Role of MAPK p38 in the cellular responses to pore-forming toxins

The intricate triangular interaction between protective microbe, pathogen and host determines fitness of the metaorganism

The microbiota shapes host biology in numerous ways. One example is protection against pathogens, which is likely critical for host fitness in consideration of the ubiquity of pathogens. The host itself can affect abundance of microbiota or pathogens, which has usually been characterized in separate studies. To date, however, it is unclear how the host influences the interaction with both simultaneously and how this triangular interaction determines fitness of the host-microbe assemblage, the so-called metaorganism. To address this current knowledge gap, we focused on a triangular model interaction, consisting of the nematode Caenorhabditis elegans, its protective symbiont Pseudomonas lurida MYb11 and its pathogen Bacillus thuringiensis Bt679. We combined the two microbes with C. elegans mutants with altered immunity and/or microbial colonization, and found that (i) under pathogen stress, immunocompetence has a larger influence on metaorganism fitness than colonization with the protective microbe; (ii) in almost all cases, MYb11 still improves fitness; and (iii) disruption of p38 MAPK signalling, which contributes centrally to immunity against Bt679, completely reverses the protective effect of MYb11, which further reduces nematode survival and fitness upon infection with Bt679. Our study highlights the complex interplay between host, protective microbe and pathogen in shaping metaorganism biology.

Transcriptional Activation of a Pro-Inflammatory Response (NF-κB, AP-1, IL-1β) by the Vibrio cholerae Cytotoxin (VCC) Monomer through the MAPK Signaling Pathway in the THP-1 Human Macrophage Cell Line

This study describes, to some extent, the VCC contribution as an early stimulation of the macrophage lineage. Regarding the onset of the innate immune response caused by infection, the β form of IL-1 is the most important interleukin involved in the onset of the inflammatory innate response. Activated macrophages treated in vitro with VCC induced the activation of the MAPK signaling pathway in a one-hour period, with the activation of transcriptional regulators for a surviving and pro-inflammatory response, suggesting an explanation inspired and supported by the inflammasome physiology. The mechanism of IL-1β production induced by VCC has been gracefully outlined in murine models, using bacterial knockdown mutants and purified molecules; nevertheless, the knowledge of this mechanism in the human immune system is still under study. This work shows the soluble form of 65 kDa of the Vibrio cholerae cytotoxin (also known as hemolysin), as it is secreted by the bacteria, inducing the production of IL-1β in the human macrophage cell line THP-1. The mechanism involves triggering the early activation of the signaling pathway MAPKs pERK and p38, with the subsequent activation of (p50) NF-κB and AP-1 (cJun and cFos), determined by real-time quantitation. The evidence shown here supports that the monomeric soluble form of the VCC in the macrophage acts as a modulator of the innate immune response, which is consistent with the assembly of the NLRP3 inflammasome actively releasing IL-1β.

The Yin and Yang of Pneumolysin During Pneumococcal Infection

Pneumolysin (PLY) is a pore-forming toxin produced by the human pathobiont Streptococcus pneumoniae, the major cause of pneumonia worldwide. PLY, a key pneumococcal virulence factor, can form transmembrane pores in host cells, disrupting plasma membrane integrity and deregulating cellular homeostasis. At lytic concentrations, PLY causes cell death. At sub-lytic concentrations, PLY triggers host cell survival pathways that cooperate to reseal the damaged plasma membrane and restore cell homeostasis. While PLY is generally considered a pivotal factor promoting S. pneumoniae colonization and survival, it is also a powerful trigger of the innate and adaptive host immune response against bacterial infection. The dichotomy of PLY as both a key bacterial virulence factor and a trigger for host immune modulation allows the toxin to display both "Yin" and "Yang" properties during infection, promoting disease by membrane perforation and activating inflammatory pathways, while also mitigating damage by triggering host cell repair and initiating anti-inflammatory responses. Due to its cytolytic activity and diverse immunomodulatory properties, PLY is integral to every stage of S. pneumoniae pathogenesis and may tip the balance towards either the pathogen or the host depending on the context of infection.

The regulation landscape of MAPK signaling cascade for thwarting Bacillus thuringiensis infection in an insect host

Host-pathogen interactions are central components of ecological networks where the MAPK signaling pathways act as central hubs of these complex interactions. We have previously shown that an insect hormone modulated MAPK signaling cascade participates as a general switch to trans-regulate differential expression of diverse midgut genes in the diamondback moth, Plutella xylostella (L.) to cope with the insecticidal action of Cry1Ac toxin, produced by the entomopathogenic bacterium Bacillus thuringiensis (Bt). The relationship between topology and functions of this four-tiered phosphorylation signaling cascade, however, is an uncharted territory. Here, we carried out a genome-wide characterization of all the MAPK orthologs in P. xylostella to define their phylogenetic relationships and to confirm their evolutionary conserved modules. Results from quantitative phosphoproteomic analyses, combined with functional validations studies using specific inhibitors and dsRNAs lead us to establish a MAPK "road map", where p38 and ERK MAPK signaling pathways, in large part, mount a resistance response against Bt toxins through regulating the differential expression of multiple Cry toxin receptors and their non-receptor paralogs in P. xylostella midgut. These data not only advance our understanding of host-pathogen interactions in agricultural pests, but also inform the future development of biopesticides that could suppress Cry resistance phenotypes.

Beyond pore formation: reorganization of the plasma membrane induced by pore-forming proteins

Pore-forming proteins (PFPs) are a heterogeneous group of proteins that are expressed and secreted by a wide range of organisms. PFPs are produced as soluble monomers that bind to a receptor molecule in the host cell membrane. They then assemble into oligomers that are incorporated into the lipid membrane to form transmembrane pores. Such pore formation alters the permeability of the plasma membrane and is one of the most common mechanisms used by PFPs to destroy target cells. Interestingly, PFPs can also indirectly manipulate diverse cellular functions. In recent years, increasing evidence indicates that the interaction of PFPs with lipid membranes is not only limited to pore-induced membrane permeabilization but is also strongly associated with extensive plasma membrane reorganization. This includes lateral rearrangement and deformation of the lipid membrane, which can lead to the disruption of target cell function and finally death. Conversely, these modifications also constitute an essential component of the membrane repair system that protects cells from the lethal consequences of pore formation. Here, we provide an overview of the current knowledge on the changes in lipid membrane organization caused by PFPs from different organisms.

Bacterial RTX toxins and host immunity

PURPOSE OF REVIEW

RTX toxin action often defines the outcome of bacterial infections. Here, we discuss the progress in understanding the impacts of RTX toxin activities on host immunity.

RECENT FINDINGS

Bordetella pertussis CyaA activity paralyzes sentinel phagocytic cells by elevating cellular cAMP levels and blocks differentiation of infiltrating monocytes into bactericidal macrophages, promoting also de-differentiation of resident alveolar macrophages into monocyte-like cells. Vibrio cholerae multifunctional autoprocessing repeats-in-toxins (MARTX), through Rho inactivating and α/β-hydrolase (ABH) domain action blocks mitogen-activated protein kinase signaling in epithelial cells and dampens the inflammatory responses of intestinal epithelia by blocking immune cell recruitment. The action of actin crosslinking effector domain and Ras/Rap1-specific endopeptidase (RRSP) domains of MARTX compromises the phagocytic ability of macrophages. Aggregatibacter actinomycetemcomitans LtxA action triggers neutrophil elastase release into periodontal tissue, compromising the epithelial barrier and promoting bacterial spreads into deeper tissue.

