Transcription Factor PU.1 Controls Transcription Start Site Positioning and Alternative TLR4 Promoter Usage

Long non-coding RNA LncTUG1 regulates favourable compression force-induced cementocytes mineralization via PU.1/TLR4/SphK1 signalling

Orthodontic tooth movement (OTM) is a highly coordinated biomechanical response to orthodontic forces with active remodelling of alveolar bone but minor root resorption. Such antiresorptive properties of root relate to cementocyte mineralization, the mechanisms of which remain largely unknown. This study used the microarray analysis to explore long non-coding ribonucleic acids involved in stress-induced cementocyte mineralization. Gain- and loss-of-function experiments, including Alkaline phosphatase (ALP) activity and Alizarin Red S staining, quantitative real-time polymerase chain reaction (qRT-PCR), Western blot, and immunofluorescence analyses of mineralization-associated factors, were conducted to verify long non-coding ribonucleic acids taurine-upregulated gene 1 (LncTUG1) regulation in stress-induced cementocyte mineralization, via targeting the Toll-like receptor 4 (TLR4)/SphK1 axis. The luciferase reporter assays, chromatin immunoprecipitation assays, RNA pull-down, RNA immunoprecipitation, and co-localization assays were performed to elucidate the interactions between LncTUG1, PU.1, and TLR4. Our findings indicated that LncTUG1 overexpression attenuated stress-induced cementocyte mineralization, while blocking the TLR4/SphK1 axis reversed the inhibitory effect of LncTUG1 on stress-induced cementocyte mineralization. The in vivo findings also confirmed the involvement of TLR4/SphK1 signalling in cementocyte mineralization during OTM. Mechanistically, LncTUG1 bound with PU.1 subsequently enhanced TLR4 promotor activity and thus transcriptionally elevated the expression of TLR4. In conclusion, our data revealed a critical role of LncTUG1 in regulating stress-induced cementocyte mineralization via PU.1/TLR4/SphK1 signalling, which might provide further insights for developing novel therapeutic strategies that could protect roots from resorption during OTM.

Epigallocatechin gallate regulates the myeloid-specific transcription factor PU.1 in macrophages

Our previous research demonstrated that PU.1 regulates expression of the genes involved in inflammation in macrophages. Selective knockdown of PU.1 in macrophages ameliorated LPS-induced acute lung injury (ALI) in bone marrow chimera mice. Inhibitors that block the transcriptional activity of PU.1 in macrophages have the potential to mitigate the pathophysiology of LPS-induced ALI. However, complete inactivation of PU.1 gene disrupts normal myelopoiesis. Although the green tea polyphenol Epigallocatechin gallate (EGCG) has been shown to regulate inflammatory genes in various cell types, it is not known if EGCG alters the transcriptional activity of PU.1 protein. Using Schrodinger Glide docking, we have identified that EGCG binds with PU.1 protein, altering its DNA-binding and self-dimerization activity. In silico analysis shows that EGCG forms Hydrogen bonds with Glutamic Acid 209, Leucine 250 in DNA binding and Lysine 196, Tryptophan 193, and Leucine 182 in the self-dimerization domain of the PU.1 protein. Experimental validation using mouse bone marrow-derived macrophages (BMDM) confirmed that EGCG inhibits both DNA binding by PU.1 and self-dimerization. Importantly, EGCG had no impact on expression of the total PU.1 protein levels but significantly reduced expression of various inflammatory genes and generation of ROS. In summary, we report that EGCG acts as an inhibitor of the PU.1 transcription factor in macrophages.

A gain-of-function p53 mutant synergizes with oncogenic NRAS to promote acute myeloid leukemia in mice

We previously demonstrated that a subset of acute myeloid leukemia (AML) patients with concurrent RAS pathway and TP53 mutations have an extremely poor prognosis and that most of these TP53 mutations are missense mutations. Here, we report that, in contrast to the mixed AML and T cell malignancy that developed in NrasG12D/+ p53-/- (NP-/-) mice, NrasG12D/+ p53R172H/+ (NPmut) mice rapidly developed inflammation-associated AML. Under the inflammatory conditions, NPmut hematopoietic stem and progenitor cells (HSPCs) displayed imbalanced myelopoiesis and lymphopoiesis and mostly normal cell proliferation despite MEK/ERK hyperactivation. RNA-Seq analysis revealed that oncogenic NRAS signaling and mutant p53 synergized to establish an NPmut-AML transcriptome distinct from that of NP-/- cells. The NPmut-AML transcriptome showed GATA2 downregulation and elevated the expression of inflammatory genes, including those linked to NF-κB signaling. NF-κB was also upregulated in human NRAS TP53 AML. Exogenous expression of GATA2 in human NPmut KY821 AML cells downregulated inflammatory gene expression. Mouse and human NPmut AML cells were sensitive to MEK and NF-κB inhibition in vitro. The proteasome inhibitor bortezomib stabilized the NF-κB-inhibitory protein IκBα, reduced inflammatory gene expression, and potentiated the survival benefit of a MEK inhibitor in NPmut mice. Our study demonstrates that a p53 structural mutant synergized with oncogenic NRAS to promote AML through mechanisms distinct from p53 loss.

