Innate lymphoid cells (ILCs) patrol environmental interfaces to defend against infection and protect barrier integrity. Using a genetic tuning model, we demonstrate that the signal-dependent ...transcription factor (TF) STAT5 is critical for accumulation of all known ILC subsets in mice and reveal a hierarchy of STAT5 dependency for populating lymphoid and nonlymphoid tissues. We apply transcriptome and genomic distribution analyses to define a STAT5 gene signature in natural killer (NK) cells, the prototypical ILC subset, and provide a systems-based molecular rationale for its key functions downstream of IL-15. We also uncover surprising features of STAT5 behavior, most notably the wholesale redistribution that occurs when NK cells shift from tonic signaling to acute cytokine-driven signaling, and genome-wide coordination with T-bet, another key TF in ILC biology. Collectively, our data position STAT5 as a central node in the TF network that instructs ILC development, homeostasis, and function and provide mechanistic insights on how it works at cellular and molecular levels.
CD155 is an adhesion molecule belonging to the Nectin/Nectin-like family often overexpressed on tumor cells and involved in many different processes such as cell adhesion, migration and ...proliferation. In contrast to these pro-tumorigenic functions, CD155 is also a ligand for the activating receptor DNAM-1 expressed on cytotoxic lymphocytes including Natural Killer (NK) cells and involved in anti-tumor immune response. However, during tumor progression inhibitory receptors for CD155 are up-regulated on the surface of effector cells, contributing to an impairment of their cytotoxic capacity. In this review we will focus on the roles of CD155 as a ligand for the activating receptor DNAM-1 regulating immune surveillance against cancer and as pro-oncogenic molecule favoring tumor proliferation, invasion and immune evasion. A deeper understanding of the multiple roles played by CD155 in cancer development contributes to improving anti-tumor strategies aimed to potentiate immune response against cancer.
Nectin2 is a member of immunoglobulin‐like cell adhesion molecules and plays a prominent role in the establishment of adherens and tight junctions. It is also upregulated on the surface of tumor and ...virus‐infected cells where it functions as a ligand for the activating receptor CD226, thus contributing to cytotoxic lymphocyte‐mediated recognition and killing of damaged cells. Little is currently known about the regulation of Nectin2 expression and, in particular, whether posttranscriptional and posttranslational mechanisms are involved. Here, we analyzed Nectin2 expression on a panel of human tumor cell lines and primary cultures and we found that Nectin2 is mainly expressed in cytoplasmic pools. Moreover, we demonstrated that ubiquitination of Nectin2 promotes its degradation and is responsible for protein intracellular retention. Indeed, inhibition of the ubiquitin pathway results in increased Nectin2 surface expression and enhances tumor cell susceptibility to NK cell cytotoxicity. Our results demonstrate a previously unknown mechanism of Nectin2 regulation revealing that the ubiquitin pathway represents a potential target of intervention in order to increase susceptibility to NK cell‐mediated lysis.
The ubiquitin pathway negatively regulates surface expression of Nectin2, a ligand for the activating NK‐cell receptor CD226. The neo‐synthetized Nectin2 is ubiquitinated before reaching the plasma membrane and either subjected to proteasomal degradation or retained intracellularly.
In healthy cells, limiting Nectin2 membrane expression may avoid a potential aberrant NK‐cell activation, while in transformed cells may represent a mechanism to evade NK‐cell surveillance.
Innate immune responses rely on rapid and precise gene regulation mediated by accessibility of regulatory regions to transcription factors (TFs). In natural killer (NK) cells and other innate ...lymphoid cells, competent enhancers are primed during lineage acquisition, and formation of de novo enhancers characterizes the acquisition of innate memory in activated NK cells and macrophages. Here, we investigated how primed and de novo enhancers coordinate to facilitate high-magnitude gene induction during acute activation. Epigenomic and transcriptomic analyses of regions near highly induced genes (HIGs) in NK cells both in vitro and in a model of Toxoplasma gondii infection revealed de novo chromatin accessibility and enhancer remodeling controlled by signal-regulated TFs STATs. Acute NK cell activation redeployed the lineage-determining TF T-bet to de novo enhancers, independent of DNA-sequence-specific motif recognition. Thus, acute stimulation reshapes enhancer function through the combinatorial usage and repurposing of both lineage-determining and signal-regulated TFs to ensure an effective response.
