Direct regulation of Gata3 expression determines the T helper differentiation potential of Notch

Cooperation of Gata3, c-Myc and Notch in malignant transformation of double positive thymocytes

Gata transcription factors are critical regulators of proliferation and differentiation implicated in various human cancers, but specific genes activated by Gata proteins remain to be identified. We previously reported that enforced expression of Gata3 during T cell development in CD2-Gata3 transgenic mice induced CD4(+)CD8(+) double-positive (DP) T cell lymphoma. Here, we show that the presence of the DO11.10 T-cell receptor transgene, which directs DP cells towards the CD4 lineage, resulted in enhanced lymphoma development and a dramatic increase in thymocyte cell size in CD2-Gata3 transgenic mice. CD2-Gata3 DP cells expressed high levels of the proto-oncogene c-Myc but the Notch1 signaling pathway, which is known to induce c-Myc, was not activated. Gene expression profiling showed that in CD2-Gata3 lymphoma cells transcription of c-Myc and its target genes was further increased. A substantial fraction of CD2-Gata3 lymphomas had trisomy of chromosome 15, leading to an increased c-Myc gene dose. Interestingly, most lymphomas showed high expression of the Notch targets Deltex1 and Hes1, often due to activating Notch1 PEST domain mutations. Therefore, we conclude that enforced Gata3 expression converts DP thymocytes into a pre-malignant state, characterized by high c-Myc expression, whereby subsequent induction of Notch1 signaling cooperates to establish malignant transformation. The finding that Gata3 regulates c-Myc expression levels, in a direct or indirect fashion, may explain the parallel phenotypes of mice with overexpression or deficiency of either of the two transcription factors.

Activation of c-Kit in dendritic cells regulates T helper cell differentiation and allergic asthma

Dendritic cells (DCs) are integral to the differentiation of T helper cells into T helper type 1 T(H)1, T(H)2 and T(H)17 subsets. Interleukin-6 (IL-6) plays an important part in regulating these three arms of the immune response by limiting the T(H)1 response and promoting the T(H)2 and T(H)17 responses. In this study, we investigated pathways in DCs that promote IL-6 production. We show that the allergen house dust mite (HDM) or the mucosal adjuvant cholera toxin promotes cell surface expression of c-Kit and its ligand, stem cell factor (SCF), on DCs. This dual upregulation of c-Kit and SCF results in sustained signaling downstream of c-Kit, promoting IL-6 secretion. Intranasal administration of antigen into c-Kit-mutant mice or neutralization of IL-6 in cultures established from the lung-draining lymph nodes of immunized wild-type mice blunted the T(H)2 and T(H)17 responses. DCs lacking functional c-Kit or those unable to express membrane-bound SCF secreted lower amounts of IL-6 in response to HDM or cholera toxin. DCs expressing nonfunctional c-Kit were unable to induce a robust T(H)2 or T(H)17 response and elicited diminished allergic airway inflammation when adoptively transferred into mice. Expression of the Notch ligand Jagged-2, which has been associated with T(H)2 differentiation, was blunted in DCs from c-Kit-mutant mice. c-Kit upregulation was specifically induced by T(H)2- and T(H)17-skewing stimuli, as the T(H)1-inducing adjuvant, CpG oligodeoxynucleotide, did not promote either c-Kit or Jagged-2 expression. DCs generated from mice expressing a catalytically inactive form of the p110delta subunit of phosphatidylinositol-3 (PI3) kinase (p110(D910A)) secreted lower amounts of IL-6 upon stimulation with cholera toxin. Collectively, these results highlight the importance of the c-Kit-PI3 kinase-IL-6 signaling axis in DCs in regulating T cell responses.

CD41+ cmyb+ precursors colonize the zebrafish pronephros by a novel migration route to initiate adult hematopoiesis

Development of the vertebrate blood lineages is complex, with multiple waves of hematopoietic precursors arising in different embryonic locations. Monopotent, or primitive, precursors first give rise to embryonic macrophages or erythrocytes. Multipotent, or definitive, precursors are subsequently generated to produce the adult hematopoietic lineages. In both the zebrafish and the mouse, the first definitive precursors are committed erythromyeloid progenitors (EMPs) that lack lymphoid differentiation potential. We have previously shown that zebrafish EMPs arise in the posterior blood island independently from hematopoietic stem cells (HSCs). In this report, we demonstrate that a fourth wave of hematopoietic precursors arises slightly later in the zebrafish aorta/gonad/mesonephros (AGM) equivalent. We have identified and prospectively isolated these cells by CD41 (itga2b) and cmyb expression. Unlike EMPs, CD41(+) AGM cells colonize the thymus to generate rag2(+) T lymphocyte precursors. Timelapse imaging and lineage tracing analyses demonstrate that AGM-derived precursors use a previously undescribed migration pathway along the pronephric tubules to initiate adult hematopoiesis in the developing kidney, the teleostean equivalent of mammalian bone marrow. Finally, we have analyzed the gene expression profiles of EMPs and AGM precursors to better understand the molecular cues that pattern the first definitive hematopoietic cells in the embryo. Together, these studies suggest that expression of CD41 and cmyb marks nascent HSCs in the zebrafish AGM, and provide the means to further dissect HSC generation and function in the early vertebrate embryo.

