Biochemical Basis of T Cell Activation

Division Of Basic Sciences - Nci

Investigators

Linked publications, trials & patents

Abstract

Engagement of multicomponent immunoreceptors such as the T cell antigen receptor results in rapid recruitment and activation of multiple protein tyrosine kinases (PTKs) including Lck, Fyn, ZAP-70 and Itk. These PTKs then phosphorylate many enzymes and adapter molecules involved in complex signaling cascades. Our studies have focused on a critical substrate of the PTKs, LAT (linker for activation of T cells), a 36-38kD integral membrane adapter protein. We have performed studies to characterize how LAT is phosphorylated and then binds many critical signaling molecules, thus bringing other adapter molecules and enzymes in multimolecular complexes to the plasma membrane in the vicinity of the activated TCR. Biochemical, biophysical, microscopic and genetic techniques are currently employed to study the characteristics of LAT-based signaling complexes and the enzyme pathways that are coupled to and activated at LAT complexes. In the past year we have published studies that focus on different aspects of TCR-mediated signaling. The first was described briefly in the last annual report. We had already demonstrated that LAT-based complexes known as microclusters are formed upon T cell activation and are the site where signaling complexes are formed. We demonstrated that microclusters contain two spatially separate domains, one with the TCR and associated ZAP-70 PTK, and the other with LAT and LAT-bound signaling molecules. A kinetic analysis of the formation of the microclusters revealed that molecules are recruited in a step-wise fashion beginning with ZAP-70 recruitment to the TCR followed by LAT and other signaling proteins and then by molecules involved in microcluster dissociation. Current studies are expanding on these observations to understand other signaling events and to use these results to make new forms of clinically relevant chimeric antigen receptors. This year we continued our studies on another set of molecules that may have a role in T cell function and T cell signaling. TMC6 and TMC8 are highly expressed in T cells. Mutations in either of them lead to the premalignant skin condition known as epdermodysplasia verucciformis. We demonstrated this year in an article that these two proteins heterodimerize and form a trimeric complex with the protein CIB1. Knock-out of the genes encoding either TMC6 or TMC8 lead to a decrease in protein expression of all three proteins. We are currently studying these mice and a double knock-out of both TMC6 and TMC8 to determine the role of these proteins in the T cell response to antigen.