Differential effect on U937 cell differentiation by targeting transcriptional factors implicated in tissue- or stage-specific induced integrin expression

Macrophages derived from human induced pluripotent stem cells (iPSCs) serve as a high-fidelity cellular model for investigating HIV-1, dengue, and influenza viruses

Macrophages are important target cells for diverse viruses and thus represent a valuable system for studying virus biology. Isolation of primary human macrophages is done by culture of dissociated tissues or from differentiated blood monocytes, but these methods are both time consuming and result in low numbers of recovered macrophages. Here, we explore whether macrophages derived from human induced pluripotent stem cells (iPSCs)-which proliferate indefinitely and potentially provide unlimited starting material-could serve as a faithful model system for studying virus biology. Human iPSC-derived monocytes were differentiated into macrophages and then infected with HIV-1, dengue virus, or influenza virus as model human viruses. We show that iPSC-derived macrophages support the replication of these viruses with kinetics and phenotypes similar to human blood monocyte-derived macrophages. These iPSC-derived macrophages were virtually indistinguishable from human blood monocyte-derived macrophages based on surface marker expression (flow cytometry), transcriptomics (RNA sequencing), and chromatin accessibility profiling. iPSC lines were additionally generated from non-human primate (chimpanzee) fibroblasts. When challenged with dengue virus, human and chimpanzee iPSC-derived macrophages show differential susceptibility to infection, thus providing a valuable resource for studying the species-tropism of viruses. We also show that blood- and iPSC-derived macrophages both restrict influenza virus at a late stage of the virus lifecycle. Collectively, our results substantiate iPSC-derived macrophages as an alternative to blood monocyte-derived macrophages for the study of virus biology.

IMPORTANCE

Macrophages have complex relationships with viruses: while macrophages aid in the removal of pathogenic viruses from the body, macrophages are also manipulated by some viruses to serve as vessels for viral replication, dissemination, and long-term persistence. Here, we show that iPSC-derived macrophages are an excellent model that can be exploited in virology.

Structural basis underlying the synergism of NADase and SLO during group A Streptococcus infection

Group A Streptococcus (GAS) is a strict human pathogen possessing a unique pathogenic trait that utilizes the cooperative activity of NAD+-glycohydrolase (NADase) and Streptolysin O (SLO) to enhance its virulence. How NADase interacts with SLO to synergistically promote GAS cytotoxicity and intracellular survival is a long-standing question. Here, the structure and dynamic nature of the NADase/SLO complex are elucidated by X-ray crystallography and small-angle scattering, illustrating atomic details of the complex interface and functionally relevant conformations. Structure-guided studies reveal a salt-bridge interaction between NADase and SLO is important to cytotoxicity and resistance to phagocytic killing during GAS infection. Furthermore, the biological significance of the NADase/SLO complex in GAS virulence is demonstrated in a murine infection model. Overall, this work delivers the structure-functional relationship of the NADase/SLO complex and pinpoints the key interacting residues that are central to the coordinated actions of NADase and SLO in the pathogenesis of GAS infection.

Synovial Fluid in Knee Osteoarthritis Extends Proinflammatory Niche for Macrophage Polarization

Macrophage polarization is a steering factor of osteoarthritis (OA) progression. Synovial fluid (SF) obtained from OA patients with different Kellgren-Lawrence grades (KL grades) holds several proinflammatory factors and was hypothesized to induce macrophage differentiation and polarization by providing the needed microenvironment. U937 cells and peripheral-blood-mononuclear-cell-derived monocytes (PBMC-derived CD14+ cells) were induced with SFs of progressive KL grades for 48 h, and the status of the differentiated cells was evaluated by cell surface markers representing M1 and M2 macrophage phenotypes. Functional viability assessment of the differentiated cells was performed by cytokine estimation. The fraction of macrophages and their phenotypes were estimated by immunophenotyping of SF-isolated cells of different KL grades. A grade-wise proteome analysis of SFs was performed in search of the factors which are influential in macrophage differentiation and polarization. In the assay on U937 cells, induction with SF of KL grade III and IV showed a significant increase in M1 type (CD86+). The percentage of M2 phenotype (CD163+) was significantly higher after the induction with SF of KL grade II. A Significantly higher M1/M2 ratio was estimated in the cells induced with KL grade III and IV. The cell differentiation pattern in the assay on PBMC-derived CD14+ cells showed a grade-wise decline in both M1 (CD11C+, CD86+) and M2 phenotype (CD163+). Cytokine estimation specific to M1 (TNF-α, IL-6, IL-1β, IFN-γ) and M2 (IL-4 and IL-10) macrophages corelated with the differentiation pattern in the U937 cell assay, while it did not reveal any significant changes in the PBMC-derived CD14+ cells assay. SF cells' immunophenotyping showed the highest percentage of CD14+ macrophages in KL grade II; CD86+ and CD163+ cells were minimal in all KL grades' SFs. The proteome analysis revealed significantly expressed MIF, CAPG/MCP, osteopontin, and RAS-related RAB proteins in KL grade III and IV samples, which are linked with macrophages' movement, polarization, and migration-behavior. In conclusion, this study demonstrated that SF in OA joints acts as a niche and facilitates M1 phenotype polarization by providing a proinflammatory microenvironment.

