Glutamine uptake and metabolism are coordinately regulated by ERK/MAPK during T lymphocyte activation.

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.

Microarray data reveal relationship between Jag1 and Ddr1 in mouse liver.

Alagille syndrome is an autosomal dominant disorder involving bile duct paucity and cholestasis in addition to cardiac, skeletal, ophthalmologic, renal and vascular manifestations. Mutations in JAG1, encoding a ligand in the Notch signaling pathway, are found in 95% of patients meeting clinical criteria for Alagille syndrome. In order to define the role of Jag1 in the bile duct developmental abnormalities seen in ALGS, we previously created a Jag1 conditional knockout mouse model. Mice heterozygous for the Jag1 conditional and null alleles demonstrate abnormalities in postnatal bile duct growth and remodeling, with portal expansion and increased numbers of malformed bile ducts. In this study we report the results of microarray analysis and identify genes and pathways differentially expressed in the Jag1 conditional/null livers as compared with littermate controls. In the initial microarray analysis, we found that many of the genes up-regulated in the Jag1 conditional/null mutant livers were related to extracellular matrix (ECM) interactions, cell adhesion and cell migration. One of the most highly up-regulated genes was Ddr1, encoding a receptor tyrosine kinase (RTK) belonging to a large RTK family. We have found extensive co-localization of Jag1 and Ddr1 in bile ducts and blood vessels in postnatal liver. In addition, co-immunoprecipitation data provide evidence for a novel protein interaction between Jag1 and Ddr1. Further studies will be required to define the nature of this interaction and its functional consequences, which may have significant implications for bile duct remodeling and repair of liver injury.

Tsc1+ and tsc2+ regulate arginine uptake and metabolism in Schizosaccharomyces pombe.

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 wild-type rhb1+. Expression of the tsc2+ gene with a patient-derived 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.