, ERK, and Bcl2 in the prostate tumor microenvironment. In this review, we discuss the growing evidence supporting cell-free mitochondrial DNA copy number, size, and mutations in mtDNA genes as potential prognostic biomarkers in different cancers and targetable prostate cancer therapeutic candidates impacting stromal-epithelial interactions essential for chemotherapy response.

Disorders of cancer metabolism: The therapeutic potential of cannabinoids

Abnormal energy metabolism, as one of the important hallmarks of cancer, was induced by multiple carcinogenic factors and tumor-specific microenvironments. It comprises aerobic glycolysis, de novo lipid biosynthesis, and glutamine-dependent anaplerosis. Considering that metabolic reprogramming provides various nutrients for tumor survival and development, it has been considered a potential target for cancer therapy. Cannabinoids have been shown to exhibit a variety of anticancer activities by unclear mechanisms. This paper first reviews the recent progress of related signaling pathways (reactive oxygen species (ROS), AMP-activated protein kinase (AMPK), mitogen-activated protein kinases (MAPK), phosphoinositide 3-kinase (PI3K), hypoxia-inducible factor-1alpha (HIF-1α), and p53) mediating the reprogramming of cancer metabolism (including glucose metabolism, lipid metabolism, and amino acid metabolism). Then we comprehensively explore the latest discoveries and possible mechanisms of the anticancer effects of cannabinoids through the regulation of the above-mentioned related signaling pathways, to provide new targets and insights for cancer prevention and treatment.

Respiratory Complex I dysfunction in cancer: from a maze of cellular adaptive responses to potential therapeutic strategies

Mitochondria act as key organelles in cellular bioenergetics and biosynthetic processes producing signals that regulate different molecular networks for proliferation and cell death. This ability is also preserved in pathologic contexts such as tumorigenesis, during which bioenergetic changes and metabolic reprogramming confer flexibility favoring cancer cell survival in a hostile microenvironment. Although different studies epitomize mitochondrial dysfunction as a protumorigenic hit, genetic ablation or pharmacological inhibition of respiratory complex I causing a severe impairment is associated with a low-proliferative phenotype. In this scenario, it must be considered that despite the initial delay in growth, cancer cells may become able to resume proliferation exploiting molecular mechanisms to overcome growth arrest. Here, we highlight the current knowledge on molecular responses activated by complex I-defective cancer cells to bypass physiological control systems and to re-adapt their fitness during microenvironment changes. Such adaptive mechanisms could reveal possible novel molecular players in synthetic lethality with complex I impairment, thus providing new synergistic strategies for mitochondrial-based anticancer therapy.

Detection of mitochondrial DNA mutations in circulating mitochondria-originated extracellular vesicles for potential diagnostic applications in pancreatic adenocarcinoma

There is a complete lack of highly sensitive and specific biomarkers for early pancreatic ductal adenocarcinoma (PDAC) diagnosis, limiting multi-modal therapeutic options. Mitochondrial DNA (mtDNA) is an excellent resource for biomarker discovery because of its high copy number and increased mutational frequency in cancer cells. We examined if mtDNA mutations can be detected in circulating extracellular vesicles (EVs) of PDAC patients and used for discerning between cancer and non-cancer subjects. A greater yield of circulating EVs (~ 1.4 fold; p = 0.002) was obtained in PDAC patients (n = 20) than non-cancer (NC) individuals (n = 10). PDAC-EVs contained a higher quantity of total DNA (~ 5.5 folds; p = 0.0001) than NC-EVs and had greater enrichment of mtDNA (~ 14.02-fold; p = 0.0001). PDAC-EVs also had higher levels of cardiolipin (a mitochondrial inner-membrane phospholipid), suggestive of their mitochondrial origin. All mtDNA mutations in PDAC-EVs were unique and frequency was remarkably higher. Most mtDNA mutations (41.5%) in PDAC-EVs were in the respiratory complex-I (RCI) (ND1-ND6), followed by the RCIII gene (CYTB; 11.2%). Among the non-coding genes, D-Loop and RNR2 exhibited the most mutations (15.2% each). Altogether, our study establishes, for the first time, that mtDNA mutations can be detected in circulating EVs and potentially serve as a tool for reliable PDAC diagnosis.

Mitochondrial respiratory complexes: Significance in human mitochondrial disorders and cancers

Mitochondria are pivotal organelles that govern cellular energy production through the oxidative phosphorylation system utilizing five respiratory complexes. In addition, mitochondria also contribute to various critical signaling pathways including apoptosis, damage-associated molecular patterns, calcium homeostasis, lipid, and amino acid biosynthesis. Among these diverse functions, the energy generation program oversee by mitochondria represents an immaculate orchestration and functional coordination between the mitochondria and nuclear encoded molecules. Perturbation in this program through respiratory complexes' alteration results in the manifestation of various mitochondrial disorders and malignancy, which is alarmingly becoming evident in the recent literature. Considering the clinical relevance and importance of this emerging medical problem, this review sheds light on the timing and nature of molecular alterations in various respiratory complexes and their functional consequences observed in various mitochondrial disorders and human cancers. Finally, we discussed how this wealth of information could be exploited and tailored to develop respiratory complex targeted personalized therapeutics and biomarkers for better management of various incurable human mitochondrial disorders and cancers.

The Effect of Ketogenic Diet on Shared Risk Factors of Cardiovascular Disease and Cancer

Cardiovascular disease (CVD) and cancer are the first and second leading causes of death worldwide, respectively. Epidemiological evidence has demonstrated that the incidence of cancer is elevated in patients with CVD and vice versa. However, these conditions are usually regarded as separate events despite the presence of shared risk factors between both conditions, such as metabolic abnormalities and lifestyle. Cohort studies suggested that controlling for CVD risk factors may have an impact on cancer incidence. Therefore, it could be concluded that interventions that improve CVD and cancer shared risk factors may potentially be effective in preventing and treating both diseases. The ketogenic diet (KD), a low-carbohydrate and high-fat diet, has been widely prescribed in weight loss programs for metabolic abnormalities. Furthermore, recent research has investigated the effects of KD on the treatment of numerous diseases, including CVD and cancer, due to its role in promoting ketolysis, ketogenesis, and modifying many other metabolic pathways with potential favorable health effects. However, there is still great debate regarding prescribing KD in patients either with CVD or cancer. Considering the number of studies on this topic, there is a clear need to summarize potential mechanisms through which KD can improve cardiovascular health and control cell proliferation. In this review, we explained the history of KD, its types, and physiological effects and discussed how it could play a role in CVD and cancer treatment and prevention.

Interplay Between Reactive Oxygen/Reactive Nitrogen Species and Metabolism in Vascular Biology and Disease

Reactive oxygen species (ROS; e.g., superoxide [O₂^•-] and hydrogen peroxide [H₂O₂]) and reactive nitrogen species (RNS; e.g., nitric oxide [NO^•]) at the physiological level function as signaling molecules that mediate many biological responses, including cell proliferation, migration, differentiation, and gene expression. By contrast, excess ROS/RNS, a consequence of dysregulated redox homeostasis, is a hallmark of cardiovascular disease. Accumulating evidence suggests that both ROS and RNS regulate various metabolic pathways and enzymes. Recent studies indicate that cells have mechanisms that fine-tune ROS/RNS levels by tight regulation of metabolic pathways, such as glycolysis and oxidative phosphorylation. The ROS/RNS-mediated inhibition of glycolytic pathways promotes metabolic reprogramming away from glycolytic flux toward the oxidative pentose phosphate pathway to generate nicotinamide adenine dinucleotide phosphate (NADPH) for antioxidant defense. This review summarizes our current knowledge of the mechanisms by which ROS/RNS regulate metabolic enzymes and cellular metabolism and how cellular metabolism influences redox homeostasis and the pathogenesis of disease. A full understanding of these mechanisms will be important for the development of new therapeutic strategies to treat diseases associated with dysregulated redox homeostasis and metabolism. Antioxid. Redox Signal. 34, 1319-1354.

