| Understanding the spatial organization of signaling molecules is critical to understanding the outcome of signaling events. During T cell signal transduction, TCR engagement by a ligand of sufficient affinity stimulates the formation of a highly ordered array of signaling elements, termed a supramolecular activation complex (SMAC). TCR engagement by altered peptide ligands with reduced affinity for the TCR result in the formation of a disordered SMAC and a failure to transduce an activating signal. The mechanisms that drive the formation of signaling complexes, and the mechanisms by which the organization of such complexes is maintained, are not yet well understood. Critical to these processes is the reorganization of the actin cytoskeleton.; I have investigated the role of the actin cytoskeleton in T cell signal transduction leading to both T cell activation and apoptosis. I have demonstrated that perturbation of actin cytoskeletal dynamics by treatment with the actin modifying compounds jasplakinolide or cytochalasin D enhanced commitment to apoptosis in a model system of lymphocyte apoptosis induced by cytokine deprivation. By overexpression of gelsolin, an actin-binding protein, I have addressed the role of gelsolin in signaling to apoptosis in model systems of lymphocyte apoptosis induced by cytokine deprivation, ceramide treatment, and Fas ligation. I have further investigated the participation of gelsolin and the regulation of actin dynamics in TCR-mediated signal transduction, and demonstrate that overexpression of gelsolin altered tyrosine phosphorylation patterns of substrates associated with lipid raft membrane microdomains, and this alteration of phosphorylation patterns correlated with inhibition of NF-AT transcriptional activation and IL-2 production. Finally, I have begun to characterize the possible dependence of T cell signaling on gelsolin in model systems of lymphocyte development and function utilizing lymphocytes isolated from gelsolin null mice. I thus provide clear evidence that the actin cytoskeleton participates in T cell signal transduction, and have begun to define the mechanisms by which it does so. |
