The transcriptional repressor NKAP is required for the development of iNKT cells

The roles of epigenetic regulation in graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (aHSCT) is utilized as a potential curative treatment for various hematologic malignancies. However, graft-versus-host disease (GVHD) post-aHSCT is a severe complication that significantly impacts patients' quality of life and overall survival, becoming a major cause of non-relapse mortality. In recent years, the association between epigenetics and GVHD has garnered increasing attention. Epigenetics focuses on studying mechanisms that affect gene expression without altering DNA sequences, primarily including DNA methylation, histone modifications, non-coding RNAs (ncRNAs) regulation, and RNA modifications. This review summarizes the role of epigenetic regulation in the pathogenesis of GVHD, with a focus on DNA methylation, histone modifications, ncRNA, RNA modifications and their involvement and applications in the occurrence and development of GVHD. It also highlights advancements in relevant diagnostic markers and drugs, aiming to provide new insights for the clinical diagnosis and treatment of GVHD.

Mettl3-m6A-Creb1 forms an intrinsic regulatory axis in maintaining iNKT cell pool and functional differentiation

N6-methyladenosine (m6A) methyltransferase Mettl3 is involved in conventional T cell immunity; however, its role in innate immune cells remains largely unknown. Here, we show that Mettl3 intrinsically regulates invariant natural killer T (iNKT) cell development and function in an m6A-dependent manner. Conditional ablation of Mettl3 in CD4+CD8+ double-positive (DP) thymocytes impairs iNKT cell proliferation, differentiation, and cytokine secretion, which synergistically causes defects in B16F10 melanoma resistance. Transcriptomic and epi-transcriptomic analyses reveal that Mettl3 deficiency disturbs the expression of iNKT cell-related genes with altered m6A modification. Strikingly, Mettl3 modulates the stability of the Creb1 transcript, which in turn controls the protein and phosphorylation levels of Creb1. Furthermore, conditional targeting of Creb1 in DP thymocytes results in similar phenotypes of iNKT cells lacking Mettl3. Importantly, ectopic expression of Creb1 largely rectifies such developmental defects in Mettl3-deficient iNKT cells. These findings reveal that the Mettl3-m6A-Creb1 axis plays critical roles in regulating iNKT cells at the post-transcriptional layer.

Integrative scATAC-seq and scRNA-seq analyses map thymic iNKT cell development and identify Cbfβ for its commitment

Unlike conventional αβT cells, invariant natural killer T (iNKT) cells complete their terminal differentiation to functional iNKT1/2/17 cells in the thymus. However, underlying molecular programs that guide iNKT subset differentiation remain unclear. Here, we profiled the transcriptomes of over 17,000 iNKT cells and the chromatin accessibility states of over 39,000 iNKT cells across four thymic iNKT developmental stages using single-cell RNA sequencing (scRNA-seq) and single-cell assay for transposase-accessible chromatin sequencing (scATAC-seq) to define their developmental trajectories. Our study discovered novel features for iNKT precursors and different iNKT subsets and indicated that iNKT2 and iNKT17 lineage commitment may occur as early as stage 0 (ST0) by two distinct programs, while iNKT1 commitments may occur post ST0. Both iNKT1 and iNKT2 cells exhibit extensive phenotypic and functional heterogeneity, while iNKT17 cells are relatively homogenous. Furthermore, we identified that a novel transcription factor, Cbfβ, was highly expressed in iNKT progenitor commitment checkpoint, which showed a similar expression trajectory with other known transcription factors for iNKT cells development, Zbtb16 and Egr2, and could direct iNKT cells fate and drive their effector phenotype differentiation. Conditional deletion of Cbfβ blocked early iNKT cell development and led to severe impairment of iNKT1/2/17 cell differentiation. Overall, our findings uncovered distinct iNKT developmental programs as well as their cellular heterogeneity, and identified a novel transcription factor Cbfβ as a key regulator for early iNKT cell commitment.

New Insights into Epigenetic Regulation of T Cell Differentiation

Immature CD4⁻ CD8⁻ thymocytes progress through several developmental steps in the thymus, ultimately emerging as mature CD4⁺ (helper) or CD8⁺ (cytotoxic) T cells. Activation of naïve CD4⁺ and CD8⁺ T cells in the presence of specific cytokines results in the induction of transcriptional programs that result in their differentiation into effector or memory cells and in the case of CD4⁺ T cells, the adoption of distinct T-helper fates. Previous studies have shown that histone modification and DNA methylation play important roles in each of these events. More recently, the roles of specific epigenetic regulators in T cell differentiation have been clarified. The identification of the epigenetic modifications and modifiers that control mature T cell differentiation and specification has also provided further insights into how dysregulation of these processes can lead to cancer or autoimmune diseases. In this review, we summarize recent findings that have provided new insights into epigenetic regulation of T cell differentiation in both mice and humans.

Identification and characterization of the antigen recognized by the germ cell mAb TRA98 using a human comprehensive wet protein array

TRA98 is a rat monoclonal antibody (mAb) which recognizes a specific antigen in the nuclei of germ cells. mAb TRA98 has been used to understand the mechanism of germ cell development and differentiation in many studies. In mice, the antigen recognized by mAb TRA98 or GCNA1 has been reported to be a GCNA gene product, but despite the demonstration of the immunoreactivity of this mAb in human testis and sperm in 1997, the antigen in humans remains unknown, as of date. To identify the human antigen recognized by mAb TRA98, a human comprehensive wet protein array was developed containing 19,446 proteins derived from human cDNAs. Using this array, it was found that the antigen of mAb TRA98 is not a GCNA gene product, but nuclear factor-κB activating protein (NKAP). In mice, mAb TRA98 recognized both the GCNA gene product and NKAP. Furthermore, conditional knockout of Nkap in mice revealed a phenotype of Sertoli cell-only syndrome. Although NKAP is a ubiquitously expressed protein, NKAP recognized by mAb TRA98 in mouse testis was SUMOylated. These results suggest that NKAP undergoes modifications, such as SUMOylation in the testis, and plays an important role in spermatogenesis.

Chromatin assembly factor 1B critically controls the early development but not function acquisition of invariant natural killer T cells in mice

CD4⁺ CD8⁺ double-positive thymocytes give rise to both conventional TCRαβ⁺ T cells and invariant natural killer T cells (iNKT cells), but these two kinds of cells display different characteristics. The molecular mechanism underlying iNKT cell lineage development and function acquisition remain to be elucidated. We show that the loss of chromatin assembly factor 1B (CHAF1b) maintains the normal development of conventional TCRαβ⁺ T cells but severely impairs early development of iNKT cells. This dysregulation is accompanied by the impairment in chromatin activation and gene transcription at Vα14-Jα18 locus. Notably, ectopic expression of a Vα14-Jα18 TCR rescues Chaf1b-deficient iNKT cell developmental defects. Moreover, cytokine secretion and antitumor activity are substantially maintained in Vα14-Jα18 TCR transgene-rescued Chaf1b-deficient iNKT cells. Our study identifies CHAF1b as a critical factor that controls the early development but not function acquisition of iNKT cells via lineage- and stage-specific regulation.

