Critical role of transcription factor PU.1 in the expression of CD80 and CD86 on dendritic cells

Transcription factor-mediated reprogramming to antigen-presenting cells

Antigen-presenting cells (APCs) are a heterogenous group of immune cells composed by dendritic cells (DCs) and macrophages (Mϕ), which are critical for orchestrating immunity against cancer or infections. Several strategies have been explored to generate APC subsets, including enrichment from peripheral blood and differentiation from pluripotent or multipotent cells. During development, the generation of APC subsets is instructed by transcription factors (TFs). Direct cell reprogramming, also known as transdifferentiation, offers an approach to harness combinations of TFs to generate APCs from unrelated somatic cells, including cancer cells. In this review, we summarize the transcriptional specification of DC subsets, highlight transcriptional networks for their generation, and discuss future applications of DC reprogramming in cancer immunotherapy.

Positive feedback loop PU.1-IL9 in Th9 promotes rheumatoid arthritis development

OBJECTIVES

T helper 9 (Th9) cells are recognised for their characteristic expression of the transcription factor PU.1 and production of interleukin-9 (IL-9), which has been implicated in various autoimmune diseases. However, its precise relationship with rheumatoid arthritis (RA) pathogenesis needs to be further clarified.

METHODS

The expression levels of PU.1 and IL-9 in patients with RA were determined by ELISA, western blotting (WB) and immunohistochemical staining. PU.1-T cell-conditional knockout (KO) mice, IL-9 KO and IL-9R KO mice were used to establish collagen antibody-induced arthritis (CAIA), respectively. The inhibitor of PU.1 and IL-9 blocking antibody was used in collagen-induced arthritis (CIA). In an in vitro study, the effects of IL-9 were investigated using siRNAs and IL-9 recombinant proteins. Finally, the underlying mechanisms were further investigated by luciferase reporter analysis, WB and Chip-qPCR.

RESULTS

The upregulation of IL-9 expression in patients with RA exhibited a positive correlation with clinical markers. Using CAIA and CIA model, we demonstrated that interventions targeting PU.1 and IL-9 substantially mitigated the inflammatory phenotype. Furthermore, in vitro assays provided the proinflammatory role of IL-9, particularly in the hyperactivation of macrophages and fibroblast-like synoviocytes. Mechanistically, we uncovered that PU.1 and IL-9 form a positive feedback loop in RA: (1) PU.1 directly binds to the IL-9 promoter, activating its transcription and (2) Th9-derived IL-9 induces PU.1 via the IL-9R-JAK1/STAT3 pathway.

CONCLUSIONS

These results support that the PU.1-IL-9 axis forms a positive loop in Th9 dysregulation of RA. Targeting this signalling axis presents a potential target approach for treating RA.

ETS Transcription Factors in Immune Cells and Immune-Related Diseases

The development, differentiation, and function of immune cells are precisely regulated by transcription factors. The E26 transformation-specific (ETS) transcription factor family is involved in various physiological and pathological processes by regulating cell proliferation, differentiation, and apoptosis. Emerging evidence has suggested that ETS family proteins are intimately involved in the development and function of immune cells. This review summarizes the role of the ETS family in immune cells and immune-related disorders. Seven transcription factors within the ETS family, including PU.1, ETV5, ETV6, ETS1/2, ELK3, and ELF1, play essential roles in the development and function of T cells, B cells, macrophages, neutrophils, and dendritic cells. Furthermore, they are involved in the occurrence and development of immune-related diseases, including tumors, allergies, autoimmune diseases, and arteriosclerosis. This review is conducive to a comprehensive overview of the role of the ETS family in immune cells, and thus is informative for the development of novel therapeutic strategies targeting the ETS family for immune-related diseases.

GGT1 is a SNP eQTL gene involved in STAT3 activation and associated with the development of Post-ERCP pancreatitis

Post-ERCP pancreatitis (PEP) is an acute pancreatitis caused by endoscopic-retrograde-cholangiopancreatography (ERCP). About 10% of patients develop PEP after ERCP. Here we show that gamma-glutamyltransferase 1 (GGT1)-SNP rs5751901 is an eQTL in pancreatic cells associated with PEP and a positive regulator of the IL-6 amplifier. More PEP patients had the GGT1 SNP rs5751901 risk allele (C) than that of non-PEP patients at Hokkaido University Hospital. Additionally, GGT1 expression and IL-6 amplifier activation were increased in PEP pancreas samples with the risk allele. A mechanistic analysis showed that IL-6-mediated STAT3 nuclear translocation and STAT3 phosphorylation were suppressed in GGT1-deficient cells. Furthermore, GGT1 directly associated with gp130, the signal-transducer of IL-6. Importantly, GGT1-deficiency suppressed inflammation development in a STAT3/NF-κB-dependent disease model. Thus, the risk allele of GGT1-SNP rs5751901 is involved in the pathogenesis of PEP via IL-6 amplifier activation. Therefore, the GGT1-STAT3 axis in pancreas may be a prognosis marker and therapeutic target for PEP.

The gut lactic acid bacteria metabolite, 10-oxo-cis-6,trans-11-octadecadienoic acid, suppresses inflammatory bowel disease in mice by modulating the NRF2 pathway and GPCR-signaling

Various gut bacteria, including Lactobacillus plantarum, possess several enzymes that produce hydroxy fatty acids (FAs), oxo FAs, conjugated FAs, and partially saturated FAs from polyunsaturated FAs as secondary metabolites. Among these derivatives, we identified 10-oxo-cis-6,trans-11-octadecadienoic acid (γKetoC), a γ-linolenic acid (GLA)-derived enon FA, as the most effective immunomodulator, which inhibited the antigen-induced immunoactivation and LPS-induced production of inflammatory cytokines. The treatment with γKetoC significantly suppressed proliferation of CD4+ T cells, LPS-induced activation of bone marrow-derived dendritic cells (BMDCs), and LPS-induced IL-6 release from peritoneal cells, splenocytes, and CD11c+ cells isolated from the spleen. γKetoC also inhibited the release of inflammatory cytokines from BMDCs stimulated with poly-I:C, R-848, or CpG. Further in vitro experiments using an agonist of GPR40/120 suggested the involvement of these GPCRs in the effects of γKetoC on DCs. We also found that γKetoC stimulated the NRF2 pathway in DCs, and the suppressive effects of γKetoC and agonist of GPR40/120 on the release of IL-6 and IL-12 were reduced in Nrf2-/- BMDCs. We evaluated the role of NRF2 in the anti-inflammatory effects of γKetoC in a dextran sodium sulfate-induced colitis model. The oral administration of γKetoC significantly reduced body weight loss, improved stool scores, and attenuated atrophy of the colon, in wild-type C57BL/6 and Nrf2+/- mice with colitis. In contrast, the pathology of colitis was deteriorated in Nrf2-/- mice even with the administration of γKetoC. Collectively, the present results demonstrated the involvement of the NRF2 pathway and GPCRs in γKetoC-mediated anti-inflammatory responses.

