Somatic mitochondrial DNA (mtDNA) mutations in papillary thyroid carcinomas and differential mtDNA sequence variants in cases with thyroid tumours

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.

Pathogenesis of cancers derived from thyroid follicular cells

The genomic simplicity of differentiated cancers derived from thyroid follicular cells offers unique insights into how oncogenic drivers impact tumour phenotype. Essentially, the main oncoproteins in thyroid cancer activate nodes in the receptor tyrosine kinase-RAS-BRAF pathway, which constitutively induces MAPK signalling to varying degrees consistent with their specific biochemical mechanisms of action. The magnitude of the flux through the MAPK signalling pathway determines key elements of thyroid cancer biology, including differentiation state, invasive properties and the cellular composition of the tumour microenvironment. Progression of disease results from genomic lesions that drive immortalization, disrupt chromatin accessibility and cause cell cycle checkpoint dysfunction, in conjunction with a tumour microenvironment characterized by progressive immunosuppression. This Review charts the genomic trajectories of these common endocrine tumours, while connecting them to the biological states that they confer.

Development of Metabolic Synthetic Lethality and Its Implications for Thyroid Cancer

Cancer therapies targeting genetic alterations are a topic of great interest in the field of thyroid cancer, which frequently harbors mutations in the RAS, RAF, and RET genes. Unfortunately, U.S. Food and Drug Administration-approved BRAF inhibitors have relatively low therapeutic efficacy against BRAF-mutant thyroid cancer; in addition, the cancer often acquires drug resistance, which prevents effective treatment. Recent advances in genomics and transcriptomics are leading to a more complete picture of the range of mutations, both driver and messenger, present in thyroid cancer. Furthermore, our understanding of cancer suggests that oncogenic mutations drive tumorigenesis and induce rewiring of cancer cell metabolism, which promotes survival of mutated cells. Synthetic lethality (SL) is a method of neutralizing mutated genes that were previously considered untargetable by traditional genotype-targeted treatments. Because these metabolic events are specific to cancer cells, we have the opportunity to develop new therapies that target tumor cells specifically without affecting healthy tissue. Here, we describe developments in metabolism-based cancer therapy, focusing on the concept of metabolic SL in thyroid cancer. Finally, we discuss the essential implications of metabolic reprogramming and its role in the future direction of SL for thyroid cancer.

Somatic mitochondrial DNA mutations in different grades of glioma

Aim: Mitochondrial DNA (mtDNA) alterations play an important role in the multistep processes of cancer development. Gliomas are among the most diagnosed brain cancer. The relationship between mtDNA alterations and different grades of gliomas are still elusive. This study aimed to elucidate the profile of somatic mtDNA mutations in different grades of gliomas and correlate it with clinical phenotype. Materials & methods: Forty histopathologically confirmed glioma tissue samples and their matched blood were collected and subjected for mtDNA sequencing. Results & conclusion: About 75% of the gliomas harbored at least one somatic mutation in the mtDNA gene, and 45% of these mutations were pathogenic. Mutations were scattered across the mtDNA genome, and the commonest nonsynonymous mutations were located at complex I and IV of the mitochondrial respiratory chain. These findings may have implication for future research to determine the mitochondrial energetics and its downstream metabolomics on gliomas.

Can leukocytospermia predict prostate cancer via its effects on mitochondrial DNA?

Leukocytospermia was previously reported to affect sperm quality by the production of reactive oxygen species (ROS) leading to oxidative stress (OS). In turn, OS decreases sperm functional integrity, increases sperm DNA damage and ultimately alters fertility status. To elucidate the impact of leukocytospermia on sperm nuclear DNA integrity and mitochondrial DNA (mtDNA) structure, we conducted a study including 67 samples from infertile patients with low level of leucocytes (Group 1: n = 20) and with leukocytospermia (Group 2: n = 47). In addition to standard sperm parameters' assessment, we measured the levels of inflammation biomarkers [interleukin-6 (IL-6) and interleukin-8 (IL-8)] and evaluated the oxidative status [malondialdehyde (MDA) and enzymatic and non-enzymatic antioxidants]. In addition, we evaluated the level of sperm nuclear DNA fragmentation and analysed mitochondrial DNA (mtDNA) of sperm cells by sequencing of 5 genes [cytochrome oxidase I (COXI), cytochrome oxidase II (COXII), cytochrome oxidase III (COXIII), adenosine triphosphate synthase 6 (ATPase 6) and adenosine triphosphate synthase 8 (ATPase 8)]. As expected, patients with leukocytospermia had significantly higher MDA levels (32.56 ± 24.30 nmole/ml) than patients without leukocytospermia (17.59 ± 9.60 nmole/ml) (p < .018). Also, sperm DNA fragmentation index (DFI) was significantly higher in Group 2 (33.05 ± 18.14%) as compared to Group 1 (14.19 ± 9.50%) (p < .001). The sequencing of mtDNA revealed a high number of substitutions in Group 2 (n = 102) compared to Group 1 (n = 5). These substitutions were observed mainly in COXI. Among COXI substitutions found in Group 2, twelve changes were previously described in patients with prostate cancer and six of them were shown associated with this pathology. These findings suggest that leukocytospermia may predispose to the manifestation of prostate cancer through modification of mitochondrial DNA and this may be promoted by OS.

Growth Differentiation Factor 15 is a Cancer Cell-Induced Mitokine That Primes Thyroid Cancer Cells for Invasiveness

Background: Mitochondrial stress is known to activate the mitochondrial unfolded protein response (UPR^mt). The UPR^mt results in the secretion of mitochondrial cytokines (mitokines), which can promote a hormetic response cell nonautonomously, and has been reported to be protumorigenic. Growth differentiation factor 15 (GDF15) is a well-characterized mitokine, which is reported to have a mitohormetic effect. Thus, we investigated whether GDF15 induction could prime a subpopulation of thyroid cancer cells to provide invasive advantages. Methods: The UPR^mt, including mitokine expression, was assessed in the context of thyroid cancer in vitro and in vivo. GDF15 expression in 266 patients with papillary thyroid carcinoma (PTC) was determined by immunohistochemistry. The serum levels of GDF15 were measured in healthy subjects and PTC patients. In addition, our own and The Cancer Genome Atlas data were analyzed to determine the expression level of GDF15 in thyroid cancers. The role of GDF15 in tumor aggressiveness was investigated by observing the effects of GDF15 knockdown in BCPAP, TPC-1, 8505C, and FRO cells. Results: Pharmacological inhibition of mitochondrial oxidative phosphorylation function in thyroid cancer cells robustly increased GDF15 expression. The expression of GDF15 was associated with activation of the mitochondrial integrated stress response pathway in PTC patients. Circulating GDF15 levels were significantly higher in PTC patients than in the controls, and tumor expression of GDF15 was related to tumor aggressiveness. In vitro and in vivo knockdown of GDF15 in a thyroid cancer model showed decreased viability, migration, and invasion compared with the control cells via regulation of STAT3. Conclusions: In this study, we demonstrated that GDF15 is a mitokine induced in thyroid cancer cells upon mitochondrial stress. GDF15-induced STAT3 activation determined tumor progression in thyroid cancer. The GDF15-STAT3 signaling axis may be a target in aggressiveness of thyroid cancer.