Nuclear Factor-κB Activating Protein Plays an Oncogenic Role in Neuroblastoma Tumorigenesis and Recurrence Through the Phosphatidylinositol 3-Kinase/Protein Kinase B Signaling Pathway

Nuclear factor-κB activating protein (NKAP) is a conserved nuclear protein that acts as an oncogene in various cancers and is associated with a poor prognosis. This study aimed to investigate the role of NKAP in neuroblastoma (NB) progression and recurrence. We compared NKAP gene expression between 89 recurrence and 134 non-recurrence patients with NB by utilizing the ArrayExpress database. The relationship between NKAP expression and clinicopathological features was evaluated by correlation analysis. We knocked down NKAP expression in NB1 and SK-N-SH cells by small interfering RNA transfection to verify its role in tumor proliferation, apoptosis, and the phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling pathway. NKAP gene expression in NB tissues was significantly overexpressed in the recurrence group compared with the non-recurrence group, and NKAP was enriched in the PI3K/AKT pathway. Correlation analysis revealed NKAP expression was correlated with chromosome 11q deletion in patients with NB. Knockdown of NKAP expression significantly inhibited the proliferation and promoted the apoptosis of NB1 and SK-N-SH cells. Moreover, we found that small interfering NKAP significantly reduced p-PI3K and p-AKT expression. NKAP knockdown played an oncogenic role in NB by inhibiting PI3K/AKT signaling pathway activations both in vitro and in vivo. Our research revealed that NKAP mediates NB cells by inhibited proliferation and promoted apoptosis through activating the PI3K/AKT signaling pathways, and the expression of NKAP may act as a novel biomarker for predicting recurrence and chromosome 11q deletion in patients with NB.

Natural Killer T Lymphocytes Integrate Innate Sensory Information and Relay Context to Effector Immune Responses

It is now appreciated that a group of lymphoid lineage cells, collectively called innate-like effector lymphocytes, have evolved to integrate information relayed by the innate sensory immune system about the state of the local tissue environment and to pass on this context to downstream effector innate and adaptive immune responses. Thereby, innate functions engrained into such innate-like lymphoid lineage cells during development can control the quality and magnitude of an immune response to a tissue-altering pathogen and facilitate the formation of memory engrams within the immune system. These goals are accomplished by the innate lymphoid cells that lack antigen-specific receptors, γδ T cell receptor (TCR)-expressing T cells, and several αβ TCR-expressing T cell subsets-such as natural killer T cells, mucosal-associated invariant T cells, et cetera. Whilst we briefly consider the commonalities in the origins and functions of these diverse lymphoid subsets to provide context, the primary topic of this review is to discuss how the semi-invariant natural killer T cells got this way in evolution through lineage commitment and onward ontogeny. What emerges from this discourse is the question: Has a "limbic immune system" emerged (screaming quietly in plain sight!) out of what has been dubbed "in-betweeners"?

NKAP promotes renal cell carcinoma growth via AKT/mTOR signalling pathway

Renal cell carcinoma (RCC) is the seventh most common site for malignant tumours worldwide leading to a high risk of death. NKAP is a conserved nuclear protein that has critical roles in the development, maturation, and functional acquisition of T cells, iNKT cells, and cancers. But the function and underlying mechanism of NKAP in RCC is still unknown. Knockdown of NKAP by siRNA interference (siNKAP) was used to explore the roles of NAKP in human RCC cells. Here, we found that siNKAP strongly inhibited the proliferation and motility of Ketr-3 and 786-0 cells and induced cell apoptosis. Furthermore, the expression of anti-apoptotic protein Bcl2 in the siNKAP group was strongly decreased, while the expression of pro-apoptotic proteins Bax, cleaved Caspase-3, and cleaved Caspase-9 was significantly increased. Finally, to identify the potential mechanisms, we detected related proteins of the AKT/mTOR signalling pathway by western blot assay. We found that siNKAP significantly inhibited the expression of cyclin D1 and the phosphorylation of AKT and mTOR. The findings for the first time reveal that the AKT/mTOR signalling pathway is involved in the oncogenic role of NKAP in RCC, which provides an important basis for exploring the molecular regulation mechanism of RCC. SIGNIFICANCE OF THE STUDY: There is an urgent need to study the molecular mechanisms involved in RCC to promote the development of early diagnosis and more effective treatment options. This research provides an important basis for exploring the accurate regulatory mechanism of NKAP in RCC and a novel perspective to find the potential utility of NKAP inhibitors for RCC therapy.

Chromatin-Modifying Enzymes in T Cell Development

T cell development involves stepwise progression through defined stages that give rise to multiple T cell subtypes, and this is accompanied by the establishment of stage-specific gene expression. Changes in chromatin accessibility and chromatin modifications accompany changes in gene expression during T cell development. Chromatin-modifying enzymes that add or reverse covalent modifications to DNA and histones have a critical role in the dynamic regulation of gene expression throughout T cell development. As each chromatin-modifying enzyme has multiple family members that are typically all coexpressed during T cell development, their function is sometimes revealed only when two related enzymes are concurrently deleted. This work has also revealed that the biological effects of these enzymes often involve regulation of a limited set of targets. The growing diversity in the types and sites of modification, as well as the potential for a single enzyme to catalyze multiple modifications, is also highlighted.

Invariant NKT Cells Functionally Link Microbiota-Induced Butyrate Production and Joint Inflammation

Emerging evidence indicates that the gut microbiota contributes to the regulation of joint inflammation by modulating the function of immune cells. However, the mechanism by which the microbiota regulates joint inflammation is unclear. To address this, we investigated the effect of the gut microbiota on Ab-induced arthritis (AIA). Feeding mice a high-fiber diet attenuated AIA in a microbiota-dependent manner. Among the short-chain fatty acids produced by the microbiota, butyrate suppressed cytokine production by invariant NKT (iNKT) cells by inhibiting class I histone deacetylases. Furthermore, butyrate alleviated AIA in wild-type, but not iNKT cell-deficient Jα18 knockout (KO), mice. Adoptive transfer of butyrate-pretreated iNKT cells had no effect on AIA in Jα18 KO mice, whereas transfer of untreated iNKT cells into Jα18 KO mice restored AIA. In conclusion, our data indicate that gut microbiota-induced butyrate production attenuates AIA by inhibiting cytokine production by iNKT cells. Thus, the microbiota/butyrate/iNKT cell axis may be a therapeutic target for joint inflammation.