Differences in the mitochondrial microsatellite instability of Keratoacanthoma and cutaneous squamous cell carcinoma

Keratoacanthoma (KA) is a common cutaneous neoplasm which often resembles typical squamous cell carcinoma (SCC) in both its clinical and historical presentation. Several studies have attempted to identify methods for distinguishing between KA and SCC, however, none of these have proven to play any obvious roles in these tumors. Given this we went on to evaluate mitochondrial microsatellite instability (mtMSI) in KA and SCC in an effort to understand these tumors better. DNA was isolated from paired normal and tumoral tissues donated by 57 KA patients and 43 SCC patients. MtMSI was then analyzed using eight microsatellite markers and was observed in 2 (3.5%) of the 57 KA patients and 8 (18.6%) of the 43 SCC patients, respectively. MtMSI was also shown to affect different locations depending on tumor type. In KA patients, mtMSI was detected at mitochondrial D514 D-loop and presented with (CA) n repeats, in contrast, all of the SCC patient experienced mtMSI at the D310 with (C)n repeats of the D-loop region. These differences in location were found to be significant, which may support the hypothesis that KA and SCC have different pathogenetic pathways. Our results also suggest that mtMSI may be a candidate for developing novel differential diagnostic methods for KA and SCC.

Association Between Mitochondrial DNA Copy Number and Head and Neck Squamous Cell Carcinoma: A Systematic Review and Dose-Response Meta-Analysis

Background

The association between mitochondrial DNA (mtDNA) copy number and head and neck squamous cell carcinoma (HNSCC) risk remains unclear. Therefore, we aimed to evaluate the relationship between mtDNA copy number and HNSCC risk.

Material/Methods

We searched PubMed, Web of Science, and EMBASE until August 2020. Studies that assessed the association between mtDNA copy number and HNSCC as the outcome of interest were included. We performed a 2-class and dose-response meta-analysis to assess the association between cancer risk and mtDNA.

Results

Eight articles (2 cohort studies and 6 case-control studies) with a total of 3913 patients were included in our meta-analysis. The overall results showed that mean mtDNA copy number level from 9 studies was 0.71 higher in patients with cancer than in non-cancer controls (the standardized mean differences (SMD) 0.71, 95% CI: 0.28–1.15, P<0.001). However, when 4 studies were pooled by dichotomizing mtDNA copy number at the median value into high- and low-content groups, no significant association between mtDNA content and overall cancer risk was found (odds ratio (OR)=0.87, 95% CI: 0.52–1.44, P=0.584). Furthermore, we observed a non-linear association from 3 studies between increased mtDNA copy number levels (P for nonlinearity <0.001).

Conclusions

The elevated mtDNA copy number could predict the risk of HNSCC as a biomarker. Moreover, there was non-linear relationship of risk between HNSCC and mtDNA copy number.

Heterologous Inferential Analysis (HIA) and Other Emerging Concepts: In Understanding Mitochondrial Variation In Pathogenesis: There is no More Low-Hanging Fruit

Here we summarize our latest efforts to elucidate the role of mtDNA variants affecting the mitochondrial translation machinery, namely variants mapping to the mt-rRNA and mt-tRNA genes. Evidence is accumulating to suggest that the cellular response to interference with mitochondrial translation is different from that occurring as a result of mutations in genes encoding OXPHOS proteins. As a result, it appears safe to state that a complete view of mitochondrial disease will not be obtained until we understand the effect of mt-rRNA and mt-tRNA variants on mitochondrial protein synthesis. Despite the identification of a large number of potentially pathogenic variants in the mitochondrially encoded rRNA (mt-rRNA) genes, we lack direct methods to firmly establish their pathogenicity. In the absence of such methods, we have devised an indirect approach named heterologous inferential analysis (HIA ) that can be used to make predictions concerning the disruptive potential of a large subset of mt-rRNA variants. We have used HIA to explore the mutational landscape of 12S and 16S mt-rRNA genes. Our HIA studies include a thorough classification of all rare variants reported in the literature as well as others obtained from studies performed in collaboration with physicians. HIA has also been used with non-mammalian mt-rRNA genes to elucidate how mitotypes influence the interaction of the individual and the environment. Regarding mt-tRNA variations, rapidly growing evidence shows that the spectrum of mutations causing mitochondrial disease might differ between the different mitochondrial haplogroups seen in human populations.

Dual-emissive, oxygen-sensing boron nanoparticles quantify oxygen consumption rate in breast cancer cells

SIGNIFICANCE

Decreasing the oxygen consumption rate (OCR) of tumor cells is a powerful method for ameliorating tumor hypoxia. However, quantifying the change in OCR is challenging in complex experimental systems.

AIM

We present a method for quantifying the OCR of two tumor cell lines using oxygen-sensitive dual-emissive boron nanoparticles (BNPs). We hypothesize that our BNP results are equivalent to the standard Seahorse assay.

APPROACH

We quantified the spectral emissions of the BNP and accounted for external oxygen diffusion to quantify OCR over 24 h. The BNP-computed OCR of two breast cancer cell lines, E0771 and 4T07, were compared with their respective Seahorse assays. Both cell lines were also irradiated to quantify radiation-induced changes in the OCR.

RESULTS

Using a Bland-Altman analysis, our BNPs OCR was equivalent to the standard Seahorse assay. Moreover, in an additional experiment in which we irradiated the cells at their 50% survival fraction, the BNPs were sensitive enough to quantify 24% reduction in OCR after irradiation.

CONCLUSIONS

Our results conclude that the BNPs are a viable alternative to the Seahorse assay for quantifying the OCR in cells. The Bland-Altman analysis showed that these two methods result in equivalent OCR measurements. Future studies will extend the OCR measurements to complex systems including 3D cultures and in vivo models, in which OCR measurements cannot currently be made.

Multifaceted Roles of Mitochondrial Components and Metabolites in Metabolic Diseases and Cancer

Mitochondria are essential cellular components that ensure physiological metabolic functions. They provide energy in the form of adenosine triphosphate (ATP) through the electron transport chain (ETC). They also constitute a metabolic hub in which metabolites are used and processed, notably through the tricarboxylic acid (TCA) cycle. These newly generated metabolites have the capacity to feed other cellular metabolic pathways; modify cellular functions; and, ultimately, generate specific phenotypes. Mitochondria also provide intracellular signaling cues through reactive oxygen species (ROS) production. As expected with such a central cellular role, mitochondrial dysfunctions have been linked to many different diseases. The origins of some of these diseases could be pinpointed to specific mutations in both mitochondrial- and nuclear-encoded genes. In addition to their impressive intracellular tasks, mitochondria also provide intercellular signaling as they can be exchanged between cells, with resulting effects ranging from repair of damaged cells to strengthened progression and chemo-resistance of cancer cells. Several therapeutic options can now be envisioned to rescue mitochondria-defective cells. They include gene therapy for both mitochondrial and nuclear defective genes. Transferring exogenous mitochondria to target cells is also a whole new area of investigation. Finally, supplementing targeted metabolites, possibly through microbiota transplantation, appears as another therapeutic approach full of promises.