Dermal Fibroblasts Internalize Phosphatidylserine-Exposed Secretory Melanosome Clusters and Apoptotic Melanocytes

Pigmentation in the dermis is known to be caused by melanophages, defined as melanosome-laden macrophages. In this study, we show that dermal fibroblasts also have an ability to uptake melanosomes and apoptotic melanocytes. We have previously demonstrated that normal human melanocytes constantly secrete melanosome clusters from various sites of their dendrites. After adding secreted melanosome clusters collected from the culture medium of melanocytes, time-lapse imaging showed that fibroblasts actively attached to the secreted melanosome clusters and incorporated them. Annexin V staining revealed that phosphatidylserine (PtdSer), which is known as an 'eat-me' signal that triggers the internalization of apoptotic cells by macrophages, is exposed on the surface of secreted melanosome clusters. Dermal fibroblasts were able to uptake secreted melanosome clusters as did macrophages, and those fibroblasts express TIM4, a receptor for PtdSer-mediated endocytosis. Further, co-cultures of fibroblasts and melanocytes demonstrated that dermal fibroblasts internalize PtdSer-exposed apoptotic melanocytes. These results suggest that not only macrophages, but also dermal fibroblasts contribute to the collection of potentially toxic substances in the dermis, such as secreted melanosome clusters and apoptotic melanocytes, that have been occasionally observed to drop down into the dermis from the epidermis.

Effect of scopoletin on phagocytic activity of U937-derived human macrophages: Insights from transcriptomic analysis

Scopoletin is a botanical coumarin. Notably, scopoletin effect on phagocytic activity has not been addressed on transcriptomic level. Accordingly, this study investigated the effect of scopoletin on phagocytosis-linked gene transcription. Whole phagocytosis transcriptional profiling of stimulated U937-derived macrophages (SUDMs) in response to scopoletin as compared to non-treated SUDMs was studied. Regarding scopoletin effect on 92 phagocytosis-linked genes, 12 of them were significantly affected (p-value < .05). Seven genes were downregulated (CDC42, FCGR1A/FCGR1C, ITGA9, ITGB3, PLCE1, RHOD & RND3) and five were upregulated (DIRAS3, ITGA1, PIK3CA, PIK3R3 & PLCD1). Moreover, scopoletin enhanced phagocytic activity of SUDMs. The current results highlighted the potential use of scopoletin as immunity booster and as an adjuvant remedy in management of some autoimmune reactions. To the best of our knowledge, this is the first report that unravels the effect of scopoletin on phagocytosis via transcriptomic analysis.

Induction of tryptophan 2,3-dioxygenase expression in human monocytic leukemia/lymphoma cell lines THP-1 and U937

Tumor-associated macrophages are immune cells with diverse functions in tumor development. Among other functions, they downregulate immune-mediated tumor rejection by depriving lymphocytes of nutrients. The essential amino acid tryptophan is metabolized by the enzymes indoleamine 2,3-dioxygenase 1 and tryptophan 2,3-dioxygenase (TDO). Indoleamine 2,3-dioxygenase 1 is expressed in a large number of human tumors, and inhibitors are in development to improve immunotherapy. Tryptophan 2,3-dioxygenase was also found in human tumors and preclinical working models confirmed its immunosuppressive power. We explored a potential expression of TDO by macrophages. This enzyme could be induced in two human cell lines, THP-1 and U937, by incubation with phorbol myristate acetate, lipopolysaccharide, and interferon gamma. Phorbol-myristate-acetate-mediated induction was inhibited by rottlerin, a protein kinase C inhibitor. In contrast to these monocytic cell lines, other cell lines or fresh human monocytes isolated from peripheral blood mononuclear cells and differentiated into proinflammatory or anti-inflammatory macrophages could not be induced to express TDO. Our results suggest that TDO might play an immunosuppressive role in human monocytic leukemias but not in untransformed macrophages.

The Establishment and Validation of the Human U937 Cell Line as a Cellular Model to Screen Immunomodulatory Agents Regulating Cytokine Release Induced by Influenza Virus Infection

Severe influenza infections are often associated with the excessive induction of pro-inflammatory cytokines, which is also referred to as "cytokine storms". Several studies have shown that cytokine storms are directly associated with influenza-induced fatal acute lung injury and acute respiratory distress syndrome. Due to the narrow administration window, current antiviral therapies are often inadequate. The efforts to use immunomodulatory agents alone or in combination with antiviral agents in the treatment of influenza in animal models have resulted in the achievement of protective effects accompanied with reduced cytokine production. Currently, there are no immunomodulatory drugs for influenza available for clinical use. Animal models, despite being ideal to study the anti-inflammatory responses to influenza virus infection, are very costly and time-consuming. Therefore, there is an urgent need to establish fast and economical screening methods using cell-based models to screen and develop novel immunomodulatory agents. In this study, we screened seven human cell lines and found that the human monocytic cell U937 supports the replication of different subtypes of influenza viruses as well as the production of the important pro-inflammatory cytokines and was selected to develop the cell-based model. The U937 cell model was validated by testing a panel of known antiviral and immunomodulatory agents and screening a drug library consisting of 1280 compounds comprised mostly of FDA-approved drugs. We demonstrated that the U937 cell model is robust and suitable for the high-throughput screening of immunomodulators and antivirals against influenza infection.

