PROJECT SUMMARY Adaptive immune surveillance depends on the ability of T cells to successfully migrate through secondary lymphoid tissues and form immune-synapses with antigen-presenting cells. Precise and dynamic organization of the actin cytoskeleton is essential for both of these processes. In migrating T cells rapid reorganization of the actin cytoskeleton is essential for cell polarization and chemotactic responses required for tissue entry and proper micro-environmental positioning. During T cell activation, changes in the actin cytoskeleton control proper formation of the immunological synapse, a highly organized cellular structure that allows T cells to properly integrate signals from the T cell receptor with those from co-stimulatory molecules such as CD28 and integrins such as LFA-1 (αLβ2). Flightless-1 (Flii) was initially identified in Drosophila as an actin modifying protein that controls actin myofibril structure in the muscles that control flight. Flii contains an N-terminal leucine-rich repeat (LRR) domain that facilitates protein-protein interaction and has been implicated in control of Ras activation of Erk/Mapk signaling, Rac1 activation and PI3K signaling. The Flii C-terminus encodes 6 gelsolin-related domains that can interact with actin and regulate actin filament assembly/disassembly. Based on its unique domain structure, we hypothesize that Flii acts as a key regulator of CD8+ T cell homeostasis and function by linking changes in the actin cytoskeleton during cell migration and activation with spatial control of various signaling cascades. We will use state-of-the-art cellular and molecular techniques to study Flii function in physiologically relevant and innovative mouse models. Completion of these studies will provide important new insights into a novel and completely uncharacterized signaling hub that regulates CD8+ T cell-mediated immunity.

PROJECT NARRATIVE We hypothesize that Flightless-I (Flii) links changes in the actin cytoskeleton to the activation and spatial organization of key signaling pathways during T cell migration and activation, and thereby acts as a key and completely uncharacterized regulator of CD8+ T cell responses. Using Flii conditional knockout mice, we will determine how Flii regulates actin dynamics and spatial control of key signaling pathways during T cell migration and activation, and to determine how this impacts CD8+ T cell responses in vivo.