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Mitochondrial DNA changes can contribute to both an increased and decreased likelihood of cancer. This process is complex and not fully understood. Polymorphisms and mutations, especially those of the missense type, can affect mitochondrial functions, particularly if the conservative domain of the protein is concerned. This study aimed to identify the possible relationships between brain gliomas and the occurrence of specific mitochondrial DNA polymorphisms and mutations in respiratory complexes III, IV and V. The investigated material included blood and tumour material collected from 30 Caucasian patients diagnosed with WHO grade II, III or IV glioma. The mitochondrial genetic variants were investigated across the mitochondrial genome using next-generation sequencing (MiSeq/FGx system—Illumina). The study investigated, in silico, the effects of missense mutations on the biochemical properties, structure and functioning of the encoded protein, as well as their potential harmfulness. The A14793G (MTCYB), A15758G, (MT-CYB), A15218G (MT-CYB), G7444A (MT-CO1) polymorphisms, and the T15663C (MT-CYB) and G8959A (ATP6) mutations were assessed in silico as harmful alterations that could be involved in oncogenesis. The G8959A (E145K) ATP6 missense mutation has not been described in the literature so far. In light of these results, further research into the role of mtDNA changes in brain tumours should be conducted.

We report on a sporadic patient suffering Leigh syndrome characterized by bilateral lesions in the lenticular nuclei and spastic dystonia, intellectual disability, sensorineural deafness, hypertrophic cardiomyopathy, exercise intolerance, and retinitis pigmentosa. Complete sequencing of mitochondrial DNA revealed the heteroplasmic nucleotide change m.15635T>C affecting a highly conserved amino acid position (p.Ser297Pro) in the cytochrome b (MT-CYB) gene on a haplogroup K1c1a background, which includes a set of four non-synonymous polymorphisms also present in the same gene. Biochemical studies documented respiratory chain impairment due to complex III defect. This variant fulfils the criteria for being pathogenic and was previously reported in a sporadic case of fatal neonatal polyvisceral failure.

Reactive oxygen species (ROS) are by-products of cellular aerobic metabolism, playing a crucial role in the development of multiple diseases, such as cancer. ROS are generated by various enzymes, including respiratory complexes such as respiratory complex III (a.k.a. bc 1 complex), which encompasses four redox centers (Fe 2 S 2 , heme b L , heme b H, and heme c 1 ) and two native binding sites (Q o and Q i sites). In the current study, we explored a novel anti-cancer mechanism by binding electron tunneling (ET)-modulating agents at the newly discovered Non-Q or NQ site in the bc 1 complex, thereby controlling the conformation of a key phenylalanine 90 (Phe90) residue, which acts as an internal ET switch between heme b L and heme b H . Our proposed mechanism would potentially enhance or reduce ET between heme b L and heme b H , ultimately reducing or increasing the cellular ROS levels. To explore our proposed mechanism, we performed extensive virtual screening of 1,489,806 ligands from the ZINC20 database against the Q o , Q i , and NQ sites of the bc 1 complex, obtaining 272 patented ligands that bind preferentially at the NQ site compared to the Q o and Q i sites. Biochemical assays for the top hit ligands, examining their ROS-regulatory and cytotoxic activities against breast cancer MCF7 cells, led to the discovery of potential compounds that upregulate and downregulate ROS. We found significant cytotoxic activity for the single treatment of a lead-hit ROS upregulator and even more synergistic cytotoxic activity for the sequential treatment of ROS upregulator and ROS downregulator ligands, which could be reserved for more resistant cancer cells.

Background Metabolic reprogramming is an important issue in tumor biology. A recently-identified actor in this regard is the molecular chaperone TRAP1, that is considered an oncogene in several cancers for its high expression but an oncosuppressor in others with predominant oxidative metabolism. TRAP1 is mainly localized in mitochondria, where it interacts with respiratory complexes, although alternative localizations have been described, particularly on the endoplasmic reticulum, where it interacts with the translational machinery with relevant roles in protein synthesis regulation. Results Herein we show that, inside mitochondria, TRAP1 binds the complex III core component UQCRC2 and regulates complex III activity. This decreases respiration rate during basal conditions but allows sustained oxidative phosphorylation when glucose is limiting, a condition in which the direct TRAP1-UQCRC2 binding is disrupted, but not TRAP1-complex III binding. Interestingly, several complex III components and assembly factors show an inverse correlation with survival and response to platinum-based therapy in high grade serous ovarian cancers, where TRAP1 inversely correlates with stage and grade and directly correlates with survival. Accordingly, drug-resistant ovarian cancer cells show high levels of complex III components and high sensitivity to complex III inhibitory drug antimycin A. Conclusions These results shed new light on the molecular mechanisms involved in TRAP1-dependent regulation of cancer cell metabolism and point out a potential novel target for metabolic therapy in ovarian cancer.

