Greater than 95% of infectious agents enter through exposed mucosal surfaces, such as the respiratory, gastrointestinal and genitourinary tracts. These include AIDS, sexually transmitted diseases, numerous opportunistic infections, many emerging and re-emerging infections, and biological warfare/terrorist agents, such as anthrax. Most mucosalsurfaces are lined by a monolayer of polarized epithelial cells, which forms the principal barrier to entry by infectious agents. In essence, the epithelial layer can be considered the most basic component of the innate mucosal immune system. Some pathogens cross the epithelial layer by disrupting it. Other pathogens exploit disruptions in the monolayer, which can be caused by tissue injury secondary to inflammation, trauma, or may result from cell death or division within the monolayer. To maintain their function as a barrier to infection, epithelial tissues have developed efficient wound healing mechanisms. Wound healing is central to mucosal defense against infection. The epithelial barrier must be restored as quickly as possible, to minimize the opportunity for entry of infectious agents. Some infectious agents, such as Pseudomonas aeruginosa, not only exploit pre-existing wounds, but also impede the wound healing process. Epithelial wound healing can be divided into two major phases, "Start" and "Stop." Our first Specific Aim is to analyze the factors that control the Start phase and directed cell migration into the wound. We will examine the roles of phosphatidyl inositol 3-kinase, Raf, Cdc42, atypical protein kinase C, Par3/Par6 complex, and matrix metalloproteinases. We will test how these proteins control the initiation of migration into the wound and how cells migrate as an epithelial sheet or, alternatively, as dissociated cells. Our second Specific Aim is to analyze the factors that control the Stop phase of wound healing. We will test the role of phosphatidyl inositol 3-kinase and the Pakl/PIX/paxillin/Pkl complex in arresting motility and proliferation in the Stop phase and avoiding multilayering. This work will be in collaboration with Projects 2, 3 and 4, and supported by Cores B and C.