SUMMARY

Action of RTX toxins enables bacterial pathogens to cope with the fierce host immune defenses. RTX toxins often block phagocytosis and bactericidal reactive oxygen species and NO production. Some RTX toxins can reprogram the macrophages to less bactericidal cell types. Autophagy is hijacked for example by the activity of the V. cholerae ABH effector domain of the MARTX protein. Subversion of immune functions by RTX toxins thus promotes bacterial survival and proliferation in the host.

Panorama of the Intracellular Molecular Concert Orchestrated by Actinoporins, Pore-Forming Toxins from Sea Anemones

Actinoporins (APs) are soluble pore-forming proteins secreted by sea anemones that experience conformational changes originating in pores in the membranes that can lead to cell death. The processes involved in the binding and pore-formation of members of this protein family have been deeply examined in recent years; however, the intracellular responses to APs are only beginning to be understood. Unlike pore formers of bacterial origin, whose intracellular impact has been studied in more detail, currently, we only have knowledge of a few poorly integrated elements of the APs’ intracellular action. In this review, we present and discuss an updated landscape of the studies aimed at understanding the intracellular pathways triggered in response to APs attack with particular reference to sticholysin II, the most active isoform produced by the Caribbean Sea anemone Stichodactyla helianthus. To achieve this, we first describe the major alterations these cytolysins elicit on simpler cells, such as non-nucleated mammalian erythrocytes, and then onto more complex eukaryotic cells, including tumor cells. This understanding has provided the basis for the development of novel applications of sticholysins such as the construction of immunotoxins directed against undesirable cells, such as tumor cells, and the design of a cancer vaccine platform. These are among the most interesting potential uses for the members of this toxin family that have been carried out in our laboratory.

Take a Walk to the Wild Side of Caenorhabditis elegans-Pathogen Interactions

Microbiomes form intimate functional associations with their hosts. Much has been learned from correlating changes in microbiome composition to host organismal functions. However, in-depth functional studies require the manipulation of microbiome composition coupled with the precise interrogation of organismal physiology-features available in few host study systems. Caenorhabditis elegans has proven to be an excellent genetic model organism to study innate immunity and, more recently, microbiome interactions. The study of C. elegans-pathogen interactions has provided in depth understanding of innate immune pathways, many of which are conserved in other animals. However, many bacteria were chosen for these studies because of their convenience in the lab setting or their implication in human health rather than their native interactions with C. elegans In their natural environment, C. elegans feed on a variety of bacteria found in rotting organic matter, such as rotting fruits, flowers, and stems. Recent work has begun to characterize the native microbiome and has identified a common set of bacteria found in the microbiome of C. elegans While some of these bacteria are beneficial to C. elegans health, others are detrimental, leading to a complex, multifaceted understanding of bacterium-nematode interactions. Current research on nematode-bacterium interactions is focused on these native microbiome components, both their interactions with each other and with C. elegans We will summarize our knowledge of bacterial pathogen-host interactions in C. elegans, as well as recent work on the native microbiome, and explore the incorporation of these bacterium-nematode interactions into studies of innate immunity and pathogenesis.

Pore-forming toxins of foodborne pathogens

Pore-forming toxins (PFTs) are water-soluble molecules that have been identified as the most crucial virulence factors during bacterial pathogenesis. PFTs disrupt the host cell membrane to internalize or to deliver other bacterial or virulence factors for establishing infections. Disruption of the host cell membrane by PFTs can lead to uncontrollable exchanges between the extracellular and the intracellular matrix, thereby disturbing the cellular homeostasis. Recent studies have provided insights into the molecular mechanism of PFTs during pathogenesis. Evidence also suggests the activation of several signal transduction pathways in the host cell on recognition of PFTs. Additionally, numerous distinctive host defense mechanisms as well as membrane repair mechanisms have been reported; however, studies reveal that PFTs aid in host immune evasion of the bacteria through numerous pathways. PFTs have been primarily associated with foodborne pathogens. Infection and death from diseases by consuming contaminated food are a constant threat to public health worldwide, affecting socioeconomic development. Moreover, the emergence of new foodborne pathogens has led to the rise of bacterial antimicrobial resistance affecting the population. Hence, this review focuses on the role of PFTs secreted by foodborne pathogens. The review highlights the molecular mechanism of foodborne bacterial PFTs, assisting bacterial survival from the host immune responses and understanding the downstream mechanism in the activation of various signaling pathways in the host upon PFT recognition. PFT research is a remarkable and an important field for exploring novel and broad applications of antimicrobial compounds as therapeutics.

Low-Intensity Sonoporation-Induced Intracellular Signalling of Pancreatic Cancer Cells, Fibroblasts and Endothelial Cells

The use of ultrasound (US) and microbubbles (MB), usually referred to as sonoporation, has great potential to increase the efficacy of chemotherapy. However, the molecular mechanisms that mediate sonoporation response are not well-known, and recent research suggests that cell stress induced by US + MBs may contribute to the treatment benefit. Furthermore, there is a growing understanding that the effects of US + MBs are beyond only the cancer cells and involves the tumour vasculature and microenvironment. We treated pancreatic cancer cells (MIA PaCa-2) and stromal cells, fibroblasts (BJ) and human umbilical vein endothelial cells (HUVECs), with US ± MB, and investigated the extent of uptake of cell impermeable dye (calcein, by flow cytometry), viability (cell count, Annexin/PI and WST-1 assays) and activation of a number of key proteins in important intracellular signalling pathways immediately and 2 h after sonoporation (phospho flow cytometry). Different cell types responded differently to US ± MBs in all these aspects. In general, sonoporation induces immediate, transient activation of MAP-kinases (p38, ERK1/2), and an increase in phosphorylation of ribosomal protein S6 together with dephosphorylation of 4E-BP1. The sonoporation stress-response resembles cellular responses to electroporation and pore-forming toxins in membrane repair and restoring cellular homeostasis, and may be exploited therapeutically. The stromal cells were more sensitive to sonoporation than tumoural cells, and further efforts in optimising sonoporation-enhanced therapy should be targeted at the microenvironment.

Exotoxins from Staphylococcus aureus activate 5-lipoxygenase and induce leukotriene biosynthesis

Massive neutrophil infiltration is an early key event in infectious inflammation, accompanied by chemotactic leukotriene (LT)B4 generation. LTB4 biosynthesis is mediated by 5-lipoxygenase (5-LOX), but which pathogenic factors cause 5-LOX activation during bacterial infections is elusive. Here, we reveal staphylococcal exotoxins as 5-LOX activators. Conditioned medium of wild-type Staphylococcus aureus but not of exotoxin-deficient strains induced 5-LOX activation in transfected HEK293 cells. Two different staphylococcal exotoxins mimicked the effects of S. aureus-conditioned medium: (1) the pore-forming toxin α-hemolysin and (2) amphipathic α-helical phenol-soluble modulin (PSM) peptides. Interestingly, in human neutrophils, 5-LOX activation was exclusively evoked by PSMs, which was prevented by the selective FPR2/ALX receptor antagonist WRW4. 5-LOX activation by PSMs was confirmed in vivo as LT formation in infected paws of mice was impaired in response to PSM-deficient S. aureus. Conclusively, exotoxins from S. aureus are potent pathogenic factors that activate 5-LOX and induce LT formation in neutrophils.

