No description available.

No description available.

Le cytosquelette d'actine est une structure dynamique capitale pour la cellule, qui intervient dans les processus de signalisation et génère des forces mécaniques pour compléter des fonctions aussi diverses que l'adhésion, la migration, la division ou la différenciation. Les protéines qui régulent cette structure sont capables de moduler ces fonctions. J'ai identifié une nouvelle famille de protéines régulatrices de l'actine, les protéines Refilines (RefilineA et RefilineB), dont l'expression est corrélée avec l'engagement des cellules dans des programmes de différenciation. La RefilineA est induite lors de la différenciation des cellules précurseurs neurales multipotentes en cellules progénitrices gliales. La RefilineB est stabilisée dans les cellules épithéliales lors de la transition épithélio-mésenchymateuse (TEM) induite par le TGF-β. Dans ces cellules, les Refilines agissent en se complexant à la FilamineA, une protéine qui se lie aux filaments d'actine et forme le maillage. Des syndromes génétiques de mutations sur le gène de la FilamineA entrainent d'importants défauts développementaux, cependant la fonction précise de la protéine reste à ce jour obscure. Le complexe Refiline/FilamineA induit la formation de câbles d'actine et génère également une nouvelle structure d'actine périnucléaire appelée coiffe d'actine (« actin cap ») ou « ligne TAN» qui s'ancre à l'enveloppe nucléaire pour réguler les mouvements et la morphologie du noyau. Les Refilines sont les seules protéines identifiées à ce jour capables de catalyser la formation de structures périnucléaires d'actine. Ces résultats ouvrent donc de nouvelles perspectives pour appréhender les fonctions de la FilamineA ainsi que la biologie et les fonctions des structures périnucléaires d'actine. / The actin cytoskeleton is a highly dynamic structure involved in cell signaling and that creates mechanical force for the completion of diverse functions such as adhesion, migration, division or differentiation. Proteins that regulate this structure can modulate its function. We identified a new protein family that regulates the actin cytoskeleton, Refilin proteins (RefilinA and RefilinB), and whose expression correlates with differentiation switches. RefilinA is induced during differentiation of neural multipotent precursors into glial progenitors, while RefilinB is stabilized in epithelial cells during epithelial-mesenchymal transition (EMT) induced by TGF-β. In cells, Refilins interact with FilaminA, a protein that binds actin filaments to organize them into a network. Genetic syndromes where the FilaminA gene is mutated lead to important developmental defects, The Refilin/FilaminA complex generates actin cables as well as a new perinuclear structure called « actin cap » or «TAN line» that interacts with the nuclear envelope to regulate nuclear movement and shape. Refilin proteins are the only proteins identified so far that induce the formation of perinuclear actin structures. These results open up new perspective for the understanding of FilaminA's function as well as for the biology and functions of perinuclear actin structures.

ABSTRACT Individuals that carry deleterious mutations in the breast and ovarian cancer susceptibility gene 1 (BRCA1) have much more elevated risk to develop breast and/or ovarian cancer than the individuals from the general population. The BRCA1 gene product has been implicated in several aspects of the DNA damage response, but its biochemical function in these processes has remained elusive. In order to probe BRCA1 functions we conducted a yeast two-hybrid screening to identify interacting partners to a conserved motif (Motif 6) in the central region of BRCA1. In this dissertation, we report the identification of the actin-binding protein Filamin A (FLNA) as a BRCA1 partner and demonstrate that FLNA is required for the efficient regulation of DNA repair process at its early stages. Cells lacking FLNA display a diminished ionizing radiation (IR)-induced BRCA1 focus formation and a slow kinetics of Rad51 focus formation. In addition, our data demonstrate that FLNA is required to stabilize the interaction between DNA-PK holoenzyme components such as DNA-PKcs and Ku86 in a BRCA1-independent manner. Our data are consistent with a model in which the absence of FLNA compromises homologous recombination and non-homologous end joining. Our findings have implications for our understanding of the response to irradiation-induced DNA damage.