Genetics, Diagnosis, and Management of Hürthle Cell Thyroid Neoplasms

Hürthle cell lesions have been a diagnostic conundrum in pathology since they were first recognized over a century ago. Controversy as to the name of the cell, the origin of the cell, and even which cells in particular may be designated as such still challenge pathologists and confound those treating patients with a diagnosis of "Hürthle cell" anything within the diagnosis, especially if that anything is a sizable mass lesion. The diagnosis of Hürthle cell adenoma (HCA) or Hürthle cell carcinoma (HCC) has typically relied on a judgement call by pathologists as to the presence or absence of capsular and/or vascular invasion of the adjacent thyroid parenchyma, easy to note in widely invasive disease and a somewhat subjective diagnosis for minimally invasive or borderline invasive disease. Diagnostic specificity, which has incorporated a sharp increase in molecular genetic studies of thyroid tumor subtypes and the integration of molecular testing into preoperative management protocols, continues to be challenged by Hürthle cell neoplasia. Here, we provide the improving yet still murky state of what is known about Hürthle cell tumor genetics, clinical management, and based upon what we are learning about the genetics of other thyroid tumors, how to manage expectations, by pathologists, clinicians, and patients, for more actionable, precise classifications of Hürthle cell tumors of the thyroid.

Mitochondrial DNA Mutation Analysis in Breast Cancer: Shifting From Germline Heteroplasmy Toward Homoplasmy in Tumors

Studies have suggested a potential role of somatic mitochondrial mutations in cancer development. To analyze the landscape of somatic mitochondrial mutation in breast cancer and to determine whether mitochondrial DNA (mtDNA) mutational burden is correlated with overall survival (OS), we sequenced whole mtDNA from 92 matched-paired primary breast tumors and peripheral blood. A total of 324 germline variants and 173 somatic mutations were found in the tumors. The most common germline allele was 663G (12S), showing lower heteroplasmy levels in peripheral blood lymphocytes than in their matched tumors, even reaching homoplasmic status in several cases. The heteroplasmy load was higher in tumors than in their paired normal tissues. Somatic mtDNA mutations were found in 73.9% of breast tumors; 59% of these mutations were located in the coding region (66.7% non-synonymous and 33.3% synonymous). Although the CO1 gene presented the highest number of mutations, tRNA genes (T,C, and W), rRNA 12S, and CO1 and ATP6 exhibited the highest mutation rates. No specific mtDNA mutational profile was associated with molecular subtypes of breast cancer, and we found no correlation between mtDNA mutational burden and OS. Future investigations will provide insight into the molecular mechanisms through which mtDNA mutations and heteroplasmy shifting contribute to breast cancer development.

Deregulated Mitochondrial DNA in Diseases

Mitochondria play various important roles in energy production, metabolism, and apoptosis. Mitochondrial dysfunction caused by alterations in mitochondrial DNA (mtDNA) can lead to the initiation and progression of cancers and other diseases. These alterations include mutations and copy number variations. Especially, the mutations in D-loop, MT-ND1, and MT-ND5 affect mitochondrial functions and are widely detected in various cancers. Meanwhile, several other mutations have been correlated with muscular and neuronal diseases, especially MT-TL1 is deeply related. These pieces of evidence indicated mtDNA alterations in diseases show potential as a novel therapeutic target. mtDNA repair enzymes are the target for delaying or stalling the mtDNA damage-induced cancer progression and metastasis. Moreover, some mutations reveal a prognosis ability of the drug resistance. Current efforts aim to develop mitochondrial transplantation technique as a direct cure for deregulated mitochondria-associated diseases. This review summarizes the implications of mitochondrial dysfunction in cancers and other pathologies; and discusses the relevance of mitochondria-targeted therapies, along with their contribution as potential biomarkers.

Detection of novel mitochondrial mutations in cytochrome C oxidase subunit 1 (COX1) in patients with familial adenomatous polyposis (FAP)

BACKGROUND

Familial adenomatous polyposis (FAP) is an Autosomal dominant inherited disorder and a rare form‌ of colorectal cancer (CRC) that is characterized by the development of hundreds to thousands of adenomas in the rectum and colon. Mostly, cancers develop after the advent of the polyps. It appears in both sexes evenly, and the occurrence of the disease is in the second decade of life. Mitochondrial genome mutations have been reported with a variety of Tumors, but the precise role of these mutations in the pathogenicity and tumor progression is not exactly clear. Cytochrome c oxidase subunit I (COX1) is the terminal enzyme of the mitochondrial respiratory chain. The present study aims at assessing the occurrence of mtDNA mutations in COX1 gene in FAP patients and attempts to find out the cause and effect relationship between mitochondrial mutations and tumor progression.

METHODS

In this study, 56 FAP patients were investigated for the presence of the mutations in mitochondrial COX1 coding gene by PCR and sequencing analysis. All sequences that differed from the revised Cambridge Reference Sequence (rCRS) were classified as missense/ nonsense or silent mutations. Functional genomic studies using Bio-informatics tools were performed on the founded mutations to understand the downstream alterations in structure and function of protein.

RESULTS

We identified 38 changes in the COX1 gene in patients with FAP symptoms. Most of them were heteroplasmic changes of missense type (25/38). Tree of the changes (G6145A, C6988A, and T7306G) were nonsense mutations and had not been reported in the literature before. Our results of bioinformatics predictions showed that the identified mutations can affect mitochondrial functions, especially if the conservative domain of the protein is concerned.

CONCLUSION

Our findings indicate a high frequency of mtDNA mutations in all of the FAP cases compared to matched controls. These data significantly enhance our understanding of how such mutations contribute to cancer pathologies and develop the cancer treatment methods by new diagnostic biomarkers, and new drugs for gene therapy.

Emerging evidence for targeting mitochondrial metabolic dysfunction in cancer therapy

Mammalian cells use a complex network of redox-dependent processes necessary to maintain cellular integrity during oxidative metabolism, as well as to protect against and/or adapt to stress. The disruption of these redox-dependent processes, including those in the mitochondria, creates a cellular environment permissive for progression to a malignant phenotype and the development of resistance to commonly used anticancer agents. An extension of this paradigm is that when these mitochondrial functions are altered by the events leading to transformation and ensuing downstream metabolic processes, they can be used as molecular biomarkers or targets in the development of new therapeutic interventions to selectively kill and/or sensitize cancer versus normal cells. In this Review we propose that mitochondrial oxidative metabolism is altered in tumor cells, and the central theme of this dysregulation is electron transport chain activity, folate metabolism, NADH/NADPH metabolism, thiol-mediated detoxification pathways, and redox-active metal ion metabolism. It is proposed that specific subgroups of human malignancies display distinct mitochondrial transformative and/or tumor signatures that may benefit from agents that target these pathways.