pKr-2 induces neurodegeneration via upregulation of microglial TLR4 in the hippocampus of AD brain

We recently demonstrated that prothrombin kringle-2 (pKr-2) derived from blood-brain barrier (BBB) disruption could induce hippocampal neurodegeneration and object recognition impairment through neurotoxic inflammatory responses in the five familial Alzheimer's disease mutation (5XFAD) mice. In the present study, we aimed to determine whether pKr-2 induces microglial activation by stimulating toll-like receptor 4 (TLR4) upregulation and examine whether this response contributes to pKr-2-induced neuroinflammatory damage in the hippocampi of mice models. We observed that inflammatory responses induced by pKr-2 administration in the hippocampi of wild-type mice were significantly abrogated in TLR4-deficient mice (TLR4^-/-), and caffeine supply or rivaroxaban treatment that inhibits the overexpression of hippocampal pKr-2 reduced TLR4 upregulation in 5XFAD mice, resulting in the inhibition of neuroinflammatory responses. Similar to the expression patterns of pKr-2, TLR4, and the TLR4 transcription factors, PU.1 and p-c-Jun, seen in the postmortem hippocampal tissues of Alzheimer's disease (AD) patients, our results additionally showed the influence of transcriptional regulation on TLR4 expression following pKr-2 expression in triggering the production of neurotoxic inflammatory mediators. Therefore, we conclude that pKr-2 may play a role in initiating upregulation of microglial TLR4, consequently inducing hippocampal neurodegeneration. Furthermore, the control of pKr-2-induced microglial TLR4 could be a useful therapeutic strategy against hippocampal neurodegeneration in AD.

Ulmoidol, an unusual nortriterpenoid from Eucommia ulmoides Oliv. Leaves prevents neuroinflammation by targeting the PU.1 transcriptional signaling pathway

Chronic neuroinflammation is closely associated with the development of neurodegenerative diseases, including Alzheimer's disease (AD). In the current study, 13 anti-neuroinflammatory compounds were isolated from Eucommia ulmoides Oliv. leaves. Among these compounds, trans-sinapaldehyde (6), 3',4',5,7-tetrahydroxy-3-methylflavone (7), and amarusine A (13) were isolated from E. ulmoides leaves for the first time. The ursane-type C₂₉-triterpenoid, ulmoidol (ULM, 9), significantly inhibited the production of proinflammatory mediators and reduced the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Moreover, ULM inhibited the cluster of differentiation 14 (CD14)/Toll-like receptor 4 (TLR4) signaling pathway and consequently limited the activation of nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways. Notably, electrophoretic mobility shift assay (EMSA) and molecular docking analyses indicated that ULM could prevent PU box binding-1 (PU.1) from binding to DNA, suggesting that PU.1 might be a potential ULM target. In conclusion, ULM alleviates neuroinflammatory responses in microglia, which could be partly explained by its targeting of PU.1 and the resulting suppression of the TLR4/MAPK/NF-κB signaling pathways. These results suggested that ULM may have therapeutic potential as an agent for treating neuroinflammation-related neurodegenerative diseases.

Transcriptional Regulation of the Human IL5RA Gene through Alternative Promoter Usage during Eosinophil Development

Regulation of the IL-5 receptor alpha (IL5RA) gene is complicated, with two known promoters (P1 and P2) driving transcription, and two known isoforms (transmembrane and soluble) dichotomously affecting the signaling potential of the protein products. Here, we sought to determine the patterns of P1 and P2 promoter usage and transcription factor occupancy during primary human eosinophil development from CD34⁺ hematopoietic stem cell progenitors. We found that during eosinophilopoiesis, both promoters were active but subject to distinct temporal regulation, coincident with combinatorial interactions of transcription factors, including GATA-1, PU.1, and C/EBP family members. P1 displayed a relatively constant level of activity throughout eosinophil development, while P2 activity peaked early and waned thereafter. The soluble IL-5Rα mRNA peaked early and showed the greatest magnitude fold-induction, while the signaling-competent transmembrane isoform peaked moderately. Two human eosinophilic cell lines whose relative use of P1 and P2 were similar to eosinophils differentiated in culture were used to functionally test putative transcription factor binding sites. Transcription factor occupancy was then validated in primary cultures by ChIP. We conclude that IL-5-dependent generation of eosinophils from CD34⁺ precursors involves complex and dynamic activity including both promoters, several interacting transcription factors, and both signaling and antagonistic protein products.

