The Lipid Transfer Protein CERT Interacts with the Chlamydia Inclusion Protein IncD and Participates to ER-Chlamydia Inclusion Membrane Contact Sites

Abstract

Bacterial pathogens that reside in membrane bound compartment manipulate the host cell machinery to establish and maintain their intracellular niche. The hijacking of inter-organelle vesicular trafficking through the targeting of small GTPases or SNARE proteins has been well established. Here, we show that intracellular pathogens also establish direct membrane contact sites with organelles and exploit non-vesicular transport machinery. We identified the ER-to-Golgi ceramide transfer protein CERT as a host cell factor specifically recruited to the inclusion, a membrane-bound compartment harboring the obligate intracellular pathogen Chlamydia trachomatis. We further showed that CERT recruitment to the inclusion correlated with the recruitment of VAPA/B-positive tubules in close proximity of the inclusion membrane, suggesting that ER-Inclusion membrane contact sites are formed upon C. trachomatis infection. Moreover, we identified the C. trachomatis effector protein IncD as a specific binding partner for CERT. Finally we showed that depletion of either CERT or the VAP proteins impaired bacterial development. We propose that the presence of IncD, CERT, VAPA/B, and potentially additional host and/or bacterial factors, at points of contact between the ER and the inclusion membrane provides a specialized metabolic and/or signaling microenvironment favorable to bacterial development. The obligate intracellular bacterial pathogen Chlamydia has developed strategies to invade, survive and replicate within the host genital, ocular and pulmonary epithelial surfaces. Chlamydia developmental cycle occurs in a membrane bound vacuole, the inclusion. The Chlamydia-dependent remodeling of the inclusion membrane leads to a unique and specialized compartment that allows for the specific interaction with cellular organelles and the acquisition of molecules and nutrients required for bacterial survival and replication. This study provides an example of how the insertion of C. trachomatis proteins into the inclusion membrane may allow the bacteria to manipulate the host cells to its own benefit. We showed that the lipid transfer protein CERT localized to C. trachomatis inclusion membrane and partly co-localized with the endoplasmic reticulum (ER) protein VAPB. Moreover, VAPB positive tubules made close contact with the inclusion membrane, suggesting the formation of ER-Inclusion membrane contact sites upon C. trachomatis infection. Finally, we have shown that CERT interacted with the C. trachomatis inclusion protein IncD. We propose that the presence of CERT, VAPB and IncD at ER-Inclusion membrane contact sites allow C. trachomatis to exploit the non-vesicular lipid transport machinery of the host cell and generate platforms specialized in metabolism and signaling events favorable to bacterial development.