Régulation des systèmes d'adhérence cellulaire par le CRF2 (un effecteur du stress dans le tube digestif)

Le stress est impliqué dans le développement et l'exacerbation de diverses pathologies notamment au niveau intestinal. Les effets du stress dépendent de l'expression de neuromédiateurs spécifiques (CRF) et de leurs récepteurs. Notre étude porte sur la régulation et la fonction du CRF2 au niveau des entérocytes et des cellules tumorales coliques humaines. In vivo, nous avons montré que le stress et l'inflammation conduisent à l'augmentation de l'expression du CRF2 dans les colonocytes chez le rat. Dans les tumeurs, l'expression du CRF2 augmente avec le grade tumoral. In vitro, dans les cellules HT-29, l'activation du CRF2 induit une altération des jonctions adhérentes et des adhérences focales par la voie Src/ERK/FAK. Ces mécanismes sont responsables de la régulation de la perméabilité épithéliale et de l'augmentation de la migration des cellules tumorales. Ces travaux contribuent à la compréhension des mécanismes impliquant le stress dans le développement des pathologies intestinales.Stress is involved in the initiation and the exacerbation of several diseases especially in the intestine. Stress effects depends on the expression of specific neuromediators (CRF) and there receptors. Our study is about regulation and function of the CRF2, a stress receptor expressed in human enterocytes and colorectal cancer cells. In vivo, we showed that stress and inflammation are responsible for the increased expression of the CRF2 in colon epithelial cells of rats. In tumors, the CRF2 expression is increased with the tumor. In vitro, in HT-29 cells, the CRF2 activation leads to the alteration of adherens junctions and focal adhesions by a Src/ERK/FAK pathway. These mechanisms are responsible for the regulation of epithelial cell permeability and the increased migration of tumor cells. This work contributes to the understanding of the pathways involved in the regulation of intestinal diseases by stress.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

A modularity based spectral method for simultaneous community and anti-community detection

In a graph or complex network, communities and anti-communities are node sets whose modularity attains extremely large values, positive and negative, respectively. We consider the simultaneous detection of communities and anti-communities, by looking at spectral methods based on various matrix-based definitions of the modularity of a vertex set. Invariant subspaces associated to extreme eigenvalues of these matrices provide indications on the presence of both kinds of modular structure in the network. The localization of the relevant invariant subspaces can be estimated by looking at particular matrix angles based on Frobenius inner products

Exposure of monocytes to heat shock does not increase class II expression but modulates antigen-dependent T cell responses

Expression of heat shock (HS) proteins (HSP) increases after exposure to elevated temperatures or other types of injury, such as oxldative injury. Because of their function as ‘molecular chaperones', HSP are suggested to participate in antigen processing and presentation. We have previously reported that HS modulates antigen presentation in a human EBV-transformed B cell line. Here we investigated the effects of HS on MHC class II expression and on antigen processing and presentation by human monocytes. Monocytes were isolated from peripheral blood of normal human volunteers, purified by adherence, then exposed to temperatures ranging from 37 to 45°C for 20 min, allowed to recover for 2 h at 37°C and used for immunofluorescence or as antigen presenting cells in autologous and heterologous lymphocyte proliferation assays. No increase in class II expression was detected as assessed by flow cytometry. Monocytes (3 × 104) and lymphocytes (1 × 105) were co-cultured for 5 days in the presence of several antigens [diphtheria toxold, tetanus toxold or purified peptlde derivative (PPD)] and labeled with 1 μCI [3H]thymldlne for 16 h. Pre-exposure to HS (44°C) significantly (P < 0.001) increased T cell responses to diphtheria toxold, whereas the effect on the responses to other antigens (tetanus toxold or PPD) were not significant. HS did not increase heterologous T cell responses nor T cell proliferation induced by the non-processed superantigens such as staphylococcal enterotoxln B. The effect of HS was inhibited by actlnomycln B and thus appeared dependent upon HSP synthesis. HSP-mediated increases in antigen processing may potentiate the ongoing immune response at inflammatory site

A new role for complement C3: regulation of antigen processing through an inhibitory activity.