Landscape of Mitochondria Genome and Clinical Outcomes in Stage 1 Lung Adenocarcinoma

Risk factors including genetic effects are still being investigated in lung adenocarcinoma (LUAD). Mitochondria play an important role in controlling imperative cellular parameters, and anomalies in mitochondrial function might be crucial for cancer development. The mitochondrial genomic aberrations found in lung adenocarcinoma and their associations with cancer development and progression are not yet clearly characterized. Here, we identified a spectrum of mitochondrial genome mutations in early-stage lung adenocarcinoma and explored their association with prognosis and clinical outcomes. Next-generation sequencing was used to reveal the mitochondrial genomes of tumor and conditionally normal adjacent tissues from 61 Stage 1 LUADs. Mitochondrial somatic mutations and clinical outcomes including relapse-free survival (RFS) were analyzed. Patients with somatic mutations in the D-loop region had longer RFS (adjusted hazard ratio, adjHR = 0.18, p = 0.027), whereas somatic mutations in mitochondrial Complex IV and Complex V genes were associated with shorter RFS (adjHR = 3.69, p = 0.012, and adjHR = 6.63, p = 0.002, respectively). The risk scores derived from mitochondrial somatic mutations were predictive of RFS (adjHR = 9.10, 95%CI: 2.93-28.32, p < 0.001). Our findings demonstrated the vulnerability of the mitochondrial genome to mutations and the potential prediction ability of somatic mutations. This research may contribute to improving molecular guidance for patient treatment in precision medicine.

Somatic mitochondrial mutation discovery using ultra-deep sequencing of the mitochondrial genome reveals spatial tumor heterogeneity in head and neck squamous cell carcinoma

Mutations in mitochondrial DNA (mtDNA) have been linked to risk, progression, and treatment response of head and neck squamous cell carcinoma (HNSCC). Due to their clonal nature and high copy number, mitochondrial mutations could serve as powerful molecular markers for detection of cancer cells in bodily fluids, surgical margins, biopsies and lymph node (LN) metastasis, especially at sites where tumor involvement is not histologically apparent. Despite a pressing need for high-throughput, cost-effective mtDNA mutation profiling system, current methods for library preparation are still imperfect for detection of low prevalence heteroplasmic mutations. To this end, we have designed an ultra-deep amplicon-based sequencing library preparation approach that covers the entire mitochondrial genome. We sequenced mtDNA in 28 HNSCCs, matched LNs, surgical margins and bodily fluids, and applied multiregional sequencing approach on 14 primary tumors. Our results demonstrate that this quick, sensitive and cost-efficient method allows obtaining a snapshot on the mitochondrial heterogeneity, and can be used for detection of low frequency tumor-associated mtDNA mutations in LNs, sputum and serum specimens. These findings provide the foundation for using mitochondrial sequencing for risk assessment, early detection, and tumor surveillance.

Role of ectopically expressed mtDNA encoded cytochrome c oxidase subunit I (MT-COI) in tumorigenesis

Somatic mutations within mitochondrial DNA (mtDNA) encoded cytochrome c oxidase subunit I (MT-CO1 or MT-COI) are frequent in various cancer types. In addition, perturbation from orchestrated expression of mitochondrial DNA encoded genes is also associated with complex disorders, including cancer. Since codon bias and the mitochondrial translation system restricts functional characterization of over-expressed wild type or mutant mitochondrial DNA encoded genes, the codon optimization and artificial synthesis of entire MT-CO1 allowed us to over-express the wild type and one of its deleterious mutants into the mitochondria of the transfected cells. Ectopically expressed MT-CO1 was observed to efficiently express and localized to mitochondria but showed high level of aggregation under denaturing condition. Over-expression of wild type or mutant variant of MT-CO1 promoted anchorage dependent and independent proliferation potential in in-vitro experiments and introduced the cancer cell metabolic phenotype of high glucose uptake and lactate release. Reactive oxygen species generated in cells over-expressing MT-CO1 variants acted as key effectors mediating differential expression of apoptosis and DNA damage pathway related genes. High ROS generated also down-regulated the expression of global regulators of gene expression, DNMT3A and DNMT3B. The down-regulated expression of DNMTs co-related with differential methylation of the CpG islands in the promoter region of a select set of studied genes, in a manner to promote pro-cancerous phenotype. Apart from assigning the mechanistic role to the MT-CO1 variants and their perturbed expression in cancer development, the present study provides novel insights into the functional role of somatic mutations within MT-CO1 promoting cancer phenotype.

Whole mitochondrial genome sequencing highlights mitochondrial impact in gastric cancer

Mitochondria are organelles that perform major roles in cellular operation. Thus, alterations in mitochondrial genome (mtGenome) may lead to mitochondrial dysfunction and cellular deregulation, influencing carcinogenesis. Gastric cancer (GC) is one of the most incident and mortal types of cancer in Brazil, particularly in the Amazon region. Here, we sequenced and compared the whole mtGenome extracted from FFPE tissue samples of GC patients (tumor and internal control – IC) and cancer-free individuals (external control – EC) from this region. We found 3-fold more variants and up to 9-fold more heteroplasmic regions in tumor when compared to paired IC samples. Moreover, tumor presented more heteroplasmic variants when compared to EC, while IC and EC showed no significant difference when compared to each other. Tumor also presented substantially more variants in the following regions: MT-RNR1, MT-ND5, MT-ND4, MT-ND2, MT-DLOOP1 and MT-CO1. In addition, our haplogroup results indicate an association of Native American ancestry (particularly haplogroup C) to gastric cancer development. To the best of our knowledge, this is the first study to sequence the whole mtGenome from FFPE samples and to apply mtGenome analysis in association to GC in Brazil.

Weighted gene coexpression network analysis reveals hub genes involved in cholangiocarcinoma progression and prognosis

AIM

Cholangiocarcinoma (CCA) is a highly malignant tumor found in the bile duct epithelial cells, and the second most common primary tumor of the liver. However, the pivotal roles of molecular biomarkers in oncogenesis of CCA are unclear. Therefore, we aim to explore the underlying mechanisms of progression and screen for novel prognostic biomarkers and treatment targets.

METHOD

The data of mRNA sequencing and clinical information of CCA patients in The Cancer Genome Atlas was analyzed by weighted gene coexpression network analysis (WGCNA). Modules and clinical traits were constructed according to Pearson's correlation analysis, and Gene Ontology and pathway enrichment analysis were applied. Hub genes of these modules were screened by intramodule analysis; Cytoscape with Search Tool for the Retrieval of Interacting Genes was utilized to visualize protein-protein interaction of these modules; hub genes of these modules were validated afterwards. Furthermore, the significance of these genes was confirmed by survival analysis.

RESULTS

Genes MRPS18A, CST1, and SCP2 were identified as candidate genes in the module, which was associated with clinical traits including pathological stage, histological grade, and liver function and which also affected overall survival of CCA patients. Nineteen hub genes were analyzed together and were associated with progression and prognosis of CCA. Survival analyses found that several of the multiple genes could serve as biomarkers to stratify CCA patients into low- and high-risk groups.

