Annuaire
2012
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Tax protein-induced expression of antiapoptotic Bfl-1 protein contributes to survival of human T-cell leukemia virus type 1 (HTLV-1)-infected T-cells.
- Journal : J Biol Chem
- 2012
- Human T lymphotropic virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia/lymphoma (ATLL). ATLL is a severe malignancy with no effective treatment. HTLV-1 regulatory proteins Tax and HTLV-1 basic leucine zipper factor(HBZ) play a major role in ATLL development, by interfering with cellular functions such as CD4(+) T-cell survival. In this study, we observed that the expression of Bfl-1, an antiapoptotic protein of the Bcl-2 family, is restrictedto HTLV-1-infected T-cell lines and to T-cells expressing both Tax and HBZ proteins. We showed that Tax-induced bfl-1 transcription through the canonical NF-kappaB pathway. Moreover, we demonstrated that Tax cooperated with c-Jun or JunD, but not JunB, transcription factors of the AP-1 family to stimulate bfl-1 gene activation. By contrast, HBZ inhibited c-Jun-induced bfl-1 gene activation,whereas it increased JunD-induced bfl-1 gene activation. We identified one NF-kappaB, targeted by RelA, c-Rel, RelB, p105/p50, and p100/p52, and two AP-1, targeted by both c-Jun and JunD, binding sites in the bfl-1 promoter of T-cells expressing both Tax and HBZ. Analyzing the potential role of antiapoptotic Bcl-2proteins in HTLV-1-infected T-cell survival, we demonstrated that these cells are differentially sensitive to silencing of Bfl-1, Bcl-x(L), and Bcl-2. Indeed, both Bfl-1 and Bcl-x(L) knockdowns decreased the survival of HTLV-1-infected T-cell lines, although no cell death was observed after Bcl-2 knockdown. Furthermore, we demonstrated that Bfl-1 knockdown sensitizes HTLV-1-infected T-cells to ABT-737 or etoposide treatment. Our results directly implicate Bfl-1 and Bcl-x(L) in HTLV-1-infected T-cell survival and suggest that both Bfl-1 and Bcl-x(L) represent potential therapeutic targets for ATLL treatment.
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The Andes hantavirus NSs protein is expressed from the viral small mRNA by a leaky scanning mechanism.
- Journal : J Virol
- 2012
- The small mRNA (SmRNA) of all Bunyaviridae encodes the nucleocapsid (N) protein.In 4 out of 5 genera in the Bunyaviridae, the smRNA encodes an additional nonstructural protein denominated NSs. In this study, we show that Andes hantavirus (ANDV) SmRNA encodes an NSs protein. Data show that the NSs protein is expressed in the context of an ANDV infection. Additionally, our results suggestthat translation initiation from the NSs initiation codon is mediated by ribosomal subunits that have bypassed the upstream N protein initiation codon through a leaky scanning mechanism.
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The human T-lymphotropic virus type 1 tax protein inhibits nonsense-mediated mRNA decay by interacting with INT6/EIF3E and UPF1.
- Journal : J Virol
- 2012
- In this report, we analyzed whether the degradation of mRNAs by the nonsense-mediated mRNA decay (NMD) pathway was affected in human T-lymphotropic virus type 1 (HTLV-1)-infected cells. This pathway was indeed strongly inhibitedin C91PL, HUT102, and MT2 cells, and such an effect was also observed by the sole expression of the Tax protein in Jurkat and HeLa cells. In line with this activity, Tax binds INT6/EIF3E (here called INT6), which is a subunit of the translation initiation factor eukaryotic initiation factor 3 (eIF3) required forefficient NMD, as well as the NMD core factor upstream frameshift protein 1 (UPF1). It was also observed that Tax expression alters the morphology of processing bodies (P-bodies), the cytoplasmic structures which concentrate RNA degradation factors. The presence of UPF1 in these subcellular compartments was increased by Tax, whereas that of INT6 was decreased. In line with these effects, the level of the phosphorylated form of UPF1 was increased in the presence of Tax. Analysis of several mutants of the viral protein showed that the interaction with INT6 is necessary for NMD inhibition. The alteration of mRNA stability was observed to affect viral transcripts, such as that coding for the HTLV-1 basic leucine zipper factor (HBZ), and also several cellular mRNAs sensitive to the NMD pathway. Our data indicate that the effect of Tax on viral and cellular gene expression is not restricted to transcriptional control but can also involve posttranscriptional regulation.
