Biochemistry (Moscow) (v.81, #10)
Detection of mutations in mitochondrial DNA by droplet digital PCR by J. K. Sofronova; Y. Y. Ilinsky; K. E. Orishchenko; E. G. Chupakhin; E. A. Lunev; I. O. Mazunin (1031-1037).
Mutations in mitochondrial DNA (mtDNA) may result in various pathological processes. Detection of mutant mtDNAs is a problem for diagnostic practice that is complicated by heteroplasmy – a phenomenon of the inferring presence of at least two allelic variants of the mitochondrial genome. Also, the level of heteroplasmy largely determines the profile and severity of clinical manifestations. Here we discuss detection of mutations in heteroplasmic mtDNA using up-todate methods that have not yet been introduced as routine clinical assays. These methods can be used for detecting mutations in mtDNA to verify diagnosis of “mitochondrial disease”, studying dynamics of mutant mtDNA in body tissues of patients, as well as investigating structural features of mtDNAs. Original data on allele-specific discrimination of m.11778G>A mutation by droplet digital PCR are presented, which demonstrate an opportunity for simultaneous detection and quantitative assessment of mutations in mtDNAs.
Keywords: mitochondria; mutations; mitochondrial diseases; heteroplasmy; droplet digital PCR
Localization of nuclear-encoded mRNAs to mitochondria outer surface by A. Golani-Armon; Y. Arava (1038-1043).
The diverse functions of mitochondria depend on hundreds of different proteins. The vast majority of these proteins is encoded in the nucleus, translated in the cytosol, and must be imported into the organelle. Import was shown to occur after complete synthesis of the protein, with the assistance of cytosolic chaperones that maintain it in an unfolded state and target it to the mitochondrial translocase of the outer membrane (TOM complex). Recent studies, however, identified many mRNAs encoding mitochondrial proteins near the outer membrane of mitochondria. Translation studies suggest that many of these mRNAs are translated locally, presumably allowing cotranslational import into mitochondria. Herein we review these data and discuss its relevance for local protein synthesis. We also suggest alternative roles for mRNA localization to mitochondria. Finally, we suggest future research directions, including revealing the significance of localization to mitochondria physiology and the molecular players that regulate it.
Keywords: mitochondria; translation; mRNA localization; ribosome; RNA binding proteins
DNA import into mitochondria by Yu. M. Konstantinov; A. Dietrich; F. Weber-Lotfi; N. Ibrahim; E. S. Klimenko; V. I. Tarasenko; T. A. Bolotova; M. V. Koulintchenko (1044-1056).
In recent decades, it has become evident that the condition for normal functioning of mitochondria in higher eukaryotes is the presence of membrane transport systems of macromolecules (proteins and nucleic acids). Natural competence of the mitochondria in plants, animals, and yeasts to actively uptake DNA may be directly related to horizontal gene transfer into these organelles occurring at much higher rate compared to the nuclear and chloroplast genomes. However, in contrast with import of proteins and tRNAs, little is known about the biological role and molecular mechanism underlying import of DNA into eukaryotic mitochondria. In this review, we discuss current state of investigations in this area, particularly specificity of DNA import into mitochondria and its features in plants, animals, and yeasts; a tentative mechanism of DNA import across the mitochondrial outer and inner membranes; experimental data evidencing several existing, but not yet fully understood mechanisms of DNA transfer into mitochondria. Currently available data regarding transport of informational macromolecules (DNA, RNA, and proteins) into the mitochondria do not rule out that the mechanism of protein and tRNA import as well as tRNA and DNA import into the mitochondria may partially overlap.
Keywords: mitochondria; DNA; import; mitochondrial permeability transition pore; porin; adenine nucleotide translocator; plants; yeasts; mammals
The mitochondrial genome. The nucleoid by A. A. Kolesnikov (1057-1065).