Alterations of Oxidative Phosphorylation Complexes in Papillary Thyroid Carcinoma

The papillary thyroid carcinoma (PTC) is the most common malignant tumor of the thyroid gland, with disruptive mutations in mitochondrial complex I subunits reported at very low frequency. Furthermore, metabolic diversity of PTC has been postulated owing to variable messenger RNA (mRNA) expression of genes encoding subunits of the oxidative phosphorylation (OXHPOS) complexes. The aim of the present study was to evaluate the metabolic diversity of the OXPHOS system at the protein level by using immunohistochemical staining. Analysis of 18 human PTCs revealed elevated mitochondrial biogenesis but significantly lower levels of OXPHOS complex I in the tumor tissue (p < 0.0001) compared to the adjacent normal tissue. In contrast, OXPHOS complexes II–V were increased in the majority of PTCs. In three PTCs, we found pathologic mutations within mitochondrially encoded complex I subunits. Our data indicate that PTCs are characterized by an oncocytic metabolic signature that is in low complex I is combined with elevated mitochondrial mass and high complex II–V levels, which might be an important factor for tumor formation.

Mitochondrial 10398A>G NADH-Dehydrogenase Subunit 3 of Complex I Is Frequently Altered in Intra-Axial Brain Tumors in Malaysia

Background

Mitochondria are major cellular sources of reactive oxygen species (ROS) generation which can induce mitochondrial DNA damage and lead to carcinogenesis. The mitochondrial 10398A>G alteration in NADH-dehydrogenase subunit 3 (ND3) can severely impair complex I, a key component of ROS production in the mitochondrial electron transport chain. Alteration in ND3 10398A>G has been reported to be linked with diverse neurodegenerative disorders and cancers. The aim of this study was to find out the association of mitochondrial ND3 10398A>G alteration in brain tumor of Malaysian patients.

Methods

Brain tumor tissues and corresponding blood specimens were obtained from 45 patients. The ND3 10398A>G alteration at target codon 114 was detected using the PCR-RFLP analysis and later was confirmed by DNA sequencing.

Results

Twenty-six (57.8%) patients showed ND3 10398A>G mutation in their tumor specimens, in which 26.9% of these mutations were heterozygous mutations. ND3 10398A>G mutation was not significantly correlated with age, gender, and histological tumor grade, however was found more frequently in intra-axial than in extra-axial tumors (62.5% vs. 46.2%, p<0.01).

Conclusion

For the first time, we have been able to describe the occurrence of ND3 10398A>G mutations in a Malaysian brain tumor population. It can be concluded that mitochondrial ND3 10398A>G alteration is frequently present in brain tumors among Malaysian population and it shows an impact on the intra-axial tumors.

Defining the momiome: Promiscuous information transfer by mobile mitochondria and the mitochondrial genome

Mitochondria are complex intracellular organelles that have long been identified as the powerhouses of eukaryotic cells because of the central role they play in oxidative metabolism. A resurgence of interest in the study of mitochondria during the past decade has revealed that mitochondria also play key roles in cell signaling, proliferation, cell metabolism and cell death, and that genetic and/or metabolic alterations in mitochondria contribute to a number of diseases, including cancer. Mitochondria have been identified as signaling organelles, capable of mediating bidirectional intracellular information transfer: anterograde (from nucleus to mitochondria) and retrograde (from mitochondria to nucleus). More recently, evidence is now building that the role of mitochondria extends to intercellular communication as well, and that the mitochondrial genome (mtDNA) and even whole mitochondria are indeed mobile and can mediate information transfer between cells. We define this promiscuous information transfer function of mitochondria and mtDNA as "momiome" to include all mobile functions of mitochondria and the mitochondrial genome. Herein, we review the "momiome" and explore its role in cancer development, progression, and treatment.

Mitochondrial genome variation and prostate cancer: a review of the mutational landscape and application to clinical management

Prostate cancer is a genetic disease. While next generation sequencing has allowed for the emergence of molecular taxonomy, classification is restricted to the nuclear genome. Mutations within the maternally inherited mitochondrial genome are known to impact cancer pathogenesis, as a result of disturbances in energy metabolism and apoptosis. With a higher mutation rate, limited repair and increased copy number compared to the nuclear genome, the clinical relevance of mitochondrial DNA (mtDNA) variation requires deeper exploration. Here we provide a systematic review of the landscape of prostate cancer associated mtDNA variation. While the jury is still out on the association between inherited mtDNA variation and prostate cancer risk, we collate a total of 749 uniquely reported prostate cancer associated somatic mutations. Support exists for number of somatic events, extent of heteroplasmy, and rate of recurrence of mtDNA mutations, increasing with disease aggression. While, the predicted pathogenic impact for recurrent prostate cancer associated mutations appears negligible, evidence exists for carcinogenic mutations impacting the cytochrome c oxidase complex and regulating metastasis through elevated reactive oxygen species production. Due to a lack of lethal cohort analyses, we provide additional unpublished data for metastatic disease. Discussing the advantages of mtDNA as a prostate cancer biomarker, we provide a review of current progress of including elevated mtDNA levels, of a large somatic deletion, acquired tRNAs mutations, heteroplasmy and total number of somatic events (mutational load). We confirm via meta-analysis a significant association between mtDNA mutational load and pathological staging at diagnosis or surgery (p < 0.0001).

Oncogenes, mitochondrial metabolism, and quality control in differentiated thyroid cancer

Thyroid cancer is one of the most common malignancies of endocrine organs, and its incidence rate has increased steadily over the past several decades. Most differentiated thyroid tumors derived from thyroid epithelial cells exhibit slow-growing cancers, and patients with these tumors can achieve a good prognosis with surgical removal and radioiodine treatment. However, a small proportion of patients present with advanced thyroid cancer and are unusually resistant to current drug treatment modalities. Thyroid tumorigenesis is a complex process that is regulated by the activation of oncogenes, inactivation of tumor suppressors, and alterations in programmed cell death. Mitochondria play an essential role during tumor formation, progression, and metastasis of thyroid cancer. Recent studies have successfully observed the mitochondrial etiology of thyroid carcinogenesis. This review focuses on the recent progress in understanding the molecular mechanisms of thyroid cancer relating to altered mitochondrial metabolism.