International audienceIncreasing evidence underlines the involvement of complement component C3 in the establishment of acquired immunity which appears to play a complex role and to act at different levels. As antigen proteolysis by antigen presenting cells is a key event in the control of antigen presentation efficiency, and consequently in the quality of the immune response, we investigated whether C3 could modulate this step. Our results demonstrate for the first time that C3 can interfere with antigen proteolysis: (i) proteolysis of tetanus toxin (TT) by the lysosomal fraction from a human monocytic cell line (U937) is impaired in the presence of C3, (ii) this effect is C3-specific and involves the C3c fragment of the protein, (iii) C3c is effective even after disulfide disruption, but none of its three constitutive peptides is individually accountable for this inhibitory effect and (iv) the target-protease(s) exhibit(s) a serine-protease activity. The physiological relevance of our results is demonstrated by experiments showing a subcellular colocalisation of TT and C3 after their uptake by U937 and the reduction of TT proteolysis once internalised together with C3. These results highlight a novel role for C3 that broadens its capacity to modulate acquired immune response

Disulfide relays and phosphorylative cascades: Partners in redox-mediated signaling pathways

Modifications of specific amino-acid residues of proteins are fundamental in order to modulate different signaling processes among which the cascade of phosphorylation represents the most effective example. Recently, also, the modification of the redox state of cysteine residues of certain proteins, which is a widespread mechanism in the regulation of protein function, has been proposed to be involved in signaling pathways. Growing evidence shows that some transcription factors could be modulated by both oxidation and phosphorylation. In particular, the pathways regulated by the mitogen activated protein (MAP) kinases represent well-established examples of the cross talk between redox-mediated signaling and phosphorylative cascades. This review will compare the two modes of signal transduction and propose an evolutionary model of a partnership of the two mechanisms in the eukaryotic cell, with redox-mediated signals being more specific and ancestral and phosphorylative signals being more diffuse but predominant in signal propagation. © 2005 Nature Publishing Group All rights reserved

Functional imaging studies of cognition using 99mTc-HMPAO SPECT: empirical validation using the n-back working memory paradigm

{Purpose} Functional activation protocols are widely applied for the study of brain-cognition relations. Only few take advantage of the intrinsic characteristics of SPECT, particularly those allowing cognitive assessment outside of the camera, in settings close to the standard clinical or laboratory ones. The purpose of the study was to assess the feasibility of a split-dose activation protocol with 99mTc-HMPAO using low irradiation dose. {Materials and methods} A two-scans protocol was applied to 12 healthy young volunteers using 270 MBq of 99mTc-HMPAO per scan, with each image associated to a particular experimental condition of the verbal {n}-back working memory task (0-back, 2-back). Subtraction method was used to identify regional brain activity related to the task. {Results} Voxel-wise statistical analysis showed left lateralized activity associated with the 2-back task, compared to the 0-back task. Activated regions, mainly prefrontal and parietal, were similar to those observed in previous fMRI and 15O-PET studies. {Conclusion} The results support the use of 99mTc-HMPAO SPECT for the investigation of brain-cognition relations and demonstrate the feasibility of optimal quality images despite low radiopharmaceutical doses. The findings also acknowledge the use of HMPAO as a radioligand to capture neuro-energetic modulations linked to cognitive activity. They encourage extending the application of the described activation protocol to clinical populations

Mise en place des jonctions adhérentes lors de la différenciation entérocytaire et rôles de p120ctn dans l'homéostasie intestinale

