Hepatitis c virus infection induces pro- and antiapoptotic cell response: who is the winner?

Introduction: Apoptosis plays a central role in chronic hepatitis C virus (HCV) infection. Although the activation of cell death signals has been reported, HCV infection persists in most patients suggesting a pro-survival adaptation, eventually developing hepatocellular carcinoma. This study focused on the role of mitochondria in the activation of pro- and antiapoptotic response in cells expressing HCV proteins. Materials and Methods: Human Osteosarcoma U2-OS cells inducibly expressing the HCV polyprotein; huh7.5 hepatoma cells transfected with full length HCV genome. Results: Long term induction of viral proteins in U2-OS cells induced a cyclosporine A-sensitive cytochrome c partial release from mitochondria, revealed by immunofluorescence, western blot and spectral analysis. In HCV-transfected Huh7.5 cells, release of the apoptosis inducing factor (AIF) with no apparent nuclear translocation was also observed. HCV positive cells displayed an HIF-dependent enhanced glycolysis, charachterized by up-regulation of the mitochondria-bound Hexokinase II (HKII); preliminary data on signal transduction pathway revealed the iperphosphorylation of Glycogen synthase kinase 3b(GSK3b). Conclusion: HCV causes a cell stress activating an early apoptotic response, the entity of which likely depends on the cell type. Nevertheless a wide series of cell survival mechanisms are also triggered resulting in a metabolic adaptation possibly favouring carcinogenesis. Based on our results, we propose a pro-survival mechanism linking HCV infection to inhibition of GSK-3b, stabilization of HIF1a and up-regulation of HKII, the last events causing a glycolytic shift and protecting from apoptosis.

Mechanisms of eosinophil cytokine release

Human eosinophils have been demonstrated to contain a multitude of cytokines and chemokines that exist pre-formed within these cells. This content of pre-formed cytokines, with diverse potential biologic activities, provides eosinophils with capabilities distinct from most other leukocytes. The localization of pre-formed cytokines within eosinophils is both within specific granules and associated with substantial numbers of morphologically distinct cytoplasmic vesicles. Stimulation for release of specific cytokines, such as IL-4, leads to a regulated signal transduction cascade, which is dependent on the formation of leukotriene C4 within eosinophils where it acts as an intracrine mediator. IL-4 release occurs selectively and is by means of vesicular transport. The capabilities of eosinophils not only to rapidly release pre-formed cytokines but also to differentially regulate which cytokines are released endow eosinophils with distinct abilities in innate and acquired immunity.

Epithelial cell signaling responses to enterohemorrhagic Escherichia coli infection

Enterohemorrhagic Escherichia coli, including the serotype O157:H7 that is most commonly identified with human disease, cause both sporadic cases and outbreaks of non-bloody diarrhea and hemorrhagic colitis. In about 10% of infected subjects, the hemolytic uremic syndrome (hemolytic anemic, thrombocytopenia, and acute renal failure) develops, likely as a consequence of systemic spread of bacterial-derived toxins variously referred to as Shiga-like toxin, Shiga toxin, and Verotoxin. Increasing evidence points to a complex interplay between bacterial products - for example, adhesins and toxins - and host signal transduction pathways in mediating responses to infection. Identification of critical signaling pathways could result in the development of novel strategies for intervention to both prevent and treat this microbial infection in humans.

Good bug, bad bug: in the case of enteric inflammatory disease does the epithelium decide?

