RESUMO
Transcription in human mitochondria is driven by a single-subunit, factor-dependent RNA polymerase (mtRNAP). Despite its critical role in both expression and replication of the mitochondrial genome, transcription initiation by mtRNAP remains poorly understood. Here, we report crystal structures of human mitochondrial transcription initiation complexes assembled on both light and heavy strand promoters. The structures reveal how transcription factors TFAM and TFB2M assist mtRNAP to achieve promoter-dependent initiation. TFAM tethers the N-terminal region of mtRNAP to recruit the polymerase to the promoter whereas TFB2M induces structural changes in mtRNAP to enable promoter opening and trapping of the DNA non-template strand. Structural comparisons demonstrate that the initiation mechanism in mitochondria is distinct from that in the well-studied nuclear, bacterial, or bacteriophage transcription systems but that similarities are found on the topological and conceptual level. These results provide a framework for studying the regulation of gene expression and DNA replication in mitochondria.
Assuntos
DNA Mitocondrial/metabolismo , Proteínas de Ligação a DNA/química , Metiltransferases/química , Mitocôndrias/metabolismo , Proteínas Mitocondriais/química , Fatores de Transcrição/química , Iniciação da Transcrição Genética , Sequência de Aminoácidos , Bacteriófago T7/enzimologia , Bacteriófago T7/metabolismo , DNA Mitocondrial/química , Proteínas de Ligação a DNA/isolamento & purificação , Proteínas de Ligação a DNA/metabolismo , RNA Polimerases Dirigidas por DNA/metabolismo , Regulação da Expressão Gênica , Humanos , Metiltransferases/isolamento & purificação , Metiltransferases/metabolismo , Mitocôndrias/genética , Proteínas Mitocondriais/isolamento & purificação , Proteínas Mitocondriais/metabolismo , Modelos Moleculares , Complexos Multiproteicos/química , Regiões Promotoras Genéticas , Alinhamento de Sequência , Fatores de Transcrição/isolamento & purificação , Fatores de Transcrição/metabolismo , Transcrição GênicaRESUMO
In human mitochondria, transcription termination events at a G-quadruplex region near the replication origin are thought to drive replication of mtDNA by generation of an RNA primer. This process is suppressed by a key regulator of mtDNA-the transcription factor TEFM. We determined the structure of an anti-termination complex in which TEFM is bound to transcribing mtRNAP. The structure reveals interactions of the dimeric pseudonuclease core of TEFM with mobile structural elements in mtRNAP and the nucleic acid components of the elongation complex (EC). Binding of TEFM to the DNA forms a downstream "sliding clamp," providing high processivity to the EC. TEFM also binds near the RNA exit channel to prevent formation of the RNA G-quadruplex structure required for termination and thus synthesis of the replication primer. Our data provide insights into target specificity of TEFM and mechanisms by which it regulates the switch between transcription and replication of mtDNA.
Assuntos
Replicação do DNA , DNA Mitocondrial/genética , Quadruplex G , Proteínas Mitocondriais/metabolismo , Fatores de Transcrição/metabolismo , Transcrição Gênica , Sequência de Aminoácidos , DNA Mitocondrial/química , Humanos , Mitocôndrias/metabolismo , Proteínas Mitocondriais/química , Modelos Moleculares , Elongação da Transcrição Genética , Fatores de Transcrição/química , Terminação da Transcrição GenéticaRESUMO
Proteins from the Bcl-2 family play an essential role in the regulation of apoptosis. However, they also possess cell death-unrelated activities that are less well understood. This prompted us to study apoptosis-unrelated activities of the Bax and Bak, pro-apoptotic members of the Bcl-2 family. We prepared Bax/Bak-deficient human cancer cells of different origin and found that while respiration in the glioblastoma U87 Bax/Bak-deficient cells was greatly enhanced, respiration of Bax/Bak-deficient B lymphoma HBL-2 cells was slightly suppressed. Bax/Bak-deficient U87 cells also proliferated faster in culture, formed tumours more rapidly in mice, and showed modulation of metabolism with a considerably increased NAD+/NADH ratio. Follow-up analyses documented increased/decreased expression of mitochondria-encoded subunits of respiratory complexes and stabilization/destabilization of the mitochondrial transcription elongation factor TEFM in Bax/Bak-deficient U87 and HBL-2 cells, respectively. TEFM downregulation using shRNAs attenuated mitochondrial respiration in Bax/Bak-deficient U87 as well as in parental HBL-2 cells. We propose that (post)translational regulation of TEFM levels in Bax/Bak-deficient cells modulates levels of subunits of mitochondrial respiratory complexes that, in turn, contribute to respiration and the accompanying changes in metabolism and proliferation in these cells.