Mutations in the Mitochondrial ND1 Gene Are Associated with Postoperative Prognosis of Localized Renal Cell Carcinoma

We analyzed mutations in the mitochondrial ND1 gene to determine their association with clinicopathological parameters and postoperative recurrence of renal cell carcinoma (RCC) in Japanese patients. Among 62 RCC cases for which tumor pathology was confirmed by histopathology, ND1 sequencing revealed the presence of 30 mutation sites in 19 cases. Most mutations were heteroplasmic, with 16 of 19 cases harboring one or more heteroplasmic sites. Additionally, 12 sites had amino acid mutations, which were frequent in 10 of the cases. The 5-year recurrence-free survival (RFS) rate was significantly worse in patients with tumors >40 mm in diameter (p = 0.0091), pathological T (pT) stage ≥3 (p = 0.0122), Fuhrman nuclear atypia grade ≥III (p = 0.0070), and ND1 mutations (p = 0.0006). Multivariate analysis using these factors revealed that mutations in ND1 were significantly associated with the 5-year RFS rate (p = 0.0044). These results suggest a strong correlation between the presence of ND1 mutations in cancer tissue and postoperative recurrence of localized RCC in Japanese patients.

Mitochondrial Genetic Variation in Iranian Infertile Men with Varicocele

Background:

Several recent studies have shown that mitochondrial DNA mutations lead to major disabilities and premature death in carriers. More than 150 mutations in human mitochondrial DNA (mtDNA) genes have been associated with a wide spectrum of disorders. Varicocele, one of the causes of infertility in men wherein abnormal inflexion and distension of veins of the pampiniform plexus is observed within spermatic cord, can increase reactive oxygen species (ROS) production in semen and cause oxidative stress and sperm dysfunction in patients. Given that mitochondria are the source of ROS production in cells, the aim of this study was to scan nine mitochondrial genes (MT-COX2, MT-tRNA^Lys , MT-ATP8, MT-ATP6, MT-COX3, MT-tRNA^Gly , MT-ND3, MT-tRNA^Arg and MT-ND4L) for mutations in infertile patients with varicocele.

Materials and Methods:

In this cross-sectional study, polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and DNA sequencing were used to detect and identify point mutations respectively in 9 mitochondrial genes in 72 infertile men with varicocele and 159 fertile men. In brief, the samples showing altered electrophoretic patterns of DNA in the SSCP gel were sent for DNA sequencing to identify the exact nucleotide variation.

Results:

Ten type nucleotide variants were detected exclusively in mitochondrial DNA of infertile men. These include six novel nucleotide changes and four variants previously reported for other disorders.

Conclusion:

Mutations in mitochondrial genes may affect respiratory complexes in combination with environmental risk factors. Therefore these nucleotide variants probably lead to impaired ATP synthesis and mitochondrial function ultimately interfering with sperm motility and infertility.

Mitochondrial DNA depletion causes decreased ROS production and resistance to apoptosis

Mitochondrial DNA (mtDNA) depletion occurs frequently in many diseases including cancer. The present study was designed in order to examine the hypothesis that mtDNA‑depleted cells are resistant to apoptosis and to explore the possible mechanisms responsible for this effect. Parental human osteosarcoma 143B cells and mtDNA‑deficient (Rho˚ or ρ˚) 206 cells (derived from 143B cells) were exposed to different doses of solar-simulated ultraviolet (UV) radiation. The effects of solar irradiation on cell morphology were observed under both light and fluorescence microscopes. Furthermore, apoptosis, mitochondrial membrane potential (MMP) disruption and reactive oxygen species (ROS) production were detected and measured by flow cytometry. In both cell lines, apoptosis and ROS production were clearly increased, whereas MMP was slightly decreased. However, apoptosis and ROS production were reduced in the Rho˚206 cells compared with the 143B cells. We also performed western blot analysis and demonstrated the increased release of cytosolic Cyt c from mitochondria in the 143B cells compared with that in the Rho˚206 cells. Thus, we concluded that Rho˚206 cells exhibit more resistance to solar‑simulated UV radiation‑induced apoptosis at certain doses than 143B cells and this is possibly due to decreased ROS production.

Variants in mitochondrial tRNA gene may not be associated with thyroid carcinoma

Thyroid cancer is a very common form of endocrine system malignancy. To date, the molecular mechanism underlying thyroid cancer remains poorly understood. Studies of oncocytic tumors have led to a hypothesis which proposes that defects in oxidative phosphorylation (OX- PHOS) may result in a compensatory increase in mitochondrial replication and gene expression. As a result, mitochondrial DNA (mtDNA) mutation analysis has become a useful tool to explore the molecular basis of this disease. Among these mutations, mitochondrial transfer RNAs (mttRNAs) are the hot spots for pathogenic mutations associated with thyroid cancer. However, due to its high mutation rate, the role of mt-tRNA variants in thyroid cancer is still controversial. To address this problem, in this study, we reassessed seven reported mt-tRNA variants: tRNA^Asp G7521A, tRNA^Arg T10411C and T10463C, tRNA^Leu(CUN) A12308G, tRNA^Ile G4292C and C4312T, and tRNA^Ala T5655C, in clinical manifestations of thyroid cancer. We first performed the phylogenetic conservation analysis for these variants; moreover, we used a bioinformatic tool to compare the minimum free energy (G) of mt-tRNA with and without mutations. Most strikingly, none of these variants caused the significant change of the G between the wild-type and the mutant form, suggesting that they may not play an important roles in thyroid cancer. In addition, we screened the frequency of the “pathogenic” A12308G alternation in 300 patients with thyroid cancer and 200 healthy controls. We found that there were five patients and three control subjects carrying this variant. It seemed that the A12308G variant may be a common polymorphism in the human population. Taken together, our study indicated that variants in mt-tRNA genes may not play active roles in patients with thyroid cancer.

Multicompartment metabolism in papillary thyroid cancer

OBJECTIVES/HYPOTHESIS

In many cancers, varying regions within the tumor are often phenotypically heterogeneous, including their metabolic phenotype. Further, tumor regions can be metabolically compartmentalized, with metabolites transferred between compartments. When present, this metabolic coupling can promote aggressive behavior. Tumor metabolism in papillary thyroid cancer (PTC) is poorly characterized.

STUDY DESIGN

Immunohistochemical staining of tissue samples.

METHODS

Papillary thyroid cancer specimens from 46 patients with (n = 19) and without advanced disease (n = 27) were compared to noncancerous thyroid tissue (NCT) and benign thyroid specimens (n = 6 follicular adenoma [FA] and n = 5 nodular goiter [NG]). Advanced disease was defined as the presence of lateral neck lymphadenopathy. Immunohistochemistry was performed for translocase of outer mitochondrial membrane 20 (TOMM20), a marker of oxidative phosphorylation, and monocarboxylate transporter 4 (MCT4), a marker of glycolysis.

