Differential requirement for the transcription factor PU.1 in the generation of natural killer cells versus B and T cells

PU.1 inhibition does not attenuate cardiac function deterioration or fibrosis in a murine model of myocardial infarction

Activated cardiac fibroblasts are involved in both reparative wound healing and maladaptive cardiac fibrosis after myocardial infarction (MI). Recent evidence suggests that PU.1 inhibition can enable reprogramming of profibrotic fibroblasts to quiescent fibroblasts, leading to attenuation of pathologic fibrosis in several fibrosis models. The role of PU.1 in acute MI has not been tested. We designed a randomized, blinded study to evaluate whether DB1976, a PU.1 inhibitor, attenuates cardiac function deterioration and fibrosis in a murine model of MI. A total of 44 Ai9 periostin-Cre transgenic mice were subjected to 60 min of coronary occlusion followed by reperfusion. At 7 days after MI, 37 mice were randomly assigned to control (vehicle) or DB1976 treatment and followed for 2 weeks. Left ventricular ejection fraction (EF), assessed by echocardiography, did not differ between the two groups before or after treatment (final EF, 33.3 ± 1.0% in control group and 31.2 ± 1.3% in DB1976 group). Subgroup analysis of female and male mice showed the same results. There were no differences in cardiac scar (trichrome stain) and fibrosis (interstitial/perivascular collagen; picrosirius stain) between groups. Results from the per-protocol dataset (including mice with pre-treatment EF < 35% only) were consistent with the full dataset. In conclusion, this randomized, blinded study demonstrates that DB1976, a PU.1 inhibitor, does not attenuate cardiac functional deterioration or cardiac fibrosis in a mouse model of MI caused by coronary occlusion/reperfusion.

Tcf1 Sustains the Expression of Multiple Regulators in Promoting Early Natural Killer Cell Development

T cell factor 1 (Tcf1) is known as a critical mediator for natural killer (NK) cell development and terminal maturation. However, its essential targets and precise mechanisms involved in early NK progenitors (NKP) are not well clarified. To investigate the role of Tcf1 in NK cells at distinct developmental phases, we employed three kinds of genetic mouse models, namely, Tcf7^fl/flVav^Cre/+, Tcf7^fl/flCD122^Cre/+ and Tcf7^fl/flNcr1^Cre/+ mice, respectively. Similar to Tcf1 germline knockout mice, we found notably diminished cell number and defective development in BM NK cells from all strains. In contrast, Tcf7^fl/flNcr1^Cre/+ mice exhibited modest defects in splenic NK cells compared with those in the other two strains. By analyzing the published ATAC-seq and ChIP-seq data, we found that Tcf1 directly targeted 110 NK cell-related genes which displayed differential accessibility in the absence of Tcf1. Along with this clue, we further confirmed that a series of essential regulators were expressed aberrantly in distinct BM NK subsets with conditional ablating Tcf1 at NKP stage. Eomes, Ets1, Gata3, Ikzf1, Ikzf2, Nfil3, Runx3, Sh2d1a, Slamf6, Tbx21, Tox, and Zeb2 were downregulated, whereas Spi1 and Gzmb were upregulated in distinct NK subsets due to Tcf1 deficiency. The dysregulation of these genes jointly caused severe defects in NK cells lacking Tcf1. Thus, our study identified essential targets of Tcf1 in NK cells, providing new insights into Tcf1-dependent regulatory programs in step-wise governing NK cell development.

MiRNAs and lncRNAs in NK cell biology and NK/T-cell lymphoma

The important role of lncRNAs and miRNAs in directing immune responses has become increasingly clear. Recent evidence conforms that miRNAs and lncRNAs are involved in NK cell biology and diseases through RNA-protein, RNA-RNA, or RNA-DNA interactions. In this view, we summarize the contribution of miRNAs and lncRNAs to NK cell lineage development, activation and function, highlight the biological significance of functional miRNAs or lncRNAs in NKTL and discuss the potential of these miRNAs and lncRNAs as innovative biomarkers/targets for NKTL early diagnosis, target treatment and prognostic evaluations.

Cytokines and signaling pathways involved in differentiation potential of hematopoietic stem cells towards natural killer cells

NK cells are innate immune cells derived from common lymphoid progenitor and are developed primarily in the bone marrow. These cells respond to stress signals, inflammatory cytokines, and cancerous cells through the secretion of active immune mediators. Previous studies revealed that NK cells can be used as an essential cell in the defense against cancers. According to the literature, a set of cytokines and factors play a crucial role during differentiation of NK cells. In other words, developmental events of NK cells are regulated through multiple critical cytokines, including interleukins (ILs), kit ligand, fms-like tyrosine kinase three ligand, transforming growth factor-β, and typical γ chain family of cytokines. Among previously investigated ILs, IL-2, IL-3, IL-7, and IL-15 are the most important. In addition to ILs, transcription factors and MicroRNAs are involved in NK cell development. In this review study, after presenting a brief description of developmental stages and production of the NK cells, the factors and signaling pathways involved in differentiation of NK cells were discussed.

PU.1 drives specification of pluripotent stem cell-derived endothelial cells to LSEC-like cells

To date, there is no representative in vitro model for liver sinusoidal endothelial cells (LSECs), as primary LSECs dedifferentiate very fast in culture and no combination of cytokines or growth factors can induce an LSEC fate in (pluripotent stem cell (PSC)-derived) endothelial cells (ECs). Furthermore, the transcriptional programmes driving an LSEC fate have not yet been described. Here, we first present a computational workflow (CenTFinder) that can identify transcription factors (TFs) that are crucial for modulating pathways involved in cell lineage specification. Using CenTFinder, we identified several novel LSEC-specific protein markers, such as FCN2 and FCN3, which were validated by analysis of previously published single-cell RNAseq data. We also identified PU.1 (encoded by the SPI1 gene) as a major regulator of LSEC-specific immune functions. We show that SPI1 overexpression (combined with the general EC TF ETV2) in human PSCs induces ECs with an LSEC-like phenotype. The ETV2-SPI1-ECs display increased expression of LSEC markers, such as CD32B and MRC1, as well as several of the proposed novel markers. More importantly, ETV2-SPI1-ECs acquire LSEC functions, including uptake of FSA-FITC, as well as labelled IgG. In conclusion, we present the CenTFinder computational tool to identify key regulatory TFs within specific pathways, in this work pathways of lineage specification, and we demonstrate its use by the identification and validation of PU.1 as a master regulator for LSEC fating.