Assuntos
Apoptose , Proteína Killer-Antagonista Homóloga a bcl-2 , Humanos , Animais , Camundongos , Proteína X Associada a bcl-2/genética , Proteína X Associada a bcl-2/metabolismo , Apoptose/genética , Proteína Killer-Antagonista Homóloga a bcl-2/genética , Proteína Killer-Antagonista Homóloga a bcl-2/metabolismo , Proteínas Proto-Oncogênicas c-bcl-2/genética , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Mitocôndrias/genética , Mitocôndrias/metabolismo , RespiraçãoRESUMO
BACKGROUND: Molecularly targeted therapies have recently become a hotspot in the treatment of LUAD, with ongoing efforts to identify new effective targets due to individual variability. Among these potential targets, the mitochondrial transcription elongation factor (TEFM) stands out as a crucial molecule involved in mitochondrial synthetic transcriptional processing. Dysregulation of TEFM has been implicated in the development of various diseases; however, its specific role in LUAD remains unclear. METHODS: We conducted a comprehensive analysis of TEFM expression in LUAD, leveraging data from the TCGA database. Subsequently, we validated these findings using clinical specimens obtained from the First Affiliated Hospital of Soochow University, employing western blotting and qRT-PCR techniques. Further experimental validation was performed through the transfection of cells with TEFM overexpression, knockdown, and knockout lentiviruses. The effects of TEFM on LUAD were evaluated both in vitro and in vivo using a range of assays, including CCK-8, colony formation, EdU incorporation, Transwell migration, Tunel assay, flow cytometry, JC-1 staining, and xenograft tumour models. RESULTS: Our investigation uncovered that TEFM exhibited elevated expression levels in LUAD and exhibited co-localization with mitochondria. Overexpression of TEFM facilitated malignant processes in LUAD cells, whereas its silencing notably curbed these behaviors and induced mitochondrial depolarization, along with ROS production, culminating in apoptosis. Moreover, the absence of TEFM substantially influenced the expression of mitochondrial transcripts and respiratory chain complexes. Results from nude mouse xenograft tumors further validated that inhibiting TEFM expression markedly hindered tumor growth. CONCLUSION: TEFM promotes LUAD malignant progression through the EMT pathway and determines apoptosis by affecting the expression of mitochondrial transcripts and respiratory chain complexes, providing a new therapeutic direction for LUAD-targeted therapy.
Assuntos
Apoptose , Mitocôndrias , Fatores de Elongação da Transcrição , Humanos , Animais , Mitocôndrias/metabolismo , Linhagem Celular Tumoral , Fatores de Elongação da Transcrição/metabolismo , Fatores de Elongação da Transcrição/genética , Apoptose/genética , Neoplasias Pulmonares/patologia , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/metabolismo , Neoplasias Pulmonares/terapia , Camundongos Nus , Regulação Neoplásica da Expressão Gênica , Proliferação de Células , Carcinoma Pulmonar de Células não Pequenas/patologia , Carcinoma Pulmonar de Células não Pequenas/genética , Carcinoma Pulmonar de Células não Pequenas/metabolismo , Carcinoma Pulmonar de Células não Pequenas/terapia , Movimento Celular , Ensaios Antitumorais Modelo de Xenoenxerto , Camundongos , Espécies Reativas de Oxigênio/metabolismo , Terapia de Alvo Molecular , Feminino , MasculinoRESUMO
Congenital myasthenic syndromes (CMS) are a group of rare, neuromuscular disorders that usually present in childhood or infancy. While the phenotypic presentation of these disorders is diverse, the unifying feature is a pathomechanism that disrupts neuromuscular transmission. Recently, two mitochondrial genes-SLC25A1 and TEFM-have been reported in patients with suspected CMS, prompting a discussion about the role of mitochondria at the neuromuscular junction (NMJ). Mitochondrial disease and CMS can present with similar symptoms, and potentially one in four patients with mitochondrial myopathy exhibit NMJ defects. This review highlights research indicating the prominent roles of mitochondria at both the pre- and postsynapse, demonstrating the potential for mitochondrial involvement in neuromuscular transmission defects. We propose the establishment of a novel subcategorization for CMS-mitochondrial CMS, due to unifying clinical features and the potential for mitochondrial defects to impede transmission at the pre- and postsynapse. Finally, we highlight the potential of targeting the neuromuscular transmission in mitochondrial disease to improve patient outcomes.