RESULTS

Papillary thyroid cancer and FA thyrocytes had high staining for TOMM20 compared to NCT and nodular goiter (NG) (P < 0.01). High MCT4 staining in fibroblasts was more common in PTC with advanced disease than in any other tissue type studied (P < 0.01). High MCT4 staining was found in all 19 cases of PTC with advanced disease, in 11 of 19 samples with low-stage disease, in one of five samples of FA, in one of 34 NCT, and in 0 of six NG samples. Low fibroblast MCT4 staining in PTC correlated with the absence of clinical adenopathy (P = 0.028); the absence of extrathyroidal extension (P = 0.004); low American Thyroid Association risk (P = 0.001); low AGES (age, grade, extent, size) score (P = 0.004); and low age, metastasis, extent of disease, size risk (P = 0.002).

CONCLUSION

This study suggests that multiple metabolic compartments exist in PTC, and low fibroblast MCT4 may be a biomarker of indolent disease.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 126:2410-2418, 2016.

Mitochondrial Energy Metabolism and Thyroid Cancers

Primary thyroid cancers including papillary, follicular, poorly differentiated, and anaplastic carcinomas show substantial differences in biological and clinical behaviors. Even in the same pathological type, there is wide variability in the clinical course of disease progression. The molecular carcinogenesis of thyroid cancer has advanced tremendously in the last decade. However, specific inhibition of oncogenic pathways did not provide a significant survival benefit in advanced progressive thyroid cancer that is resistant to radioactive iodine therapy. Accumulating evidence clearly shows that cellular energy metabolism, which is controlled by oncogenes and other tumor-related factors, is a critical factor determining the clinical phenotypes of cancer. However, the role and nature of energy metabolism in thyroid cancer remain unclear. In this article, we discuss the role of cellular energy metabolism, particularly mitochondrial energy metabolism, in thyroid cancer. Determining the molecular nature of metabolic remodeling in thyroid cancer may provide new biomarkers and therapeutic targets that may be useful in the management of refractory thyroid cancers.

Complete mitochondrial genome analysis and clinical documentation of a five-generational Indian family with mitochondrial 1555A>G mutation and postlingual hearing loss

Hearing loss is the most common sensory disorder and is genetically heterogeneous. Apart from nuclear gene mutations, a number of inherited mitochondrial mutations have also been implicated. The m.1555A>G mutation in the mitochondrial MT-RNR1 gene is reported as the most common mutation causing nonsyndromic hearing loss in various ethnic populations. We report here for the first time the clinical, genetic and molecular characterisation of a single large five-generational Tamil-speaking South Indian family with maternally inherited nonsyndromic postlingual hearing loss. Molecular analysis led to identification of m.1555A>G in 28 maternal relatives with variable degree of phenotypic expression. The penetrance of hearing loss among the maternal relatives in this family was 55%. Sequence analysis of the complete mitochondrial genome in 36 members of this pedigree identified 25 known variants and one novel variant co-transmitted along with m.1555A>G mutation. The mtDNA haplotype analysis revealed that the maternal relatives carry the R*T2 haplotype similar to Europeans and South Asians. Sequencing of the coding exon of GJB2 nuclear gene did not show any pathogenic mutations. The results suggest that other nuclear or environmental modifying factors could have played a role in the differential expression of mutation m.1555A>G in postlingual hearing loss in this family.

Single nucleotide polymorphisms in the mitochondrial displacement loop region and outcome of malignant fibrous histiocytoma

PURPOSE

Single nucleotide polymorphisms (SNPs) in the mitochondrial DNA displacement-loop (D-loop) region have been reported to be associated with cancer risk and disease outcome in several types of cancer. In this study, we investigated whether the SNPs in mitochondrial D-loop were associated with the outcome of malignant fibrous histiocytoma (MFH).

EXPERIMENTAL DESIGN

The D-loop region of mtDNA was sequenced for 80 MFH patients. The 3 years survival curve were calculated with the Kaplan-Meier method and compared by the log-rank test at each SNP site, a multivariate survival analysis was also performed with the Cox proportional hazards method.

RESULTS

The SNP sites of nucleotides 152T/C, 16,390G/A, 16,290C/T, 16,304T/C and the AC deletion at sites 523 and 524 were identified for prediction of post-operational survival by the log-rank test. In an overall multivariate analysis, the 16,290 and 16,390 alleles were identified as independent predictors of MFH outcome. The length of survival for patients with the rare allele 16,390A genotype was significantly shorter than that for patients with the frequent allele 16,390Gat the site 16,390. The same was seen for the rare allele 16,290T genotype when compared with matched allele 16,290C at the site 16,290 in MFH patients.

CONCLUSIONS

These results suggested that SNPs in the D-loop are independent prognostic markers for patients with MFH. The analysis of genetic polymorphisms in the D-loop can help identify patient subgroups at higher risk of a poor disease outcome.

Identification of sequence polymorphisms in the D-loop region of mitochondrial DNA as risk biomarkers for malignant fibrous histiocytoma

Single nucleotide polymorphisms (SNPs) in the mitochondrial DNA Displacement-loop (D-loop) region particularly in a highly polymorphic homopolymeric C stretch named D310 have been reported to be associated with cancer risk in several types of cancer. In order to evaluate the frequency of D-loop SNPs in a large series of malignant fibrous histiocytoma (MFH) and establish correlations with cancer risk, we sequenced the D-loop of 92 MFH patients and analyzed their use as predictive biomarkers for MFH risk. The minor alleles of nucleotides 73G, 151T were associated with an increased risk for MFH patients, whereas the alleles of nucleotides 16,298C, 152C, and insertion of C at the site 315 (located within the D310) were associated with a decreased risk for MFH patients. These results suggest that SNPs in the mitochondrial D-loop should be considered as a biomarker which may be useful for the early detection of MFH in individuals at risk of this cancer.

The mitochondrial genome: a biosensor for early cancer detection?

Mutations in the mitochondrial genome have been reported as biomarkers for the detection of cancer. Hallmarks of cancer development include the accumulation of genetic alterations in the mitochondrial and nuclear genomes. Damage to mitochondria affects energy metabolism, generation of reactive oxygen species, apoptosis, cell growth and other processes that contribute to the neoplastic process. Furthermore, mitochondrial DNA mutations occur frequently in cancer. Little work has been done to link a pathway between mitochondrial mutations and cancer etiology. Volumes of work have been reported on the association of mitochondrial mutations and almost all types of cancer including the use of body fluids for early detection. This review examines the measurement of mitochondrial mutations for the application of detecting human tumor tissue.

Mitochondrial DNA and carcinogenesis (review)

The role of the mitochondria in the process of carcinogenesis has drawn researchers' attention since the discovery of respiratory deficit in cells, particularly those characterized by rapid proliferation. The deficit was assumed to stimulate further differentiation of the cells and initiate the process of neoplastic transformation. As many as 25-80% of somatic mutations in mitochondrial DNA (mtDNA) are found in various neoplasms. These mutations are considered to trigger the neoplastic transformation through shifts of cell energy resources, an increase in the mitochondrial oxidative stress and modulation of apoptosis. The question arises as to whether the mtDNA mutations precede a neoplasm or whether they are a result of changes and processes that take place during neoplastic proliferation.

