Disruption of cell/ECM interactions resulting from uncontrolled pericellular proteolysis leads to detachment-induced cell apoptosis (anoikis), contributing to the morbid evolution of inflammatory vascular diseases. During cardiovascular infections, bacterial proteinases might induce vascular cells to enter a similar pathway. We focused on LasB, the predominant metalloproteinase secreted by the haematotropic pathogen Pseudomonas aeruginosa. While the exosecretome of the LasB-deficient pseudomonal strain PAO1lasBΔ had limited impact on human vascular cell adherence and viability, secretomes from the LasB-expressing reference strain, PAO1, or clinical isolates from patients with cardiac infection all induced anoikis, as did purified LasB. Immunofluorescence and/or immunoblotting analysis of heart valve myofibroblast cultures or whole tissue revealed an extensive, LasB-dependent degradation of ECM-associated fibronectin and vitronectin, that preceded cell de-adherence, whereas type I collagen showed limited degradation. Moreover, LasB produced a rapid endoproteolysis of the cell-associated urokinase receptor/uPAR, leaving a truncated receptor that is unable to support cell adherence and survival via interactions with vitronectin and integrins. Conversely, major myofibroblast integrins showed no or only minor alterations. Thus, among P. aeruginosa-secreted metalloproteinases, LasB can induce vascular cell anoikis through simultaneous proteolysis of ECM components and cell receptors, suggesting the uPAR-vitronectin axis as a major target in this process. 相似文献
Endogenous small interfering RNAs (siRNAs) are a class of naturally occuring regulatory RNAs found in fungi, plants, and animals. Some endogenous siRNAs are required to silence transposons or function in chromosome segregation; however, the specific roles of most endogenous siRNAs are unclear. The helicase gene eri-6/7 was identified in the nematode Caenorhabditis elegans by the enhanced response to exogenous double-stranded RNAs (dsRNAs) of the null mutant. eri-6/7 encodes a helicase homologous to small RNA factors Armitage in Drosophila, SDE3 in Arabidopsis, and Mov10 in humans. Here we show that eri-6/7 mutations cause the loss of 26-nucleotide (nt) endogenous siRNAs derived from genes and pseudogenes in oocytes and embryos, as well as deficiencies in somatic 22-nucleotide secondary siRNAs corresponding to the same loci. About 80 genes are eri-6/7 targets that generate the embryonic endogenous siRNAs that silence the corresponding mRNAs. These 80 genes share extensive nucleotide sequence homology and are poorly conserved, suggesting a role for these endogenous siRNAs in silencing of and thereby directing the fate of recently acquired, duplicated genes. Unlike most endogenous siRNAs in C. elegans, eri-6/7-dependent siRNAs require Dicer. We identify that the eri-6/7-dependent siRNAs have a passenger strand that is ~19 nt and is inset by ~3-4 nts from both ends of the 26 nt guide siRNA, suggesting non-canonical Dicer processing. Mutations in the Argonaute ERGO-1, which associates with eri-6/7-dependent 26 nt siRNAs, cause passenger strand stabilization, indicating that ERGO-1 is required to separate the siRNA duplex, presumably through endonucleolytic cleavage of the passenger strand. Thus, like several other siRNA-associated Argonautes with a conserved RNaseH motif, ERGO-1 appears to be required for siRNA maturation. 相似文献
Barbary macaques, like other non-human primates living in highly seasonal temperate environments, display high monthly variations in their diet. In addition, their diet changes according to the habitat type they colonize and to the degree of habitat degradation due to resource exploitation by local people, in particular through pastoralism. We studied the time-budget adjustments of wild Barbary macaques in three cedar–oak forests impacted by different intensities of grazing pressure from goats and sheep. We examined how diet variations influenced the time monkeys spent in their activities and their day range lengths (i.e. their energy costs). At three studied sites, diet composition and time budgets showed marked seasonal variations. Diet composition had a strong influence on monkeys’ time budget. In the forest where pastoralism was the highest, diet included a greater proportion of underground resources, shrub fruit and acorns, which led to an increase in the time spent foraging and moving, as well as an important increase in day range lengths. Energy costs were therefore higher in a degraded environment than in a suitable habitat. The monkeys living in forests subjected to pastoralism took advantage of increased day lengths to spend more time searching for food. However, in the forest with the highest pastoralism pressure, although monkeys spent more time foraging, they spent less time feeding than monkeys at the other sites. In addition, they appeared to have reached the limits of the available time they could devote to these activities, as their diurnal resting time was at its lowest level over several months. Temperature variations did not appear to modify monkeys’ time budgets. In the least favourable habitat, saving time from resting activity allowed monkeys to maintain a relatively high level of social activity, partly linked to rearing constraints. 相似文献
The strategies by which intracellular pathogenic bacteria manipulate innate immunity to establish chronicity are poorly understood. Here, we show that Brucella abortus outer membrane protein Omp25 specifically binds the immune cell receptor SLAMF1 in vitro. The Omp25‐dependent engagement of SLAMF1 by B. abortus limits NF‐κB translocation in dendritic cells (DCs) with no impact on Brucella intracellular trafficking and replication. This in turn decreases pro‐inflammatory cytokine secretion and impairs DC activation. The Omp25‐SLAMF1 axis also dampens the immune response without affecting bacterial replication in vivo during the acute phase of Brucella infection in a mouse model. In contrast, at the chronic stage of infection, the Omp25/SLAMF1 engagement is essential for Brucella persistence. Interaction of a specific bacterial protein with an immune cell receptor expressed on the DC surface at the acute stage of infection is thus a powerful mechanism to support microbe settling in its replicative niche and progression to chronicity. 相似文献