Assuntos
Doenças Mitocondriais , Síndromes Miastênicas Congênitas , Transportadores de Ânions Orgânicos , Humanos , Síndromes Miastênicas Congênitas/genética , Junção Neuromuscular/genética , Sinapses , Mutação , Proteínas Mitocondriais/genética , Transportadores de Ânions Orgânicos/genéticaRESUMO
BACKGROUND: Mitochondrial transcription elongation factor (TEFM) is an essential molecule that regulates the replication-transcription switch of mitochondrial DNA. TEFM modulates both transcription elongation and RNA processing in mitochondria. The purpose of the present study was to determine the association of TEFM with tumor progression and prognosis in hepatocellular carcinoma (HCC) patients. METHODS: The different protein expression level of TEFM among HCC cell lines was detected by Western blotting. The gene expression profiling interactive analysis (GEPIA) was used to dynamically analyze the mRNA expression of TEFM gene in different stages of HCC. The protein and mRNA expression levels of TEFM were detected by immunohistochemistry, Western blotting and qRT-PCR. The mRNA-SeqV2 expression of TEFM and clinical information of HCC patients were downloaded from the TCGA database by using R3.6.3 software. Next, the relationships between the expression level of TEFM and clinicopathological characteristics and the prognostic value of TEFM were analyzed. A Cox regression model was used for multivariate analysis of the factors that affected the prognosis of HCC. Finally, the association between the expression levels of TEFM and other mitochondrial regulatory genes and HCC biomarker genes was analyzed by GEPIA. RESULTS: TEFM is upregulated in HCC cell lines compared to noncancerous liver cell line. TEFM protein and mRNA expression levels in HCC tissues were significantly upregulated compared with those in noncancerous liver tissues. In addition, the mRNA expression level of TEFM was significantly correlated with sex, serum AFP level, and vascular invasion (P<0.05). Further analysis showed that high expression level of TEFM was unfavorable in terms of the prognosis of patients with HCC. Cox multivariate regression analysis showed that patient age, vascular invasion, and TEFM expression were independent factors affecting the prognosis of HCC patients (P<0.05). The expression level of the TEFM gene was significantly positively correlated with the expression of multiple mitochondrial regulatory genes and biomarker genes of HCC (P<0.01, R>0). CONCLUSIONS: Our findings reveal that TEFM may play an important role in the progression of HCC. More importantly, the elevated expression of TEFM may potentially predict poor overall survival (OS) and disease-free survival (DFS) in patients with HCC.
