Mode of Action of the Sesquiterpene Lactones Psilostachyin and Psilostachyin C on Trypanosoma cruzi

Trypanosoma cruzi is the causative agent of Chagas’ disease, which is a major endemic disease in Latin America and is recognized by the WHO as one of the 17 neglected tropical diseases in the world. Psilostachyin and psilostachyin C, two sesquiterpene lactones isolated from Ambrosia spp., have been demonstrated to have trypanocidal activity. Considering both the potential therapeutic targets present in the parasite, and the several mechanisms of action proposed for sesquiterpene lactones, the aim of this work was to characterize the mode of action of psilostachyin and psilostachyin C on Trypanosoma cruzi and to identify the possible targets for these molecules. Psilostachyin and psilostachyin C were isolated from Ambrosia tenuifolia and Ambrosia scabra, respectively. Interaction of sesquiterpene lactones with hemin, the induction of oxidative stress, the inhibition of cruzipain and trypanothione reductase and their ability to inhibit sterol biosynthesis were evaluated. The induction of cell death by apoptosis was also evaluated by analyzing phosphatidylserine exposure detected using annexin-V/propidium iodide, decreased mitochondrial membrane potential, assessed with Rhodamine 123 and nuclear DNA fragmentation evaluated by the TUNEL assay. Both STLs were capable of interacting with hemin. Psilostachyin increased about 5 times the generation of reactive oxygen species in Trypanosoma cruzi after a 4h treatment, unlike psilostachyin C which induced an increase in reactive oxygen species levels of only 1.5 times. Only psilostachyin C was able to inhibit the biosynthesis of ergosterol, causing an accumulation of squalene. Both sesquiterpene lactones induced parasite death by apoptosis. Upon evaluating the combination of both compounds, and additive trypanocidal effect was observed. Despite their structural similarity, both sesquiterpene lactones exerted their anti-T. cruzi activity through interaction with different targets. Psilostachyin accomplished its antiparasitic effect by interacting with hemin, while psilostachyin C interfered with sterol synthesis.     

Predominance of Th2 cytokines, CXC chemokines and innate immunity mediators at the mucosal level during severe respiratory syncytial virus infection in children

Profiling of immune mediators in both nasal and plasma samples is a common approach to the study of pathogenesis in respiratory viral infections. Nevertheless, mucosal immunity functions essentially independently from peripheral immunity. In our study, 27 immune mediators were profiled in parallel, in nasopharyngeal aspirates (NPAs) and plasma from 22 < 2 year-old children with a severe respiratory syncytial virus infection involving the lower respiratory tract, using a multiplex assay. NPAs from 22 children with innocent heart murmurs were used as controls. Differences in mediator concentrations between NPAs from patients and controls were assessed using the Mann-Whitney test. Ratios of innate/adaptive-immunity mediators, Th2/Th1-cytokines and CXC/CC-chemokines were calculated for NPAs and plasmas and differences were assessed using the Wilcoxon test. Associations mediators, severity and leukocyte counts were studied using the Spearman-Karber test. Results: increased levels of Th1 cytokines (IL-1beta, IL-2, IL-12p70, IFNgamma, TNFalpha), Th2 cytokines (IL-13, IL-4, IL-6, IL-10), chemokines (IP-10, IL-8, MIP1alpha, MIP-1beta), growth factors (FGFb, PDGFbb, GCSF) and IL-1RA, IL-17 were observed in patient NPAs in comparison to controls. In the relative comparisons between patient NPAs and plasmas, a predominance of innate immunity mediators, Th2 cytokines and CXC chemokines was found at the mucosal level. No association between the level of each mediator in NPAs and plasma was found. In plasma, PDGFbb, VEGF, MIP-1alpha, IL-8 correlated with severity; RANTES and IL-6 correlated with leukocyte counts. Conclusions: acute respiratory syncytial virus infection induces a relative predominance of innate-immunity mediators, Th2 cytokines and CXC chemokines in the mucosal compartment in infected children.     

Stress-inducible flavodoxin from photosynthetic microorganisms. The mystery of flavodoxin loss from the plant genome

Flavodoxins (Flds) are mobile electron carriers containing flavin mononucleotide as the prosthetic group. They are isofunctional with the ubiquitous electron shuttle ferredoxin (Fd), mediating essentially the same redox processes among a promiscuous lot of donors and acceptors. While Fds are distributed throughout all kingdoms from prokaryotes to animals, Flds are only found in some bacteria and oceanic algae, in which they are induced to replace Fd functions under conditions of iron starvation and environmental stress that cause Fd decline. They thus play a key adaptive role in photosynthetic microorganisms, allowing survival and reproduction under adverse situations. The Fld gene disappeared from the plant genome somewhere between the green algal ancestor and the first terrestrial plants, and the advantages of this adaptive resource were irreversibly lost. However, reintroduction of a cyanobacterial Fld gene in the chloroplasts of transgenic tobacco resulted in remarkably enhanced tolerance to iron starvation and abiotic stress, indicating that the compensatory functions of Fld were still valuable in higher plants. A hypothesis is formulated to explain why Fld, in spite of its proven advantage, was lost from the plant genetic pool. The contention is based on two tenets: (i) iron availability was the major imperative for Fld conservation and adaptive value, and (ii) photosynthetic eukaryotes followed a succession of ecological adaptations, from the open oceans to coastal regions, and from there to the firm land, facing very different scenarios with respect to iron abundance and accessibility.     