Toll-like receptor 4 is a master regulator for colorectal cancer growth under high-fat diet by programming cancer metabolism

Although high-fat diet (HFD) has been implicated in the development of colorectal cancer (CRC), the critical signaling molecule that mediates the cancer growth is not well-defined. Identifying the master regulator that controls CRC growth under HFD can facilitate the development of effective therapeutics for the cancer treatment. In this study, the global lipidomics and RNA sequencing data show that, in the tumor tissues of CRC-bearing mouse models, HFD not only increases tumor weight, but also the palmitic acid level and TLR4 expression, which are reduced when HFD is replaced by control diet. These concomitant changes suggest the roles of palmitic acid and TLR4 in CRC growth. Subsequent studies show that palmitic acid regulates TLR4 expression in PU.1-dependent manner. Knockdown of PU.1 or mutations of PU.1-binding site on TLR4 promoter abolish the palmitic acid-increased TLR4 expression. The role of palmitic acid/PU.1/TLR4 axis in CRC growth is further examined in cell model and animal models that are fed either HFD or palmitic acid-rich diet. More importantly, iTRAQ proteomics data show that knockdown of TLR4 changes the metabolic enzyme profiles in the tumor tissues, which completely abolish the HFD-enhanced ATP production and cancer growth. Our data clearly demonstrate that TLR4 is a master regulator for CRC growth under HFD by programming cancer metabolism.

Activation of STAT3 is a key event in TLR4 signaling-mediated melanoma progression

Malignant melanoma is aggressive and has a high mortality rate. Toll-like receptor 4 (TLR4) has been linked to melanoma growth, angiogenesis and metastasis. However, signal transduction mediated by TLR4 for driving melanoma progression is not fully understood. Signal transducer and activator of transcription 3 (STAT3) has been identified as a major oncogene in melanoma progression. We found: that TLR4 expression positively correlates with activation/phosphorylation of STAT3 in human melanoma samples; that TLR4 ligands activate STAT3 through MYD88 and TRIF in melanoma cells; and that intratumoral activation of TLR4 increases STAT3 activation in the tumor and promotes tumor growth, angiogenesis, epithelial-mesenchymal transition (EMT) and the formation of an immunosuppressive tumor microenvironment in mice. Further, we found that the effects mediated by activating TLR4 are weakened by suppressing STAT3 function with a dominant negative STAT3 variant in melanoma. Collectively, our work identifies STAT3 activation as a key event in TLR4 signaling-mediated melanoma progression, shedding new light on the pathophysiology of melanoma.

Minor C allele of the SNP rs7873784 associated with rheumatoid arthritis and type-2 diabetes mellitus binds PU.1 and enhances TLR4 expression

Toll-like receptor 4 (TLR4) is an innate immunity receptor predominantly expressed on myeloid cells and involved in the development of various diseases, many of them with complex genetics. Here we present data on functionality of single nucleotide polymorphism rs7873784 located in the 3'-untranslated region (3'-UTR) of TLR4 gene and associated with various pathologies involving chronic inflammation. We demonstrate that TLR4 3'-UTR strongly enhanced the activity of TLR4 promoter in U937 human monocytic cell line while minor rs7873784(C) allele created a binding site for transcription factor PU.1 (encoded by SPI1 gene), a known regulator of TLR4 expression. Increased binding of PU.1 further augmented the TLR4 transcription while PU.1 knockdown or complete disruption of the PU.1 binding site abrogated the effect. We hypothesize that additional functional PU.1 site may increase TLR4 expression in individuals carrying minor C variant of rs7873784 and modulate the development of certain pathologies, such as rheumatoid arthritis and type-2 diabetes mellitus.

Hidden Aspects of Valency in Immune System Regulation

Valency can be defined as the number of discrete interactions a biomolecule can engage in. Valency can be critical for function, such as determining whether a molecule acts as a scaffold for assembling large supramolecular complexes or forms a functional dimer. Here, we highlight the importance of the role of valency in regulating immune responses, with a focus on innate immunity. We discuss some of the ways in which valency itself is regulated through transcriptional, post-transcriptional, and post-translational modifications. Finally, we propose that the valency model can be applied at the whole cell level to study differences in individual cell responses with relevance to putative therapeutic applications.

Effect of Various Agents on the Direction of THP-1 Cell Differentiation

The ability of physiological (1α,25-dihydroxyvitamin D3, retinoic acid) and non-physiological (various LPS) agents and their combinations to influence the direction of promonocytic THP-1 cell differentiation was studied.

The differentiating activity of the agents was evaluated by the expression and the ratio of surface receptors (TLR4, CD11b, and CD14) as well as by the change in THP-1 cell phagocytic activity of different degree of differentiation by Flow cytometry.

The THP-1 cell differentiation by VD3 was shown to lead probably to the formation of classical monocytes.

Summarizing we can conclude that VD3 induces the THP-1 cells differentiation with the formation of classical monocytes and the sequence of 1α, 25-dihydroxyvitamin D3 and non-toxic LPS R. capsulatus PG causes the THP-1 cells differentiation with the formation of inflammatory or intermediate monocytes.