Global gene expression changes induced by knockout of a protease gene cluster in Helicoverpa armigera with CRISPR/Cas9

Helicoverpa armigera is one of the most serious agricultural insect pests of global importance. It is highly polyphagous and depends on digestive serine proteases to degrade proteins to peptides and to amino acids. H. armigera has evolved adaptive ability to compensate for the inhibition of plant defensive protease inhibitors (PIs) in its diet by overproduction of digestive enzymes. As far as we know, compensation for deletion of serine protease genes has not yet been studied in any herbivorous insect. In this study, we used CRISPR/Cas9 to knock out a cluster of 18 trypsin-like genes in H. armigera. Compared with the wild type SCD strain, activities of the total proteases, trypsins and chymotrypsins were not significantly changed in the gene cluster knockout strain (Tryp-KO). RNA-seq data showed 1492 upregulated and 461 downregulated DEGs in Try-KO. GO function classification and KEGG pathway analyses revealed these differentially expressed genes were enriched for terms related to binding, catalytic activity, metabolic process and signal transduction. In regard to serine protease genes, 35 were upregulated and 12 downregulated in Tryp-KO strain. Our study indicated that H. armigera can compensate for the deleted protease genes by overexpression of other trypsin and chymotrypsin genes in order to maintain its genetic and metabolic robustness. It also suggests that genetic perturbations created by genome editing tools can induce global gene expression changes.

Phobalysin: Fisheye View of Membrane Perforation, Repair, Chemotaxis and Adhesion

Phobalysin P (PhlyP, for photobacterial lysin encoded on a plasmid) is a recently described small β-pore forming toxin of Photobacterium damselae subsp. damselae (Pdd). This organism, belonging to the family of Vibrionaceae, is an emerging pathogen of fish and various marine animals, which occasionally causes life-threatening soft tissue infections and septicemia in humans. By using genetically modified Pdd strains, PhlyP was found to be an important virulence factor. More recently, in vitro studies with purified PhlyP elucidated some basic consequences of pore formation. Being the first bacterial small β-pore forming toxin shown to trigger calcium-influx dependent membrane repair, PhlyP has advanced to a revealing model toxin to study this important cellular function. Further, results from co-culture experiments employing various Pdd strains and epithelial cells together with data on other bacterial toxins indicate that limited membrane damage may generally enhance the association of bacteria with target cells. Thereby, remodeling of plasma membrane and cytoskeleton during membrane repair could be involved. In addition, a chemotaxis-dependent attack-and track mechanism influenced by environmental factors like salinity may contribute to PhlyP-dependent association of Pdd with cells. Obviously, a synoptic approach is required to capture the regulatory links governing the interaction of Pdd with target cells. The characterization of Pdd’s secretome may hold additional clues because it may lead to the identification of proteases activating PhlyP’s pro-form. Current findings on PhlyP support the notion that pore forming toxins are not just killer proteins but serve bacteria to fulfill more subtle functions, like accessing their host.

The role of membrane-bound metal ions in toxicity of a human cancer cell-active pore-forming toxin Cry41Aa from Bacillus thuringiensis

Bacillus thuringiensis crystal (Cry) proteins, used for decades as insecticidal toxins, are well known to be toxic to certain insects, but not to mammals. A novel group of Cry toxins called parasporins possess a strong cytocidal activity against some human cancer cells. Cry41Aa, or parasporin3, closely resembles commercially used insecticidal toxins and yet is toxic to the human hepatic cancer cell line HepG2, disrupting membranes of susceptible cells, similar to its insecticidal counterparts. In this study, we explore the protective effect that the common divalent metal chelator EGTA exerts on Cry41Aa's activity on HepG2 cells. Our results indicate that rather than interfering with a signalling pathway as a result of chelating cations in the medium, the chelator prevented the toxin's interaction with the membrane, and thus the subsequent steps of membrane damage and p38 phosphorylation, by removing cations bound to plasma membrane components. BAPTA and DTPA also inhibited Cry41Aa toxicity but at higher concentrations. We also show for the first time that Cry41Aa induces pore formation in planar lipid bilayers. This activity is not altered by EGTA, consistent with a biological context of chelation. Salt supplementation assays identified Ca²⁺, Mn²⁺ and Zn²⁺ as being able to reinstate Cry41Aa activity. Our data suggest the existence of one or more metal cation-dependent receptors in the Cry41Aa mechanism of action.

Mechanisms protecting host cells against bacterial pore-forming toxins

Pore-forming toxins (PFTs) are key virulence determinants produced and secreted by a variety of human bacterial pathogens. They disrupt the plasma membrane (PM) by generating stable protein pores, which allow uncontrolled exchanges between the extracellular and intracellular milieus, dramatically disturbing cellular homeostasis. In recent years, many advances were made regarding the characterization of conserved repair mechanisms that allow eukaryotic cells to recover from mechanical disruption of the PM membrane. However, the specificities of the cell recovery pathways that protect host cells against PFT-induced damage remain remarkably elusive. During bacterial infections, the coordinated action of such cell recovery processes defines the outcome of infected cells and is, thus, critical for our understanding of bacterial pathogenesis. Here, we review the cellular pathways reported to be involved in the response to bacterial PFTs and discuss their impact in single-cell recovery and infection.

Involvement of P38 and ERK1/2 in mitochondrial pathways independent cell apoptosis in oviduct magnum epithelial cells of layers challenged with vanadium

Vanadium (V) can induce cell apoptosis in layers' oviduct resulting in egg quality reduction. In this study, we investigated the relationship between the mitogen-activated protein kinase (MAPK)-signaling pathway and V-induced apoptosis in poultry oviduct magnum epithelial cells (OMECs). Cultured OMECs were divided into 8 treatment groups: 0 μmol/L V (control), 100 μmol/L V (V100), V100 + P38MAPK inhibitor (SB203580), SB203580, V100 + extracellular signal-regulated kinases 1 and 2 (ERK1/2) inhibitor (U0126), U0126, V100 + c-JUN NH₂ -terminal kinase (JNK) inhibitor (SP600125), and SP600125. The OMECs were pretreated with the MAPK inhibitors before their treatment with V100 for 12 h. V100 increased the apoptosis of OMECs (P < .05), while 3 MAPK inhibitors suppressed V100-induced apoptosis P < .05); V100 enhanced the depolarization of △ψm (P < .05), and SB203580 and U0126 alleviated the V100-induced △ψm decrease (P < .05); V100 downregulated B-cell lymphoma-2 (Bcl-2) and poly [Adenosine diphosphate ribose] polymerase 1 (PARP1) mRNA expression (P < .05), meanwhile it upregulated Bcl-2 associated x (Bax), Apaf1, cytochrome C (CytC) and cysteine aspartase (caspase) 3, 8, 9 mRNA expression (P < .05). All MAPKs inhibitors alleviated the up-regulation of V100 for Bax and caspase 3 mRNA expression and down-regulation of V100 for Bcl-2 expression (P < .05). SB203580 and U0126 upregulated CytC expression treated by V100 (P < .05), except SP600125, while SB203580 administration resulted in a similar upregulation of PARP1 expression (P < .05). SP600125 can alleviated V triggered p-P38MAPK (phosphor-P38), p-ERK1/2 (phosphor-ERK1/2), p-JNK (phosphor-JNK) increase on OME cells, and SB203580 and U0126 had a similar response to phosphor-P38 and p-JNK (P < .05). It concluded that V-induced apoptosis in OMECs through the activation of P38 and ERK1/2, and by increasing the ratio of Bax/Bcl-2, which resulted in △ψm decrease, CytC release into the cytosol; consequently caspase 3 is recruited and activated, PARP1 is cleaved, eventually leading to apoptosis.