DDX6 is involved in the pathogenesis of inflammatory diseases via NF-κB activation

The IL-6 amplifier was originally discovered as a mechanism for the enhanced activation of NF-κB in non-immune cells. In the IL-6 amplifier, IL-6-STAT3 and NF-κB stimulation is followed by an excessive production of IL-6, chemokines, and growth factors to develop chronic inflammation preceding the development of inflammatory diseases. Previously, using a shRNA-mediated genome-wide screening, we found that DEAD-Box Helicase 6 (DDX6) is a candidate positive regulator of the amplifier. Here, we investigate whether DDX6 is involved in the pathogenesis of inflammatory diseases via the IL-6 amplifier. We found that DDX6-silencing in non-immune cells suppressed the NF-κB pathway and inhibited activation of the IL-6 amplifier, while the forced expression of DDX6 enhanced NF-κB promoter activity independent of the RNA helicase activity of DDX6. The imiquimod-mediated dermatitis model was suppressed by the siRNA-mediated gene downregulation of DDX6. Furthermore, silencing DDX6 significantly reduced the TNF-α-induced phosphorylation of p65/RelA and IκBα, nuclear localization of p65, and the protein levels of IκBα. Mechanistically, DDX6 is strongly associated with p65 and IκBα, but not TRADD, RIP, or TRAF2, suggesting a novel function of DDX6 as an adaptor protein in the NF-κB pathway. Thus, our findings demonstrate a possible role of DDX6 beyond RNA metabolism and suggest DDX6 is a therapeutic target for inflammatory diseases.

Bacteria-derived nanovesicles enhance tumour vaccination by trained immunity

Trained immunity enhances the responsiveness of immune cells to subsequent infections or vaccinations. Here we demonstrate that pre-vaccination with bacteria-derived outer-membrane vesicles, which contain large amounts of pathogen-associated molecular patterns, can be used to potentiate, and enhance, tumour vaccination by trained immunity. Intraperitoneal administration of these outer-membrane vesicles to mice activates inflammasome signalling pathways and induces interleukin-1β secretion. The elevated interleukin-1β increases the generation of antigen-presenting cell progenitors. This results in increased immune response when tumour antigens are delivered, and increases tumour-antigen-specific T-cell activation. This trained immunity increased protection from tumour challenge in two distinct cancer models.

Butyrate, Valerate, and Niacin Ameliorate Anaphylaxis by Suppressing IgE-Dependent Mast Cell Activation: Roles of GPR109A, PGE2, and Epigenetic Regulation

Short-chain fatty acids (SCFAs) are produced by the intestinal microbiota during the fermentation of dietary fibers as secondary metabolites. Several recent studies reported that SCFAs modulate the development and function of immune-related cells. However, the molecular mechanisms by which SCFAs regulate mast cells (MCs) remain unclear. In the current study, we analyzed the function and gene expression of mouse MCs in the presence of SCFAs in vitro and in vivo. We found that the oral administration of valerate or butyrate ameliorated passive systemic anaphylaxis and passive cutaneous anaphylaxis in mice. The majority of SCFAs, particularly propionate, butyrate, valerate, and isovalerate, suppressed the IgE-mediated degranulation of bone marrow-derived MCs, which were eliminated by the Gi protein inhibitor pertussis toxin and by the knockdown of Gpr109a. A treatment with the HDAC inhibitor trichostatin A also suppressed IgE-mediated MC activation and reduced the surface expression level of FcεRI on MCs. Acetylsalicylic acid and indomethacin attenuated the suppressive effects of SCFAs on degranulation. The degranulation degree was significantly reduced by PGE2 but not by PGD2. Furthermore, SCFAs enhanced PGE2 release from stimulated MCs. The SCFA-mediated amelioration of anaphylaxis was exacerbated by COX inhibitors and an EP3 antagonist, but not by an EP4 antagonist. The administration of niacin, a ligand of GPR109A, alleviated the symptoms of passive cutaneous anaphylaxis, which was inhibited by cyclooxygenase inhibitors and the EP3 antagonist. We conclude that SCFAs suppress IgE-mediated activation of MCs in vivo and in vitro involving GPR109A, PGE2, and epigenetic regulation.

Screening Allergenic Potencies of Skin-Contact Products Using the Human-Derived THP-1 Cell Activation Test

With the prevalence of allergic contact dermatitis (ACD) from the usage of skin-contact products, like wearable, skin care, and hair care products, screening their skin sensitizing potential is necessary, for the sake of alleviating the consequent public health impact. In the present study, a total of 77 skin-contact products classified by four categories, watch bands (WBs), skin care products (SCPs), hair care products (HCPs), and rubber gloves (RGs), were investigated, using an optimized in vitro assay of human cell line activation test (h-CLAT). Extracting the products using neutral artificial sweat simulated well the practical usage scenarios, and testing the extracts showed that 26 of them were allergy test positive, including nine WBs, six SCPs, two HCPs, and nine RGs. The allergenic response was mainly characterized by the induction of CD54 expression, and diverse paradigms of CD54 and CD86 levels were observed by analyzing dose-response curves, which could also be influenced by the compromised viability of the THP-1 cells. The data implicated the intricate regulation by different contributors to suspicious ingredients in the test samples. Altogether, a promising methodology for testing skin allergy potential was well established for commonly used commodities by neutral artificial sweat extraction coupled with h-CLAT screening. The findings would be of great help in tracing the potential allergens in practical products and improving their qualities.

NK cells propagate T cell immunity following in situ tumor vaccination

We report an in situ vaccination, adaptable to nearly any type of cancer, that combines radiotherapy targeting one tumor and intratumoral injection of this site with tumor-specific antibody and interleukin-2 (IL-2; 3xTx). In a phase I clinical trial, administration of 3xTx (with an immunocytokine fusion of tumor-specific antibody and IL-2, hu14.18-IL2) to subjects with metastatic melanoma increases peripheral CD8+ T cell effector polyfunctionality. This suggests the potential for 3xTx to promote antitumor immunity against metastatic tumors. In poorly immunogenic syngeneic murine melanoma or head and neck carcinoma models, 3xTx stimulates CD8+ T cell-mediated antitumor responses at targeted and non-targeted tumors. During 3xTx treatment, natural killer (NK) cells promote CTLA4+ regulatory T cell (Treg) apoptosis in non-targeted tumors. This is dependent on NK cell expression of CD86, which is upregulated downstream of KLRK1. NK cell depletion increases Treg infiltration, diminishing CD8+ T cell-dependent antitumor response. These findings demonstrate that NK cells sustain and propagate CD8+ T cell immunity following 3xTx.

Mechanism and therapeutic implications of pomalidomide-induced immune surface marker upregulation in EBV-positive lymphomas

Epstein-Barr virus (EBV) downregulates immune surface markers to avoid immune recognition. Pomalidomide (Pom) was previously shown to increase immune surface marker expression in EBV-infected tumor cells. We explored the mechanism by which Pom leads to these effects in EBV-infected cells. Pom increased B7-2/CD86 mRNA, protein, and surface expression in EBV-infected cells but this was virtually eliminated in EBV-infected cells made resistant to Pom-induced cytostatic effects. This indicates that Pom initiates the upregulation of these markers by interacting with its target, cereblon. Interestingly, Pom increased the proinflammatory cytokines IP-10 and MIP-1∝/β in EBV infected cells, supporting a possible role for the phosphoinositide 3-kinase (PI3K)/AKT pathway in Pom's effects. Idelalisib, an inhibitor of the delta subunit of PI3 Kinase, blocked AKT-Ser phosphorylation and Pom-induced B7-2 surface expression. PU.1 is a downstream target for AKT that is expressed in EBV-infected cells. Pom treatment led to an increase in PU.1 binding to the B7-2 promoter based on ChIP analysis. Thus, our data indicates Pom acts through cereblon leading to degradation of Ikaros and activation of the PI3K/AKT/PU.1 pathway resulting in upregulation of B7-2 mRNA and protein expression. The increased immune recognition in addition to the increases in proinflammatory cytokines upon Pom treatment suggests Pom may be useful in the treatment of EBV-positive lymphomas.