Single Nucleotide Polymorphisms in 5' Upstream Region of Bovine TLR4 Gene Affecting Expression Profile and Transcription Factor Binding Sites

The present study in the 5' upstream region of TLR4 gene revealed four Single Nucleotide Polymorphisms (SNPs) in Vrindavani and Tharparkar cattle. The polymorphic information content (PIC), heterozygosity and allelic diversity values were low to moderate for these SNPs. In Vrindavani cattle, one SNP was found to be in Hardy-Weinberg Equilibrium (HWE) and the remaining three were found to be in linkage disequilibrium (LD) as indicated statistically (P > 0.05). In Tharparkar cattle, two SNPs were found to be in HWE and were not in LD as indicated statistically (P > 0.05). These SNPs were used for construction of haplotypes. In-silico analysis of these SNPs predicted abolition of eight transcription factor binding sites and creation of eight new sites. The quantitative real time PCR analysis did not show any significant variation of gene expression among haplotypes. However, gene expression between breed was found to be significant (P < 0.05) which suggested that upstream region of bovine TLR4 gene has a crucial role in its expression. These findings in TLR4 gene offer essential evidence that can be useful in future research exploring its role in immunity. TLR4 can be used as a marker for selection for disease resistance in bovines.

Species-specific engagement of human nucleotide oligomerization domain 2 (NOD)2 and Toll-like receptor (TLR) signalling upon intracellular bacterial infection: role of Crohn's associated NOD2 gene variants

Recognition of bacterial peptidoglycan-derived muramyl-dipeptide (MDP) by nucleotide oligomerization domain 2 (NOD2) induces crucial innate immune responses. Most bacteria carry the N-acetylated form of MDP (A-MDP) in their cell membranes, whereas N-glycolyl MDP (G-MDP) is typical for mycobacteria. Experimental murine studies have reported G-MDP to have a greater NOD2-stimulating capacity than A-MDP. As NOD2 polymorphisms are associated with Crohn's disease (CD), a link has been suggested between mycobacterial infections and CD. Thus, the aim was to investigate if NOD2 responses are dependent upon type of MDP and further to determine the role of NOD2 gene variants for the bacterial recognition in CD. The response pattern to A-MDP, G-MDP, Mycobacterium segmatis (expressing mainly G-MDP) and M. segmatisΔnamH (expressing A-MDP), Listeria monocytogenes (LM) (an A-MDP-containing bacteria) and M. avium paratuberculosis (MAP) (a G-MDP-containing bacteria associated with CD) was investigated in human peripheral blood mononuclear cells (PBMCs). A-MDP and M. segmatisΔnamH induced significantly higher tumour necrosis factor (TNF)-α protein levels in healthy wild-type NOD2 PBMCs compared with G-MDP and M. segmatis. NOD2 mutations resulted in a low tumour necrosis factor (TNF)-α protein secretion following stimulation with LM. Contrary to this, TNF-α levels were unchanged upon MAP stimulation regardless of NOD2 genotype and MAP solely activated NOD2- and Toll-like receptor (TLRs)-pathway with an enhanced production of interleukin (IL)-1β and IL-10. In conclusion, the results indicate that CD-associated NOD2 deficiencies might affect the response towards a broader array of commensal and pathogenic bacteria expressing A-MDP, whereas they attenuate the role of mycobacteria in the pathogenesis of CD.

Reciprocal effects of Toll-like receptors and miRNAs on biological processes in human health and disease: a systematic review

The roles of miRNAs in human diseases are emerging. Manipulation of miRNA expression seems to be an effective approach to control disease severity. It has recently been found that Toll-like receptors and miRNAs work by exerting reciprocal effects. Toll-like receptor stimulation can lead to up-/down-regulation of various miRNA expressions. Lipopolysaccharide induction may result in interactions between different miRNAs. Several miRNAs are involved in cancers, indicating the importance of identifying strategies to properly manipulate their expression level. The control of various miRNA expression levels, taking into consideration the plethora of their target genes and the possibility that this may lead to contracting function, which is an important issue in treatment of any miRNA-based (phenotype) disease.

Suppression of PU.1-linked TLR4 expression by cilostazol with decrease of cytokine production in macrophages from patients with rheumatoid arthritis

BACKGROUND AND PURPOSE

The present study assessed the effects of cilostazol on LPS-stimulated TLR4 signal pathways in synovial macrophages from patients with rheumatoid arthritis (RA). These effects were confirmed in collagen-induced arthritis (CIA) in mice.

EXPERIMENTAL APPROACH

Expression of TLR4, PU.1, NF-κB p65 and IκBα on synovial fluid macrophages from RA patients was determined by Western blotting, and cytokines were measured by ELISA. Anti-arthritic effects were evaluated in CIA mice.

