ABSTRACT
T cell responses are determined by the environment in which antigen is encountered. In the absence of proper costimulation, anergizing stimuli induce the activation of a specific program of gene expression. Proteins encoded by these genes impose a state of functional unresponsiveness in anergic T cells through the activation of different mechanisms that include dampening of the T cell receptor signaling and direct inhibition of cytokine expression. Anergy can be reversed by stimulating T cells in the presence of interleukin (IL-)2. Signaling through the IL-2 receptor has been shown to activate mTOR, which plays an important role in the integration of signals that determine the fate of T cells. The mechanisms underlying the IL-2-dependent regulation of T cell tolerance are still not fully elucidated. In this study we show that IL-2 receptor signaling mediated through JAK3 and mTOR inhibits the expression of anergy-inducing genes independently of any effect on cell cycle progression. Interestingly, we also show that this effect is likely due to changes on the levels of AP-1 activation induced by IL-2 receptor signaling in T cells. Our data identifies a mechanism that can explain how IL-2 may prevent or reverse the establishment of anergy in T cells and, therefore, helps to understand how the cytokine environment can be determinant to shape the outcome of T cell responses - tolerance or activation - when antigen is encountered.
Subject(s)
Cell Cycle/immunology , Gene Expression Regulation/immunology , Interleukin-2/immunology , Signal Transduction/immunology , T-Lymphocytes/immunology , Animals , Clonal Anergy , Janus Kinase 3/immunology , Mice , Mice, Inbred BALB C , Protein Kinases/immunology , Receptors, Interleukin-2/immunology , T-Lymphocytes/cytology , TOR Serine-Threonine Kinases , Transcription Factor AP-1/immunologyABSTRACT
In T cells anergy may be evoked by an unbalanced stimulation of the T-cell receptor in the absence of costimulation. Anergic T cells are unresponsive to new antigen receptor engagement and do not produce interleukin 2. We present evidence that anergizing stimuli induce changes in histone acetylation, which mediates transcriptional repression of interleukin 2 expression. In response to calcium signaling, anergic T cells up-regulate the expression of Ikaros, a zinc finger transcription factor essential for lymphoid lineage determination. Ikaros binds to the interleukin 2 promoter where it induces histone deacetylation. Confirming the role of Ikaros in the induction of T-cell anergy, cells with reduced Ikaros activity show defective inactivation in response to an anergizing stimulus. We propose a model in which tolerizing stimuli induce epigenetic changes on the interleukin 2 locus that are responsible for the stable inhibition of the expression of this cytokine in anergic T cells.
Subject(s)
Clonal Anergy/genetics , Clonal Anergy/immunology , Histones/metabolism , Ikaros Transcription Factor/metabolism , Interleukin-2/genetics , T-Lymphocytes/immunology , T-Lymphocytes/metabolism , Acetylation , Animals , Epigenesis, Genetic , Humans , Ikaros Transcription Factor/genetics , In Vitro Techniques , Jurkat Cells , Lymphocyte Activation , Mice , Mice, Inbred C57BL , Models, Immunological , Promoter Regions, Genetic , Th1 Cells/immunology , Th1 Cells/metabolism , Transcription, GeneticABSTRACT
The conformational flexibility of a series of diastereomeric cyclic urea HIV-1 protease inhibitors has been examined using the Low Mode:Monte Carlo conformational search method. Force fields were validated by a comparison of the energetic ordering of the minimum energy structures on the AMBER/GBSA(water), OPLSAA/GBSA(water) and HF/6-311G/SCRF(water) surfaces. The energetic ordering of the minima on the OPLSAA /GBSA(water) surface was in better agreement with the quantum calculations than the ordering on the AMBER/GBSA(water) surface. An ensemble of low energy structures was generated using OPLSAA/GBSA(water) and used to compare the molecular shape and flexibility of each diastereomer to the experimentally determined binding affinities and crystal structures of closely related systems. The results indicate that diastereomeric solution-phase energetic stability, conformational rigidity and ability to adopt a chair conformation correlate strongly with experimental binding affinities. Rigid body docking suggests that all of the diastereomers adopt solution-phase conformations suitable for alignment with the HIV-1 protease; however, these results indicate that the binding affinities are dependent upon subtle differences in the P1/P1' and P2/P2' substituent orientations.
Subject(s)
HIV Protease Inhibitors/chemistry , HIV Protease/metabolism , Models, Molecular , Monte Carlo Method , Binding Sites , HIV Protease/chemistry , HIV Protease Inhibitors/metabolism , Molecular Conformation , Protein Conformation , Solutions , Stereoisomerism , Urea/chemistryABSTRACT
The Low Mode (LM) and Monte Carlo (MC) conformational search methods were compared on three diverse molecular systems; (4R, 5S, 6S, 7R)-hexahydro-5,6-dihydroxy-1,3,4,7-tetrakis(phenylmethyl)-2H-1,3-diazapin-2-one (1), 2-methoxy-2-phenyl-2-triflouromethyl-N-alpha-methyl benzyl propanamide (2) and a trimeric 39-membered polyazamacrolide (3). We find that either method, or a combination of the methods, is equally efficient at searching the conformational space of the smaller molecular systems while a 50:50 hybrid of Low Mode and Monte Carlo is most efficient at searching the space of the larger molecular system.
