Runt-related transcription factor 3 is involved in the altered phenotype and function in ThPok-deficient invariant natural killer T cells

Markers and makers of NKT17 cells

Invariant natural killer T (iNKT) cells are thymus-generated innate-like αβ T cells that undergo terminal differentiation in the thymus. Such a developmental pathway differs from that of conventional αβ T cells, which are generated in the thymus but complete their functional maturation in peripheral tissues. Multiple subsets of iNKT cells have been described, among which IL-17-producing iNKT cells are commonly referred to as NKT17 cells. IL-17 is considered a proinflammatory cytokine that can play both protective and pathogenic roles and has been implicated as a key regulatory factor in many disease settings. Akin to other iNKT subsets, NKT17 cells acquire their effector function during thymic development. However, the cellular mechanisms that drive NKT17 subset specification, and how iNKT cells in general acquire their effector function prior to antigen encounter, remain largely unknown. Considering that all iNKT cells express the canonical Vα14-Jα18 TCRα chain and all iNKT subsets display the same ligand specificity, i.e., glycolipid antigens in the context of the nonclassical MHC-I molecule CD1d, the conundrum is explaining how thymic NKT17 cell specification is determined. Mapping of the molecular circuitry of NKT17 cell differentiation, combined with the discovery of markers that identify NKT17 cells, has provided new insights into the developmental pathway of NKT17 cells. The current review aims to highlight recent advances in our understanding of thymic NKT17 cell development and to place these findings in the larger context of iNKT subset specification and differentiation.

NuRD complex recruitment to Thpok mediates CD4+ T cell lineage differentiation

Although BTB-zinc finger (BTB-ZF) transcription factors control the differentiation of multiple hematopoietic and immune lineages, how they function is poorly understood. The BTB-ZF factor Thpok controls intrathymic CD4⁺ T cell development and the expression of most CD4⁺ and CD8⁺ lineage genes. Here, we identify the nucleosome remodeling and deacetylase (NuRD) complex as a critical Thpok cofactor. Using mass spectrometry and coimmunoprecipitation in primary T cells, we show that Thpok binds NuRD components independently of DNA association. We locate three amino acid residues within the Thpok BTB domain that are required for both NuRD binding and Thpok functions. Conversely, a chimeric protein merging the NuRD component Mta2 to a BTB-less version of Thpok supports CD4⁺ T cell development, indicating that NuRD recruitment recapitulates the functions of the Thpok BTB domain. We found that NuRD mediates Thpok repression of CD8⁺ lineage genes, including the transcription factor Runx3, but is dispensable for Cd4 expression. We show that these functions cannot be performed by the BTB domain of the Thpok-related factor Bcl6, which fails to bind NuRD. Thus, cofactor binding critically contributes to the functional specificity of BTB-ZF factors, which control the differentiation of most hematopoietic subsets.

Waiting in the wings: RUNX3 reveals hidden depths of immune regulation with potential implications for inflammatory bowel disease

BACKGROUND

Complex interactions between the environment and the mucosal immune system underlie inflammatory bowel disease (IBD). The involved cytokine signalling pathways are modulated by a number of transcription factors, one of which is runt-related transcription factor 3 (RUNX3).

OBJECTIVE

To systematically review the immune roles of RUNX3 in immune regulation, with a focus on the context of IBD.

METHODS

Relevant articles and reviews were identified through a Scopus search in April 2020. Information was categorized by immune cell types, analysed and synthesized. IBD transcriptome data sets and FANTOM5 regulatory networks were processed in order to complement the literature review.

RESULTS

The available evidence on the immune roles of RUNX3 allowed for its description in twelve cell types: intraepithelial lymphocyte, Th1, Th2, Th17, Treg, double-positive T, cytotoxic T, B, dendritic, innate lymphoid, natural killer and macrophages. In the gut, the activity of RUNX3 is multifaceted and context-dependent: it may promote homeostasis or exacerbated reactions via cytokine signalling and regulation of receptor expression. RUNX3 is mostly engaged in pathways involving ThPOK, T-bet, IFN-γ, TGF-β/IL-2Rβ, GATA/CBF-β, SMAD/p300 and a number of miRNAs. RUNX3 targets relevant to IBD may include RAG1, OSM and IL-17B. Moreover, in IBD RUNX3 expression correlates positively with GZMM, and negatively with IFNAR1, whereas in controls, it strongly associates with TGFBR3.

CONCLUSIONS

Dysregulation of RUNX3, mostly in the form of deficiency, likely contributes to IBD pathogenesis. More clinical research is needed to examine RUNX3 in IBD.

The zinc-finger transcription factor MAZR regulates iNKT cell subset differentiation

Invariant natural killer T (iNKT) cells represent a subgroup of innate-like T cells and play an important role in immune responses against certain pathogens. In addition, they have been linked to autoimmunity and antitumor immunity. iNKT cells consist of several subsets with distinct functions; however, the transcriptional networks controlling iNKT subset differentiation are still not fully characterized. Myc-associated zinc-finger-related factor (MAZR, also known as PATZ1) is an essential transcription factor for CD8+ lineage differentiation of conventional T cells. Here, we show that MAZR plays an important role in iNKT cells. T-cell lineage-specific deletion of MAZR resulted in an iNKT cell-intrinsic defect that led to an increase in iNKT2 cell numbers, concurrent with a reduction in iNKT1 and iNKT17 cells. Consistent with the alteration in the subset distribution, deletion of MAZR also resulted in an increase in the percentage of IL-4-producing cells. Moreover, MAZR-deficient iNKT cells displayed an enhanced expression of Erg2 and ThPOK, key factors for iNKT cell generation and subset differentiation, indicating that MAZR controls iNKT cell development through fine-tuning of their expression levels. Taken together, our study identified MAZR as an essential transcription factor regulating iNKT cell subset differentiation and effector function.

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.

Runx3 Mediates Resistance to Intracellular Bacterial Infection by Promoting IL12 Signaling in Group 1 ILC and NCR+ILC3

Innate lymphoid cells (ILCs) are the most recently identified family of the innate immune system and are hypothesized to modulate immune functions prior to the generation of adaptive immune responses. Subsets of ILCs reside in the mucosa and regulate immune responses to external pathogens; however, their role and the mechanism by which they protect against intracellular bacterial infection is not completely understood. In this report, using S. typhimurium and L. monocytogenes, we found that the levels of group 1 ILCs and NCR⁺ ILC3s were increased upon infection and that these increases were associated with Runt-related transcription factor 3 (Runx3) expression. Runx3 ^fl/fl PLZF-cre mice were much more sensitive to infection with the intracellular bacterial pathogens S. typhimurium and L. monocytogenes partially due to abnormal Group 1 ILC and NCR⁺ILC3 function. We also found that Runx3 directly binds to the Il12Rβ2 promoter and intron 8 to accelerate the expression of Il12Rβ2 and modulates IFNγ secretion triggered by the IL12/ STAT4 axis. Therefore, we demonstrate that Runx3 influences group 1 ILC- and NCR+ILC3-mediated immune protection against intracellular bacterial infections of both the gut and liver.

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.