The research of this unit focuses on (i) the mechanisms of entry, signaling and the intracellular fate of receptors (ii) the mechanisms of entry and development of the intracellular bacterium, Chlamydia.

Receptor dynamics and intracellular traffic

Membrane receptors bind their ligands, are endocytosed, and sorted towards degradation or recycling. Endocytosis modulates the expression of membrane components and their signaling activity.

Endocytosis pathways

Receptor-mediated endocytosis through clathrin-coated pits has been by far the most thoroughly investigated. However, other internalization pathways exist, and we have shown that two members of the type I cytokine receptor family, the interleukin-2 receptor (IL-2R) β and the common cytokine receptor γc, are internalized by a clathrin-independent pathway. We are investigating the molecular machinery underlying this process. Recent results show that the GTPases RhoA, Rac1 and dynamin are required for this pathway, as well as partners of these factors, the kinases Pak, cortactin and N-WASP. Most of these proteins should be involved in the fission of the vesicle, thereby providing a cross-talk between endocytosis, signal transduction and the actin network (See figure).

Regulation of IL-2R sorting and intracellular fate

Ubiquitination has been shown to be important for receptor internalization, sorting, and degradation. We have demonstrated that cytokine receptors, IL-2Rβ and γc are ubiquitinated, and their cell surface expression is regulated by a ubiquitination/de-ubiquitination machinery, namely by the couple of enzymes c-Cbl/DUB2. In addition, the ubiquitin-ligase NEDD4 associates constitutively with γc and participates to the regulation of its half-life. Ectodomain shedding can also contribute to receptor turn over. We have shown that IL-2Rβ undergoes a proteolytic cleavage, generating an intracellular fragment that remains associated with signaling molecules.

Chlamydiae species pathogenic to humans, mainly Chlamydia trachomatis and Chlamydia pneumoniae, cause a number of diseases, including trachoma, pelvic inflammatory disease and pneumonia. We analyze the mechanisms used by the bacteria to enter cells and to sustain their growth.

Identification of type III secreted proteins and functional studies

Throughout their cycle in the host cell, chlamydiae remain in a membrane-bound compartment called an inclusion. They use a secretion mechanism called type III to translocate probably about 10% of their proteins out of the inclusion, into the host cell or into the incluision membrane. These proteins are very likely to be important in Chlamydia pathogenicity and most of our research is dedicated to understanding their function during infection. We have shown that some bacterial inclusion proteins possess SNARE domains that interact with SNARE proteins of the host, which are molecules specialized specialized in membrane compartment recognition and fusion recruiting several intracellular compartments to the inclusion membrane. This study demonstrated for the first time mimicry of the SNARE domain by a bacterium. More recently, we have shown that upon infection, epithelial cells transiently produces reactive oxygen species (ROS). The activity of the host NADPH oxidase is later turned down by infection, indicating that the bacteria controls the production of ROS by the host.

Keywords: endocytosis, membrane receptor, Chlamydia, intracellular pathogen

Delevoye, C., Nilges, M., Dehoux, P., Paumet, F., Perrinet, S., Dautry-Varsat, A. and Subtil, A. 2008. SNARE Protein Mimicry by an Intracellular Bacterium. PLoS Path. 4, e1000022.

Grassart, A., Dujeancourt, A., Lazarow, P. B., Dautry-Varsat, A. and Sauvonnet, N. 2008. Clathrin-independent endocytosis used by the IL-2 receptor is regulated by Rac1, Pak1 and Pak2. EMBO Rep 9, 356-62.

Muschiol S., Normark S., Henriques-Normark B., Subtil, A 2009. Small molecule inhibitors of the Yersinia type III secretion system impair the development of Chlamydia after entry into host cells. BMC Microbiol., 9 75

Malardé V, Proust R, Dautry-Varsat A., Gesbert F. 2009.NEDD4-2 associates with gamma(c) and regulates its degradation rate. Biochem Biophys Res Commun., 387(2) :409-413.

Boncompain, G., B. Schneider, C. Delevoye, O. Kellermann, A. Dautry-Varsat, and A. Subtil. 2010. Production of reactive oxygen species is turned on and rapidly shut down in epithelial cells infected with Chlamydia trachomatis. Infect Immun. 78: 80-7.