Mitochondrial DNA (mtDNA) in cells is organized in nucleoids containing DNA and various proteins. This review discusses questions of organization and structural dynamics of nucleoids as well as their protein components. The structures of mt-nucleoid from different organisms are compared. The currently accepted model of nucleoid organization is described and questions needing answers for better understanding of the fine mechanisms of the mitochondrial genetic apparatus functioning are discussed.
Keywords: mitochondrial nucleoid; mitochondrial genome
Iron-sulfur clusters in mitochondrial metabolism: Multifaceted roles of a simple cofactor by Johnny Stiban; Minyoung So; Laurie S. Kaguni (1066-1080).
Iron-sulfur metabolism is essential for cellular function and is a key process in mitochondria. In this review, we focus on the structure and assembly of mitochondrial iron-sulfur clusters and their roles in various metabolic processes that occur in mitochondria. Iron-sulfur clusters are crucial in mitochondrial respiration, in which they are required for the assembly, stability, and function of respiratory complexes I, II, and III. They also serve important functions in the citric acid cycle, DNA metabolism, and apoptosis. Whereas the identification of iron-sulfur containing proteins and their roles in numerous aspects of cellular function has been a long-standing research area, that in mitochondria is comparatively recent, and it is likely that their roles within mitochondria have been only partially revealed. We review the status of the field and provide examples of other cellular iron-sulfur proteins to highlight their multifarious roles.
Keywords: iron-sulfur clusters; iron-sulfur metabolism; mitochondria; respiration; citric acid cycle; DNA metabolism
Procedure for purification of recombinant preMsk1p from E. coli determines its properties as a factor of tRNA import into yeast mitochondria by E. V. Smirnova; I. V. Chicherin; M. V. Baleva; N. S. Entelis; I. A. Tarassov; P. A. Kamenski (1081-1088).
Mitochondrial genomes of many eukaryotic organisms do not code for the full tRNA set necessary for organellar translation. Missing tRNA species are imported from the cytosol. In particular, one out of two cytosolic lysine tRNAs of the yeast Saccharomyces cerevisiae is partially internalized by mitochondria. The key protein factor of this process is the precursor of mitochondrial lysyl-tRNA synthetase, preMsk1p. In this work, we show that recombinant preMsk1p purified from E. coli in native conditions, when used in an in vitro tRNA import system, demonstrates some properties different from those shown by the renatured protein purified from E. coli in the denatured state. We also discuss the possible mechanistic reasons for this phenomenon.
Keywords: mitochondria; tRNA; tRNA import into mitochondria; preMsk1p; Eno2p; import mechanisms; protein conformation
Sustained early disruption of mitochondrial function contributes to arsenic-induced prostate tumorigenesis by B. Singh; M. Kulawiec; K. M. Owens; A. Singh; K. K. Singh (1089-1100).
Arsenic is a well-known human carcinogen that affects millions of people worldwide, but the underlying mechanisms of carcinogenesis are unclear. Several epidemiological studies have suggested increased prostate cancer incidence and mortality due to exposure to arsenic. Due to lack of an animal model of arsenic-induced carcinogenesis, we used a prostate epithelial cell culture model to identify a role for mitochondria in arsenic-induced prostate cancer. Mitochondrial morphology and membrane potential was impacted within a few hours of arsenic exposure of non-neoplastic prostate epithelial cells. Chronic arsenic treatment induced mutations in mitochondrial genes and altered mitochondrial functions. Human non-neoplastic prostate epithelial cells continuously cultured for seven months in the presence of 5 µM arsenite showed tumorigenic properties in vitro and induced tumors in SCID mice, which indicated transformation of these cells. Protein and mRNA expression of subunits of mtOXPHOS complex I were decreased in arsenic-transformed cells. Alterations in complex I, a main site for reactive oxygen species (ROS) production as well as increased expression of ROS-producing NOX4 in arsenic-transformed cells suggested a role of oxidative stress in tumorigenic transformation of prostate epithelial cells. Whole genome cGH array analyses of arsenic-transformed prostate cells identified extensive genomic instability. Our study revealed mitochondrial dysfunction induced oxidative stress and decreased expression of p53 in arsenic-transformed cells as an underlying mechanism of the mitochondrial and nuclear genomic instability. These studies suggest that early changes in mitochondrial functions are sustained during prolong arsenic exposure. Overall, our study provides evidence that arsenic disruption of mitochondrial function is an early and key step in tumorigenic transformation of prostate epithelial cells.