KEY RESULTS

Intracellular cAMP was concentration-dependently raised by cilostazol (1-100 μM). Cilostazol significantly suppressed LPS-stimulated increase of TLR4 expression by blocking PU.1 transcriptional activity in RA macrophages. In addition, cilostazol decreased LPS-induced myeloid differentiation factor 88 (MyD88) expression, but not that of TNF receptor-associated factor 6 (TRAF6). Cilostazol also suppressed IkBα degradation and NF-κB p65 nuclear translocation. Moreover, LPS-induced increase of cytokine production (TNF-α, IL-1β) was inhibited by cilostazol, an effect which was accompanied by suppression of IκBα degradation, and NF-κB p65 nuclear translocation. However, expression of anti-inflammatory IL-10 was elevated by cilostazol and forskolin/IBMX. In mice with CIA, post-treatment with cilostazol (30 mg kg⁻¹ day⁻¹) decreased expression of TLR4 in knee joints in association with decreased recruitment of macrophages. Consequently, synovial inflammation, proteoglycan depletion and bone erosion were significantly inhibited by cilostazol treatment.

CONCLUSIONS AND IMPLICATIONS

Cilostazol down-regulated LPS-stimulated PU.1-linked TLR4 expression and TLR4/MyD88/NF-κB signal pathways, and then suppressed inflammatory cytokine production in synovial macrophages from RA patients. Also cilostazol markedly inhibited the severity of CIA in mice.

Innate immune signalling at the intestinal epithelium in homeostasis and disease

The intestinal epithelium--which constitutes the interface between the enteric microbiota and host tissues--actively contributes to the maintenance of mucosal homeostasis and defends against pathogenic microbes. The recognition of conserved microbial products by cytosolic or transmembrane pattern recognition receptors in epithelial cells initiates signal transduction and influences effector cell function. However, the signalling pathways, effector molecules and regulatory mechanisms involved are not yet fully understood, and the functional outcome is poorly defined. This review analyses the complex and dynamic role of intestinal epithelial innate immune recognition and signalling, on the basis of results in intestinal epithelial cell-specific transgene or gene-deficient animals. This approach identifies specific epithelial cell functions within the diverse cellular composition of the mucosal tissue, in the presence of the complex and dynamic gut microbiota. These insights have thus provided a more comprehensive understanding of the role of the intestinal epithelium in innate immunity during homeostasis and disease.

Functional PU.1 in macrophages has a pivotal role in NF-κB activation and neutrophilic lung inflammation during endotoxemia

Although the role of ETS family transcriptional factor PU.1 is well established in macrophage maturation, its role in mature macrophages with reference to sepsis- related animal model has not been elucidated. Here, we report the in vivo function of PU.1 in mediating mature macrophage inflammatory phenotype by using bone marrow chimera mice with conditional PU.1 knockout. We observed that the expression of monocyte/macrophage-specific markers CD 11b, F4/80 in fetal liver cells, and bone marrow-derived macrophages were dependent on functional PU.1. Systemic inflammation as measured in terms of NF-κB reporter activity in lung, liver, and spleen tissues was significantly decreased in PU.1-deficient chimera mice compared with wild-type chimeras on lipopolysaccharide (LPS) challenge. Unlike wild-type chimera mice, LPS challenge in PU.1-deficient chimera mice resulted in decreased lung neu-trophilic inflammation and myeloperoxidase activity. Similarly, we found attenuated inflammatory gene expression (cyclooxygenase-2, inducible nitric-oxide synthase, and TLR4) and inflammatory cytokine secretion (IL-6, MCP-1, IL-1β, TNF-α, and neutrophilic chemokine keratinocyte-derived chemokine) in PU.1-deficient mice. Most importantly, this attenuated lung and systemic inflammatory phenotype was associated with survival benefit in LPS-challenged heterozygotic PU.1-deficient mice, establishing a novel protective mechanistic role for the lineage-specific transcription factor PU.1.

Genetics of innate immunity and UTI susceptibility

A functional and well-balanced immune response is required to resist most infections. Slight dysfunctions in innate immunity can turn the 'friendly' host defense into an unpleasant foe and give rise to disease. Beneficial and destructive forces of innate immunity have been discovered in the urinary tract and mechanisms by which they influence the severity of urinary tract infections (UTIs) have been elucidated. By modifying specific aspects of the innate immune response to UTI, genetic variation either exaggerates the severity of acute pyelonephritis to include urosepsis and renal scarring or protects against symptomatic disease by suppressing innate immune signaling, as in asymptomatic bacteriuria (ABU). Different genes are polymorphic in patients prone to acute pyelonephritis or ABU, respectively, and yet discussions of UTI susceptibility in clinical practice still focus mainly on social and behavioral factors or dysfunctional voiding. Is it not time for UTIs to enter the era of molecular medicine? Defining why certain individuals are protected from UTI while others have severe, recurrent infections has long been difficult, but progress is now being made, encouraging new approaches to risk assessment and therapy in this large and important patient group, as well as revealing promising facets of 'good' versus 'bad' inflammation.

