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.

Interactions between Chlamydia and the host

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 compartment called an inclusion. They use a type III secretion mechanism to translocate probably about 10% of their proteins out of the inclusion, into the host cell or into the inclusion 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 discovered a novel bacterial protein that is targeted to the nucleus of the host. NUE has histone methyl transferase activity in vitro, indicating that it might modify the chromatin of the host at the epigenetic level during infection. In addition 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 control the production of ROS by the host.

Keywords: endocytosis, membrane receptor, Chlamydia, intracellular pathogen, nuclear effector

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

Montes de Oca P, Malardé V, Proust R, Dautry-Varsat A, Gesbert F. 2010. Ectodomain shedding of interleukin-2 receptor beta and generation of an intracellular functional fragment. J Biol Chem. 285(29):22050-8.

Grassart A, Meas-Yedid V, Dufour A, Olivo-Marin JC, Dautry-Varsat A, Sauvonnet N. 2010. Pak1 phosphorylation enhances cortactin-N-WASP interaction in clathrin-caveolin-independent endocytosis. Traffic. 11(8):1079-91

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.

Pennini, M.E., Perrinet S., Dautry-Varsat A., and Subtil A. 2010. Histone methylation by NUE, a novel nuclear effector of the intracellular pathogen Chlamydia trachomatis. PLoS Pathog. . 6, e1000995