Keywords: arsenic; mitochondria; mtOXPHOS; genomic instability; tumorigenic transformation; prostate cancer
Pentatricopeptide motifs in the N-terminal extension domain of yeast mitochondrial RNA polymerase Rpo41p are not essential for its function by J. Kruszewski; P. Golik (1101-1110).
The core mitochondrial RNA polymerase is a single-subunit enzyme that in yeast Saccharomyces cerevisiae is encoded by the nuclear RPO41 gene. It is an evolutionary descendant of the bacteriophage RNA polymerases, but it includes an additional unconserved N-terminal extension (NTE) domain that is unique to the organellar enzymes. This domain mediates interactions between the polymerase and accessory regulatory factors, such as yeast Sls1p and Nam1p. Previous studies demonstrated that deletion of the entire NTE domain results only in a temperature-dependent respiratory deficiency. Several sequences related to the pentatricopeptide (PPR) motifs were identified in silico in Rpo41p, three of which are located in the NTE domain. PPR repeat proteins are a large family of organellar RNA-binding factors, mostly involved in posttranscriptional gene expression mechanisms. To study their function, we analyzed the phenotype of strains bearing Rpo41p variants where each of these motifs was deleted. We found that deletion of any of the three PPR motifs in the NTE domain does not affect respiratory growth at normal temperature, and it results in a moderate decrease in mtDNA stability. Steady-state levels of COX1 and COX2 mRNAs are also moderately affected. Only the deletion of the second motif results in a partial respiratory deficiency, manifested only at elevated temperature. Our results thus indicate that the PPR motifs do not play an essential role in the function of the NTE domain of the mitochondrial RNA polymerase.
Keywords: mitochondria; RNA polymerase; pentatricopeptide motifs; yeast
Interaction between Saccharomyces cerevisiae mitochondrial DNA-binding protein Abf2p and Cce1p resolvase by E. O. Samoilova; I. A. Krasheninnikov; S. A. Levitskii (1111-1117).
Mitochondrial DNA is susceptible to the action of reactive oxygen species generated by the reactions of oxidative phosphorylation. Homologous recombination is one of the mechanisms providing integrity of the mitochondrial genome. Some proteins that take part in this process in budding yeast mitochondria have been identified. These include Abf2p, the major protein of the mt-nucleoid that specifically binds cruciform DNA, and Cce1p – Holliday junction resolvase. Here we show that Abf2p does not significantly affect either binding of Cce1p to branched DNA or rate and specificity of Holliday junction resolution. These data suggest the existence of an alternative homologous recombination pathway in yeast mitochondria.
Keywords: mitochondrion; homologous recombination; Cce1p; Abf2p
Plant factories for the production of monoclonal antibodies by E. V. Sheshukova; T. V. Komarova; Y. L. Dorokhov (1118-1135).
Like animal cells, plant cells bear mechanisms for protein synthesis and posttranslational modification (glycosylation and phosphorylation) that allow them to be seriously considered as factories for therapeutic proteins, including antibodies, with the development of biotechnology. The plant platform for monoclonal antibody production is an attractive approach due to its flexibility, speed, scalability, low cost of production, and lack of contamination risk from animal-derived pathogens. Contemporary production approaches for therapeutic proteins rely on transgenic plants that are obtained via the stable transformation of plant cells as well as the transient (temporary) expression of foreign proteins. In this review, we discuss present-day approaches for monoclonal antibody production in plants (MAPP), features of carbohydrate composition, and methods for the humanization of the MAPP carbohydrate profile. MAPPs that have successfully passed preclinical studies and may be promising for use in clinical practice are presented here. Perspectives on using MAPPs are determined by analyzing their economic benefits and production rates, which are especially important in personalized cancer therapy as well as in cases of bioterrorism and pandemics.