Many studies demonstrate that intestinal inflammation is either initiated or exaggerated by a component of the normal microbiota, most likely commensal bacteria or products derived from these organisms. We review the nature of human inflammatory bowel disease, the evidence for the involvement of the normal bacterial flora in these disorders and the relevance of maintaining the integrity of the epithelial barrier. Moreover, we, and others, have shown abnormal mitochondria structure in tissue resections from patients with inflammatory bowel disease and tissues from rodents that demonstrated psychological stress-induced increases in epithelial permeability. Thus, we also consider the possibility that a defect in epithelial mitochondrial function would predispose an individual to respond to their commensal bacteria flora - no longer considering them as a beneficial passive inhabitant, but rather perceiving them as a threatening and pro-inflammatory stimulus. In support of this postulate, we discuss our recent findings from an in vitro model showing that the human colon-derived T84 cell line exposed to the metabolic stressor, dinitrophenol, and the non-pathogenic, non-invasive, Escherichia coli (strain HB101) display a loss of barrier function, increased signal transduction and increased production of the chemokine, interleukin 8.

Steady-state expression of self-regulated genes.

MOTIVATION: Regulatory gene networks contain generic modules such as feedback loops that are essential for the regulation of many biological functions. The study of the stochastic mechanisms of gene regulation is instrumental for the understanding of how cells maintain their expression at levels commensurate with their biological role, as well as to engineer gene expression switches of appropriate behavior. The lack of precise knowledge on the steady-state distribution of gene expression requires the use of Gillespie algorithms and Monte-Carlo approximations. METHODOLOGY: In this study, we provide new exact formulas and efficient numerical algorithms for computing/modeling the steady-state of a class of self-regulated genes, and we use it to model/compute the stochastic expression of a gene of interest in an engineered network introduced in mammalian cells. The behavior of the genetic network is then analyzed experimentally in living cells. RESULTS: Stochastic models often reveal counter-intuitive experimental behaviors, and we find that this genetic architecture displays a unimodal behavior in mammalian cells, which was unexpected given its known bimodal response in unicellular organisms. We provide a molecular rationale for this behavior, and we implement it in the mathematical picture to explain the experimental results obtained from this network.

Jasmonates and related oxylipins in plant responses to pathogenesis and herbivory.

The vigorous production of oxygenated fatty acids (oxylipins) is a characteristic response to pathogenesis and herbivory, and is often accompanied by the substantial release of small and reactive lipid-fragmentation products. Some oxylipins, most notably those of the jasmonate family, have key roles as potent regulators. Recent advances have been made in understanding oxylipin-regulated signal transduction in response to attack. Much jasmonate signaling takes place via a genetically defined signal network that is linked to the ethylene, auxin, and salicylic acid signal pathways, but a second aspect of jasmonate signaling is emerging. Some jasmonates and several newly discovered cyclopentenone lipids can activate or repress gene expression through the activities of a conserved electrophilic atom group.

Caspase-induced inactivation of the anti-apoptotic TRAF1 during Fas ligand-mediated apoptosis.

The activation of the transcription factor NF-kappaB often results in protection against apoptosis. In particular, pro-apoptotic tumor necrosis factor (TNF) signals are blocked by proteins that are induced by NF-kappaB such as TNFR-associated factor 1 (TRAF1). Here we show that TRAF1 is cleaved after Asp-163 when cells are induced to undergo apoptosis by Fas ligand (FasL). The C-terminal cleavage product blocks the induction of NF-kappaB by TNF and therefore functions as a dominant negative (DN) form of TRAF1. Our results suggest that the generation of DN-TRAF1 is part of a pro-apoptotic amplification system to assure rapid cell death.

Danger signaling through the inflammasome acts as a master switch between tolerance and sensitization.

Efficient priming of adaptive immunity depends on danger signals provided by innate immune pathways. As an example, inflammasome-mediated activation of caspase-1 and IL-1beta is crucial for the development of reactive T cells targeting sensitizers like dinitrofluorobenzene (DNFB). Surprisingly, DNFB and dinitrothiocyanobenzene provide cross-reactive Ags yet drive opposing, sensitizing vs tolerizing, T cell responses. In this study, we show that, in mice, inflammasome-signaling levels can be modulated to turn dinitrothiocyanobenzene into a sensitizer and DNFB into a tolerizer, and that it correlates with the IL-6 and IL-12 secretion levels, affecting Th1, Th17, and regulatory T cell development. Hence, our data provide the first evidence that the inflammasome can define the type of adaptive immune response elicited by an Ag, and hint at new strategies to modulate T cell responses in vivo.

mitoKATP channel activation in the postanoxic developing heart protects E-C coupling via NO-, ROS-, and PKC-dependent pathways.