Landscape and Dynamics of the Transcriptional Regulatory Network During Natural Killer Cell Differentiation

Natural killer (NK) cells are essential in controlling cancer and infection. However, little is known about the dynamics of the transcriptional regulatory machinery during NK cell differentiation. In this study, we applied the assay of transposase accessible chromatin with sequencing (ATAC-seq) technique in a home-developed in vitro NK cell differentiation system. Analysis of ATAC-seq data illustrated two distinct transcription factor (TF) clusters that dynamically regulate NK cell differentiation. Moreover, two TFs from the second cluster, FOS-like 2 (FOSL2) and early growth response 2 (EGR2), were identified as novel essential TFs that control NK cell maturation and function. Knocking down either of these two TFs significantly impacted NK cell differentiation. Finally, we constructed a genome-wide transcriptional regulatory network that provides a better understanding of the regulatory dynamics during NK cell differentiation.

NK Cell Development in Times of Innate Lymphoid Cell Diversity

After being described in the 1970s as cytotoxic cells that do not require MHC-dependent pre-activation, natural killer (NK) cells remained the sole member of innate lymphocytes for decades until lymphoid tissue-inducer cells in the 1990s and helper-like innate lymphoid lineages from 2008 onward completed the picture of innate lymphoid cell (ILC) diversity. Since some of the ILC members, such as ILC1s and CCR6^- ILC3s, share specific markers previously used to identify NK cells, these findings provoked the question of how to delineate the development of NK cell and helper-like ILCs and how to properly identify and genetically interfere with NK cells. The description of eomesodermin (EOMES) as a lineage-specifying transcription factor of NK cells provided a candidate that may serve as a selective marker for the genetic targeting and identification of NK cells. Unlike helper-like ILCs, NK cell activation is, to a large degree, regulated by the engagement of activating and inhibitory surface receptors. NK cell research has revealed some elegant mechanisms of immunosurveillance, coined "missing-self" and "induced-self" recognition, thus complementing "non-self recognition", which is predominantly utilized by adaptive lymphocytes and myeloid cells. Notably, the balance of activating and inhibitory signals perceived by surface receptors can be therapeutically harnessed for anti-tumor immunity mediated by NK cells. This review aims to summarize the similarities and the differences in development, function, localization, and phenotype of NK cells and helper-like ILCs, with the purpose to highlight the unique feature of NK cell development and regulation.

Dual Roles of PU.1 in the Expression of PD-L2: Direct Transactivation with IRF4 and Indirect Epigenetic Regulation

PD-L2, which has been identified as a PD-1 ligand, is specifically expressed in dendritic cells (DCs) and macrophages. The transcription factors that determine the cell type-specific expression of PD-L2 are largely unknown, although PD-1 and its ligands, which have been shown to play important roles in T cell suppression, have been vigorously analyzed in the field of cancer immunology. To reveal the mechanism by which Pdcd1lg2 gene expression is regulated, we focused on DCs, which play key roles in innate and acquired immunity. The knockdown of the hematopoietic cell-specific transcription factors PU.1 and IRF4 decreased PD-L2 expression in GM-CSF-induced mouse bone marrow-derived DCs. Chromatin immunoprecipitation assays, luciferase assays, and electrophoretic mobility shift assays demonstrated that PU.1 and IRF4 bound directly to the Pdcd1lg2 gene via an Ets-IRF composite element sequence and coordinately transactivated the Pdcd1lg2 gene. Furthermore, PU.1 knockdown reduced the histone acetylation of the Pdcd1lg2 gene. The knockdown of the typical histone acetyltransferase p300, which has been reported to interact with PU.1, decreased the expression and H3K27 acetylation of the Pdcd1lg2 gene. GM-CSF stimulation upregulated the Pdcd1lg2 gene expression, which was accompanied by an increase in PU.1 binding and histone acetylation in Flt3L-generated mouse bone marrow-derived DCs. The involvement of PU.1, IRF4, and p300 were also observed in mouse splenic DCs. Overall, these results indicate that PU.1 positively regulates Pdcd1lg2 gene expression as a transactivator and an epigenetic regulator in DCs.

Transcriptional Regulation of Natural Killer Cell Development and Functions

Natural killer (NK) cells are the major lymphocyte subset of the innate immune system. Their ability to mediate anti-tumor cytotoxicity and produce cytokines is well-established. However, the molecular mechanisms associated with the development of human or murine NK cells are not fully understood. Knowledge is being gained about the environmental cues, the receptors that sense the cues, signaling pathways, and the transcriptional programs responsible for the development of NK cells. Specifically, a complex network of transcription factors (TFs) following microenvironmental stimuli coordinate the development and maturation of NK cells. Multiple TFs are involved in the development of NK cells in a stage-specific manner. In this review, we summarize the recent advances in the understandings of TFs involved in the regulation of NK cell development, maturation, and effector function, in the aspects of their mechanisms, potential targets, and functions.

Single-cell transcriptome reveals the novel role of T-bet in suppressing the immature NK gene signature

The transcriptional activation and repression during NK cell ontology are poorly understood. Here, using single-cell RNA-sequencing, we reveal a novel role for T-bet in suppressing the immature gene signature during murine NK cell development. Based on transcriptome, we identified five distinct NK cell clusters and define their relative developmental maturity in the bone marrow. Transcriptome-based machine-learning classifiers revealed that half of the mTORC2-deficient NK cells belongs to the least mature NK cluster. Mechanistically, loss of mTORC2 results in an increased expression of signature genes representing immature NK cells. Since mTORC2 regulates the expression of T-bet through Akt^S473-FoxO1 axis, we further characterized the T-bet-deficient NK cells and found an augmented immature transcriptomic signature. Moreover, deletion of Foxo1 restores the expression of T-bet and corrects the abnormal expression of immature NK genes. Collectively, our study reveals a novel role for mTORC2-Akt^S473-FoxO1-T-bet axis in suppressing the transcriptional signature of immature NK cells.