Keywords: monoclonal antibody; immunoglobulin G; glycosylation; antibody-dependent cellular cytotoxicity; immunotherapy; plant viruses; vector
Thermodynamic analysis of fast stages of specific lesion recognition by DNA repair enzymes by N. A. Kuznetsov; O. S. Fedorova (1136-1152).
The methodology of determination of the thermodynamic parameters of fast stages of recognition and cleavage of DNA substrates is described for the enzymatic processes catalyzed by DNA glycosylases Fpg and hOGG1 and AP endonuclease APE1 during base excision repair (BER) pathway. For this purpose, stopped-flow pre-steady-state kinetic analysis of tryptophan fluorescence intensity changes in proteins and fluorophores in DNA substrates was performed at various temperatures. This approach made it possible to determine the changes of standard Gibbs free energy, enthalpy, and entropy of sequential steps of DNA-substrate binding, as well as activation enthalpy and entropy for the transition complex formation of the catalytic stage. The unified features of mechanism for search and recognition of damaged DNA sites by various enzymes of the BER pathway were discovered.
Keywords: thermodynamics; pre-steady-state kinetics; DNA glycosylase; AP endonuclease; DNA damage; base excision repair
Protein transphosphorylation during the mutual interaction between phytochrome a and a nuclear isoform of nucleoside diphosphate kinase is regulated by red light by A. Hetmann; M. Wujak; S. Kowalczyk (1153-1162).
The nuclear isoform of nucleoside diphosphate kinase isoenzyme NDPK-In undergoes strong catalytic activation upon its interaction with the active form of phytochrome A (Pfr) in red light. The autophosphorylation or intermolecular transphosphorylation of NDPK-In leads to the formation of phosphoester bonds stable in acidic solution. The phosphate residue of the phosphamide bond in the active center of NDPK-In can also be transferred to serine and threonine residues localized in other proteins, including phytochrome A. Phytochrome A, similarly to NDPK-In, undergoes autophosphorylation on serine and threonine residues and can phosphorylate some potential substrate proteins. The physical interaction between phytochrome A in the Pfr form and NDPK-In results in a significant increase in the kinase activity of NDPK-In. The results presented in this work indicate that NDPK-In may function as a protein kinase regulated by light.
Keywords: nucleoside diphosphate kinase; phytochrome; signal transduction; transphosphorylation
New fluorescent macrolide derivatives for studying interactions of antibiotics and their analogs with the ribosomal exit tunnel by A. G. Tereshchenkov; A. V. Shishkina; V. V. Karpenko; V. A. Chertkov; A. L. Konevega; P. S. Kasatsky; A. A. Bogdanov; N. V. Sumbatyan (1163-1172).
Novel fluorescent derivatives of macrolide antibiotics related to tylosin bearing rhodamine, fluorescein, Alexa Fluor 488, BODIPY FL, and nitrobenzoxadiazole (NBD) residues were synthesized. The formation of complexes of these compounds with 70S E. coli ribosomes was studied by measuring the fluorescence polarization depending on the ribosome amount at constant concentration of the fluorescent substance. With the synthesized fluorescent tylosin derivatives, the dissociation constants for ribosome complexes with several known antibiotics and macrolide analogs previously obtained were determined. It was found that the fluorescent tylosin derivatives containing BODIPY FL and NBD groups could be used to screen the binding of novel antibiotics to bacterial ribosomes in the macrolide-binding site.
Keywords: macrolides; tylosin; fluorescent derivatives; nascent peptide exit tunnel; fluorescent polarization
Molecular cloning, biochemical characterization, and antitumor properties of a novel L-asparaginase from Synechococcus elongatus PCC6803 by R. Kebeish; A. El-Sayed; H. Fahmy; A. Abdel-Ghany (1173-1181).