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Thermodynamics and kinetics of large-time-step molecular dynamics.
- Journal : J Comput Chem
- 2012
- Molecular dynamics (MD) simulations provide essential information about the thermodynamics and kinetics of proteins. Technological advances in both hardwareand algorithms have seen this method accessing timescales that used to be unreachable only few years ago. The quest to simulate slow, biologically relevant macromolecular conformational changes, is still open. Here, we present an approximate approach to increase the speed of MD simulations by a factor of approximately 4.5. This is achieved by using a large integration time step of 7 fs, in combination with frozen covalent bonds and look-up tables for nonbonded interactions of the solvent. Extensive atomistic MD simulations for a flexible peptide in water show that the approach reproduces the peptide's equilibrium conformational changes, preserving the essential properties of both thermodynamics and kinetics. Comparison of this approximate method with state-of-the-art implicit solvation simulations indicates that the former provides a better description of the underlying free-energy surface. Finally, simulations of a 33-residue peptide show that these fast MD settings are readilyapplicable to investigate biologically relevant systems.
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Towards experimental manipulation of stochasticity in gene expression.
- Journal : Prog Biophys Mol Biol
- 2012
- For decades, most of molecular biology was driven by the "central dogma" in which the phenotype is defined by the genotype following a fully deterministic point of view. However, during the last 10 years, a wealth of studies has demonstrated that a given genotype can generate multiple phenotypes in identical environmental conditions, mainly because of the inherently probabilistic nature of the transcription process. It has also been shown that cells can tune this variability at the molecular level. Although previously described as a useless "noise", stochastic gene expression has now been shown by many authors to be an essential part of diverse biological processes. Chromatin dynamics having a central role in higher eukaryotes, we decided to investigate its involvement in the generation and control of stochasticity in gene expression (SGE). Our experiments reveal that the chromatin environment of a gene plays an important role in regulating SGE. Indeed, we find that histone acetylation and DNA methylation significantly affect SGE, suggesting that cells are able to adjust the variability of the expression of their genes through modification of chromatin marks. Given that the alteration of chromatin marks is itself subject to the expression of chromatin modifiers, our results shed light on a complex circular causality with on the one hand, the effect of gene expression on chromatin and on the other hand, the influence of the local chromatin environment of a gene on the dynamics of its expression.
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Transgenerational propagation and quantitative maintenance of paternal centromeres depends on Cid/Cenp-A presence in Drosophila sperm.
- Journal : PLoS Biol
- 2012
- In Drosophila melanogaster, as in many animal and plant species, centromere identity is specified epigenetically. In proliferating cells, a centromere-specific histone H3 variant (CenH3), named Cid in Drosophila and Cenp-A in humans, is a crucial component of the epigenetic centromere mark. Hence, maintenance of the amount and chromosomal location of CenH3 during mitotic proliferation is important. Interestingly, CenH3 may have different roles duringmeiosis and the onset of embryogenesis. In gametes of Caenorhabditis elegans, and possibly in plants, centromere marking is independent of CenH3. Moreover, male gamete differentiation in animals often includes global nucleosome for protamineexchange that potentially could remove CenH3 nucleosomes. Here we demonstrate that the control of Cid loading during male meiosis is distinct from the regulation observed during the mitotic cycles of early embryogenesis. But Cid ispresent in mature sperm. After strong Cid depletion in sperm, paternal centromeres fail to integrate into the gonomeric spindle of the first mitosis, resulting in gynogenetic haploid embryos. Furthermore, after moderate depletion,paternal centromeres are unable to re-acquire normal Cid levels in the next generation. We conclude that Cid in sperm is an essential component of the epigenetic centromere mark on paternal chromosomes and it exerts quantitative control over centromeric Cid levels throughout development. Hence, the amount ofCid that is loaded during each cell cycle appears to be determined primarily by the preexisting centromeric Cid, with little flexibility for compensation of accidental losses.
Link to PubMed entry