The mitochondrion is a major hub of cellular metabolism and involved directly or indirectly in almost all biological processes of the cell. In mitochondrial diseases, compromised respiratory electron transfer and oxidative phosphorylation (OXPHOS) lead to compensatory rewiring of metabolism with resemblance to the Warburg-like metabolic state of cancer cells. The transcription factor MYC (or c-MYC) is a major regulator of metabolic rewiring in cancer, stimulating glycolysis, nucleotide biosynthesis, and glutamine utilization, which are known or predicted to be affected also in mitochondrial diseases. Albeit not widely acknowledged thus far, several cell and mouse models of mitochondrial disease show upregulation of MYC and/or its typical transcriptional signatures. Moreover, gene expression and metabolite-level changes associated with mitochondrial integrated stress response (mt-ISR) show remarkable overlap with those of MYC overexpression. In addition to being a metabolic regulator, MYC promotes cellular proliferation and modifies the cell cycle kinetics and, especially at high expression levels, promotes replication stress and genomic instability, and sensitizes cells to apoptosis. Because cell proliferation requires energy and doubling of the cellular biomass, replicating cells should be particularly sensitive to defective OXPHOS. On the other hand, OXPHOS-defective replicating cells are predicted to be especially vulnerable to high levels of MYC as it facilitates evasion of metabolic checkpoints and accelerates cell cycle progression. Indeed, a few recent studies demonstrate cell cycle defects and nuclear DNA damage in OXPHOS deficiency. Here, we give an overview of key mitochondria-dependent metabolic pathways known to be regulated by MYC, review the current literature on MYC expression in mitochondrial diseases, and speculate how its upregulation may be triggered by OXPHOS deficiency and what implications this has for the pathogenesis of these diseases.

Mutations in BCS1L are the most frequent cause of human mitochondrial disease linked to complex III deficiency. Different forms of BCS1L-related diseases and more than 20 pathogenic alleles have been reported to date. Clinical symptoms are highly heterogenous, and multisystem involvement is often present, with liver and brain being the most frequently affected organs. BCS1L encodes a mitochondrial AAA + -family member with essential roles in the latest steps in the biogenesis of mitochondrial respiratory chain complex III. Since Bcs1 has been investigated mostly in yeast and mammals, its function in invertebrates remains largely unknown. Here, we describe the phenotypical, biochemical and metabolic consequences of Bcs1 genetic manipulation in Drosophila melanogaster. Our data demonstrate the fundamental role of Bcs1 in complex III biogenesis in invertebrates and provide novel, reliable models for BCS1L-related human mitochondrial diseases. These models recapitulate several features of the human disorders, collectively pointing to a crucial role of Bcs1 and, in turn, of complex III, in development, organismal fitness and physiology of several tissues.

Purpose Strobilurins act as antifungal agents by inhibiting the mitochondrial respiratory chain. The cytotoxic activity of strobilurins, focusing on its anticancer activities, has been reported. However, the mechanisms involved in these activities remain unclear. Methods The cytotoxic effects of strobilurin X isolated from the mycelium of Mucidula. venosolamellata were examined in human cancer cell lines (A549 and HeLa) and normal fibroblasts (WI-38). Results Strobilurin X significantly decreased the viability of A549 and HeLa cells compared to that in the WI-38 cells after 48 h of exposure. The EC 50 values for cytotoxicity in the A549, HeLa, and WI-38 cells were 3.4, 5.4, and 16.8 μg/mL, respectively. Strobilurin X inhibited the mitochondrial respiratory chain and enhanced the release of lactate in the A549 cells. The IC 50 value of strobilurin X against the mitochondrial respiratory chain complex III activity was 139.8 ng/mL. The cytotoxicity induced by strobilurin X was not completely rescued after adding uridine, methyl pyruvate, or N -acetyl cysteine. Furthermore, pharmacological approaches demonstrated that strobilurin X failed to modulate the mitogen-activated protein kinase family and phosphoinositide 3-kinase-Akt pathways; alternatively, it suppressed protein synthesis independent of uridine. Conclusion Strobilurin X induced cytotoxicity by blocking the mitochondrial respiratory chain and suppressing protein synthesis. These findings may aid in the development of novel anticancer drugs using strobilurins.

