Discs Large Homolog 1: Identifying Molecular Mechanisms that Guide Functional Specificity in Lymphocytes
Lymphocytes, including T and B cells, are the cornerstone of the adaptive immune response. Recognition of foreign antigen by the T cell receptor or B cell receptor (collectively known as immunoreceptors) triggers transcriptional and cytoskeletal changes leading to proliferation, differentiation and execution of cell specific effector functions. Immunoreceptors have the unique ability to discriminate subtleties in antigen quality and translate these differences into specific biological responses. In T cells, scaffold protein Discs Large Homolog 1 (Dlg1) associates with signaling and cytoskeletal mediators including: Lck, Zap70, p38, ezrin and WASp. Through these interactions Dlg1 couples T cell receptor (TCR) stimulation to activation of MAPK p38 and transcription factor NFAT, and facilitates cytoskeletal events including receptor clustering, actin polymerization and cell-mediated cytotoxicity. This thesis identifies a role for Dlg1 in receptor clustering, synapse formation and p38 activation in B cells and examines the molecular mechanisms that individually and collectively regulate Dlg1-mediated pathways that guide functional specificity in lymphocytes. We show that T cells express two Dlg1 variants that form unique signaling complexes and drive distinct CTL effector responses. We also identify Dlg1 tyrosine phosphorylation as a key point of control required for Dlg1-mediated transcriptional, but not cytoskeletal events. Finally, we use a novel inducible Dlg1 knockout model to characterize the role of Dlg1 in vivo. Together this work identifies changes in Dlg1 splice variant expression, recruitment, utilization and/or modification as a method to guide lymphocyte fate and function, and characterizes a knockout model that can be used to extend these findings in future studies.