Cell-autonomous requirement for TCF1 and LEF1 in the development of Natural Killer T cells.

Natural killer T (NKT) cells develop from common CD4(+) CD8(+) thymocyte precursors. Transcriptional programs that regulate the development of NKT cells in the thymus development remain to be fully delineated. Here, we demonstrate a cell-intrinsic requirement for transcription factors TCF1 and LEF1 for the development of all subsets of NKT cells. Conditional deletion of TCF1 alone results in a substantial reduction in NKT cells. The remaining NKT cells are eliminated when TCF1 and LEF1 are both deleted. These data reveal an essential role for TCF1 and LEF1 in development of NKT cells.

ß-Catenin is required for the differentiation of iNKT2 and iNKT17 cells that augment IL-25-dependent lung inflammation.

BACKGROUND: Invariant Natural Killer T (iNKT) cells have been implicated in lung inflammation in humans and also shown to be a key cell type in inducing allergic lung inflammation in mouse models. iNKT cells differentiate and acquire functional characteristics during development in the thymus. However, the correlation between development of iNKT cells in the thymus and role in lung inflammation remains unknown. In addition, transcriptional control of differentiation of iNKT cells into iNKT cell effector subsets in the thymus during development is also unclear. In this report we show that ß-catenin dependent mechanisms direct differentiation of iNKT2 and iNKT17 subsets but not iNKT1 cells. METHODS: To study the role for ß-catenin in lung inflammation we utilize mice with conditional deletion and enforced expression of ß-catenin in a well-established mouse model for IL-25-dependen lung inflammation. RESULTS: Specifically, we demonstrate that conditional deletion of ß-catenin permitted development of mature iNKT1 cells while impeding maturation of iNKT2 and 17 cells. A role for ß-catenin expression in promoting iNKT2 and iNKT17 subsets was confirmed when we noted that enforced transgenic expression of ß-catenin in iNKT cell precursors enhanced the frequency and number of iNKT2 and iNKT17 cells at the cost of iNKT1 cells. This effect of expression of ß-catenin in iNKT cell precursors was cell autonomous. Furthermore, iNKT2 cells acquired greater capability to produce type-2 cytokines when ß-catenin expression was enhanced. DISCUSSION: This report shows that ß-catenin deficiency resulted in a profound decrease in iNKT2 and iNKT17 subsets of iNKT cells whereas iNKT1 cells developed normally. By contrast, enforced expression of ß-catenin promoted the development of iNKT2 and iNKT17 cells. It was important to note that the majority of iNKT cells in the thymus of C57BL/6 mice were iNKT1 cells and enforced expression of ß-catenin altered the pattern to iNKT2 and iNKT17 cells suggesting that ß-catenin may be a major factor in the distinct pathways that critically direct differentiation of iNKT effector subsets. CONCLUSIONS: Thus, we demonstrate that ß-catenin expression in iNKT cell precursors promotes differentiation toward iNKT2 and iNKT17 effector subsets and supports enhanced capacity to produce type 2 and 17 cytokines which in turn augment lung inflammation in mice.

Transcription factors and target genes of pre-TCR signaling.

Almost 30 years ago pioneering work by the laboratories of Harald von Boehmer and Susumo Tonegawa provided the first indications that developing thymocytes could assemble a functional TCRß chain-containing receptor complex, the pre-TCR, before TCRα expression. The discovery and study of the pre-TCR complex revealed paradigms of signaling pathways in control of cell survival and proliferation, and culminated in the recognition of the multifunctional nature of this receptor. As a receptor integrated in a dynamic developmental process, the pre-TCR must be viewed not only in the light of the biological outcomes it promotes, but also in context with those molecular processes that drive its expression in thymocytes. This review article focuses on transcription factors and target genes activated by the pre-TCR to drive its different outcomes.

T cell factor-1 controls the lifetime of CD4+ CD8+ thymocytes in vivo and distal T cell receptor α-chain rearrangement required for NKT cell development.

Natural killer T (NKT) cells are a component of innate and adaptive immune systems implicated in immune, autoimmune responses and in the control of obesity and cancer. NKT cells develop from common CD4+ CD8+ double positive (DP) thymocyte precursors after the rearrangement and expression of T cell receptor (TCR) Vα14-Jα18 gene. Temporal regulation and late appearance of Vα14-Jα18 rearrangement in immature DP thymocytes has been demonstrated. However, the precise control of lifetime of DP thymocytes in vivo that enables distal rearrangements remains incompletely defined. Here we demonstrate that T cell factor (TCF)-1, encoded by the Tcf7 gene, is critical for the extended lifetime of DP thymocytes. TCF-1-deficient DP thymocytes fail to undergo TCR Vα14-Jα18 rearrangement and produce significantly fewer NKT cells. Ectopic expression of Bcl-xL permits Vα14-Jα18 rearrangement and rescues NKT cell development. We report that TCF-1 regulates expression of RORγt, which regulates DP thymocyte survival by controlling expression of Bcl-xL. We posit that TCF-1 along with its cofactors controls the lifetime of DP thymocytes in vivo.

NFAT5 induction by the pre-T-cell receptor serves as a selective survival signal in T-lymphocyte development.

