Viral infections, mitochondrial stress and APOBEC3 cytidine deaminases

La famille de cytidines désaminases APOBEC3 (A3) est composée chez l’homme de 6 enzymes fonctionnelles (A3A-C, A3F-H). Elles sont impliquées dans la restriction virale, le catabolisme de l’ADN et la tumorigenèse. La première partie de ces travaux a mis en évidence que dans un modèle cellulaire humain les virus de l’herpès Simplex de type 1 et de la rougeole entrainent une fragmentation du réseau mitochondrial et un relargage de l’ADN mitochondrial dans le cytosol des cellules infectées. Ceci induit la production d’interféron et la surexpression d’A3A via la voie de détection des ADN cytosoliques impliquant l’ARN polymérase III et RIG-I. Un polymorphisme présent dans les populations humaines d’Afrique centrale sur le gène A3C permet la substitution de la serine 188 d’APOBEC3C en isoleucine et confère à l’enzyme une activité désaminase accrue. Nous avons étudié l’impact de cette substitution sur la réplication du virus de l’hépatite B in vitro et in vivo. L’analyse des mutations induites dans le génome du virus de l’hépatite B nous a permis de confirmer qu’A3CI188 Était une enzyme plus active et d’identifier un contexte de mutation spécifique dans lequel son activité Était renforcée. Enfin, nous avons étudié la capacité de l’APOBEC murine à participer au catabolisme de l’ADN et à l’induction de mutations dans le génome nucléaire. Contrairement à l’Homme, la souris est dépourvue de locus A3, cependant nos résultats suggèrent que l’A1 murine est active sur les séquences traditionnellement ciblées par les A3. L’étude de son expression chez la souris a révélé plusieurs organes exprimant constitutivement cette enzyme, dans lesquels elle pourrait avoir un impact sur la tumorigenèse.In humans the APOBEC3 family of cytidine deaminases is composed of six active members (A31-C, A3F-H). They are involved in viral restriction, DNA catabolism and tumorigenesis. In the first part of the work presented here, we show in a human cellular model that herpes simplex virus type 1 and measles virus induce a fragmentation of the mitochondrial network and a release of mitochondrial DNA into the cytosol of infected cells. This primes the interferon response and leads to the overexpression of A3A. We have showed the implication of the RNA polymerase III / RIG-I pathway in the overexpression of A3A. Finally, we put forward the role of A3A in the degradation of the agonistic DNA via its deaminase activity. A polymorphism found mostly in central Africa on the A3C gene allows for the substitution of the serine 188 of A3C into an isoleucine, enhancing the deaminase activity of the enzyme. We have studied the impact of this substitution on the replication of hepatitis B virus both in vitro and in vivo. The analysis of mutations detected in the hepatitis B virus genome confirmed that A3CI188 was a more active enzyme and allowed us to identify a specific mutation context in wich the deaminase activity was increased. Finally, we studied the capacity of mouse APOBEC1 (A1) to participate in DNA catabolism and the induction of mutations in nuclear DNA. Unlike humans, mice are devoid of A3 enzymes, however, our results suggest that mouse A1 is active on sequences usually target by A3 enzymes in humans. The profiling of A1 expression in mice revealed several organs of interest where A1 constitutive expression could play a role in tumorigenesis

Microstructural and electrical characterization of bulk YBa2Cu3O7−δ ceramics

International audienceThe value of critical current density at 77 K in “zero” applied field (Jc) characterizing the superconducting state for YBa2Cu3O7−δ ceramics is closely related to the microstructure.The interrelationships between the microstructural factors such as pore volume fraction, oxygen content, average grain size, are complex. However, these factors also influence the normal state resistivity measured at room temperature (ρ300). We demonstrate how the current carrying cross section influences Jc and ρ300 in a similar way. Data, reported for two classes of YBa2Cu3O7−δ: small grain porous ceramics and larger-grain denser ceramics, reveal an approximate linear relation between ρ300 K and Jc. Extrapolation of this relation to a fully dense small grain YBa2Cu3O7−δ ceramic yields values of ρ300 = 0.4 mΩ cm and Jc = 103 A cm−2