Plant and Soil - Plant-parasitic nematodes are able to sense and respond to gradients of chemical signals. How pH and inorganic salts in the rhizosphere affect nematode accumulation and... 相似文献
Increasing ocean temperatures associated with ongoing climate change have resulted in regional reductions in the cover of live coral and increasing concerns that coral reefs will be overgrown by macroalgae. The likelihood of macroalgal overgrowth will, however, depend on the thermal sensitivities of the macroalgae themselves. We exposed recently settled propagules of the common canopy-forming macroalga Sargassum swartzii and adult thalli of three species of Sargassum (S. swatzii, S. cristaefolium, S. polycystum) to three experimental temperatures: ambient, + 2 °C, and + 3.5 °C, reflective of summer minimum, mean, and maximum temperatures for the region. Growth and survival of Sargassum swartzii propagules were assessed over 48 days, and the growth, physical toughness, elemental composition, and susceptibility to herbivory of adult thalli were assessed after short-term exposure (2-weeks) to experimental temperatures. Growth and survival of S. swartzii propagules were reduced by 43% and 84%, respectively, when cultured at the elevated (+ 3.5 °C) temperature compared to ambient temperature. Similarly, elevated temperature resulted in a 17–49% decline in the growth of adult Sargassum thalli relative to controls. Susceptability of S. swartzii and S. cristaefolium to herbivory (i.e. mass removed by herbivores) was 50% less for thalli cultured at elevated (+ 3.5 °C) compared to ambient temperature, but this pattern was not related to changes in the physical or chemical properties of the thalli as a result of elevated temperature. The negative effects of elevated temperatures on the growth and survival of both Sargassum propagules and adult thalli will likely restrict the capacity of Sargassum, and potentially other macroalgae, to establish in new areas, and may also threaten the persistence of existing macroalgal meadows under future ocean temperatures. The thermal sensitivities of tropical Sargassum, together with those of corals, suggest ongoing ocean warming may lead to novel reef ecosystems that are low in both coral cover and macroalgal cover.
ATP-sensitive K(+) (K(ATP)) channels are the target of a number of pharmacological agents, blockers like hypoglycemic sulfonylureas and openers like the hypotensive cromakalim and diazoxide. These agents act on the channel regulatory subunit, the sulfonylurea receptor (SUR), which is an ABC protein with homologies to P-glycoprotein (P-gp). P-gp is a multidrug transporter expressed in tumor cells and in some healthy tissues. Because these two ABC proteins both exhibit multispecific recognition properties, we have tested whether SUR ligands could be substrates of P-gp. Interaction with P-gp was assayed by monitoring ATPase activity of P-gp-enriched vesicles. The blockers glibenclamide, tolbutamide, and meglitinide increased ATPase activity, with a rank order of potencies that correlated with their capacity to block K(ATP) channels. P-gp ATPase activity was also increased by the openers SR47063 (a cromakalim analog), P1075 (a pinacidil analog), and diazoxide. Thus, these molecules bind to P-gp (although with lower affinities than for SUR) and are possibly transported by P-gp. Competition experiments among these molecules as well as with typical P-gp substrates revealed a structural similarity between drug binding domains in the two proteins. To rationalize the observed data, we addressed the molecular features of these proteins and compared structural models, computerized by homology from the recently solved structures of murine P-gp and bacterial ABC transporters MsbA and Sav1866. Considering the various residues experimentally assigned to be involved in drug binding, we uncovered several hot spots, which organized spatially in two main binding domains, selective for SR47063 and for glibenclamide, in matching regions of both P-gp and SUR. 相似文献
Semiconductor nanocrystals or quantum dots (QDs) are becoming widely used as fluorescent labels for biological applications. Here we demonstrate that fluorescence fluctuation analysis of their diffusional mobility using temporal image correlation spectroscopy is highly susceptible to systematic errors caused by fluorescence blinking of the nanoparticles. Temporal correlation analysis of fluorescence microscopy image time series of streptavidin-functionalized (CdSe)ZnS QDs freely diffusing in two dimensions shows that the correlation functions are fit well to a commonly used diffusion decay model, but the transport coefficients can have significant systematic errors in the measurements due to blinking. Image correlation measurements of the diffusing QD samples measured at different laser excitation powers and analysis of computer simulated image time series verified that the effect we observe is caused by fluorescence intermittency. We show that reciprocal space image correlation analysis can be used for mobility measurements in the presence of blinking emission because it separates the contributions of fluctuations due to photophysics from those due to transport. We also demonstrate application of the image correlation methods for measurement of the diffusion coefficient of glycosyl phosphatidylinositol-anchored proteins tagged with QDs as imaged on living fibroblasts. 相似文献