A filamina A (FLNA) é uma proteína de citoesqueleto com diversas funções, dentre as quais estão motilidade celular e ancoragem de receptores de membrana. A alteração de sua expressão foi anteriormente descrita em diversos tipos de neoplasia. Em tumores hipofisários, demonstrou-se que sua expressão se correlacionou à expressão de receptores de dopamina tipo 2 (DRD2) em prolactinomas, e com a sinalização intracelular do receptor de somatostatina tipo 2 (SSTR2) após ativação por agonista, em somatotropinomas. Neste estudo, avalariam-se a expressão da FLNA, DRD2, SSTR2 e SSTR5 em diversos tumores hipofisários: prolactinomas, somatotropinomas, corticotropinomas e adenomas clinicamente não funcionantes (ACNF). Avaliou-se também a correlação entre a expressão da FLNA e resposta aos tratamentos medicamentosos, com agonista dopaminérgico (AD) ou com ligantes do receptor de somatostatina (LRS), e entre FLNA e as características de invasividade e/ou agressividade tumorais. Houve correlação entre a expressão de FLNA e a expressão de DRD2 e, entre FLNA e a resposta ao AD, nos ACNFs. Nos corticotropinomas, houve correlação entre a expressão da FLNA e critérios de invasividade tumoral. Portanto, o papel da FLNA nos tumores hipofisários pode depender do tipo celular implicado. Além disso, o envolvimento da FLNA nos mecanismos de resistência aos medicamentos utilizados nos tumores hipofisários, AD ou LRS, não deve estar relacionado apenas à sua ação na ancoragem e reciclagem dos receptores DRD2 e SSTRs, mas também à sua ação na motilidade celular, propiciando caratecterísticas de invasividade / Filamin A (FLNA) is a cytoskeletal protein with a variety of functions, including cell motility and membrane receptor anchorage. Changes in FLNA expression has already been described in several types of neoplasia. In pituitary tumors, its expression has been shown to correlate with the expression of dopamine type 2 receptors (DRD2) in prolactinomas and with intracellular somatostatin type 2 receptor (SSTR2) signaling after agonist activation in somatotropinomas. The expression of FLNA, DRD2, SSTR2 and SSTR5 in different pituitary tumors: prolactinomas, somatotrophinomas, corticotrophinomas and clinically nonfunctioning adenomas (CNFA) were evaluated. We also correlate FLNA expression to sensibility to drug treatments with dopamin agonists (DA) or somatostatin receptor ligands (SRL), and to tumor invasiveness and/or aggressiveness. Positive correlation between FLNA expression and DRD2 expression and between FLNA and DA response were found in CNFA. In corticotrophinomas, there was correlation between FLNA expression and tumor invasiveness. Therefore, the role of FLNA in pituitary tumors seems to depend on the cell type involved. Additionally, FLNA involvement in the mechanisms of drug (DA or SRL) resistance in pituitary tumors could not be related only to its action in the anchoring and recycling of DRD2 and SSTR receptors, but also to its action on cellular motility and invasiveness

Embargoed until 1 January 2011 / The filamin family act as scaffolding proteins associating with actin filmanents, acting through a highly conserved actin binding domain (ABD). The ABD of the filamins is homologous to that found in other F-actin binding proteins such as dystrophin. Mutations in the filamin A gene cause a wide range of disease symptoms in humans reflecting the diversity of the roles that filamin A has in cell structure and signalling pathways. The diseases fall into two separate phenotypic groups. Periventricular nodular heterotopia (PVNH) generally results from the complete loss of filamin A protein, and affects the central nervous system. The clinically separate otopalatodigital disorders (OPD) spectrum disorders are skeletal disorders and were hypothesised to be gain of function phenotype diseases. At the beginning of this work, there was very little structural data available for the human filamins, and none for the crucial highly conserved actin binding domain. This lack of structural data limited the interpretation of the biochemical and genetic data and constrained our understanding of the disease associated mutations that cluster in this domain. These studies aimed to provide insights into the structure and mechanism of actin binding domains, and thus provide a better understanding of the diseases caused when this domain is mutated. A secondary structural analysis and crystal structures of the wildtype and OPD2 associated mutant ABDs were obtained. The overall fold of the three proteins was equivalent as determined by circular dichroism spectroscopy and x-ray crystallography. The ABD from filamin A E254K showed 3.7 fold increased F-actin affinity, accompanied by a reduced thermostability (of 5.6 °C). Western blotting of OPD2, frontometaphyseal dysplasia (FMD) and PVNH patient fibroblast lysates showed similar levels of filamin A compared to the control cells. In addition the OPD and PVNH patient fibroblasts were able to adhere to fibronectin and migrate with an equivalent rate to control cells. Together these results have allowed correlations to be developed between structure, protein stability, actin affinity, cellular phenotype and the overall clinical phenotype. Showing that, at least in one example, OPD2 may be due to an increased actin affinity providing further evidence for a gain of function mechanism of OPD2.