Dupuytren's contracture-associated SNPs increase SFRP4 expression in non-immune cells including fibroblasts to enhance inflammation development

Dupuytren's contracture (DC) is an inflammatory fibrosis characterized by fibroproliferative disorders of the palmar aponeurosis, for which there is no effective treatment. Although several genome-wide association studies have identified risk alleles associated with DC, the functional linkage between these alleles and the pathogenesis remains elusive. We here focused on two single nucleotide polymorphisms (SNPs) associated with DC, rs16879765 and rs17171229, in secreted frizzled related protein 4 (SFRP4). We investigated the association of SRFP4 with the IL-6 amplifier, which amplifies the production of IL-6, growth factors and chemokines in non-immune cells and aggravates inflammatory diseases via NF-κB enhancement. Knockdown of SFRP4 suppressed activation of the IL-6 amplifier in vitro and in vivo, whereas the overexpression of SFRP4 induced the activation of NF-κB-mediated transcription activity. Mechanistically, SFRP4 induced NF-κB activation by directly binding to molecules of the ubiquitination SFC complex, such as IkBα and βTrCP, followed by IkBα degradation. Furthermore, SFRP4 expression was significantly increased in fibroblasts derived from DC patients bearing the risk alleles. Consistently, fibroblasts with the risk alleles enhanced activation of the IL-6 amplifier. These findings indicate that the IL-6 amplifier is involved in the pathogenesis of DC, particularly in patients harboring the SFRP4 risk alleles. Therefore, SFRP4 is a potential therapeutic target for various inflammatory diseases and disorders, including DC.

Dynamic polarization of tumor-associated macrophages and their interaction with intratumoral T cells in an inflamed tumor microenvironment: from mechanistic insights to therapeutic opportunities

Immunotherapy has brought a paradigm shift in the treatment of tumors in recent decades. However, a significant proportion of patients remain unresponsive, largely due to the immunosuppressive tumor microenvironment (TME). Tumor-associated macrophages (TAMs) play crucial roles in shaping the TME by exhibiting dual identities as both mediators and responders of inflammation. TAMs closely interact with intratumoral T cells, regulating their infiltration, activation, expansion, effector function, and exhaustion through multiple secretory and surface factors. Nevertheless, the heterogeneous and plastic nature of TAMs renders the targeting of any of these factors alone inadequate and poses significant challenges for mechanistic studies and clinical translation of corresponding therapies. In this review, we present a comprehensive summary of the mechanisms by which TAMs dynamically polarize to influence intratumoral T cells, with a focus on their interaction with other TME cells and metabolic competition. For each mechanism, we also discuss relevant therapeutic opportunities, including non-specific and targeted approaches in combination with checkpoint inhibitors and cellular therapies. Our ultimate goal is to develop macrophage-centered therapies that can fine-tune tumor inflammation and empower immunotherapy.

Loss of Lkb1 in CD11c+ myeloid cells protects mice from diet-induced obesity while enhancing glucose intolerance and IL-17/IFN-γ imbalance

Adipose tissue CD11c⁺ myeloid cell is an independent risk factor associated with obesity and metabolic disorders. However, the underlying molecular basis remains elusive. Here, we demonstrated that liver kinase B1 (Lkb1), a key bioenergetic sensor, is involved in CD11c⁺ cell-mediated immune responses in diet-induced obesity. Loss of Lkb1 in CD11c⁺ cells results in obesity resistance but lower glucose tolerance, which accompanies tissue-specific immune abnormalities. The accumulation and CD80's expression of Lkb1 deficient adipose-tissue specific dendritic cells but not macrophages is restrained. Additionally, the balance of IL-17A and IFN-γ remarkably tips towards the latter in fat T cells and CD11c^- macrophages. Mechanistically, IFN-γ promotes apoptosis of preadipocytes and inhibits their adipogenesis while IL-17A promotes the adipogenesis in vitro, which might account in part for the fat gain resistant phenotype. In summary, these findings reveal that Lkb1 is essential for fat CD11c⁺ dendritic cells responding to HFD exposure and provides new insights into the IL-17A/IFN-γ balance in HFD-induced obesity.

A rose flavor compound activating the NRF2 pathway in dendritic cells ameliorates contact hypersensitivity in mice

Dendritic cells (DCs), which are typical antigen-presenting cells, localize to various sites in the body, particularly the front line of infection as sentinels, and are involved in innate and adaptive immune responses. Although the functions of DCs, such as pathogen-induced cytokine production and antigen-specific T cell activation, are important for host defenses against infection and tumorigenesis, the hyper- and/or extended activation of DCs leads to inflammatory and autoimmune diseases. In the present study, β-damascone, a major ingredient of rose fragrance, was selected from an aroma library as a candidate compound that suppresses antigen-induced immune responses. β-Damascone inhibited the functions of DCs, including the antigen-dependent proliferation of T cells, DC-induced Th1 development, and the TLR ligand-induced production of inflammatory cytokines by DCs. The β-damascone treatment also increased the protein level of the transcription factor NF-E2-related factor 2 (NRF2), which plays key roles in antioxidant responses, and the transcription of Hmox1 and Nqo1, target genes of NRF2, in DCs. Nrf2 ^{-/ -} DCs induced Th1-development and produced large amount of IL-12p40 even in the presence of β-damascone, whereas these functions by Nrf2 ^+/- DCs were inhibited by β-damascone under the same conditions. The intake of β-damascone suppressed ear swelling in contact hypersensitivity (CHS) model mice, but not in CHS-induced Nrf2 ^{-/ -} mice. Collectively, the present results indicate the potential of the rose aroma compound β-damascone, which suppresses DC-mediated immune responses by activating the NRF2 pathway in DCs, for the prevention and/or attenuation of immune-mediated diseases.

Using a Network-Based Analysis Approach to Investigate the Involvement of S. aureus in the Pathogenesis of Granulomatosis with Polyangiitis

Chronic nasal carriage of Staphylococcus aureus (SA) has been shown to be significantly higher in GPA patients when compared to healthy subjects, as well as being associated with increased endonasal activity and disease relapse. The aim of this study was to investigate SA involvement in GPA by applying a network-based analysis (NBA) approach to publicly available nasal transcriptomic data. Using these data, our NBA pipeline generated a proteinase 3 (PR3) positive ANCA associated vasculitis (AAV) disease network integrating differentially expressed genes, dysregulated transcription factors (TFs), disease-specific genes derived from GWAS studies, drug-target and protein-protein interactions. The PR3+ AAV disease network captured genes previously reported to be dysregulated in AAV associated. A subnetwork focussing on interactions between SA virulence factors and enriched biological processes revealed potential mechanisms for SA's involvement in PR3+ AAV. Immunosuppressant treatment reduced differential expression and absolute TF activities in this subnetwork for patients with inactive nasal disease but not active nasal disease symptoms at the time of sampling. The disease network generated identified the key molecular signatures and highlighted the associated biological processes in PR3+ AAV and revealed potential mechanisms for SA to affect these processes.

