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Caspase-1 activation by Salmonella   总被引:7,自引:0,他引:7  
Salmonella is an interesting example of how the selective pressure of host environments has led to the evolution of sophisticated bacterial virulence mechanisms. This microbe exploits the first-line of defence, the macrophage, as a crucial tool in the initiation of disease. After invasion of intestinal macrophages, a virulence protein secreted by Salmonella specifically induces apoptotic cell death by activating the cysteine protease caspase-1. The pro-apoptotic capability is necessary for successful pathogenesis. The study of mechanisms by which Salmonella induces programmed cell death offers new insights into how pathogens cause disease and into general mechanisms of activation of the innate immune system.  相似文献   
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The Bacillus Calmette - Guerin (BCG) vaccine provides a critical but limited defense against Mycobacterium tuberculosis (M.tb). More than 60 years after the widespread introduction of BCG, there is an urgent need for a better vaccine. A large body of pre-clinical research continues to support ongoing clinical trials to assess whether viral vectors expressing M.tb antigens that are shared by BCG and M.tb, can be used alongside BCG to enhance protection. A major focus involves using multiple unique viral vectors to limit anti-vector immunity and thereby enhance responses to the insert antigen delivered. The successful introduction of viral vector vaccines to target M.tb and other pathogens will be reliant on reducing the costs when using multiple vectors and inhibiting the development of unwanted anti-vector responses that interfere with the response to insert antigen. This study examines methods to reduce the logistical costs of vaccination by mixing different viral vectors that share the same insert antigen in one vaccine; and whether combining different viral vectors reduces anti-vector immunity to improve immunogenicity to the insert antigen. Here we show that a homologous prime-boost regimen with a mixture of MVA (Modified Vaccinia virus Ankara) and Ad5 (human adenovirus type 5) vectors both expressing Ag85A in a single vaccine preparation is able to reduce anti-vector immunity, compared with a homologous prime-boost regimen with either vector alone. However, the level of immunogenicity induced by the homologous mixture remained comparable to that induced with single viral vectors and was less immunogenic than a heterologous Ad5 prime-MVA-boost regimen. These findings advance the understanding of how anti-vector immunity maybe reduced in viral vector vaccination regimens. Furthermore, an insight is provided to the impact on vaccine immunogenicity from altering vaccination methods to reduce the logistical demands of using separate vaccine preparations in the field.  相似文献   
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Most mAbs to the capsular polysaccharide glucuronoxylomannan (GXM) of Cryptococcus neoformans are generated from the same VH and VL gene families. Prior Ab studies have assessed protective efficacy, Id structure and binding to capsular polysaccharides, and peptide mimetics. These data have been interpreted as indicating that most mAbs to GXM have the same specificity. A new approach to Ab specificity analysis was investigated that uses genetic manipulation to generate C. neoformans variants with structurally different capsules. C. neoformans mutants expressing GXM with defective O-acetylation were isolated and complemented by the C. neoformans gene CAS1, which is necessary for the O-acetylation of GXM. The mAbs exhibited differences in their binding to the GXM from these mutant strains, indicating previously unsuspected differences in specificity. Analysis of three closely related IgMs revealed that one (mAb 12A1) bound to an epitope that did not require O-acetylation, another (mAb 21D2) was inhibited by O-acetylation, and the third (mAb 13F1) recognized an O-acetylation-dependent conformational epitope. Furthermore, an IgG Ab (mAb 18B7) in clinical development retained binding to de-O-acetylated polysaccharide; however, greater binding was observed to O-acetylated GXM. Our findings suggest that microbial genetic techniques can provide a new approach for epitope mapping of polysaccharide-binding Abs and suggest that this method may applicable for studying the antigenic complexity of polysaccharide Ags in other capsulated microorganisms.  相似文献   
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The chaperonin GroEL consists of a double-ring structure made of identical subunits and displays unusual allosteric properties caused by the interaction between its constituent subunits. Cooperative binding of ATP to a protein ring allows binding of GroES to that ring, and at the same time negative inter-ring cooperativity discharges the ligands from the opposite ring, thus driving the protein-folding cycle. Biochemical and electron microscopy analysis of wild type GroEL, a single-ring mutant (SR1), and two mutants with one inter-ring salt bridge of the chaperonin disrupted (E461K and E434K) indicate that these ion pairs form part of the interactions that allow the inter-ring allosteric signal to be transmitted. The wild type-like activities of the ion pair mutants at 25 degrees C are in contrast with their lack of inter-ring communication and folding activity at physiological temperatures. These salt bridges stabilize the inter-ring interface and maintain the inter-ring spacing so that functional communication between protein heptamers takes place. The characterization of GroEL hybrids containing different amounts of wild type and mutant subunits also indicates that as the number of inter-ring salt bridges increases the functional properties of the hybrids recover. Taken together, these results strongly suggest that inter-ring salt bridges form a stabilizing ring-shaped, ionic zipper that ensures inter-ring communication at the contact sites and therefore a functional protein-folding cycle. Furthermore, they regulate the chaperonin thermostat, allowing GroEL to distinguish physiological (37 degrees C) from stress temperatures (42 degrees C).  相似文献   
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Background