Embargoed until 1 January 2011 / The filamin family act as scaffolding proteins associating with actin filmanents, acting through a highly conserved actin binding domain (ABD). The ABD of the filamins is homologous to that found in other F-actin binding proteins such as dystrophin. Mutations in the filamin A gene cause a wide range of disease symptoms in humans reflecting the diversity of the roles that filamin A has in cell structure and signalling pathways. The diseases fall into two separate phenotypic groups. Periventricular nodular heterotopia (PVNH) generally results from the complete loss of filamin A protein, and affects the central nervous system. The clinically separate otopalatodigital disorders (OPD) spectrum disorders are skeletal disorders and were hypothesised to be gain of function phenotype diseases. At the beginning of this work, there was very little structural data available for the human filamins, and none for the crucial highly conserved actin binding domain. This lack of structural data limited the interpretation of the biochemical and genetic data and constrained our understanding of the disease associated mutations that cluster in this domain. These studies aimed to provide insights into the structure and mechanism of actin binding domains, and thus provide a better understanding of the diseases caused when this domain is mutated. A secondary structural analysis and crystal structures of the wildtype and OPD2 associated mutant ABDs were obtained. The overall fold of the three proteins was equivalent as determined by circular dichroism spectroscopy and x-ray crystallography. The ABD from filamin A E254K showed 3.7 fold increased F-actin affinity, accompanied by a reduced thermostability (of 5.6 °C). Western blotting of OPD2, frontometaphyseal dysplasia (FMD) and PVNH patient fibroblast lysates showed similar levels of filamin A compared to the control cells. In addition the OPD and PVNH patient fibroblasts were able to adhere to fibronectin and migrate with an equivalent rate to control cells. Together these results have allowed correlations to be developed between structure, protein stability, actin affinity, cellular phenotype and the overall clinical phenotype. Showing that, at least in one example, OPD2 may be due to an increased actin affinity providing further evidence for a gain of function mechanism of OPD2.

Embargoed until 1 January 2011 / The filamin family act as scaffolding proteins associating with actin filmanents, acting through a highly conserved actin binding domain (ABD). The ABD of the filamins is homologous to that found in other F-actin binding proteins such as dystrophin. Mutations in the filamin A gene cause a wide range of disease symptoms in humans reflecting the diversity of the roles that filamin A has in cell structure and signalling pathways. The diseases fall into two separate phenotypic groups. Periventricular nodular heterotopia (PVNH) generally results from the complete loss of filamin A protein, and affects the central nervous system. The clinically separate otopalatodigital disorders (OPD) spectrum disorders are skeletal disorders and were hypothesised to be gain of function phenotype diseases. At the beginning of this work, there was very little structural data available for the human filamins, and none for the crucial highly conserved actin binding domain. This lack of structural data limited the interpretation of the biochemical and genetic data and constrained our understanding of the disease associated mutations that cluster in this domain. These studies aimed to provide insights into the structure and mechanism of actin binding domains, and thus provide a better understanding of the diseases caused when this domain is mutated. A secondary structural analysis and crystal structures of the wildtype and OPD2 associated mutant ABDs were obtained. The overall fold of the three proteins was equivalent as determined by circular dichroism spectroscopy and x-ray crystallography. The ABD from filamin A E254K showed 3.7 fold increased F-actin affinity, accompanied by a reduced thermostability (of 5.6 °C). Western blotting of OPD2, frontometaphyseal dysplasia (FMD) and PVNH patient fibroblast lysates showed similar levels of filamin A compared to the control cells. In addition the OPD and PVNH patient fibroblasts were able to adhere to fibronectin and migrate with an equivalent rate to control cells. Together these results have allowed correlations to be developed between structure, protein stability, actin affinity, cellular phenotype and the overall clinical phenotype. Showing that, at least in one example, OPD2 may be due to an increased actin affinity providing further evidence for a gain of function mechanism of OPD2.