Dendritic Cells: The Long and Evolving Road towards Successful Targetability in Cancer

Dendritic cells (DCs) are a unique myeloid cell lineage that play a central role in the priming of the adaptive immune response. As such, they are an attractive target for immune oncology based therapeutic approaches. However, targeting these cells has proven challenging with many studies proving inconclusive or of no benefit in a clinical trial setting. In this review, we highlight the known and unknown about this rare but powerful immune cell. As technologies have expanded our understanding of the complexity of DC development, subsets and response features, we are now left to apply this knowledge to the design of new therapeutic strategies in cancer. We propose that utilization of these technologies through a multiomics approach will allow for an improved directed targeting of DCs in a clinical trial setting. In addition, the DC research community should consider a consensus on subset nomenclature to distinguish new subsets from functional or phenotypic changes in response to their environment.

Kinetic Changes in B7 Costimulatory Molecules and IRF4 Expression in Human Dendritic Cells during LPS Exposure

A key aspect of the inflammatory phenomenon is the involvement of costimulatory molecules expressed by antigen-presenting cells (APCs) and their ability to secrete cytokines to set instructions for an adaptive immune response and to generate tolerance or inflammation. In a novel integrative approach, we aimed to evaluate the kinetic expression of the membrane and soluble B7 costimulatory molecules CD86, ICOS-L, PDL1, PDL2, the transcription factor Interferon Regulatory Factor 4 (IRF4), and the cytokines produced by monocyte-derived dendritic cells (Mo-DCs) after challenging them with different concentrations of stimulation with E. coli lipopolysaccharide (LPS) for different lengths of time. Our results showed that the stimuli concentration and time of exposure to an antigen are key factors in modulating the dynamic expression pattern of membrane and soluble B7 molecules and cytokines.

Zbtb46 Controls Dendritic Cell Activation by Reprogramming Epigenetic Regulation of cd80/86 and cd40 Costimulatory Signals in a Zebrafish Model

The establishment of an appropriate costimulatory phenotype is crucial for dendritic cells (DCs) to maintain a homeostatic state with optimal immune surveillance and immunogenic activities. The upregulation of CD80/86 and CD40 is a hallmark costimulatory phenotypic switch of DCs from a steady state to an activated one for T cell activation. However, knowledge of the regulatory mechanisms underlying this process remains limited. In this study, we identified a Zbtb46 homolog from a zebrafish model. Zbtb46 deficiency resulted in upregulated cd80/86 and cd40 expression in kidney marrow-derived DCs (KMDCs) of zebrafish, which was accompanied with a remarkable expansion of CD4⁺/CD8⁺ T cells and accumulation of KMDCs in spleen of naive fish. Zbtb46 ^-/- splenic KMDCs exhibited strong stimulatory activity for CD4⁺ T cell activation. Chromatin immunoprecipitation-quantitative PCR and mass spectrometry assays showed that Zbtb46 was associated with promoters of cd80/86 and cd40 genes by binding to a 5'-TGACGT-3' motif in resting KMDCs, wherein it helped establish a repressive histone epigenetic modification pattern (H3K4me0/H3K9me3/H3K27me3) by organizing Mdb3/organizing nucleosome remodeling and deacetylase and Hdac3/nuclear receptor corepressor 1 corepressor complexes through the recruitment of Hdac1/2 and Hdac3. On stimulation with infection signs, Zbtb46 disassociated from the promoters via E3 ubiquitin ligase Cullin1/Fbxw11-mediated degradation, and this reaction can be triggered by the TLR9 signaling pathway. Thereafter, cd80/86 and cd40 promoters underwent epigenetic reprogramming from the repressed histone modification pattern to an activated pattern (H3K4me3/H3K9ac/H3K27ac), leading to cd80/86 and cd40 expression and DC activation. These findings revealed the essential role of Zbtb46 in maintaining DC homeostasis by suppressing cd80/86 and cd40 expression through epigenetic mechanisms.

A Functional GM-CSF Receptor on Dendritic Cells Is Required for Efficient Protective Anti-Tumor Immunity

Dendritic cells (DC) play a major role during the priming phase of anti-tumor immunization, as they are required for an efficient tumor-associated antigens presentation. At least one dendritic cell-based therapy has already been successfully approved by regulators for clinical application in prostate cancer patients. Moreover, DC development is dependent on the granulocyte macrophage colony stimulating factor (GM-CSF), a cytokine that has been successfully used as a potent inducer of anti-tumoral immunity. To better understand the relation between DC and GM-CSF in anti-tumor immunity, we studied the DC function in mice lacking the cytokine receptor common subunit beta (βc-/-) for GM-CSF, IL-3 and IL-5 and immunized with irradiated tumor cells. Such immunization induces a protective, specific tumor immunization in wild-type mice, while βc-/- mice failed to mount an immune response. Upon in vitro stimulation, DC from βc-/- mice (DCβc-/-) are unable to undergo a full maturation level. In vivo experiments show that they lack the ability to prevent tumor growth, in contrast to DCWT. Moreover, matured DCWT rescued immunization in βc-/- mice. DC maturation is dependent on a functional pathway involving GM-CSF signaling through a biologically functional receptor. These findings may contribute to new strategies for efficient anti-tumor immunotherapies.

PU.1 and IRF8 Modulate Activation of NLRP3 Inflammasome via Regulating Its Expression in Human Macrophages

NLRP3 inflammasomes play crucial roles in the initiation of host defense by converting pro-Caspase-1 to mature Caspase-1, which in turn processes immature IL-1β and IL-18 into their biologically active forms. Although NLRP3 expression is restricted to monocytic lineages such as monocytes, macrophages, and dendritic cells, the mechanisms determining the lineage-specific expression of NLRP3 remain largely unknown. In this study, we investigated the transcription factors involved in cell-type-specific transcription of NLRP3. We found that a distal, rather than a proximal, promoter of human NLRP3 was predominantly used in the human monocytic cell lines and macrophages. Reporter analysis showed that an Ets/IRF composite element (EICE) at -309/-300 and an Ets motif at +5/+8 were critical for transcriptional activity of the distal promoter. Electrophoretic mobility shift assays and chromatin immunoprecipitation assays demonstrated that two transcription factors, PU.1 and IRF8, both of which play essential roles in development and gene expression of the monocytic lineage, were bound to the EICE site, whereas PU.1 alone was bound to the Ets site. Knockdown of PU.1 and/or IRF8 mediated by small interfering RNA downregulated expression of NLRP3 and related molecules and markedly diminished the LPS-induced release of IL-1β in THP-1, suggesting that activity of the NLRP3 inflammasome was suppressed by knockdown of PU.1 and IRF8. Taken together, these results indicate that PU.1 and IRF8 are involved in the monocytic lineage-specific expression of NLRP3 by binding to regulatory elements within its promoter and that PU.1 and IRF8 are potential targets for regulating the activity of the NLRP3 inflammasome.

Comparison of the PU.1 transcriptional regulome and interactome in human and mouse inflammatory dendritic cells

Dendritic cells (DCs) are key immune modulators and are able to mount immune responses or tolerance. DC differentiation and activation imply a plethora of molecular and cellular responses, including transcriptional changes. PU.1 is a highly expressed transcription factor in DCs and coordinates relevant aspects of DC biology. Due to their role as immune regulators, DCs pose as a promising immunotherapy tool. However, some of their functional features, such as survival, activation, or migration, are compromised due to the limitations to simulate in vitro the physiologic DC differentiation process. A better knowledge of transcriptional programs would allow the identification of potential targets for manipulation with the aim of obtaining "qualified" DCs for immunotherapy purposes. Most of the current knowledge regarding DC biology derives from studies using mouse models, which not always find a parallel in human. In the present study, we dissect the PU.1 transcriptional regulome and interactome in mouse and human DCs, in the steady state or LPS activated. The PU.1 transcriptional regulome was identified by performing PU.1 chromatin immunoprecipitation followed by high-throughput sequencing and pairing these data with RNAsequencing data. The PU.1 interactome was identified by performing PU.1 immunoprecipitation followed by mass spectrometry analysis. Our results portray PU.1 as a pivotal factor that plays an important role in the regulation of genes required for proper DC activation and function, and assures the repression of nonlineage genes. The interspecies differences between human and mouse DCs are surprisingly substantial, highlighting the need to study the biology of human DCs.

