Circular RNA mitochondrial translation optimization 1 correlates with less lymph node metastasis, longer disease-free survival, and higher chemotherapy sensitivity in gastric cancer.

OBJECTIVE: Circular-mitochondrial translation optimization 1 (circ-MTO1) inhibits the progression of gastric cancer by regulating the growth, apoptosis, and invasion of tumor cells. However, its clinical potential as a biomarker for gastric cancer remains to be further evaluated. This study aimed to assess circ-MTO1 expression and its correlation with clinical features and prognosis in gastric cancer patients, as well as the effect of circ-MTO1 on the sensitivity to chemotherapy in gastric cancer cells. METHODS: Circ-MTO1 in tumor and adjacent tissues of 97 gastric cancer patients undergoing resection was examined by reverse transcription-quantitative polymerase chain reaction. HGC-27 and NCI-N87 cells transfected by circ-MOT1 overexpression plasmid (OE-circ-MOT1) and negative control (OE-NC) were treated with 0-6.4 µM oxaliplatin. Relative cell viability was detected using Cell Counting Kit-8. RESULTS: Circ-MTO1 was insufficiently expressed in gastric tumor tissue (median (interquartile range): 0.403 (0.288-0.518)) compared with adjacent tissue (median (interquartile range): 1.000 (0.715-1.524)) (p < 0.001). Besides, tumor circ-MTO1 was correlated with less lymph node metastasis (p = 0.014) and low TNM stage (p = 0.039), while was not correlated with demographic features or other clinical characteristics (all p > 0.05). Furthermore, tumor circ-MTO1 high expression was independently correlated with prolonged disease-free survival (DFS) (p = 0.013, adjusted hazard ratio (95% confidential interval): 0.314 (0.126-0.782)), but was not correlated with overall survival (p > 0.05). Lastly, in gastric cancer cells, OE-circ-MTO1 apparently decreased relative cell viabilities at oxaliplatin concentrations of 0.4, 0.8, 1.6, and 3.2 µM (all p < 0.05). CONCLUSION: Circ-MTO1 correlates with less lymph node metastasis, prolonged DFS, and improved chemotherapy sensitivity in gastric cancer.

Hotspots and development frontiers of circRNA based on bibliometric analysis.

Background and purpose: Circular RNAs (circRNAs) are a big group of members of the noncoding RNA family following long non-coding RNA and microRNA. They play a regulatory role in many biological processes. Analyzing their current research status and future development trends is conducive to a more comprehensive understanding of circRNAs and contributes to the dedication to the biological field. Methods: The literature on circRNA from 2000 to 2021 in the Web of Science Core Collection of the Web of Science database with "circular RNA" as the subject was searched. R Studio's Bibliometrix package and biblioshiny software were used for publication trend analysis, citation analysis, keyword analysis, author analysis, research institution analysis, source analysis, country analysis, and collaboration analysis for all documents and highly cited documents. Results: From 2000 to 2021, 3,186 circRNA-related articles were published worldwide, of which 193 were highly cited. The number of published articles had shown an explosive increase after 2013. These articles were mainly from Chinese research institutions and authors, but the country with the highest average number of citations per year in highly cited documents was Germany. Scientific research institutions came from countries represented by Germany, USA, China, Australia and Canada all had different degrees of cooperation. The theme and key points of the research had evolved over time from expression to the role and mechanism of circRNA in diseases, especially in cancer. CDR1as, circFOXO3, circHIPK3, circITCH, circMTO1, circSMARCA5 and circZNF609 are circRNAs that are mainly studied currently, their studies mainly involve cell biology, biological functions and cancer. The future research direction and trend would still be the application of circRNA in diseases. Conclusion: The basic situation and development trend of circRNA related research we described provide a direction for future research.

Clinical and genetic analysis of combined oxidative phosphorylation defificiency-10 caused by MTO1 mutation.