NKAP Regulates Senescence and Cell Death Pathways in Hematopoietic Progenitors

NKAP is a multi-functional nuclear protein that has been shown to be essential for hematopoiesis. Deletion of NKAP in hematopoietic stem cells (HSCs) was previously found to result in rapid lethality and hematopoietic failure. NKAP deficient cells also exhibited diminished proliferation and increased expression of the cyclin dependent kinase inhibitors (CDKIs) p19 Ink4d and p21 Cip1. To determine how dysregulation of CDKI expression contributes to the effects of NKAP deficiency, NKAP was deleted in mice also deficient in p19 Ink4d or p21 Cip1 using poly-IC treatment to induce Mx1-cre. Hematopoietic failure and lethality were not prevented by deficiency in either CDKI when NKAP was deleted. Inducible deletion of NKAP in cultured hematopoietic progenitors ex vivo resulted in a senescent phenotype and altered expression of numerous cell cycle regulators including the CDKI p16 INK4a. Interestingly, while combined deficiency in p16 INK4a and p21 Cip1 did not reverse the effect of NKAP deficiency on hematopoiesis in vivo, it did shift the consequence of NKAP deficiency from senescence to apoptosis in ex vivo cultures. These results suggest that NKAP may limit cellular stress that can trigger cell cycle withdrawal or cell death, a role critical for the maintenance of a viable pool of hematopoietic progenitors.

The Transcription Factor PLZF Is Necessary for the Development and Function of Mouse Basophils

Basophils are innate immune cells associated with type 2 immunity, allergic reactions, and host defense against parasite infections. In this study, we show that the transcription factor PLZF, which is known for its essential role in the function and development of several innate lymphocyte subsets, is also important for the myeloid-derived basophil lineage. PLZF-deficient mice had decreased numbers of basophil progenitors in the bone marrow and mature basophils in multiple peripheral tissues. Functionally, PLZF-deficient basophils were less responsive to IgE activation and produced reduced amounts of IL-4. The altered function of basophils resulted in a blunted Th2 T cell response to a protein allergen. Additionally, PLZF-deficient basophils had reduced expression of the IL-18 receptor, which impacted migration to lungs. PLZF, therefore, is a major player in controlling type 2 immune responses mediated not only by innate lymphocytes but also by myeloid-derived cells.

NKAP functions as an oncogene in Ewing sarcoma cells partly through the AKT signaling pathway

NF-κB activating protein (NKAP) is a highly conserved protein involved in transcriptional repression, immune cell development, maturation, acquisition of functional competency and maintenance of hematopoiesis. In the present study, the function of NKAP in the progress of Ewing sarcoma (ES) was investigated. It was identified that NKAP is highly expressed in ES cells when compared with human mesenchymal stem cells (MSCs). NKAP was knocked-down in human ES cell lines A673 and RD-ES using small interfering (si)RNA transfection. The effectiveness of transfection was then verified using reverse transcription-quantitative PCR and western blot analysis to determine mRNA and protein levels, respectively. The results of the proliferation assays indicated that the knockdown of NKAP inhibited the proliferation and clonogenic abilities of human ES cells. Transwell assays further indicated that cell invasion and migration were significantly inhibited by NKAP knockdown, which may be mediated by downregulation of matrix metalloproteinase (MMP)-9 activity. Gain-of-function analysis also demonstrated the positive role NKAP played in the proliferation, invasion and migration of ES cells. Cell apoptosis was evaluated by flow cytometry, which identified that apoptotic cells were significantly increased when NKAP was silenced. In addition, downregulation of NKAP increased the levels of Bax and cleaved caspase 3, but decreased Bcl2 levels, which suggested that the mitochondrial apoptosis pathway was activated. To explore the action mechanism of NKAP, the status of the AKT signaling pathway in NKAP-silenced A673 and RD-ES cells was investigated. Results indicated that NKAP knockdown led to decreased phosphorylation of AKT and expression of cyclin D1, a down-stream effector of the AKT signaling pathway, suggesting inactivation of the AKT signaling pathway. In conclusion, the present study revealed that NKAP promoted the proliferation, migration and invasion of ES cells, at least partly, through the AKT signaling pathway, providing new approaches for the therapeutic application of NKAP in ES.

The Interaction between NKAP and HDAC3 Is Critical for T Cell Maturation

NKAP and HDAC3 are critical for T cell maturation. NKAP and HDAC3 physically associate, and a point mutation in NKAP, NKAP(Y352A), abrogates this interaction. To evaluate the significance of NKAP and HDAC3 association in T cell maturation, transgenic mice were engineered for cre-mediated endogenous NKAP gene deletion coupled to induction of NKAP(Y352A) or a wild type (WT) control transgene, NKAP(WT), in double positive thymocytes or regulatory T cells (Tregs). T cell maturation was normal in mice with endogenous NKAP deletion coupled to NKAP(WT) induction. However, severe defects occurred in T cell and Treg maturation and in iNKT cell development when NKAP(Y352A) was induced, recapitulating NKAP deficiency. Conventional T cells expressing NKAP(Y352A) failed to enter the long-term T cell pool, did not produce cytokines, and remained complement susceptible, whereas Tregs expressing NKAP(Y352A) were eliminated as recent thymic emigrants leading to lethal autoimmunity. Overall, these results demonstrate the significance of NKAP-HDAC3 association in T cells.

NKAP alters tumor immune microenvironment and promotes glioma growth via Notch1 signaling

Background

Glioma is one of the most aggressive malignant brain tumors which is characterized with highly infiltrative growth and poor prognosis. NKAP (NF-κB activating protein) is a widely expressed 415-amino acid nuclear protein that is overexpressed by gliomas, but its function in glioma was still unknown.

Methods

CCK8 and EDU assay was used to examine the cell viability in vitro, and the xenograft models in nude mice were established to explore the roles of NAKP in vivo. The expressions of NKAP, Notch1 and SDF-1 were analyzed by immunofluorescence analysis. The expression of NKAP and Notch1 in glioma and normal human brain samples were analyzed by immunohistochemical analysis. In addition, CHIP, Gene chip, western blot, flow cytometry, immunofluorescence, ELISA and luciferase assay were used to investigate the internal connection between NKAP and Notch1.