CONCLUSION

These candidate genes could be involved in progression of CCA, which could serve as novel prognostic markers and treatment targets. Moreover, most of them were first reported in CCA and deserve further research.

Chronic Exposure to Chewing Tobacco Induces Metabolic Reprogramming and Cancer Stem Cell-Like Properties in Esophageal Epithelial Cells

Tobacco in its smoke and smokeless form are major risk factors for esophageal squamous cell carcinoma (ESCC). However, molecular alterations associated with smokeless tobacco exposure are poorly understood. In the Indian subcontinent, tobacco is predominantly consumed in chewing form. An understanding of molecular alterations associated with chewing tobacco exposure is vital for identifying molecular markers and potential targets. We developed an in vitro cellular model by exposing non-transformed esophageal epithelial cells to chewing tobacco over an eight-month period. Chronic exposure to chewing tobacco led to increase in cell proliferation, invasive ability and anchorage independent growth, indicating cell transformation. Molecular alterations associated with chewing tobacco exposure were characterized by carrying out exome sequencing and quantitative proteomic profiling of parental cells and chewing tobacco exposed cells. Quantitative proteomic analysis revealed increased expression of cancer stem cell markers in tobacco treated cells. In addition, tobacco exposed cells showed the Oxidative Phosphorylation (OXPHOS) phenotype with decreased expression of enzymes associated with glycolytic pathway and increased expression of a large number of mitochondrial proteins involved in electron transport chain as well as enzymes of the tricarboxylic acid (TCA) cycle. Electron micrographs revealed increase in number and size of mitochondria. Based on these observations, we propose that chronic exposure of esophageal epithelial cells to tobacco leads to cancer stem cell-like phenotype. These cells show the characteristic OXPHOS phenotype, which can be potentially targeted as a therapeutic strategy.

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.

Down-regulation of mitochondrial NADH and cytochrome b gene associated with high tumor stages in head and neck squamous cell carcinoma

OBJECTIVE

This study aimed to determine mitochondrial mRNA expression levels and the relationships between these expression levels and various adverse clinicopathological characteristics.

METHODS

The mRNA expression levels of all 12 genes encoded protein, located on the heavy-strand of mitochondrial DNA including cytochrome b, NADH1, NADH2, NADH3, NADH4, NADH4L, NADH5, ATPase6, ATPase8, cytochrome c oxidase subunit 1, cytochrome c oxidase subunit 2, cytochrome c oxidase subunit 3 were analyzed in 30 head and neck squamous cell carcinoma (HNSCC) and the corresponding normal tissues using reverse transcriptase quantitative real time PCR. Pearson Chi-square test was used to determine the relationships between these expression levels and categorical parameters.

RESULTS

The expression levels of 12 mitochondrial mRNAs were observed in all 30 HNSCC patients with down-regulation, ranging from 43.3% to 76.7% and up-regulation, ranging from 10.0% to 36.7%. Furthermore, the number of cases with down-regulations in all 6 NADH and cytochrome b mRNA with TMN stages III and IV were significantly higher than that in stages I and II (p=0.049 and 0.007, respectively).

CONCLUSION

Down-regulation of all mitochondrial NADH mRNA as well as mitochondrial cytochrome b mRNA was associated with high tumor stage among HNSCC patients.

The Emerging Role of Estrogens in Thyroid Redox Homeostasis and Carcinogenesis

Reactive oxygen species (ROS) are the most critical class of free radicals or reactive metabolites produced by all living organisms. ROS regulate several cellular functions through redox-dependent mechanisms, including proliferation, differentiation, hormone synthesis, and stress defense response. However, ROS overproduction or lack of appropriate detoxification is harmful to cells and can be linked to the development of several diseases, such as cancer. Oxidative damage in cellular components, especially in DNA, can promote the malignant transformation that has already been described in thyroid tissue. In thyrocyte physiology, NADPH oxidase enzymes produce large amounts of ROS that are necessary for hormone biosynthesis and might contribute to the high spontaneous mutation rate found in this tissue. Thyroid cancer is the most common endocrine malignancy, and its incidence is significantly higher in women than in men. Several lines of evidence suggest the sex hormone estrogen as a risk factor for thyroid cancer development. Estrogen in turn, besides being a potent growth factor for both normal and tumor thyroid cells, regulates different mechanisms of ROS generation. Our group demonstrated that the thyroid gland of adult female rats exhibits higher hydrogen peroxide (H₂O₂) production and lower enzymatic antioxidant defense in comparison with male glands. In this review, we discuss the possible involvement of thyroid redox homeostasis and estrogen in the development of thyroid carcinogenesis.

Mitochondrial DNA variations in tongue squamous cell carcinoma

Tongue squamous cell carcinoma (TSCC) is the most common type of oral carcinoma. Mitochondrial DNA (mtDNA) is a circular DNA molecule of 16,569 bp, which functionally encompasses a regulatory non-coding region (D-loop) and 37 encoding genes that correspond to 13 subunits of respiratory chain complexes (I, III, IV and V), 22 transfer RNAs and 2 ribosomal (r)RNAs. Recently, mtDNA has been implicated as a mutation hotspot in various tumors. However, to our knowledge mtDNA alteration in TSCC has not been investigated to date. In the present study, the mitochondrial genomes of tongue carcinoma, adjacent non-cancerous tissue and peripheral blood samples from 8 patients with TSCC were sequenced and aligned with the revised Cambridge Reference Sequence. Overall, only one synonymous mutation, which mapped to the NADH:ubiquinone oxidoreductase core subunit 5 gene, was observed in the tongue carcinoma sample from a single patient. A further 21 polymorphisms were identified, including six in the non-coding region (D-loop), five in Complex I, three in Complex III, two in Complex IV, two in Complex V and three in rRNA. In addition, mitochondrial microsatellite instability (mtMSI) was detected in 2/8 tongue carcinoma samples, and localized in the D310 region. These variations, particularly the polymorphisms and mtMSI, imply that the mitochondrial genome may be a hotspot of genome alteration in tongue cancer. Further investigation is expected to reveal the role of mtDNA alteration in TSCC development, as well as its clinical implications.

The Roles of p53 in Mitochondrial Dynamics and Cancer Metabolism: The Pendulum between Survival and Death in Breast Cancer?

Cancer research has been heavily geared towards genomic events in the development and progression of cancer. In contrast, metabolic regulation, such as aberrant metabolism in cancer, is poorly understood. Alteration in cellular metabolism was once regarded simply as a consequence of cancer rather than as playing a primary role in cancer promotion and maintenance. Resurgence of cancer metabolism research has identified critical metabolic reprogramming events within biosynthetic and bioenergetic pathways needed to fulfill the requirements of cancer cell growth and maintenance. The tumor suppressor protein p53 is emerging as a key regulator of metabolic processes and metabolic reprogramming in cancer cells&mdash;balancing the pendulum between cell death and survival. This review provides an overview of the classical and emerging non-classical tumor suppressor roles of p53 in regulating mitochondrial dynamics: mitochondrial engagement in cell death processes in the prevention of cancer. On the other hand, we discuss p53 as a key metabolic switch in cellular function and survival. The focus is then on the conceivable roles of p53 in breast cancer metabolism. Understanding the metabolic functions of p53 within breast cancer metabolism will, in due course, reveal critical metabolic hotspots that cancers advantageously re-engineer for sustenance. Illustration of these events will pave the way for finding novel therapeutics that target cancer metabolism and serve to overcome the breast cancer burden.