The mitochondrial translation optimization factor 1(MTO1) gene mutations had been reported to be linked to combined oxidative phosphorylation defificiency-10 (COXPD10). In this study, we presented the detailed clinical features and genetic analysis of the patient with two variants in MTO1, and reviewed 42 different cases available in publications. Whole exome sequencing and bioinformatics analysis were employed to detect the genetic variants of a 6-month-old boy with metabolic disorder and multiple organ failure; Sanger sequencing was performed to confirm the origin of variants; and clinical data of the patients was retrospectively collected and analyzed. Variant classification was followed to ACMG guidline. The proband was diagnosed with multiple organ failure, severe pneumonia, sepsis, hyperlactatemia, metabolic acidosis, and moderate anemia. Compound heterozygous mutations in the coding region of MTO1 gene (c.1291C > T/p.Arg431Trp and c.1390C > T/p.Arg464Cys) were identified, and the results of family verification experiment showed that the mutations were inherited from the parents, respectively. Combined with clinical symptoms, the patient was diagnosed as COXPD10. In summary, hallmark features of MTO1 mutations were lactic acidosis and hypertrophic cardiomyopathy. Of note, patients with the same genetic mutation may not have the same clinical presentation. Additional MTO1 defificiency cases will help to make genotype-phenotype correlations clearer.

Case report of compound oxidative phosphorylation deficiency type 10 caused by a new site mutation of MTO1 gene / 中华实用儿科临床杂志

The clinical data of a case of compound oxidative phosphorylation deficiency type 10 (COXPD10) caused by a new site mutation of MTO1 gene in the Department of Pediatrics, Affiliated Hospital of Southwest Medical University on December 29, 2020 were retrospectively analyzed.The patient was a 2 months and 19 days old boy of Han nationality.The main clinical manifestations were shortness of breath, hyperlactic acidemia, hyperammonemia and brain damage.Cardiac hypertrophy was not obvious.Heterozygous mutations at c. 344delA and c. 1055C>T sites in the MTO1 gene have not been reported in domestic and foreign literature.COXPD10 caused by MTO1 gene mutations may result in diversified clinical manifestations due to inconsistent mutation sites.For hyperlactic acidemia with unknown predisposing factors, early genetic examination should be conducted to confirm the possibility of COXPD10.

Circular RNA MTO1 intercorrelates with microRNA-630, both associate with Enneking stage and/or pathological fracture as well as prognosis in osteosarcoma patients.

OBJECTIVE: Circular RNA-mitochondrial tRNA translation optimization 1 (circ-MTO1) not only involves in bioprocess of various cancers, but also regulates osteosarcoma progression by regulating microRNA-630 (miR-630). However, the clinical role of circ-MTO1 and miR-630 in osteosarcoma is still obscure. This study aimed to assess the correlation of circ-MTO1 and miR-630 with disease features and prognosis and to explore their association with each other in osteosarcoma patients. METHODS: Forty-four osteosarcoma patients who received neoadjuvant chemotherapy to surgical resection were analyzed in this retrospective study. Then, circ-MTO1 and miR-630 expressions were evaluated in tumor and adjacent non-tumor specimens by reverse transcription quantitative polymerase chain reaction. RESULTS: Circ-MTO1 was lower in tumor than in non-tumor tissues (p<0.001); meanwhile, its elevated tumor expression was correlated with less advanced Enneking stage (p=0.049), good neoadjuvant chemotherapy response (p=0.029), and longer disease-free survival (DFS) (p=0.047). However, no association was found between circ-MTO1 and overall survival (OS) (p=0.122). Additionally, miR-630 in tumor was higher than in non-tumor tissues (p<0.001), while its raised tumor expression was associated with pathological fracture occurrence (p=0.003), advanced Enneking stage (p=0.036), poor neoadjuvant chemotherapy response (p=0.035), and shorter DFS (p=0.011). However, no association was found between miR-630 and OS (p=0.066). In addition, tumor circ-MTO1 was negatively associated with miR-630 (r=-0.323, p=0.032). CONCLUSION: Circ-MTO1 and miR-630 expressions are inter-correlated and dysregulated in osteosarcoma patients. Besides, they associate with Enneking stage and/or pathological fracture, as well as neoadjuvant treatment response and accumulating DFS in these patients.