Cytotoxicity and Survival Fitness of Invasive covS Mutant of Group A Streptococcus in Phagocytic Cells

Group A streptococci (GAS) with spontaneous mutations in the CovR/CovS regulatory system are more invasive and related to severe manifestations. GAS can replicate inside phagocytic cells; therefore, phagocytic cells could serve as the niche to select invasive covS mutants. Nonetheless, the encapsulated covS mutant is resistant to phagocytosis. The fate of intracellular covS mutant in phagocytic cells and whether the intracellular covS mutant contributes to invasive infections are unclear. In this study, capsule-deficient (cap^-) strains were utilized to study how intracellular bacteria interacted with phagocytic cells. Results from the competitive infection model showed that the cap^-covS mutant had better survival fitness than the cap^- wild-type strain in the PMA-activated U937 cells. In addition, the cap^-covS mutant caused more cell damages than the cap^- wild-type strain and encapsulated covS mutant. Furthermore, treatments with infected cells with clindamycin to inhibit the intracellular bacteria growth was more effective to reduce bacterial toxicity than utilized penicillin to kill the extracellular bacteria. These results not only suggest that the covS mutant could be selected from the intracellular niche of phagocytic cells but also indicating that inactivating or killing intracellular GAS may be critical to prevent invasive infection.

Isolation, Synthesis, and Antisepsis Effects of a C-Methylcoumarinochromone Isolated from Abronia nana Cell Culture

Only a few isoflavones have been isolated from plants of the genus Abronia. The biological properties of compounds isolated from Abronia species have not been well established, and their antisepsis effects have not been reported yet. In the present study, a new C-methylcoumarinochromone, was isolated from Abronia nana suspension cultures. Its structure was deduced as 9,11-dihydroxy-10-methylcoumarinochromone (boeravinone Y, 1) by spectroscopic data analysis and verified by chemical synthesis. The potential inhibitory effects of 1 against high mobility group box 1 (HMGB1)-mediated septic responses were investigated. Results showed that 1 effectively inhibited lipopolysaccharide-induced release of HMGB1 and suppressed HMGB1-mediated septic responses, in terms of reduction of hyperpermeability, leukocyte adhesion and migration, and cell adhesion molecule expression. In addition, 1 increased the phagocytic activity of macrophages and exhibited bacterial clearance effects in the peritoneal fluid and blood of mice with cecal ligation and puncture-induced sepsis. Collectively, these results suggested that 1 might have potential therapeutic activity against various severe vascular inflammatory diseases via inhibition of the HMGB1 signaling pathway.

Comparative genotypic and phenotypic analysis of human peripheral blood monocytes and surrogate monocyte-like cell lines commonly used in metabolic disease research

Monocyte-like cell lines (MCLCs), including THP-1, HL-60 and U-937 cells, are used routinely as surrogates for isolated human peripheral blood mononuclear cells (PBMCs). To systematically evaluate these immortalised cells and PBMCs as model systems to study inflammation relevant to the pathogenesis of type II diabetes and immuno-metabolism, we compared mRNA expression of inflammation-relevant genes, cell surface expression of cluster of differentiation (CD) markers, and chemotactic responses to inflammatory stimuli. Messenger RNA expression analysis suggested most genes were present at similar levels across all undifferentiated cells, though notably, IDO1, which encodes for indoleamine 2,3-dioxygenase and catabolises tryptophan to kynureninase (shown to be elevated in serum from diabetic patients), was not expressed in any PMA-treated MCLC, but present in GM-CSF-treated PBMCs. There was little overall difference in the pattern of expression of CD markers across all cells, though absolute expression levels varied considerably and the correlation between MCLCs and PBMCs was improved upon MCLC differentiation. Functionally, THP-1 and PBMCs migrated in response to chemoattractants in a transwell assay, with varying sensitivity to MCP-1, MIP-1α and LTB-4. However, despite similar gene and CD expression profiles, U-937 cells were functionally impaired as no migration was observed to any chemoattractant. Our analysis reveals that the MCLCs examined only partly replicate the genotypic and phenotypic properties of human PBMCs. To overcome such issues a universal differentiation protocol should be implemented for these cell lines, similar to those already used with isolated monocytes. Although not perfect, in our hands the THP-1 cells represent the closest, simplified surrogate model of PBMCs for study of inflammatory cell migration.

Fish oil emulsion supplementation might improve quality of life of diabetic patients due to its antioxidant and anti-inflammatory properties

Diabetes-related complications, including cardiovascular disease, retinopathy, nephropathy, and neuropathy, are a significant cause of increased morbidity and mortality among people with diabetes. Previous studies have confirmed that hyperglycemia has pro-oxidative and proinflammatory properties which cause diabetic complications. We hypothesized that supplementation of fish oil emulsion (FOE), rich in omega-3 polyunsaturated fatty acids, to diabetic patients might reduce hyperglycemia-induced pathological changes due to specific properties of FOE. Omega-3 polyunsaturated fatty acids have a wide range of biological effects. In this project, we have examined the potential protective effect of the FOE on hyperglycemia-induced oxidative stress and cytokine generation in monocytes/macrophages U937 system in vitro. The monocytes/macrophages U937 were cultivated under normal or hyperglycemic (35 mmol/L glucose) conditions with/without FOE for 72 hours. We have focused on specific markers of oxidative stress (antioxidant capacity; superoxide dismutase activity; oxidative damage to DNA, proteins, and lipids) and inflammation (tumor necrosis factor, interleukin-6, interleukin-8, monocytic chemotactic protein-1). Hyperglycemia caused reduction of antioxidant capacity, induction of DNA damage, and proinflammatory cytokine secretion. FOE significantly increased antioxidant capacity of cells as well as superoxide dismutase activity and significantly reduced tumor necrosis factor, interleukin-6, interleukin-8, and monocytic chemotactic protein-1 release. No effect was observed on oxidative damage to DNA, proteins, and lipids. Our results indicate that FOE can reduce hyperglycemia-induced pathological mechanisms by its antioxidant and anti-inflammatory properties.