The Rel-like transcription factors nuclear factor kappa B (NF-κB) and the calcineurin-dependent nuclear factor of activated T cells (NFATc) control specific points of thymocyte maturation. Thymocytes also express a distinct member of the Rel family, the calcineurin-independent, osmostress response regulator NFAT5. Here we show that IKKß regulates the expression of NFAT5 in thymocytes, which in turn contributes to the survival of T-cell receptor αß thymocytes and the transition from the ß-selection checkpoint to the double-positive stage in an osmostress-independent manner. NFAT5-deficient thymocytes had normal expression and proximal signaling of the pre-T-cell receptor but exhibited a partial defect in ß-chain allelic exclusion and increased apoptosis. Further analysis showed that NFAT5 regulated the expression of the prosurvival factors A1 and Bcl2 and attenuated the proapoptotic p53/Noxa axis. These findings position NFAT5 as a target of the IKKß/NF-κB pathway in thymocytes and as a downstream effector of the prosurvival role of the pre-T-cell receptor.

IL-4 and IL-4 receptor expression is dispensable for the development and function of natural killer T cells.

CD4 T cells acquire functional properties including cytokine production upon antigenic stimulation through the T cell receptor (TCR) and differentiate into T helper (Th) cells. Th1 cells produce interferon (IFN)-γ and Th2 cells produce interleukin (IL)-4. Th1 and 2 cells utilize IFN-γ and IL-4 for further maturation and maintenance, respectively. Promyelocytic leukemia zinc finger (PLZF)-expressing invariant natural killer T (iNKT) cells develop in the thymus and acquire functional ability to produce IL-4 and IFN-γ in the thymus in the absence of antigenic stimulation. In response to antigenic stimulation, iNKT cells rapidly produce IFN-γ and IL-4. However, it is still unknown as to whether iNKT cells require these cytokines for maturation or survival in vivo. In this study, using IL-4- and IL-4 receptor- (IL-4R) deficient mice, we demonstrate that IL-4 as well as IL-4R expression is dispensable for the development, function and maintenance of iNKT cells.

Gene expression induced by Toll-like receptors in macrophages requires the transcription factor NFAT5.

Toll-like receptors (TLRs) engage networks of transcriptional regulators to induce genes essential for antimicrobial immunity. We report that NFAT5, previously characterized as an osmostress responsive factor, regulates the expression of multiple TLR-induced genes in macrophages independently of osmotic stress. NFAT5 was essential for the induction of the key antimicrobial gene Nos2 (inducible nitric oxide synthase [iNOS]) in response to low and high doses of TLR agonists but is required for Tnf and Il6 mainly under mild stimulatory conditions, indicating that NFAT5 could regulate specific gene patterns depending on pathogen burden intensity. NFAT5 exhibited two modes of association with target genes, as it was constitutively bound to Tnf and other genes regardless of TLR stimulation, whereas its recruitment to Nos2 or Il6 required TLR activation. Further analysis revealed that TLR-induced recruitment of NFAT5 to Nos2 was dependent on inhibitor of κB kinase (IKK) ß activity and de novo protein synthesis, and was sensitive to histone deacetylases. In vivo, NFAT5 was necessary for effective immunity against Leishmania major, a parasite whose clearance requires TLRs and iNOS expression in macrophages. These findings identify NFAT5 as a novel regulator of mammalian anti-pathogen responses.

NFAT5 regulates T lymphocyte homeostasis and CD24-dependent T cell expansion under pathologic hypernatremia.

Immune cells rely on the transcription factor NFAT5 to adapt to hypertonic stress. The hypertonicity-dependent role of NFAT5 in T cells in vivo remains unclear because mouse models of NFAT5 deficiency have produced substantially different T cell phenotypes. In this study, we analyzed the T cell compartment in NFAT5-null and T cell-specific NFAT5 knockout mice. We found that NFAT5-null mice had constitutive, pronounced hypernatremia and suffered a severe immunodeficiency, with T cell lymphopenia, altered CD8 naive/memory homeostasis, and inability to reject allogeneic tumors. By contrast, T cell-specific NFAT5 knockout mice had normal plasma tonicity, rejected allogeneic tumors, and exhibited only a mild, low-penetrance memory bias in CD8 cells. Notably, when T cells from these mice were cultured ex vivo in hypernatremic media, they exhibited features found in NFAT5-null mice, with pronounced naive/memory imbalance and impaired homeostatic survival in response to IL-7, as well as a severe inhibition of their mitogen-induced proliferation. By analyzing surface receptors whose expression might be affected in NFAT5-deficient cells, we identified CD24 as a novel NFAT5 target induced by hypertonicity both in vitro and in vivo, and required to sustain T cell expansion under osmostress. NFAT5 bound to the Cd24 promoter in response to hypertonicity facilitated the local derepression of chromatin and enhanced the expression of CD24 mRNA and protein. Altogether, our results indicate that the systemic hypernatremia of NFAT5-null mice is a major contributor to their immunodeficiency, and highlight the role of NFAT5 and CD24 in the homeostasis of T cells under osmostress in vivo.