L-asparaginase (EC 18.104.22.168), which catalyzes the deamidation of L-asparagine to L-aspartic acid and ammonia, has been widely used as a key therapeutic tool in the treatment of tumors. The current commercially available L-asparaginases, produced from bacteria, have signs of toxicity and hypersensitivity reactions during the course of tumor therapy. Therefore, searching for L-asparaginases with unique biochemical properties and fewer adverse effects was the objective of this work. In this study, cyanobacterial strain Synechococcus elongatus PCC6803 was found as a novel source of L-asparaginase. The L-asparaginase gene coding sequence (gi:939195038) was cloned and expressed in E. coli BL21(DE3), and the recombinant protein (Se.ASPII) was purified by affinity chromatography. The enzyme has high affinity towards Lasparagine and shows very weak affinity towards L-glutamine. The enzymatic properties of the recombinant enzyme were investigated, and the kinetic parameters (K m, V max) were measured. The pH and temperature dependence profiles of the novel enzyme were analyzed. The work was extended to measure the antitumor properties of the novel enzyme against different human tumor cell lines.
Keywords: cyanobacteria; L-asparaginase; molecular cloning; antitumor properties
Participation of two carbonic anhydrases of the alpha family in photosynthetic reactions in Arabidopsis thaliana by E. M. Zhurikova; L. K. Ignatova; N. N. Rudenko; V. A. Mudrik; D. V. Vetoshkina; B. N. Ivanov (1182-1187).
The expression of genes of two carbonic anhydrases (CA) belonging to the a-family, α-CA2 and α-CA4 (according to the nomenclature in N. Fabre et al. (2007) Plant Cell Environ., 30, 617-629), was studied in arabidopsis (Arabidopsis thaliana, var. Columbia) leaves. The expression of the At2g28210 gene coding α-CA2 decreased under increase in plant illumination, while the expression of the At4g20990 gene coding α-CA4 increased. Under conditions close to optimal for photosynthesis, in plants with gene At2g28210 knockout, the effective quantum yield of photosystem 2 and the light-induced accumulation of hydrogen peroxide in leaves were lower than in wild type plants, while the coefficient of non-photochemical quenching of leaf chlorophyll a fluorescence and the rate of CO2 assimilation in leaves were higher. In plants with At4g20990 gene knockout, the same characteristics changed in opposite ways relative to wild type. Possible mechanisms of the participation of αa-CA2 and α-CA4 in photosynthetic reactions are discussed, taking into account that protons can be either consumed or released in the reactions they catalyze.
Keywords: photosynthesis; carbonic anhydrase; arabidopsis; gene expression; mutants
Mitochondria-targeted antioxidant SkQR1 reduces TNF-induced endothelial permeability in vitro by I. I. Galkin; O. Yu. Pletjushkina; R. A. Zinovkin; V. V. Zakharova; B. V. Chernyak; E. N. Popova (1188-1197).
Prolonged or excessive increase in the circulatory level of proinflammatory tumor necrosis factor (TNF) leads to abnormal activation and subsequent damage to endothelium. TNF at high concentrations causes apoptosis of endothelial cells. Previously, using mitochondria-targeted antioxidants of SkQ family, we have shown that apoptosis of endothelial cells is dependent on the production of reactive oxygen species (ROS) in mitochondria (mito-ROS). Now we have found that TNF at low concentrations does not cause cell death but activates caspase-3 and caspase-dependent increase in endothelial permeability in vitro. This effect is probably due to the cleavage of β-catenin–an adherent junction protein localized in the cytoplasm. We have also shown that extracellular matrix metalloprotease 9 (MMP9) VE-cadherin shedding plays a major role in the TNF-induced endothelial permeability. The mechanisms of the caspase-3 and MMP9 activation are probably not related to each other since caspase inhibition did not affect VE-cadherin cleavage and MMP9 inhibition had no effect on the caspase-3 activation. Mitochondria-targeted antioxidant SkQR1 inhibited TNF-induced increase in endothelial permeability. SkQR1 also inhibited caspase-3 activation, β-catenin cleavage, and MMP9-dependent VE-cadherin shedding. The data suggest that mito-ROS are involved in the increase in endothelial permeability due to the activation of both caspase-dependent cleavage of intracellular proteins and of MMP9-dependent cleavage of the transmembrane cell-to-cell contact proteins.