PBX1 promotes development of natural killer cells by binding directly to the Nfil3 promoter

The transcription factor nuclear factor interleukin-3-regulated protein (NFIL3, also called E4BP4) is crucial for commitment of natural killer (NK) cells from common lymphoid progenitors (CLPs). However, the identity of the factor that can regulate NFIL3 directly during the NK-cell development is not known. Here, we reveal that pre-B-cell leukemia transcription factor 1 (PBX1) can upregulate the NFIL3 expression directly. We used conditional knockout mice in which PBX1 in hematopoietic cells was specifically absent. The number of NK-committed progenitor pre-NKP cells and rNKP cells was reduced significantly in the absence of PBX1, which was consistent with NFIL3 deficiency. Also, the NFIL3 expression in NK cells was decreased if PBX1 was absent. We demonstrated that PBX1 was bound directly to the promoter of Nfil3 and facilitated transcription. Upon knockout of the binding site of PBX1 in the Nfil3 promoter, mice showed fewer NK-precursor cells and NK cells, just like that observed in Nfil3 knockout mice. Furthermore, asparagine N286 in the homeodomain of PBX1 controlled the binding of PBX1 to the Nfil3 promoter. Collectively, these findings demonstrate that the transcription factor PBX1 promotes the early development of NK cells by upregulating the Nfil3 expression directly.

On the Way to Become a Natural Killer Cell

Natural Killer (NK) cells are innate lymphocytes playing pivotal roles in host defense and immune-surveillance. The homeostatic modulation of germ-line encoded/non-rearranged activating and inhibitory NK cell receptors (NKRs) determines the capability of these innate lymphocytes to either spare "self" cells or to kill viral-infected, tumor-transformed and heterologous cell targets. However, despite being discovered more than 40 years ago, several aspects of NK cell biology remain unknown or are still being debated. In particular, our knowledge of human NK cell ontogenesis and differentiation is still in its infancy as the majority of our experimental evidence on this topic mainly comes from findings obtained in vitro or with animal models in vivo. Although both the generation and the maintenance of human NK cells are sustained by hematopoietic stem cells (HSCs), the precise site(s) of NK cell development are still poorly defined. Indeed, HSCs and hematopoietic precursors are localized in different anatomical compartments that also change their ontogenic commitments before and after birth as well as in aging. Currently, the main site of NK cell generation and maturation in adulthood is considered the bone marrow, where their interactions with stromal cells, cytokines, growth factors, and other soluble molecules support and drive maturation. Different sequential stages of NK cell development have been identified on the basis of the differential expression of specific markers and NKRs as well as on the acquisition of specific effector-functions. All these phenotypic and functional features are key in inducing and regulating homing, activation and tissue-residency of NK cells in different human anatomic sites, where different homeostatic mechanisms ensure a perfect balance between immune tolerance and immune-surveillance. The present review summarizes our current knowledge on human NK cell ontogenesis and on the related pathways orchestrating a proper maturation, functions, and distributions.

PU.1 plays a pivotal role in dendritic cell migration from the periphery to secondary lymphoid organs via regulating CCR7 expression

C-C chemokine receptor type 7 (CCR7) is essential for migration of dendritic cells (DCs) to draining lymph nodes. PU.1/Spi1 is a transcription factor playing a critical role in the gene regulation of DCs. PU.1 knockdown decreased the expression of CCR7 in bone marrow-derived DCs and subsequently attenuated migration in vitro and in vivo. Reporter assays, EMSA, and chromatin immunoprecipitation assays revealed that PU.1 binds to the most proximal Ets motif of the Ccr7 promoter, which is involved in transcriptional activation. The CCR7 expression level, which was higher in the programmed cell death 1 ligand 2 (PD-L2)⁺ population than in the PD-L2^- population and was markedly suppressed by TGF-β treatment, coincided with the binding level of PU.1 to the Ccr7 promoter. The PU.1 binding level in CCR7^high mesenteric lymph nodes DCs was higher than in other DC subtypes. The involvement of PU.1 in the expression of the CCR7 gene was also observed in human DCs. We conclude that PU.1 plays a pivotal role in DC migration by transactivating the CCR7 gene via the Ets motif in the promoter in both humans and mice.-Yashiro, T., Takeuchi, H., Nakamura, S., Tanabe, A., Hara, M., Uchida, K., Okumura, K., Kasakura, K., Nishiyama, C. PU.1 plays a pivotal role in dendritic cell migration from the periphery to secondary lymphoid organs via regulating CCR7 expression.

Transcriptional control of natural killer cell differentiation

Natural killer (NK) cells are highly specialized cytotoxic lymphocytes that provide protection against pathogens and malignant cells. They develop from common lymphoid progenitors via a multi-stage lineage commitment and differentiation process that gives rise to mature NK cells with potent cytotoxic functionality. Although generally considered cells of the innate immune system, recent studies have demonstrated that NK cells have the capacity to mount immune responses with features of adaptive immunity, including robust antigen-specific clonal-like expansion and the generation of long-lived memory cells that mediate enhanced recall responses. Here, we discuss specific transcription factors that have been shown to commonly and uniquely regulate NK cell development and effector and memory responses in experimental mouse models.

Transcriptional regulation of murine natural killer cell development, differentiation and maturation

Natural killer (NK) cells are innate cytotoxic effector cells that play important protective roles against certain pathogens as well as against pathogen-infected and transformed host cells. NK cells continuously arise from adult bone marrow-resident haematopoietic progenitors. Their generation can be sub-divided into three phases. The early NK cell development phase from multipotent common lymphoid progenitors occurs at least in part in common with that of additional members of a family of innate lymphoid cells, for which NK cells are the founding member. An intermediate phase of NK cell differentiation is characterized by the acquisition of IL-15 responsiveness and lineage-defining properties such as the transcription of genes coding for cytotoxic effector molecules. This is followed by a late maturation phase during which NK cells lose homeostatic expansion and increase effector capacity. These three phases are regulated by multiple stage-specific but not NK cell-specific transcription factors. This review summarizes the NK cell developmental and maturation processes and their transcriptional regulation with an emphasis on data derived from genetically modified mouse models.

The Transcription Factor ZNF683/HOBIT Regulates Human NK-Cell Development

We identified ZNF683/HOBIT as the most highly upregulated transcription factor gene during ex vivo differentiation of human CD34⁺ cord blood progenitor cells to CD56⁺ natural killer (NK) cells. ZNF683/HOBIT mRNA was preferentially expressed in NK cells compared to other human peripheral blood lymphocytes and monocytes. During ex vivo differentiation, ZNF683/HOBIT mRNA started to increase shortly after addition of IL-15 and further accumulated in parallel to the generation of CD56⁺ NK cells. shRNA-mediated knockdown of ZNF683/HOBIT resulted in a substantial reduction of CD56⁻CD14⁻ NK-cell progenitors and the following generation of CD56⁺ NK cells was largely abrogated. The few CD56⁺ NK cells, which escaped the developmental inhibition in the ZNF683/HOBIT knockdown cultures, displayed normal levels of NKG2A and KIR receptors. Functional analyses of these cells showed no differences in degranulation capacity from control cultures. However, the proportion of IFN-γ-producing cells appeared to be increased upon ZNF683/HOBIT knockdown. These results indicate a key role of ZNF683/HOBIT for the differentiation of the human NK-cell lineage and further suggest a potential negative control on IFN-γ production in more mature human NK cells.

