Activation of a naive T cell is a highly energetic event, which requires a substantial increase in nutrient metabolism. Upon stimulation, T cells increase in size, rapidly proliferate, and differentiate, all of which lead to a high demand for energetic and biosynthetic precursors. Although amino acids are the basic building blocks of protein biosynthesis and contribute to many other metabolic processes, the role of amino acid metabolism in T cell activation has not been well characterized. We have found that glutamine in particular is required for T cell function. Depletion of glutamine blocks proliferation and cytokine production, and this cannot be rescued by supplying biosynthetic precursors of glutamine. Correlating with the absolute requirement for glutamine, T cell activation induces a large increase in glutamine import, but not glutamate import, and this increase is CD28-dependent. Activation coordinately enhances expression of glutamine transporters and activities of enzymes required to allow the use of glutamine as a Krebs cycle substrate in T cells. The induction of glutamine uptake and metabolism requires ERK function, providing a link to TCR signaling. Together, these data indicate that regulation of glutamine use is an important component of T cell activation. Thus, a better understanding of glutamine sensing and use in T cells may reveal novel targets for immunomodulation.

Mutations in either TSC1 or TSC2 cause tuberous sclerosis complex, an autosomal dominant disorder characterized by seizures, mental retardation, and benign tumors of the skin, brain, heart, and kidneys. Homologs for the TSC1 and TSC2 genes have been identified in mouse, rat, Fugu, Drosophila, and in the yeast Schizosaccharomyces pombe. Here we show that S. pombe lacking tsc1 ؉ or tsc2؉ have similar phenotypes including decreased arginine uptake, decreased expression of three amino acid permeases, and low intracellular levels of four members of the arginine biosynthesis pathway. Recently, the small GTPase Rheb was identified as a target of the GTPase-activating domain of tuberin in mammalian cells and in Drosophila. We show that the defect in arginine uptake in cells lacking tsc2 ؉ is rescued by the expression of a dominant negative form of rhb1 ؉ , the Rheb homolog in S. pombe, but not by expressing wildtype rhb1 ؉ . Expression of the tsc2 ؉ gene with a patientderived mutation within the GAP domain did not rescue the arginine uptake defect in tsc2 ؉ mutant yeast. Taken together, these findings support a model in which arginine uptake is regulated through tsc1 ؉ , tsc2 ؉ , and rhb1 ؉ in S. pombe and also suggest a role for the Tsc1 and Tsc2 proteins in amino acid biosynthesis and sensing.Tuberous sclerosis complex (TSC) 1 is a tumor suppressor syndrome that is characterized by the development of a variety of benign tumors (hamartomas) and severe neurological problems including seizures, mental retardation, and autism. TSC is caused by mutations in either TSC1 (1) or TSC2 (2). Hamartin, the TSC1 gene product, and tuberin, the TSC2 gene product, are known to interact (3, 4) and function in a complex. Tuberin has a highly conserved GTPase-activating protein (GAP) domain with activity for Rheb1 (Ras homolog enriched in brain) (5-11), a small GTPase that may be involved in nutrient signaling and cell cycle regulation (12).Studies in Drosophila and mammalian systems have shown that the hamartin-tuberin complex negatively regulates p70S6 kinase (pS6K) within the PI3K signaling pathway (13,14). The regulation of pS6K is mediated by Rheb and by the target of rapamycin, which are components in pathways that control cell size by integrating mitogenic signals and nutrient availability with protein synthesis (11,13,(15)(16)(17)(18). Both hamartin and tuberin are regulated by phosphorylation. Hamartin is phosphorylated by cyclin-dependent kinase CDK1 (19), and tuberin is a substrate for Akt (protein kinase B) (14,20,21), p38-activated kinase MK2 (22), and the AMP-activated protein kinase (23).Schizosaccharomyces pombe contains genes with significant similarity to TSC1 and TSC2, which were named tsc1 ϩ and tsc2 ϩ (24). The GAP domain of tuberin is particularly highly conserved with 39% identity. In addition to TSC1 and TSC2 homologs, S. pombe also has a Rheb homolog, rhb1 ϩ . Loss of rhb1 ϩ in S. pombe results in growth arrest, similar to that caused by nitrogen starvation (25), and loss of farnesylation of the Rhb1 protein has...