Response of Cellular Innate Immunity to Cnidarian Pore-Forming Toxins

A group of stable, water-soluble and membrane-bound proteins constitute the pore forming toxins (PFTs) in cnidarians. They interact with membranes to physically alter the membrane structure and permeability, resulting in the formation of pores. These lesions on the plasma membrane causes an imbalance of cellular ionic gradients, resulting in swelling of the cell and eventually its rupture. Of all cnidarian PFTs, actinoporins are by far the best studied subgroup with established knowledge of their molecular structure and their mode of pore-forming action. However, the current view of necrotic action by actinoporins may not be the only mechanism that induces cell death since there is increasing evidence showing that pore-forming toxins can induce either necrosis or apoptosis in a cell-type, receptor and dose-dependent manner. In this review, we focus on the response of the cellular immune system to the cnidarian pore-forming toxins and the signaling pathways that might be involved in these cellular responses. Since PFTs represent potential candidates for targeted toxin therapy for the treatment of numerous cancers, we also address the challenge to overcoming the immunogenicity of these toxins when used as therapeutics.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Vanadate oxidative and apoptotic effects are mediated by the MAPK-Nrf2 pathway in layer oviduct magnum epithelial cells

Vanadium is a metal of high physiological, environmental and industrial importance. However, vanadium-induced oxidative stress can reduce the egg quality of poultry, and be potentially harmful to humans, and the underlying mechanism is not clear. In this study, we investigated the underlying relationship between the oxidant-sensitive mitogen-activated protein kinase (MAPK) signaling pathway and vanadium-induced oxidative stress in oviduct magnum epithelial (OME) cells. Cultured OME cells were treated with 100 μmol L^-1 vanadium and/or MAPK inhibitors [P38 MAPK inhibitor, SB203580; extracellular regulated protein kinase 1 and 2 (ERK1/2) inhibitor, U0126; c-JUN N-terminal kinases (JNK) inhibitor, SP600125]. Cell viability, apoptosis, and generation of reactive oxygen species (ROS) were assessed using flow cytometry. The expression of oxidative stress-related genes and their proteins was measured by reverse transcription-polymerase chain reaction and western blotting. Vanadium treatment reduced cell viability, whereas pretreated OME cells with SB203580 and U0126 prevented the reducing effect of vanadium on cell viability (P < 0.05). Likewise, MAPK inhibitors effectively suppressed vanadium-induced apoptosis and ROS generation (P < 0.05). In the OME cells treated with vanadium, SB203580 (P < 0.05) and SP600125 (P = 0.08) increased catalase activity by 89.3% and 55.3%; SB203580 and U0126 increased (P < 0.05) glutathione peroxidase activity by 44.9% and 51.1%, respectively. Incubation of OME cells with MAPK inhibitors also prevents malondialdehyde concentration increase and lactic dehydrogenase activity decrease in response to vanadium (P < 0.05). Vanadium downregulated P38, ERK1/2, JNK, Nrf2, sMaf, GCLC, NQO1 and HO-1 mRNA expression (P < 0.05). In contrast, inhibition of JNK with SP600125 upregulated P38, ERK1/2, JNK, Nrf2, GCLC and HO-1 mRNA expression (P < 0.05); inhibition of P38 with SB203580 upregulated JNK, NQO1 and HO-1 mRNA expression (P < 0.05); and inhibition of ERK1/2 with U0126 upregulated ERK1/2, GCLC and HO-1 mRNA expression (P < 0.05). Moreover, phosphorylation of P38, ERK1/2, JNK, and Nrf2 proteins was enhanced by V incubation; however, SP600125 blocked the phosphorylation of these proteins, whereas SB203580 blocked the phosphorylation of P38 and Nrf2. These results indicate that vanadium inducing oxidative stress in OME cells might be, at least, associated with the phosphorylation of the P38MAPK/JNK-Nrf2 pathway, which reduces the expression of phase II detoxifying enzymes.

KGF inhibits hypoxia-induced intestinal epithelial cell apoptosis by upregulating AKT/ERK pathway-dependent E-cadherin expression

OBJECTIVE

Intestinal ischemia-reperfusion (I/R) causes direct cellular damage, and the potential injury to the mucosal structure and barrier function. Keratinocyte growth factor (KGF) is highly expressed in gastrointestinal tract and exerts beneficial effects for intestinal epithelial growth and maintenance. E-cadherin plays an important role in intestinal epithelium renewal. However, the regulatory role of KGF on E-cadherin levels and I/R-induced apoptosis remain to be explored. The present study aimed to identify the effect of KGF on E-cadherin expression and I/R-induced intestinal epithelial cell apoptosis.

METHODS

Caco2 cells were treated with KGF (100 ng/ml) for 0, 4, 8, 12, and 24 h under hypoxia or normoxia. An E-cadherin-knockdown model was successfully established by treatment with E-cadherin RNAi. Western blotting and immunofluorescence labeling were performed to assess E-cadherin expression. Levels of PI3K|[sol]|Akt/mitogen-activated protein kinases (MAPKs), phosphoinositide 3-kinase (PI3K|[sol]|Akt)/PI3K|[sol]|Akt pathway-related proteins, and apoptosis-related proteins were also detected by western blot. Finally, a rat model of acute intestinal I/R was established and treated with KGF. Hematoxylin-eosin (HE), terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL), and immunofluorescence staining were performed to detect morphological changes in intestinal mucosal epithelium and Caco2 cell apoptosis.

RESULTS

KGF enhanced E-cadherin expression in differentiated intestinal epithelial cells under hypoxia via AKT/extracellular-regulated kinase (ERK) pathway regulation. In vitro, E-cadherin downregulation aggravates hypoxia-induced intestinal epithelial cell apoptosis. In the rat model, KGF increased E-cadherin expression, which was associated with the reduced apoptosis.

CONCLUSIONS

KGF exerts protective effects on intestinal epithelial cells under hypoxia by elevating E-cadherin levels or activating AKT/ERK signaling.

Inhibition of miR-126 protects chondrocytes from IL-1β induced inflammation via upregulation of Bcl-2

OBJECTIVES

The aim of this study was to investigate the role of miR-126 in the development of osteoarthritis, as well as the potential molecular mechanisms involved, in order to provide a theoretical basis for osteoarthritis treatment and a novel perspective for clinical therapy.

METHODS

Human chondrocyte cell line CHON-001 was administrated by different doses of interleukin (IL)-1β to simulate inflammation. Cell viability, migration, apoptosis, IL-6, IL-8, and tumour necrosis factor (TNF)-α expression, as well as expression of apoptosis-related factors, were measured to assess inflammation. miR-126 expression was measured by quantitative polymerase chain reaction (qPCR). Cells were then transfected with miR-126 inhibitor to assess the effect of miR-126 on IL-1β-injured CHON-001 cells. Expression of B-cell lymphoma 2 (Bcl-2) and the activity of mitogen-activated protein kinase (MAPK) / Jun N-terminal kinase (JNK) signaling pathway were measured by Western blot to explore the underlying mechanism through which miR-126 affects IL-1β-induced inflammation.

RESULTS

After IL-1β administration, cell viability and migration were suppressed while apoptosis was enhanced. Expression of IL-6, IL-8, and TNF-α were all increased, and miR-126 was upregulated. In IL-1β-administrated CHON-001 cells, miR-126 inhibitor suppressed the effect of IL-1β on cell viability, migration, apoptosis, and inflammatory response. Bcl-2 expression was negatively regulated with miR-126 in IL-1β-administrated cells, and thus affected expressions of phosphorylated MAPK and JNK.