Pterostilbene reduces colonic inflammation by suppressing dendritic cell activation and promoting regulatory T cell development

Dendritic cells (DCs) and T cells play important roles in immune regulation, and modulating their function is an approach for developing preventive or therapeutic strategies against immune disorders. Herein, the effect of pterostilbene (PSB) (3',5'-dimethoxy-resveratrol)-a resveratrol-related polyphenol found in blueberries-on immune regulation was evaluated. Using an in vitro co-culture system, PSB was found to exert the strongest inhibitory effect among all tested resveratrol derivatives on DC-mediated T cell proliferation; moreover, PSB treatment decreased the Th1 and Th17 populations and increased the regulatory T cell (Treg) population. Upon co-stimulation with anti-CD3 and anti-CD28 antibodies, PSB inhibited CD4⁺ T cell proliferation and differentiation into Th1 cells. Additionally, PSB acted on DCs to suppress the lipopolysaccharide-induced transactivation of genes encoding antigen presentation-related molecules and inflammatory cytokines by attenuating the DNA-binding ability of the transcription factor PU.1. Furthermore, PSB promoted DC-mediated Foxp3⁺ Treg differentiation, and PU.1 knockdown increased DC-induced Treg activity. Oral administration of PSB alleviated the symptoms of dextran sulfate sodium-induced colitis and decreased tumor necrosis factor-α expression in mice. Thus, PSB treatment ameliorates colonic inflammation.

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.

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.

Molecular Aspects of Dendritic Cell Activation in Leishmaniasis: An Immunobiological View

Dendritic cells (DC) are a diverse group of leukocytes responsible for bridging innate and adaptive immunity. Despite their functional versatility, DCs exist primarily in two basic functional states: immature and mature. A large body of evidence suggests that upon interactions with pathogens, DCs undergo intricate cellular processes that culminate in their activation, which is paramount to the orchestration of effective immune responses against Leishmania parasites. Herein we offer a concise review of the emerging hallmarks of DCs activation in leishmaniasis as well as a comprehensive discussion of the following underlying molecular events: DC-Leishmania interaction, antigen uptake, costimulatory molecule expression, parasite ability to affect DC migration, antigen presentation, metabolic reprogramming, and epigenetic alterations.

A transcription factor PU.1 is critical for Ccl22 gene expression in dendritic cells and macrophages

The chemokine CCL22 is predominantly produced by dendritic cells (DCs) and macrophages. CCL22 acts on CCR4-expressing cells including Th2 and Treg. Although a correlation between the CCL22-CCR4 axis and allergic diseases has been established, the mechanism of monocyte lineage-specific Ccl22 gene expression is largely unknown. In the current study, we investigated transcriptional regulation of the Ccl22 gene in DCs and macrophages. Using reporter assays, we identified the critical cis-enhancing elements at 21/−18 and −10/−4 in the Ccl22 promoter. Electrophoretic mobility shift assays proved that transcription factor PU.1 directly binds to the cis-elements. Knockdown of PU.1 markedly decreased Ccl22 expression in bone marrow-derived DCs (BMDCs) and BM macrophages (BMDMs). Chromatin immunoprecipitation assays revealed that PU.1 bound to the Ccl22 promoter in not only BMDCs and BMDMs, but also splenic DCs and peritoneal macrophages. LPS stimulation increased the amount of PU.1 recruited to the promoter, accompanied by upregulation of the Ccl22 mRNA level, which was diminished by Spi1 knockdown. We identified similar cis-elements on the human CCL22 promoter, which were bound with PU.1 in human monocytes. Taken together, these findings indicate that PU.1 transactivates the Ccl22 gene in DCs and macrophages by directly binding to the two elements in the promoter.

Efficacy of different hemodialysis methods on dendritic cell marker CD40 and CD80 and platelet activation marker CD62P and P10 in patients with chronic renal failure

BACKGROUND

Chronic renal failure (CRF) has become a major public health concern, which increases the risk of stroke and systemic thromboembolism. Therefore, therapeutic strategies are in urgent requirement. This study was conducted for investigating efficacy of hemodialysis (HD), hemodiafiltration (HDF), and hemoperfusion (HP) in patients with CRF and the correlation with the presence of complications following HD therapy.

METHODS

The therapeutic effect, living quality, biochemical indicators, and dry weight were detected before and after the treatment regimens. Flow cytometry was conducted to detect expressions of dendritic cell markers (CD40 and CD80) and platelet activation markers (CD62P and P10), and the relationship between their expression and therapeutic effect as well as the association of these expressions with complications was analyzed.

RESULTS

After HD therapy, patients presented with decreased serum creatinine, serum phosphorus, triglyceride, parathyroid hormone, and β₂ -MG expression; increased hemoglobin, plasma albumin expressions, and dry weight; and enhanced therapeutic effect and living quality. CD62P and P10 expressions decreased, while CD40 and CD80 expressions increased following HD therapy. The therapeutic effect improved in patients with low expressions of CD40 and CD80 and high expressions of CD62P and P10 following HP treatment and complications were lower after treatment of HDF and HP.

CONCLUSION

The aforementioned results indicated that CRF patients treated with HP exhibited higher expression of CD40 and CD80 and lower expression of CD62P and P10, suggesting that HP is conferred to have better efficacy than HDF and HD. Therefore, HP may be a promising clinical regimen for treatment of CRF patients.

The Transcription Factors PU.1 and IRF4 Determine Dendritic Cell-Specific Expression of RALDH2

RALDH2 expressed in dendritic cells (DCs) plays a critical role in the development of regulatory T cells in mesenteric lymph nodes. Despite the importance of RALDH2 in intestinal immunity, little is known about the mechanism of DC-specific expression of RALDH2. In the current study, we focused on the hematopoietic cell-specific transcription factors PU.1 and IRF4 as the determinants of Aldh1a2 gene expression. The mRNA level of Aldh1a2, and subsequently the enzyme activity, were decreased by knockdown of PU.1 and IRF4 in bone marrow-derived DCs (BMDCs) of BALB/c mice. Chromatin immunoprecipitation assays showed that PU.1 and IRF4 bound to the Aldh1a2 gene ∼2 kb upstream from the transcription start site in BMDCs. A reporter assay and an EMSA revealed that the Aldh1a2 promoter was synergistically transactivated by a heterodimer composed with PU.1 and IRF4 via the EICE motif at -1961/-1952 of the gene. The effect of small interfering RNAs for Spi1 and Irf4 and specific binding of PU.1 and IRF4 on the Aldh1a2 gene were also observed in DCs freshly isolated from spleen and mesenteric lymph nodes, respectively. GM-CSF stimulation upregulated the Aldh1a2 transcription in Flt3 ligand-generated BMDCs, in which the IRF4 expression and the PU.1 recruitment to the Aldh1a2 promoter were enhanced. We conclude that PU.1 and IRF4 are transactivators of the Aldh1a2 gene in vitro and ex vivo.