Characterization and gene expression of transcription factors, PU.1 and C/EBPα driving transcription from the tumor necrosis factor α promoter in Japanese flounder, Paralichthys olivaceus

Both PU.1 and C/EBPα transcription factors play important roles in myeloid development and inflammatory response. These transcripts were cloned from the Japanese flounder (Paralichthys olivaceus) and were highly conserved with those of other vertebrates. PU.1 mRNA was mainly expressed in lymphoid tissues while C/EBPα mRNA was widely expressed in all tissues examined. Higher levels of PU.1 mRNA were expressed in the IgM(+) cells of both PBL and KL, while C/EBPα expression was higher only in the IgM(-) cells of KL. The expression of C/EBPα mRNA was induced only in KL stimulated with LPS. Interestingly, PU.1 mRNA expression was induced by Edwardsiella tarda, whereas the expression of C/EBPα mRNA was induced by Streptococcus iniae infection. Both PU.1 and C/EBPα drove transcription from the LPS-responsive region of the Japanese flounder TNFα gene, suggesting that both PU.1 and C/EBPα induced by bacterial infection are involved in inflammation mediated through TNFα expression.

MicroRNAs in inflammatory lung disease--master regulators or target practice?

MicroRNAs (miRNAs) have emerged as a class of regulatory RNAs with immense significance in numerous biological processes. When aberrantly expressed miRNAs have been shown to play a role in the pathogenesis of several disease states. Extensive research has explored miRNA involvement in the development and fate of immune cells and in both the innate and adaptive immune responses whereby strong evidence links miRNA expression to signalling pathways and receptors with critical roles in the inflammatory response such as NF-κB and the toll-like receptors, respectively. Recent studies have revealed that unique miRNA expression profiles exist in inflammatory lung diseases such as cystic fibrosis, chronic obstructive pulmonary disease, asthma, idiopathic pulmonary fibrosis and lung cancer. Evaluation of the global expression of miRNAs provides a unique opportunity to identify important target gene sets regulating susceptibility and response to infection and treatment, and control of inflammation in chronic airway disorders. Over 800 human miRNAs have been discovered to date, however the biological function of the majority remains to be uncovered. Understanding the role that miRNAs play in the modulation of gene expression leading to sustained chronic pulmonary inflammation is important for the development of new therapies which focus on prevention of disease progression rather than symptom relief. Here we discuss the current understanding of miRNA involvement in innate immunity, specifically in LPS/TLR4 signalling and in the progression of the chronic inflammatory lung diseases cystic fibrosis, COPD and asthma. miRNA in lung cancer and IPF are also reviewed.

Maintaining cell identity through global control of genomic organization

Cell differentiation entails early lineage choices leading to the activation, and the subsequent maintenance, of the gene expression program characteristic of each cell type. Alternative lineage choices involve the activation of different regulatory and coding regions of the genome, a process instructed by lineage-determining transcription factors, and at least in part mediated by the deposition of chromatin marks that modify functionality and accessibility of the underlying genome. According to classic epigenetics, subsequent maintenance of chromatin marks across mitoses and in spite of environmental perturbations occurs largely through autonomous and unsupervised mechanisms. However, paradigmatic genetic and biochemical studies in immune system and hematopoietic cells strongly point to the concept that both induction and maintenance of the differentiated state require constant supervision by lineage-determining transcription factors, which may act to globally organize the genome in both the one- and the three-dimensional space.

Simple combinations of lineage-determining transcription factors prime cis-regulatory elements required for macrophage and B cell identities

Genome-scale studies have revealed extensive, cell type-specific colocalization of transcription factors, but the mechanisms underlying this phenomenon remain poorly understood. Here, we demonstrate in macrophages and B cells that collaborative interactions of the common factor PU.1 with small sets of macrophage- or B cell lineage-determining transcription factors establish cell-specific binding sites that are associated with the majority of promoter-distal H3K4me1-marked genomic regions. PU.1 binding initiates nucleosome remodeling, followed by H3K4 monomethylation at large numbers of genomic regions associated with both broadly and specifically expressed genes. These locations serve as beacons for additional factors, exemplified by liver X receptors, which drive both cell-specific gene expression and signal-dependent responses. Together with analyses of transcription factor binding and H3K4me1 patterns in other cell types, these studies suggest that simple combinations of lineage-determining transcription factors can specify the genomic sites ultimately responsible for both cell identity and cell type-specific responses to diverse signaling inputs.

Toll-like receptor 4 promoter polymorphisms: common TLR4 variants may protect against severe urinary tract infection

Background

Polymorphisms affecting Toll-like receptor (TLR) structure appear to be rare, as would be expected due to their essential coordinator role in innate immunity. Here, we assess variation in TLR4 expression, rather than structure, as a mechanism to diversify innate immune responses.

