The transcription factor NFAT promotes exhaustion of activated CD8⁺ T cells.

During persistent antigen stimulation, CD8(+) T cells show a gradual decrease in effector function, referred to as exhaustion, which impairs responses in the setting of tumors and infections. Here we demonstrate that the transcription factor NFAT controls the program of T cell exhaustion. When expressed in cells, an engineered form of NFAT1 unable to interact with AP-1 transcription factors diminished T cell receptor (TCR) signaling, increased the expression of inhibitory cell surface receptors, and interfered with the ability of CD8(+) T cells to protect against Listeria infection and attenuate tumor growth in vivo. We defined the genomic regions occupied by endogenous and engineered NFAT1 in primary CD8(+) T cells and showed that genes directly induced by the engineered NFAT1 overlapped with genes expressed in exhausted CD8(+) T cells in vivo. Our data show that NFAT promotes T cell anergy and exhaustion by binding at sites that do not require cooperation with AP-1.

Selective inhibition of CD4+ T-cell cytokine production and autoimmunity by BET protein and c-Myc inhibitors.

Bromodomain-containing proteins bind acetylated lysine residues on histone tails and are involved in the recruitment of additional factors that mediate histone modifications and enable transcription. A compound, I-BET-762, that inhibits binding of an acetylated histone peptide to proteins of the bromodomain and extra-terminal domain (BET) family, was previously shown to suppress the production of proinflammatory proteins by macrophages and block acute inflammation in mice. Here, we investigated the effect of short-term treatment with I-BET-762 on T-cell function. Treatment of naïve CD4(+) T cells with I-BET-762 during the first 2 d of differentiation had long-lasting effects on subsequent gene expression and cytokine production. Gene expression analysis revealed up-regulated expression of several antiinflammatory gene products, including IL-10, Lag3, and Egr2, and down-regulated expression of several proinflammatory cytokines including GM-CSF and IL-17. The short 2-d treatment with I-BET-762 inhibited the ability of antigen-specific T cells, differentiated under Th1 but not Th17 conditions in vitro, to induce pathogenesis in an adoptive transfer model of experimental autoimmune encephalomyelitis. The suppressive effects of I-BET-762 on T-cell mediated inflammation in vivo were accompanied by decreased recruitment of macrophages, consistent with decreased GM-CSF production by CNS-infiltrating T cells. These effects were mimicked by an inhibitor of c-myc function, implicating reduced expression of c-myc and GM-CSF as one avenue by which I-BET-762 suppresses the inflammatory functions of T cells. Our study demonstrates that inhibiting the functions of BET-family proteins during early T-cell differentiation causes long-lasting suppression of the proinflammatory functions of Th1 cells.

Ten-Eleven-Translocation 2 (TET2) negatively regulates homeostasis and differentiation of hematopoietic stem cells in mice.

The Ten-Eleven-Translocation 2 (TET2) gene encodes a member of TET family enzymes that alters the epigenetic status of DNA by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). Somatic loss-of-function mutations of TET2 are frequently observed in patients with diverse myeloid malignancies, including myelodysplastic syndromes, myeloproliferative neoplasms, and chronic myelomonocytic leukemia. By analyzing mice with targeted disruption of the Tet2 catalytic domain, we show here that Tet2 is a critical regulator of self-renewal and differentiation of hematopoietic stem cells (HSCs). Tet2 deficiency led to decreased genomic levels of 5hmC and augmented the size of the hematopoietic stem/progenitor cell pool in a cell-autonomous manner. In competitive transplantation assays, Tet2-deficient HSCs were capable of multilineage reconstitution and possessed a competitive advantage over wild-type HSCs, resulting in enhanced hematopoiesis into both lymphoid and myeloid lineages. In vitro, Tet2 deficiency delayed HSC differentiation and skewed development toward the monocyte/macrophage lineage. Our data indicate that Tet2 has a critical role in regulating the expansion and function of HSCs, presumably by controlling 5hmC levels at genes important for the self-renewal, proliferation, and differentiation of HSCs.

NFATc1 affects mouse splenic B cell function by controlling the calcineurin--NFAT signaling network.