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•Inducible high-density p300 enhancers form in proximity to highly dynamic genes•Strong transcriptional induction occurs with both primed and non-primed enhancers•De novo enhancers form in vivo during NK cell response to Toxoplasma gondii infection•STATs initiate chromatin opening with T-bet redeployment to non-canonical sites
During development, innate lymphocytes acquire defined sets of primed enhancers facilitating the rapid immune response. In this issue of Immunity, Sciumè et al. delineate the epigenetic changes occurring during acute NK cell activation, revealing the formation of de novo enhancers and repurposing of both lineage-determining and signal-regulated transcription factors.
Anti-cancer immune responses may contribute to the control of tumors after conventional chemotherapy, and different observations have indicated that chemotherapeutic agents can induce immune ...responses resulting in cancer cell death and immune-stimulatory side effects. Increasing experimental and clinical evidence highlight the importance of natural killer (NK) cells in immune responses toward multiple myeloma (MM), and combination therapies able to enhance the activity of NK cells against MM are showing promise in treating this hematologic cancer. The epigenetic readers of acetylated histones bromodomain and extra-terminal (BET) proteins are critical regulators of gene expression. In cancer, they can upregulate transcription of key oncogenes such as cMYC, IRF4, and BCL-2. In addition, the activity of these proteins can regulate the expression of osteoclastogenic cytokines during cancer progression. Here, we investigated the effect of BET bromodomain protein inhibition, on the expression of NK cell-activating ligands in MM cells.
Five MM cell lines SKO-007(J3), U266, RPMI-8226, ARP-1, JJN3 and CD138
MM cells isolated from MM patients were used to investigate the activity of BET bromodomain inhibitors (BETi) (JQ1 and I-BET151) and of the selective BRD4-degrader proteolysis targeting chimera (PROTAC) (ARV-825), on the expression and function of several NK cell-activating ligands (NKG2DLs and DNAM-1Ls), using flow cytometry, real-time PCR, transient transfections, and degranulation assays.
Our results indicate that inhibition of BET proteins via small molecule inhibitors or their degradation via a hetero-bifunctional PROTAC probe can enhance the expression of MICA, a ligand of the NKG2D receptor, in human MM cell lines and primary malignant plasma cells, rendering myeloma cells more efficient to activate NK cell degranulation. Noteworthy, similar results were obtained using selective CBP/EP300 bromodomain inhibition. Mechanistically, we found that BETi-mediated inhibition of cMYC correlates with the upregulation of miR-125b-5p and the downregulation of the cMYC/miR-125b-5p target gene IRF4, a transcriptional repressor of MICA.
These findings provide new insights on the immuno-mediated antitumor activities of BETi and further elucidate the molecular mechanisms that regulate NK cell-activating ligand expression in MM.
Most immune cells, particularly phagocytes, express various receptors for the Fc portion of the different immunoglobulin isotypes (Fc receptors, FcRs). By binding to the antibody, they provide a link ...between the adaptive immune system and the powerful effector functions triggered by innate immune cells such as mast cells, neutrophils, macrophages, and NK cells. Upon ligation of the immune complexes, the downstream signaling pathways initiated by the different receptors are quite similar for different FcR classes leading to the secretion of preformed and de novo synthesized pro-inflammatory mediators. FcR engagement also promotes negative signals through the combined action of several molecules that limit the extent and duration of positive signaling. To this regard, ligand-induced ubiquitination of FcRs for IgE (FcεR) and IgG (FcγR) has become recognized as a key modification that generates signals for the internalization and/or delivery of engaged receptor complexes to lysosomes or cytoplasmic proteasomes for degradation, providing negative-feedback regulation of Fc receptor activity. In this review, we discuss recent advances in our understanding of the molecular mechanisms that ensure the clearance of engaged Fcε and Fcγ receptor complexes from the cell surface with an emphasis given to the cooperation between the ubiquitin pathway and endosomal adaptors including the endosomal sorting complex required for transport (ESCRT) in controlling receptor internalization and sorting along the endocytic compartments.
