Interplay between a New HNF3 and the HNF1 Transcriptional Factors in the Duck Hepatitis B Virus Enhancer

AbstractWe identified a new hepatocyte nuclear factor 3 (HNF3) binding site in the DHBV enhancer. This site is close to the hepatocyte nuclear factor 1 (HNF1) binding site, responsible for most of the enhancing activity. No differences in the migrating properties were found between this new site and the two other HNF3 sites recently described in this enhancer. Factor HNF1 strongly inhibits binding of the HNF3 factor in this newly characterized site. The two factors were never detected simultaneously on the DNA fragment, even when their respective concentrations were modified. Competition persisted after enlarging by 5 and 10 nucleotides the space between the two sites. On the contrary, when the HNF3 binding site was changed into the perfect consensus site, binding of the HNF3 factor was not inhibited any longer by HNF1 and a supershift, corresponding to the binding of both factors, was observed. Thus a limited mismatching appears to modulate the interaction between transcriptional proteins and DNA and allows a second transcriptional protein to interplay with the former one

Robust simplifications of multiscale biochemical networks

<p>Abstract</p> <p>Background</p> <p>Cellular processes such as metabolism, decision making in development and differentiation, signalling, etc., can be modeled as large networks of biochemical reactions. In order to understand the functioning of these systems, there is a strong need for general model reduction techniques allowing to simplify models without loosing their main properties. In systems biology we also need to compare models or to couple them as parts of larger models. In these situations reduction to a common level of complexity is needed.</p> <p>Results</p> <p>We propose a systematic treatment of model reduction of multiscale biochemical networks. First, we consider linear kinetic models, which appear as "pseudo-monomolecular" subsystems of multiscale nonlinear reaction networks. For such linear models, we propose a reduction algorithm which is based on a generalized theory of the limiting step that we have developed in <abbrgrp><abbr bid="B1">1</abbr></abbrgrp>. Second, for non-linear systems we develop an algorithm based on dominant solutions of quasi-stationarity equations. For oscillating systems, quasi-stationarity and averaging are combined to eliminate time scales much faster and much slower than the period of the oscillations. In all cases, we obtain robust simplifications and also identify the critical parameters of the model. The methods are demonstrated for simple examples and for a more complex model of NF-<it>κ</it>B pathway.</p> <p>Conclusion</p> <p>Our approach allows critical parameter identification and produces hierarchies of models. Hierarchical modeling is important in "middle-out" approaches when there is need to zoom in and out several levels of complexity. Critical parameter identification is an important issue in systems biology with potential applications to biological control and therapeutics. Our approach also deals naturally with the presence of multiple time scales, which is a general property of systems biology models.</p

Expression du gene de la vimentine au cours de la proliferation cellulaire

SIGLEINIST T 74097 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Voies de signalisation et rôle de l'aB-cristalline suite à la désorganisation du cytosquelette

Le premier objectif de ce travail de recherche a été d identifier les voies de signalisation impliquées dans la transduction du signal engendré par la perturbation/désorganisation spécifique des trois principales structures du cytosquelette au sein du système musculaire. Ces stress spécifiques se caractérisent par l induction de la phosphorylation spécifique de l B-cristalline, modification qui induit des changements de localisation et régulerait les fonctions de la protéine en augmentant son affinité pour certains éléments du cytosquelette. Dans un deuxième temps, le rôle de la phosphorylation de l B-cristalline a été étudié dans le phénomène de résistance de cellules de carcinomes mammaires vis-à-vis des traitements anti-tumoraux altérant le cytosquelette. Lors de ce travail, nous avons mis en évidence que la phosphorylation du résidu sérine 59 de l B-cristalline jouerait un rôle clé dans la régulation des propriétés anti-apoptotiques de la protéine.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Arachidonic Acid Differentially Affects Basal and Lipopolysaccharide-Induced sPLA 2 -IIA Expression in Alveolar Macrophages through NF-κB and PPAR-γ–Dependent Pathways

