The role of the GRB2 family of adaptor proteins in T cell receptor-mediated signaling

[摘要] CD4+ T cells are critical in the fight against parasitic, bacterial, and viral infections, but are also involved in many autoimmune and pathological disorders. Ligation of the T Cell Receptor (TCR) is the primary signal required for T cell activation proliferation, differentiation and cytokine release. Upon TCR activation, several kinases and adaptor proteins are assembled at the TCR/linker for activation of T cells (LAT) signaling complexes, a process indispensable for optimal signal transduction. One important group of proteins recruited to the TCR/LAT complexes is the GRB2 family of adaptors. Due to their role in mediating signaling complexes, the GRB2 family of adaptors are critical for development, proliferation, and survival of diverse cell types. These proteins have been linked to the initiation and progression of numerous pathological conditions including diabetes, asthma/allergy, and solid and hematopoietic malignancies. Therefore, it is essential to characterize and understand the complete functions of these proteins for the generation of safe and efficient targeting treatments for diseases mediated by these proteins. In T cells, GRB2 and its homologs, GADS and GRAP, are crucial for the propagation of signaling pathways through the TCR and adaptor protein LAT. These proteins recruit distinct sets of proline-rich ligands to LAT thereby inducing multiple signaling pathways such as MAP kinase activation, calcium influx and cellular adhesion. However, the role of GRB2 family members in controlling TCR and LAT mediated signaling in mature human T cells is not completely understood. Moreover, the relative role of GRB2 family members in the extent and timing of the recruitment of SH3 domain ligands to the LAT complex is unknown. Our hypothesis is that these proteins recruit distinct sets of ligands to the LAT complex that can drive differential downstream signaling events. As presented in CHAPTER III, we developed microRNA and shRNA targeting viral vectors to effectively inhibit the expression of GRB2 and GADS in human CD4+ T cells to examine the role of these adaptors in mature human T cells. We also established optimized protocols for high efficacy retro or lentiviral transduction of human T cell lines, activated and hard-to-transduce non-activated primary human CD4+ T cells. In CHAPTER IV, we demonstrate the requirement for GRB2 in TCR-induced IL-2 and IFN-γ release. The defects in cytokine release in the absence of GRB2 were attributed to diminished formation of LAT signaling microclusters, which resulted in reduced MAP kinase activation, calcium flux and PLC-γ1 recruitment to LAT signaling clusters.

[发布机构] University of Iowa