The hematopoietic cell-specific transcription factor PU.1 is critical for expression of CD11c

PU.1 is a hematopoietic cell-specific transcription factor belonging to the Ets family, which plays an important role in the development of dendritic cells (DCs). CD11c (encoded by Itgax) is well established as a characteristic marker of hematopoietic lineages including DCs. In the present study, we analyzed the role of PU.1 (encoded by Spi-1) in the expression of CD11c. When small interfering RNA (siRNA) for Spi-1 was introduced into bone marrow-derived DCs (BMDCs), the mRNA level and cell surface expression of CD11c were dramatically reduced. Using reporter assays, the TTCC sequence at -56/-53 was identified to be critical for PU.1-mediated activation of the promoter. An EMSA showed that PU.1 directly bound to this region. ChIP assays demonstrated that a significant amount of PU.1 bound to this region on chromosomal DNA in BMDCs, which was decreased in LPS-stimulated BMDCs in accordance with the reduced levels of mRNAs of Itgax and Spi-1, and the histone acetylation degree. Enforced expression of exogenous PU.1 induced the expression of the CD11c protein on the cell surface of mast cells, whereas control transfectants rarely expressed CD11c. Quantitative RT-PCR also showed that the expression of a transcription factor Irf4, which is a partner molecule of PU.1, was reduced in PU.1-knocked down BMDCs. IRF4 transactivated the Itgax gene in a synergistic manner with PU.1. Taken together, these results indicate that PU.1 functions as a positive regulator of CD11c gene expression by directly binding to the Itgax promoter and through transactivation of the Irf4 gene.

The Development and Diversity of ILCs, NK Cells and Their Relevance in Health and Diseases

Next to T and B cells, natural killer (NK) cells are the third largest lymphocyte population. They are recently re-categorized as innate lymphocytes (ILCs), which also include ILC1, ILC2, ILC3, and the lymphoid tissue inducer (LTi) cells. Both NK cells and ILC1 cells are designated as group 1 ILCs because they secrete interferon-γ (IFN-γ) and tumor necrosis factor (TNF). However, in contrast to ILC1 and all other ILCs, NK cells possess potent cytolytic functions that resemble cytotoxic T lymphocytes (CTL). In addition, NK cells express, in a stochastic manner, an array of germ line-encoded activating and inhibitory receptors that recognize the polymorphic regions of major histocompatibility class I (MHC-I) molecules and self-proteins. Recognition of self renders NK cell tolerance to self-healthy tissues, but fail to recognize self ('missing-self') leads to activation to neoplastic transformation and infections of certain viruses. In this chapter, we will summarize the development of NK cells in the context of ILCs, describe the diversity of phenotype and function in blood and tissues, and discuss their involvement in health and diseases in humans.

Biallelic mutations in IRF8 impair human NK cell maturation and function

Human NK cell deficiencies are rare yet result in severe and often fatal disease, particularly as a result of viral susceptibility. NK cells develop from hematopoietic stem cells, and few monogenic errors that specifically interrupt NK cell development have been reported. Here we have described biallelic mutations in IRF8, which encodes an interferon regulatory factor, as a cause of familial NK cell deficiency that results in fatal and severe viral disease. Compound heterozygous or homozygous mutations in IRF8 in 3 unrelated families resulted in a paucity of mature CD56dim NK cells and an increase in the frequency of the immature CD56bright NK cells, and this impairment in terminal maturation was also observed in Irf8-/-, but not Irf8+/-, mice. We then determined that impaired maturation was NK cell intrinsic, and gene expression analysis of human NK cell developmental subsets showed that multiple genes were dysregulated by IRF8 mutation. The phenotype was accompanied by deficient NK cell function and was stable over time. Together, these data indicate that human NK cells require IRF8 for development and functional maturation and that dysregulation of this function results in severe human disease, thereby emphasizing a critical role for NK cells in human antiviral defense.

Role of PU.1 in MHC Class II Expression via CIITA Transcription in Plasmacytoid Dendritic Cells

The cofactor CIITA is a master regulator of MHC class II expression and several transcription factors regulating the cell type-specific expression of CIITA have been identified. Although the MHC class II expression in plasmacytoid dendritic cells (pDCs) is also mediated by CIITA, the transcription factors involved in the CIITA expression in pDCs are largely unknown. In the present study, we analyzed the role of a hematopoietic lineage-specific transcription factor, PU.1, in CIITA transcription in pDCs. The introduction of PU.1 siRNA into mouse pDCs and a human pDC cell line, CAL-1, reduced the mRNA levels of MHC class II and CIITA. When the binding of PU.1 to the 3rd promoter of CIITA (pIII) in CAL-1 and mouse pDCs was analyzed by a chromatin immunoprecipitation assay, a significant amount of PU.1 binding to the pIII was detected, which was definitely decreased in PU.1 siRNA-transfected cells. Reporter assays showed that PU.1 knockdown reduced the pIII promoter activity and that three Ets-motifs in the human pIII promoter were candidates of cis-enhancing elements. By electrophoretic mobility shift assays, it was confirmed that two Ets-motifs, GGAA (-181/-178) and AGAA (-114/-111), among three candidates, were directly bound with PU.1. When mouse pDCs and CAL-1 cells were stimulated by GM-CSF, mRNA levels of PU.1, pIII-driven CIITA, total CIITA, MHC class II, and the amount of PU.1 binding to pIII were significantly increased. The GM-CSF-mediated up-regulation of these mRNAs was canceled in PU.1 siRNA-introduced cells. Taking these results together, we conclude that PU.1 transactivates the pIII through direct binding to Ets-motifs in the promoter in pDCs.

Development and maturation of natural killer cells

Natural killer (NK) cells are innate lymphocytes that are critical for host protection against pathogens and cancer due to their ability to rapidly release inflammatory cytokines and kill infected or transformed cells. In the 40 years since their initial discovery, much has been learned about how this important cellular lineage develops and functions. We now know that NK cells are the founding members of an expanded family of lymphocyte known as innate lymphoid cells (ILC). Furthermore, we have recently discovered that NK cells can possess features of adaptive immunity such as antigen specificity and long-lived memory responses. Here we will review our current understanding of the molecular mechanisms driving development of NK cells from the common lymphoid progenitor (CLP) to mature NK cells, and from activated effectors to long-lived memory NK cells.