Proteomic discovery of MNT as a novel interacting partner of E3 ubiquitin ligase E6AP and a key mediator of myeloid differentiation

Perturbed stability of regulatory proteins is a major cause of transformations leading to cancer, including several leukemia subtypes. Here, for the first time we demonstrate that E6-associated protein (E6AP), an E3 ubiquitin ligase negatively targets MAX binding protein MNT for ubiquitin-mediated proteasome degradation and impedes ATRA mediated myeloid cell differentiation. MNT is a member of the Myc/Max/Mad network of transcription factor that regulates cell proliferation, differentiation, cellular transformation and tumorigenesis. Wild-type E6AP promoted proteasome dependent degradation of MNT, while catalytically inactive E6AP having cysteine replaced with alanine at amino-acid 843 position (E6APC843A) rather stabilized it. Further, these proteins physically associated with each other both in non-myeloid (HEK293T) and myeloid cells. MNT overexpression induced G0-G1 growth arrest and promoted myeloid differentiation while its knockdown mitigated even ATRA induced differentiation suggesting MNT to be crucial for myeloid differentiation. We further showed that ATRA inhibited E6AP and stabilized MNT expression by protecting it from E6AP mediated ubiquitin-proteasome degradation. Notably, E6AP knockdown in HL60 cells restored MNT expression and promoted myeloid differentiation. Taken together, our data demonstrated that E6AP negatively regulates granulocytic differentiation by targeting MNT for degradation which is required for growth arrest and subsequent myeloid differentiation by various differentiation inducing agents.

NRF2 Signaling Negatively Regulates Phorbol-12-Myristate-13-Acetate (PMA)-Induced Differentiation of Human Monocytic U937 Cells into Pro-Inflammatory Macrophages

Blood monocytes are recruited to injured tissue sites and differentiate into macrophages, which protect against pathogens and repair damaged tissues. Reactive oxygen species (ROS) are known to be an important contributor to monocytes’ differentiation and macrophages’ function. NF-E2-related factor 2 (NRF2), a transcription factor regulating cellular redox homeostasis, is known to be a critical modulator of inflammatory responses. We herein investigated the role of NRF2 in macrophage differentiation using the human monocytic U937 cell line and phorbol-12-myristate-13-acetate (PMA). In U937 cells with NRF2 silencing, PMA-stimulated cell adherence was significantly facilitated when compared to control U937 cells. Both transcript and protein levels for pro-inflammatory cytokines, including interleukine-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNFα) were highly elevated in PMA-stimulated NRF2-silenced U937 compared to the control. In addition, PMA-inducible secretion of monocyte chemotactic protein 1 (MCP-1) was significantly high in NRF2-silenced U937. As an underlying mechanism, we showed that NRF2-knockdown U937 retained high levels of cellular ROS and endoplasmic reticulum (ER) stress markers expression; and subsequently, PMA-stimulated levels of Ca²⁺ and PKCα were greater in NRF2-knockdown U937 cells, which caused enhanced nuclear accumulation of nuclear factor-ҡB (NFҡB) p50 and extracellular signal-regulated kinase (ERK)-1/2 phosphorylation. Whereas the treatment of NRF2-silenced U937 cells with pharmacological inhibitors of NFҡB or ERK1/2 largely blocked PMA-induced IL-1β and IL-6 expression, indicating that these pathways are associated with cell differentiation. Taken together, our results suggest that the NRF2 system functions to suppress PMA-stimulated U937 cell differentiation into pro-inflammatory macrophages and provide evidence that the ROS-PKCα-ERK-NFҡB axis is involved in PMA-facilitated differentiation of NRF2-silenced U937 cells.

Effects of CoCr metal wear debris generated from metal-on-metal hip implants and Co ions on human monocyte-like U937 cells

Hip resurfacing with cobalt-chromium (CoCr) alloy was developed as a surgical alternative to total hip replacement. However, the biological effects of nanoparticles generated by wear at the metal-on-metal articulating surfaces has limited the success of such implants. The aim of this study was to investigate the effects of the combined exposure to CoCr nanoparticles and cobalt ions released from a resurfacing implant on monocytes (U937 cells) and whether these resulted in morphology changes, proliferation alterations, toxicity and cytokine release. The interaction between prior exposure to Co ions and the cellular response to nanoparticulate debris was determined to simulate the situation in patients with metal-on-metal implants receiving a second implant. Effects on U937 cells were mainly seen after 120h of treatment. Prior exposure to Co ions increased the toxic effects induced by the debris, and by Co ions themselves, suggesting the potential for interaction in vivo. Increased TNF-α secretion by resting cells exposed to nanoparticles could contribute to osteolysis processes in vivo, while increased IFN-γ production by activated cells could represent cellular protection against tissue damage. Data suggest that interactions between Co ions and CoCr nanoparticles would occur in vivo, and could threaten the survival of a CoCr metal implant.