The effect of PU.1 knockdown on gene expression and function of mast cells

PU.1 is a hematopoietic cell-specific transcription factor. In the current study, we investigated the role of PU.1 in the gene expression and the function of mouse mast cells (MCs) in vitro and in vivo. When PU.1 siRNA was introduced into bone marrow-derived MCs (BMMCs), IgE-mediated activation was reduced, and the Syk and FcεRIβ mRNA levels were significantly decreased. As the regulatory mechanism of the Syk gene is largely unknown, we performed promoter analysis and found that PU.1 transactivated the Syk promoter through direct binding to a cis-element in the 5′-untranslated region. The involvement of PU.1 in the Syk promoter was also observed in mouse dendritic cells and human MCs, suggesting that the relationship between PU.1 and Syk is common in mammals and in hematopoietic lineages. When antigen was administrated intravenously after the transfusion of siRNA-transfected BMMCs in the mouse footpad, the footpad thickening was significantly suppressed by PU.1 knockdown. Finally, administration of the immunomodulator pomalidomide suppressed passive systemic anaphylaxis of mice. Taken together, these results indicate that PU.1 knockdown might be an efficacious strategy for the prevention of MC-mediated allergic diseases.

Effects of CTLA4-Ig on human monocytes

Background

Abatacept, a CTLA4-Ig fusion protein attenuates T cell activation by inhibiting the CD80/86-CD28 costimulatory pathway that is required for the proper T cell activation and thus displays beneficial effects in the treatment of rheumatoid arthritis (RA). Although some studies have disclosed the in vitro effects of this biological agent on the immune-competent cells, the precise mechanisms of action in RA still remain unclear. The current studies were therefore undertaken to explore the effects of abatacept on monocytes in detail.

Methods

Monocytes from healthy donors were cultured in the presence of staphylococcal enterotoxin B (SEB) with pharmacologically attainable concentrations of abatacept or control IgG-Fc. The expression of CD80 and CD86 and the induction of apoptosis of monocytes were measured by flow cytometry. The expression of CD80 and CD86 messenger RNA (mRNA) was determined by quantitative RT-PCR.

Results

Abatacept promoted apoptosis of SEB-stimulated monocytes. The induction of apoptosis of monocytes by these biological agents was reversed by the addition of IgG, but not IgG-F(ab′)₂ fragments. Furthermore, abatacept significantly suppressed the expression of CD80, but not that of CD86 at protein levels. Finally, abatacept significantly suppressed the expression of mRNA for CD80 of monocytes stimulated with SEB, but not that of CD86.

Conclusions

These results demonstrate that one of the mechanisms of action of abatacept involves the induction of apoptosis of monocytes, which involves interaction with Fc receptor on monocytes. Moreover, the data also demonstrate that abatacept selectively suppresses the expression of CD80 at mRNA levels.

The Orphan Nuclear Receptor NR4A3 Is Involved in the Function of Dendritic Cells

NR4A3/NOR1 belongs to the NR4A subfamily of the nuclear hormone receptor superfamily, which is activated in a ligand-independent manner. To examine the role of NR4A3 in gene expression of dendritic cells (DCs), we introduced NR4A3 small interfering RNA (siRNA) into bone marrow-derived DCs and determined the expression levels of mRNA and proteins of cytokines, cell surface molecules, NF-κB signaling-related proteins, and transcription factors. The expression level of NR4A3 was markedly upregulated by TLR-mediated stimulation in DCs. NR4A3 knockdown significantly suppressed LPS, CpG, or poly(I:C)-mediated upregulation of CD80, CD86, IL-10, IL-6, and IL-12. Proliferation and IL-2 production levels of T cells cocultured with NR4A3 knocked-down DCs were significantly lower than that of T cells cocultured with control DCs. Furthermore, the expression of IKKβ, IRF4, and IRF8 was significantly decreased in NR4A3 siRNA-introduced bone marrow-derived DCs. The knockdown experiments using siRNAs for IKKβ, IRF4, and/or IRF8 indicated that LPS-induced upregulation of IL-10 and IL-6 was reduced in IKKβ knocked-down cells, and that the upregulation of IL-12 was suppressed by the knockdown of IRF4 and IRF8. Taken together, these results indicate that NR4A3 is involved in TLR-mediated activation and gene expression of DCs.

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.

Role of PU.1 Expression as an Inflammatory Marker in Experimental Autoimmune Uveoretinitis

PURPOSE

PU.1 is an Ets family transcription factor, which is essential for the development of immune system through generation of myeloid and lymphoid lineages. In this study, we investigated PU.1 expression in the retina of mice with experimental autoimmune uveoretinitis (EAU) and the association between PU.1 expression level and inflammation in EAU.

METHODS

IRBP 1-20 peptide-immunized mice were used. Quantitative PCR, ELISA analysis, cytometric bead array (CBA), assay and immunostaining were conducted using ocular tissues and lymph nodes.

RESULTS

Quantitative PCR showed significant increases in mRNA levels of PU.1 in the retina at the peak of inflammation. Immunostaining of retina flat mounts revealed that most PU.1-positive cells were co-stained with anti-CD11c and anti-F4/80 antibodies. PU.1 knockdown in lymph node cells significantly suppressed IRBP-stimulated IFN-γ production measured by ELISA and IL-2 production measured by CBA.

CONCLUSION

PU.1 may play crucial roles in the development and progression of inflammation in EAU.

PU.1 serves a critical role in the innate defense against Aspergillus fumigatus via dendritic cell-associated C-type lectin receptor-1 and toll-like receptors-2 and 4 in THP-1-derived macrophages

Aspergillus fumigatus (A. fumigatus) is one of the most common fungal pathogens of invasive pulmonary aspergillosis (IPA), which may be life threatening in immunocompromised individuals. The dendritic cell-associated C-type lectin receptor (Dectin-1), toll-like receptor (TLR)-2 and TLR-4 are major pattern recognition receptors in alveolar macrophages that recognize A. fumigatus components. The PU.1 transcription factor is known to be important for the transcriptional control of these three receptors in mature macrophages. The present study investigated whether alterations of PU.1 expression may affect the innate defense against A. fumigatus in the human monocyte THP-1 cell line. THP-1-derived macrophages were transduced with PU.1 adenoviral vectors and transfected with PU.1 small interfering RNA, and the mRNA and protein expression levels of Dectin-1, TLR-2 and TLR-4 were measured. In addition, the levels of tumor necrosis factor (TNF)-α and interleukin (IL)-1β were ascertained, and fungal phagocytosis and killing were assessed. The results demonstrated that overexpression of PU.1 by recombinant adenoviral vectors resulted in a significant upregulation of Dectin-1, TLR-2 and TLR-4 at the transcriptional and translational levels. In response to A. fumigatus stimulation, PU.1 overexpression increased TNF-α and IL-1β production. In addition, Dectin-1, TLR-2 and TLR-4 upregulation may have enhanced the phagocytosis and killing ability of THP-1-derived macrophages. As expected, silencing of PU.1 led to downregulation of Dectin-1, TLR-2, TLR-4 and the expression of pro-inflammatory cytokines, as well as decreased phagocytosis and the killing ability of THP1-derived macrophages. In conclusion, the results indicate that PU.1 may be a critical factor for the innate defense against A. fumigatus, and may therefore be a potential target for the prophylaxis and treatment of IPA.