Keywords: endothelium; permeability; apoptosis; intercellular junctions; mitochondria-targeted antioxidants; inflammation; tumor necrosis factor (TNF)
Free initiation factors eIF4A and eIF4B are dispensable for translation initiation on uncapped mRNAs by P. A. Sakharov; S. Ch. Agalarov (1198-1204).
The formation of ribosomal 48S initiation complexes at the start AUG codon of uncapped mRNA leader sequences was studied using the methodology of primer extension inhibition (toe-printing). The experiments were performed in the system composed of purified individual components required for translation initiation. The formation of ribosomal 48S initiation complexes at the initiation codon was tested depending on the presence of the initiation factors eIF4F, eIF4A, and eIF4B. Several mRNAs containing short leader sequences lacking the extended secondary structure were studied. It was found that 48S ribosomal complexes at mRNAs with such leaders were not formed in the absence of eIF4F. In contrast, the removal of either eIF4A or eIF4B from the experimental system was found to be dispensable for the formation of the 48S complex.
Keywords: translation initiation; 48S ribosomal initiation complex; initiation factors; eIF4F; eIF4A; eIF4B; toe-printing
Perfect hemihedral twinning in crystals of the γ-subunit of translation initiation factor 2 from Sulfolobus solfataricus: Cause and effect by O. V. Kravchenko; O. S. Nikonov; N. A. Nevskaya; E. A. Stolboushkina; V. I. Arkhipova; M. B. Garber; S. V. Nikonov (1205-1212).
The crystal structure of the γ-subunit of translation initiation factor 2 from the archaeon Sulfolobus solfataricus (SsoIF2γ) has been solved based on perfectly hemihedral twinned data. The protein was cocrystallized with the 10-fold molar excess of GTP analog (GDPCP) over protein. However, no nucleotide was found in the structure, and the model demonstrated the apo form of the protein. Two slightly different molecules in the asymmetric unit of the crystal are related by the non-crystallographic 2-fold axis and form a tightly associated dimer. This dimer is stabilized by an intermolecular hydrophobic core and hydrogen bonds. Lack of GDPCP in the nucleotide-binding pocket of the γ-subunit and significant excess of dimers over monomers in the crystallization solution suggest that these dimers are the building blocks of the crystal. Contrary to SsoIF2γ monomers, these dimers are able to crystallize in two oppositely oriented slightly different crystal domains, thus forming a twinned crystal. Comparison of crystallization conditions for the twinned and untwinned crystals of apo SsoIF2γ showed that stabilization of the dimers in the solution may be caused by higher sodium salt concentration. Since amino acid residues involved in intermolecular contacts in the dimer are responsible for binding of the γand α-subunits within SsoIF2, increase in sodium salt concentration may prevent functioning of SsoIF2 in the cell.
Keywords: translation initiation factor 2; Sulfolobus solfataricus ; crystal structure; hemihedral twinning
Inhibition of chaperonin GroEL by a monomer of ovine prion protein and its oligomeric forms by S. S. Kudryavtseva; Y. Y. Stroylova; I. A. Zanyatkin; T. Haertle; V. I. Muronetz (1213-1220).