The biology and the genetics of Hurthle cell tumors of the thyroid

The biology and the genetics of Hürthle cell tumors are reviewed starting from the characterization and differential diagnosis of the numerous benign and malignant, neoplastic and nonneoplastic lesions of the thyroid in which Hürthle cell transformation is frequently observed. The clinicopathologic and molecular evidence obtained from the comparative study of the aforementioned conditions indicate that Hürthle cell appearance represents a phenotype that is superimposed on the genotypic and conventional histopathologic features of the tumors. Hürthle cell tumors differ from their non-Hürthle counterparts regarding the prevalence of large deletions of mitochondrial DNA (mtDNA), mutations of mtDNA genes coding for oxidative phosphorylation (OXPHOS) proteins (namely mutations of complex I subunit genes) and mutations of nuclear genes coding also for mitochondrial OXPHOS proteins. Such mitochondrial alterations lead to energy production defects in Hürthle cell tumors; the increased proliferation of mitochondria may reflect a compensatory mechanism for such defects and is associated with the overexpression of factors involved in mitochondrial biogenesis. The mitochondrial abnormalities are also thought to play a major role in the predisposition for necrosis instead of apoptosis which seems to be blocked in most Hürthle cell tumors. Finally, the results obtained in experimental models using cybrid cell lines and the data obtained from histopathologic and molecular studies of familial Hürthle cell tumors are used, together with the aforementioned genetic and epigenetic alterations, to progress in the understanding of the mechanisms through which mitochondrial abnormalities may be involved in the different steps of thyroid carcinogenesis, from tumor initiation to metastization.

Mitochondrial DNA mutations---candidate biomarkers for breast cancer diagnosis in Bangladesh

Breast cancer is a major health problem that affects more than 24% of women in Bangladesh. Furthermore, among low-income countries including Bangladesh, individuals have a high risk for developing breast cancer. This study aimed to identify candidate mitochondrial DNA (mtDNA) biomarkers for breast cancer diagnosis in Bangladeshi women to be used as a preventive approach. We screened the blood samples from 24 breast cancer patients and 20 healthy controls to detect polymorphisms in the D-loop and the ND3- and ND4-coding regions of mtDNA by direct sequencing. Among 14 distinct mutations, 10 polymorphisms were found in the D-loop, 3 were found in the ND3-coding region, and 1 was found in the ND4-coding region. The frequency of two novel polymorphisms in the D-loop, one at position 16290 (T-ins) and the other at position 16293 (A-del), was higher in breast cancer patients than in control subjects (position 16290: odds ratio = 6.011, 95% confidence interval = 1.2482 to 28.8411, P = 0.002; position 16293: odds ratio = 5.6028, 95% confidence interval = 1.4357 to 21.8925, P = 0.010). We also observed one novel mutation in the ND3-coding region at position 10316 (A > G) in 69% of breast cancer patients but not in control subjects. The study suggests that two novel polymorphisms in the D-loop may be candidate biomarkers for breast cancer diagnosis in Bangladeshi women.

Somatic mitochondrial DNA mutations in cancer escape purifying selection and high pathogenicity mutations lead to the oncocytic phenotype: pathogenicity analysis of reported somatic mtDNA mutations in tumors

BACKGROUND

The presence of somatic mitochondrial DNA (mtDNA) mutations in cancer cells has been interpreted in controversial ways, ranging from random neutral accumulation of mutations, to positive selection for high pathogenicity, or conversely to purifying selection against high pathogenicity variants as occurs at the population level.

METHODS

Here we evaluated the predicted pathogenicity of somatic mtDNA mutations described in cancer and compare these to the distribution of variations observed in the global human population and all possible protein variations that could occur in human mtDNA. We focus on oncocytic tumors, which are clearly associated with mitochondrial dysfunction. The protein variant pathogenicity was predicted using two computational methods, MutPred and SNPs&GO.

RESULTS

The pathogenicity score of the somatic mtDNA variants were significantly higher in oncocytic tumors compared to non-oncocytic tumors. Variations in subunits of Complex I of the electron transfer chain were significantly more common in tumors with the oncocytic phenotype, while variations in Complex V subunits were significantly more common in non-oncocytic tumors.

CONCLUSIONS

Our results show that the somatic mtDNA mutations reported over all tumors are indistinguishable from a random selection from the set of all possible amino acid variations, and have therefore escaped the effects of purifying selection that act strongly at the population level. We show that the pathogenicity of somatic mtDNA mutations is a determining factor for the oncocytic phenotype. The opposite associations of the Complex I and Complex V variants with the oncocytic and non-oncocytic tumors implies that low mitochondrial membrane potential may play an important role in determining the oncocytic phenotype.

Somatic mitochondrial DNA mutations in human cancers

Mitochondria are ubiquitous organelles in eukaryotic cells principally responsible for regulating cellular energy metabolism, free radical production, and the execution of apoptotic pathways. Abnormal oxidative phosphorylation (OXPHOS) and aerobic metabolism as a result of mitochondrial dysfunction have long been hypothesized to be involved in tumorigenesis. In the past decades, numerous somatic mutations in both the coding and control regions of mitochondrial DNA (mtDNA) have been extensively examined in a broad range of primary human cancers, underscoring that accumulation of mtDNA alterations may be a critical factor in eliciting persistent mitochondrial defects and consequently contributing to cancer initiation and progression. However, the roles of these mtDNA mutations in the carcinogenic process remain largely unknown. This review outlines a wide variety of somatic mtDNA mutations identified in common human malignancies and highlights recent advances in understanding the causal roles of mtDNA variations in neoplastic transformation and tumor progression. In addition, it briefly illustrates how mtDNA alterations activate mitochondria-to-nucleus retrograde signaling so as to modulate the expression of relevant nuclear genes or induce epigenetic changes and promote malignant phenotypes in cancer cells. The present state of our knowledge regarding how mutational changes in the mitochondrial genome could be used as a diagnostic biomarker for early detection of cancer and as a potential target in the development of new therapeutic approaches is also discussed. These findings strongly indicate that mtDNA mutations exert a crucial role in the pathogenic mechanisms of tumor development, but continued investigations are definitely required to further elucidate the functional significance of specific mtDNA mutations in the etiology of human cancers.

Frequent somatic mutations of mitochondrial DNA in traditional serrated adenomas but not in sessile serrated adenomas of the colorectum

BACKGROUND AND AIM

Serrated adenomas (SAs), recently subdivided into traditional SAs (TSAs) and sessile SAs (SSAs), are recognized as a distinct form of neoplasia of the colorectum. One of the characteristics of SAs is hypermaturation of the gland epithelium due to the low extent of cell loss by apoptosis. Mutations of mitochondrial DNA (mtDNA) are closely associated with abnormality in apoptosis. We therefore examined mtDNA mutations in colorectal lesions including hyperplastic polyps (HPs), SSAs, TSAs, and carcinomas.

