Pseudomonas exotoxin kills Drosophila S2 cells via apoptosis

Drosophila melanogaster as an organism model for studying cystic fibrosis and its major associated microbial infections

Cystic fibrosis (CF) is a human genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator gene that encodes a chloride channel. The most severe clinical manifestation is associated with chronic pulmonary infections by pathogenic and opportunistic microbes. Drosophila melanogaster has become the invertebrate model of choice for modeling microbial infections and studying the induced innate immune response. Here, we review its contribution to the understanding of infections with six major pathogens associated with CF (Staphylococcus aureus, Pseudomonas aeruginosa, Burkholderia cepacia, Mycobacterium abscessus, Streptococcus pneumoniae, and Aspergillus fumigatus) together with the perspectives opened by the recent availability of two CF models in this model organism.

Pseudomonas aeruginosa exotoxin A induces apoptosis in Galleria mellonella hemocytes

The cellular immune response of the greater wax moth Galleria mellonella to Pseudomonas aeruginosa exotoxin A was investigated for the first time. The insects were challenged with a sublethal dose of exoA, and then hemocyte parameters were assessed. The analysis showed a statistically significant decrease in the total hemocyte count (THC), which was associated with significant decreases in the number of granulocytes and plasmatocytes. In turn, no statistically significant changes were observed in the number of spherulocytes and oenocytoides. Fluorescent staining indicated that cells collected from the exoA-challenged larvae exhibited features characteristic for apoptotic and autophagic cell death, e.g. cytoplasm vacuolization and chromatin condensation. The flow cytometry analysis revealed a significant increase in the number of phosphatidylserine- and active caspase 3-positive hemocytes challenged with exoA, which proved apoptosis induction. Our results will help in understanding the role of exotoxin A during P. aeruginosa infections not only in insects but also in mammals, including humans.

Advances on Delivery of Cytotoxic Enzymes as Anticancer Agents

Cancer is one of the most serious human diseases, causing millions of deaths worldwide annually, and, therefore, it is one of the most investigated research disciplines. Developing efficient anticancer tools includes studying the effects of different natural enzymes of plant and microbial origin on tumor cells. The development of various smart delivery systems based on enzyme drugs has been conducted for more than two decades. Some of these delivery systems have been developed to the point that they have reached clinical stages, and a few have even found application in selected cancer treatments. Various biological, chemical, and physical approaches have been utilized to enhance their efficiencies by improving their delivery and targeting. In this paper, we review advanced delivery systems for enzyme drugs for use in cancer therapy. Their structure-based functions, mechanisms of action, fused forms with other peptides in terms of targeting and penetration, and other main results from in vivo and clinical studies of these advanced delivery systems are highlighted.

Host-pathogen interactions: The role of Pseudomonas aeruginosa exotoxin A in modulation of Galleria mellonella immune response

The role of Pseudomonas aeruginosa exotoxin A in the modulation of humoral immune response parameters in the hemolymph of Galleria mellonella larvae was investigated. Our results indicate that exoA can play a role of a virulence factor by inhibiting insect PO, lysozyme, and antibacterial activity and decreasing the apoLp-III protein level significantly. No peptide bands with molecular mass below 6.5 kDa were detected in the hemolymph of exoA-treated larvae. We provided evidence for involvement of exoA in the pathogenicity of P. aeruginosa against G. mellonella and the usefulness of the insect as a model for analysis of P. aeruginosa toxins.