Results

Here we showed that overexpression of NKAP in gliomas could promote tumor growth by contributing to a Notch1-dependent immune-suppressive tumor microenvironment. Downregulation of NKAP in gliomas had abrogated tumor growth and invasion in vitro and in vivo. Interestingly, compared to the control group, inhibiting NKAP set up obstacles to tumor-associated macrophage (TAM) polarization and recruitment by decreasing the secretion of SDF-1 and M-CSF. To identify the potential mechanisms involved, we performed RNA sequencing analysis and found that Notch1 appeared to positively correlate with the expression of NKAP. Furthermore, we proved that NKAP performed its function via directly binding to Notch1 promoter and trans-activating it. Notch1 inhibition could alleviate NKAP’s gliomagenesis effects.

Conclusion

these observations suggest that NKAP promotes glioma growth by TAM chemoattraction through upregulation of Notch1 and this finding introduces the potential utility of NKAP inhibitors for glioma therapy.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1281-1) contains supplementary material, which is available to authorized users.

NKAP Must Associate with HDAC3 to Regulate Hematopoietic Stem Cell Maintenance and Survival

NKAP is a multifunctional nuclear protein that associates with the histone deacetylase HDAC3. Although both NKAP and HDAC3 are critical for hematopoietic stem cell (HSC) maintenance and survival, it was not known whether these two proteins work together. To assess the importance of their association in vivo, serial truncation and alanine scanning was performed on NKAP to identify the minimal binding site for HDAC3. Mutation of either Y352 or F347 to alanine abrogated the association of NKAP with HDAC3, but did not alter NKAP localization or expression. Using a linked conditional deletion/re-expression system in vivo, we demonstrated that re-expression of the Y352A NKAP mutant failed to restore HSC maintenance and survival in mice when endogenous NKAP expression was eliminated using Mx1-cre and poly-IC, whereas re-expression of wild type NKAP maintained the HSC pool. However, Y352A NKAP did restore proliferation in murine embryonic fibroblasts when endogenous NKAP expression was eliminated using ER-cre and tamoxifen. Therefore, Y352 in NKAP is critical for association with HDAC3 and for HSC maintenance and survival but is not important for proliferation of murine embryonic fibroblasts, demonstrating that NKAP functions in different complexes in different cell types.

The Role of the Thymus in the Immune Response

The thymus is a primary lymphoid organ essential for the development of T lymphocytes, which orchestrate adaptive immune responses. T-cell development in the thymus is spatially regulated; key checkpoints in T-cell maturation and selection occur in cortical and medullary regions to eliminate self-reactive T cells, establish central tolerance, and export naïve T cells to the periphery with the potential to recognize diverse pathogens. Thymic output is also temporally regulated due to age-related involution of the thymus accompanied by loss of epithelial cells. This review discusses the structural and age-related control of thymus function in humans.

The ins and outs of type I iNKT cell development

Natural killer T (NKT) cells are innate-like lymphocytes that bridge the gap between the innate and adaptive immune responses. Like innate immune cells, they have a mature, effector phenotype that allows them to rapidly respond to threats, compared to adaptive cells. NKT cells express T cell receptors (TCRs) like conventional T cells, but instead of responding to peptide antigen presented by MHC class I or II, NKT cell TCRs recognize glycolipid antigen in the context of CD1d. NKT cells are subdivided into classes based on their TCR and antigen reactivity. This review will focus on type I iNKT cells that express a semi invariant Vα14Jα18 TCR and respond to the canonical glycolipid antigen, α-galactosylceramide. The innate-like effector functions of these cells combined with their T cell identity make their developmental path quite unique. In addition to the extrinsic factors that affect iNKT cell development such as lipid:CD1d complexes, co-stimulation, and cytokines, this review will provide a comprehensive delineation of the cell intrinsic factors that impact iNKT cell development, differentiation, and effector functions - including TCR rearrangement, survival and metabolism signaling, transcription factor expression, and gene regulation.

The Role of Autophagy in iNKT Cell Development

CD1d-restricted invariant natural killer T (iNKT) cells are innate-like T cells that express an invariant T cell receptor (TCR) α-chain and recognize self and foreign glycolipid antigens. They can rapidly respond to agonist activation and stimulate an extensive array of immune responses. Thymic development and function of iNKT cells are regulated by many different cellular processes, including autophagy, a self-degradation mechanism. In this mini review, we discuss the current understanding of how autophagy regulates iNKT cell development and effector lineage differentiation. Importantly, we propose that iNKT cell development is tightly controlled by metabolic reprogramming.

How Lipid-Specific T Cells Become Effectors: The Differentiation of iNKT Subsets

In contrast to peptide-recognizing T cells, invariant natural killer T (iNKT) cells express a semi-invariant T cell receptor that specifically recognizes self- or foreign-lipids presented by CD1d molecules. There are three major functionally distinct effector states for iNKT cells. Owning to these innate-like effector states, iNKT cells have been implicated in early protective immunity against pathogens. Yet, growing evidence suggests that iNKT cells play a role in tissue homeostasis as well. In this review, we discuss current knowledge about the underlying mechanisms that regulate the effector states of iNKT subsets, with a highlight on the roles of a variety of transcription factors and describe how each subset influences different facets of thymus homeostasis.

Histone Deacetylase 7 mediates tissue-specific autoimmunity via control of innate effector function in invariant Natural Killer T Cells

We report that Histone Deacetylase 7 (HDAC7) controls the thymic effector programming of Natural Killer T (NKT) cells, and that interference with this function contributes to tissue-specific autoimmunity. Gain of HDAC7 function in thymocytes blocks both negative selection and NKT development, and diverts Vα14/Jα18 TCR transgenic thymocytes into a Tconv-like lineage. Conversely, HDAC7 deletion promotes thymocyte apoptosis and causes expansion of innate-effector cells. Investigating the mechanisms involved, we found that HDAC7 binds PLZF and modulates PLZF-dependent transcription. Moreover, HDAC7 and many of its transcriptional targets are human risk loci for IBD and PSC, autoimmune diseases that strikingly resemble the disease we observe in HDAC7 gain-of-function in mice. Importantly, reconstitution of iNKT cells in these mice mitigated their disease, suggesting that the combined defects in negative selection and iNKT cells due to altered HDAC7 function can cause tissue-restricted autoimmunity, a finding that may explain the association between HDAC7 and hepatobiliary autoimmunity.

