Regulation of interferon-γ gene expression by nuclear factor of activated T cells

Abstract

IntroductionIn response to antigen stimulation, cells of the immune system initiate the expression of activation-induced genes through the coordinate action of transcription factors at gene regulatory elements. The nuclear factor of activated T cells (NFAT), originally identified as a nuclear complex binding to the antigen-response element of the IL-2 gene, 1 has been implicated in the regulation of various inducible genes, particularly those encoding cytokines and cell surface receptors. 2 Sequence inspection, in vitro binding assays, and overexpression studies have identified potential binding sites for NFAT in the promoters and enhancers of numerous genes, including those encoding interleukin-2 (IL-2), IL-3, IL-4, IL-5, tumor necrosis factor ␣ (TNF-␣), granulocyte macrophagecolony-stimulating factor (GM-CSF), CD40L, FasL, CD25, b-type natriuretic peptide, and the adipocyte-specific protein aP2. [2][3][4][5] In general, NFAT is thought to act as a positive regulator of gene expression. For instance, IL-2 production is profoundly compromised in patients unable to generate functional NFAT complexes, 6 and peptides based on the calcineurin-docking site of NFAT proteins, which specifically inhibit the activation of NFAT, impair the production of IL-2 and other cytokines in vitro. 7 To date, 4 calcium-regulated members of the NFAT family (NFAT1-4; also known as NFATc1-4 and hereafter abbreviated NFAT), with distinct but overlapping tissue distributions, have been identified. [8][9][10][11][12][13][14][15] A fifth protein, NFAT5/TonEBP, 16,17 is regulated by osmotic shock. NFAT3 is expressed predominantly outside the immune system, whereas NFAT1 (NFATp, NFATc2), NFAT2 (NFATc, NFATc1), and NFAT4 (NFATx, NFATc3) can be found in immune cells including T cells, B cells, natural killer (NK) cells, macrophages, and mast cells. 2,10,[18][19][20][21] Although NFAT proteins are expressed in multiple cell types, their regulation has been extensively studied in T and B cells, where they are present as phosphoproteins in the cytoplasm of resting cells. After cell stimulation, 4 consecutive steps lead to the activation of NFAT: dephosphorylation by the calcium-dependent phosphatase calcineurin, a process inhibited by the immunosuppressive drugs cyclosporin A and FK506 [22][23][24][25][26] ; translocation into the nucleus 18,23,27 ; binding to specific DNA elements in the regulatory regions of target genes, which occurs in physical or functional cooperation with other transcription factors including AP-1 (Fos/Jun), c-Maf (Maf), and GATA-family proteins 2,4,22,[28][29][30] ; and interaction with known or putative coactivator proteins such as p300, CBP, and NIP-45. [31][32][33] After antigen stimulation, CD4 ϩ T cells differentiate into at least 2 types of effector cells that differ as to the pattern of cytokines they produce on restimulation. [34][35][36] Th1 cells are defined by the production of interferon-␥ (IFN-␥) and mediate predominantly cellular immune responses, whereas the signature cytokines of Th2 cells-IL-4, IL-5, and ...

Selective inhibition of calcineurin-NFAT signaling by blocking protein–protein interaction with small organic molecules

“…Treatment of Cl.7W2 T cells with the phorbol ester phorbol 12-myristate 13-acetate (PMA) and ionomycin caused rapid induction of the mRNAs for tumor necrosis factor (TNF)-␣, IFN-␥, granulocyte-macrophage͞colony-stimulating factor (GM-CSF), lymphotactin (Ltn), macrophage inflammatory protein (MIP)-1␣, and MIP-1␤. Consistent with previous work (51)(52)(53)(54)(55), the increase in levels of these mRNAs was blocked by inhibiting calcineurin with a combination of CsA and FK506. Cytokine mRNA induction was likewise inhibited by 20 M or 40 M INCA-6, with 40 M INCA-6 reducing mRNA levels to those in unstimulated cells.…”

A Distal Enhancer in the Interferon-γ (IFN-γ) Locus Revealed by Genome Sequence Comparison

“…Interestingly, mice deficient in T-bet exhibit a drastic reduction in IFN-␥ expression by CD4 T cells and NK cells, whereas CD8 T cells seem largely unaffected (22). In contrast, NFAT is required for IFN-␥ expression by both CD4 and CD8 T cells (21). It will be interesting to determine, therefore, whether targeted deletion of the 5Ј CNS in the mouse IFN-␥ locus results in decreased expression in all IFN-␥-producing cell types or only in a subset of lineages.…”

“…This process involves NFAT, a transcription factor that is regulated by calcineurin and cooperates with AP-1 (Fos-Jun) to induce the transcription of numerous immune response genes (18,19). Th1 cells lacking one or more members of the NFAT family show decreased expression of IFN-␥ upon activation, indicating an important cell-intrinsic role for NFAT in regulating the transcription of this cytokine gene (20,21). Secreted IFN-␥ feeds back through STAT1 to activate T-bet, a member of the T-box family of transcription factors that is essential for optimal IFN-␥ expression by CD4 T cells (22)(23)(24)(25)(26).…”

Ionizing radiation synergistic induction of cyclooxygenase-2 with benzo[a]pyrene diol-epoxide through nuclear factor of activated T cells in mouse epidermal Cl 41 cells

“…NFAT has been reported to bind to the promoter sequences of cytokine genes or the early immune response gene, and up-regulate expression of these genes in T-cells during immune responses (39). Different isoforms of NFAT are distributed in various tissues and show different patterns of inducibility by various stimuli (39).…”

“…Different isoforms of NFAT are distributed in various tissues and show different patterns of inducibility by various stimuli (39). COX-2 is induced in a variety of cell types by diverse stimuli including growth factors, mitogens, cytokines, and tumor promoters (40).…”