Development of Anti-Virulence Therapeutics against Mono-ADP-Ribosyltransferase Toxins

Mono-ADP-ribosyltransferase toxins are often key virulence factors produced by pathogenic bacteria as tools to compromise the target host cell. These toxins are enzymes that use host cellular NAD⁺ as the substrate to modify a critical macromolecule target in the host cell machinery. This post-translational modification of the target macromolecule (usually protein or DNA) acts like a switch to turn the target activity on or off resulting in impairment of a critical process or pathway in the host. One approach to stymie bacterial pathogens is to curtail the toxic action of these factors by designing small molecules that bind tightly to the enzyme active site and prevent catalytic function. The inactivation of these toxins/enzymes is targeted for the site of action within the host cell and small molecule therapeutics can function as anti-virulence agents by disarming the pathogen. This represents an alternative strategy to antibiotic therapy with the potential as a paradigm shift that may circumvent multi-drug resistance in the offending microbe. In this review, work that has been accomplished during the past two decades on this approach to develop anti-virulence compounds against mono-ADP-ribosyltransferase toxins will be discussed.

Evidence for a rapid cold hardening response in cultured Drosophila S2 cells

The ability to quickly respond to changes in environmental temperature is critical for organisms living in thermally variable environments. To cope with sudden drops in temperature, insects and other ectotherms are capable of rapid cold hardening (RCH), in which mild chilling significantly enhances cold tolerance within minutes. While the ecological significance of RCH is well established, the mechanisms underlying RCH are still poorly understood. Previous work has demonstrated that RCH is regulated at the cellular level by post-translational signaling mechanisms, and here we tested the hypothesis that cultured cells are capable of RCH. A 2 h cold shock at -8°C significantly reduced the metabolic viability of Drosophila S2 cells, but pre-treatment with RCH at 4°C for 2 h prevented this decrease in viability. Thus, S2 cells are capable of RCH in a similar manner to whole insects and provide a new system for investigating the cell biology of RCH.

Selective staining and eradication of cancer cells by protein-carrying DARPin-functionalized liposomes

Since their discovery, liposomes have been widely employed in biomedical research. These nano-size spherical vesicles consisting one or few phospholipid bilayers surrounding an aqueous core are capable of carrying a wide variety of bioactive compounds, including drugs, peptides, nucleic acids, proteins and others. Despite considerable success achieved in synthesis of liposome constructs containing bioactive compounds, preparation of ligand-targeted liposomes comprising large quantities of encapsulated proteins that are capable of affecting pathological cells still remains a big challenge. Here we described a novel method for preparation of small (80-90 nm in diameter) unilamellar liposomes containing very large quantities (thousands of protein molecules per liposome) of heme-containing cytochrome c, highly fluorescent mCherry and highly toxic PE40 (Pseudomonas aeruginosa Exotoxin A domain). Efficient encapsulation of the proteins was achieved through electrostatic interaction between positively charged proteins (at pH lower than pI) and negatively charged liposome membrane. The proteoliposomes containing large quantities of mCherry or PE40 and functionalized with designed ankyrin repeat protein (DARPin)_9-29, which targets human epidermal growth factor receptor 2 (HER2) were shown to specifically stain and kill in sub-nanomolar concentrations HER2-positive cells, overexpressing HER2, respectively. Specific staining and eradication of the receptor-positive cells demonstrated here makes the DARPin-functionalized liposomes carrying large quantities of fluorescent and/or toxic proteins a promising candidate for tumor detection and therapy.

HER2-specific recombinant immunotoxin 4D5scFv-PE40 passes through retrograde trafficking route and forces cells to enter apoptosis

Immunotoxin 4D5scFv-PE40 is a recombinant protein that comprises 4D5scFv antibody as a targeting module and fragment of Pseudomonas exotoxin A as an effector (toxic) one. The immunotoxin has shown pronounced antitumor effect on cancer cells overexpressing HER2 receptor in vitro and on HER2-positive experimental tumors in vivo. We clarified the mechanism of 4D5scFv-PE40 activity that is of particular importance in the case of targeted therapeutic agent aimed at personalizing treatment of disease in relation to molecular genetic characteristics of each patient. After specific binding to HER2 on the cell surface and clathrin-mediated endocytosis the immunotoxin passes through retrograde trafficking route. During this route the immunotoxin molecule is supposed to undergo enzymatic processing that ends in separation of C-terminal and N-terminal fragments of the immunotoxin. Finally, C-terminal functionally active fragment of 4D5scFv-PE40 arrests protein synthesis in cytoplasm followed by cell death via apoptosis.