The possibility of inhibition of chaperonin functional activity by amyloid proteins was studied. It was found that the ovine prion protein PrP as well as its oligomeric and fibrillar forms are capable of binding with the chaperonin GroEL. Besides, GroEL was shown to promote amyloid aggregation of the monomeric and oligomeric PrP as well as PrP fibrils. The monomeric PrP was shown to inhibit the GroEL-assisted reactivation of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The oligomers of PrP decelerate the GroEL-assisted reactivation of GAPDH, and PrP fibrils did not affect this process. The chaperonin GroEL is capable of interacting with GAPDH and different PrP forms simultaneously. A possible role of the inhibition of chaperonins by amyloid proteins in the misfolding of the enzymes involved in cell metabolism and in progression of neurodegenerative diseases of amyloid nature is discussed.
Keywords: amyloid proteins; chaperonin GroEL; prion PrP; oligomeric forms of prion protein; glyceraldehyde-3-phosphate dehydrogenase; reactivation; inhibition of chaperonin
Knockdown of minichromosome maintenance proteins inhibits foci forming of mediator of DNA-damage checkpoint 1 in response to DNA damage in human esophageal squamous cell carcinoma TE-1 cells by Jinzhong Yu; Ruijie Wang; Jinfeng Wu; Zhongqin Dang; Qinsheng Zhang; Bo Li (1221-1228).
Esophageal squamous cell carcinoma (ESCC) has a high morbidity in China and its treatment depends greatly on adjuvant chemotherapy. However, DNA damage repair in cancer cells severely affects the outcome of treatment. This study investigated the potential mechanism regarding mediator of DNA-damage checkpoint 1 (MDC1) and minichromosome maintenance proteins (MCMs) during DNA damage in ESCC. Recombinant vectors of MDC1 and MCMs with tags were constructed and transfected into human ESCC cell line TE-1. Immunoprecipitation and mass spectrometry were performed to screen the MCMs interacting with MDC1, and direct interaction was confirmed by glutathione S-transferase (GST) pulldown assay in vitro. MCM2 and MCM6 were knocked down by shRNAs, after which chromatin fraction and foci forming of MDC1 upon bleomycin-induced DNA damage were examined. The results showed that MCM2/3/5/6 were immunoprecipitated by antibodies against the tag of MDC1 in TE-1 nuclei, and the GST pull-down assay indicated the direct interaction. Knockdown of MCM2 or MCM6 reduced the chromatin fraction of MDC1 according to Western blot results. Moreover, knockdown of MCM2 or MCM6 could significantly inhibit foci forming of MDC1 in TE-1 nuclei in response to bleomycin-induced DNA damage (p < 0.001). This study indicates the direct interaction between MDC1 and MCMs in TE-1 nuclei. Downregulation of MCMs can inhibit chromatin fraction and foci forming of MDC1 in TE-1 cells upon DNA damage, which suggests MCMs and MDC1 as potential targets to improve the outcome of chemotherapy in ESCC.
Keywords: esophageal squamous cell carcinoma (ESCC); DNA damage repair; mediator of DNA-damage checkpoint 1 (MDC1); minichromosome maintenance protein (MCM)
Do mitochondria have an immune system? by V. A. Popkov; L. D. Zorova; I. O. Korvigo; D. N. Silachev; S. S. Jankauskas; V. A. Babenko; I. B. Pevzner; T. I. Danilina; S. D. Zorov; E. Y. Plotnikov; D. B. Zorov (1229-1236).
The question if mitochondria have some kind of immune system is not trivial. The basis for raising this question is the fact that bacteria, which are progenitors of mitochondria, do have an immune system. The CRISPR system in bacteria based on the principle of RNA interference serves as an organized mechanism for destroying alien nucleic acids, primarily those of viral origin. We have shown that mitochondria are also a target for viral attacks, probably due to a related organization of genomes in these organelles and bacteria. Bioinformatic analysis performed in this study has not given a clear answer if there is a CRISPR-like immune system in mitochondria. However, this does not preclude the possibility of mitochondrial immunity that can be difficult to decipher or that is based on some principles other than those of CRISPR.
Keywords: mitochondria; immune system; virus