Critical Role of Transcription Factor PU.1 in the Function of the OX40L/TNFSF4 Promoter in Dendritic Cells

PU.1 is a hematopoietic lineage-specific transcription factor belonging to the Ets family. We investigated the role of PU.1 in the expression of OX40L in dendritic cells (DCs), because the regulatory mechanism of cell type-specific expression of OX40L, which is mainly restricted to antigen-presenting cells, is largely unknown despite the critical involvement in Th2 and Tfh development. PU.1 knockdown decreased the expression of OX40L in mouse DCs. Chromatin immunoprecipitation (ChIP) assays demonstrated that PU.1 constitutively bound to the proximal region of the OX40L promoter. Reporter assays and electrophoretic mobility shift assays revealed that PU.1 transactivated the OX40L promoter through direct binding to the most-proximal Ets motif. We found that this Ets motif is conserved between mouse and human, and that PU.1 bound to the human OX40L promoter in ChIP assay using human monocyte-derived DCs. ChIP assays based on ChIP-seq datasets revealed that PU.1 binds to several sites distant from the transcription start site on the OX40L gene in addition to the most-proximal site in mouse DCs. In the present study, the structure of the OX40L promoter regulated by PU.1 is determined. It is also suggested that PU.1 is involved in mouse OX40L expression via multiple binding sites on the gene.

The Ability of Precursory Monocytes (MO) to Differentiate Varies Among Individuals But Is Stable Over Time

Background

The ability to generate dendritic cells (DCs) from precursory monocytes (MOs) was a breakthrough in the field of immunology. However, it is unknown whether the ability of MOs to differentiate into immature DCs (iDCs) differs across subjects or is time dependent. Given that the study of immune system function is gaining recognition in the field of clinical medicine, it is important to know how certain immunologic features vary over time.

Material/Methods

This study investigates how much individuals’ MO-to-iDC differentiation potential changes over time. We estimated this potential by measuring the expression of an iDC marker (CD1a), cytokine secretion (interleukin [IL]-12p70), and the ability of IL-4 and granulocyte macrophage colony-stimulating factor (GM-CSF) differentiation MOs to stimulate T cells. We collected MOs obtained from different subjects (n=17) at least 1 month apart. Furthermore, we investigated several variables (expression for cytokine receptors, timing, and emergence of DC-related transcriptional factor PU.1).

Results

The ability of MOs to become DCs under the influence of IL-4 and GM-CSF varied greatly between individuals (range of CD1a expression, 20–80%) but was stable over time (change of CD1a expression between sampling, ~5%). A similar pattern emerged when production of IL-12p70 was analyzed. The ability to stimulate T cells was variable and depended on the T-cell source. The ability of MOs to become iDCs was not linked to the surface expression of receptors for IL-4 and GM-CSF but rather to the activation of PU.1 in the precursory MO. It took 5 days for all committed MOs to become iDCs under in vitro influence of IL-4 and GM-CSF.

Conclusions

We concluded that the potential of MO to become iDC is an individual feature and depends on activation of PU.1.

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.

Negative regulatory roles of ORMDL3 in the FcεRI-triggered expression of proinflammatory mediators and chemotactic response in murine mast cells

Single-nucleotide polymorphism studies have linked the chromosome 17q12-q21 region, where the human orosomucoid-like (ORMDL)3 gene is localized, to the risk of asthma and several other inflammatory diseases. Although mast cells are involved in the development of these diseases, the contribution of ORMDL3 to the mast cell physiology is unknown. In this study, we examined the role of ORMDL3 in antigen-induced activation of murine mast cells with reduced or enhanced ORMDL3 expression. Our data show that in antigen-activated mast cells, reduced expression of the ORMDL3 protein had no effect on degranulation and calcium response, but significantly enhanced phosphorylation of AKT kinase at Ser 473 followed by enhanced phosphorylation and degradation of IκBα and translocation of the NF-κB p65 subunit into the nucleus. These events were associated with an increased expression of proinflammatory cytokines (TNF-α, IL-6, and IL-13), chemokines (CCL3 and CCL4), and cyclooxygenase-2 dependent synthesis of prostaglandin D2. Antigen-mediated chemotaxis was also enhanced in ORMDL3-deficient cells, whereas spreading on fibronectin was decreased. On the other hand, increased expression of ORMDL3 had no significant effect on the studied signaling events, except for reduced antigen-mediated chemotaxis. These data were corroborated by increased IgE-antigen-dependent passive cutaneous anaphylaxis in mice with locally silenced ORMDL3 using short interfering RNAs. Our data also show that antigen triggers suppression of ORMDL3 expression in the mast cells. In summary, we provide evidence that downregulation of ORMDL3 expression in mast cells enhances AKT and NF-κB-directed signaling pathways and chemotaxis and contributes to the development of mast cell-mediated local inflammation in vivo.

Collagen I-induced dendritic cells activation is regulated by TNF-alpha production through down-regulation of IRF4

Previously we have shown that collagen I enhances the maturation and function of dendritic cells (DCs). Inflammatory mediators such as tumour necrosis factor (TNF)- alpha, interleukin (IL)-1 beta and lipopolysaccharide (LPS) are also known to activate DCs. Here we investigated the involvement of TNF-alpha on the collagen I-induced DCs activation. TNF-a neutralization inhibited collagen I-induced IL-12 secretions by DCs. Additionally, we observed suppression of collagen I-induced costimulatory molecules expression along with down-regulation of genes involved in DCs activation pathway. Furthermore, TNF- alpha inhibition upon collagen Istimulation up-regulated the expression of interferon regulatory transcription factor IRF4, when compared to collagen I only treated cells. Collectively, our data demonstrate that collagen I induce TNF- alpha production, which is crucial for the activation and function of DCs, through down-regulation of IRF4, and implicates the importance in development of anti- TNF-alpha therapeutics for several inflammatory diseases.

PU.1 Suppresses Th2 Cytokine Expression via Silencing of GATA3 Transcription in Dendritic Cells

The transcription factor PU.1 is predominantly expressed in dendritic cells (DCs) and is essential for DC differentiation. Although there are several reports that PU.1 positively regulates the expression of DC-specific genes, whether PU.1 also has a suppressive effect on DCs is largely unknown. Here we demonstrate that PU.1 suppresses the expression of Th2 cytokines including IL-13 and IL-5 in bone marrow-derived DCs (BMDCs), through repression of the expression of GATA3, which is a master regulator of Th2 differentiations. When PU.1 siRNA was introduced into BMDCs, LPS-induced expression of IL-13 and IL-5 was increased along with upregulation of the constitutive expression of GATA2 and GATA3. The additional introduction of GATA3 siRNA but not of GATA2 siRNA abrogated PU.1 siRNA-mediated upregulation of IL-13 and IL-5. A chromatin immunoprecipitation assay showed that PU.1 bound to Gata3 proximal promoter region, which is more dominant than the distal promoter in driving GATA3 transcription in DCs. The degree of histone acetylation at the Gata3 promoter was decreased in PU.1 siRNA-introduced DCs, suggesting the involvement of PU.1 in chromatin modification of the Gata3 promoter. Treatment with a histone deacetylase (HDAC) inhibitor, trichostatin A, increased the degree of histone H3 acetylation at the Gata3 promoter and induced the subsequent expression of GATA3. Experiments using HDAC inhibitors and siRNAs showed that HDAC3 suppressed GATA3 expression. The recruitment of HDAC3 to the Gata3 promoter was decreased by PU.1 knockdown. LPS-induced IL-13 expression was dramatically reduced in BMDCs generated from mice lacking the conserved GATA3 response element, termed CGRE, which is an essential site for the binding of GATA3 on the Il-13 promoter. The degree of H3K4me3 at CGRE was significantly increased in PU.1 siRNA-transfected stimulated DCs. Our results indicate that PU.1 plays pivotal roles in DC development and function, serving not only as a transcriptional activator but also as a repressor.

