Identification and Functional Characterisation of Genes regulated by Monomeric Actin

Monomeric actin controls the activity of the transcription factor Serum Response Factor (SRF) via its coactivator MAL/MRTF-A. Upon signal induction, MAL is released from actin, binds SRF and activates target gene expression. In order to characterise the physiological role of this signalling pathway, I screened on a genome wide basis for target genes by transcriptome analysis. A combination of actin binding drugs (Cytochalasin D and Latrunculin B), targeting monomeric actin, was used to specifically and differentially interfere with the complex between MAL and actin. 210 genes primarily controlled by monomeric actin were identified in mouse fibroblasts. Among them more than 30% have been already found in screens for SRF target genes, supporting the validity of the screening approach. As expected, a lot of genes were involved in cytoskeleton organization. However, genes having anti-proliferative or pro-apoptotic features were identified surprisingly to the same extent. Consistently, I could demonstrate an antiproliferative function of MAL. More specifically, several genes interfering with the MAPK pathway were identified. One of them was Mig6/Errfi1, a negative regulator of EGF receptors. Mig6 induction by LPA or FCS revealed to be dependent on MAL, monomeric actin and the small GTPases Rho. Activated forms of MAL or SRF were sufficient to induce Mig6 expression. Subsequently, a Mig6 promoter element was found to be necessary to mediate MAL/SRF induction. Moreover, induction of Mig6 through the Actin-MAL pathway led to the downregulation of the mitogenic EGFR-MAP kinase cascade. For the first time a transcriptional link between G-actin levels sensed by MAL and the regulation of EGFR signalling was established. Furthermore, after having demonstrated that MAL induces apoptosis, I focused on the characterisation of two proapototic targets identified in the screen: Bok and Noxa. Bok and Noxa were induced by activators of the Rho-Actin-Mal-Srf pathway on a MAL dependent manner. The study of the Bok promoter revealed the existence of a response element that was necessary for the induction by MAL-SRF. Interestingly, apoptotic inducers like staurosporine, TNFα, or the DNA damaging agent Doxorubicin triggered MAL-SRF mediated transcription. As SRF controls the expression of the anti-apoptotic genes Bcl2 and Mcl1, the results from this work places thus SRF as a key transcription factor controlling the balance between pro and anti apoptotic genes in response to external cues

Epithelial Protein Lost in Neoplasm α (Eplin-α) is transcriptionally regulated by G-actin and MAL/MRTF coactivators

Epithelial Protein Lost in Neoplasm α is a novel cytoskeleton-associated tumor suppressor whose expression inversely correlates with cell growth, motility, invasion and cancer mortality. Here we show that Eplin-α transcription is regulated by actin-MAL-SRF signalling. Upon signal induction, the coactivator MAL/MRTF is released from a repressive complex with monomeric actin, binds the transcription factor SRF and activates target gene expression. In a transcriptome analysis with a combination of actin binding drugs which specifically and differentially interfere with the actin-MAL complex (Descot et al., 2009), we identified Eplin to be primarily controlled by monomeric actin. Further analysis revealed that induction of the Eplin-α mRNA and its promoter was sensitive to drugs and mutant actins which stabilise the repressive actin-MAL complex. In contrast, the Eplin-β isoform remained unaffected. Knockdown of MRTFs or dominant negative MAL which inhibits SRF-mediated transcription impaired Eplin-α expression. Conversely, constitutively active mutant actins and MAL induced Eplin-α. MAL and SRF were bound to a consensus SRF binding site of the Eplin-α promoter; the recruitment of MAL to this region was enhanced severalfold upon induction. The tumor suppressor Eplin-α is thus a novel cytoskeletal target gene transcriptionally regulated by the actin-MAL-SRF pathway, which supports a role in cancer biology

Calcium-mediated actin reset (CaAR) mediates acute cell adaptations

Actin has well established functions in cellular morphogenesis. However, it is not well understood how the various actin assemblies in a cell are kept in a dynamic equilibrium, in particular when cells have to respond to acute signals. Here, we characterize a rapid and transient actin reset in response to increased intracellular calcium levels. Within seconds of calcium influx, the formin INF2 stimulates filament polymerization at the endoplasmic reticulum (ER), while cortical actin is disassembled. The reaction is then reversed within a few minutes. This Calcium-mediated actin reset (CaAR) occurs in a wide range of mammalian cell types and in response to many physiological cues. CaAR leads to transient immobilization of organelles, drives reorganization of actin during cell cortex repair, cell spreading and wound healing, and induces long-lasting changes in gene expression. Our findings suggest that CaAR acts as fundamental facilitator of cellular adaptations in response to acute signals and stress

Le juge judiciaire en matière pénale et l'espace européen des libertés

International audienceIn the European Union, judicial authorities are expected to ensure security and justice using judicial cooperation tools such as European Arrest Warrants and European Investigation Orders or creating Joint Investigation Teams, as often as necessary. Nevertheless, the implementation of these tools shows that national judicial authorities are key for the protection of parties' freedoms and fundamental rights, and that their ruling can affect the European Court of Justice's jurisprudence.Au sein de l'Union européenne, on attend des autorités judiciaires qu'elles oeuvrent pour protéger la sécurité et rendre la Justice en utilisant des outils de coopération judiciaire tels que le mandat d'arrêt européen et la décision d'enquête européenne ou en créant des équipes communes d'enquête dès que nécessaires. La mise en oeuvre de ces instruments a cependant montré que les autorités judiciaires nationales constituent des éléments clés de protection des libertés et des droits fondamentaux des justiciables dont les positions peuvent exercer une influence sur la jurisprudence de la Cour de justice de l'Union européenne