Scientists : Laurence Abrami, Numa Piot, Oksana Sergeeva

Anthrax toxin is an A2B toxin, in which the A-subunit may either be the lethal factor (LF) or edema factor (EF) and the B-subunit is the receptor-binding protective antigen (PA). PA binds to the anthrax cell-surface receptors with three-four molecules of LF or EF, and is the endocytosed into the cell. Once the complex has successfully entered the cell, it is shuttled to early endosomes and is sorted into nascent intraluminal vesicles (ILVs). The low pH inside the endosome permits the PA heptamer to insert itself into the membrane, forming a translocation pore for the LF or EF. Then, these enzymatic subunits, upon partial unfolding, are passed into the lumen of the ILV, which is topologically equivalent to the cytoplasm.

In late endosomes, ILVs can undergo back fusion with the limiting membrane, releasing EF or LF into the cytoplasm. Once inside the cytoplasm, LF, a metalloproteinase, cleaves MAP kinase kinases (MAPKKs) and inactivate cellular signaling pathways, causing apoptosis, while EF, an adenylate cyclase, increases cAMP levels of the cell, causing edema. A fraction of late endosomes contain ILV with LF actually end of fusing with the plasma membrane, thereby releasing the ILVs as exosomes. Anthrax intoxication can spread when other cells take up these exosomes and end up with LF in their cytoplasms.

Because anthrax toxin hijacks cellular process to hurt the cell, our lab uses anthrax toxin to better understand eukaryotic endocytic pathways. We do this primarily with cellular and biochemical assays in the lab but also have collaborations with Prisca Liberali (FMI) and Howard Reizman (UniGe).

Scientists : Giorgia Brambilla Pisoni, Francisco Mesquita

Cell compartmentalization is a really puzzling topic of eukaryotic biology. Lipid membranes delimit functionally and physically specialized organelles, which are known to undergo dynamic remodelling in order to fulfil functions and maintain homeostasis. At the same time, membranes also enter in close apposition (but not fusion) with the membrane of other organelles, creating protein-mediated contact sites (MCSs).

For our group, the study of membrane structure and homeostasis gains visibility especially when connected to post-translational modifications, and primarily to palmitoylation.

In this regard, our main obsessions and key questions concern the endoplasmic reticulum (ER) and how its architecture and physiology are tuned by palmitoylation.We are currently investigating how palmitoylation does regulate protein trafficking from the ER, how ER membrane proteins’ palmitoylation impacts on ER morphology and, since several proteins residing at MCSs are known to be palmitoylated, how and at which extent formation and function of these sites are controlled by this modification.

Scientists : Olha Novokhatska, Oksana Sergeeva

Hyaline Fibromatosis Syndrome (HFS) is a severe disease that manifests in symptoms ranging from bone fragility and joint contractures to protein enteropathy, and subcutaneous nodules, eventually leading to disability or death in its most acute infantile form. HFS results from a single point mutation in cell surface protein Capillary Morphogenesis Gene 2 (CMG2).

A combination of our expertise in cell biology and in vivo animal models together with extensive collaborations with EPFL computational biology labs, Broad Institute (Boston, US), Swiss Institute of Bioinformatics, and public hospitals, allows us integrating various inputs to gain insights in CMG2 physiological role and possible ways of correcting its loss-of-function.

Our laboratory has several approaches to understand HFS mechanisms by investigating CMG2 loss-of-function phenotypes. Using the HFS mouse model, we identified CMG2 as a regulator of extracellular matrix and collagen VI homeostasis, and we are currently developing strategies to rescue excessive extracellular matrix accumulation. Further, using mice deficient in CMG2, we discovered altered energy metabolism and weight gain associated with changes in the extracellular matrix due to lack of CMG2. To understand the role of planar cell polarity pathway in HFS pathogenesis, we investigate defects in lymphatic valves formation in mice lacking CMG2.

Another approach to study HFS is transcriptomic profiling of patient-derived cells and screening of 1,000 approved drugs to identify biological pathways affected by different CMG2 mutations. Currently, we are developing in vitro system to monitor TGFβ signaling downstream CMG2 as a candidate pathway for drug screening and identifying the effect of individual patients’ mutations on cell-autonomous phenotypes.

Scientists : Lucie Bracq, Laurence Abrami, Audrey Chuat, Béatrice Kunz, Numa Piot

Capillary Morphogenesis Gene 2 (CMG2) and Tumor Endothelial Marker 8 (TEM8) are two type I transmembrane proteins shown to be the receptors used by anthrax toxin to enter cells. Similar to integrins, their structure includes an extracellular domain responsible for ligand binding, a transmembrane domain and a disordered cytosolic tail. On the physiological aspect, mutations in any domain of CMG2 and TEM8 induce Hyaline Fibromatosis Syndrome (HFS) and GAPO syndrome, respectively, two rare and very disfiguring diseases. These diseases suggest that both receptors have important physiological roles, which remain, however, poorly understood. As mentioned by its name, TEM8 was shown to be overexpressed in certain types of cancer and current evidences point towards roles in cell proliferation, adhesion and migration. In addition, it is also involved in Wnt signaling, angiogenesis and ECM homeostasis. While CMG2 also seems to be involved in Wnt signaling, angiogenesis and ECM homeostasis, in particular by internalizing and degrading collagen Type VI, the literature suggests a role for CMG2 in cancer invasiveness and migration.

In our lab, we use different approaches to investigate the role of both CMG2 and TEM8, including biochemistry, immunofluorescence and live microscopy, proteomics, RNA-Seq and animal models (mouse and zebrafish) among others. The projects involve collaborations with the laboratories of Matteo Dal Perraro, Marcos Gonzalez-Gaitan, Tatiana Petrova as well as with different facilities at EPFL and at the University of Geneva.

Scientists : Umair Anwar, Laurence Abrami, Giorgia Brambilla Pisoni, Sylvia Ho

S-Palmitoylation is the only reversible lipid post-translational modification of proteins. It is mediated by members of the DHHC family of palmitoyltransferases that are all very poorly understood. We are interested in all aspects of palmitoylation with a special focus on membrane protein substrates and the enzymes themselves.

To address these issues we have chosen a very multidisciplinary approach including: cell biology, biochemistry, microscopy, modeling, proteomics and lipidomics.

These projects involve intense collaborations with the lab of Vassily Hatzimanikatis, with members of the LipidX consortium of and of the NCCR Chemical Biology.