The Role of TOR Complex 2 in the Maintenance of Plasma Membrane Tension Homeostasis

Constant changes in the environment constitute a threat for the maintenance of the homeostasis of an organism, and require all uni- or multicellular species to adapt in order to survive and prosper. The two multiprotein TOR Complexes, both nucleated around the conserved Target Of Rapamycin kinase, are now broadly considered as major regulators of eukaryotic cellular growth, serving as direct transducers of extracellular biotic and abiotic signals. On top of this traditional view, there is growing evidence that they also act as mediators of various aspects of cellular and organismal homeostasis. Specifically, TORC2 plays a key role in the maintenance of plasma membrane tensile homeostasis. Indeed, despite its established importance in the orchestration of many biological processes both at the cellular and tissue levels, little is known about the necessary mechanisms that regulate plasma membrane tension under ever-changing conditions due to extrinsic stressors or intrinsic phenomena such as growth. The general goal of this project was thus to investigate TORC2-mediated control of plasma membrane tensionL'homéostasie d'un organisme quel qu'il soit est en permanence menacée par les perturbations incessantes de son environnement, et qui exigent de toutes les espèces uni- ou multicellulaires qu'elles soient capables de s'adapter pour survivre et se développer. Les Eucaryotes ont optimisé des mécanismes de régulation finement ajustés et très conservés au cours de l'évolution, permettant leur croissance en cas de conditions propices, tout en garantissant leur survie lors de périodes défavorables.Les deux complexes multi-protéiques TORC1 et TORC2, tous deux organisés autour de la kinase TOR, sont aujourd'hui généralement considérés comme les principaux régulateurs de la croissance cellulaire chez les Eucaryotes, détectant de multiples informations biotiques et abiotiques en provenance de l'environnement, puis les transmettant à la machinerie cellulaire. En plus de cette vision traditionnelle, les complexes TOR sont désormais également envisagés comme étant les médiateurs de nombreux aspects de l'homéostasie cellulaire et de l'organisme. En particulier, TORC2complexe joue un rôle central dans le maintien de la tension de la membrane plasmique.En effet, bien que la tension membranaire soit clairement reconnue comme étant un facteur clé dans l'orchestration de nombreux processus biologiques, tant à l'échelle cellulaire que tissulaire, les mécanismes assurant sa régulation face à de constantes perturbations aussi bien environnementales que résultant de phénomènes intrinsèques (comme la croissance cellulaire par exemple), restent encore très mal connus. L'objectif général de ce projet était donc d'étudier comment TORC2 participe à la régulation de la tension de la membrane plasmique

The flipside of the TOR coin – TORC2 and plasma membrane homeostasis at a glance

Target of rapamycin (TOR) is a serine/threonine protein kinase conserved in most eukaryote organisms. TOR assembles into two multiprotein complexes (TORC1 and TORC2), which function as regulators of cellular growth and homeostasis by serving as direct transducers of extracellular biotic and abiotic signals, and, through their participation in intrinsic feedback loops, respectively. TORC1, the better-studied complex, is mainly involved in cell volume homeostasis through regulating accumulation of proteins and other macromolecules, while the functions of the lesser-studied TORC2 are only now starting to emerge. In this Cell Science at a Glance article and accompanying poster, we aim to highlight recent advances in our understanding of TORC2 signalling, particularly those derived from studies in yeast wherein TORC2 has emerged as a major regulator of cell surface homeostasis.</p

A new tool for annotating scientific animations and supporting scientific dialogue

A new interactive annotation interface supports a detailed molecular animation of the SARS-CoV-2 life cycle. With this tool, users can interactively explore the data used to create the animation and engage in scientific discourse through comments and questions.Funding Agencies|National Science Foundation [2033695]; Coronavirus Structural Task Force; University of Utah</p