The alternative translated MDMXp60 isoform regulates MDM2 activity

Isoforms derived from alternative splicing, mRNA translation initiation or promoter usage extend the functional repertoire of the p53, p63 and p73 genes family and of their regulators MDM2 and MDMX. Here we show cap-independent translation of an N-terminal truncated isoform of hMDMX, hMDMX^p60, which is initiated at the 7th AUG codon downstream of the initiation site for full length hMDMX^FL at position +384. hMDMX^p60 lacks the p53 binding motif but retains the RING domain and interacts with hMDM2 and hMDMX^FL. hMDMX^p60 shows higher affinity for hMDM2, as compared to hMDMX^FL. In vitro data reveal a positive cooperative interaction between hMDMX^p60 and hMDM2 and in cellulo data show that low levels of hMDMX^p60 promote degradation of hMDM2 whereas higher levels stabilize hMDM2 and prevent hMDM2-mediated degradation of hMDMX^FL. These results describe a novel alternatively translated hMDMX isoform that exhibits unique regulatory activity toward hMDM2 autoubiquitination. The data illustrate how the N-terminus of hMDMX regulates its C-terminal RING domain and the hMDM2 activity.     

CCS52 and DEL1 genes are key components of the endocycle in nematode‐induced feeding sites

The establishment of galls and syncytia as feeding sites induced by root‐knot and cyst nematodes, respectively, involves a progressive increase in nuclear and cellular size. Here we describe the functional characterization of endocycle activators CCS52A, CCS52B and a repressor of the endocycle, DEL1, during two types of nematode feeding site development in Arabidopsis thaliana. In situ hybridization analysis showed that expression of CCS52A1 and CCS52B was strongly induced in galls and syncytia and DEL1 was stably but weakly expressed throughout feeding site development. Down‐regulation and over‐expression of CCS52 and DEL1 in Arabidopsis drastically affected giant cell and syncytium growth, resulting in restrained nematode development, illustrating the need for mitotic activity and endo‐reduplication for feeding site maturation. Exploiting the mechanism of endo‐reduplication may be envisaged as a strategy to control plant‐parasitic nematodes.     

The function of peroxiredoxins in plant organelle redox metabolism

In 1996, cDNA sequences referred to as plant peroxiredoxins (Prx), i.e. a 1-Cys Prx and a 2-Cys Prx, were reported from barley. Ten years of research have advanced our understanding of plant Prx as thiol-based peroxide reductases with a broad substrate specificity, ranging from hydrogen peroxide to alkyl hydroperoxides and peroxinitrite. Prx have several features in common. (i) They are abundant proteins that are routinely detected in proteomics approaches. (ii) They interact with proteins such as glutaredoxins, thioredoxins, and cyclophilins as reductants, but also non-dithiol-disulphide exchange proteins. By work with transgenic plants, their activity was shown to (iii) affect metabolic integrity, (iv) protect DNA from damage in vitro and as shown here in vivo, and (v) modulate intracellular signalling related to reactive oxygen species and reactive nitrogen species. (vi) In all organisms Prx are encoded by small gene families that are of particular complexity in higher plants. A comparison of the Prx gene families in rice and Arabidopsis thaliana supports previous suggestions on Prx function in specific subcellular and metabolic context. (vii) Prx gene expression and activity are subjected to complex regulation realized by an integration of various signalling pathways. 2-Cys Prx expression depends on redox signals, abscisic acid, and protein kinase cascades. Besides these general properties, the chloroplast Prx have acquired specific roles in the context of photosynthesis. The thioredoxin-dependent peroxidase activity can be measured in crude plant extracts and contributes significantly to the overall H(2)O(2) detoxification capacity. Thus organellar Prx proteins enable an alternative water-water cycle for detoxification of photochemically produced H(2)O(2), which acts independently from the ascorbate-dependent Asada-Halliwell-Foyer cycle. 2-Cys Prx and Prx Q associate with thylakoid membrane components. The mitochondrial PrxII F is essential for root growth under stress. Following a more general introduction, the paper summarizes present knowledge on plant organellar Prx, addressing Prx in signalling, and also suggests some lines for future research.     

An octameric prokaryotic glutamine synthetase from the haloarchaeon Haloferax mediterranei

The glutamine synthetase (EC 6.3.1.2) from the haloarchaeon Haloferax mediterranei has been purified and characterized in order to understand the ammonium assimilation in haloarchaea. Based on sodium dodecyl sulfate polyacrylamide gel electrophoresis and gel-filtration chromatography, the enzyme consists of eight subunits of 51.7 kDa, suggesting that this enzyme belongs to the glutamine synthetase type II. The purified enzyme has been characterized with respect to its optimum temperature (45 degrees C) and pH value (8.0). The optimal NaCl or KCl concentrations for the reaction were 0.5 and 0.25 M, respectively. The effect of l-methionine-d, l-sulphoximine and different divalent metal ions has also been tested. The glutamine synthetase presented here is unusual; it shows the typical characteristic of eukaryotic and soil bacteria glutamine synthetases.