CONCLUSION

IL-1β-induced inflammatory markers and miR-126 was upregulated. Inhibition of miR-126 decreased IL-1β-induced inflammation and cell apoptosis, and upregulated Bcl-2 expression via inactivating the MAKP/JNK signalling pathway.Cite this article: C. D. Yu, W. H. Miao, Y. Y. Zhang, M. J. Zou, X. F. Yan. Inhibition of miR-126 protects chondrocytes from IL-1β induced inflammation via upregulation of Bcl-2. Bone Joint Res 2018;7:414-421. DOI: 10.1302/2046-3758.76.BJR-2017-0138.R1.

c-Jun Proto-Oncoprotein Plays a Protective Role in Lung Epithelial Cells Exposed to Staphylococcal α-Toxin

c-Jun is a member of the early mammalian transcriptional regulators belonging to the AP-1 family, which participates in a wide range of cellular processes such as proliferation, apoptosis, tumorigenesis, and differentiation. Despite its established role in cell survival upon stress, its participation in the stress response induced by bacterial infections has been poorly investigated. To study the potential role of c-Jun in this context we choose the widely studied α-toxin produced by Staphylococcus aureus, a pore-forming toxin that is a critical virulence factor in the pathogenesis of these bacteria. We analyzed the effect of α-toxin treatment in the activation, expression, and protein levels of c-Jun in A549 lung epithelial cells. Furthermore, we explored the role of c-Jun in the cellular fate after exposure to α-toxin. Our results show that staphylococcal α-toxin per se is able to activate c-Jun by inducing phosphorylation of its Serine 73 residue. Silencing of the JNK (c-Jun N-terminal Kinase) signaling pathway abrogated most of this activation. On the contrary, silencing of the ERK (Extracellular Signal-Regulated Kinase) pathway exacerbated this response. Intriguingly, while the exposure to α-toxin induced a marked increase in the levels of c-Jun transcripts, c-Jun protein levels noticeably decreased in the same time-frame as a consequence of active proteolytic degradation through the proteasome-dependent pathway. In addition, we established that c-Jun promoted cell survival when cells were challenged with α-toxin. Similarly, c-Jun phosphorylation was also induced in cells upon intoxication with the cytolysin produced by Vibrio cholerae in a JNK-dependent manner, suggesting that c-Jun-JNK axis would be a conserved responsive cellular pathway to pore-forming toxins. This study contributes to understanding the role of the multifaceted c-Jun proto-oncoprotein in cell response to bacterial pore-forming toxins, positioning it as a relevant component of the complex early machinery mounted to deal with staphylococcal infections.

Biophysical and biochemical strategies to understand membrane binding and pore formation by sticholysins, pore-forming proteins from a sea anemone

Actinoporins constitute a unique class of pore-forming toxins found in sea anemones that are able to bind and oligomerize in membranes, leading to cell swelling, impairment of ionic gradients and, eventually, to cell death. In this review we summarize the knowledge generated from the combination of biochemical and biophysical approaches to the study of sticholysins I and II (Sts, StI/II), two actinoporins largely characterized by the Center of Protein Studies at the University of Havana during the last 20 years. These approaches include strategies for understanding the toxin structure-function relationship, the protein-membrane association process leading to pore formation and the interaction of toxin with cells. The rational combination of experimental and theoretical tools have allowed unraveling, at least partially, of the complex mechanisms involved in toxin-membrane interaction and of the molecular pathways triggered upon this interaction. The study of actinoporins is important not only to gain an understanding of their biological roles in anemone venom but also to investigate basic molecular mechanisms of protein insertion into membranes, protein-lipid interactions and the modulation of protein conformation by lipid binding. A deeper knowledge of the basic molecular mechanisms involved in Sts-cell interaction, as described in this review, will support the current investigations conducted by our group which focus on the design of immunotoxins against tumor cells and antigen-releasing systems to cell cytosol as Sts-based vaccine platforms.

Damage of eukaryotic cells by the pore-forming toxin sticholysin II: Consequences of the potassium efflux

Pore-forming toxins (PFTs) form holes in membranes causing one of the most catastrophic damages to a target cell. Target organisms have evolved a regulated response against PFTs damage including cell membrane repair. This ability of cells strongly depends on the toxin concentration and the properties of the pores. It has been hypothesized that there is an inverse correlation between the size of the pores and the time required to repair the membrane, which has been for long a non-intuitive concept and far to be completely understood. Moreover, there is a lack of information about how cells react to the injury triggered by eukaryotic PFTs. Here, we investigated some molecular events related with eukaryotic cells response against the membrane damage caused by sticholysin II (StII), a eukaryotic PFT produced by a sea anemone. We evaluated the change in the cytoplasmic potassium, identified the main MAPK pathways activated after pore-formation by StII, and compared its effect with those from two well-studied bacterial PFTs: aerolysin and listeriolysin O (LLO). Strikingly, we found that membrane recovery upon StII damage takes place in a time scale similar to LLO in spite of the fact that they form pores by far different in size. Furthermore, our data support a common role of the potassium ion, as well as MAPKs in the mechanism that cells use to cope with these toxins injury.

Non-hemolytic enterotoxin of Bacillus cereus induces apoptosis in Vero cells

Bacillus cereus is an opportunistic pathogen that often causes foodborne infectious diseases and food poisoning. Non-hemolytic enterotoxin (Nhe) is the major toxin found in almost all enteropathogenic B. cereus and B. thuringiensis isolates. However, little is known about the cellular response after Nhe triggered pore formation on cell membrane. Here, we demonstrate that Nhe induced cell cycle arrest at G₀ /G₁ phase and provoked apoptosis in Vero cells, most likely associated with mitogen-activated protein kinase (MAPK) and death receptor pathways. The influx of extracellular calcium ions and increased level of reactive oxygen species in cytoplasm were sensed by apoptosis signal-regulating kinase 1 (ASK1) and p38 MAPK. Extrinsic death receptor Fas could also promote the activation of p38 MAPK. Subsequently, ASK1 and p38 MAPK triggered downstream caspase-8 and 3 to initiate apoptosis. Our results clearly demonstrate that ASK1, and Fas-p38 MAPK-mediated caspase-8 dependent pathways are involved in apoptotic cell death provoked by the pore-forming enterotoxin Nhe.

Implementation of a Permeable Membrane Insert-based Infection System to Study the Effects of Secreted Bacterial Toxins on Mammalian Host Cells

Many bacterial pathogens secrete potent toxins to aid in the destruction of host tissue, to initiate signaling changes in host cells or to manipulate immune system responses during the course of infection. Though methods have been developed to successfully purify and produce many of these important virulence factors, there are still many bacterial toxins whose unique structure or extensive post-translational modifications make them difficult to purify and study in in vitro systems. Furthermore, even when pure toxin can be obtained, there are many challenges associated with studying the specific effects of a toxin under relevant physiological conditions. Most in vitro cell culture models designed to assess the effects of secreted bacterial toxins on host cells involve incubating host cells with a one-time dose of toxin. Such methods poorly approximate what host cells actually experience during an infection, where toxin is continually produced by bacterial cells and allowed to accumulate gradually during the course of infection. This protocol describes the design of a permeable membrane insert-based bacterial infection system to study the effects of Streptolysin S, a potent toxin produced by Group A Streptococcus, on human epithelial keratinocytes. This system more closely mimics the natural physiological environment during an infection than methods where pure toxin or bacterial supernatants are directly applied to host cells. Importantly, this method also eliminates the bias of host responses that are due to direct contact between the bacteria and host cells. This system has been utilized to effectively assess the effects of Streptolysin S (SLS) on host membrane integrity, cellular viability, and cellular signaling responses. This technique can be readily applied to the study of other secreted virulence factors on a variety of mammalian host cell types to investigate the specific role of a secreted bacterial factor during the course of infection.

Signaling beyond Punching Holes: Modulation of Cellular Responses by Vibrio cholerae Cytolysin

Pore-forming toxins (PFTs) are a distinct class of membrane-damaging cytolytic proteins that contribute significantly towards the virulence processes employed by various pathogenic bacteria. Vibrio cholerae cytolysin (VCC) is a prominent member of the beta-barrel PFT (beta-PFT) family. It is secreted by most of the pathogenic strains of the intestinal pathogen V. cholerae. Owing to its potent membrane-damaging cell-killing activity, VCC is believed to play critical roles in V. cholerae pathogenesis, particularly in those strains that lack the cholera toxin. Large numbers of studies have explored the mechanistic basis of the cell-killing activity of VCC. Consistent with the beta-PFT mode of action, VCC has been shown to act on the target cells by forming transmembrane oligomeric beta-barrel pores, thereby leading to permeabilization of the target cell membranes. Apart from the pore-formation-induced direct cell-killing action, VCC exhibits the potential to initiate a plethora of signal transduction pathways that may lead to apoptosis, or may act to enhance the cell survival/activation responses, depending on the type of target cells. In this review, we will present a concise view of our current understanding regarding the multiple aspects of these cellular responses, and their underlying signaling mechanisms, evoked by VCC.