Involvement of PU.1 in NFATc1 promoter function in osteoclast development

BACKGROUND

The transcription factors NFATc1 and PU.1 play important roles in osteoclast development. NFATc1 and PU.1 transactivate osteoclast-specific gene expression and a deficiency in NFATc1 or PU.1 genes causes osteopetrosis due to an insufficient development of osteoclasts. However, the existence of cross-regulation between NFATc1 and PU.1 is largely unknown. In the present study, the role of PU.1 in NFATc1 expression was investigated.

METHODS

Osteoclasts were generated from mouse bone marrow cells. PU.1 knockdown was performed with siRNA introduction. The mRNA levels in siRNA-introduced cells were determined by quantitative RT-PCR. The involvement of PU.1 in the NFATc1 promoter was analyzed by using a chromatin immunoprecipitation (ChIP) assay and a reporter assay. Retrovirus vector was used for enforced expression of PU.1.

RESULTS

Introduction of PU.1 siRNA into bone marrow-derived osteoclasts resulted in a decrease in NFATc1 mRNA level. A ChIP assay showed that PU.1 bound to the NFATc1 promoter in osteoclasts. NFATc1 promoter activity was reduced in PU.1 knockdown cells as assessed by a reporter assay. PU.1 siRNA introduction also downregulated the expression of osteoclast-specific genes and tartrate resistant acid phosphatase (TRAP) activity. Enforced expression of PU.1 using a retrovirus vector increased NFATc1 expression and TRAP activity. When NFATc1 expression was knocked down by using siRNA, the induction of osteoclast-specific genes and TRAP-positive cells was suppressed without affecting the expression level of PU.1.

CONCLUSIONS

These results indicate that PU.1 is involved in osteoclast development by transactivating NFATc1 expression via direct binding to the NFATc1 promoter.

The miR-155-PU.1 axis acts on Pax5 to enable efficient terminal B cell differentiation

A single microRNA (miRNA) can regulate the expression of many genes, though the level of repression imparted on any given target is generally low. How then is the selective pressure for a single miRNA/target interaction maintained across long evolutionary distances? We addressed this problem by disrupting in vivo the interaction between miR-155 and PU.1 in mice. Remarkably, this interaction proved to be key to promoting optimal T cell-dependent B cell responses, a previously unrecognized role for PU.1. Mechanistically, miR-155 inhibits PU.1 expression, leading to Pax5 down-regulation and the initiation of the plasma cell differentiation pathway. Additional PU.1 targets include a network of genes whose products are involved in adhesion, with direct links to B-T cell interactions. We conclude that the evolutionary adaptive selection of the miR-155-PU.1 interaction is exercised through the effectiveness of terminal B cell differentiation.

Critical Roles for PU.1, GATA1, and GATA2 in the expression of human FcεRI on mast cells: PU.1 and GATA1 transactivate FCER1A, and GATA2 transactivates FCER1A and MS4A2

The high-affinity IgE receptor, FcεRI, which is composed of α-, β-, and γ-chains, plays an important role in IgE-mediated allergic responses. In the current study, involvement of the transcription factors, PU.1, GATA1, and GATA2, in the expression of FcεRI on human mast cells was investigated. Transfection of small interfering RNAs (siRNAs) against PU.1, GATA1, and GATA2 into the human mast cell line, LAD2, caused significant downregulation of cell surface expression of FcεRI. Quantification of the mRNA levels revealed that PU.1, GATA1, and GATA2 siRNAs suppressed the α transcript, whereas the amount of β mRNA was reduced in only GATA2 siRNA transfectants. In contrast, γ mRNA levels were not affected by any of the knockdowns. Chromatin immunoprecipitation assay showed that significant amounts of PU.1, GATA1, and GATA2 bind to the promoter region of FCER1A (encoding FcεRIα) and that GATA2 binds to the promoter of MS4A2 (encoding FcεRIβ). Luciferase assay and EMSA showed that GATA2 transactivates the MS4A2 promoter via direct binding. These knockdowns of transcription factors also suppressed the IgE-mediated degranulation activity of LAD2. Similarly, all three knockdowns suppressed FcεRI expression in primary mast cells, especially PU.1 siRNA and GATA2 siRNA, which target FcεRIα and FcεRIβ, respectively. From these results, we conclude that PU.1 and GATA1 are involved in FcεRIα transcription through recruitment to its promoter, whereas GATA2 positively regulates FcεRIβ transcription. Suppression of these transcription factors leads to downregulation of FcεRI expression and IgE-mediated degranulation activity. Our findings will contribute to the development of new therapeutic approaches for FcεRI-mediated allergic diseases.

The splicing factor hnRNP C regulates expression of co-stimulatory molecules CD80 and CD40 in dendritic cells

Maturation of dendritic cells is a key step during induction of adaptive immune responses. Multiple pathways and factors are involved in the regulation of dendritic cell maturation. Alternative splicing of pre-mRNA, which is regulated by splicing factors, plays an important role in many biological processes, including immune responses. To understand the roles of splicing factors in the maturation of dendritic cells, we analyzed the expression of the splicing factors hnRNP C and hnRNP A1 during maturation of the mouse dendritic cell line DC2.4 upon treatment with lipopolysaccharides (LPS). The expression of hnRNP C significantly increased after LPS stimulation. Knockdown or overexpression of hnRNP C respectively downregulated or upregulated the expression of nuclear factor-kappa B p65 as well as its downstream targets CD80 and CD40. Our results indicate that hnRNP C regulates the maturation of dendritic cells by affecting the expression of p65, CD80 and CD40.

Coordinated regulation of the immunoproteasome subunits by PML/RARα and PU.1 in acute promyelocytic leukemia

Recognition and elimination of malignant cells by cytotoxic T lymphocytes depends on antigenic peptides generated by proteasomes. It has been established that impairment of the immunoproteasome subunits, that is, PSMB8, PSMB9 and PSMB10 (PSMBs), is critical for malignant cells to escape immune recognition. We report here the regulatory mechanism of the repression of PU.1-dependent activation of PSMBs by PML/RARα in the pathogenesis of acute promyelocytic leukemia (APL) and the unidentified function of all-trans retinoic acid (ATRA) as an immunomodulator in the treatment of APL. Chromatin immunoprecipitation and luciferase reporter assays showed that PU.1 directly bound to and coordinately transactivated the promoters of PSMBs, indicating that PSMBs were transcriptional targets of PU.1 and PU.1 regulated their basal expression. Analysis of expression profiling data from a large population of acute myeloid leukemia (AML) patients revealed that the expression levels of PSMBs were significantly lower in APL patients than in non-APL AML patients. Further evidence demonstrated that the decrease in their expression was achieved through PML/RARα-mediated repression of both PU.1-dependent transactivation and PU.1 expression. Moreover, ATRA but not arsenic trioxide induced the expression of PSMBs in APL cells, indicating that ATRA treatment might activate the antigen-processing/presentation machinery. Finally, the above observations were confirmed in primary APL samples. Collectively, our data demonstrate that PML/RARα suppresses PU.1-dependent activation of the immunosubunits, which may facilitate the escape of APL cells from immune surveillance in leukemia development, and ATRA treatment is able to reactivate their expression, which would promote more efficient T-cell-mediated recognition in the treatment.