Title: Modulation of Host Cell Function by Campylobacter jejuni Effector Proteins Project Summary Infection with Campylobacter jejuni is responsible for millions of cases of diarrhea per year and is associated with Guillain-Barré syndrome, the leading cause of flaccid paralysis in the post-polio era. Although researchers have surmised for more than two decades that C. jejuni-mediated enteritis is dependent on invasion of the cells lining the gastrointestinal tract and is accompanied by a robust inflammatory response, the pathogen and host responses that contribute to C. jejuni-mediated enteritis are ill-defined. My lab discovered that this pathogen- induced event (cell invasion) requires the delivery of proteins from C. jejuni to the cytosol of host cells. We have designated these secreted proteins the Campylobacter invasion antigens (Cia). The Cia proteins co-opt components of the focal complex (a cell-matrix adhesion structure) and the MEK/ERK signaling pathway to trigger membrane ruffling (lamellipodia and filopodia extensions – cellular protrusions supported by actin filaments). Our overall goal is to identify the mechanism(s) that C. jejuni utilizes to subvert components of the focal complex (FC) to promote cell invasion through cytoskeletal reorganization. Contextually, these studies will provide insight into how microbes modulate cellular signaling pathways to favor pathogen survival and dissemination. We have shown that the CiaC and CiaD effectors are necessary for C. jejuni cellular invasion. Our working hypothesis is that these two effectors contain domains that direct the formation of the Campylobacter invasion complex. More specifically, we hypothesize that CiaC and CiaD co-opt components of the FC and FC- associated proteins that enable the cross-talk (convergence) of cellular pathways and trigger cytoskeletal reorganization and chemokine production (IL-8) in host cells. The precise mechanism(s) that CiaC and CiaD use to modulate cytoskeletal rearrangement and bacterial uptake are not known. Thus, our goal of elucidating how the CiaC and CiaD effectors drive C. jejuni-cell invasion and chemokine induction is essential for understanding the molecular and cellular basis of C. jejuni-mediated enteritis and is a prerequisite for the development of targeted methods to prevent and treat C. jejuni disease. The Specific Aims of this proposal are to: 1) Establish the host cell targets of both CiaC and CiaD; 2) Identify the host cell proteins phosphorylated in a CiaC- and CiaD-dependent manner and determine the role of these phosphorylation events in modulating host cell signaling pathways; and 3) Test whether the C. jejuni CiaC and CiaD effectors are required for disease in piglets and determine if deficiency of either protein results in a unique disease phenotype.