International audienceSecretory type IIA phospholipase A(2) (sPLA(2)-IIA) is a critical enzyme involved in inflammatory diseases. We have previously identified alveolar macrophages (AMs) as the major pulmonary source of lipopolysaccharide (LPS)-induced sPLA(2)-IIA expression in a guinea pig model of acute lung injury (ALI). Here, we examined the role of arachidonic acid (AA) in the regulation of basal and LPS-induced sPLA(2)-IIA expression in AMs. We showed that both AA and its nonmetabolizable analog, 5,8,11,14-eicosatetraynoic acid (ETYA), inhibited sPLA(2)-IIA synthesis in unstimulated AMs. However, only AA inhibited sPLA(2)-IIA expression in LPS-stimulated cells, suggesting that this effect requires metabolic conversion of AA. Indeed, cyclooxygenase inhibitors abolished this down-regulation. Prostaglandins PGE(2), PGA(2), and 15d-PGJ(2) also inhibited the LPS-induced sPLA(2)-IIA expression. Nuclear factor-kappaB (NF-kappaB) was found to regulate sPLA(2)-IIA expression in AMs. Both AA and ETYA inhibited basal activation of NF-kappaB but had no effect on LPS-induced NF-kappaB translocation, suggesting that suppression of sPLA(2)-IIA synthesis by AA in LPS-stimulated cells occurs via a NF-kappaB-independent pathway. 15-Deoxy-Delta(12,14)-PGJ(2) and ciglitazone, which are, respectively, natural and synthetic ligands for peroxisome proliferator-activated receptor-gamma (PPAR-gamma), inhibited LPS-induced sPLA(2)-IIA synthesis, whereas PPAR-alpha ligands were ineffective. Moreover, electrophoretic mobility shift assay showed PPAR activation by AA and PPAR-gamma ligands in LPS-stimulated AMs. Our results suggest that the down-regulation of basal sPLA(2)-IIA expression is unrelated to the metabolic conversion of AA but is dependent on the impairment of NF-kappaB activation. In contrast, the inhibition of LPS-stimulated sPLA(2)-IIA expression is mediated by cyclooxygenase-derived metabolites of AA and involves a PPAR-gamma-dependent pathway. These findings provide new insights for the treatment of ALI

Arachidonic acid differentially affects basal and lipopolysaccharide-induced sPLA2-IIA expression in alveolar macrophages through NF-kappa B and PPAR-gamma -dependent pathways

ABSTRACT Secretory type IIA phospholipase A 2 (sPLA 2 -IIA) is a critical enzyme involved in inflammatory diseases. We have previously identified alveolar macrophages (AMs) as the major pulmonary source of lipopolysaccharide (LPS)-induced sPLA 2 -IIA expression in a guinea pig model of acute lung injury (ALI). Here, we examined the role of arachidonic acid (AA) in the regulation of basal and LPS-induced sPLA 2 -IIA expression in AMs. We showed that both AA and its nonmetabolizable analog, 5,8,11,14-eicosatetraynoic acid (ETYA), inhibited sPLA 2 -IIA synthesis in unstimulated AMs. However, only AA inhibited sPLA 2 -IIA expression in LPS-stimulated cells, suggesting that this effect requires metabolic conversion of AA. Indeed, cyclooxygenase inhibitors abolished this down-regulation. Prostaglandins PGE 2 , PGA 2 , and 15d-PGJ 2 also inhibited the LPSinduced sPLA 2 -IIA expression. Nuclear factor-B (NF-B) was found to regulate sPLA 2 -IIA expression in AMs. Both AA and ETYA inhibited basal activation of NF-B but had no effect on LPS-induced NF-B translocation, suggesting that suppression of sPLA 2 -IIA synthesis by AA in LPS-stimulated cells occurs via a NF-B-independent pathway. 15-Deoxy-⌬ 12,14 -PGJ 2 and ciglitazone, which are, respectively, natural and synthetic ligands for peroxisome proliferator-activated receptor-␥ (PPAR-␥), inhibited LPS-induced sPLA 2 -IIA synthesis, whereas PPAR-␣ ligands were ineffective. Moreover, electrophoretic mobility shift assay showed PPAR activation by AA and PPAR-␥ ligands in LPS-stimulated AMs. Our results suggest that the down-regulation of basal sPLA 2 -IIA expression is unrelated to the metabolic conversion of AA but is dependent on the impairment of NF-B activation. In contrast, the inhibition of LPS-stimulated sPLA 2 -IIA expression is mediated by cyclooxygenase-derived metabolites of AA and involves a PPAR-␥-dependent pathway. These findings provide new insights for the treatment of ALI