Viral proteins targeting mitochondria: controlling cell death

AbstractMitochondrial membrane permeabilization (MMP) is a critical step regulating apoptosis. Viruses have evolved multiple strategies to modulate apoptosis for their own benefit. Thus, many viruses code for proteins that act on mitochondria and control apoptosis of infected cells. Viral proapoptotic proteins translocate to mitochondrial membranes and induce MMP, which is often accompanied by mitochondrial swelling and fragmentation. From a structural point of view, all the viral proapoptotic proteins discovered so far contain amphipathic α-helices that are necessary for the proapoptotic effects and seem to have pore-forming properties, as it has been shown for Vpr from human immunodeficiency virus-1 (HIV-1) and HBx from hepatitis B virus (HBV). In contrast, antiapoptotic viral proteins (e.g., M11L from myxoma virus, F1L from vaccinia virus and BHRF1 from Epstein–Barr virus) contain mitochondrial targeting sequences (MTS) in their C-terminus that are homologous to tail-anchoring domains. These domains are similar to those present in many proteins of the Bcl-2 family and are responsible for inserting the protein in the outer mitochondrial membrane leaving the N-terminus of the protein facing the cytosol. The antiapoptotic proteins K7 and K15 from avian encephalomyelitis virus (AEV) and viral mitochondria inhibitor of apoptosis (vMIA) from cytomegalovirus are capable of binding host-specific apoptosis-modulatory proteins such as Bax, Bcl-2, activated caspase 3, CAML, CIDE-B and HAX. In conclusion, viruses modulate apoptosis at the mitochondrial level by multiple different strategies

Lysosomal Membrane Permeabilization Induces Cell Death in a Mitochondrion-dependent Fashion

A number of diseases are due to lysosomal destabilization, which results in damaging cell loss. To investigate the mechanisms of lysosomal cell death, we characterized the cytotoxic action of two widely used quinolone antibiotics: ciprofloxacin (CPX) or norfloxacin (NFX). CPX or NFX plus UV light (NFX*) induce lysosomal membrane permeabilization (LMP), as detected by the release of cathepsins from lysosomes. Inhibition of the lysosomal accumulation of CPX or NFX suppresses their capacity to induce LMP and to kill cells. CPX- or NFX-triggered LMP results in caspase-independent cell death, with hallmarks of apoptosis such as chromatin condensation and phosphatidylserine exposure on the plasma membrane. LMP triggers mitochondrial membrane permeabilization (MMP), as detected by the release of cytochrome c. Both CPX and NFX* cause Bax and Bak to adopt their apoptotic conformation and to insert into mitochondrial membranes. Bax−/− Bak−/− double knockout cells fail to undergo MMP and cell death in response to CPX- or NFX-induced LMP. The single knockout of Bax or Bak (but not Bid) or the transfection-enforced expression of mitochondrion-targeted (but not endoplasmic reticulum–targeted) Bcl-2 conferred protection against CPX (but not NFX*)-induced MMP and death. Altogether, our data indicate that mitochondria are indispensable for cell death initiated by lysosomal destabilization

Cytopathic effects of the cytomegalovirus-encoded apoptosis inhibitory protein vMIA

Replication of human cytomegalovirus (CMV) requires the expression of the viral mitochondria–localized inhibitor of apoptosis (vMIA). vMIA inhibits apoptosis by recruiting Bax to mitochondria, resulting in its neutralization. We show that vMIA decreases cell size, reduces actin polymerization, and induces cell rounding. As compared with vMIA-expressing CMV, vMIA-deficient CMV, which replicates in fibroblasts expressing the adenoviral apoptosis suppressor E1B19K, induces less cytopathic effects. These vMIA effects can be separated from its cell death–inhibitory function because vMIA modulates cellular morphology in Bax-deficient cells. Expression of vMIA coincided with a reduction in the cellular adenosine triphosphate (ATP) level. vMIA selectively inhibited one component of the ATP synthasome, namely, the mitochondrial phosphate carrier. Exposure of cells to inhibitors of oxidative phosphorylation produced similar effects, such as an ATP level reduced by 30%, smaller cell size, and deficient actin polymerization. Similarly, knockdown of the phosphate carrier reduced cell size. Our data suggest that the cytopathic effect of CMV can be explained by vMIA effects on mitochondrial bioenergetics

Évaluation à long terme de la continence d'une dérivation urinaire cutanée de type Mitrofanoff : résultats à 5 ans