Streptolysin S Promotes Programmed Cell Death and Enhances Inflammatory Signaling in Epithelial Keratinocytes during Group A Streptococcus Infection

Streptococcus pyogenes, or group A Streptococcus (GAS), is a pathogen that causes a multitude of human diseases from pharyngitis to severe infections such as toxic shock syndrome and necrotizing fasciitis. One of the primary virulence factors produced by GAS is the peptide toxin streptolysin S (SLS). In addition to its well-recognized role as a cytolysin, recent evidence has indicated that SLS may influence host cell signaling pathways at sublytic concentrations during infection. We employed an antibody array-based approach to comprehensively identify global host cell changes in human epithelial keratinocytes in response to the SLS toxin. We identified key SLS-dependent host responses, including the initiation of specific programmed cell death and inflammatory cascades with concomitant downregulation of Akt-mediated cytoprotection. Significant signaling responses identified by our array analysis were confirmed using biochemical and protein identification methods. To further demonstrate that the observed SLS-dependent host signaling changes were mediated primarily by the secreted toxin, we designed a Transwell infection system in which direct bacterial attachment to host cells was prevented, while secreted factors were allowed access to host cells. The results using this approach were consistent with our direct infection studies and reveal that SLS is a bacterial toxin that does not require bacterial attachment to host cells for activity. In light of these findings, we propose that the production of SLS by GAS during skin infection promotes invasive outcomes by triggering programmed cell death and inflammatory cascades in host cells to breach the keratinocyte barrier for dissemination into deeper tissues.

eIF2α Confers Cellular Tolerance to S. aureus α-Toxin

We report on the role of conserved stress-response pathways for cellular tolerance to a pore forming toxin. First, we observed that small molecular weight inhibitors including of eIF2α-phosphatase, jun-N-terminal kinase (JNK), and PI3-kinase sensitized normal mouse embryonal fibroblasts (MEFs) to the small pore forming S. aureus α-toxin. Sensitization depended on expression of mADAM10, the murine ortholog of a proposed high-affinity receptor for α-toxin in human cells. Similarly, eIF2α (S51A/S51A) MEFs, which harbor an Ala knock-in mutation at the regulated Ser51 phosphorylation site of eukaryotic translation initiation factor 2α, were hyper-sensitive to α-toxin. Inhibition of translation with cycloheximide did not mimic the tolerogenic effect of eIF2α-phosphorylation. Notably, eIF2α-dependent tolerance of MEFs was toxin-selective, as wild-type MEFs and eIF2α (S51A/S51A) MEFs exhibited virtually equal sensitivity to Vibrio cholerae cytolysin. Binding of S. aureus α-toxin to eIF2α (S51A/S51A) MEFs and toxicity in these cells were enhanced as compared to wild-type cells. This led to the unexpected finding that the mutant cells carried more ADAM10. Because basal phosphorylation of eIF2α in MEFs required amino acid deprivation-activated eIF2α-kinase 4/GCN2, the data reveal that basal activity of this kinase mediates tolerance of MEFs to α-toxin. Further, they suggest that modulation of ADAM10 is involved. During infection, bacterial growth may cause nutrient shortage in tissues, which might activate this response. Tolerance to α-toxin was robust in macrophages and did not depend on GCN2. However, JNKs appeared to play a role, suggesting differential cell type and toxin selectivity of tolerogenic stress responses. Understanding their function or failure will be important to comprehend anti-bacterial immune responses.

MAPK signaling pathway alters expression of midgut ALP and ABCC genes and causes resistance to Bacillus thuringiensis Cry1Ac toxin in diamondback moth

Insecticidal crystal toxins derived from the soil bacterium Bacillus thuringiensis (Bt) are widely used as biopesticide sprays or expressed in transgenic crops to control insect pests. However, large-scale use of Bt has led to field-evolved resistance in several lepidopteran pests. Resistance to Bt Cry1Ac toxin in the diamondback moth, Plutella xylostella (L.), was previously mapped to a multigenic resistance locus (BtR-1). Here, we assembled the 3.15 Mb BtR-1 locus and found high-level resistance to Cry1Ac and Bt biopesticide in four independent P. xylostella strains were all associated with differential expression of a midgut membrane-bound alkaline phosphatase (ALP) outside this locus and a suite of ATP-binding cassette transporter subfamily C (ABCC) genes inside this locus. The interplay between these resistance genes is controlled by a previously uncharacterized trans-regulatory mechanism via the mitogen-activated protein kinase (MAPK) signaling pathway. Molecular, biochemical, and functional analyses have established ALP as a functional Cry1Ac receptor. Phenotypic association experiments revealed that the recessive Cry1Ac resistance was tightly linked to down-regulation of ALP, ABCC2 and ABCC3, whereas it was not linked to up-regulation of ABCC1. Silencing of ABCC2 and ABCC3 in susceptible larvae reduced their susceptibility to Cry1Ac but did not affect the expression of ALP, whereas suppression of MAP4K4, a constitutively transcriptionally-activated MAPK upstream gene within the BtR-1 locus, led to a transient recovery of gene expression thereby restoring the susceptibility in resistant larvae. These results highlight a crucial role for ALP and ABCC genes in field-evolved resistance to Cry1Ac and reveal a novel trans-regulatory signaling mechanism responsible for modulating the expression of these pivotal genes in P. xylostella.

Biopesticide and transgenic crops based on Bacillus thuringiensis (Bt) Cry toxins are widely used worldwide, yet the development of field resistance seriously threatens their sustainability. Unraveling these resistance mechanisms are of great importance for delaying insect field resistance evolution. The diamondback moth was the first insect to evolve field resistance to Bt biopesticides and it is an excellent model for the study of Bt resistance mechanisms. In this work, we present strong empirical evidence supporting that (1) field-evolved resistance to Bt in P. xylostella is tightly associated with differential expression of a membrane-bound alkaline phosphatase (ALP) and a suite of ATP-binding cassette transporter subfamily C (ABCC) genes, and (2) a constitutively transcriptionally-activated upstream gene (MAP4K4) in the MAPK signaling pathway is responsible for this trans-regulatory signaling mechanism. These findings identify key resistance genes and provide the first comprehensive mechanistic description responsible for the field-evolved Bt resistance in P. xylostella. Given that expression alterations of multiple receptor genes result in Bt resistance in many other insects, it can now be tested to determine whether the previously unidentified trans-regulatory mechanism characterized in this study is also involved in these cases.

Down-regulation of a novel ABC transporter gene (Pxwhite) is associated with Cry1Ac resistance in the diamondback moth, Plutella xylostella (L.)