Methodology/Principal Findings

We sequenced the TLR4 promoter (4,3 kb) in Swedish blood donors. Since TLR4 plays a vital role in susceptibility to urinary tract infection (UTI), promoter sequences were obtained from children with mild or severe disease. We performed a case-control study of pediatric patients with asymptomatic bacteriuria (ABU) or those prone to recurrent acute pyelonephritis (APN). Promoter activity of the single SNPs or multiple allelic changes corresponding to the genotype patterns (GPs) was tested. We then conducted a replication study in an independent cohort of adult patients with a history of childhood APN. Last, in vivo effects of the different GPs were examined after therapeutic intravesical inoculation of 19 patients with Escherichia coli 83972. We identified in total eight TLR4 promoter sequence variants in the Swedish control population, forming 19 haplotypes and 29 genotype patterns, some with effects on promoter activity. Compared to symptomatic patients and healthy controls, ABU patients had fewer genotype patterns, and their promoter sequence variants reduced TLR4 expression in response to infection. The ABU associated GPs also reduced innate immune responses in patients who were subjected to therapeutic urinary E. coli tract inoculation.

Conclusions

The results suggest that genetic variation in the TLR4 promoter may be an essential, largely overlooked mechanism to influence TLR4 expression and UTI susceptibility.

Function and phenotype of microglia are determined by toll-like receptor 2/toll-like receptor 4 activation sequence

Toll-like receptors (TLRs) initiate and maintain host defenses. These receptors play important roles in innate immunity and in various diseases. Different TLRs bind to diverse ligands that trigger distinct protein expression patterns. Few studies have focused on the interaction between different TLRs. We found that TLR2 priming downregulates TLR4 transcription, and expression of TLR4 activation induced major histocompatibility complex II (MHC II), adhesion molecule intercellular adhesion molecule-1 (ICAM-1), phagocytosis marker CD11b/CD18, and Fcgamma receptor (FcgammaR) expression. In contrast, TLR4 priming increases TLR2 transcription and expression. In addition, TLR4 priming increases secretion of certain proinflammatory mediators. Expression of costimulatory molecules CD80/CD86 increases with TLR2 or TLR4 activation sequences. Our results reveal that TLR2/TLR4 activation may determine disease pathogenesis and prognosis.

Helicobacter pylori lipopolysaccharides upregulate toll-like receptor 4 expression and proliferation of gastric epithelial cells via the MEK1/2-ERK1/2 mitogen-activated protein kinase pathway

Helicobacter pylori is recognized as an etiological agent of gastroduodenal diseases. H. pylori produces various toxic substances, including lipopolysaccharide (LPS). However, H. pylori LPS exhibits extremely weakly endotoxic activity compared to the typical LPS, such as that produced by Escherichia coli, which acts through Toll-like receptor 4 (TLR4) to induce inflammatory molecules. The gastric epithelial cell lines MKN28 and MKN45 express TLR4 at very low levels, so they show very weak interleukin-8 (IL-8) production in response to E. coli LPS, but pretreatment with H. pylori LPS markedly enhanced IL-8 production induced by E. coli LPS by upregulating TLR4 via TLR2 and the MEK1/2-ERK1/2 pathway. The transcription factor NF-Y was activated by this signal and promoted transcription of the tlr4 gene. These MEK1/2-ERK1/2 signal-mediated activities were more potently activated by LPS carrying a weakly antigenic epitope, which is frequently found in gastric cancers, than by LPS carrying a highly antigenic epitope, which is associated with chronic gastritis. H. pylori LPS also augmented the proliferation rate of gastric epithelial cells via the MEK1/2-ERK1/2 pathway. H. pylori LPS may be a pathogenic factor causing gastric tumors by enhancing cell proliferation and inflammation via the MEK1/2-ERK1/2 mitogen-activated protein kinase cascade in gastric epithelial cells.

Antagonism of microRNA-126 suppresses the effector function of TH2 cells and the development of allergic airways disease

Allergic asthma is an inflammatory disease of the lung characterized by abnormal T helper-2 (T(H)2) lymphocyte responses to inhaled antigens. The molecular mechanisms leading to the generation of T(H)2 responses remain unclear, although toll-like receptors (TLRs) present on innate immune cells play a pivotal role in sensing molecular patterns and in programming adaptive T cell responses. Here we show that in vivo activation of TLR4 by house dust mite antigens leads to the induction of allergic disease, a process that is associated with expression of a unique subset of small, noncoding microRNAs. Selective blockade of microRNA (miR)-126 suppressed the asthmatic phenotype, resulting in diminished T(H)2 responses, inflammation, airways hyperresponsiveness, eosinophil recruitment, and mucus hypersecretion. miR-126 blockade resulted in augmented expression of POU domain class 2 associating factor 1, which activates the transcription factor PU.1 that alters T(H)2 cell function via negative regulation of GATA3 expression. In summary, this study presents a functional connection between miRNA expression and asthma pathogenesis, and our data suggest that targeting miRNA in the airways may lead to anti-inflammatory treatments for allergic asthma.