The role of Aspergillus nidulans polo-like kinase PlkA in microtubule-organizing center control.

Centrosomes are important microtubule-organizing centers (MTOC) in animal cells. In addition, non-centrosomal MTOCs (ncMTOCs) have been described in many cell types. The functional analogs of centrosomes in fungi are the spindle pole bodies (SPBs). In Aspergillus nidulans, additional MTOCs have been discovered at septa (sMTOC). Although the core components are conserved in both MTOCs, their composition and organization are different and dynamic. Here, we show that the polo-like kinase PlkA binds the γ-tubulin ring complex (γ-TuRC) receptor protein ApsB and contributes to targeting ApsB to both MTOCs. PlkA coordinates the activities of the SPB outer plaque and the sMTOC. PlkA kinase activity was required for astral MT formation involving ApsB recruitment. PlkA also interacted with the γ-TuRC inner plaque receptor protein PcpA. Mitosis was delayed without PlkA, and the PlkA protein was required for proper mitotic spindle morphology, although this function was independent of its catalytic activity. Our results suggest that the polo-like kinase is a regulator of MTOC activities and acts as a scaffolding unit through interaction with γ-TuRC receptors.

Circ-MTO1 correlates with favorable prognosis and inhibits cell proliferation, invasion as well as miR-17-5p expression in prostate cancer.

BACKGROUND: This study aimed to investigate circular RNA-mitochondrial tRNA translation optimization 1 (circ-MTO1) expression in tumor tissue and its correlation with clinical characteristics and survival profiles, as well as its effect on cancer cell functions in prostate cancer. METHODS: A total of 298 primary prostate cancer patients were included. Reverse transcription-quantitative polymerase chain reaction was conducted to evaluate circ-MTO1 expression in tumor tissue and paired adjacent tissue. Disease-free survival (DFS) and overall survival (OS) were recorded. In in vitro experiment, prostate cancer cells were transfected with circ-MTO1 over-expression and negative-control over-expression plasmids. Then cell proliferation, cell invasion and miR-630 as well as miR-17-5p expressions in prostate cancer cells were detected. RESULTS: Circular RNA-mitochondrial tRNA translation optimization 1 expression was downregulated in tumor tissue compared with paired adjacent tissue (P < .001) in patients with prostate cancer. Circ-MTO1 high expression in tumor tissue was correlated with decreased pathological T stage (P = .001) as well as lower pathological N stage (P = .020). As for survival profiles, the DFS (P = .006) and OS (P = .018) were both longer in patients who had circ-MTO1 high expression compared with patients who had circ-MTO1 low expression. In addition, circ-MTO1 high expression independently predicted favorable DFS and OS. Besides, further in vitro experiments illustrated that circ-MTO1 inhibited proliferation (P < .05) and invasion (P < .05) as well as downregulated miR-17-5p expression in prostate cancer cells (P < .05). CONCLUSION: Circ-MTO1 correlates with decreased pathological T/N stage and favorable survival profiles, and it also inhibits cell proliferation, invasion as well as miR-17-5p expression in prostate cancer.

The MELAS mutation m.3243A>G alters the expression of mitochondrial tRNA fragments.