TORC2 controls endocytosis through plasma membrane tension

Target of rapamycin complex 2 (TORC2) is a conserved protein kinase that regulates multiple plasma membrane (PM)–related processes, including endocytosis. Direct, chemical inhibition of TORC2 arrests endocytosis but with kinetics that is relatively slow and therefore inconsistent with signaling being mediated solely through simple phosphorylation cascades. Here, we show that in addition to and independently from regulation of the phosphorylation of endocytic proteins, TORC2 also controls endocytosis by modulating PM tension. Elevated PM tension, upon TORC2 inhibition, impinges on endocytosis at two different levels by (1) severing the bonds between the PM adaptor proteins Sla2 and Ent1 and the actin cytoskeleton and (2) hindering recruitment of Rvs167, an N-BAR–containing protein important for vesicle fission to endocytosis sites. These results underline the importance of biophysical cues in the regulation of cellular and molecular processes

3D reconstructions of parasite development and the intracellular niche of the microsporidian pathogen Encephalitozoon intestinalis

Abstract Microsporidia are an early-diverging group of fungal pathogens with a wide host range. Several microsporidian species cause opportunistic infections in humans that can be fatal. As obligate intracellular parasites with highly reduced genomes, microsporidia are dependent on host metabolites for successful replication and development. Our knowledge of microsporidian intracellular development remains rudimentary, and our understanding of the intracellular niche occupied by microsporidia has relied on 2D TEM images and light microscopy. Here, we use serial block-face scanning electron microscopy (SBF-SEM) to capture 3D snapshots of the human-infecting species, Encephalitozoon intestinalis, within host cells. We track E. intestinalis development through its life cycle, which allows us to propose a model for how its infection organelle, the polar tube, is assembled de novo in developing spores. 3D reconstructions of parasite-infected cells provide insights into the physical interactions between host cell organelles and parasitophorous vacuoles, which contain the developing parasites. The host cell mitochondrial network is substantially remodeled during E. intestinalis infection, leading to mitochondrial fragmentation. SBF-SEM analysis shows changes in mitochondrial morphology in infected cells, and live-cell imaging provides insights into mitochondrial dynamics during infection. Our data provide insights into parasite development, polar tube assembly, and microsporidia-induced host mitochondria remodeling

Decrease in plasma membrane tension triggers PtdIns(4,5)P₂ phase separation to inactivate TORC2

The target of rapamycin complex 2 (TORC2) plays a key role in maintaining the homeostasis of plasma membrane (PM) tension. TORC2 activation following increased PM tension involves redistribution of the Slm1 and 2 paralogues from PM invaginations known as eisosomes into membrane compartments containing TORC2. How Slm1/2 relocalization is triggered, and if/how this plays a role in TORC2 inactivation with decreased PM tension, is unknown. Using osmotic shocks and palmitoylcarnitine as orthogonal tools to manipulate PM tension, we demonstrate that decreased PM tension triggers spontaneous, energy-independent reorganization of pre-existing phosphatidylinositol-4,5-bisphosphate into discrete invaginated membrane domains, which cluster and inactivate TORC2. These results demonstrate that increased and decreased membrane tension are sensed through different mechanisms, highlighting a role for membrane lipid phase separation in mechanotransduction

Flipper Probes for the Community

This article describes four fluorescent membrane tension probes that have been designed, synthesized, evaluated, commercialized and applied to current biology challenges in the context of the NCCR Chemical Biology. Their names are Flipper-TR ® , ER Flipper-TR ® , Lyso Flipper-TR ® , and Mito Flipper-TR ® . They are available from Spirochrome. </p

Data from: Systematic analysis of complex genetic interactions

To systematically explore complex genetic interactions, we constructed ~200,000 yeast triple mutants and scored negative trigenic interactions. We selected double-mutant query genes across a broad spectrum of biological processes, spanning a range of quantitative features of the global digenic interaction network and tested for a genetic interaction with a third mutation. Trigenic interactions often occurred among functionally related genes, and essential genes were hubs on the trigenic network. Despite their functional enrichment, trigenic interactions tended to link genes in distant bioprocesses and displayed a weaker magnitude than digenic interactions. We estimate that the global trigenic interaction network is ~100 times as large as the global digenic network, highlighting the potential for complex genetic interactions to affect the biology of inheritance, including the genotype-to-phenotype relationship