Involvement of PU.1 in the transcriptional regulation of TNF-alpha

PU.1 is a myeloid- and lymphoid-specific transcription factor that serves many important roles in the development and specific gene regulation of hematopoietic lineages. Mast cells (MC) and dendritic cells (DC) express PU.1 at low and high levels, respectively. Previously, we found that enforced expression of PU.1 in MC resulted in acquisition of DC-like characteristics, including repression of several IgE-mediated responses due to reduced expression of IgE-signaling related molecules. In contrast, PU.1 overexpression in MC up-regulated TNF-alpha production in response to IgE- and LPS-stimulation suggesting that PU.1 positively regulates TNF-alpha expression. However, the role of PU.1 in the expression of TNF-alpha is largely unknown. In the present study, the effects of PU.1 on the TNF-alpha promoter in mouse bone marrow-derived (BM) MC and DC were studied. Real-time PCR, ELISA, and chromatin immunoprecipitation assays indicated that the kinetics and magnitude of TNF-alpha expression levels following LPS- or IgE-stimulation are related to the amount of PU.1 binding to the promoter. In brief, higher and delayed up-regulation of TNF-alpha promoter function was observed in DC, whereas there were lower and rapid responses in MC. When PU.1-overexpressing retrovirus vector was introduced into MC, the amount of PU.1 recruited to the TNF-alpha promoter markedly increased. The knockdown of PU.1 in BMDC by siRNA resulted in a reduction of TNF-alpha protein produced from LPS-stimulated BMDC. These observations indicate that PU.1 transactivates the TNF-alpha promoter and that the amount of PU.1 binding on the promoter is associated with promoter activity.

Cooperation between PU.1 and CAAT/enhancer-binding protein beta is necessary to induce the expression of the MD-2 gene

Myeloid differentiation factor 2 (MD-2) binds Gram-negative bacterial lipopolysaccharide with high affinity and is essential for Toll-like receptor 4-dependent signal transduction. MD-2 has recently been recognized as a type II acute phase protein. Plasma concentrations of the soluble form of MD-2 increase markedly during the course of severe infections. Its production is regulated in hepatocytes and myeloid cells by interleukin-6 (IL-6) but not IL-1beta. In the present work we show that two transcription factors (TF), PU.1 and CAAT/enhancer-binding protein beta (C/EBPbeta), participate in the activation of the human MD-2 gene in hepatocytic cells after stimulation with IL-6. PU.1 TF and proximal PU.1 binding sites in the MD-2 promoter were shown to be critical for the basal activity of the promoter as well as for IL-6-induced soluble MD-2 production. Deletions of proximal portions of the MD-2 promoter containing PU.1 and/or NF-IL-6 consensus binding sites as well as site-directed mutagenesis of these binding sites abrogated IL-6-dependent MD-2 gene activation. We show that the cooperation between C/EBPbeta and PU.1 is critical for the transcriptional activation of the MD-2 gene by IL-6. PU.1 was essentially known as a TF involved in the differentiation of myeloid precursor cells and the expression of surface receptors of the innate immunity. Herein, we show that it also participates in the regulation of an acute phase protein, MD-2, in nonmyeloid cells cooperatively with C/EBPbeta, a classical IL-6-inducible TF.

Pulmonary surfactant protein A regulates TLR expression and activity in human macrophages

The pulmonary innate immune system responds to various airborne microbes. Although its specificity is broad and based on the recognition of pathogen-associated molecular patterns, it is uniquely regulated to limit inflammation and thereby prevent damage to the gas-exchanging alveoli. Macrophages, critical cell determinants of this system, recognize microbes through pattern recognition receptors such as TLRs, which typically mediate proinflammatory responses. The lung collectin, surfactant protein A (SP-A), has emerged as an important innate immune determinant that regulates microbe-macrophage interactions in this environment. In this study, we report the basal and SP-A-induced transcriptional and posttranslational regulation of TLR2 and TLR4 expression during the differentiation of primary human monocytes into macrophages. Despite SP-A's ability to up-regulate TLR2 expression on human macrophages, it dampens TLR2 and TLR4 signaling in these cells. SP-A decreases the phosphorylation of IkappaBalpha, a key regulator of NF-kappaB activity, and nuclear translocation of p65 which result in diminished TNF-alpha secretion in response to TLR ligands. SP-A also reduces the phosphorylation of TLR signaling proteins upstream of NF-kappaB, including members of the MAPK family. Finally, we report for the first time that SP-A decreases the phosphorylation of Akt, a major cell regulator of NF-kappaB and potentially MAPKs. These data identify a critical role for SP-A in modulating the lung inflammatory response by regulating macrophage TLR activity.