Unraveling Natural Killer T-Cells Development

Natural killer T-cells are a subset of innate-like T-cells with the ability to bridge innate and adaptive immunity. There is great interest in harnessing these cells to improve tumor therapy; however, greater understanding of invariant NKT (iNKT) cell biology is needed. The first step is to learn more about NKT development within the thymus. Recent studies suggest lineage separation of murine iNKT cells into iNKT1, iNKT2, and iNKT17 cells instead of shared developmental stages. This review will focus on these new studies and will discuss the evidence for lineage separation in contrast to shared developmental stages. The author will also highlight the classifications of murine iNKT cells according to identified transcription factors and cytokine production, and will discuss transcriptional and posttranscriptional regulations, and the role of mammalian target of rapamycin. Finally, the importance of these findings for human cancer therapy will be briefly discussed.

Natural Killer T Cells: An Ecological Evolutionary Developmental Biology Perspective

Type I natural killer T (NKT) cells are innate-like T lymphocytes that recognize glycolipid antigens presented by the MHC class I-like protein CD1d. Agonistic activation of NKT cells leads to rapid pro-inflammatory and immune modulatory cytokine and chemokine responses. This property of NKT cells, in conjunction with their interactions with antigen-presenting cells, controls downstream innate and adaptive immune responses against cancers and infectious diseases, as well as in several inflammatory disorders. NKT cell properties are acquired during development in the thymus and by interactions with the host microbial consortium in the gut, the nature of which can be influenced by NKT cells. This latter property, together with the role of the host microbiota in cancer therapy, necessitates a new perspective. Hence, this review provides an initial approach to understanding NKT cells from an ecological evolutionary developmental biology (eco-evo-devo) perspective.

The corepressor NCOR1 regulates the survival of single-positive thymocytes

Nuclear receptor corepressor 1 (NCOR1) is a transcriptional regulator bridging repressive chromatin modifying enzymes with transcription factors. NCOR1 regulates many biological processes, however its role in T cells is not known. Here we show that Cd4-Cre-mediated deletion of NCOR1 (NCOR1 cKO^Cd4) resulted in a reduction of peripheral T cell numbers due to a decrease in single-positive (SP) thymocytes. In contrast, double-positive (DP) thymocyte numbers were not affected in the absence of NCOR1. The reduction in SP cells was due to diminished survival of NCOR1-null postselection TCRβ^hiCD69⁺ and mature TCRβ^hiCD69^- thymocytes. NCOR1-null thymocytes expressed elevated levels of the pro-apoptotic factor BIM and showed a higher fraction of cleaved caspase 3-positive cells upon TCR stimulation ex vivo. However, staphylococcal enterotoxin B (SEB)-mediated deletion of Vβ8⁺ CD4SP thymocytes was normal, suggesting that negative selection is not altered in the absence of NCOR1. Finally, transgenic expression of the pro-survival protein BCL2 restored the population of CD69⁺ thymocytes in NCOR1 cKO^Cd4 mice to a similar percentage as observed in WT mice. Together, these data identify NCOR1 as a crucial regulator of the survival of SP thymocytes and revealed that NCOR1 is essential for the proper generation of the peripheral T cell pool.

HDAC4 is expressed on multiple T cell lineages but dispensable for their development and function

Histone deacetylation, reciprocally mediated by histone deacetylases (HDAC) and acetyltransferases, represents one major form of post-translational modification. Previous research indicates that HDACs play an essential regulatory role in the development of various immune cells. However, the specific function of individual HDACs remains largely unexplored. HDAC4, a member of class II HDACs, profoundly investigated in the nervous system, while the expression profile and function of HDAC4 in T cells are barely known. For the first time, we report here that HDAC4 is expressed in the multiple T cell lineages. Using T-cell-specific HDAC4-deficient mice, we discovered that lack of HDAC4 did not alter the frequencies of conventional T cells, invariant NKT (iNKT) cells or regulatory T cells within both the thymus and secondary lymphoid organs. Moreover, conventional T cells and iNKT cells from wild-type and HDAC4-deficient mice displayed no significant difference in cytokine production. In conclusion, our results imply that under steady stage, HDAC4 is not required for the development and function of multiple T cell lineages, including conventional T cells and iNKT cells.

Isoform-selective inhibitor of histone deacetylase 3 (HDAC3) limits pancreatic islet infiltration and protects female nonobese diabetic mice from diabetes

Preservation of insulin-secreting β-cells is an important goal for therapies aimed at restoring normoglycemia in patients with diabetes. One approach, the inhibition of histone deacetylases (HDACs), has been reported to suppress pancreatic islet inflammation and β-cell apoptosis in vitro In this report, we demonstrate the efficacy of HDAC inhibitors (HDACi) in vivo We show that daily administration of BRD3308, an isoform-selective HDAC3 inhibitor, for 2 weeks to female nonobese diabetic (NOD) mice, beginning at 3 weeks of age, followed by twice-weekly injections until age 25 weeks, protects the animals from diabetes. The preservation of β-cells was because of a significant decrease in islet infiltration of mononuclear cells. Moreover, the BRD3308 treatment increased basal insulin secretion from islets cultured in vitro All metabolic tissues tested in vehicle- or BRD3308-treated groups showed virtually no sign of immune cell infiltration, except minimal infiltration in white adipose tissue in animals treated with the highest BRD3308 dose (10 mg/kg), providing additional evidence of protection from immune attack in the treated groups. Furthermore, pancreata from animals treated with 10 mg/kg BRD3308 exhibited significantly decreased numbers of apoptotic β-cells compared with those treated with vehicle or low-dose BRD3308. Finally, animals treated with 1 or 10 mg/kg BRD3308 had enhanced β-cell proliferation. These in vivo results point to the potential use of selective HDAC3 inhibitors as a therapeutic approach to suppress pancreatic islet infiltration and prevent β-cell death with the long-term goal of limiting the progression of type 1 diabetes.

The differentiation of ROR-γt expressing iNKT17 cells is orchestrated by Runx1

iNKT cells are a unique lineage of T cells that recognize glycolipid presented by CD1d. In the thymus, they differentiate into iNKT1, iNKT2 and iNKT17 effector subsets, characterized by preferential expression of Tbet, Gata3 and ROR-γt and production of IFN-γ, IL-4 and IL-17, respectively. We demonstrate that the transcriptional regulator Runx1 is essential for the generation of ROR-γt expressing iNKT17 cells. PLZF-cre Runx1 cKO mice lack iNKT17 cells in the thymus, spleen and liver. Runx1-deficient iNKT cells have altered expression of several genes important for iNKT17 differentiation, including decreased expression of IL-7Rα, BATF and c-Maf and increased expression of Bcl11b and Lef1. However, reduction of Lef1 expression or introduction of an IL-7Rα transgene is not sufficient to correct the defect in iNKT17 differentiation, demonstrating that Runx1 is a key regulator of several genes required for iNKT17 differentiation. Loss of Runx1 leads to a severe decrease in iNKT cell numbers in the thymus, spleen and liver. The decrease in cell number is due to a combined decrease in proliferation at Stage 1 during thymic development and increased apoptosis. Thus, we describe a novel role of Runx1 in iNKT cell development and differentiation, particularly in orchestrating iNKT17 differentiation.