In patients with acute respiratory failure, gas exchange is impaired due to the accumulation of fluid in the lung airspaces. This life-threatening syndrome is treated with mechanical ventilation, which is adjusted to maintain gas exchange, but can be associated with the accumulation of carbon dioxide in the lung. Carbon dioxide (CO2) is a by-product of cellular energy utilization and its elimination is affected via alveolar epithelial cells. Signaling pathways sensitive to changes in CO2 levels were described in plants and neuronal mammalian cells. However, it has not been fully elucidated whether non-neuronal cells sense and respond to CO2. The Na,K-ATPase consumes ∼40% of the cellular metabolism to maintain cell homeostasis. Our study examines the effects of increased pCO2 on the epithelial Na,K-ATPase a major contributor to alveolar fluid reabsorption which is a marker of alveolar epithelial function.

Principal Findings

We found that short-term increases in pCO2 impaired alveolar fluid reabsorption in rats. Also, we provide evidence that non-excitable, alveolar epithelial cells sense and respond to high levels of CO2, independently of extracellular and intracellular pH, by inhibiting Na,K-ATPase function, via activation of PKCζ which phosphorylates the Na,K-ATPase, causing it to endocytose from the plasma membrane into intracellular pools.

Conclusions

Our data suggest that alveolar epithelial cells, through which CO2 is eliminated in mammals, are highly sensitive to hypercapnia. Elevated CO2 levels impair alveolar epithelial function, independently of pH, which is relevant in patients with lung diseases and altered alveolar gas exchange.  相似文献   
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Topoisomerase (Topo) IIIalpha associates with BLM helicase, which is proposed to be important in the alternative lengthening of telomeres (ALT) pathway that allows telomere recombination in the absence of telomerase. Here, we show that human Topo IIIalpha colocalizes with telomeric proteins at ALT-associated promyelocytic bodies from ALT cells. In these cells, Topo IIIalpha immunoprecipitated with telomere binding protein (TRF) 2 and BLM and was shown to be associated with telomeric DNA by chromatin immunoprecipitation, suggesting that these proteins form a complex at telomere sequences. Topo IIIalpha depletion by small interfering RNA reduced ALT cell survival, but did not affect telomerase-positive cell lines. Moreover, repression of Topo IIIalpha expression in ALT cells reduced the levels of TRF2 and BLM proteins, provoked a strong increase in the formation of anaphase bridges, induced the degradation of the G-overhang signal, and resulted in the appearance of DNA damage at telomeres. In contrast, telomere maintenance and TRF2 levels were unaffected in telomerase-positive cells. We conclude that Topo IIIalpha is an important telomere-associated factor, essential for telomere maintenance and chromosome stability in ALT cells, and speculate on its potential mechanistic function.  相似文献   
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