Transcriptional and post-transcriptional regulation of NK cell development and function

Natural killer (NK) cells are specialized innate lymphoid cells that survey against viral infections and malignancy. Numerous advances have improved our understanding of the molecular mechanisms that control NK cell development and function over the past decade. These include both studies on the regulatory effects of transcription factors and translational repression via microRNAs. In this review, we summarize our current knowledge of DNA-binding transcription factors that regulate gene expression and thereby orchestrate NK cell development and activation, with an emphasis on recent discoveries. Additionally, we highlight our understanding of how RNA-binding microRNAs fine tune the NK cell molecular program. We also underscore the large number of open questions in the field that are now being addressed using new technological approaches and genetically engineered model organisms. Ultimately, a deeper understanding of the basic molecular biology of NK cells will facilitate new strategies to manipulate NK cells for the treatment of human disease.

Regulatory T cells inhibit CD34+ cell differentiation into NK cells by blocking their proliferation

Graft versus Host Disease (GvHD) remains one of the main complications after hematopoietic stem cell transplantation (HSCT). Due to their ability to suppress effector cells, regulatory T cells (Tregs) have been proposed as a cellular therapy to prevent GvHD, however they also inhibit the functions of natural killer (NK) cells, key effectors of the Graft versus Leukemia effect. In this study, we have explored whether a Tregs therapy will also impact on NK cell differentiation. Using an in vitro model of hematopoietic stem cell (HSC) differentiation into NK cells, we found that activated Tregs led to a 90% reduction in NK cell numbers when added at the time of commitment to the NK cell lineage. This effect was contact dependent and was reversible upon Tregs depletion. The few NK cells that developed in these cultures were mature and exhibited normal functions. Furthermore, adoptive transfer of activated Tregs in rag(-/-) γc(-/-) mice abrogated HSC differentiation into NK cells thus confirming our in vitro findings. Collectively, these results demonstrate for the first time that activated Tregs can inhibit NK cell differentiation from HSC under specific conditions.

Repressing PU.1 by miR-29a∗ in NK cells of HCV patients, diminishes its cytolytic effect on HCV infected cell models

OBJECTIVES

Natural killer cells are immune safeguards against HCV infection. PU.1 is a pivotal transcription factor in the development of NK cells. This study aimed at studying the regulatory effect of miRNAs on both development and function of NK cells isolated from HCV patients.

METHODS

NK cells were isolated from 17 chronic HCV patients and 12 healthy controls; after which miRNA and mRNA were quantified using qRT-PCR. Manipulating miRNA expression using mimics and antagomirs, was performed followed by investigating downstream targets as well as viral abundance.

RESULTS

PU.1 expression levels were upregulated in NK cells of HCV patients. In silico analysis revealed PU.1 to be a potential downstream target of miR-29a(∗), where miR-29a(∗) overexpression in NK cells caused a significant downregulation in PU.1 mRNA. Forcing miR-29a(∗) caused a downregulation of the cytotoxicity determinant NK activating receptor (NKG2D) via upregulation of miR-155. Moreover, perforin-1 mRNA was found to be downregulated upon forcing the expression of miR-29a(∗) in NK cells of HCV patients. This decrease in NK cytolytic function was accompanied by an 80% viral load increase in cocultured HCVcc cell models.

CONCLUSIONS

This study showed that HCV infection might abrogate NK cytotoxic potential through altering PU.1, NKG2D receptor and perforin molecules.

Re-examining the origin and function of liver-resident NK cells

Recent studies have identified a population of liver-resident innate lymphoid cells (ILCs) that, based on the expression of certain phenotypic markers, were termed 'liver-resident NK cells' and considered to be a new subset of conventional natural killer (cNK) cells. However, different transcriptional networks control the development of liver-resident NK cells and cNK cells and, furthermore, these cells exhibit features that characterize mucosal ILC1s. Here, we review findings providing insight into the origin, phenotype, and function of liver-resident NK cells, and discuss these in the context of the current understanding of lineage relations of ILC subsets. We propose that the similarities between liver-resident NK cells and mucosal ILC1s should be considered when revising the categorization framework for these cells, and discuss implications of this revision for other tissue-specific NK cells.

Understanding of molecular mechanisms in natural killer cell therapy

Cancer cells and the immune system are closely related and thus influence each other. Although immune cells can suppress cancer cell growth, cancer cells can evade immune cell attack via immune escape mechanisms. Natural killer (NK) cells kill cancer cells by secreting perforins and granzymes. Upon contact with cancer cells, NK cells form immune synapses to deliver the lethal hit. Mature NK cells are differentiated from hematopoietic stem cells in the bone marrow. They move to lymph nodes, where they are activated through interactions with dendritic cells. Interleukin-15 (IL-15) is a key molecule that activates mature NK cells. The adoptive transfer of NK cells to treat incurable cancer is an attractive approach. A certain number of activated NK cells are required for adoptive NK cell therapy. To prepare these NK cells, mature NK cells can be amplified to obtain sufficient numbers of NK cells. Alternatively, NK cells can be differentiated and amplified from hematopoietic stem cells. In addition, the selection of donors is important to achieve maximal efficacy. In this review, we discuss the overall procedures and strategies of NK cell therapy against cancer.

Transcriptional Control of NK Cells

Natural killer (NK) cells are innate lymphocytes that survey the environment and protect the host from infected and cancerous cells. As their name implies, NK cells represent an early line of defense during pathogen invasion by directly killing infected cells and secreting inflammatory cytokines. Although the function of NK cells was first described more than four decades ago, the development of this cytotoxic lineage is not well understood. In recent years, we have begun to identify specific transcription factors that control each stage of development and maturation, from ontogeny of the NK cell progenitor to the effector functions of activated NK cells in peripheral organs. This chapter highlights the transcription factors that are unique to NK cells, or shared between NK cells and other hematopoietic cell lineages, but govern the biology of this cytolytic lymphocyte.