Effect of walnut oil on hyperglycemia-induced oxidative stress and pro-inflammatory cytokines production

PURPOSE

In this study, we focused on the effect of hyperglycemia on the generation of reactive oxygen species and on the release of pro-inflammatory cytokines in the human monocytic cell line (U937). We also monitored potential anti-inflammatory effects of walnut oil as well as its protective effect against oxidative damage to biopolymers (DNA and proteins).

METHODS

We cultured U937 cells under normoglycemic or hyperglycemic conditions for 72 h, in the absence or presence of walnut oil. We detected cell proliferation by the MTT test. To determine the antioxidant status of cells, we used the trolox equivalent antioxidant capacity method. We determined the activity of superoxide dismutase (SOD) spectrophotometrically, the oxidative damage to DNA by an enzyme-modified comet assay, and the oxidative damage to proteins by the marker-protein carbonyls and the levels of pro-inflammatory cytokines by the ELISA method.

RESULTS

Hyperglycemia reduced the antioxidant capacity of cells, induced oxidative damage to DNA, and increased the release of pro-inflammatory cytokines. It had no effect on cell proliferation, SOD activity, nor oxidative damage to proteins. Walnut oil significantly increased the antioxidant capacity of cells as well as SOD activity on the second and third day of incubation, but had no effect on cell proliferation and showed no protective effect against oxidative damage to DNA and proteins. The walnut oil showed both anti-inflammatory and pro-inflammatory properties depending on its concentration and time of its incubation with the monocytic cell line.

CONCLUSION

Our in vitro results indicate that walnut oil can diminish oxidative stress with its antioxidant properties. However, we could not confirm its protective effect against oxidative damage to DNA and proteins.

Reciprocal bystander effect between α-irradiated macrophage and hepatocyte is mediated by cAMP through a membrane signaling pathway

Irradiated cells can induce biological effects on vicinal non-irradiated bystander cells, meanwhile the bystander cells may rescue the irradiated cells through a feedback signal stress. To elucidate the nature of this reciprocal effect, we examined the interaction between α-irradiated human macrophage cells U937 and its bystander HL-7702 hepatocyte cells using a cell co-culture system. Results showed that after 6h of cell co-culture, mitochondria depolarization corresponding to apoptosis was significantly induced in the HL-7702 cells, but the formation of micronuclei in the irradiated U937 cells was markedly decreased compared to that without cell co-culture treatment. This reciprocal effect was not observed when the cell membrane signaling pathway was blocked by filipin that inhibited cAMP transmission from bystander cells to irradiated cells. After treatment of cells with exogenous cAMP, forskolin (an activator of cAMP) or KH-7 (an inhibitor of cAMP), respectively, it was confirmed that cAMP communication from bystander cells to targeted cells could mitigate radiation damage in U739 cells, and this cAMP insufficiency in the bystander cells contributed to the enhancement of bystander apoptosis. Moreover, the bystander apoptosis in HL-7702 cells was aggravated by cAMP inhibition but it could not be evoked when p53 of HL-7702 cells was knocked down no matter of forskolin and KH-7 treatment. In conclusion, this study disclosed that cAMP could be released from bystander HL-7702 cells and compensated to α-irradiated U937 cells through a membrane signaling pathway and this cAMP communication played a profound role in regulating the reciprocal bystander effects.

Bacillus cereus enterotoxins act as major virulence factors and exhibit distinct cytotoxicity to different human cell lines

A comparative analysis on the relevance of the Bacillus cereus enterotoxins Nhe (nonhemolytic enterotoxin), HBL (haemolysin BL) and CytK (cytotoxin K) was accomplished, concerning their toxic activity towards different target cell lines. Overall, among the components secreted by the reference strains for Nhe and HBL, the enterotoxin complexes accounted for over 90% of the total toxicity. Vero and primary endothelial cells (HUVEC) were highly susceptible to Nhe, whereas Hep-G2, Vero and A549 reacted most sensitive to Nhe plus HBL. For CytK the highest toxicity was observed on CaCo-2 cells. As HBL positive strains always produce Nhe in parallel, the specific contribution of both enterotoxin complexes to the overall observed cytotoxic effects was determined by consecutively removing their single components. While in most cell lines Nhe and HBL contributed more or less equally (40-60%) to cytotoxicity, the relative activity of Nhe was approximately 90% in HUVEC, and that of HBL 75% in A549 cells. With U937, a nearly Nhe resistant cell line was identified for the first time. This distinct susceptibility of cell lines was confirmed by investigating a set of 37 B. cereus strains. Interestingly, whereas Nhe is the enterotoxin mainly responsible for cell death as determined by WST-1 bioassays, more rapid pore formation was observed when HBL was present, pointing to a different mode of action of the two enterotoxin complexes. Furthermore, correlation was observed between cytotoxicity of solely Nhe producing strains and NheB. Cytotoxicity of Nhe/HBL producing isolates correlated with the expression of HBL L1, NheB and HBL B. In conclusion, the observed susceptibilities of target cell lines of different histological origin underline that B. cereus enterotoxins represent major virulence factors and that toxicity is not restricted to gastrointestinal infections. The varying contribution of Nhe and HBL to total cytotoxicity strongly indicates that Nhe as well as HBL specific B. cereus enterotoxin receptors exist.