Background TTC19 deficiency is a progressive neurodegenerative disease associated with isolated mitochondrial respiratory chain (MRC) complex III deficiency and loss-of-function mutations in the TT19 gene in the few patients reported so far. Methods We performed exome sequencing and selective mutational analysis of TTC19 , respectively, in patients from three unrelated families presenting with initially unspecific clinical signs of muscular hypotonia and global developmental delay followed by regression, ataxia, loss of speech, and rapid neurological deterioration. One patient showed severe lactic acidosis at the neonatal age and during intercurrent illness. Results We identified homozygous mutations in all three index cases, in two families novel missense mutations (c.544 T > C/p.Leu185Pro; c.917 T > C/p.Leu324Pro). The younger sister of the severely affected patient 3 showed only mild delay of motor skills and muscular hypotonia so far but is also homozygous for the same mutation. Notably, one patient revealed normal activities of MRC complex III in two independent muscle biopsies. Neuroimaging of the severely affected patients demonstrated lesions in putamen and caudate nuclei, cerebellar atrophy, and the unusual finding of hypertrophic olivary nuclei degeneration. Reviewing the literature revealed striking similarities regarding neuroimaging and clinical course in pediatric patients with TTC19 deficiency: patterns consistent with Leigh or Leigh-like syndrome were found in almost all, hypertrophic olivary nucleus degeneration in all patients reported so far. The clinical course in pediatric patients is characterized by an initially unspecific developmental delay, followed by regression, progressive signs and symptoms of cerebellar, basal ganglia and brainstem affection, especially loss of speech and ataxia. Subsequently, neurological deterioration leading to a vegetative state occurs. Conclusions Our findings add to the phenotypic, genetic, and biochemical spectrum of TTC19 deficiency. However, TTC19 deficient patients do show characteristic clinical and neuroimaging features, which may facilitate diagnosis of this yet rare disorder. Normal MRC complex III activity does not exclude the diagnosis.

Background Spinocerebellar ataxias (SCAs) are heterogeneous diseases characterized by progressive cerebellar ataxia associated with dysarthria, oculomotor abnormalities, and mental impairment. To identify the causative gene, we performed exome sequencing on a Japanese patient clinically diagnosed with recessive SCA. Method The patient is a 37-year-old Japanese woman with consanguineous parents. The head magnetic resonance imaging (MRI) showed cerebellar atrophy and T1 low/T2 high intensity at the bilateral inferior olives. Single-nucleotide polymorphism (SNP) genotyping and next-generation sequencing were performed, and the variants obtained were filtered and prioritized. Results After these manipulations, we identified a homozygous nonsense mutation of the TTC19 gene (p.Q277*). TTC19 has been reported to be a causative gene of a neurodegenerative disease in Italian and Portuguese families and to be involved in the pathogenesis of mitochondrial respiratory chain complex III (cIII) deficiency. This report is the first description of a TTC19 mutation in an Asian population. Clinical symptoms and neuroimaging are consistent with previous reports. The head MRI already showed abnormal features four years before her blood lactate and pyruvate levels were elevated. Conclusions We should consider the genetic analysis of TTC19 when we observe such characteristic MRI abnormalities. Genes associated with mitochondrial function cause many types of SCAs; the mutation we identified should help to elucidate the pathology of these disorders.

The BCS1L gene encodes a chaperone responsible for assembly of respiratory chain complex III (CIII). A homozygous point mutation (232A→G) has been found as the genetic etiology for fetal growth retardation, amino aciduria, cholestasis, iron overload, lactic acidosis, and early death (GRACILE) syndrome (MIM 603358). Variable phenotypes have been found with other mutations. Our aim was to assess whether 232A→G or other BCS1L mutations were present in infants ( n  = 21) of Finnish origin with severe, lethal disease compatible with mitochondrial disorder. A further aim was to confirm the GRACILE genotype–phenotype constancy ( n  = 8). Three new cases with homozygous 232A→G mutation were identified; all had the primary GRACILE characteristics. No other mutations were found in the gene in other cases. All infants with GRACILE syndrome had the typical mutation. In conclusion, the rather homogenous population of Finns seems to have a specific BCS1L mutation that, as homozygous state, causes GRACILE syndrome, whereas other mutations are rare or not occurring. Thus, the novel clinical implication of this study is to screen for BCS1L mutations only if CIII is dysfunctioning or lacking Rieske protein, and to assess 232A→G mutation in cases with GRACILE syndrome.