Recent evidences highlight the importance of mitochondria-nucleus communication for the clinical phenotype of oxidative phosphorylation (OXPHOS) diseases. However, the participation of small non-coding RNAs (sncRNAs) in this communication has been poorly explored. We asked whether OXPHOS dysfunction alters the production of a new class of sncRNAs, mitochondrial tRNA fragments (mt tRFs), and, if so, whether mt tRFs play a physiological role and their accumulation is controlled by the action of mt tRNA modification enzymes. To address these questions, we used a cybrid model of MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes), an OXPHOS disease mostly caused by mutation m.3243A>G in the mitochondrial tRNALeu(UUR) gene. High-throughput analysis of small-RNA-Seq data indicated that m.3243A>G significantly changed the expression pattern of mt tRFs. A functional analysis of potential mt tRFs targets (performed under the assumption that these tRFs act as miRNAs) indicated an association with processes that involve the most common affected tissues in MELAS. We present evidences that mt tRFs may be biologically relevant, as one of them (mt i-tRF GluUUC), likely produced by the action of the nuclease Dicer and whose levels are Ago2 dependent, down-regulates the expression of mitochondrial pyruvate carrier 1 (MPC1), promoting the build-up of extracellular lactate. Therefore, our study underpins the idea that retrograde signaling from mitochondria is also mediated by mt tRFs. Finally, we show that accumulation of mt i-tRF GluUUC depends on the modification status of mt tRNAs, which is regulated by the action of stress-responsive miRNAs on mt tRNA modification enzymes.

A regulatory circuit of circ-MTO1/miR-17/QKI-5 inhibits the proliferation of lung adenocarcinoma.

Circular RNA (circRNA) is a new class of non-coding RNA that plays a pivotal role in carcinogenesis. Recently, circ-MTO1 (hsa_circ_0007874) was shown to be a cancer-related circRNA. However, its role in lung adenocarcinoma (LUAD) has not been reported. Here, we found that circ-MTO1 was significantly down-regulated in LUAD, which was closely associated with malignant features and dismal prognosis. Enforced expression of circ-MTO1 suppressed the growth of LUAD cells both in vitro and in vivo. Subsequent mechanism experiments showed that circ-MTO1 served as a sponge of oncogenic miR-17 to increase the expression of RNA-binding protein QKI-5, leading to the inactivation of Notch signaling pathway, thereby restraining the growth of LUAD. Importantly, increased QKI-5 expression caused by circ-MTO1 overexpression in turn promoted circ-MTO1 expression. Clinically, circ-MTO1 expression was strongly positively correlated with QKI-5 expression, but negatively correlated with miR-17 expression. Taken together, our data suggest that circ-MTO1 is a critical negative regulator of LUAD and elucidate the potential molecular mechanism of a novel circ-MTO1/miR-17/QKI-5 feedback loop in inhibiting LUAD progression.

An Alternative Homodimerization Interface of MnmG Reveals a Conformational Dynamics that Is Essential for Its tRNA Modification Function.

The Escherichia coli homodimeric proteins MnmE and MnmG form a functional complex, MnmEG, that modifies tRNAs using GTP, methylene-tetrahydrofolate, FAD, and glycine or ammonium. MnmE is a tetrahydrofolate- and GTP-binding protein, whereas MnmG is a FAD-binding protein with each protomer composed of the FAD-binding domain, two insertion domains, and the helical C-terminal domain. The detailed mechanism of the MnmEG-mediated reaction remains unclear partially due to incomplete structural information on the free- and substrate-bound forms of the complex. In this study, we show that MnmG can adopt in solution a dimer arrangement (form I) different from that currently considered as the only biologically active (form II). Normal mode analysis indicates that form I can oscillate in a range of open and closed conformations. Using isothermal titration calorimetry and native red electrophoresis, we show that a form-I open conformation, which can be stabilized in vitro by the formation of an interprotomer disulfide bond between the catalytic C277 residues, appears to be involved in the assembly of the MnmEG catalytic center. We also show that residues R196, D253, R436, R554 and E585 are important for the stabilization of form I and the tRNA modification function. We propose that the form I dynamics regulates the alternative access of MnmE and tRNA to the MnmG FAD active site. Finally, we show that the C-terminal region of MnmG contains a sterile alpha motif domain responsible for tRNA-protein and protein-protein interactions.

The homozygous R504C mutation in MTO1 gene is responsible for ONCE syndrome.