Whereas previous studies have shown that opening of the mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channel protects the adult heart against ischemia-reperfusion injury, it remains to be established whether this mechanism also operates in the developing heart. Isolated spontaneously beating hearts from 4-day-old chick embryos were subjected to 30 min of anoxia followed by 60 min of reoxygenation. The chrono-, dromo-, and inotropic disturbances, as well as alterations of the electromechanical delay (EMD), reflecting excitation-contraction (E-C) coupling, were investigated. Production of reactive oxygen species (ROS) in the ventricle was determined using the intracellular fluorescent probe 2',7'-dichlorofluorescin (DCFH). Effects of the specific mitoK(ATP) channel opener diazoxide (Diazo, 50 microM) or the blocker 5-hydroxydecanoate (5-HD, 500 microM), the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 50 microM), the antioxidant N-(2-mercaptopropionyl)glycine (MPG, 1 mM), and the PKC inhibitor chelerythrine (Chel, 5 microM) on oxidative stress and postanoxic functional recovery were determined. Under normoxia, the baseline parameters were not altered by any of these pharmacological agents, alone or in combination. During the first 20 min of postanoxic reoxygenation, Diazo doubled the peak of ROS production and, interestingly, accelerated recovery of ventricular EMD and the PR interval. Diazo-induced ROS production was suppressed by 5-HD, MPG, or L-NAME, but not by Chel. Protection of ventricular EMD by Diazo was abolished by 5-HD, MPG, L-NAME, or Chel, whereas protection of the PR interval was abolished by L-NAME exclusively. Thus pharmacological opening of the mitoK(ATP) channel selectively improves postanoxic recovery of cell-to-cell communication and ventricular E-C coupling. Although the NO-, ROS-, and PKC-dependent pathways also seem to be involved in this cardioprotection, their interrelation in the developing heart can differ markedly from that in the adult myocardium.

The role of queen pheromones in social insects: queen control or queen signal?

Queens and workers in social insect colonies can differ in reproductive goals such as colony-level sex allocation and production of males by workers. That the presence of queen(s) often seems to affect worker behaviour in situations of potential conflict has given rise to the idea of queen control over reproduction. In small colonies queen control is possible via direct aggression against workers, but in large colonies queens cannot be effectively aggressive towards all the workers. This, plus evidence that queen-produced chemicals affect worker behaviour, has led to the conclusion that physical intimidation has been replaced by pheromonal queen control, whereby queen(s) chemically manipulate workers into behaving in ways that increase the queen's fitness at the worker's expense. It is argued in this paper, however, that pheromonal queen control has never conclusively been demonstrated and is evolutionarily difficult to justify. Proposed examples of pheromonal control are more likely to be honest signals, with workers' responses increasing their own inclusive fitness. A series of experimental and field studies in which positive results would give prima facie evidence for pheromonal queen control is suggested. Finally, three terms are defined: (1) pheromonal queen control for workers or subordinate queens being chemically manipulated into acting against their own best interests; (2) pheromonal queen signal for situations where workers or subordinate queens react to queen pheromones in ways that increase their, and possibly the queens', inclusive fitness; and (3) pheromonal queen effect where changes in the workers' or subordinate queens' behaviour have an unknown consequence on their inclusive fitness.

Extensive remodeling of DC function by rapid maturation-induced transcriptional silencing.

