A variety of gastrointestinal disorders, that include H. pylori, NSAID induced gastritis and inflammatory bowel disease, involve the recruitment of leukocytes from the circulation to the site of injury. The severity of the mucosal injury in these disease processes has been directly correlated with the extent of the neutrophil infiltration. In addition, the persistent neutrophil infiltrate which is the hallmark of chronic H. pylori infection, has been implicated as a possible mechanism facilitating malignant transformation in the gastric mucosa. Central to the modulation of adhesion and migration of leukocytes in inflammatory processes such as these, is a subfamily of cell surface receptors, the beta2 integrins. Adhesion through beta2 integrins is a complex process that involves activation of the integrin through an inside out signaling mechanism, triggered by the engagement of well characterized receptors such as the chemokine receptors, IL-8, C5a, and N-Formylmethionlleucyl- phenylalanine (FMLP), cytokine receptors, such as TNF, and activation of Protein Kinase C. Integrin activation results in enhanced binding to ligand, and subsequently, generation of an outside-in signal cascade that may lead to changes in gene expression and cytoskeletal rearrangement, enabling the leukocyte to migrate to sites of injury, and facilitating the physiologic response of the cell. Recent reports have identified Interleukin-8 as an important epithelial-derived inflammatory mediator in both IBD and H. pylori gastritis. In neutrophils, I1-8 has been shown to induce chemotaxis, respiratory burst and granule release, and to enhance cellular adhesion. However, the specific effects of IL-8 on beta2 integrin activation and ligand binding have not been closely examined. In addition, while recent reports indicate that IL-8 activates the MAPK pathway through Ras/Raf-mediated events, the relationship of these events to beta2 integrin function has yet to be elucidated. Our goal, within this proposal, is to delineate the signal transduction cascades involved in beta2 integrin activation, with a particular focus on the physiologic stimulus at the chemokine receptor. In addition, we will examine post-ligand-binding events, including protein tyrosine phosphorylation and protein-protein interactions that are central to the outside-in signaling cascade initiated by engagement of beta2 integrins on human neutrophils. We will examine the relationship of these events to the complex shape changes involved in aggregation and transmigration. And, as a biological model, we will explore the way in which exposure to Helicobacter pylori, may impact these signals and affect neutrophil adhesion and migration on epithelial surfaces.
| Takami, Mimi; Terry, Valeri; Petruzzelli, Lilli (2002) Signaling pathways involved in IL-8-dependent activation of adhesion through Mac-1. J Immunol 168:4559-66 |