Deacetylase activity of histone deacetylase 3 is required for productive VDJ recombination and B-cell development

Histone deacetylase 3 (HDAC3) is the catalytic component of NCoR/SMRT corepressor complexes that mediate the actions of transcription factors implicated in the regulation of B-cell development and function. We crossed Hdac3 conditional knockout mice with Mb1-Cre knockin animals to delete Hdac3 in early progenitor B cells. The spleens of Hdac3^F/-Mb1-Cre^+/- mice were virtually devoid of mature B cells, and B220⁺CD43⁺ B-cell progenitors accumulated within the bone marrow. Quantitative deep sequencing of the Ig heavy chain locus from B220⁺CD43⁺ populations identified a defect in V_HDJ_H recombination with a severe reduction in productive rearrangements, which directly corresponded to the loss of pre-B cells from Hdac3^Δ/- bone marrow. For Hdac3^Δ/- B cells that did show productive VDJ rearrangement, there was significant skewing toward the incorporation of proximal V_H gene segments and a corresponding reduction in distal V_H gene segment use. Although transcriptional effects within these loci were modest, Hdac3^Δ/- progenitor cells displayed global changes in chromatin structure that likely hindered effective distal V-DJ recombination. Reintroduction of wild-type Hdac3 restored normal B-cell development, whereas an Hdac3 point mutant lacking deacetylase activity failed to complement this defect. Thus, the deacetylase activity of Hdac3 is required for the generation of mature B cells.

Histone deacetylase 3 is required for iNKT cell development

NKT cells are a distinct subset that have developmental requirements that often differ from conventional T cells. Here, we show that NKT-specific deletion of Hdac3 results in a severe reduction in the number of iNKT cells, particularly of NKT1 cells. In addition, there is decreased cytokine production by Hdac3-deficient NKT2 and NKT17 cells. Hdac3-deficient iNKT cells have increased cell death that is not rescued by transgenic expression of Bcl-2 or Bcl-xL. Hdac3-deficient iNKT cells have less Cyto-ID staining and lower LC3A/B expression, indicative of reduced autophagy. Interestingly, Hdac3-deficient iNKT cells also have lower expression of the nutrient receptors GLUT1, CD71 and CD98, which would increase the need for autophagy when nutrients are limiting. Therefore, Hdac3 is required for iNKT cell development and differentiation.

Atlantic salmon populations reveal adaptive divergence of immune related genes - a duplicated genome under selection

Background

Populations of Atlantic salmon display highly significant genetic differences with unresolved molecular basis. These differences may result from separate postglacial colonization patterns, diversifying natural selection and adaptation, or a combination. Adaptation could be influenced or even facilitated by the recent whole genome duplication in the salmonid lineage which resulted in a partly tetraploid species with duplicated genes and regions.

Results

In order to elucidate the genes and genomic regions underlying the genetic differences, we conducted a genome wide association study using whole genome resequencing data from eight populations from Northern and Southern Norway. From a total of ~4.5 million sequencing-derived SNPs, more than 10 % showed significant differentiation between populations from these two regions and ten selective sweeps on chromosomes 5, 10, 11, 13–15, 21, 24 and 25 were identified. These comprised 59 genes, of which 15 had one or more differentiated missense mutation. Our analysis showed that most sweeps have paralogous regions in the partially tetraploid genome, each lacking the high number of significant SNPs found in the sweeps. The most significant sweep was found on Chr 25 and carried several missense mutations in the antiviral mx genes, suggesting that these populations have experienced differing viral pressures. Interestingly the second most significant sweep, found on Chr 5, contains two genes involved in the NF-KB pathway (nkap and nkrf), which is also a known pathogen target that controls a large number of processes in animals.

Conclusion

Our results show that natural selection acting on immune related genes has contributed to genetic divergence between salmon populations in Norway. The differences between populations may have been facilitated by the plasticity of the salmon genome. The observed signatures of selection in duplicated genomic regions suggest that the recently duplicated genome has provided raw material for evolutionary adaptation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2867-z) contains supplementary material, which is available to authorized users.

Transcription factor Bcl11b sustains iNKT1 and iNKT2 cell programs, restricts iNKT17 cell program, and governs iNKT cell survival

Invariant natural killer T (iNKT) cells are innate-like T cells that recognize glycolipid antigens and play critical roles in regulation of immune responses. Based on expression of the transcription factors (TFs) Tbet, Plzf, and Rorγt, iNKT cells have been classified in effector subsets that emerge in the thymus, namely, iNKT1, iNKT2, and iNKT17. Deficiency in the TF Bcl11b in double-positive (DP) thymocytes has been shown to cause absence of iNKT cells in the thymus and periphery due to defective self glycolipid processing and presentation by DP thymocytes and undefined intrinsic alterations in iNKT precursors. We used a model of cre-mediated postselection deletion of Bcl11b in iNKT cells to determine its intrinsic role in these cells. We found that Bcl11b is expressed equivalently in all three effector iNKT subsets, and its removal caused a reduction in the numbers of iNKT1 and iNKT2 cells, but not in the numbers of iNKT17 cells. Additionally, we show that Bcl11b sustains subset-specific cytokine production by iNKT1 and iNKT2 cells and restricts expression of iNKT17 genes in iNKT1 and iNKT2 subsets, overall restraining the iNKT17 program in iNKT cells. The total numbers of iNKT cells were reduced in the absence of Bcl11b both in the thymus and periphery, associated with the decrease in iNKT1 and iNKT2 cell numbers and decrease in survival, related to changes in survival/apoptosis genes. Thus, these results extend our understanding of the role of Bcl11b in iNKT cells beyond their selection and demonstrate that Bcl11b is a key regulator of iNKT effector subsets, their function, identity, and survival.

HDAC3 Is Required for the Downregulation of RORγt during Thymocyte Positive Selection

To generate functional peripheral T cells, proper gene regulation during T cell development is critical. In this study, we found that histone deacetylase (HDAC) 3 is required for T cell development. T cell development in CD2-icre HDAC3 conditional knockout (cKO) mice (HDAC3-cKO) was blocked at positive selection, resulting in few CD4 and CD8 T cells, and it could not be rescued by a TCR transgene. These single-positive thymocytes failed to upregulate Bcl-2, leading to increased apoptosis. HDAC3-cKO mice failed to downregulate retinoic acid-related orphan receptor (ROR) γt during positive selection, similar to the block in positive selection in RORγt transgenic mice. In the absence of HDAC3, the RORC promoter was hyperacetylated. In the periphery, the few CD4 T cells present were skewed toward RORγt(+) IL-17-producing Th17 cells, leading to inflammatory bowel disease. Positive selection of CD8 single-positive thymocytes was restored in RORγt-KO Bcl-xL transgenic HDAC3-cKO mice, demonstrating that HDAC3 is required at positive selection to downregulate RORγt.