METHODS

Examined were 25 HPs, 32 SSAs, 19 TSAs, and 138 carcinomas. The D310 region of the mtDNAs was examined by microsatellite assay.

RESULTS

mtDNA mutations were detected in none of 25 (0%) HPs, one of 32 (3%) SSAs, six of 19 (32%) TSAs, and eleven of 133 (8%) carcinomas (five of the 138 carcinomas were not informative). The frequency of mtDNA mutations in the TSAs was significantly higher than that in the HPs, SSAs, and carcinomas (P = 0.004, P = 0.008, and P = 0.009, respectively). The frequency of mtDNA mutations in carcinomas was not significantly higher than that in HPs and SSAs (P = 0.14 and P = 0.28, respectively).

CONCLUSION

Our data suggest that mtDNA mutations may play an important role in the development of TSAs and could be used as a genetic marker to aid in the diagnosis of colorectal lesions.

The awakening of an advanced malignant cancer: an insult to the mitochondrial genome

BACKGROUND

In only months-to-years a primary cancer can progress to an advanced phenotype that is metastatic and resistant to clinical treatments. As early as the 1900s, it was discovered that the progression of a cancer to the advanced phenotype is often associated with a shift in the metabolic profile of the disease from a state of respiration to anaerobic fermentation - a phenomenon denoted as the Warburg Effect.

SCOPE OF REVIEW

Reports in the literature strongly suggest that the Warburg Effect is generated as a response to a loss in the integrity of the sequence and/or copy number of the mitochondrial genome content within a cancer.

MAJOR CONCLUSIONS

Multiple studies regarding the progression of cancer indicate that mutation, and/or, a flux in the copy number, of the mitochondrial genome content can support the early development of a cancer, until; the mutational load and/or the reduction-to-depletion of the copy number of the mitochondrial genome content induces the progression of the disease to an advanced phenotype.

GENERAL SIGNIFICANCE

Collectively, evidence has revealed that the human cell has incorporated the mitochondrial genome content into a cellular mechanism that, when pathologically actuated, can de(un)differentiate a cancer from the parental tissue of origin into an autonomous disease that disrupts the hierarchical structure-and-function of the human body. This article is part of a Special Issue entitled: Biochemistry of Mitochondria.

Mutational hotspots in the mitochondrial D-loop region of cancerous and precancerous colorectal lesions in Egyptian patients

Mutations in the mitochondrial genome (mtDNA) are associated with different types of cancer, specifically colorectal cancer (CRC). However, few studies have been performed on precancerous lesions, such as ulcerative colitis (UC) lesions and adenomatous polyps (AP). The aim of this study was to identify mtDNA mutations in the cancerous and precancerous lesions of Egyptian patients. An analysis of the mutations found in six regions of the mtDNA genome (ND1, ND5, COI, tRNAser, D-loop 1, and 2) in 80 Egyptian patients (40 CRC, 20 UC, and 20 AP) was performed using polymerase chain reaction-single-strand conformational polymorphism techniques and followed up by direct sequencing. The overall incidence of mutations was 25%, 25%, and 35% in CRC, UC, and AP cases, respectively. Although there was no common mutation pattern within each group, a large number of mutations were detected in the D-loop region in all of the groups. Some mutations (e.g., T414G) were detected repeatedly in precancerous (UC and AP) and cancerous lesions. Mutations detected in patients with CRC were predominantly found in the ND1 gene (40%). Our preliminary study suggests that Egyptian patients with CRC have a large number of mtDNA mutations, especially in the D-loop region, which have not been previously reported. Mutations in the mtDNA of precancerous lesions (i.e., AP and UC) may contribute to transformation events that lead to CRC.

Mitochondrial-nuclear epistasis: implications for human aging and longevity

There is substantial evidence that mitochondria are involved in the aging process. Mitochondrial function requires the coordinated expression of hundreds of nuclear genes and a few dozen mitochondrial genes, many of which have been associated with either extended or shortened life span. Impaired mitochondrial function resulting from mtDNA and nuclear DNA variation is likely to contribute to an imbalance in cellular energy homeostasis, increased vulnerability to oxidative stress, and an increased rate of cellular senescence and aging. The complex genetic architecture of mitochondria suggests that there may be an equally complex set of gene interactions (epistases) involving genetic variation in the nuclear and mitochondrial genomes. Results from Drosophila suggest that the effects of mtDNA haplotypes on longevity vary among different nuclear allelic backgrounds, which could account for the inconsistent associations that have been observed between mitochondrial DNA (mtDNA) haplogroups and survival in humans. A diversity of pathways may influence the way mitochondria and nuclear-mitochondrial interactions modulate longevity, including: oxidative phosphorylation; mitochondrial uncoupling; antioxidant defenses; mitochondrial fission and fusion; and sirtuin regulation of mitochondrial genes. We hypothesize that aging and longevity, as complex traits having a significant genetic component, are likely to be controlled by nuclear gene variants interacting with both inherited and somatic mtDNA variability.

Expression and somatic mutations of SDHAF2 (SDH5), a novel endocrine tumor suppressor gene in parathyroid tumors of primary hyperparathyroidism

To investigate the SDHAF2 gene and its effect on primary hyperparathyroidism. Parathyroid tumors causing primary hyperparathyroidism (pHPT) are one of the more common endocrine neoplasias. Loss of heterozygosity at chromosome 11q13 is the most common chromosomal aberration in parathyroid tumors occurring in about 40% of sporadic tumors. Only 15-19% display somatic mutations in the MEN1 gene, which suggest that this chromosomal region may harbor additional genes of importance in parathyroid tumor development. The SDHAF2 (formerly SDH5) gene is a recently identified neuroendocrine tumor suppressor gene at this locus, and inherited mutations of the SDHAF2 gene has been linked to familial paraganglioma. We demonstrate that the SDHAF2 gene is expressed in parathyroid tissue using RT-PCR. Because detection of inactivating mutations is the major criterion for validating a candidate tumor suppressor, we used automated sequencing of the coding region and intron/exon boundaries in 80 sporadic parathyroid adenomas from patients with pHPT. A known polymorphisms (A to G substitution; rs879647) was identified in 9/80 parathyroid tumors but no tumor-specific somatic mutational aberrations, such as nonsense, frameshift, or other inactivating mutations were identified. The SDHAF2 gene is expressed in parathyroid tissue. However, somatic mutations of the SDHAF2 tumor suppressor gene are unlikely to frequently contribute to parathyroid tumor development in sporadic pHPT.

Generation, function, and prognostic utility of somatic mitochondrial DNA mutations in cancer

Exciting new studies are increasingly strengthening the link between mitochondrial mutagenesis and tumor progression. Here we provide a comprehensive review and meta-analysis of studies reporting on mitochondrial DNA mutations in common human cancers. We discuss possible mechanisms by which mitochondrial DNA mutations may influence carcinogenesis, outline important caveats for interpreting the detected mutations--particularly differentiating causality from association--and suggest how new mutational assays may help resolve fundamental controversies in the field and delineate the origin and expansion of neoplastic cell lineages. Finally, we discuss the potential clinical utility of mtDNA mutations for improving the sensitivity of early cancer diagnosis, rapidly detecting cancer recurrence, and predicting the disease outcome.