Les autosondages sont nécessaires pour assurer une vidange régulière de la vessie, chez des patients porteurs d’une vessie neurologique. L’accès à l’urètre est difficile pour des patients à mobilité réduite, obèses ou impossible en cas d’urètre sténosé. La dérivation urinaire cutanée continente est une alternative chirurgicale aux auto-sondages urétraux et au Bricker. L’objectif de cette étude était d’évaluer la continence urinaire stomiale à long terme. Les objectifs secondaires évaluaient les complications chirurgicales entre les 2 types de montages; transappendiculaire et tube iléal remodelé. Un questionnaire a estimé l’impact sur la qualité de vie du patient. Notre étude de cohorte, rétrospective, était établie sur une population de patients opérés d’une cystostomie continente première. La cohorte est composée de patients porteurs de vessies neurologiques (84%) avec 54% de blessés médullaires. 45 patients ont été opérés entre Juin 1997 et Mars 2015, La dérivation urinaire cutanée a été réalisée en transappendiculaire (67%). Avec un suivi médian de 64 mois, la continence urinaire stomiale était de 88%. 64,5% des patients ont nécessité une ou des réinterventions, notamment pour sténose stomiale (31%). La qualité de vie était améliorée. Aucune différence en terme de continence urinaire ou de complications n’a été mise en évidence entre les deux montages. La dérivation urinaire cutanée selon Mitrofanoff est une alternative chirurgicale fiable sur le long terme, mais nécessitant des réinterventions pour maintenir un conduit fonctionnel continent et cathétérisable. En dépit des réinterventions les patients restent satisfaits de ce mode mictionnel

Mode d'action anti-apoptotique de la protéine virale vMIA

LYON1-BU Santé (693882101) / SudocSudocFranceF

Replication Stress at Telomeric and Mitochondrial DNA: Common Origins and Consequences on Ageing

Senescence is defined as a stress-induced durable cell cycle arrest. We herein revisit the origin of two of these stresses, namely mitochondrial metabolic compromise, associated with reactive oxygen species (ROS) production, and replicative senescence, activated by extreme telomere shortening. We discuss how replication stress-induced DNA damage of telomeric DNA (telDNA) and mitochondrial DNA (mtDNA) can be considered a common origin of senescence in vitro, with consequences on ageing in vivo. Unexpectedly, mtDNA and telDNA share common features indicative of a high degree of replicative stress, such as G-quadruplexes, D-loops, RNA:DNA heteroduplexes, epigenetic marks, or supercoiling. To avoid these stresses, both compartments use similar enzymatic strategies involving, for instance, endonucleases, topoisomerases, helicases, or primases. Surprisingly, many of these replication helpers are active at both telDNA and mtDNA (e.g., RNAse H1, FEN1, DNA2, RecQ helicases, Top2α, Top2β, TOP3A, DNMT1/3a/3b, SIRT1). In addition, specialized telomeric proteins, such as TERT (telomerase reverse transcriptase) and TERC (telomerase RNA component), or TIN2 (shelterin complex), shuttle from telomeres to mitochondria, and, by doing so, modulate mitochondrial metabolism and the production of ROS, in a feedback manner. Hence, mitochondria and telomeres use common weapons and cooperate to resist/prevent replication stresses, otherwise producing common consequences, namely senescence and ageing

Normality and Sample Size Do Not Matter for the Selection of an Appropriate Statistical Test for Two-Group Comparisons

Abstract. Many applied researchers are taught to use the t-test when distributions appear normal and/or sample sizes are large and non-parametric tests otherwise, and fear inflated error rates if the “wrong” test is used. In a simulation study (four tests: t-test, Mann-Whitney test, Robust t-test, Permutation test; seven sample sizes between 2 × 10 and 2 × 500; four distributions: normal, uniform, log-normal, bimodal; under the null and alternate hypotheses), we show that type 1 errors are well controlled in all conditions. The t-test is most powerful under the normal and the uniform distributions, the Mann-Whitney test under the lognormal distribution, and the robust t-test under the bimodal distribution. Importantly, even the t-test was more powerful under asymmetric distributions than under the normal distribution for the same effect size. It appears that normality and sample size do not matter for the selection of a test to compare two groups of same size and variance. The researcher can opt for the test that fits the scientific hypothesis the best, without fear of poor test performance. </jats:p

Spatial structure and clonal distribution of genotypes in the rare Typha minima Hoppe (Typhaceae) along a river system

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