Response to Mechanical Stress Is Mediated by the TRPA Channel Painless in the Drosophila Heart

Mechanotransduction modulates cellular functions as diverse as migration, proliferation, differentiation, and apoptosis. It is crucial for organ development and homeostasis and leads to pathologies when defective. However, despite considerable efforts made in the past, the molecular basis of mechanotransduction remains poorly understood. Here, we have investigated the genetic basis of mechanotransduction in Drosophila. We show that the fly heart senses and responds to mechanical forces by regulating cardiac activity. In particular, pauses in heart activity are observed under acute mechanical constraints in vivo. We further confirm by a variety of in situ tests that these cardiac arrests constitute the biological force-induced response. In order to identify molecular components of the mechanotransduction pathway, we carried out a genetic screen based on the dependence of cardiac activity upon mechanical constraints and identified Painless, a TRPA channel. We observe a clear absence of in vivo cardiac arrest following inactivation of painless and further demonstrate that painless is autonomously required in the heart to mediate the response to mechanical stress. Furthermore, direct activation of Painless is sufficient to produce pauses in heartbeat, mimicking the pressure-induced response. Painless thus constitutes part of a mechanosensitive pathway that adjusts cardiac muscle activity to mechanical constraints. This constitutes the first in vivo demonstration that a TRPA channel can mediate cardiac mechanotransduction. Furthermore, by establishing a high-throughput system to identify the molecular players involved in mechanotransduction in the cardiovascular system, our study paves the way for understanding the mechanisms underlying a mechanotransduction pathway

Protein kinases and the proteasome join in the combinatorial control of transcription by nuclear retinoic acid receptors.

Nuclear retinoic acid receptors (RARs) are transcriptional transregulators that control the expression of specific subsets of genes in a ligand-dependent manner. The basic mechanism for switching on gene transcription by agonist-liganded RARs involves their binding at specific response elements located in target genes. It also involves interactions with coregulatory protein complexes, the assembly of which is directed by the C-terminal ligand-binding domain of RARs. In addition to this scenario, several recent studies highlighted a fundamental role for the N-terminal domain in the transcriptional activity of RARs, following phosphorylation by the CDK7 kinase of the general transcription factor TFIIH and by p38MAPK. It has also emerged that the ubiquitin-proteasome system has a key role in RAR-mediated transcription. Here, we review new insights into how N-terminal domain and the proteasome pathway can influence the dynamics of RAR transcriptional activity

Vinexin beta interacts with the non-phosphorylated AF-1 domain of retinoid receptor gamma (RARgamma) and represses RARgamma-mediated transcription.

International audienceNuclear retinoic acid receptors (RARs) are ligand-dependent transcription factors that regulate the expression of retinoic acid target genes. Although the importance of RAR phosphorylation in their N-terminal domain is clearly established, the underlying mechanism for the phosphorylation-dependent transcriptional activity of the receptors had not been elucidated yet. Here, using a yeast two-hybrid system, we report the isolation of vinexin beta as a new cofactor that interacts with the N-terminal A/B domain of the RARgamma isotype. Vinexin beta is a multiple SH3 motif-containing protein associated with the cytoskeleton and also present in the nucleus. We demonstrate that vinexin beta colocalizes with RARgamma in the nucleus and interacts with the non-phosphorylated form of the AF-1 domain of RARgamma. We also show that this interaction is prevented upon phosphorylation of the AF-1 domain. Using F9 cells stably overexpressing vinexin beta or vinexin knockdown by RNA interference, we demonstrate that vinexin beta is an inhibitor of RARgamma-mediated transcription. We propose a model in which phosphorylation of the AF-1 domain controls RARgamma-mediated transcription through triggering the dissociation of vinexin beta

Polyelectrolyte complexes via desalting mixtures of hyaluronic acid and chitosan-Physicochemical study and structural analysis

International audiencePolyelectrolyte complexes (PECs) were prepared from Chitosan (CS) and Hyaluronic Acid (HYA) homogeneous mixtures of aqueous solutions. The method consisted of preparing a homogeneous mixture of the two polysaccharides via charge screening at high salt concentrations. Then, the mixture was dialyzed, leading to the controlled self -assembly of the two polyelectrolytes. Critical parameters like the chitosan degree of acetylation (DA) and molar mass (Mw), the residual salt concentration and the molar charge ratio r = n(NH3)(+) (CS)In-coo(-) (HYA) accounted for the transition from homogeneous aqueous solutions to colloidal suspensions (r = 0.1) or gel coacervates (r=0.5). The influence of the DA and Mw of CS was evaluated by visual observations, light scattering and rheological measurements. For low values of r, Small lAngle X-ray Scattering (SAXS) experiments revealed that the HYA nanostructure was weakly affected by the presence of PECs. On the contrary, the structure was impacted when increasing r, revealing a heterogeneous aggregate morphology with ladder-like chain interactions

SUG-1 plays proteolytic and non-proteolytic roles in the control of retinoic acid target genes via its interaction with SRC-3.