The Oncojanus Paradigm of Respiratory Complex I

Mitochondrial respiratory function is now recognized as a pivotal player in all the aspects of cancer biology, from tumorigenesis to aggressiveness and chemotherapy resistance. Among the enzymes that compose the respiratory chain, by contributing to energy production, redox equilibrium and oxidative stress, complex I assumes a central role. Complex I defects may arise from mutations in mitochondrial or nuclear DNA, in both structural genes or assembly factors, from alteration of the expression levels of its subunits, or from drug exposure. Since cancer cells have a high-energy demand and require macromolecules for proliferation, it is not surprising that severe complex I defects, caused either by mutations or treatment with specific inhibitors, prevent tumor progression, while contributing to resistance to certain chemotherapeutic agents. On the other hand, enhanced oxidative stress due to mild complex I dysfunction drives an opposite phenotype, as it stimulates cancer cell proliferation and invasiveness. We here review the current knowledge on the contribution of respiratory complex I to cancer biology, highlighting the double-edged role of this metabolic enzyme in tumor progression, metastasis formation, and response to chemotherapy.

Mitochondrial genome variability: the effect on cellular functional activity

Mitochondria are the key players in cell metabolism, calcium homeostasis, and reactive oxygen species (ROS) production. Mitochondrial genome alterations are reported to be associated with numerous human disorders affecting nearly all tissues. In this review, we discuss the available information on the involvement of mitochondrial DNA (mtDNA) mutations in cell dysfunction.

Mitochondrial NADH Dehydrogenase Subunit 3 (MTND3) Polymorphisms are Associated with Gastric Cancer Susceptibility

Accumulating evidence indicates that mitochondrial DNA alterations contribute to cancer development and progression. In this study, we evaluated the relationship between polymorphisms of mitochondrial NADH dehydrogenase subunit 3 (MTND3) and the risk of gastric cancer (GC). Five single nucleotide polymorphisms (SNPs; rs28358278, rs2853826, rs201397417, rs41467651, and rs28358275) were identified and genotyped in 377 patients with GC patients and 363 controls by direct sequencing. The rs41467651 T allele was significantly associated with GC risk [adjusted odds ratio (OR) = 2.11, 95% confidence interval (CI) = 1.25-3.55, P = 0.005). In stratified analysis, rs28358278, rs2853826, and rs41467651 were associated with subgroups of GC, with the rs28358278 G, rs2853826 T, and rs41467651 T alleles associated with an increased GC risk in females (adjusted OR = 1.70, 95% CI = 1.08-2.69, P = 0.023; adjusted OR = 1.78, 95% CI = 1.11-2.85, P = 0.016; adjusted OR = 2.07, 95% CI = 1.04-4.12, P = 0.038, respectively). The rs441467651 T allele was also related with GC risk in diffuse-type subjects compared to that of controls (adjusted OR = 2.61, 95% CI = 1.43-4.89, P = 0.002). In addition, The rs441467651 T allele was significantly related with increased GC risk regardless of lymph node metastasis (LNM), T classification, and tumor stage compared to that of controls (adjusted OR = 2.00, 95% CI = 1.12-3.55, P = 0.019 in LNM-negative subjects; adjusted OR = 2.10, 95% CI = 1.05-4.22, P = 0.0379 in LNM-positive subjects; adjusted OR = 1.82, 95% CI = 1.02-3.24, P = 0.042 in T1/T2 subjects; adjusted OR = 2.60, 95% CI = 1.29-5.24, P = 0.007 in T3/T4 subjects; adjusted OR = 1.91, 95% CI = 1.09-3.34, P = 0.025 in tumor stage I (A+B)/II (A+B+C) subjects; adjusted OR = 2.36, 95% CI = 1.12-5.13, P = 0.025 in tumor stage III (A+B+C) subjects) compared to that of controls. Our findings suggest that the rs28358278, rs2853826, and rs41467651 polymorphisms of MTND3 increase the susceptibility to GC development.

ROS-induced near-homozygous genomes in thyroid cancer

A near-homozygous genome (NHG) is especially seen in a subset of follicular thyroid cancer of the oncocytic type (FTC-OV). An NHG was also observed in the metabolically relatively quiescent cell lines XTC.UC1, a model for FTC-OV, and in FTC-133, -236 and -238, the latter three derived from one single patient with follicular thyroid cancer. FTC-236 subclones showed subtle whole-chromosome differences indicative of sustained reciprocal mitotic missegregations. Reactive oxygen species (ROS) scavenger experiments reduced the number of chromosomal missegregations in XTC.UC1 and FTC-236, while pCHK2 was downregulated in these cells. Treatment with antimycin A increased ROS indicated by enhanced MitoSOX Red and pCHK2 fluorescence in metaphase cells. In a selected set of oncocytic follicular thyroid tumors, increasing numbers of whole-chromosome losses were observed toward an aggressive phenotype, but with retention of chromosome 7. Together, ROS activates CHK2 and links to the stepwise loss of whole chromosomes during tumor progression in these lesions. We postulate that sequential loss of whole chromosomes is a dominant driver of the oncogenesis of a subset of follicular thyroid tumors.

Reactive oxygen species (ROS) are a key determinant of cancer's metabolic phenotype

Cancer cells exhibit a wide range of metabolic phenotypes, ranging from strict aerobic glycolysis to increased mitochondrial respiration. The cause and utility of this metabolic variation is poorly understood. Given that cancer cells experience heavy selection within their microenvironment, survival requires metabolic adaptation to both extracellular and intracellular conditions. Herein, we suggest that reactive oxygen species (ROS) are a key determinant of cancer's metabolic phenotype. Intracellular ROS levels can be modified by an assortment of critical parameters including oxygenation, glucose availability and growth factors. ROS act as integrators of environmental information as well as downstream effectors of signaling pathways. Maintaining ROS within a narrow range allows malignant cells to enhance growth and invasion while limiting their apoptotic susceptibility. Cancer cells actively modify their metabolism to optimize intracellular ROS levels and thereby improve survival. Furthermore, we highlight distinct metabolic phenotypes in response to oxidative stress and their tumorigenic drivers.

Mitochondrial ND5 mutation mediated elevated ROS regulates apoptotic pathway epigenetically in a P53 dependent manner for generating pro-cancerous phenotypes

We have previously observed concomitant events of mutations in mitochondrial and nuclear genes, along with elevated reactive oxygen species (ROS) and differential methylation within the promoters of nuclear genes in tumors and in vitro experiments of tumorigenesis. These observations have made it pertinent to replicate and understand the role of acquired mitochondrial condition in tuning a cell to accomplish a pro-cancerous state. Using a codon optimized vector system for exogenous over-expression and mitochondrial localization; we have characterized here the role of over-expressed wild type mtND5 and one of its non-synonymous somatic mutation, ND5:P265H. The ectopically over-expressed ND5:P265H in mitochondria resulted in a reduced Complex I activity, generation of higher ADP/ATP ratio, reactive oxygen species (ROS) and carbonylation of proteins as compared to mock-transfected cells. Cells over-expressing mtND5 variant produced both peroxide as well as super-oxide ROS; the generation of which was dependent on the functional status of P53; modulating epigenetically the expression of key apoptosis pathway genes. The pro-cancerous phenotypes, of anchorage dependent and independent growth; increased glucose uptake and lactate production, were selectively observed only in P53 non-functional cells over-expressing mutant ND5:P265H. We propose that somatic mutation in mtND5 resulting in down-regulated complex I enzyme activity, elevated ROS and up-regulation of a set of nuclear anti-apoptotic genes epigenetically in the P53 dysfunctional cellular background, has provided a unique understanding of the molecular mechanism of mitochondrial mutation; and the concomitant existence of somatically acquired mitochondrial and nuclear p53 mutations, in cancer progression and promotion.