Both mature KIR+ and immature KIR- NK cells control pediatric acute B-cell precursor leukemia in NOD.Cg-Prkdcscid IL2rgtmWjl/Sz mice

Therapeutic natural killer (NK)-cell-mediated alloreactivity toward acute myeloid leukemia has largely been attributed to mismatches between killer immunoglobulin-like receptors (KIRs) on NK cells and their ligands, HLA class I molecules, on target cells. While adult acute B-cell precursor leukemia (BCP-ALL) appears to be resistant to NK-cell-mediated lysis, recent data indicate that pediatric BCP-ALL might yet be a target of NK cells. In this study, we demonstrate in a donor-patient-specific NOD.Cg-Prkdc(scid) IL2rg(tmWjl)/Sz (NSG) xenotransplantation model that NK cells mediate considerable alloreactivity toward pediatric BCP-ALL in vivo. Notably, both adoptively transferred mature KIR(+) NK cells and immature KIR(-) NK cells arising early posttransplantation in humanized NSG mice exerted substantial antileukemic activity. Low-dose and long-term treatment of humanized NSG mice with the DNA-demethylating agent 5-aza-cytidine distinctly enhanced the antitumor response, interestingly without inducing common inhibitory KIR expression but rather by promoting the differentiation of various NK-cell precursor subsets. Collectively, these data indicate that the future design of innovative therapy protocols should consider further exploitation of NK-cell-mediated immune responses for poor prognosis pediatric BCP-ALL patients.

Integrated mRNA-microRNA profiling of human NK cell differentiation identifies MiR-583 as a negative regulator of IL2Rγ expression

Natural killer (NK) cells are innate immune effector cells that protect against cancer and some viral infections. Until recently, most studies have investigated the molecular signatures of human or mouse NK cells to identify genes that are specifically expressed during NK cell development. However, the mechanism regulating NK cell development remains unclear. Here, we report a regulatory network of potential interactions during in vitro differentiation of human NK cells, identified using genome-wide mRNA and miRNA databases through hierarchical clustering analysis, gene ontology analysis and a miRNA target prediction program. The microRNA (miR)-583, which demonstrated the largest ratio change in mature NK cells, was highly correlated with IL2 receptor gamma (IL2Rγ) expression. The overexpression of miR-583 had an inhibitory effect on NK cell differentiation. In a reporter assay, the suppressive effect of miR-583 was ablated by mutating the putative miR-583 binding site of the IL2Rγ 3′ UTR. Therefore, we show that miR-583 acts as a negative regulator of NK cell differentiation by silencing IL2Rγ. Additionally, we provide a comprehensive database of genome-wide mRNA and miRNA expression during human NK cell differentiation, offering a better understanding of basic human NK cell biology for the application of human NK cells in immunotherapy.

Human natural killer cells: origin, receptors, function, and clinical applications

Natural killer (NK) cells are important effectors playing a relevant role in innate immunity, primarily in tumor surveillance and in defenses against viruses. Human NK cells recognize HLA class I molecules through surface receptors (KIR and NKG2A) that inhibit NK cell function and kill target cells that have lost (or underexpress) HLA class I molecules as it occurs in tumors or virus-infected cells. NK cell activation is mediated by an array of activating receptors and co-receptors that recognize ligands expressed primarily on tumors or virus-infected cells. In vivo anti-tumor NK cell activity may be suppressed by tumor or tumor-associated cells. Alloreactive NK cells (i.e. those that are not inhibited by the HLA class I alleles of the patient) derived from HSC of haploidentical donors play a major role in the cure of high-risk leukemia, by killing leukemia blasts and patient's DC, thus preventing tumor relapses and graft-versus-host disease. The expression of the HLA-C2-specific activating KIR2DS1 may also contribute to NK alloreactivity in patients expressing C2 alleles. A clear correlation has been proven between the size of the alloreactive NK cell population and the clinical outcome. Recently, haplo-HSCT has been further improved with the direct infusion, together with HSC, of donor-derived, mature alloreactive NK cells and TCRγδ(+) T cells - both contributing to a prompt anti-leukemia effect together with an efficient defense against pathogens during the 6- to 8-week interval required for the generation of alloreactive NK cells from HSC.

Subsets of human natural killer cells and their regulatory effects

Human natural killer (NK) cells have distinct functions as NK(tolerant) , NK(cytotoxic) and NK(regulatory) cells and can be divided into different subsets based on the relative expression of the surface markers CD27 and CD11b. CD27⁺ NK cells, which are abundant cytokine producers, are numerically in the minority in human peripheral blood but constitute the large population of NK cells in cord blood, spleen, tonsil and decidua tissues. Recent data suggest that these NK cells may have immunoregulatory properties under certain conditions. In this review, we will focus on these new NK cell subsets and discuss how regulatory NK cells may serve as rheostats or sentinels in controlling inflammation and maintaining immune homeostasis in various organs.

Understanding the role of ETS-mediated gene regulation in complex biological processes

Ets factors are members of one of the largest families of evolutionarily conserved transcription factors, regulating critical functions in normal cell homeostasis, which when perturbed contribute to tumor progression. The well-documented alterations in ETS factor expression and function during cancer progression result in pleiotropic effects manifested by the downstream effect on their target genes. Multiple ETS factors bind to the same regulatory sites present on target genes, suggesting redundant or competitive functions. The anti- and prometastatic signatures obtained by examining specific ETS regulatory networks will significantly improve our ability to accurately predict tumor progression and advance our understanding of gene regulation in cancer. Coordination of multiple ETS gene functions also mediates interactions between tumor and stromal cells and thus contributes to the cancer phenotype. As such, these new insights may provide a novel view of the ETS gene family as well as a focal point for studying the complex biological control involved in tumor progression. One of the goals of molecular biology is to elucidate the mechanisms that contribute to the development and progression of cancer. Such an understanding of the molecular basis of cancer will provide new possibilities for: (1) earlier detection, as well as better diagnosis and staging of disease; (2) detection of minimal residual disease recurrences and evaluation of response to therapy; (3) prevention; and (4) novel treatment strategies. Increased understanding of ETS-regulated biological pathways will directly impact these areas.