Mitochondrial mutations in adenoid cystic carcinoma of the salivary glands

Background

The MitoChip v2.0 resequencing array is an array-based technique allowing for accurate and complete sequencing of the mitochondrial genome. No studies have investigated mitochondrial mutation in salivary gland adenoid cystic carcinomas.

Methodology

The entire mitochondrial genome of 22 salivary gland adenoid cystic carcinomas (ACC) of salivary glands and matched leukocyte DNA was sequenced to determine the frequency and distribution of mitochondrial mutations in ACC tumors.

Principal Findings

Seventeen of 22 ACCs (77%) carried mitochondrial mutations, ranging in number from 1 to 37 mutations. A disproportionate number of mutations occurred in the D-loop. Twelve of 17 tumors (70.6%) carried mutations resulting in amino acid changes of translated proteins. Nine of 17 tumors (52.9%) with a mutation carried an amino acid changing mutation in the nicotinamide adenine dinucleotide dehydrogenase (NADH) complex.

Conclusions/Significance

Mitochondrial mutation is frequent in salivary ACCs. The high incidence of amino acid changing mutations implicates alterations in aerobic respiration in ACC carcinogenesis. D-loop mutations are of unclear significance, but may be associated with alterations in transcription or replication.

Clinical implications of molecular markers in follicular cell-derived thyroid cancer

The increasing use/applications of molecular biology techniques have provided new insights on the genetic changes that underlie carcinogenesis and tumor progression in thyroid cancer. Molecular analysis may improve the histopathologic evaluation of follicular cell-derived thyroid carcinoma, not only elucidating some unresolved problems related to the diagnosis and disease prognosis, but also by improving patient management. Besides increasing our comprehension of cancer biology, either genetic alterations or gene expression profiles implicated in thyroid carcinogenesis shed new light on innovative diagnostic procedures as well as on targeted therapies.

Implications of mitochondrial DNA mutations and mitochondrial dysfunction in tumorigenesis

Alterations in oxidative phosphorylation resulting from mitochondrial dysfunction have long been hypothesized to be involved in tumorigenesis. Mitochondria have recently been shown to play an important role in regulating both programmed cell death and cell proliferation. Furthermore, mitochondrial DNA (mtDNA) mutations have been found in various cancer cells. However, the role of these mtDNA mutations in tumorigenesis remains largely unknown. This review focuses on basic mitochondrial genetics, mtDNA mutations and consequential mitochondrial dysfunction associated with cancer. The potential molecular mechanisms, mediating the pathogenesis from mtDNA mutations and mitochondrial dysfunction to tumorigenesis are also discussed.

mtDNA G10398A variant in African-American women with breast cancer provides resistance to apoptosis and promotes metastasis in mice

We investigated the effect of the mitochondrial DNA (mtDNA) polymorphism G10398A found in African-American women with aggressive breast cancer on apoptosis and tumorigenesis. We generated human cytoplasmic hybrid (cybrid) by repopulation of recipient rho(0) cells (devoid of mtDNA) with donor mtDNA derived from patients with breast cancer harboring the G10398A polymorphism. We investigated a number of functional phenotypes of the G10398A cybrid. The G10398A cybrid showed a slower proliferation rate and progression through the cell cycle, as well as increased complex I activity, increased levels of reactive oxygen species and depolarized mitochondria. The G10398A cybrid also showed resistance to apoptosis triggered by etoposide. Resistance to apoptosis was mediated by Akt activation. In addition, our studies showed that the G10398A cybrid cells form an increased number of anchorage-independent colonies in vitro and metastases in mice. Together our studies suggest that the G10398A variant confers resistance to apoptosis and promotes metastasis.

Sequence variation in the mitochondrial gene cytochrome c oxidase subunit I and prostate cancer in African American men

BACKGROUND

Previous studies have found associations between mitochondrial DNA (mtDNA) mutations and several cancer types. Recently, we found that mutations in the mtDNA gene cytochrome c oxidase subunit 1 (COI) were both linked to and associated with prostate cancer (PCa) in Caucasian men. Here we examine the association between COI mutations and PCa in African American men.

METHODS

The entire COI gene was directly sequenced in 132 PCa cases and 135 controls from the Flint Men's Health Study, a community-based sample of African American men with and without PCa. Associations between all variants and PCa were evaluated.

RESULTS

We identified 102 COI single nucleotide polymorphisms (SNPs), including 15 missense variants. Overall, the presence of one or more COI missense variants was not significantly associated with PCa. Individually, two SNPs (T6221C and T7389C) were significantly associated with prostate cancer (P < 0.05) and in strong linkage disequilibrium with each other (r(2) > 0.6).

CONCLUSIONS

Of the two significantly associated SNPs, one is a synonymous substitution and the other is part of the African-specific mitochondrial haplogroup (L). Additional research will be needed to determine the clinical relevance of these associations in African populations.

Mitochondrial D-loop mutation is a common event in colorectal cancers with p53 mutations

PURPOSE

p53 is the most frequently mutated gene in colorectal cancer. In mitochondria, p53 protein is involved in regulation of transcription/replication and maintenance of genomic stability. Our aim was to examine the relationship between p53, D-loop mutation, and mitochondrial DNA content in colorectal cancer (CRC).

METHODS

A total of 194 patients with sporadic CRC without microsatellite instability who underwent surgery in Taipei Veterans General Hospital from January 1999 to December 2000 were included. The mitochondrial DNA content and D-loop mutation were quantified using real-time PCR and sequencing.

RESULTS

D-loop mutation occurred at significantly higher frequency in tumors with p53 mutation (34/88; 38.6%) than in tumors without p53 mutation (23/106; 21.7%). The frequency of the decreased mtDNA content was significantly associated with TNM stage (p = 0.009) and p53 mutation (p = 0.036). The 5-year DFS rate was 39% in patients exhibiting tumors with decreased mtDNA content, and was significantly poorer in these patients than in those exhibiting tumors with normal level of mtDNA content (61%, p = 0.01). The presence of D-loop mutations had no effect on 5-year DFS rate. In multivariate survival analysis, TNM stage, and p53 mutation, but not decreased mtDNA content and D-loop instability, had significant impacts on prognosis.

CONCLUSION

Change of mitochondrial DNA is a common event in colorectal cancer with p53 mutation, but is not associated with prognosis of CRC patients.

Mitochondria and cancer

The authors review the role played by mutations in mitochondrial DNA and in nuclear genes encoding mitochondrial proteins in cancer development, with an emphasis on the alterations of the oxidative phosphorylation system and glycolysis.