bims-cytox1 2021-03-14 papers

Issue of 2021–03–14
four papers selected by
Gavin McStay, Staffordshire University

Biochemistry (Mosc). 2021 Jan;86(1): 33-43

Molecular and Functional Effects of Loss of Cytochrome c Oxidase Subunit 8A.

Daria Rotko, Alexei P Kudin, Gábor Zsurka, Bogusz Kulawiak, Adam Szewczyk, Wolfram S Kunz.

In this work we studied molecular and functional effects of the loss of the smallest nuclear encoded subunit of cytochrome c oxidase COX8A in fibroblasts from a patient with a homozygous splice site mutation and in CRISPR/Cas9 genome-edited HEK293T cells. In both cellular model systems, between 20 to 30% of the residual enzymatic activity of cytochrome c oxidase (COX) was detectable. In immunoblots of BN-PAGE separated mitochondria from both cellular models almost no monomers and dimers of the fully assembled COX could be visualized. Interestingly, supercomplexes of COX formed with complex III and also with complexes I and III retained considerable immunoreactivity, while nearly no immunoreactivity attributable to subassemblies was found. That indicates that COX lacking subunit 8A is stabilized in supercomplexes, while monomers and dimers are rapidly degraded. With transcriptome analysis by 3'-RNA sequencing we failed to detect in our cellular models of COX8A deficiency transcriptional changes of genes involved in the mitochondrial unfolded protein response (mtUPR) and the integrated stress response (ISR). Thus, our data strongly suggest that the smallest subunit of cytochrome c oxidase COX8A is required for maintenance of the structural stability of COX monomers and dimers.

Keywords: cytochrome c oxidase; mitochondria; respiratory chain super complexes; subunit 8A

DOI: https://doi.org/10.1134/S0006297921010041

Int J Mol Cell Med. 2020 ;9(4): 255-265

Association of Pathogenic Missense and Nonsense Mutations in Mitochondrial COII Gene with Familial Adenomatous Polyposis (FAP).

Zahra Shaker Ardakani, Mohammad Mehdi Heidari, Mehri Khatami, Morteza Bitaraf Sani.

Nuclear genetic mutations have been extensively investigated in solid tumors. However, the role of the mitochondrial genome remains uncertain. Since the metabolism of solid tumors is associated with aerobic glycolysis and high lactate production, tumors may have mitochondrial dysfunctions. Familial adenomatous polyposis (FAP) is a rare form‌ of colorectal cancer and an autosomal dominant inherited condition that is characterized by the progress of numerous adenomatous polyps in the rectum and colon. The present study aimed at understanding the nature and effect of mitochondrial cytochrome c oxidase subunit 2 (COII) gene mutations in FAP tumorigenesis. Fifty-six (26 familial and 30 sporadic) FAP patients and 60 normal controls were enrolled in this study. COII point mutations were evaluated by PCR and direct sequencing methods, and a total of 7 mtDNA mutations were detected (3 missense, 1 nonsense, and 3 synonymous variations). Novel non-synonymous COII gene mutations were mostly in heteroplasmic state. These mutations change amino acid residues in the N-terminal and C-terminal regions of COXII. Bioinformatics analysis and three-dimensional structural modeling predicted that these missense and nonsense mutations have functional importance, and mainly affected on cytochrome c oxidase (complex IV). Also, FAP patients carried a meaningfully higher prevalence of mutations in the COII gene in comparison with healthy controls (P <0.001). Analysis of cancer-associated mtDNA mutation could be an invaluable tool for molecular assessment of FAP so that these findings can be helpful for the development of potential new biomarkers in the diagnosis of cancer for future clinical assessments.

Keywords: COII; Familial adenomatous polyposis; mitochondrial genes; point mutations

DOI: https://doi.org/10.22088/IJMCM.BUMS.9.4.255

Prog Mol Biol Transl Sci. 2021 ;pii: S1877-1173(20)30179-4. [Epub ahead of print]178 193-211

Mitochondrial DNA modification by CRISPR/Cas system: Challenges and future direction.

Rajalakshmi Prakash, Anbarasu Kannan.

CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas (CRISPR associated endonuclease), a hotshot genome editing tool which is originally known to be the form of prokaryotic adaptive immune system against viral infections has gained all the attention of scientific community as a promising genome editing platform. This review encompasses a brief description of mitochondrial disease conditions associated with the alteration in mitochondrial genome (mtDNA) and highlights the key role of the CRISPR/Cas system pertaining to its working mechanism and its involvement in gene-based therapeutics in treating the foresaid mitochondrial diseases. Here, we also extend the perception related to the detailed mechanism of CRISPR/Cas system in mtDNA modification.

Keywords: CRISP/Cas; Genome editing; Mitochondria; Mitochondrial disease; mtDNA

DOI: https://doi.org/10.1016/bs.pmbts.2020.12.009

Commun Biol. 2021 Mar 08. 4(1): 300

A stalled-ribosome rescue factor Pth3 is required for mitochondrial translation against antibiotics in Saccharomyces cerevisiae.

Soichiro Hoshino, Ryohei Kanemura, Daisuke Kurita, Yukihiro Soutome, Hyouta Himeno, Masak Takaine, Masakatsu Watanabe, Nobukazu Nameki.

Mitochondrial translation appears to involve two stalled-ribosome rescue factors (srRFs). One srRF is an ICT1 protein from humans that rescues a "non-stop" type of mitochondrial ribosomes (mitoribosomes) stalled on mRNA lacking a stop codon, while the other, C12orf65, reportedly has functions that overlap with those of ICT1; however, its primary role remains unclear. We herein demonstrated that the Saccharomyces cerevisiae homolog of C12orf65, Pth3 (Rso55), preferentially rescued antibiotic-dependent stalled mitoribosomes, which appear to represent a "no-go" type of ribosomes stalled on intact mRNA. On media containing a non-fermentable carbon source, which requires mitochondrial gene expression, respiratory growth was impaired significantly more by the deletion of PTH3 than that of the ICT1 homolog PTH4 in the presence of antibiotics that inhibit mitochondrial translation, such as tetracyclines and macrolides. Additionally, the in organello labeling of mitochondrial translation products and quantification of mRNA levels by quantitative RT-PCR suggested that in the presence of tetracycline, the deletion of PTH3, but not PTH4, reduced the protein expression of all eight mtDNA-encoded genes at the post-transcriptional or translational level. These results indicate that Pth3 can function as a mitochondrial srRF specific for ribosomes stalled by antibiotics and plays a role in antibiotic resistance in fungi.

DOI: https://doi.org/10.1038/s42003-021-01835-6