bims-cytox1 2019-07-14 papers

Issue of 2019–07–14
four papers selected by
Gavin McStay, Staffordshire University

Nucleic Acids Res. 2019 Jul 09. pii: gkz575. [Epub ahead of print]

Mammalian NSUN2 introduces 5-methylcytidines into mitochondrial tRNAs.

Saori Shinoda, Sho Kitagawa, Shinichi Nakagawa, Fan-Yan Wei, Kazuhito Tomizawa, Kimi Araki, Masatake Araki, Takeo Suzuki, Tsutomu Suzuki.

Post-transcriptional modifications in mitochondrial tRNAs (mt-tRNAs) play critical roles in mitochondrial protein synthesis, which produces respiratory chain complexes. In this study, we took advantage of mass spectrometric analysis to map 5-methylcytidine (m5C) at positions 48-50 in eight mouse and six human mt-tRNAs. We also confirmed the absence of m5C in mt-tRNAs isolated from Nsun2 knockout (KO) mice, as well as from NSUN2 KO human culture cells. In addition, we successfully reconstituted m5C at positions 48-50 of mt-tRNA in vitro with NSUN2 protein in the presence of S-adenosylmethionine. Although NSUN2 is predominantly localized to the nucleus and introduces m5C into cytoplasmic tRNAs and mRNAs, structured illumination microscopy clearly revealed NSUN2 foci inside mitochondria. These observations provide novel insights into the role of NSUN2 in the physiology and pathology of mitochondrial functions.

DOI: https://doi.org/10.1093/nar/gkz575

Mitochondrion. 2019 Jul 09. pii: S1567-7249(18)30294-0. [Epub ahead of print]

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

Rajnish Kumar Singh, Sunil Kumar Saini, Gopinath Prakasam, Ponnuusamy Kalairasan, Rameshwar N K Bamezai.

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

DOI: https://doi.org/10.1016/j.mito.2019.07.002

BMC Biol. 2019 Jul 08. 17(1): 53

Mitochondrial DNA: the overlooked oncogenome?

Payam A Gammage, Christian Frezza.

Perturbed mitochondrial bioenergetics constitute a core pillar of cancer-associated metabolic dysfunction. While mitochondrial dysfunction in cancer may result from myriad biochemical causes, a historically neglected source is that of the mitochondrial genome. Recent large-scale sequencing efforts and clinical studies have highlighted the prevalence of mutations in mitochondrial DNA (mtDNA) in human tumours and their potential roles in cancer progression. In this review we discuss the biology of the mitochondrial genome, sources of mtDNA mutations, and experimental evidence of a role for mtDNA mutations in cancer. We also propose a 'metabolic licensing' model for mtDNA mutation-derived dysfunction in cancer initiation and progression.

Keywords: Cancer; Metabolism; Mitochondria; mtDNA

DOI: https://doi.org/10.1186/s12915-019-0668-y

Am J Med Genet A. 2019 Jul 10.

Biallelic variants in COX4I1 associated with a novel phenotype resembling Leigh syndrome with developmental regression, intellectual disability, and seizures.

Nishitha R Pillai, Noura S AlDhaheri, Rajarshi Ghosh, Jaehyung Lim, Haley Streff, Anuranjita Nayak, Brett H Graham, Neil A Hanchard, Sarah H Elsea, Fernando Scaglia.

Autosomal recessive COX4I1 deficiency has been previously reported in a single individual with a homozygous pathogenic variant in COX4I1, who presented with short stature, poor weight gain, dysmorphic features, and features of Fanconi anemia. COX4I1 encodes subunit 4, isoform 1 of cytochrome c oxidase. Cytochrome c oxidase is a respiratory chain enzyme that plays an important role in mitochondrial electron transport and reduces molecular oxygen to water leading to the formation of ATP. Defective production of cytochrome c oxidase leads to a variable phenotypic spectrum ranging from isolated myopathy to Leigh syndrome. Here, we describe two siblings, born to consanguineous parents, who presented with encephalopathy, developmental regression, hypotonia, pathognomonic brain imaging findings resembling Leigh-syndrome, and a novel homozygous variant on COX4I1, expanding the known clinical phenotype associated with pathogenic variants in COX4I1.

Keywords: COX4I1; Leigh syndrome; cytochrome c oxidase; mitochondrial disease

DOI: https://doi.org/10.1002/ajmg.a.61288