Biopesticides or transgenic crops based on Cry toxins from the soil bacterium Bacillus thuringiensis (Bt) effectively control agricultural insect pests. The sustainable use of Bt biopesticides and Bt crops is threatened, however, by the development of Cry resistance in the target pests. The diamondback moth, Plutella xylostella (L.), is the first pest that developed resistance to a Bt biopesticide in the field, and a recent study has shown that the resistance of P. xylostella to Cry1Ac is caused by a mutation in an ATP-binding cassette (ABC) transporter gene (ABCC2). In this study, we report that down-regulation of a novel ABC transporter gene from ABCG subfamily (Pxwhite) is associated with Cry1Ac resistance in P. xylostella. The full-length cDNA sequence of Pxwhite was cloned and analyzed. Spatial-temporal expression detection revealed that Pxwhite was expressed in all tissues and developmental stages, and highest expressed in Malpighian tubule tissue and in egg stage. Sequence variation analysis of Pxwhite indicated the absence of constant non-synonymous mutations between susceptible and resistant strains, whereas midgut transcript analysis showed that Pxwhite was remarkably reduced in all resistant strains and further reduced when larvae of the moderately resistant SZ-R strain were subjected to selection with Cry1Ac toxin. Furthermore, RNA interference (RNAi)-mediated suppression of Pxwhite gene expression significantly reduced larval susceptibility to Cry1Ac toxin, and genetic linkage analysis confirmed that down-regulation of Pxwhite gene is tightly linked to Cry1Ac resistance in P. xylostella. To our knowledge, this is the first report indicating that Pxwhite gene is involved in Cry1Ac resistance in P. xylostella.

The pathogenesis, detection, and prevention of Vibrio parahaemolyticus

Vibrio parahaemolyticus, a Gram-negative motile bacterium that inhabits marine and estuarine environments throughout the world, is a major food-borne pathogen that causes life-threatening diseases in humans after the consumption of raw or undercooked seafood. The global occurrence of V. parahaemolyticus accentuates the importance of investigating its virulence factors and their effects on the human host. This review describes the virulence factors of V. parahaemolyticus reported to date, including hemolysin, urease, two type III secretion systems and two type VI secretion systems, which both cause both cytotoxicity in cultured cells and enterotoxicity in animal models. We describe various types of detection methods, based on virulence factors, that are used for quantitative detection of V. parahaemolyticus in seafood. We also discuss some useful preventive measures and therapeutic strategies for the diseases mediated by V. parahaemolyticus, which can reduce, to some extent, the damage to humans and aquatic animals attributable to V. parahaemolyticus. This review extends our understanding of the pathogenic mechanisms of V. parahaemolyticus mediated by virulence factors and the diseases it causes in its human host. It should provide new insights for the diagnosis, treatment, and prevention of V. parahaemolyticus infection.

The pore-forming α-toxin from clostridium septicum activates the MAPK pathway in a Ras-c-Raf-dependent and independent manner

Clostridium septicum is the causative agent of atraumatic gas gangrene, with α-toxin, an extracellular pore-forming toxin, essential for disease. How C. septicum modulates the host’s innate immune response is poorly defined, although α-toxin-intoxicated muscle cells undergo cellular oncosis, characterised by mitochondrial dysfunction and release of reactive oxygen species. Nonetheless, the signalling events that occur prior to the initiation of oncosis are poorly characterised. Our aims were to characterise the ability of α-toxin to activate the host mitogen activated protein kinase (MAPK) signalling pathway both in vitro and in vivo. Treatment of Vero cells with purified α-toxin activated the extracellular-signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 arms of the MAPK pathway and stimulated the release of TNF-α in a dose-dependent manner. Studies using inhibitors of all three MAPK components suggested that activation of ERK occurred in a Ras-c-Raf dependent manner, whereas activation of JNK and p38 occurred by a Ras-independent mechanism. Toxin-mediated activation was dependent on efficient receptor binding and pore formation and on an influx of extracellular calcium ions. In the mouse myonecrosis model we showed that the MAPK pathway was activated in tissues of infected mice, implying that it has an important role in the disease process.

MEK/ERK signaling pathway is required for enterovirus 71 replication in immature dendritic cells

Background

The mitogen-activated protein kinase kinase/extracellular-signal-regulated kinase (MEK/ERK) signaling pathway is involved in viral life cycle. However, the effect of MEK/ERK pathway in enterovirus 71(EV71)-infected immature dendritic cells (iDCs) is still unclear.

Methods

Human peripheral blood mononuclear cells (PBMCs) were isolated and induced to generate iDCs. Unifected iDCs and EV71-infected iDCs with a multiplicity of infection (MOI = 5) were analyzed by flow cytometry. Differential gene expressions of MEK/ERK signaling pathway molecules in EV71-infected iDCs were performed by PCR arrays. The phosphorylation of MEK/ERK pathway molecules in EV71-infected iDCs preincubated without or with U0126 (20 μM) at indicated times was detected by Western blot. The concentrations of IL-1α, IL-2, IL-6, IL-12, TNF-α, IFN-α1, IFN-β and IFN-γ in culture supernatant were analyzed by the luminex fluorescent technique.

Results

When iDCs were infected with EV71 for 24 h, the percentage of CD80, CD83, CD86 and HLA-DR expressed on iDCs significantly increased. PCR arrays showed that gene expressions of molecules in MEK/ERK signaling pathway were remarkably upregulated in EV71-infected iDCs. EV71 infection activated both MEK1/2 and ERK1/2, which phosphorylated their downstream transcription factor c-Fos, c-Jun, c-myc and Elk1. Importantly, the treatment of U0126 significantly inhibited MEK/ERK signaling pathway molecules and severely impaired virus replication., Additionally, EV71 infection promoted the expression of son of sevenless (SOS1) and increased the secretion of IL-1α, IL-2, IL-6, IL-12, TNF-α,IFN-β and IFN-γ. Furthermore,the release of IL-1α, IL-2,IL-6 and TNF-α could be effectively suppressed by inhibitor U0126.

Conclusions

Our data suggest that the MEK/ERK signaling pathway plays an important role in EV71-infected iDCs and these molecules may be potential targets for the development of new anti-EV71 drugs.

Protective role of the dynamin inhibitor Dynasore against the cholesterol-dependent cytolysin of Trueperella pyogenes

The virulence of many Gram-positive bacteria depends on cholesterol-dependent cytolysins (CDCs), which form pores in eukaryotic cell plasma membranes. Pyolysin (PLO) from Trueperella pyogenes provided a unique opportunity to explore cellular responses to CDCs because it does not require thiol activation. Sublytic concentrations of PLO stimulated phosphorylation of MAPK ERK and p38 in primary stromal cells, and induced autophagy as determined by protein light-chain 3B cleavage. Although, inhibitors of MAPK or autophagy did not affect PLO-induced cytolysis. However, 10 μM 3-hydroxynaphthalene-2-carboxylic acid-(3,4-dihydroxybenzylidene)-hydrazide (Dynasore), a dynamin guanosine 5′-triphosphatase inhibitor, protected stromal cells against PLO-induced cytolysis as determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay (85 ± 17% versus 50 ± 9% cell viability), measuring extracellular ATP, and kinetic assays. This was a generalized mechanism because Dynasore also protected HeLa cells against streptolysin O. Furthermore, the effect was reversible, with stromal cell sensitivity to PLO restored within 30 minutes of Dynasore removal. The protective effect of Dynasore was not conferred by dynamin inhibition, induction of ERK phosphorylation, or Dynasore binding to PLO. Rather, Dynasore reduced cellular cholesterol and disrupted plasma membrane lipid rafts, similar to positive control methyl-β-cyclodextrin. Dynasore is a tractable tool to explore the complexity of cholesterol homeostasis in eukaryotic cells and to develop strategies to counter CDCs.—Preta, G., Lotti, V., Cronin, J. G., and Sheldon, I. M. Protective role of the dynamin inhibitor Dynasore against the cholesterol-dependent cytolysin of Trueperella pyogenes.