First described 40 years ago, natural killer (NK) cells represent the founding members of the innate lymphoid cell (ILC) family. They were initially defined by their ability to kill cancer cells of ...hematopoietic origin. More recently, NK cells are recognized not only for their ability to kill infected or malignant cells, but also for mediating cytotoxicity against a range of normal immune cells. They thereby play an important physiological role in controlling immune responses and maintaining homeostasis. Besides cytotoxic activity, NK cells activation is accompanied by secretion of pro-inflammatory cytokines. Hence, NK cells have the potential to act both in driving inflammation and in restricting adaptive immune responses that may otherwise lead to excessive inflammation or even autoimmunity. Here, we highlight how NK cell activity is linked to inflammasome activation and review new molecular insights to the roles of NK cells in inflammation and autoimmunity. Furthermore, in light of new insights to NK cell differentiation and memory, we deliberate on how distinct NK cell subsets may impact immunoregulatory functions. Hypothetically, memory-like or adaptive NK cells could drive NK cell-mediated autoreactive diseases. Together, new findings underscore the complex yet important physiological roles of NK cells in both promoting inflammation and exerting immunoregulation and maintenance of immune homeostasis. Insights raise intriguing questions as to how NK cells themselves maintain self-tolerance.
Efficient elimination of transformed and virus-infected cells by natural killer (NK) cells mainly depends on the recognition of “induced self” ligands by activating receptors, including NKG2D and ...DNAM1. The surface expression of these ligands in stressed or diseased cells results from the integration of transcriptional, post-transcriptional and post-translational mechanisms. Among post-translational mechanisms, recent findings indicate that ubiquitin and ubiquitin-like modifications, namely ubiquitination and SUMOylation, contribute to a very rapid negative regulation of NKG2D and DNAM1 ligand surface expression promoting either ligand degradation or ligand intracellular retention. On the other hand, accumulating evidences demonstrate that NKG2D receptor expression is down-regulated by ubiquitin-dependent endocytosis upon ligand stimulation. In this scenario, the overall consequence of the post-translational modifications of activating NK cell receptors and of their ligands on target cells is to impair effector cell-mediated recognition of damaged cells. Our review summarizes recent findings on the role of post-translational modifications in the modulation of target cell susceptibility to NK cell-mediated killing.
Resident T cells are implicated in the maintenance and recurrence of psoriatic lesions. Whether skin that has not yet experienced psoriasis in patients with established disease harbors pathogenic T ...cells is less investigated.
We sought to analyze the composition of resident T cells and T cell–driven tissue responses in skin never affected by psoriasis from patients with mild disease.
Never-lesional skin from patients with psoriasis (NLP) was collected from those with mild disease. T-cell profiles were assessed by using confocal imaging and flow cytometry. Tissue responses to T-cell stimulation were measured by using multiplex and NanoString technology.
T-cell activation ex vivo triggered psoriasiform and type I interferon tissue responses in NLP psoriasis. Accordingly, keratinocytes from NLP responded to IFN-γ stimulation with myxovirus 1 (MX1) expression and IFN-α release. Additionally, CCR6-expressing resident T cells poised to produce IFN-γ and IL-17 were enriched in epidermis from NLP, whereas dermal tissue responses and T-cell compositions were similar to those in healthy skin. Finally, keratinocytes from NLP exposed to IL-17 and skin explants exposed to common fungal antigens responded with upregulation of the CCR6 ligand CCL20.
Epidermal resident T cells capable of triggering psoriasiform tissue responses accumulate in epidermis from NLP. Our global analysis of NLP reveals that microbial interplay with genetically predisposed keratinocytes might shape the local pool of resident T cells.
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NKG2D is an activating receptor that can bind to a large number of stress-induced ligands that are expressed in the context of cancer or viral infection. This receptor is expressed on many cytotoxic ...lymphocytes, and plays a crucial role in antitumor and antiviral immune responses. However, exposure to NKG2D ligand-expressing target cells promotes receptor endocytosis, ultimately leading to lysosomal receptor degradation and impairment of NKG2D-mediated functions. Interestingly, before being degraded, internalized receptors can signal from the endosomal compartment, leading to the appropriate activation of cellular functional programs. This review summarizes recent findings on ligand-induced receptor internalization, with particular emphasis on the role of endocytosis in the control of both NKG2D-mediated intracellular signaling and receptor degradation.
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