By studying mice in which the Nfatc1 gene was inactivated in bone marrow, spleen, or germinal center B cells, we show that NFATc1 supports the proliferation and suppresses the activation-induced cell death of splenic B cells upon B cell receptor (BCR) stimulation. BCR triggering leads to expression of NFATc1/αA, a short isoform of NFATc1, in splenic B cells. NFATc1 ablation impaired Ig class switch to IgG3 induced by T cell-independent type II antigens, as well as IgG3(+) plasmablast formation. Mice bearing NFATc1(-/-) B cells harbor twofold more interleukin 10-producing B cells. NFATc1(-/-) B cells suppress the synthesis of interferon-γ by T cells in vitro, and these mice exhibit a mild clinical course of experimental autoimmune encephalomyelitis. In large part, the defective functions of NFATc1(-/-) B cells are caused by decreased BCR-induced Ca(2+) flux and calcineurin (Cn) activation. By affecting CD22, Rcan1, CnA, and NFATc1/αA expression, NFATc1 controls the Ca(2+)-dependent Cn-NFAT signaling network and, thereby, the fate of splenic B cells upon BCR stimulation.

Impaired hydroxylation of 5-methylcytosine in myeloid cancers with mutant TET2.

TET2 is a close relative of TET1, an enzyme that converts 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) in DNA. The gene encoding TET2 resides at chromosome 4q24, in a region showing recurrent microdeletions and copy-neutral loss of heterozygosity (CN-LOH) in patients with diverse myeloid malignancies. Somatic TET2 mutations are frequently observed in myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), MDS/MPN overlap syndromes including chronic myelomonocytic leukaemia (CMML), acute myeloid leukaemias (AML) and secondary AML (sAML). We show here that TET2 mutations associated with myeloid malignancies compromise catalytic activity. Bone marrow samples from patients with TET2 mutations displayed uniformly low levels of 5hmC in genomic DNA compared to bone marrow samples from healthy controls. Moreover, small hairpin RNA (shRNA)-mediated depletion of Tet2 in mouse haematopoietic precursors skewed their differentiation towards monocyte/macrophage lineages in culture. There was no significant difference in DNA methylation between bone marrow samples from patients with high 5hmC versus healthy controls, but samples from patients with low 5hmC showed hypomethylation relative to controls at the majority of differentially methylated CpG sites. Our results demonstrate that Tet2 is important for normal myelopoiesis, and suggest that disruption of TET2 enzymatic activity favours myeloid tumorigenesis. Measurement of 5hmC levels in myeloid malignancies may prove valuable as a diagnostic and prognostic tool, to tailor therapies and assess responses to anticancer drugs.

Requirement for balanced Ca/NFAT signaling in hematopoietic and embryonic development.

NFAT transcription factors are highly phosphorylated proteins residing in the cytoplasm of resting cells. Upon dephosphorylation by the phosphatase calcineurin, NFAT proteins translocate to the nucleus, where they orchestrate developmental and activation programs in diverse cell types. NFAT is rephosphorylated and inactivated through the concerted action of at least 3 different kinases: CK1, GSK-3, and DYRK. The major docking sites for calcineurin and CK1 are strongly conserved throughout vertebrate evolution, and conversion of either the calcineurin docking site to a high-affinity version or the CK1 docking site to a low-affinity version results in generation of hyperactivable NFAT proteins that are still fully responsive to stimulation. In this study, we generated transgenic mice expressing hyperactivable versions of NFAT1 from the ROSA26 locus. We show that hyperactivable NFAT increases the expression of NFAT-dependent cytokines by differentiated T cells as expected, but exerts unexpected signal-dependent effects during T cell differentiation in the thymus, and is progressively deleterious for the development of B cells from hematopoietic stem cells. Moreover, progressively hyperactivable versions of NFAT1 are increasingly deleterious for embryonic development, particularly when normal embryos are also present in utero. Forced expression of hyperactivable NFAT1 in the developing embryo leads to mosaic expression in many tissues, and the hyperactivable proteins are barely tolerated in organs such as brain, and cardiac and skeletal muscle. Our results highlight the need for balanced Ca/NFAT signaling in hematopoietic stem cells and progenitor cells of the developing embryo, and emphasize the evolutionary importance of kinase and phosphatase docking sites in preventing inappropriate activation of NFAT.

Hair loss and defective T- and B-cell function in mice lacking ORAI1.

