A molecular and cellular investigation of Helicobacter pylori's Cag pathogenicity island and interactions with host cells

Helicobacter pylori is a human specific pathogen that infects the nearly half of the world's population and is associated with an increased risk for stomach ulcers and gastric cancer. Several host and bacterial factors increase risk for H. pylori-associated diseases. The strongest indicator of a severe disease outcome is infection with bacterial strains harboring the cytotoxin associated gene pathogenicity island ( cag PAT), which encodes several homologues of a Type IV Secretion System (TFSS) and a delivered effector molecule, CagA. Gastric carcinoma is the second leading cause of cancer death worldwide, representing a significant impact on human health. Therefore, the function of the genes encoded by the cag PAT, both the structure of the TFSS apparatus and the effects of CagA on host cell signaling, has been a focus of intense study.; It is now known that CagA alters normal cell signaling through receptor tyrosine kinase (RTK) pathways and this abnormal signaling gives rise to ulceration and cancer. In a tissue culture model of infection, H. pylori leads to dramatic changes in the morphology of gastric epithelial cells (AGS cells), which is a direct result of CagA activation of RTK pathways.; In my dissertation I address two important questions about H. pylori and its interaction with host cells. First, I investigated a cag PAI protein of unknown function, CagN, and its possible role in TFSS assembly and function. While CagN does not appear to be involved in CagA delivery, I discovered that it is processed and undergoes cleavage at a unique C-terminal site. In the second part of my dissertation, I investigated the specific AGS cell signaling events that result in morphology changes. I demonstrated that the elongation phenotype is caused by a cell retraction defect and is independent of actin polymerization via the Arp2/3 complex that is commonly exploited by pathogens. Collectively, this work has led to a greater understanding of the composition of the cag PAI and has documented important observations about CagA's manipulation of normal host cell biology.; This dissertation includes previously published co-authored materials.