Frozen cord blood hematopoietic stem cells differentiate into higher numbers of functional natural killer cells in vitro than mobilized hematopoietic stem cells or freshly isolated cord blood hematopoietic stem cells

Adoptive natural killer (NK) cell therapy relies on the acquisition of large numbers of NK cells that are cytotoxic but not exhausted. NK cell differentiation from hematopoietic stem cells (HSC) has become an alluring option for NK cell therapy, with umbilical cord blood (UCB) and mobilized peripheral blood (PBCD34⁺) being the most accessible HSC sources as collection procedures are less invasive. In this study we compared the capacity of frozen or freshly isolated UCB hematopoietic stem cells (CBCD34⁺) and frozen PBCD34⁺ to generate NK cells in vitro. By modifying a previously published protocol, we showed that frozen CBCD34⁺ cultures generated higher NK cell numbers without loss of function compared to fresh CBCD34⁺ cultures. NK cells generated from CBCD34⁺ and PBCD34⁺ expressed low levels of killer-cell immunoglobulin-like receptors but high levels of activating receptors and of the myeloid marker CD33. However, blocking studies showed that CD33 expression did not impact on the functions of the generated cells. CBCD34⁺-NK cells exhibited increased capacity to secrete IFN-γ and kill K562 in vitro and in vivo as compared to PBCD34⁺-NK cells. Moreover, K562 killing by the generated NK cells could be further enhanced by IL-12 stimulation. Our data indicate that the use of frozen CBCD34⁺ for the production of NK cells in vitro results in higher cell numbers than PBCD34⁺, without jeopardizing their functionality, rendering them suitable for NK cell immunotherapy. The results presented here provide an optimal strategy to generate NK cells in vitro for immunotherapy that exhibit enhanced effector function when compared to alternate sources of HSC.

Transcription factor Runx3 regulates interleukin-15-dependent natural killer cell activation

Natural killer cells belong to the family of innate lymphoid cells comprising the frontline defense against infected and transformed cells. Development and activation of natural killer cells is highly dependent on interleukin-15 signaling. However, very little is known about the transcription program driving this process. The transcription factor Runx3 is highly expressed in natural killer cells, but its function in these cells is largely unknown. We show that loss of Runx3 impaired interleukin-15-dependent accumulation of mature natural killer cells in vivo and under culture conditions and pregnant Runx3(-/-) mice completely lack the unique population of interleukin-15-dependent uterine natural killer cells. Combined chromatin immunoprecipitation sequencing and differential gene expression analysis of wild-type versus Runx3-deficient in vivo activated splenic natural killer cells revealed that Runx3 cooperates with ETS and T-box transcription factors to drive the interleukin-15-mediated transcription program during activation of these cells. Runx3 functions as a nuclear regulator during interleukin-15-dependent activation of natural killer cells by regulating the expression of genes involved in proliferation, maturation, and migration. Similar studies with additional transcription factors will allow the construction of a more detailed transcriptional network that controls natural killer cell development and function.

KLRG1+ NK cells protect T-bet-deficient mice from pulmonary metastatic colorectal carcinoma

We studied the developmental and functional mechanisms behind NK cell-mediated antitumor responses against metastatic colorectal carcinoma (CRC) in mice. In particular, we focused on investigating the significance of T-box transcription factors and the immunotherapeutic relevance of IL-15 in the development and function of tumor-reactive NK cells. Pulmonary CRC metastases were experimentally seeded via an adoptive i.v. transfer of luciferase-expressing CT26 CRC cells that form viewable masses via an in vivo imaging device; genetically deficient mice were used to dissect the antitumor effects of developmentally different NK cell subsets. IL-15 precomplexed to IL-15 receptor-α was used in immunotherapy experiments. We found that mice deficient for the T-box transcription factor T-bet lack terminally differentiated antitumor CD27(low)KLRG1(+) NK cells, leading to a terminal course of rapid-onset pulmonary CRC metastases. The importance of this NK cell subset for effective antitumor immunity was shown by adoptively transferring purified CD27(low)KLRG1(+) NK cells into T-bet-deficient mice and, thereby, restoring immunity against lung metastasis formation. Importantly, immunity to metastasis formation could also be restored in T-bet-deficient recipients by treating mice with IL-15 precomplexed to IL-15 receptor-α, which induced the development of eomesodermin(+)KLRG1(+) NK cells from existing NK cell populations. Thus, contingent upon their T-bet-dependent development and activation status, NK cells can control metastatic CRC in mice, which is highly relevant for the development of immunotherapeutic approaches in the clinic.

Single-cell analysis of thymocyte differentiation: identification of transcription factor interactions and a major stochastic component in αβ-lineage commitment

T cell commitment and αβ/γδ lineage specification in the thymus involves interactions between many different genes. Characterization of these interactions thus requires a multiparameter analysis of individual thymocytes. We developed two efficient single-cell methods: (i) the quantitative evaluation of the co-expression levels of nine different genes, with a plating efficiency of 99–100% and a detection limit of 2 mRNA molecules/cell; and (ii) single-cell differentiation cultures, in the presence of OP9 cells transfected with the thymus Notch1 ligand DeltaL4. We show that during T cell commitment, Gata3 has a fundamental, dose-dependent role in maintaining Notch1 expression, with thymocytes becoming T-cell-committed when they co-express Notch1, Gata3 and Bc11b. Of the transcription factor expression patterns studied here, only that of Bcl11b was suggestive of a role in Pu1 down-regulation. Individual thymocytes became αβ/γδ lineage-committed at very different stages (from the TN2a stage onwards). However, 20% of TN3 cells are not αβ/γδ-lineage committed and TN4 cells comprise two main subpopulations with different degrees of maturity. The existence of a correlation between differentiation potential and expression of the pre-TCR showed that 83% of αβ-committed cells do not express the pre-TCR and revealed a major stochastic component in αβ-lineage specification.

Tissue-specific effector functions of innate lymphoid cells

Innate lymphoid cells (ILCs) is the collective term for a group of related innate lymphocytes, including natural killer (NK) cells and the more recently discovered non-NK ILCs, which all lack rearranged antigen receptors such as those expressed by T and B cells. Similar to NK cells, the newly discovered ILCs depend on the transcription factor Id2 and the common γ-chain of the interleukin-2 receptor for development. However, in contrast to NK cells, non-NK ILCs also require interleukin-7. In addition to the cytotoxic functions of NK cells, assuring protection against tumour development and viruses, new data indicate that ILCs contribute to a wide range of homeostatic and pathophysiological conditions in various organs via specialized cytokine production capabilities. Here we summarize current knowledge on ILCs with a particular emphasis on their tissue-specific effector functions, in the gut, liver, lungs and uterus. When possible, we try to highlight the role that these cells play in humans.

Epigenetic regulation of NK cell differentiation and effector functions

Upon maturation, natural killer (NK) cells acquire effector functions and regulatory receptors. New insights suggest a considerable functional heterogeneity and dynamic regulation of receptor expression in mature human NK cell subsets based on different developmental axes. Such processes include acquisition of lytic granules as well as regulation of cytokine production in response to exogenous cytokine stimulation or target cell interactions. One axis is regulated by expression of inhibitory receptors for self-MHC class I molecules, whereas other axes are less well defined but likely are driven by different activating receptor engagements or cytokines. Moreover, the recent identification of long-lived NK cell subsets in mice that are able to expand and respond rapidly following a secondary viral challenge suggest previously unappreciated plasticity in the programming of NK cell differentiation. Here, we review advances in our understanding of mature NK cell development and plasticity with regards to regulation of cellular function. Furthermore, we highlight some of the major questions that remain pertaining to the epigenetic changes that underlie the differentiation and functional specialization of NK cells and the regulation of their responses.

