This application is a renewal of an ongoing Program Project in which five investigators with different but complementary expertise have worked together to understand two fundamentally important levels of TCR signaling: 1) how the TCR regulates the tyrosine kinases (SFKs, Syk kinases and Tec kinases) that control critical downstream tyrosine phosphorylation; and, 2) how Ras activation, a critical downstream signaling pathway, is regulated by Ras guanine nucleotide exchange factors (GEFs) whose activities themselves are coupled to TCR signaling via the set of substrates of the kinases controlled by the TCR. Our collaborative studies have resulted in considerable progress. In this renewal, our overall goal is to capitalize on our current progress and bring together approaches from structural biology, proteomics, immunology, and computational biology to understand TCR signaling. In project #1, we will study the distinct features of the T cell-expressed SFKs, Syk and Tec kinases that make these more suitable for antigen receptor signaling in T cells than their counterparts in B cells. We hypothesize that the characteristics of Lck and Fyn, ZAP-70 and Itk and their signaling regulators have been optimized in T cells to establish signaling circuitry that serves to maintain a basal signaling state that is resistant to perturbations by non-agonist peptides and also establishes a sensitive threshold for optimal recognition and response to agonist pMHC. In project #2, we hope to understand how basal and TCR-induced RasGEF signaling regulates the primed but controlled state of peripheral T cells while allowing for efficient T cell activation. We hypothesize that the SOS1 and RasGRP1 RasGEFs have evolved to be regulated in distinct manners to allow for non-redundant Ras signals in T cells that establish the homeostasis/activation balance.
In this program project renewal, our overall goal is to capitalize on our current progress and bring together approaches from structural biology, proteomics, immunology, and computational biology to understand TCR signaling. In project #1, we will study the distinct features of the T cell-expressed tyrosine kinases that make these most suitable for antigen receptor (TCR) signaling in T cells. In project #2, we hope to understand how TCR signaling regulates Ras, a critical regulator of cell activation, to establish basal homeostasis and allow for efficient activation of T cell responses. Project-001: Project 1 Project Leader (PL): Weiss, Arthur DESCRIPTION (provided by applicant): This application is a renewal of an ongoing project in which four investigators with different but complementary expertise have worked together to understand how the T cell antigen receptor (TCR) regulates the proximal tyrosine kinases (SFKs, Syk kinases and Tec kinases) that control critical downstream tyrosine phosphorylation. We have made considerable progress in understanding the structural basis for the specificity differences that are encoded in the kinase domains and the autoregulatory constraints that control the activities of these kinases, but a full understanding will require new approaches. We propose to capitalize on our current progress and bring together approaches from structural biology, physical sciences, proteomics, immunology, and computational biology to perform studies that are aimed at understanding the distinct features of the T cell-expressed SFKs, Syk and Tec kinases that make the individual kinases more suitable for antigen receptor signaling in T cells than in B cells. We hypothesize that the characteristics of Lck and Fyn, ZAP-70 and Itk and their signaling regulators have been optimized in T cells to establish signaling circuitry that serves to maintain a basal signaling state that is resistant to perturbations by non- agonist peptides and also establishes a sensitive threshold for optimal recognition and response to agonist pMHC. We will explore this hypothesis in experiments designed to: 1) understand the unique features of the proximal kinases that are advantageous in TCR signaling; 2) define the regulatory mechanisms that constrain the activity of the proximal tyrosine kinases; 3) determine how TCRs maintain basal homeostasis and distinguish biological noise from antigenic stimuli; and, 4) define the key intracellular events needed to initiate downstream signal propagation by the TCR.
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