DNA-PKcs controls the cytotoxic T cell response to cancer and transplant allograft through regulating LAT-dependent signaling.

Formation of the immune synapse (IS) following T cell antigen recognition includes recruitment of the linker for activation of T cells (LAT). Once at the IS, LAT tyrosines are phosphorylated, allowing it to serve as a scaffold for the formation of the "signalosome," a multiprotein complex that drives T cell receptor signaling. Here, we show that upon T cell activation, DNA-dependent protein kinase catalytic subunit (DNA-PKcs) interacts with LAT and localizes to the IS. Inhibition of DNA-PKcs diminishes LAT localization at the IS. We identified two LAT serines phosphorylated by DNA-PKcs, S224 and S241, that impact LAT tyrosine phosphorylation, protein binding, and cytokine production. Using our mouse model designed to delete DNA-PKcs expression in mature CD4(+) or CD8(+) T cells, we show that loss of DNA-PKcs results in T cells that are unable to control tumor growth or induce allogeneic graft rejection. These data highlight DNA-PKcs as a pivotal protein in T cell function.