We report clinical and biochemical finding from three unrelated patients presenting ONCE (Optic Neuropathy, Cardiomyopathy and Encephalopathy with lactic acidosis and combined oxidative phosphorylation deficiency) syndrome. Whole-exome sequencing (WES) of the three patients and the healthy sister of one of them was used to identify the carry gene. Clinical and biochemical findings were used to filter variants, and molecular, in silico and genetic studies were performed to characterize the candidate variants. Mitochondrial DNA (mtDNA) defects involving mutations, deletions or depletion were discarded, whereas WES uncovered a double homozygous mutation in the MTO1 gene (NM_001123226:c.1510C>T, p.R504C, and c.1669G>A, p.V557M) in two of the patients and the homozygous mutation p.R504C in the other. Therefore, our data confirm p.R504C as pathogenic mutation responsible of ONCE syndrome, and p.V557M as a rare polymorphic variant.

Severe respiratory complex III defect prevents liver adaptation to prolonged fasting.

BACKGROUND & AIMS: Next generation sequencing approaches have tremendously improved the diagnosis of rare genetic diseases. It may however be faced with difficult clinical interpretation of variants. Inherited enzymatic diseases provide an invaluable possibility to evaluate the function of the defective enzyme in human cell biology. This is the case for respiratory complex III, which has 11 structural subunits and requires several assembly factors. An important role of complex III in liver function is suggested by its frequent impairment in human cases of genetic complex III defects. METHODS: We report the case of a child with complex III defect and acute liver dysfunction with lactic acidosis, hypoglycemia, and hyperammonemia. Mitochondrial activities were assessed in liver and fibroblasts using spectrophotometric assays. Genetic analysis was done by exome followed by Sanger sequencing. Functional complementation of defective fibroblasts was performed using lentiviral transduction followed by enzymatic analyses and expression assays. RESULTS: Homozygous, truncating, mutations in LYRM7 and MTO1, two genes encoding essential mitochondrial proteins were found. Functional complementation of the complex III defect in fibroblasts demonstrated the causal role of LYRM7 mutations. Comparison of the patient's clinical history to previously reported patients with complex III defect due to nuclear DNA mutations, some actually followed by us, showed striking similarities allowing us to propose common pathophysiology. CONCLUSIONS: Profound complex III defect in liver does not induce actual liver failure but impedes liver adaptation to prolonged fasting leading to severe lactic acidosis, hypoglycemia, and hyperammonemia, potentially leading to irreversible brain damage. LAY SUMMARY: The diagnosis of rare genetic disease has been tremendously accelerated by the development of high throughput sequencing technology. In this paper we report the investigations that have led to identify LYRM7 mutations causing severe hepatic defect of respiratory complex III. Based on the comparison of the patient's phenotype with other cases of complex III defect, we propose that profound complex III defect in liver does not induce actual liver failure but impedes liver adaptation to prolonged fasting.

Optic neuropathy, cardiomyopathy, cognitive disability in patients with a homozygous mutation in the nuclear MTO1 and a mitochondrial MT-TF variant.

We report on clinical, genetic and metabolic investigations in a family with optic neuropathy, non-progressive cardiomyopathy and cognitive disability. Ophthalmic investigations (slit lamp examination, funduscopy, OCT scan of the optic nerve, ERG and VEP) disclosed mild or no decreased visual acuity, but pale optic disc, loss of temporal optic fibers and decreased VEPs. Mitochondrial DNA and exome sequencing revealed a novel homozygous mutation in the nuclear MTO1 gene and the homoplasmic m.593T>G mutation in the mitochondrial MT-TF gene. Muscle biopsy analyses revealed decreased oxygraphic Vmax values for complexes I+III+IV, and severely decreased activities of the respiratory chain complexes (RCC) I, III and IV, while muscle histopathology was normal. Fibroblast analysis revealed decreased complex I and IV activity and assembly, while cybrid analysis revealed a partial complex I deficiency with normal assembly of the RCC. Thus, in patients with a moderate clinical presentation due to MTO1 mutations, the presence of an optic atrophy should be considered. The association with the mitochondrial mutation m.593T>G could act synergistically to worsen the complex I deficiency and modulate the MTO1-related disease.

The N-terminal cleavable pre-sequence encoded in the first exon of cystathionine γ-synthase contains two different functional domains for chloroplast targeting and regulation of gene expression.