Rooperol as an antioxidant and its role in the innate immune system: an in vitro study

ETHNOPHARMACOLOGICAL RELEVANCE

Biologically active rooperol is formed when the glucose subunits of the nontoxic glycoside, hypoxoside, are cleaved by β-glucosidase. Hypoxoside is isolated from Hypoxis, a medicinal plant genus frequently used by the indigenous people of South Africa as an immune system booster. The aim of this study was to investigate rooperol's antioxidant and anti-inflammatory properties using the ferric reducing ability of plasma (FRAP) assay, NO and ROS production, and phagocytosis.

MATERIALS AND METHODS

Differentiation of human promonocytic U937 leukemia cells to monocyte-macrophages was induced using 10-100 nM 1,25(OH)(2)D(3) and PMA over 72 h. Differentiation was confirmed by light microscopy and flow cytometry. Undifferentiated and/or differentiated cells were treated with DMSO (0.25 v/v%, vehicle control), hypoxoside (50 μg/mL), rooperol (20 μg/mL) or PMA (10/20 nM, positive control). ROS production was measured in undifferentiated and differentiated monocyte-macrophages using DCFH-DA and flow cytometry. Phagocytosis of pHrodo™ Escherichia coli BioParticles(®) was measured using pre-treated monocyte-macrophage differentiated U937 cells. NO production was measured in monocyte-macrophage differentiated U937 cells using DAF-2 DA and flow cytometry.

RESULTS

Rooperol was shown to have similar or greater antioxidant potential than ascorbic acid. Differentiation of human promonocytic U937 leukemia cells to monocyte-macrophages were confirmed morphologically (cell attachment, clump- and pseudopodia-formation) and biochemically (CD11b and CD14 cell surface marker expression). Rooperol significantly increased ROS and NO production, and phagocytosis in undifferentiated and/or differentiated human promonocytic U937 leukemia cells. Hypoxoside had no or very little effect on ROS and NO production, and phagocytosis.

CONCLUSION

This study confirms previous reports that hypoxoside has to be converted to rooperol to be biologically active. The FRAP assay confirms the antioxidant capacity of rooperol seen in previous studies, whereas rooperol's induction of ROS and NO production, and phagocytosis constitute novel findings. Possible mode(s) of action for the in vitro anti-inflammatory activities of rooperol may be explained by ROS and NO production, and phagocytosis.

A new pharmacological agent (AKB-4924) stabilizes hypoxia inducible factor-1 (HIF-1) and increases skin innate defenses against bacterial infection

Hypoxia inducible factor-1 (HIF-1) is a transcription factor that is a major regulator of energy homeostasis and cellular adaptation to low oxygen stress. HIF-1 is also activated in response to bacterial pathogens and supports the innate immune response of both phagocytes and keratinocytes. In this work, we show that a new pharmacological compound AKB-4924 increases HIF-1 levels and enhances the antibacterial activity of phagocytes and keratinocytes against both methicillin-sensitive and methicillin-resistant strains of Staphylococcus aureus in vitro. AKB-4924 is also effective in stimulating the killing capacity of keratinocytes against the important opportunistic skin pathogens Pseudomonas aeruginosa and Acinetobacter baumanii. The effect of AKB-4924 is mediated through the activity of host cells, as the compound exerts no direct antimicrobial activity. Administered locally as a single agent, AKB-4924 limits S. aureus proliferation and lesion formation in a mouse skin abscess model. This approach to pharmacologically boost the innate immune response via HIF-1 stabilization may serve as a useful adjunctive treatment for antibiotic-resistant bacterial infections.

The homeobox transcription factor VentX controls human macrophage terminal differentiation and proinflammatory activation

Macrophages are critical players in both innate and adaptive immunity. While the exogenous signaling events leading to the terminal differentiation of macrophages from monocytes have been studied extensively, the underlying intracellular transcriptional mechanisms remain poorly understood. Here we report that the homeobox transcription factor VentX plays a pivotal role in human macrophage terminal differentiation and proinflammatory function. Our study showed that VentX expression was upregulated upon human primary monocyte-to-macrophage differentiation induced by cytokines such as M-CSF, GM-CSF, and IL-3. Moreover, ablation of VentX expression in primary monocytes profoundly impaired their differentiation to macrophages, and ectopic expression of VentX in a myeloid progenitor cell line triggered its differentiation with prominent macrophage features. Further analysis revealed that VentX was pivotal for the proinflammatory response of terminally differentiated macrophages. Mechanistically, VentX was found to control expression of proteins key to macrophage differentiation and activation, including M-CSF receptor. Importantly, preliminary analysis of gene expression in leukocytes from patients with autoimmune diseases revealed a strong correlation between levels of VentX and those of proinflammatory cytokines. Our results provide mechanistic insight into the crucial roles of VentX in macrophage differentiation and proinflammatory activation and suggest that dysregulation of VentX may play a role in the pathogenesis of autoimmune diseases.