International audienceNuclear retinoic acid receptor alpha (RARalpha) activates gene expression through dynamic interactions with coregulatory protein complexes, the assembly of which is directed by the ligand and the AF-2 domain of RARalpha. Then RARalpha and its coactivator SRC-3 are degraded by the proteasome. Recently it has emerged that the proteasome also plays a key role in RARalpha-mediated transcription. Here we show that SUG-1, one of the six ATPases of the 19 S regulatory complex of the 26 S proteasome, interacts with SRC-3, is recruited at the promoters of retinoic acid (RA) target genes, and thereby participates to their transcription. In addition, SUG-1 also mediates the proteasomal degradation of SRC-3. However, when present in excess amounts, SUG-1 blocks the activation of RARalpha target genes and the degradation of RARalpha that occurs in response to RA, via its ability to interfere with the recruitment of SRC-3 and other coregulators at the AF-2 domain of RARalpha. We propose a model in which the ratio between SUG-1 and SRC-3 is crucial for the control of RARalpha functioning. This study provides new insights into how SUG-1 has a unique role in linking the transcription and degradation processes via its ability to interact with SRC-3

Cyclin H binding to the RARalpha activation function (AF)-2 domain directs phosphorylation of the AF-1 domain by cyclin-dependent kinase 7.

International audienceThe transcriptional activity of nuclear retinoic acid receptors (RARs), which act as RAR/retinoid X receptor (RXR) heterodimers, depends on two activation functions, AF-1 and AF-2, which are targets for phosphorylations and synergize for the activation of retinoic acid target genes. The N-terminal AF-1 domain of RARalpha is phosphorylated at S77 by the cyclin-dependent kinase (cdk)-activating kinase (CAK) subcomplex (cdk7/cyclin H/MAT1) of the general transcription factor TFIIH. Here, we show that phosphorylation of S77 governing the transcriptional activity of RARalpha depends on cyclin H binding at a RARalpha region that encompasses loop 8-9 and the N-terminal tip of helix 9 of the AF-2 domain. We propose a model in which the structural constraints of this region control the architecture of the RAR/RXR/TFIIH complex and therefore the efficiency of RARalpha phosphorylation by cdk7. To our knowledge, this study provides the first example of a cooperation between the AF-2 and AF-1 domains of RARs through a kinase complex

Cutaneous Kikuchi disease-like inflammatory pattern without lymph node involvement is associated with systemic disease and severe features in lupus erythematous: A case-control study

International audienceIntroductionKikuchi-Fujimoto disease (KFD) is a self-limited histiocytic necrotizing lymphadenitis sometimes affecting the skin. “Kikuchi disease-like inflammatory pattern” (KLIP) has been described in cutaneous lesions as similar pathological features in patients without lymph node involvement and as a potential clue for the diagnosis of lupus. We aimed to describe KLIP-associated clinical and immunological features in lupus patients with a retrospective case-control study.MethodsThirteen cases of KLIP were included as well as thirty-nine age- and sex-matched control lupus patients without KLIP. At the time of KLIP diagnosis, 4/13 patients (31%) had isolated cutaneous lupus erythematosus (CLE) and 9/13 had (69%) systemic lupus erythematosus (SLE) including 6 (46%) with severe haematological, lung, cardiac or renal disease. KLIP features were observed in skin biopsies of different clinical presentations.ResultsCompared with our control group, KLIP patients more frequently had SLE 9/13 (69%) versus 8/39 (21%) (OR 12.9; IC95% [2.86–58.2]; p = 0.0004) and more frequently severe SLE. Two out of four CLE exhibiting KLIP lesions (50%) developed severe SLE with cardiac or renal involvement after 12 and 24 months, respectively.Treatment with thalidomide 100 mg/day allowed rapid and complete clearance of cutaneous lesions in 6/6 KLIP patients. The need to use thalidomide tended to be more frequent in KLIP patients than in controls.ConclusionOur study suggests that KLIP features in lupus skin lesions are associated with SLE and severe systemic features. Despite a limited number of isolated CLE patients with KLIP features in the skin, this observation may warrant closer follow-up on patients with a higher risk of developing SLE