Chloroplast transit peptide sequences (cTPs) located in the N-terminal region of nuclear-encoded chloroplast proteins are essential for their sorting, and are generally cleaved from the proteins after their import into the chloroplasts. The Arabidopsis thaliana cystathionine γ-synthase (CGS), the first committed enzyme of methionine biosynthesis, is a nuclear-encoded chloroplast protein. Arabidopsis CGS possesses an N-terminal extension region that is dispensable for enzymatic activity. This N-terminal extension contains the cTP and several functional domains including an MTO1 region, the cis-element for post-transcriptional feedback regulation of CGS1 that codes for CGS. A previous report suggested that the cTP cleavage site of CGS is located upstream of the MTO1 region. However, the region required for protein sorting has not been analyzed. In this study, we carried out functional analyses to elucidate the region required for chloroplast targeting by using a chimeric protein, Ex1:GFP, in which the CGS1 exon 1 coding region containing the N-terminal extension was tagged with green fluorescent protein. The sequence upstream of the MTO1 region was responsible for efficient chloroplast targeting and for avoidance of missorting to the mitochondria. Our data also showed that the major N-terminus of Ex1:GFP is Ala91, which is located immediately downstream of the MTO1 region, and the MTO1 region is not retained in the mature Ex1:GFP accumulated in the chloroplast. These findings suggest that the N-terminal cleavable pre-sequence harbors dual functions in protein sorting and in regulating gene expression. Our study highlights the unique properties of Arabidopsis CGS cTP among chloroplast-targeted proteins.

Modification of the wobble uridine in bacterial and mitochondrial tRNAs reading NNA/NNG triplets of 2-codon boxes.

Posttranscriptional modification of the uridine located at the wobble position (U34) of tRNAs is crucial for optimization of translation. Defects in the U34 modification of mitochondrial-tRNAs are associated with a group of rare diseases collectively characterized by the impairment of the oxidative phosphorylation system. Retrograde signaling pathways from mitochondria to nucleus are involved in the pathophysiology of these diseases. These pathways may be triggered by not only the disturbance of the mitochondrial (mt) translation caused by hypomodification of tRNAs, but also as a result of nonconventional roles of mt-tRNAs and mt-tRNA-modifying enzymes. The evolutionary conservation of these enzymes supports their importance for cell and organismal functions. Interestingly, bacterial and eukaryotic cells respond to stress by altering the expression or activity of these tRNA-modifying enzymes, which leads to changes in the modification status of tRNAs. This review summarizes recent findings about these enzymes and sets them within the previous data context.

MTO1 mutations are associated with hypertrophic cardiomyopathy and lactic acidosis and cause respiratory chain deficiency in humans and yeast.

We report three families presenting with hypertrophic cardiomyopathy, lactic acidosis, and multiple defects of mitochondrial respiratory chain (MRC) activities. By direct sequencing of the candidate gene MTO1, encoding the mitochondrial-tRNA modifier 1, or whole exome sequencing analysis, we identified novel missense mutations. All MTO1 mutations were predicted to be deleterious on MTO1 function. Their pathogenic role was experimentally validated in a recombinant yeast model, by assessing oxidative growth, respiratory activity, mitochondrial protein synthesis, and complex IV activity. In one case, we also demonstrated that expression of wt MTO1 could rescue the respiratory defect in mutant fibroblasts. The severity of the yeast respiratory phenotypes partly correlated with the different clinical presentations observed in MTO1 mutant patients, although the clinical outcome was highly variable in patients with the same mutation and seemed also to depend on timely start of pharmacological treatment, centered on the control of lactic acidosis by dichloroacetate. Our results indicate that MTO1 mutations are commonly associated with a presentation of hypertrophic cardiomyopathy, lactic acidosis, and MRC deficiency, and that ad hoc recombinant yeast models represent a useful system to test the pathogenic potential of uncommon variants, and provide insight into their effects on the expression of a biochemical phenotype.