MtDNA As a Cancer Marker: A Finally Closed Chapter?

Sequence alterations of the mitochondrial DNA (mtDNA) have been identified in many tu-mor types. Their nature is not entirely clear. Somatic mutation or shifts of heteroplasmic mtDNA vari-ants may play a role. These sequence alterations exhibit a sufficient frequency in all tumor types investi-gated thus far to justify their use as a tumor marker. This statement is supported by the high copy num-ber of mtDNA, which facilitates the detection of aberrant tumor-derived DNA in bodily fluids. This will be of special interest in tumors, which release a relatively high number of cells into bodily fluids, which are easily accessible, most strikingly in urinary bladder carcinoma. Due to the wide distribution of the observed base substitutions, deletions or insertions within the mitochondrial genome, high efforts for whole mtDNA sequencing (16.5 kb) from bodily fluids would be required, if the method would be in-tended for initial tumor screening. However, the usage of mtDNA for sensitive surveillance of known tumor diseases is a meaningful option, which may allow an improved non-invasive follow-up for the urinary bladder carcinoma, as compared to the currently existing cytological or molecular methods. Fol-lowing a short general introduction into mtDNA, this review demonstrates that the scenario of a sensi-tive cancer follow-up by mtDNA-analysis deserves more attention. It would be most important to inves-tigate precisely in the most relevant tumor types, if sequencing approaches in combination with simple PCR-assays for deletions/insertions in homopolymeric tracts has sufficient sensitivity to find most tu-mor-derived mtDNAs in bodily fluids.

Altered Mitochondrial Signalling and Metabolism in Cancer

Mitochondria being the central organelle for metabolism and other cell signalling pathways have remained the topic of interest to tumour biologists. In spite of the wide acceptance of Warburg’s hypothesis, role of mitochondrial metabolism in cancer is still unclear. Uncontrolled growth and proliferation, hallmarks of tumour cells, are maintained when the cells adapt to metabolic reprogramming with the help of altered metabolism of mitochondria. This review has focussed on different aspects of mitochondrial metabolism and inter-related signalling pathways which have been found to be modified in cancer.

Erythrocytosis in hepatocellular carcinoma portends poor prognosis by respiratory dysfunction secondary to mitochondrial DNA mutations

Erythrocytosis is a common paraneoplastic syndrome associated with hepatocellular carcinoma. Although increased erythropoietin (EPO) is found in these patients, the clinical significance and molecular mechanisms underlying this observation are unclear. We demonstrate an inverse relationship between EPO production and overall prognosis in our cohort of 664 patients as well as in data from The Cancer Genome Atlas. In the subset of hepatocellular carcinoma patients with erythrocytosis, we identified somatic mutations of mitochondrial DNA, resulting in impairment of respiratory metabolism, which sequentially led to depletion of α-ketoglutarate, stabilization of hypoxia inducible factor-α, and expression of target genes such as EPO. Cell lines and patient-derived xenograft models were used to demonstrate that EPO promoted cancer stem cell self-renewal and expansion in an autocrine/paracrine manner through enhanced Janus kinase/signal transducer and activator of transcription signaling both in vitro and in vivo. Furthermore, to explore the therapeutic targeting of EPO-induced tumor changes, we found that blocking EPO signaling with soluble EPO receptor extracellular domain Fc fusion protein could inhibit tumor growth both in vitro and in vivo.

CONCLUSION

These findings suggest clinical and therapeutic implications for erythrocytosis in hepatocellular carcinoma. There is an underlying link between mitochondrial function and hypoxia inducible factor alpha signaling, revealing a mechanism of erythrocytosis in a subset of hepatocellular carcinoma patients who may benefit from treatment involving EPO signaling interference. (Hepatology 2017;65:134-151).

Decoding Warburg's hypothesis: tumor-related mutations in the mitochondrial respiratory chain

Otto Warburg observed that cancer cells derived their energy from aerobic glycolysis by converting glucose to lactate. This mechanism is in opposition to the higher energy requirements of cancer cells because oxidative phosphorylation (OxPhos) produces more ATP from glucose. Warburg hypothesized that this phenomenon occurs due to the malfunction of mitochondria in cancer cells. The rediscovery of Warburg's hypothesis coincided with the discovery of mitochondrial tumor suppressor genes that may conform to Warburg's hypothesis along with the demonstrated negative impact of HIF-1 on PDH activity and the activation of HIF-1 by oncogenic signals such as activated AKT. This work summarizes the alterations in mitochondrial respiratory chain proteins that have been identified and their involvement in cancer. Also discussed is the fact that most of the mitochondrial mutations have been found in homoplasmy, indicating a positive selection during tumor evolution, thereby supporting their causal role.

Redox Homeostasis and Cellular Antioxidant Systems: Crucial Players in Cancer Growth and Therapy

Reactive oxygen species (ROS) and their products are components of cell signaling pathways and play important roles in cellular physiology and pathophysiology. Under physiological conditions, cells control ROS levels by the use of scavenging systems such as superoxide dismutases, peroxiredoxins, and glutathione that balance ROS generation and elimination. Under oxidative stress conditions, excessive ROS can damage cellular proteins, lipids, and DNA, leading to cell damage that may contribute to carcinogenesis. Several studies have shown that cancer cells display an adaptive response to oxidative stress by increasing expression of antioxidant enzymes and molecules. As a double-edged sword, ROS influence signaling pathways determining beneficial or detrimental outcomes in cancer therapy. In this review, we address the role of redox homeostasis in cancer growth and therapy and examine the current literature regarding the redox regulatory systems that become upregulated in cancer and their role in promoting tumor progression and resistance to chemotherapy.

High-performance detection of somatic D-loop mutation in urothelial cell carcinoma patients by polymorphism ratio sequencing

Utilizing a polymorphism ratio sequencing platform, we performed a complete somatic mutation analysis of the mitochondrial D-loop region in 14 urothelial cell carcinomas. A total of 28 somatic mutations, all heteroplasmic, were detected in 8 of 14 individuals (57.1 %). Insertion/deletion changes in unstable mono- and dinucleotide repeat segments comprise the most pervasive class of mutations (9 of 28), while two recurring single-base substitution loci were identified. Seven variants, mostly insertion/deletions, represent population shifts from a heteroplasmic germline toward dominance in the tumor. In four cases, DNA from matched urine samples was similarly analyzed, with all somatic variants present in associated tumors readily detectable in the bodily fluid. Consistent with previous findings, mutant populations in urine were similar to those detected in tumor and in three of four cases were more prominent in urine.

KEY MESSAGES

PRS accurately detects high mtDNA mutations in UCCs and their body fluids. mtDNA mutations are universally heteroplasmic and often appear at low levels. The PRS technology could be a viable approach to develop mitochondrial biomarkers.