The activation, or maturation, of dendritic cells (DCs) is crucial for the initiation of adaptive T-cell mediated immune responses. Research on the molecular mechanisms implicated in DC maturation has focused primarily on inducible gene-expression events promoting the acquisition of new functions, such as cytokine production and enhanced T-cell-stimulatory capacity. In contrast, mechanisms that modulate DC function by inducing widespread gene-silencing remain poorly understood. Yet the termination of key functions is known to be critical for the function of activated DCs. Genome-wide analysis of activation-induced histone deacetylation, combined with genome-wide quantification of activation-induced silencing of nascent transcription, led us to identify a novel inducible transcriptional-repression pathway that makes major contributions to the DC-maturation process. This silencing response is a rapid primary event distinct from repression mechanisms known to operate at later stages of DC maturation. The repressed genes function in pivotal processes--including antigen-presentation, extracellular signal detection, intracellular signal transduction and lipid-mediator biosynthesis--underscoring the central contribution of the silencing mechanism to rapid reshaping of DC function. Interestingly, promoters of the repressed genes exhibit a surprisingly high frequency of PU.1-occupied sites, suggesting a novel role for this lineage-specific transcription factor in marking genes poised for inducible repression.

Protein tyrosine kinases in Schistosoma mansoni

The identification and description of signal transduction molecules and mechanisms are essential to elucidate Schistosoma mansoni host-parasite interactions and parasite biology. This mini review focuses on recent advancements in the study of signalling molecules and transduction mechanisms in S. mansoni, drawing special attention to the recently identified and characterised protein tyrosine kinases of S. mansoni.

TRADD protein is an essential component of the RIG-like helicase antiviral pathway

Upon detection of viral RNA, the helicases RIG-I and/or MDA5 trigger, via their adaptor Cardif (also known as IPS-1, MAVS, or VISA), the activation of the transcription factors NF-kappaB and IRF3, which collaborate to induce an antiviral type I interferon (IFN) response. FADD and RIP1, known as mediators of death-receptor signaling, are implicated in this antiviral pathway; however, the link between death-receptor and antiviral signaling is not known. Here we showed that TRADD, a crucial adaptor of tumor necrosis factor receptor (TNFRI), was important in RIG-like helicase (RLH)-mediated signal transduction. TRADD is recruited to Cardif and orchestrated complex formation with the E3 ubiquitin ligase TRAF3 and TANK and with FADD and RIP1, leading to the activation of IRF3 and NF-kappaB. Loss of TRADD prevented Cardif-dependent activation of IFN-beta, reduced the production of IFN-beta in response to RNA viruses, and enhanced vesicular stomatitis virus replication. Thus, TRADD is not only an essential component of proinflammatory TNFRI signaling, but is also required for RLH-Cardif-dependent antiviral immune responses

STAT3 links IL-22 signaling in intestinal epithelial cells to mucosal wound healing.

Signal transducer and activator of transcription (STAT) 3 is a pleiotropic transcription factor with important functions in cytokine signaling in a variety of tissues. However, the role of STAT3 in the intestinal epithelium is not well understood. We demonstrate that development of colonic inflammation is associated with the induction of STAT3 activity in intestinal epithelial cells (IECs). Studies in genetically engineered mice showed that epithelial STAT3 activation in dextran sodium sulfate colitis is dependent on interleukin (IL)-22 rather than IL-6. IL-22 was secreted by colonic CD11c(+) cells in response to Toll-like receptor stimulation. Conditional knockout mice with an IEC-specific deletion of STAT3 activity were highly susceptible to experimental colitis, indicating that epithelial STAT3 regulates gut homeostasis. STAT3(IEC-KO) mice, upon induction of colitis, showed a striking defect of epithelial restitution. Gene chip analysis indicated that STAT3 regulates the cellular stress response, apoptosis, and pathways associated with wound healing in IECs. Consistently, both IL-22 and epithelial STAT3 were found to be important in wound-healing experiments in vivo. In summary, our data suggest that intestinal epithelial STAT3 activation regulates immune homeostasis in the gut by promoting IL-22-dependent mucosal wound healing.