Embargoed until 1 January 2011 / The filamin family act as scaffolding proteins associating with actin filmanents, acting through a highly conserved actin binding domain (ABD). The ABD of the filamins is homologous to that found in other F-actin binding proteins such as dystrophin. Mutations in the filamin A gene cause a wide range of disease symptoms in humans reflecting the diversity of the roles that filamin A has in cell structure and signalling pathways. The diseases fall into two separate phenotypic groups. Periventricular nodular heterotopia (PVNH) generally results from the complete loss of filamin A protein, and affects the central nervous system. The clinically separate otopalatodigital disorders (OPD) spectrum disorders are skeletal disorders and were hypothesised to be gain of function phenotype diseases. At the beginning of this work, there was very little structural data available for the human filamins, and none for the crucial highly conserved actin binding domain. This lack of structural data limited the interpretation of the biochemical and genetic data and constrained our understanding of the disease associated mutations that cluster in this domain. These studies aimed to provide insights into the structure and mechanism of actin binding domains, and thus provide a better understanding of the diseases caused when this domain is mutated. A secondary structural analysis and crystal structures of the wildtype and OPD2 associated mutant ABDs were obtained. The overall fold of the three proteins was equivalent as determined by circular dichroism spectroscopy and x-ray crystallography. The ABD from filamin A E254K showed 3.7 fold increased F-actin affinity, accompanied by a reduced thermostability (of 5.6 °C). Western blotting of OPD2, frontometaphyseal dysplasia (FMD) and PVNH patient fibroblast lysates showed similar levels of filamin A compared to the control cells. In addition the OPD and PVNH patient fibroblasts were able to adhere to fibronectin and migrate with an equivalent rate to control cells. Together these results have allowed correlations to be developed between structure, protein stability, actin affinity, cellular phenotype and the overall clinical phenotype. Showing that, at least in one example, OPD2 may be due to an increased actin affinity providing further evidence for a gain of function mechanism of OPD2.

Embargoed until 1 January 2011 / The filamin family act as scaffolding proteins associating with actin filmanents, acting through a highly conserved actin binding domain (ABD). The ABD of the filamins is homologous to that found in other F-actin binding proteins such as dystrophin. Mutations in the filamin A gene cause a wide range of disease symptoms in humans reflecting the diversity of the roles that filamin A has in cell structure and signalling pathways. The diseases fall into two separate phenotypic groups. Periventricular nodular heterotopia (PVNH) generally results from the complete loss of filamin A protein, and affects the central nervous system. The clinically separate otopalatodigital disorders (OPD) spectrum disorders are skeletal disorders and were hypothesised to be gain of function phenotype diseases. At the beginning of this work, there was very little structural data available for the human filamins, and none for the crucial highly conserved actin binding domain. This lack of structural data limited the interpretation of the biochemical and genetic data and constrained our understanding of the disease associated mutations that cluster in this domain. These studies aimed to provide insights into the structure and mechanism of actin binding domains, and thus provide a better understanding of the diseases caused when this domain is mutated. A secondary structural analysis and crystal structures of the wildtype and OPD2 associated mutant ABDs were obtained. The overall fold of the three proteins was equivalent as determined by circular dichroism spectroscopy and x-ray crystallography. The ABD from filamin A E254K showed 3.7 fold increased F-actin affinity, accompanied by a reduced thermostability (of 5.6 °C). Western blotting of OPD2, frontometaphyseal dysplasia (FMD) and PVNH patient fibroblast lysates showed similar levels of filamin A compared to the control cells. In addition the OPD and PVNH patient fibroblasts were able to adhere to fibronectin and migrate with an equivalent rate to control cells. Together these results have allowed correlations to be developed between structure, protein stability, actin affinity, cellular phenotype and the overall clinical phenotype. Showing that, at least in one example, OPD2 may be due to an increased actin affinity providing further evidence for a gain of function mechanism of OPD2.