Chlamydia trachomatis manipulates (PI)CALM to carry on - PROJECT SUMMARY The CDC estimates that 10% of women between the ages of 15 to 19 test positive for Chlamydia trachomatis and 50-70% of these infections are asymptomatic. This increases the risk of widespread transmission and untreated infections, which can lead to pelvic inflammatory disease or infertility in a significant portion of women of childbearing age. Hence, there is a great need to identify strategies to reduce/prevent transmission and limit infections to the primary site of inoculation. Within the host cell, infectious elementary bodies (EBs) differentiate into non-infectious reticulate bodies (RBs) in a pathogen-specified organelle termed the chlamydial inclusion. During later stages of chlamydial development that precede egress, RBs will undergo secondary differentiation to form new EBs. The success of Chlamydia as a pathogen is owed to its obligate intracellular lifestyle and successful completion of its developmental cycle within the inclusion. The size of the inclusion enlarges over the course of chlamydial development to accommodate the increased number of organisms and at later stages, the inclusion can occlude much of the cytoplasm and dislocate organelles to the periphery of the host cell. Yet, the host cell remains relatively unstressed, which allows Chlamydia to promote a “silent” infection that does not attract unwanted attention from the host immune system. We hypothesize that one mechanism of maintaining a silent infection is the multiple pathways from which Chlamydia draw nutrients. Early in infection, the inclusion will intercept free amino acids from the lysosome and form membrane contact sites with the endoplasmic reticulum. During mid- to late- cycle, the inclusion intercepts post-Golgi exocytic vesicles to obtain sphingomyelin and cholesterol and recruits transferrin to the periphery of the inclusion via the slow-transferrin recycling pathway. A previous study in the laboratory demonstrated that the clathrin adaptor molecule, PICALM, localizes to the chlamydial inclusion. PICALM plays a central role in maintaining cholesterol homeostasis and regulates transferrin recycling. siRNA knockdown of PICALM in chlamydial infected cells increased lipid trafficking and transferrin trafficking to the inclusion. These data suggest that PICALM may function during chlamydial infection to limit host cell stress by maintaining a balance in nutrient trafficking within the cell. Current data in the field have linked PICALM to managing trafficking in the trans- Golgi, as part of its role in recycling pathways. Our data also indicate that PICALM may function in part to maintain Golgi structure and play a role in intra-Golgi trafficking—a previously undescribed finding. For this current proposal, we hypothesize that Chlamydia manipulates PICALM activity in the Golgi and slow-transferrin recycling pathways to support host cell homeostasis. A better understanding of how Chlamydia manipulates these pathways may be useful towards improving efficiency of delivery of novel anti-chlamydial compounds and/or defining novel mechanisms of previously undefined intersections of subcellular pathways.