En utilisant la lignée cellulaire d'adénocarcinome colique humain HT-29, nous étudions la mise en place des jonctions adhérentes accompagnant la différenciation entérocytaire et nous soulignons l'importance de différents facteurs dans les étapes successives de maturation de ces jonctions. Ainsi, nous montrons que la laminine 5 est capable d'induire une augmentation d'expression de la E-cadhérine et permet d'initier la mise en place des jonctions adhérentes par un mécanisme dépendant de l'adhérence cellule-matrice extracellulaire: en activant les intégrines a[alpha ] 3b[Bêta ]1 et a[alpha ] 6b[Bêta ]4, la laminine 5 induit une augmentation transitoire de l'activité de la PI3 Kinase qui active à son tour la GTPase monomérique Rac1 et son variant Rac 1 b. Nous montrons que la maturation des jonctions adhérentes est ensuite favorisée par l'émergence de radeaux lipidiques au sein desquels la E-cadhérine et la p 120ctn interagissent de façon préférentielle. Le recrutement des protéines des jonctions adhérentes dans ces microdomaines est dépendant de l'activité de Rac1 et conduit à l'apparition de marqueurs de différenciation entérocytaire. Dans une seconde partie, nous étudions le rôle spécifique de la p120ctn dans la régulation de l'homéostasie des cellules intestinales. Nous montrons que l'augmentation du pool cytoplasmique de p120ctn induit une baisse de prolifération des cellules HT-29 suite à l'interaction de p120ctn avec le complexe cycline E /cdk2. Cette association se traduit par une augmentation de la stabilité de la cycline E et conduit à des défauts de duplication des centrosomes. Des effets similaires sont observés dans les cellules cancéreuses et pourraient être à l'origine du développement tumoral.During intestinal differentiation, epithelial cells modifY their shape and genes activities in response to environmental signais. ln particular, intestinal ce Ils modulate their cell-matrix and ce Il-ce Il adhesion through protein complexes associated with integrins and cadherins respectively.Using the human adenocarcinoma cell line HT-29, we study adherens junction's formation along enterocytic differentiation and we highlight key factors implicated in the successive steps that allow the maturation of these junctions. We show that laminine 5 induces an increase in E-cadherin expression and allows the initiation of adherent junction's assembly through cell -matrix adhesion: laminine 5 - dependent activation of a[alpha ] 3b[Bêta ]1 et a[alpha ] 6b[Bêta ]4 integrins induces a transitional activation of PB Kinase that activates monomeric GTP Ases Rac1 and its variant Rac 1 b. Then we show that adherens junction maturation is favoured by lipid rafts emergence. p 120ctn interacts preferentially with Ecadherin in lipid rafts and their recruitment into this fraction is Rac1-dependent. Furthermore this process is correlated with epithelial cell differentiation. ln a second part, we describe a new function of p 120ctn in intestinal ce Ils homeostasis. We show that the increase in p120ctn cytoplasmic level induces a downregulation of HT-29 cells proliferation. This effect results from the interaction ofp120ctn with the cyclin E / cdk2 complex in the centrosome which leads to cyclin E overexpression. This process leads to centrosome overduplication, a phenomenon often observed in tumor cells.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Stress neuromediators are key regulators of the intestinal barrier: Link to inflammation and cancer: Stress neuromediators regulate the intestinal barrier

ReviewInternational audienceIn the past year, the influence of psychosocial and environmental stressors in different pathogenesis received increased awareness. The brain is the master manager of the interpretation of what is stressful and of the physiological responses that are produced. Animals have developed conserved strategies to respond to stressful conditions, in particular, the secretion of stress-specific neuromediators which mediate protective and adaptative effects in the short run and yet can accelerate pathophysiology when they are over-produced or mis-managed. The Cortico-Releasing Factor (CRF) and their derived peptides are the majors stress neuromediators. Their localization has originally been described in the central nervous system where they play a pivotal role to activate the hypothalamic-pituitary-adrenal (HPA) axis and was recently extended to the periphery. While the peripheral effects of CRF signalling need to be more thoroughly investigated, it has been described to influence disease negatively, in particular in the intestine. The epithelial barrier is a crucial checkpoint to control body entrances. Prolonged exposure to stress can cause ultrastructural epithelial abnormalities and can increase barrier permeability, which favors luminal translocation, immune activation and thus induces inflammation. This review summarizes the present knowledge on the stress response and the effects of both acute and chronic stress to induce pathological damage to the intestine. We present the potential pathways involved, and the proposed mechanisms of action, mediating these effects. The CRF system is potentially useful as a diagnostic marker or a therapy target for inflammatory diseases and cancer