NKAP Regulates Invariant NKT Cell Proliferation and Differentiation into ROR-γt-Expressing NKT17 Cells

Invariant NKT (iNKT) cells are a unique lineage with characteristics of both adaptive and innate lymphocytes, and they recognize glycolipids presented by an MHC class I-like CD1d molecule. During thymic development, iNKT cells also differentiate into NKT1, NKT2, and NKT17 functional subsets that preferentially produce cytokines IFN-γ, IL-4, and IL-17, respectively, upon activation. Newly selected iNKT cells undergo a burst of proliferation, which is defective in mice with a specific deletion of NKAP in the iNKT cell lineage, leading to severe reductions in thymic and peripheral iNKT cell numbers. The decreased cell number is not due to defective homeostasis or increased apoptosis, and it is not rescued by Bcl-xL overexpression. NKAP is also required for differentiation into NKT17 cells, but NKT1 and NKT2 cell development and function are unaffected. This failure in NKT17 development is rescued by transgenic expression of promyelocytic leukemia zinc finger; however, the promyelocytic leukemia zinc finger transgene does not restore iNKT cell numbers or the block in positive selection into the iNKT cell lineage in CD4-cre NKAP conditional knockout mice. Therefore, NKAP regulates multiple steps in iNKT cell development and differentiation.

Histone Deacetylase 3 Is Required for Efficient T Cell Development

Hdac3 is a key target for Hdac inhibitors that are efficacious in cutaneous T cell lymphoma. Moreover, the regulation of chromatin structure is critical as thymocytes transition from an immature cell with open chromatin to a mature T cell with tightly condensed chromatin. To define the phenotypes controlled by Hdac3 during T cell development, we conditionally deleted Hdac3 using the Lck-Cre transgene. This strategy inactivated Hdac3 in the double-negative stages of thymocyte development and caused a significant impairment at the CD8 immature single-positive (ISP) stage and the CD4/CD8 double-positive stage, with few mature CD4(+) or CD8(+) single-positive cells being produced. When Hdac3(-/-) mice were crossed with Bcl-xL-, Bcl2-, or TCRβ-expressing transgenic mice, a modest level of complementation was found. However, when the null mice were crossed with mice expressing a fully rearranged T cell receptor αβ transgene, normal levels of CD4 single-positive cells were produced. Thus, Hdac3 is required for the efficient transit from double-negative stage 4 through positive selection.

Zbtb16 (PLZF) is stably suppressed and not inducible in non-innate T cells via T cell receptor-mediated signaling

The transcription factor PLZF (promyelocytic leukemia zinc finger; zbtb16) is essential for nearly all of the unique characteristics of NKT cells including their rapid and potent response to antigen. In the immune system, zbtb16 expression is only found in innate cells. Conventional T cells that ectopically express PLZF spontaneously acquire an activated, effector phenotype. Activation induced expression of lineage defining transcription factors such as T-bet, FoxP3, RORγt, GATA3 and others is essential for naïve T cell differentiation into effector T cells. In this study, we used sensitive genetic-based approaches to assess the induction of PLZF expression in non-innate T cells by T cell receptor (TCR)-mediated activation. Surprisingly, we found that PLZF was stably repressed in non-innate T cells and that TCR-mediated signaling was not sufficient to induce PLZF in conventional T cells. The inactivated state of PLZF was stably maintained in mature T cells, even under inflammatory conditions imposed by bacterial infection. Collectively, our data show that, in contrast to multiple recent reports, PLZF expression is highly specific to innate T cells and cannot be induced in conventional T cells via TCR-mediated activation or inflammatory challenge.

Histone Deacetylase 3 Is Required for T Cell Maturation

Recent thymic emigrants are newly generated T cells that need to undergo postthymic maturation to gain functional competency and enter the long-lived naive T cell pool. The mechanism of T cell maturation remains incompletely understood. Previously, we demonstrated that the transcriptional repressor NKAP is required for T cell maturation. Because NKAP associates with histone deacetylase 3 (HDAC3), we examined whether HDAC3 is also required for T cell maturation. Although thymic populations are similar in CD4-cre HDAC3 conditional knockout mice compared with wild-type mice, the peripheral numbers of CD4(+) and CD8(+) T cells are dramatically decreased. In the periphery, the majority of HDAC3-deficient naive T cells are recent thymic emigrants, indicating a block in T cell maturation. CD55 upregulation during T cell maturation is substantially decreased in HDAC3-deficient T cells. Consistent with a block in functional maturation, HDAC3-deficient peripheral T cells have a defect in TNF licensing after TCR/CD28 stimulation. CD4-cre HDAC3 conditional knockout mice do not have a defect in intrathymic migration, thymic egress, T cell survival, or homeostasis. In the periphery, similar to immature NKAP-deficient peripheral T cells, HDAC3-deficient peripheral T cells were bound by IgM and complement proteins, leading to the elimination of these cells. In addition, HDAC3-deficient T cells display decreases in the sialic acid modifications on the cell surface that recruit natural IgM to initiate the classical complement pathway. Therefore, HDAC3 is required for T cell maturation.

Class I HDACs Affect DNA Replication, Repair, and Chromatin Structure: Implications for Cancer Therapy

SIGNIFICANCE

The contribution of epigenetic alterations to cancer development and progression is becoming increasingly clear, prompting the development of epigenetic therapies. Histone deacetylase inhibitors (HDIs) represent one of the first classes of such therapy. Two HDIs, Vorinostat and Romidepsin, are broad-spectrum inhibitors that target multiple histone deacetylases (HDACs) and are FDA approved for the treatment of cutaneous T-cell lymphoma. However, the mechanism of action and the basis for the cancer-selective effects of these inhibitors are still unclear.

RECENT ADVANCES

While the anti-tumor effects of HDIs have traditionally been attributed to their ability to modify gene expression after the accumulation of histone acetylation, recent studies have identified the effects of HDACs on DNA replication, DNA repair, and genome stability. In addition, the HDIs available in the clinic target multiple HDACs, making it difficult to assign either their anti-tumor effects or their associated toxicities to the inhibition of a single protein. However, recent studies in mouse models provide insights into the tissue-specific functions of individual HDACs and their involvement in mediating the effects of HDI therapy.