Alterations in cellular proteome and secretome upon differentiation from monocyte to macrophage by treatment with phorbol myristate acetate: insights into biological processes

Monocyte and macrophage are mainly involved in immune response and inflammatory processes. Monocytes circulate in the bloodstream and migrate to various tissues where they can differentiate to macrophages. However, the molecular basis of biological processes involved in this cellular differentiation remains ambiguous. This study was to investigate alterations in cellular and secreted proteins after this differentiation phase. Macrophage was differentiated from U937 human monocytic cell line by treatment with 100 ng/ml phorbol myristate acetate (PMA) for 48 h. Cellular and secreted proteins extracted from PMA-treated cells (macrophages) were compared with those of untreated cells (monocytes) using 2-DE (n=5 gels/condition; stained with Deep Purple fluorescence dye). Quantitative intensity analysis revealed 81 and 67 protein spots whose levels were significantly altered in cellular proteome and secretome. These proteins were subsequently identified by Q-TOF MS and/or MS/MS analyses. The altered levels of cellular elongation factor-2 (EF-2) and secreted alpha-tubulin were confirmed by Western blot analysis. Global protein network analysis demonstrated that these altered proteins were involved in cell death, lipid metabolism, cell morphology, cellular movement, and protein folding. Our data may provide some insights into molecular mechanisms of biological processes upon differentiation from monocytes to macrophages.

Galphas-coupled receptor signaling actively down-regulates alpha4beta1-integrin affinity: a possible mechanism for cell de-adhesion

BACKGROUND

Activation of integrins in response to inside-out signaling serves as a basis for leukocyte arrest on endothelium, and migration of immune cells. Integrin-dependent adhesion is controlled by the conformational state of the molecule (i.e. change in the affinity for the ligand and molecular unbending (extension)), which is regulated by seven-transmembrane Guanine nucleotide binding Protein-Coupled Receptors (GPCRs). alpha4beta1-integrin (CD49d/CD29, Very Late Antigen-4, VLA-4) is expressed on leukocytes, hematopoietic stem cells, hematopoietic cancer cells, and others. Affinity and extension of VLA-4 are both rapidly up-regulated by inside-out signaling through several Galphai-coupled GPCRs. The goal of the current report was to study the effect of Galphas-coupled GPCRs upon integrin activation.

RESULTS

Using real-time fluorescent ligand binding to assess affinity and a FRET based assay to probe alpha4beta1-integrin unbending, we show that two Galphas-coupled GPCRs (H2-histamine receptor and beta2-adrenergic receptor) as well as several cAMP agonists can rapidly down modulate the affinity of VLA-4 activated through two Galphai-coupled receptors (CXCR4 and FPR) in U937 cells and primary human peripheral blood monocytes. This down-modulation can be blocked by receptor-specific antagonists. The Galphas-induced responses were not associated with changes in the expression level of the Galphai-coupled receptors. In contrast, the molecular unbending of VLA-4 was not significantly affected by Galphas-coupled GPCR signaling. In a VLA-4/VCAM-1-specific myeloid cell adhesion system, inhibition of the VLA-4 affinity change by Galphas-coupled GPCR had a statistically significant effect upon cell aggregation.

CONCLUSION

We conclude that Galphas-coupled GPCRs can rapidly down modulate the affinity state of VLA-4 binding pocket through a cAMP dependent pathway. This plays an essential role in the regulation of cell adhesion. We discuss several possible implications of this described phenomenon.

Regulation of progranulin expression in myeloid cells

Progranulin (pgrn; granulin-epithelin precursor, PC-cell-derived growth factor, or acrogranin) is a multifunctional secreted glycoprotein implicated in tumorigenesis, development, inflammation, and repair. It is highly expressed in macrophage and monocyte-derived dendritic cells. Here we investigate its regulation in myeloid cells. All-trans retinoic acid (ATRA) increased pgrn mRNA levels in myelomonocytic cells (CD34(+) progenitors; monoblastic U-937; monocytic THP-1; progranulocytic HL-60; macrophage RAW 264.7) but not in nonmyeloid cells tested. Interleukin-4 impaired basal expression of pgrn in U-937. Differentiation agents DMSO, and, in U-937 only, phorbol ester [phorbol 12-myristate,13-acetate (PMA)] elevated pgrn mRNA expression late in differentiation, suggestive of roles for pgrn in more mature terminally differentiated granulocyte/monocytes rather than during growth or differentiation. The response of pgrn mRNA to ATRA differs in U-937 and HL-60 lineages. In U-937, ATRA and chemical differentiation agents greatly increased pgrn mRNA stability, whereas, in HL-60, ATRA accelerated pgrn mRNA turnover. The initial upregulation of pgrn mRNA after stimulation with ATRA was independent of de novo protein synthesis in U-937 but not HL-60. Chemical blockade of nuclear factor-kappaB (NF-kappaB) activation impaired ATRA-stimulated pgrn expression in HL-60 but not U-937, whereas in U-937 it blocked PMA-induced pgrn mRNA expression, suggestive of cell-specific roles for NF-kappaB in determining pgrn mRNA levels. We propose that: 1) ATRA regulates pgrn mRNA levels in myelomonocytic cells; 2) ATRA acts in a cell-specific manner involving the differential control of mRNA stability and differential requirement for NF-kappaB signaling; and 3) elevated pgrn mRNA expression is characteristic of more mature cells and does not stimulate differentiation.