Essential role of Notch signaling in effector memory CD8+ T cell-mediated airway hyperresponsiveness and inflammation

Adoptive transfer of in vivo-primed CD8(+) T cells or in vitro-generated effector memory CD8(+) T (T(EFF)) cells restores airway hyperresponsiveness (AHR) and airway inflammation in CD8-deficient (CD8(-/-)) mice. Examining transcription levels, there was a strong induction of Notch1 in T(EFF) cells compared with central memory CD8(+) T cells. Treatment of T(EFF) cells with a gamma-secretase inhibitor (GSI) strongly inhibited Notch signaling in these cells, and after adoptive transfer, GSI-treated T(EFF) cells failed to restore AHR and airway inflammation in sensitized and challenged recipient CD8(-/-) mice, or to enhance these responses in recipient wild-type (WT) mice. These effects of GSI were also associated with increased expression of the Notch ligand Delta1 in T(EFF) cells. Treatment of sensitized and challenged WT mice with Delta1-Fc resulted in decreased AHR and airway inflammation accompanied by higher levels of interferon gamma in bronchoalveolar lavage fluid. These results demonstrate a role for Notch in skewing the T cell response from a T helper (Th)2 to a Th1 phenotype as a consequence of the inhibition of Notch receptor activation and the up-regulation of the Notch ligand Delta1. These data are the first to show a functional role for Notch in the challenge phase of CD8(+) T cell-mediated development of AHR and airway inflammation, and identify Delta1 as an important regulator of allergic airway inflammation.

Notch signaling in CD4 and CD8 T cell development

Because Notch often acts in concert with other signaling pathways, it is able to regulate a diverse set of biological processes in a cell-context dependent manner. In lymphocytes, Notch is essential for specifying the T cell fate and for promoting early stages of T cell differentiation. At later stages of development, Notch signaling is proposed to direct CD4 versus CD8 T lineage commitment. This hypothesis has been challenged by recent studies of conditional Presenilin-deficient mice showing that Notch promotes the selection and maturation of CD4 and CD8 T cells by potentiating TCR signal transduction in immature thymocytes. While similar conclusions have not been reported with conditional mutation of other downstream mediators of Notch activation, it appears that functional inhibition may not have been achieved at a comparable stage of development and/or analogous issues have not been addressed. The differences also question whether in thymocytes Notch signals only through the canonical pathway. Further study of conditional mutants, signaling intermediates, and transcriptional regulators are needed to elucidate how Notch facilitates TCR signaling in generating mature T cells.

GATA-3 and the regulation of the mammary luminal cell fate

The GATA family of transcription factors plays essential roles in the specification and maintenance of differentiated cell types. GATA-3 was identified in a microarray screen of the mouse mammary gland as the most highly expressed transcription factor in the mammary epithelium and is expressed exclusively in the luminal epithelial cell population. Targeted deletion of GATA-3 in mammary glands leads to profound defects in mammary development and inability to specify and maintain the luminal cell fate in the adult mouse. In breast cancer, GATA-3 has emerged as a strong predictor of tumor differentiation, estrogen-receptor status, and clinical outcome. GATA-3 maintains tumor differentiation and suppresses tumor dissemination in a mouse model of breast cancer. This review explores our current understanding of GATA-3 signaling in luminal cell differentiation, both in mammary development and breast cancer.

Suppression of Th2 cell development by Notch ligands Delta1 and Delta4

Notch signaling plays important roles in Th cell activation. We show that in response to TLR ligation, dendritic cells up-regulate expression of Notch ligands Delta1 and Delta4 via a MyD88-dependent pathway. Expression of Delta1 or Delta4 by dendritic cells enhanced their ability to activate naive Th cells and promote Th1 cell development, and allowed them to strongly inhibit Th2 cell development. Promotion of Th1 cell development was dependent on IFN-gamma and T-bet expression by responding Th cells. However, the inhibition of Th2 cell development occurred independently of IFN-gamma or T-bet, and resulted from a block in IL-4-initiated commitment to the Th2 lineage. The promotion of Th1 cell development by Delta is not a reflection of the delivery of pro-Th1 instructional signal, but rather it is the result of a block in the downstream effects initiated by IL-4 signaling.