Analysis of the miRNA-mRNA networks in malignant transformation BEAS-2B cells induced by alpha-particles

The aim of this study was to determine the toxicity induced by irradiation with alpha-particles on malignant transformation of immortalized human bronchial epithelial cells (BEAS-2B) using miRNA-mRNA networks. The expression of BEAS-2B cells was determined by measuring colony formation, mtDNA, mitochondrial membrane potential (MMP), and ROS levels. Changes in BEAS-2B cell gene expression were observed and quantified using microarrays that included an increase in 157 mRNA and 20 miRNA expression and a decrease in 77 mRNA and 48 miRNA. Bioinformatic software was used to analyze these different mRNA and miRNA, which indicated that miR-107 and miR-494 play an important role in alpha-particles-mediated cellular malignant transformation processes. The pathways related to systemic lupus erythematosus, cytokine-cytokine receptor interaction, MAPK signaling pathway, regulation of actin cytoskeleton, and cell adhesion molecules (CAMs) were stimulated, while those of ribosome, transforming growth factor (TGF)-beta signaling pathway, and metabolic pathways were inhibited. Data suggest that miRNA and mRNA play a crucial role in alpha-particles-mediated malignant transformation processes. It is worth noting that three target genes associated with lung cancer were identified and upregulated PEG 10 (paternally expressed gene 10), ARHGAP26, and IRS1.

The presence of highly disruptive 16S rRNA mutations in clinical samples indicates a wider role for mutations of the mitochondrial ribosome in human disease

Mitochondrial DNA mutations are well recognized as an important cause of disease, with over two hundred variants in the protein encoding and mt-tRNA genes associated with human disorders. In contrast, the two genes encoding the mitochondrial rRNAs (mt-rRNAs) have been studied in far less detail. This is because establishing the pathogenicity of mt-rRNA mutations is a major diagnostic challenge. Only two disease causing mutations have been identified at these loci, both mapping to the small subunit (SSU). On the large subunit (LSU), however, the evidence for the presence of pathogenic LSU mt-rRNA changes is particularly sparse. We have previously expanded the list of deleterious SSU mt-rRNA mutations by identifying highly disruptive base changes capable of blocking the activity of the mitoribosomal SSU. To do this, we used a new methodology named heterologous inferential analysis (HIA). The recent arrival of near-atomic-resolution structures of the human mitoribosomal LSU, has enhanced the power of our approach by permitting the analysis of the corresponding sites of mutation within their natural structural context. Here, we have used these tools to determine whether LSU mt-rRNA mutations found in the context of human disease and/or ageing could disrupt the function of the mitoribosomal LSU. Our results clearly show that, much like the for SSU mt-rRNA, LSU mt-rRNAs mutations capable of compromising the function of the mitoribosomal LSU are indeed present in clinical samples. Thus, our work constitutes an important contribution to an emerging view of the mitoribosome as an important element in human health.

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Identification of pathogenic mutations of mitochondrial rRNAs is problematic.

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We analysed 64 rare 16S rRNA mutations obtained from clinical samples.

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The mutations underwent heterologous inferential analysis (HIA).

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We show that highly disruptive 16S rRNA mutations are present in clinical samples.

Mitochondrial DNA Haplogroup A Decreases the Risk of Drug Addiction but Conversely Increases the Risk of HIV-1 Infection in Chinese Addicts

Drug addiction is one of the most serious social problems in the world today and addicts are always at a high risk of acquiring HIV infection. Mitochondrial impairment has been reported in both drug addicts and in HIV patients undergoing treatment. In this study, we aimed to investigate whether mitochondrial DNA (mtDNA) haplogroup could affect the risk of drug addiction and HIV-1 infection in Chinese. We analyzed mtDNA sequence variations of 577 Chinese intravenous drug addicts (289 with HIV-1 infection and 288 without) and compared with 2 control populations (n = 362 and n = 850). We quantified the viral load in HIV-1-infected patients with and without haplogroup A status and investigated the potential effect of haplogroup A defining variants m.4824A > G and m.8794C > T on the cellular reactive oxygen species (ROS) levels by using an allotopic expression assay. mtDNA haplogroup A had a protective effect against drug addiction but appeared to confer an increased risk of HIV infection in addicts. HIV-1-infected addicts with haplogroup A had a trend for a higher viral load, although the mean viral load was similar between carriers of haplogroup A and those with other haplogroup. Hela cells overexpressing allele m.8794 T showed significantly decreased ROS levels as compared to cells with the allele m.8794C (P = 0.03). Our results suggested that mtDNA haplogroup A might protect against drug addiction but increase the risk of HIV-1 infection. The contradictory role of haplogroup A might be caused by an alteration in mitochondrial function due to a particular mtDNA ancestral variant.

Quantitative constraint-based computational model of tumor-to-stroma coupling via lactate shuttle

Cancer cells utilize large amounts of ATP to sustain growth, relying primarily on non-oxidative, fermentative pathways for its production. In many types of cancers this leads, even in the presence of oxygen, to the secretion of carbon equivalents (usually in the form of lactate) in the cell’s surroundings, a feature known as the Warburg effect. While the molecular basis of this phenomenon are still to be elucidated, it is clear that the spilling of energy resources contributes to creating a peculiar microenvironment for tumors, possibly characterized by a degree of toxicity. This suggests that mechanisms for recycling the fermentation products (e.g. a lactate shuttle) may be active, effectively inducing a mutually beneficial metabolic coupling between aberrant and non-aberrant cells. Here we analyze this scenario through a large-scale in silico metabolic model of interacting human cells. By going beyond the cell-autonomous description, we show that elementary physico-chemical constraints indeed favor the establishment of such a coupling under very broad conditions. The characterization we obtained by tuning the aberrant cell’s demand for ATP, amino-acids and fatty acids and/or the imbalance in nutrient partitioning provides quantitative support to the idea that synergistic multi-cell effects play a central role in cancer sustainment.

Mitochondrial genome instability in colorectal adenoma and adenocarcinoma

Mitochondrial dysfunction is regarded as a hallmark of cancer progression. In the current study, we evaluated mitochondrial genome instability and copy number in colorectal cancer using Next Generation Sequencing approach and qPCR, respectively. The results revealed higher levels of heteroplasmy and depletion of the relative mtDNA copy number in colorectal adenocarcinoma. Adenocarcinoma samples also presented an increased number of mutations in nuclear genes encoding proteins which functions are related with mitochondria fusion, fission and localization. Moreover, we found a set of mitochondrial and nuclear genes, which cooperate in the same mitochondrial function simultaneously mutated in adenocarcinoma. In summary, these results support an important role for mitochondrial function and genomic instability in colorectal tumorigenesis.

Impact of somatic mutations in the D-loop of mitochondrial DNA on the survival of oral squamous cell carcinoma patients

Objectives

The aim of this study was to investigate somatic mutations in the D-loop of mitochondrial DNA (mtDNA) and their impact on survival in oral squamous cell carcinoma patients.

Materials and Methods

Surgical specimen confirmed by pathological examination and corresponding non-cancerous tissues were collected from 120 oral squamous cell carcinoma patients. The sequence in the D-loop of mtDNA from non-cancerous tissues was compared with that from paired cancer samples and any sequence differences were recognized as somatic mutations.

Results

Somatic mutations in the D-loop of mtDNA were identified in 75 (62.5%) oral squamous cell carcinoma patients and most of them occurred in the poly-C tract. Although there were no significant differences in demographic and tumor-related features between participants with and without somatic mutation, the mutation group had a better survival rate (5 year disease-specific survival rate: 64.0% vs. 43.0%, P = 0.0266).