SET-induced calcium signaling and MAPK/ERK pathway activation mediate dendritic cell-like differentiation of U937 cells

Human SET, a target of chromosomal translocation in human leukemia encodes a highly conserved, ubiquitously expressed, nuclear phosphoprotein. SET mediates many functions including chromatin remodeling, transcription, apoptosis and cell cycle control. We report that overexpression of SET directs differentiation of the human promonocytic cell line U937 along the dendritic cell (DC) pathway, as cells display typical morphologic changes associated with DC fate and express the DC surface markers CD11b and CD86. Differentiation occurs via a calcium-dependent mechanism involving the CaMKII and MAPK/ERK pathways. Similar responses are elicited by interferon-gamma (IFN-gamma) treatment with the distinction that IFN-gamma signaling activates the DNA-binding activity of STAT1 whereas SET overexpression does not. In addition, unlike IFN-gamma signaling, SET generated stress-induced p38/MAPK activity. Interestingly, IFN-gamma treatment transiently upregulated endogenous SET in a dose-dependent manner. These results suggest that SET is part of both IFN-gamma-mediated and stress-mediated cellular responses and that SET induces cell differentiation via calcium and MAPK/ERK pathways.

Conditional gene targeting for cancer gene therapy

Current treatment of solid tumors is limited by severe adverse effects, resulting in a narrow therapeutic index. Therefore, cancer gene therapy has emerged as a targeted approach that would significantly reduce undesired side effects in normal tissues. This approach requires a clear understanding of the molecular biology of both the malignant clone and the biological vectors that serve as vehicles to target cancer cells. In this review we discuss novel approaches for conditional gene expression in cancer cells. Targeting transgene expression to malignant tissues requires the use of specific regulatory elements including promoters based on tumor biology, tissue-specific promoters and inducible regulatory elements. We also discuss the regulation of both replication and transgene expression by conditionally-replicative viruses. These approaches have the potential to restrict the expression of transgenes exclusively to tissues of interest and thereby to increase the therapeutic index of future vectors for cancer gene therapy.

Costimulatory molecule expression following exposure to orthopaedic implants wear debris

Patients with long-term orthopedic implants may develop inflammatory reactions due to the accumulation of biomaterial particles both around the implant and in distant organs. The exact impact of these particles on the normal immune cell function still remain relatively unclear. Activation of T-cells following exposure to biomaterial particles is driven by macrophages and requires synergistic signals primed by both antigen presentation and costimulation. The pattern of costimulatory molecule expression (CD80,CD86) was primarily examined using immunohistochemistry on tissue specimens of bone/implant interface membranes taken from sites of bone erosion. Additionally, costimulatory molecule expression was also assessed in the monocytic leukemia cell line U937 following exposure to clinically relevant titanium aluminum vanadium (TiAlV) and stainless steel particles (FeCrNi) cultured in vitro. This study demonstrates the induction and prominent expression of CD86 on almost all macrophage subsets at the bone/implant interface, including fused forms and large multinucleated giant cells (MNGC). In vitro analysis also indicated phagocytosis of metal particles by differentiated U937 caused significant induction of both CD80 and CD86 (p < 0.01), although the expression of CD86 dominated following prolonged exposure. The data presented highlights that CD86 is the predominant costimulatory molecule ligating to the complementary CD28 molecule at the inflammatory lesion of the interface. We propose that the intracellular presence of indigestible implant material, in addition to elevated costimulatory molecule expression, may promote T-cell inflammatory reactions at sites close to and distant from the orthopedic implant.

Desferrioxamine, an iron chelator, upregulates cyclooxygenase-2 expression and prostaglandin production in a human macrophage cell line

Prostaglandins (PGs) play regulatory roles in a variety of physiological and pathological processes, including the immune response, cytoprotection and inflammation. Desferrioxamine (DFX), an iron chelator, is known to reduce free radical-mediated cell injury and to upregulate certain inflammatory mediators. We investigated the effects of DFX on the production of PGs and the expression of cyclooxygenase-2 (COX-2), the rate-limiting enzyme in the synthesis of PGs, using a human macrophage cell line, U937. Our results showed that COX-2 expression and PGE(2) production are upregulated by DFX treatment and that this upregulation is dependent on both COX-2 promoter activity and alteration of mRNA stability. COX-2 promoter activity may be, at least in part, mediated by activation of the extracellular signal-regulated kinase pathway. These findings suggest that iron metabolism may regulate inflammatory processes by modulating PGs as well as other inflammatory mediators.

deltaFosB: a molecular switch underlying long-term neural plasticity

Numerous chronic perturbations have been shown to induce highly stable isoforms of the transcription factor deltaFosB in the brain in a region-specific manner. This review examines the functional consequences of the induction of deltaFosB in particular neuronal populations as well as its possible role in behavioral abnormalities such as drug addiction and movement disorders.

BLIMP-1: trigger for differentiation of myeloid lineage

B lymphocyte-induced maturation protein-1 (BLIMP-1 or PRDI-BF1) is induced when bone marrow-derived progenitors differentiate in response to macrophage-colony stimulating factor (M-CSF) and is present in peripheral blood monocytes and granulocytes. BLIMP-1 is also induced during differentiation of U937 and HL-60 cells into macrophages or granulocytes. Induction of BLIMP-1 mRNA during macrophage differentiation of U937 and HL-60 shows a biphasic pattern. Overexpression of BLIMP-1 is sufficient to initiate macrophage differentiation of U937 cells whereas blocking endogenous BLIMP-1 inhibits differentiation. One target of BLIMP-1-dependent transcriptional repression in U937 cells is c-myc, providing an explanation for cessation of cell division. Thus BLIMP-1 is a key regulator of terminal differentiation in two separate hematopoietic lineages: myeloid cells and B lymphocytes.