Notch regulates IL-10 production by T helper 1 cells

T helper 1 (Th1) cells mediate powerful cellular immune responses. However, if unbalanced, Th1 immunity eventually may cause pathology. Recently, it has been shown that IL-10, an antiinflammatory cytokine strongly antagonizing Th1-mediated effects, can be produced by Th1 cells and is indeed essential for self-regulation of Th1 immunity. Here, we show that Notch induces IL-10 production in newly developing and already established Th1 cells via a signal transducer and activator of transcription 4 (STAT4)-dependent process. Notch signaling in the presence of the cytokines IL-12 or IL-27 induces Th1 cells to produce large amounts of IL-10 without diminishing IFN-gamma production. Notch-modified Th1 cells completely lose their inflammatory capacity and instead are able to actively suppress a Th1 cell-induced delayed-type hypersensitivity (DTH) reaction in an IL-10-dependent fashion. IL-10 production can be elicited by active forms of all four mammalian Notch receptors but was found to be specific for the Delta-like family of Notch ligands. Dendritic cells (DC) selectively acquire Delta-like 4 expression upon stimulation with various Toll-like receptor (TLR) ligands and concomitantly induce IL-10 production by Th1 cells in vitro and in vivo. This effect can be selectively reversed by pharmacological inhibitors of Notch signaling (gamma-secretase inhibitor). Our data suggest that Notch regulates IL-10 production in Th1 cells by a STAT4-dependent process that converts proinflammatory Th1 cells into T cells with regulatory activity. This pathway may provide unique opportunities for therapeutic intervention in Th1-driven immune diseases and for Th1-associated vaccination strategies.

An insight into molecular mechanisms of human T helper cell differentiation

Selective activation of T helper (Th) cell subsets plays an important role in immune response to pathogens as well as in the pathogenesis of human allergy and inflammatory diseases. Th1 cells along with the recently discovered Th17 cells play a role in the pathogenesis of autoimmune diseases. Th2 cytokines lead to series of inflammatory processes characteristic for asthma and other atopic diseases. To understand the pathogenesis of immune-mediated diseases it is crucial to dissect pathways and regulatory networks leading to the development of distinct Th subsets. Such knowledge may lead to better strategies for developing diagnostics and therapies for these diseases. The differentiation of Th1, Th2, and Th17 effector cells is driven by signals originating from T cell and costimulatory receptors as well as cytokines in the surroundings of activated naive T helper cells. There are several proteins involved in the regulation of this differentiation process. Most of the data on T helper cell differentiation have been acquired using mouse. In this review, we have summarized what is known about human T helper differentiation. In addition, selected differences between human and mouse will be discussed.

Notch ligand Delta-like 4 regulates disease pathogenesis during respiratory viral infections by modulating Th2 cytokines

Recent data have indicated that an important instructive class of signals regulating the immune response is Notch ligand–mediated activation. Using quantitative polymerase chain reaction, we observed that only Delta-like 4 (dll4) was up-regulated on bone marrow–derived dendritic cells after respiratory syncytial virus (RSV) infection, and that it was dependent on MyD88-mediated pathways. Using a polyclonal antibody specific for dll4, the development of RSV-induced disease was examined. Animals treated with anti-dll4 had substantially increased airway hyperresponsiveness compared with control antibody-treated animals. When the lymphocytic lung infiltrate was examined, a significant increase in total CD4⁺ T cells and activated (perforin⁺) CD8⁺ T cells was observed. Isolated lung CD4⁺ T cells demonstrated significant increases in Th2-type cytokines and a decrease in interferon γ, demonstrating an association with increased disease pathogenesis. Parellel in vitro studies examining the integrated role of dll4 with interleukin-12 demonstrated that, together, both of these instructive signals direct the immune response toward a more competent, less pathogenic antiviral response. These data demonstrate that dll4-mediated Notch activation is one regulator of antiviral immunity.

Characterization of the promoter of human CRTh2, a prostaglandin D2 receptor

Chemoattractant-receptor homologous molecule expressed on Th2 cells (CRTh2) is a receptor for prostaglandin (PG)D2, a lipid mediator involved in allergic inflammation. CRTh2 is expressed by Th2 cells, eosinophils and basophils and PDG(2)-CRTh2 signaling induces calcium mobilization, cell migration and expression of the Th2 cytokines IL-4, IL-5, and IL-13. Despite the role of CRTh2 in allergic inflammation, transcriptional regulation of this gene has not been studied. Here, we demonstrated that a reporter construct of the CRTh2 promoter was induced following T cell stimulation. This activity could be further enhanced by over-expression of GATA-3, but not NFAT2 or STAT6. Electromobility shift assay demonstrated GATA-3 binding to a probe from the CRTh2 promoter. This study provides the first detailed analysis of transcriptional regulation of the human CRTh2 promoter. These findings may help identify strategies to attenuate expression of this gene and influence the maintenance and proliferation of Th2 cells in allergic inflammation.

Notch: filling a hole in T helper 2 cell differentiation

In this issue of Immunity, Amsen et al. (2007) and Fang et al. (2007) propose a direct role for Notch signaling in the expression of GATA-3 transcription factor and T helper 2 cell differentiation.