Structural complementation of the catalytic domain of pseudomonas exotoxin A

The catalytic moiety of Pseudomonas exotoxin A (domain III or PE3) inhibits protein synthesis by ADP-ribosylation of eukaryotic elongation factor 2. PE3 is widely used as a cytocidal payload in receptor-targeted protein toxin conjugates. We have designed and characterized catalytically inactive fragments of PE3 that are capable of structural complementation. We dissected PE3 at an extended loop and fused each fragment to one subunit of a heterospecific coiled coil. In vitro ADP-ribosylation and protein translation assays demonstrate that the resulting fusions-supplied exogenously as genetic elements or purified protein fragments-had no significant catalytic activity or effect on protein synthesis individually but, in combination, catalyzed the ADP-ribosylation of eukaryotic elongation factor 2 and inhibited protein synthesis. Although complementing PE3 fragments are catalytically less efficient than intact PE3 in cell-free systems, co-expression in live cells transfected with transgenes encoding the toxin fusions inhibits protein synthesis and causes cell death comparably as intact PE3. Complementation of split PE3 offers a direct extension of the immunotoxin approach to generate bispecific agents that may be useful to target complex phenotypes.

Metabolomic markers reveal novel pathways of ageing and early development in human populations

BACKGROUND

Human ageing is a complex, multifactorial process and early developmental factors affect health outcomes in old age.

METHODS

Metabolomic profiling on fasting blood was carried out in 6055 individuals from the UK. Stepwise regression was performed to identify a panel of independent metabolites which could be used as a surrogate for age. We also investigated the association with birthweight overall and within identical discordant twins and with genome-wide methylation levels.

RESULTS

We identified a panel of 22 metabolites which combined are strongly correlated with age (R(2) = 59%) and with age-related clinical traits independently of age. One particular metabolite, C-glycosyl tryptophan (C-glyTrp), correlated strongly with age (beta = 0.03, SE = 0.001, P = 7.0 × 10(-157)) and lung function (FEV1 beta = -0.04, SE = 0.008, P = 1.8 × 10(-8) adjusted for age and confounders) and was replicated in an independent population (n = 887). C-glyTrp was also associated with bone mineral density (beta = -0.01, SE = 0.002, P = 1.9 × 10(-6)) and birthweight (beta = -0.06, SE = 0.01, P = 2.5 × 10(-9)). The difference in C-glyTrp levels explained 9.4% of the variance in the difference in birthweight between monozygotic twins. An epigenome-wide association study in 172 individuals identified three CpG-sites, associated with levels of C-glyTrp (P < 2 × 10(-6)). We replicated one CpG site in the promoter of the WDR85 gene in an independent sample of 350 individuals (beta = -0.20, SE = 0.04, P = 2.9 × 10(-8)). WDR85 is a regulator of translation elongation factor 2, essential for protein synthesis in eukaryotes.

CONCLUSIONS

Our data illustrate how metabolomic profiling linked with epigenetic studies can identify some key molecular mechanisms potentially determined in early development that produce long-term physiological changes influencing human health and ageing.

A guide to taming a toxin--recombinant immunotoxins constructed from Pseudomonas exotoxin A for the treatment of cancer

Pseudomonas exotoxin A (PE) is a highly toxic protein secreted by the opportunistic pathogen Pseudomonas aeruginosa. The modular structure and corresponding mechanism of action of PE make it amenable to extensive modifications that can redirect its potent cytotoxicity from disease to a therapeutic function. In combination with a variety of artificial targeting elements, such as receptor ligands and antibody fragments, PE becomes a selective agent for the elimination of specific cell populations. This review summarizes our current understanding of PE, its intoxication pathway, and the ongoing efforts to convert this toxin into a treatment for cancer.