CONVERGENCE TO EQUILIBRIUM OF A DC ALGORITHM FOR AN EPITAXIAL GROWTH MODEL

International audienceA linear numerical scheme for an epitaxial growth model is analyzed in this work. The considered scheme is already established in the literature using a convexity splitting argument. We show that it can be naturally derived from an optimization viewpoint using a DC (difference of convex functions) programming framework. Moreover, we prove the convergence of the scheme towards equilibrium by means of the Lojasiewicz-Simon inequality. The fully discrete version, based on a Fourier collocation method, is also analyzed. Finally, numerical simulations are carried out to accommodate our analyzis

CONVERGENCE TO EQUILIBRIUM OF A DC ALGORITHM FOR AN EPITAXIAL GROWTH MODEL

International audienceA linear numerical scheme for an epitaxial growth model is analyzed in this work. The considered scheme is already established in the literature using a convexity splitting argument. We show that it can be naturally derived from an optimization viewpoint using a DC (difference of convex functions) programming framework. Moreover, we prove the convergence of the scheme towards equilibrium by means of the Lojasiewicz-Simon inequality. The fully discrete version, based on a Fourier collocation method, is also analyzed. Finally, numerical simulations are carried out to accommodate our analyzis

CONVERGENCE TO EQUILIBRIUM OF A DC ALGORITHM FOR AN EPITAXIAL GROWTH MODEL

International audienceA linear numerical scheme for an epitaxial growth model is analyzed in this work. The considered scheme is already established in the literature using a convexity splitting argument. We show that it can be naturally derived from an optimization viewpoint using a DC (difference of convex functions) programming framework. Moreover, we prove the convergence of the scheme towards equilibrium by means of the Lojasiewicz-Simon inequality. The fully discrete version, based on a Fourier collocation method, is also analyzed. Finally, numerical simulations are carried out to accommodate our analyzis

Les facteurs du pore nucléaire : un collectif gagnant pour la translocation et l’intégration du VIH-1

International audienceNo abstract availabl

Frame-shifted APOBEC3A encodes two alternative pro-apoptotic proteins that target the mitochondrial network

International audienceThe human APOBEC3A (A3A) cytidine deaminase is a powerful DNA mutator enzyme recognized as a major source of somatic mutations in tumor cell genomes. However, there is a discrepancy between APOBEC3A mRNA levels after interferon stimulation in myeloid cells and A3A detection at the protein level. To understand this difference, we investigated the expression of two novel alternative "A3Alt" proteins encoded in the +1-shifted reading frame of the APOBEC3A gene. A3Alt-L and its shorter isoform A3Alt-S appear to be transmembrane proteins targeted to the mitochondrial compartment that induce membrane depolarization and apoptosis. Thus, the APOBEC3A gene represents a new example wherein a single gene encodes two pro-apoptotic proteins, A3A cytidine deaminases that target the genome and A3Alt proteins that target mitochondria

Mouse APOBEC1 cytidine deaminase can induce somatic mutations in chromosomal DNA

International audienceBACKGROUND:APOBEC1 (A1) enzymes are cytidine deaminases involved in RNA editing. In addition to this activity, a few A1 enzymes have been shown to be active on single stranded DNA. As two human ssDNA cytidine deaminases APOBEC3A (A3A), APOBEC3B (A3B) and related enzymes across the spectrum of placental mammals have been shown to introduce somatic mutations into nuclear DNA of cancer genomes, we explored the mutagenic threat of A1 cytidine deaminases to chromosomal DNA.RESULTS:Molecular cloning and expression of various A1 enzymes reveal that the cow, pig, dog, rabbit and mouse A1 have an intracellular ssDNA substrate specificity. However, among all the enzymes studied, mouse A1 appears to be singular, being able to introduce somatic mutations into nuclear DNA with a clear 5'TpC editing context, and to deaminate 5-methylcytidine substituted DNA which are characteristic features of the cancer related mammalian A3A and A3B enzymes. However, mouse A1 activity fails to elicit formation of double stranded DNA breaks, suggesting that mouse A1 possess an attenuated nuclear DNA mutator phenotype reminiscent of human A3B.CONCLUSIONS:At an experimental level mouse APOBEC1 is remarkable among 12 mammalian A1 enzymes in that it represents a source of somatic mutations in mouse genome, potentially fueling oncogenesis. While the order Rodentia is bereft of A3A and A3B like enzymes it seems that APOBEC1 may well substitute for it, albeit remaining much less active. This modifies the paradigm that APOBEC3 and AID enzymes are the sole endogenous mutator enzymes giving rise to off-target editing of mammalian genomes