CRITICAL ISSUES

Here, we describe how altered replication contributes to the efficacy of HDAC-targeted therapies as well as discuss what knowledge mouse models have provided to our understanding of the specific functions of class I HDACs, their potential involvement in tumorigenesis, and how their disruption may contribute to toxicities associated with HDI treatment.

FUTURE DIRECTIONS

Impairment of DNA replication by HDIs has important therapeutic implications. Future studies should assess how best to exploit these findings for therapeutic gain.

FOXP3+ regulatory T cell development and function require histone/protein deacetylase 3

Treg dysfunction is associated with a variety of inflammatory diseases. Treg populations are defined by expression of the oligomeric transcription factor FOXP3 and inability to produce IL-2, a cytokine required for T cell maintenance and survival. FOXP3 activity is regulated post-translationally by histone/protein acetyltransferases and histone/protein deacetylases (HDACs). Here, we determined that HDAC3 mediates both the development and function of the two main Treg subsets, thymus-derived Tregs and induced Tregs (iTregs). We determined that HDAC3 and FOXP3 physically interact and that HDAC3 expression markedly reduces Il2 promoter activity. In murine models, conditional deletion of Hdac3 during thymic Treg development restored Treg production of IL-2 and blocked the suppressive function of Tregs. HDAC3-deficient mice died from autoimmunity by 4-6 weeks of age; however, injection of WT FOXP3+ Tregs prolonged survival. Adoptive transfer of Hdac3-deficient Tregs, unlike WT Tregs, did not control T cell proliferation in naive mice and did not prevent allograft rejection or colitis. HDAC3 also regulated the development of iTregs, as HDAC3-deficient conventional T cells were not converted into iTregs under polarizing conditions and produced large amounts of IL-2, IL-6, and IL-17. We conclude that HDAC3 is essential for the normal development and suppressive functions of thymic and peripheral FOXP3+ Tregs.

Immature recent thymic emigrants are eliminated by complement

Recent thymic emigrants (RTEs) must undergo phenotypic and functional maturation to become long-lived mature naive T cells. In CD4-cre NKAP conditional knockout mice, NKAP-deficient RTEs fail to complete T cell maturation. In this study, we demonstrate that NKAP-deficient immature RTEs do not undergo apoptosis, but are eliminated by complement. C3, C4, and C1q are bound to NKAP-deficient peripheral T cells, demonstrating activation of the classical arm of the complement pathway. As thymocytes mature and exit to the periphery, they increase sialic acid incorporation into cell surface glycans. This is essential to peripheral lymphocyte survival, as stripping sialic acid with neuraminidase leads to the binding of natural IgM and complement fixation. NKAP-deficient T cells have a defect in sialylation on cell surface glycans, leading to IgM recruitment. We demonstrate that the defect in sialylation is due to aberrant α2,8-linked sialylation, and the expression of three genes (ST8sia1, ST8sia4, and ST8sia6) that mediate α2,8 sialylation are downregulated in NKAP-defcient RTEs. The maturation of peripheral NKAP-deficient T cells is partially rescued in a C3-deficient environment. Thus, sialylation during T cell maturation is critical to protect immature RTEs from complement in the periphery.

Coactosin-like 1 antagonizes cofilin to promote lamellipodial protrusion at the immune synapse

Actin depolymerizing factor-homology (ADF-H) family proteins regulate actin filament dynamics at multiple cellular locations. Herein, we have investigated the function of the ADF-H family member coactosin-like 1 (COTL1) in the regulation of actin dynamics at the T cell immune synapse (IS). We initially identified COTL1 in a genetic screen to identify novel regulators of T cell activation, and subsequently found that it associates with F-actin and localizes at the IS in response to TCR+CD28 stimulation. Live cell microscopy showed that depletion of COTL1 protein impaired T cell spreading in response to TCR ligation and abrogated lamellipodial protrusion at the T cell – B cell contact site, producing only a band of F-actin. Significantly, re-expression of wild type COTL1, but not a mutant deficient in F-actin binding could rescue these defects. In addition, COTL1 depletion reduced T cell migration. In vitro studies showed that COTL1 and cofilin compete with each other for binding to F-actin, and COTL1 protects F-actin from cofilin-mediated depolymerization. While depletion of cofilin enhanced F-actin assembly and lamellipodial protrusion at the IS, concurrent depletion of both COTL1 and cofilin restored lamellipodia formation. Taken together, our results suggest that COTL1 regulates lamellipodia dynamics in part by protecting F-actin from cofilin-mediated disassembly.

NKT cell-TCR expression activates conventional T cells in vivo, but is largely dispensable for mature NKT cell biology

Natural killer T (NKT) cell development depends on recognition of self-glycolipids via their semi-invariant Vα14i-TCR. However, to what extent TCR-mediated signals determine identity and function of mature NKT cells remains incompletely understood. To address this issue, we developed a mouse strain allowing conditional Vα14i-TCR expression from within the endogenous Tcrα locus. We demonstrate that naïve T cells are activated upon replacement of their endogenous TCR repertoire with Vα14i-restricted TCRs, but they do not differentiate into NKT cells. On the other hand, induced TCR ablation on mature NKT cells did not affect their lineage identity, homeostasis, or innate rapid cytokine secretion abilities. We therefore propose that peripheral NKT cells become unresponsive to and thus are independent of their autoreactive TCR.

Immune system natural killer T (NKT) cells help to protect against certain strains of bacteria and viruses, and suppress the development of autoimmune diseases and cancer. However, NKT cells are also central mediators of allergic responses. The recognition of one's own glycolipid antigens (self-glycolipids) in the thymus via the unique Vα14i T cell receptor, Vα14i-TCR, triggers the NKT cell developmental program, which differs considerably from that of conventional T cells. We generated a mouse model to investigate whether the Vα14i-TCR on mature NKT cells constantly recognizes self-glycolipids and to assess whether this TCR is required for survival and continued NKT cell identity. Switching the peptide-recognizing TCR of a mature conventional T cell to a glycolipid-recognizing Vα14i-TCR led to activation of the T cells, indicating that this TCR is also autoreactive on peripheral T cells or can signal autonomously. But TCR ablation did not affect the half-life, characteristic gene expression or innate functions of mature NKT cells. Therefore, the inherently autoreactive Vα14i-TCR is dispensable for the functions of mature peripheral NKT cells after instructing thymic NKT cell development. Thus the Vα14i-TCR serves a similar function to pattern-recognition receptors, in mediating immune recognition of foreign invasion or diseased cells.