Conclusion

Somatic mutation in D-loop of mtDNA was associated with a better survival in oral squamous cell carcinoma patients.

Oxidative stress in aging human skin

Oxidative stress in skin plays a major role in the aging process. This is true for intrinsic aging and even more for extrinsic aging. Although the results are quite different in dermis and epidermis, extrinsic aging is driven to a large extent by oxidative stress caused by UV irradiation. In this review the overall effects of oxidative stress are discussed as well as the sources of ROS including the mitochondrial ETC, peroxisomal and ER localized proteins, the Fenton reaction, and such enzymes as cyclooxygenases, lipoxygenases, xanthine oxidases, and NADPH oxidases. Furthermore, the defense mechanisms against oxidative stress ranging from enzymes like superoxide dismutases, catalases, peroxiredoxins, and GSH peroxidases to organic compounds such as L-ascorbate, α-tocopherol, beta-carotene, uric acid, CoQ10, and glutathione are described in more detail. In addition the oxidative stress induced modifications caused to proteins, lipids and DNA are discussed. Finally age-related changes of the skin are also a topic of this review. They include a disruption of the epidermal calcium gradient in old skin with an accompanying change in the composition of the cornified envelope. This modified cornified envelope also leads to an altered anti-oxidative capacity and a reduced barrier function of the epidermis.

Chlorpyrifos inhibits cell proliferation through ERK1/2 phosphorylation in breast cancer cell lines

It is well known the participation of oxidative stress in the induction and development of different pathologies including cancer, diabetes, neurodegeneration and respiratory disorders among others. It has been reported that oxidative stress may be induced by pesticides and it could be the cause of health alteration mediated by pollutants exposure. Large number of registered products containing chlorpyrifos (CPF) is used to control pest worldwide. We have previously reported that 50 μM CPF induces ROS generation and produces cell cycle arrest followed by cell death. The present investigation was designed to identify the pathway involved in CPF-inhibited cell proliferation in MCF-7 and MDA-MB-231 breast cancer cell lines. In addition, we determined if CPF-induced oxidative stress is related to alterations in antioxidant defense system. Finally we studied the molecular mechanisms underlying in the cell proliferation inhibition produced by the pesticide. In this study we demonstrate that CPF (50 μM) induces redox imbalance altering the antioxidant defense system in breast cancer cells. Furthermore, we found that the main mechanism involved in the inhibition of cell proliferation induced by CPF is an increment of p-ERK1/2 levels mediated by H2O2 in breast cancer cells. As PD98059 could not abolish the increment of ROS induced by CPF, we concluded that ERK1/2 phosphorylation is subsequent to ROS production induced by CPF but not the inverse.

Oxidative stress in oral diseases

Oxidative species, including reactive oxygen species (ROS), are components of normal cellular metabolism and are required for intracellular processes as varied as proliferation, signal transduction, and apoptosis. In the situation of chronic oxidative stress, however, ROS contribute to various pathophysiologies and are involved in multiple stages of carcinogenesis. In head and neck cancers specifically, many common risk factors contribute to carcinogenesis via ROS-based mechanisms, including tobacco, areca quid, alcohol, and viruses. Given their widespread influence on the process of carcinogenesis, ROS and their related pathways are attractive targets for intervention. The effects of radiation therapy, a central component of treatment for nearly all head and neck cancers, can also be altered via interfering with oxidative pathways. These pathways are also relevant to the development of many benign oral diseases. In this review, we outline how ROS contribute to pathophysiology with a focus toward head and neck cancers and benign oral diseases, describing potential targets and pathways for intervention that exploit the role of oxidative species in these pathologic processes.

WWOX, the chromosomal fragile site FRA16D spanning gene: its role in metabolism and contribution to cancer

The WWOX gene spans the common chromosomal fragile site FRA16D that is located within a massive (780 kb) intron. The WWOX gene is very long, at 1.1 Mb, which may contribute to the very low abundance of the full-length 1.4 kb mRNA. Alternative splicing also accounts for a variety of aberrant transcripts, most of which are devoid of C-terminal sequences required for WWOX to act as an oxidoreductase. The mouse WWOX gene also spans a chromosomal fragile site implying some sort of functional relationship that confers a selective advantage. The encoded protein domains of WWOX are conserved through evolution (between humans and Drosophila melanogaster) and include WW domains, an NAD -binding site, short-chain dehydrogenase/reductase enzyme and nuclear compartmentalization signals. This homology has enabled functional analyses in D. melanogaster that demonstrate roles for WWOX in reactive oxygen species regulation and metabolism. Indeed the human WWOX gene is also responsive to altered metabolism. Cancer cells typically exhibit altered metabolism (Warburg effect). Many cancers exhibit FRA16D DNA instability that results in aberrant WWOX expression and is associated with poor prognosis for these cancers. It is therefore thought that aberrant WWOX expression contributes to the altered metabolism in cancer. In addition, others have found that a specific (low-expression) allele of WWOX genotype contributes to cancer predisposition.

D-loop somatic mutations and ∼5 kb "common" deletion in mitochondrial DNA: important molecular markers to distinguish oral precancer and cancer

Apart from genomic DNA, mutations at mitochondrial DNA (mtDNA) have been hypothesized to play vital roles in cancer development. In this study, ∼5 kb deletion and D-loop mutations in mtDNA and alteration in mtDNA content were investigated in buccal smears from 104 healthy controls and 74 leukoplakia and 117 cancer tissue samples using Taqman-based quantitative assay and re-sequencing. The ∼5 kb deletion in mtDNA was significantly less (9.8 and 10.5 folds, P < 0.0001) in cancer tissues compared to control and leukoplakia tissues, respectively. On the other hand, somatic mutations in D-loop, investigated in 54 controls, 50 leukoplakias and 56 cancer patients, were found to be significantly more in cancer tissues, but not in leukoplakia tissues, compared to control (Z-score = 5.4). MtDNA contents were observed to be significantly more in leukoplakia (2.1 folds, P = 0.004) and cancer (1.6 folds, P = 0.03) tissues compared to control tissues. So, D-loop somatic mutations and ∼5 kb deletion patterns could be used as distinguishing markers between precancer and cancer tissues. This observation further suggests that somatic mutations in D-loop may facilitate carcinogenesis and cancer cells with less ∼5 kb deletion, i.e., intact mtDNA, may become resistant to apoptosis.

Clonality analysis in primary oral squamous cell carcinoma and related lymph-node metastasis revealed by TP53 and mitochondrial DNA next generation sequencing analysis

The chance of developing a neck nodal metastasis after initial treatment of oral squamous cell carcinoma varies from 12.4% to 62%. Despite being the main reason for cancer-related mortality, nodal metastases are still rarely subjected to molecular analyses, and our knowledge of the clonal heterogeneity of multiple lesions within the same patient is limited. The aim of the present study was to evaluate the relationship between primary oral cancer and lymph node metastasis in a series of patients with synchronous and metachronous metastases by 2 clonality tests: mt-DNA and TP53 sequence analysis. The study population consisted of 10 consecutive patients. Data identified in this study demonstrate that our assay based on next-generation analysis of TP53 and mt-DNA is simple, is reliable, allows high throughput, and may be applied to retrospective cases. The combination of mt-DNA and TP53 data analysis helped us to evaluate more precisely and consistently the genetic relationship among different tumor clones.