Coordination of asparagine uptake and asparagine synthetase expression is required for T cell activation

Abstract

T cell receptor triggering by antigen results in metabolic reprogramming that, in turn, facilitates T cells exit from quiescence. The increased nutrient requirements of activated lymphocytes are met in part by upregulation of cell surface transporters and enhanced uptake of amino acids, fatty acids and glucose from the environment. However, the role of intracellular pathways of amino acid biosynthesis in T cell activation is relatively unexplored. Asparagine (Asn) is a non-essential amino acid that can be synthesized intracellularly through the glutamine-hydrolyzing enzyme asparagine synthetase (ASNS). We set out to define the requirements for uptake of extracellular Asn and ASNS activity in CD8+ T cell activation. At early timepoints of activation, T cells expressed little or no ASNS and, as a consequence, viability and TCR-stimulated growth, activation and metabolic reprogramming were substantially impaired under conditions of Asn deprivation. At later timepoints (>48h of activation), TCR-induced mTOR-dependent signals resulted in upregulation of ASNS, that endowed T cells with the capacity to function independently of extracellular Asn. Thus, we have determined that the coordinated upregulation of ASNS expression and uptake of extracellular Asn is required for optimal T cell effector responses.