Regulation of murine natural killer cell commitment

Natural killer (NK) cells can derive from the same precursors as B and T cells, however, to achieve lineage specificity, several transcription factors need to be activated or annulled. While a few important transcription factors have been identified for NK genesis the mechanisms of how this is achieved is far from resolved. Adding to the complexity of this, NK cells are found and potentially develop in diverse locations in vivo and it remains to be addressed if a common NK cell precursor seeds diverse niches and how transcription factors may differentially regulate NK cell commitment in distinct microenvironments. Here we will summarize some recent findings in NK cell commitment and discuss how a NK cell transcriptional network might be organized, while addressing some misconceptions and anomalies along the way.

Tuning the threshold of natural killer cell responses

Natural killer cells are lymphocytes of the innate immune system that can kill an array of tumor and infected cells and secrete cytokines that participate in the shaping of the adaptive immune response. While it was believed that NK cell effector responses are acquired during maturation and then fixed, it appears that the threshold of NK cell responsiveness is more adaptable than originally thought. We review here how the local context provides several signals that impact on NK cell differentiation, responsiveness and shapes the antiviral and immunoregulatory outcome of NK cell activation.

Cryptotanshinone and tanshinone IIA enhance IL-15-induced natural killer cell differentiation

Natural killer (NK) cells are a subset of lymphocytes crucial for innate and adaptive immune responses. Here we show a stimulatory effect of cryptotanshinone (CTS) and tanshinone IIA (TS), isolated from Salvia miltiorrhiza Bunge, on the differentiation of NK cells. In the presence of IL-15, tanshinones increased NK cell maturation, NK cell differentiation and the expression of several transcription factors, including Id2, GATA3, T-bet, and Ets-1. Additionally, tanshinones increased p38 MAPK phosphorylation during NK cell differentiation. Furthermore, the p38 inhibitor SB203580 blocked the developmental effects of the tanshinones and suppressed Id2, T-bet, and Ets-1 expression during NK cell differentiation. These results suggest that tanshinones significantly increased IL-15-induced NK cell differentiation via enhancing the p38 phosphorylation and the expression of transcription factors.

Kruppel-like factor 4 (KLF4) promotes the survival of natural killer cells and maintains the number of conventional dendritic cells in the spleen

The development and survival of NK cells rely on a complex, spatiotemporal gene expression pattern regulated by specific transcription factors in NK cells and tissue-specific microenvironments supported by hematopoietic cells. Here, we show that somatic deletion of the KLF4 gene, using inducible and lineage-specific cre-transgenic mice, leads to a significant reduction of NK cells (NK1.1(+) TCR-β(-)) in the blood and spleen but not in the BM, liver, or LNs. Functional and immunophenotypic analyses revealed increased apoptosis of CD27(+/-) CD11b(+) NK cells in the spleen of KLF4-deficient mice, although remaining NK cells were able to lyse tumor target cells and produce IFN-γ. A normal recovery of adoptively transferred KLF4-deficient NK cells in WT hosts suggested that the survival defect was not intrinsic of NK cells. However, BM chimeras using KLF4-deficient mice as donors indicated that reduced survival of NK cells depended on BM-derived hematopoietic cells in the spleen. The number of CD11c(hi) DCs, which are known to support NK cell survival, was reduced significantly in the spleen of KLF4-deficient mice, likely a result of a lower number of precDC progenitor cells in this tissue. Taken together, our data suggest that the pluripotency-associated gene KLF4 is required for the maintenance of DCs in the spleen and consequently, survival of differentiated NK cells in this tissue.

The transcription factors T-bet and Eomes control key checkpoints of natural killer cell maturation

Natural killer (NK) cells play critical roles defending against tumors and pathogens. We show that mice lacking both transcription factors Eomesodermin (Eomes) and T-bet failed to develop NK cells. Developmental stability of immature NK cells constitutively expressing the death ligand TRAIL depended on T-bet. Conversely, maturation characterized by loss of constitutive TRAIL expression and induction of Ly49 receptor diversity and integrin CD49b (DX5(+)) required Eomes. Mature NK cells from which Eomes was deleted reverted to phenotypic immaturity if T-bet was present or downregulated NK lineage antigens if T-bet was absent, despite retaining expression of Ly49 receptors. Fetal and adult hepatic hematopoiesis restricted Eomes expression and limited NK development to the T-bet-dependent, immature stage, whereas medullary hematopoiesis permitted Eomes-dependent NK maturation in adult mice. These findings reveal two sequential, genetically separable checkpoints of NK cell maturation, the progression of which is metered largely by the anatomic localization of hematopoiesis.

miR-150 regulates the development of NK and iNKT cells

Natural killer (NK) and invariant NK T (iNKT) cells are critical in host defense against pathogens and for the initiation of adaptive immune responses. miRNAs play important roles in NK and iNKT cell development, maturation, and function, but the roles of specific miRNAs are unclear. We show that modulation of miR-150 expression levels has a differential effect on NK and iNKT cell development. Mice with a targeted deletion of miR-150 have an impaired, cell lineage-intrinsic defect in their ability to generate mature NK cells. Conversely, a gain-of-function miR-150 transgene promotes the development of NK cells, which display a more mature phenotype and are more responsive to activation. In contrast, overexpression of miR-150 results in a substantial reduction of iNKT cells in the thymus and in the peripheral lymphoid organs. The transcription factor c-Myb has been shown to be a direct target of miR-150. Our finding of increased NK cell and decreased iNKT cell frequencies in Myb heterozygous bone marrow chimeras suggests that miR-150 differentially controls the development of NK and iNKT cell lineages by targeting c-Myb.

Transcriptional control of natural killer cell differentiation and function

Gene expression can be modulated depending on physiological and developmental requirements. A multitude of regulatory genes, which are organized in interdependent networks, guide development and eventually generate specific phenotypes. Transcription factors (TF) are a key element in the regulatory cascade controlling cell fate and effector functions. In this review, we discuss recent data on the diversity of TF that determine natural killer (NK) cell fate and NK cell function.