RESUMO
BACKGROUND: Mitochondrial transcription elongation factor (TEFM) is a key molecule for mitochondrial DNA (mtDNA) replication-transcription switch. TEFM regulates both transcription elongation and RNA processing in mitochondria. However, the expression level and prognostic value of TEFM in low grade glioma (LGG) remain unclear. Therefore, in this study, we aimed to evaluate the clinical significance and the prognostic value of TEFM in LGG based on publicly available data. METHODS: The relative mRNA expression level of TEFM in non-tumor brain tissues and LGG tissues were retrieved from Gene Expression Profiling Interactive Analysis (GEPIA). The RNA-Seq expression of TEFM and clinical information in LGG patients were collected from the updated the Cancer Genome Atlas (TCGA) database by using R3.6.1 software. Next, the relationship between the mRNA expression of TEFM and clinicopathological characteristics were analyzed. Kaplan-Meier survival curves of overall survival (OS) and disease-free survival (DFS) were implemented for the relationship between the mRNA expression of TEFM and the prognosis of LGG patients. A Cox regression model was performed for the multivariate analysis of the factors affected the prognosis of LGG patients. GEPIA online tool was used to analyze the correlation between TEFM gene expression level and other related mitochondrial regulatory genes in LGG. Finally, The Gene Set Enrichment Analysis (GSEA) was performed to identify cell processes and molecular signaling cascades affected by TEFM. RESULTS: GEPIA analysis showed that the mRNA expression levels of TEFM in LGG were significantly higher than that of non-tumor tissue. Moreover, the mRNA expression of TEFM is significantly correlated with age, World Health Organization (WHO) grade, pathological types, headache history and supratentorial location (P<0.05). Kaplan-Meier analysis showed that a high expression level of TEFM mRNA indicated a poor prognosis in OS rate (log-rank, P<0.01). Multivariate Cox regression analysis showed that age, WHO grade, pathological types and supratentorial location were the independent prognostic factors of LGG patients. The mRNA expression levels of TEFM gene were positively correlated with the TFAM, TFB1M, TFB2M, MTERF1-F4 and NRF1 gene (P<0.01, R>0), but negatively correlated with the POLRMT gene (P<0.01, R=-0.18) in LGG. The GSEA revealed that genes associated with the cell cycle, RNA degradation, spliceosome, and ubiquitin mediated proteolysis signaling pathway were remarkably enriched in higher-TEFM versus lower-TEFM tumors. CONCLUSIONS: Our findings disclosed that the expression of TEFM mRNA was significantly upregulated in human LGG tissues compared to non-tumor brain tissues. More importantly, the elevated expression of TEFM mRNA may potentially predict poor OS in LGG patients.
RESUMO
Numerous age-related human diseases have been associated with deficiencies in cellular energy production. Moreover, genetic alterations resulting in mitochondrial dysfunction are the cause of inheritable disorders commonly known as mitochondrial diseases. Many of these deficiencies have been directly or indirectly linked to deficits in mitochondrial gene expression. Transcription is an essential step in gene expression and elucidating the molecular mechanisms involved in this process is critical for understanding defects in energy production. For the past five decades, substantial efforts have been invested in the field of mitochondrial transcription. These efforts have led to the discovery of the main protein factors responsible for transcription as well as to a basic mechanistic understanding of the transcription process. They have also revealed various mechanisms of transcriptional regulation as well as the links that exist between the transcription process and downstream processes of RNA maturation. Here, we review the knowledge gathered in early mitochondrial transcription studies and focus on recent findings that shape our current understanding of mitochondrial transcription, posttranscriptional processing, as well as transcriptional regulation in mammalian systems.
Assuntos
Mamíferos/genética , Mitocôndrias/genética , Transcrição Gênica , Animais , Regulação da Expressão Gênica , Humanos , Proteínas Mitocondriais/genéticaRESUMO
BACKGROUND: The recent genome-wide association studies (GWAS) of Type 2 Diabetes (T2D) have identified the pancreatic ß-cell as the culprit in the pathogenesis of the disease. Mitochondrial metabolism plays a crucial role in the processes controlling release of insulin and ß-cell mass. This notion implies that mechanisms controlling mitochondrial function have the potential to play a decisive pathogenetic role in T2D. SCOPE OF THE REVIEW: This article reviews studies demonstrating that there is indeed mitochondrial dysfunction in islets in T2D, and that GWAS have identified a variant in the gene encoding transcription factor B1 mitochondrial (TFB1M), predisposing to T2D due to mitochondrial dysfunction and impaired insulin secretion. Mechanistic studies of the nature of this pathogenetic link, as well as of other mitochondrial transcription factors, are described. MAJOR CONCLUSIONS: Based on this, it is argued that transcription and translation in mitochondria are critical processes determining mitochondrial function in ß-cells in health and disease.