Antigen targeting to CD11b+ dendritic cells in association with TLR4/TRIF signaling promotes strong CD8+ T cell responses

Deciphering the mechanisms that allow the induction of strong immune responses is crucial to developing efficient vaccines against infectious diseases and cancer. Based on the discovery that the adenylate cyclase from Bordetella pertussis binds to the CD11b/CD18 integrin, we developed a highly efficient detoxified adenylate cyclase-based vector (CyaA) capable of delivering a large variety of Ags to the APC. This vector allows the induction of protective and therapeutic immunity against viral and tumoral challenges as well as against transplanted tumors in the absence of any added adjuvant. Two therapeutic vaccine candidates against human papilloma viruses and melanoma have been developed recently, based on the CyaA vector, and are currently in clinical trials. We took advantage of one of these highly purified vaccines, produced under good manufacturing practice-like conditions, to decipher the mechanisms by which CyaA induces immune responses. In this study, we demonstrate that CyaA binds both human and mouse CD11b(+) dendritic cells (DCs) and induces their maturation, as shown by the upregulation of costimulatory and MHC molecules and the production of proinflammatory cytokines. Importantly, we show that DCs sense CyaA through the TLR4/Toll/IL-1R domain-containing adapter-inducing IFN-β pathway, independent of the presence of LPS. These findings show that CyaA possesses the intrinsic ability to not only target DCs but also to activate them, leading to the induction of strong immune responses. Overall, this study demonstrates that Ag delivery to CD11b(+) DCs in association with TLR4/Toll/IL-1R domain-containing adapter-inducing IFN-β activation is an efficient strategy to promote strong specific CD8(+) T cell responses.

Manipulation of intestinal epithelial cell function by the cell contact-dependent type III secretion systems of Vibrio parahaemolyticus

Vibrio parahaemolyticus elicits gastroenteritis by deploying Type III Secretion Systems (TTSS) to deliver effector proteins into epithelial cells of the human intestinal tract. The bacteria must adhere to the human cells to allow colonization and operation of the TTSS translocation apparatus bridging the bacterium and the host cell. This article first reviews recent advances in identifying the molecules responsible for intercellular adherence. V. parahaemolyticus possesses two TTSS, each of which delivers an exclusive set of effectors and mediates unique effects on the host cell. TTSS effectors primarily target and alter the activation status of host cell signaling proteins, thereby bringing about changes in the regulation of cellular behavior. TTSS1 is responsible for the cytotoxicity of V. parahaemolyticus, while TTSS2 is necessary for the enterotoxicity of the pathogen. Recent publications have elucidated the function of several TTSS effectors and their importance in the virulence of the bacterium. This review will explore the ability of the TTSS to manipulate activities of human intestinal cells and how this modification of cell function favors bacterial colonization and persistence of V. parahaemolyticus in the host.

The p38 MAPK and JNK pathways protect host cells against Clostridium perfringens beta-toxin

Clostridium perfringens beta-toxin is an important agent of necrotic enteritis and enterotoxemia. Beta-toxin is a pore-forming toxin (PFT) that causes cytotoxicity. Two mitogen-activated protein kinase (MAPK) pathways (p38 and c-Jun N-terminal kinase [JNK]-like) provide cellular defense against various stresses. To investigate the role of the MAPK pathways in the toxic effect of beta-toxin, we examined cytotoxicity in five cell lines. Beta-toxin induced cytotoxicity in cells in the following order: THP-1 = U937 > HL-60 > BALL-1 = MOLT-4. In THP-1 cells, beta-toxin formed oligomers on lipid rafts in membranes and induced the efflux of K(+) from THP-1 cells in a dose- and time-dependent manner. The phosphorylation of p38 MAPK and JNK occurred in response to an attack by beta-toxin. p38 MAPK (SB203580) and JNK (SP600125) inhibitors enhanced toxin-induced cell death. Incubation in K(+)-free medium intensified p38 MAPK activation and cell death induced by the toxin, while incubation in K(+)-high medium prevented those effects. While streptolysin O (SLO) reportedly activates p38 MAPK via reactive oxygen species (ROS), we showed that this pathway did not play a major role in p38 phosphorylation in beta-toxin-treated cells. Therefore, we propose that beta-toxin induces activation of the MAPK pathway to promote host cell survival.

Effector-triggered versus pattern-triggered immunity: how animals sense pathogens

A fundamental question regarding any immune system is how it can discriminate between pathogens and non-pathogens. Here, we discuss how this discrimination can be mediated by a surveillance system distinct from pattern-recognition receptors that recognize conserved microbial patterns. It can be based instead on the ability of the host to sense perturbations in host cells induced by bacterial toxins or 'effectors' that are encoded by pathogenic microorganisms. Such 'effector-triggered immunity' was previously demonstrated mainly in plants, but recent data confirm that animals can also use this strategy.

Pathogenic pore-forming proteins: function and host response

Organisms from all kingdoms produce pore-forming proteins, with the best-characterized being of bacterial origin. The last decade of research has revealed that the channels formed by these proteins can be very diverse, thus differentially affecting target cell-membrane permeability and consequent cellular outcome. The responses to these toxins are also extremely diverse due to multiple downstream effects of pore-induced changes in ion balance. Determining the secondary effects of pore-forming toxins is essential to understand their contribution to infection.

Involvement of oxidative stress and mitogen-activated protein kinase signaling pathways in heat stress-induced injury in the rat small intestine

Extreme heat stress-induced gastrointestinal injury and dysfunction may occur during summer. We investigated possible mechanisms of heat stress-induced damage in the small intestine using male Sprague-Dawley rats subjected to 2 h of heat stress (40 °C, 60% relative humidity) daily for 10 consecutive days. Rats were killed at specific times immediately following heat treatment to determine: morphological changes by optical and electron microscopy; intestinal permeability using fluorescein isothiocyanate-dextran; production of reactive oxygen species (ROS), malondialdehyde (MDA), and activities of superoxide-dismutase and glutathione-peroxidase by specific assays; phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) by immunocytochemistry and western-blot analysis. The rat intestinal epithelial cell line (IEC-6) and specific MAPK inhibitors were used for in vitro investigation of effects of activation of MAPKs by heat stress. Heat stress caused marked morphological damage to the small intestine and significantly increased intestinal permeability. Heat stress increased ROS and MDA production, and significantly reduced anti-oxidase activity. MAPK activity in small intestine was increased by heat stress. In vitro, heat stress caused damage and apoptosis in IEC-6 cells; inhibition of ERK1/2 activation (by U0126) exacerbated these effects, which were attenuated by inhibition of JNK (by SP600125) and p38 (by SB203580) activation. Hence, heat stress caused severe small intestine injury, increased oxidative stress, and activated MAPK signaling pathways. The in vitro studies indicated that ERK1/2 activation is anti-apoptotic, and JNK and p38 activation are pro-apoptotic in heat stressed intestinal epithelial cells.

The UPEC pore-forming toxin α-hemolysin triggers proteolysis of host proteins to disrupt cell adhesion, inflammatory, and survival pathways

Uropathogenic Escherichia coli (UPEC), which are the leading cause of both acute and chronic urinary tract infections, often secrete a labile pore-forming toxin known as α-hemolysin (HlyA). We show that stable insertion of HlyA into epithelial cell and macrophage membranes triggers degradation of the cytoskeletal scaffolding protein paxillin and other host regulatory proteins, as well as components of the proinflammatory NFκB signaling cascade. Proteolysis of these factors requires host serine proteases, and paxillin degradation specifically involves the serine protease mesotrypsin. The induced activation of mesotrypsin by HlyA is preceded by redistribution of mesotrypsin precursors from the cytosol into foci along microtubules and within nuclei. HlyA intoxication also stimulated caspase activation, which occurred independently of effects on host serine proteases. HlyA-induced proteolysis of host proteins likely allows UPEC to not only modulate epithelial cell functions, but also disable macrophages and suppress inflammatory responses.