Arpp19 et ENSA, deux inhibiteurs de la phosphatase PP2A-B55 contrôlent de manière différentielle le cycle cellulaire

International audienc

RhoA GTPase Regulates M-Cadherin Activity and Myoblast Fusion

The Rho family of GTP-binding proteins plays critical roles during myogenesis induction. To elucidate their role later during myogenesis, we have analyzed RhoA function during myoblast fusion into myotubes. We find that RhoA activity is rapidly and transiently increased when cells are shifted into differentiation medium and then is decreased until myoblast fusion. RhoA activity must be down-regulated to allow fusion, because expression of a constitutively active form of RhoA (RhoAV14) inhibits this process. RhoAV14 perturbs the expression and localization of M-cadherin, a member of the Ca(2+)-dependent cell-cell adhesion molecule family that has an essential role in skeletal muscle cell differentiation. This mutant does not affect N-cadherin and other proteins involved in myoblast fusion, β1-integrin and ADAM12. Active RhoA induces the entry of M-cadherin into a degradative pathway and thus decreases its stability in correlation with the monoubiquitination of M-cadherin. Moreover, p120 catenin association with M-cadherin is decreased in RhoAV14-expressing cells, which is partially reverted by the inhibition of the RhoA effector Rho-associated kinase ROCK. ROCK inhibition also restores M-cadherin accumulation at the cell-cell contact sites. We propose that the sustained activation of the RhoA pathway inhibits myoblast fusion through the regulation of p120 activity, which controls cadherin internalization and degradation

Quantitative imaging and phenotyping of mitochondrial morphology in live cells

Mitochondria are vital cellular organelles for life due to their central role in energy production and the regulation of cellular metabolism. Their morphology is closely linked to their function, and any dysfunction of the mitochondria can have major consequences for their shape as well as for the health of cells, tissues and organisms. Their ability to transition between various structural and functional states make them excellent organelles for monitoring cell health. Healthy mitochondria are usually mobile, tubular and interconnected, whereas cells under stress or entering apoptosis often display swollen or fragmented mitochondria, marked by concurrent disruption of metabolism and excess production of reactive oxygen species. Quantitative imaging-based assessment of mitochondrial morphology can therefore provide valuable insights into tissue physiology, pathology and damage. Over the last few years, we have developed innovative computerized methods that enable accurate, multiscale, fast and cost-effective analysis of mitochondrial shape and network architecture from confocal fluorescence images. The core component of the workflow typically involves in-house, proprietary software (with APP deposit) that has evolved through successive versions (MitoShape, MitoTouch and the most recent, AI-driven version, MitoRadar). We have applied our fully automated image analysis pipeline (MITOMATICS) on rich datasets collected from living human cells to monitor pathophysiological conditions, as well as the harmfulness and/or toxicity of environmental pollutants. Our technology and software tools have potential for applications in research areas such as predictive and environmental toxicology, high-throughput drug screening, and high-content phenotypic screening

Rac1 and RhoA GTPases have antagonistic functions during N-cadherin-dependent cell-cell contact formation in C2C12 myoblasts.

BACKGROUND INFORMATION: N-cadherin, a member of the Ca(2+)-dependent cell-cell adhesion molecule family, plays an essential role in the induction of the skeletal muscle differentiation programme. However, the molecular mechanisms which govern the formation of N-cadherin-dependent cell-cell contacts in myoblasts remain unexplored. RESULTS: In the present study, we show that N-cadherin-dependent cell contact formation in myoblasts is defined by two stages. In the first phase, N-cadherin is highly mobile in the lamellipodia extensions between the contacting cells. The second stage corresponds to the formation of mature N-cadherin-dependent cell contacts, characterized by the immobilization of a pool of N-cadherin which appears to be clustered in the interdigitated membrane structures that are also membrane attachment sites for F-actin filaments. We also demonstrated that the formation of N-cadherin-dependent cell-cell contacts requires a co-ordinated and sequential activity of Rac1 and RhoA. Rac1 is involved in the first stage and facilitates N-cadherin-dependent cell-cell contact formation, but it is not absolutely required. Conversely, RhoA is necessary for N-cadherin-dependent cell contact formation, since, via ROCK (Rho-associated kinase) signalling and myosin 2 activation, it allows the stabilization of N-cadherin at the cell-cell contact sites. CONCLUSIONS: We have shown that Rac1 and RhoA have opposite effects on N-cadherin-dependent cell-cell contact formation in C2C12 myoblasts and act sequentially to allow its formation

A cell active chemical GEF inhibitor selectively targets the Trio/RhoG/Rac1 signaling pathway.

International audienc

Participation of small GTPases Rac1 and Cdc42Hs in myoblast transformation

International audienc