ORAI1 is a pore subunit of the store-operated Ca(2+) release-activated Ca(2+) (CRAC) channel. To examine the physiological consequences of ORAI1 deficiency, we generated mice with targeted disruption of the Orai1 gene. The results of immunohistochemical analysis showed that ORAI1 is expressed in lymphocytes, skin, and muscle of wild-type mice and is not expressed in Orai1(-/-) mice. Orai1(-/-) mice with the inbred C57BL/6 background showed perinatal lethality, which was overcome by crossing them to outbred ICR mice. Orai1(-/-) mice were small in size, with eyelid irritation and sporadic hair loss resembling the cyclical alopecia observed in mice with keratinocyte-specific deletion of the Cnb1 gene. T and B cells developed normally in Orai1(-/-) mice, but B cells showed a substantial decrease in Ca(2+) influx and cell proliferation in response to B-cell receptor stimulation. Naïve and differentiated Orai1(-/-) T cells showed substantial reductions in store-operated Ca(2+) entry, CRAC currents, and cytokine production. These features are consistent with the severe combined immunodeficiency and mild extraimmunological symptoms observed in a patient with a missense mutation in human ORAI1 and distinguish the ORAI1-null mice described here from a previously reported Orai1 gene-trap mutant mouse which may be a hypomorph rather than a true null.

Mouse Eri1 interacts with the ribosome and catalyzes 5.8S rRNA processing.

Eri1 is a 3'-to-5' exoribonuclease conserved from fission yeast to humans. Here we show that Eri1 associates with ribosomes and ribosomal RNA (rRNA). Ribosomes from Eri1-deficient mice contain 5.8S rRNA that is aberrantly extended at its 3' end, and Eri1, but not a catalytically inactive mutant, converts this abnormal 5.8S rRNA to the wild-type form in vitro and in cells. In human and murine cells, Eri1 localizes to the cytoplasm and nucleus, with enrichment in the nucleolus, the site of preribosome biogenesis. RNA binding residues in the Eri1 SAP and linker domains promote stable association with rRNA and thereby facilitate 5.8S rRNA 3' end processing. Taken together, our findings indicate that Eri1 catalyzes the final trimming step in 5.8S rRNA processing, functionally and spatially connecting this regulator of RNAi with the basal translation machinery.

The principal neuronal gD-type 3-O-sulfotransferases and their products in central and peripheral nervous system tissues.

Within the nervous system, heparan sulfate (HS) of the cell surface and extracellular matrix influences developmental, physiologic and pathologic processes. HS is a functionally diverse polysaccharide that employs motifs of sulfate groups to selectively bind and modulate various effector proteins. Specific HS activities are modulated by 3-O-sulfated glucosamine residues, which are generated by a family of seven 3-O-sulfotransferases (3-OSTs). Most isoforms we herein designate as gD-type 3-OSTs because they generate HS(gD+), 3-O-sulfated motifs that bind the gD envelope protein of herpes simplex virus 1 (HSV-1) and thereby mediate viral cellular entry. Certain gD-type isoforms are anticipated to modulate neurobiologic events because a Drosophila gD-type 3-OST is essential for a conserved neurogenic signaling pathway regulated by Notch. Information about 3-OST isoforms expressed in the nervous system of mammals is incomplete. Here, we identify the 3-OST isoforms having properties compatible with their participation in neurobiologic events. We show that 3-OST-2 and 3-OST-4 are principal isoforms of brain. We find these are gD-type enzymes, as they produce products similar to a prototypical gD-type isoform, and they can modify HS to generate receptors for HSV-1 entry into cells. Therefore, 3-OST-2 and 3-OST-4 catalyze modifications similar or identical to those made by the Drosophila gD-type 3-OST that has a role in regulating Notch signaling. We also find that 3-OST-2 and 3-OST-4 are the predominant isoforms expressed in neurons of the trigeminal ganglion, and 3-OST-2/4-type 3-O-sulfated residues occur in this ganglion and in select brain regions. Thus, 3-OST-2 and 3-OST-4 are the major neural gD-type 3-OSTs, and so are prime candidates for participating in HS-dependent neurobiologic events.

Activity of the A3 adenosine receptor gene promoter in transgenic mice: characterization of previously unidentified sites of expression.

Sites of A3 adenosine receptor gene expression have not been fully explored nor has this gene's promoter activity been confirmed in vivo. Transgenic mice were generated in which 2.3 kb upstream of the transcriptional start site of the mouse A3 adenosine receptor was coupled to a beta-galactosidase reporter gene. Selective transgene expression was detected in testis and brain as well as at other sites in which A3 adenosine receptor message has not been previously reported, including retinal ganglion cells and smooth muscle cells of the cerebrospinal vasculature. Our study suggests that this promoter may be useful in the selective targeting of gene expression to specific tissues.