A Toxoplasma type 2C serine-threonine phosphatase is involved in parasite growth in the mammalian host cell

Toxoplasma gondii is a human protozoan parasite that belongs to the phylum of Apicomplexa and causes toxoplasmosis. As the other members of this phylum, T. gondii obligatory multiplies within a host cell by a peculiar type of mitosis that leads to daughter cell assembly within a mother cell. Although parasite growth and virulence have been linked for years, few molecules controlling mitosis have been yet identified and they include a couple of kinases but not the counteracting phosphatases. Here, we report that in contrast to other animal cells, type 2C is by far the major type of serine threonine phosphatase activity both in extracellular and in intracellular dividing parasites. Using wild type and transgenic parasites, we characterized the 37 kDa TgPP2C molecule as an abundant cytoplasmic and nuclear enzyme with activity being under tight regulation. In addition, we showed that the increase in TgPP2C activity significantly affected parasite growth by impairing cytokinesis while nuclear division still occurred. This study supports for the first time that type 2C protein phosphatase is an important regulator of cell growth in T. gondii.     

Genotype-specific interactions and the trade-off between host and parasite fitness

Background  

Evolution of parasite traits is inextricably linked to their hosts. For instance one common definition of parasite virulence is the reduction in host fitness due to infection. Thus, traits of infection must be viewed in both protagonists and may be under shared genetic and physiological control. We investigated these questions on the oomycete Hyaloperonospora arabidopsis (= parasitica), a natural pathogen of the Brassicaceae Arabidopsis thaliana.     

RGD Surface Functionalization of the Hydrophilic Acrylic Intraocular Lens Material to Control Posterior Capsular Opacification

Posterior Capsular Opacification (PCO) is the capsule fibrosis developed on implanted IntraOcular Lens (IOL) by the de-differentiation of Lens Epithelial Cells (LECs) undergoing Epithelial Mesenchymal Transition (EMT). Literature has shown that the incidence of PCO is multifactorial including the patient''s age or disease, surgical technique, and IOL design and material. Reports comparing hydrophilic and hydrophobic acrylic IOLs have shown that the former has more severe PCO. On the other hand, we have previously demonstrated that the adhesion of LECs is favored on hydrophobic compared to hydrophilic materials. By combining these two facts and contemporary knowledge in PCO development via the EMT pathway, we propose a biomimetically inspired strategy to promote LEC adhesion without de-differentiation to reduce the risk of PCO development. By surface grafting of a cell adhesion molecule (RGD peptide) onto the conventional hydrophilic acrylic IOL material, the surface-functionalized IOL can be used to reconstitute a capsule-LEC-IOL sandwich structure, which has been considered to prevent PCO formation in literature. Our results show that the innovative biomaterial improves LEC adhesion, while also exhibiting similar optical (light transmittance, optical bench) and mechanical (haptic compression force, IOL injection force) properties compared to the starting material. In addition, compared to the hydrophobic IOL material, our bioactive biomaterial exhibits similar abilities in LEC adhesion, morphology maintenance, and EMT biomarker expression, which is the crucial pathway to induce PCO. The in vitro assays suggest that this biomaterial has the potential to reduce the risk factor of PCO development.     

Combined effects of chlorpromazine and high fat diet on lipid levels and enzyme activities in bile, liver and plasma of Wistar rats

The effects of high fat diet and injection of chlorpromazine on bile lipid secretion were studied in the rats fed a control diet (C), a saturated fat, high cholesterol diet (S) and a polyunsaturated fat, high cholesterol diet (PU). As compared to controls, injection of chlorpromazine in the S and PU diet groups caused no appreciable change in the level of bile salts and bile phospholipids. Chlorpromazine did however enhance bile cholesterol, especially in the PU group, and lower secretion of lysosomal enzyme (beta-glucuronidase) into bile. Impairment of lysosomal enzyme secretion but not of bile lipid secretion suggests that the lysosomal activity is not directly involved in the bile secretion mechanism. These data point up the risks of using chlorpromazine therapy in association with a diet high in fat and cholesterol.     

Acute effects of filipin on the plasmic, hepatic, and biliary cholesterol of the rat

Twenty-one male Wistar rats, 13 weeks old, were fed ad libitum hyperlipidic diets (28% fats) loaded with cholesterol (1.2%) for 5 weeks. One group of 11 rats was fed saturated fats (diet group "S") and another group of 10 rats was fed polyunsaturated fats (diet group "PU"). On the day they were sacrificed 10 of the rats were injected intravenously with 1 mg of filipin. Contrary to the rats in diet group "PU," the rats in diet group "S" treated with filipin presented certain characteristics that were not found in the nontreated group: They provided evidence of biliary cholestasis accompanied by a decline in the level of secretion of bile salts and phospholipids into bile. The concentrations of both free and esterified cholesterol in plasma fell and the amount of (esterified) hepatic cholesterol rose, although there was no change due to the filipin in the amounts of hepatic phospholipids. Explanatory hypotheses for these phenomena were considered, first, at the site of plasma membranes where filipin binds selectively to the cholesterol in the membrane, causing a disruption which probably disturbs the absorbance of circulating lipoproteins, especially that of hepatocyte cells, particularly in diet group "PU." Second, the effects of filipin on subcellular membranes seem to disturb the secretion of lipids and lipoproteins into bile and plasma, especially in diet group "S." Last, at the intracellular level, filipin appears to have a blocking effect on the organelles involved in biliary lipid secretion. The activity of certain enzymes such as cholesterol esterase may also be blocked, particularly in diet group "S," which would explain the accumulation of esterified cholesterol in liver.     

A quantitative dynamic concept of the interphase partition of lipids: application to bile salt-lecithin-cholesterol mixed micelles

A system is proposed for a quantitative classification of lipids, based on interphase partition coefficients. This system enables calculation of exchanges of lipid molecules between phases. The mass/volume chemical unit mol X cm-3, strictly derived from the CGS system, is used, thus simplifying mathematical relations. Applied to bile salt-lecithin-cholesterol mixed micelles, this dynamic concept gives new insight into the variations of physico-chemical parameters. Experimental results obtained with the glycodesoxycholate and the taurocholate show a striking difference in partition coefficients between aqueous and mixed bile salt-lecithin interfacial phases. A new model applying triangular co-ordinates to a bile salt-lecithin-cholesterol mixed lipid phase is described.     

Effects of dietary corn oil and salmon oil on the oxidation of fatty acids and prostaglandin E2 in rat gastric mucosa

The investigations previously carried out by Grataroli and colleagues (1) to elucidate the relationships between dietary fatty acids, lipid composition, prostaglandin E2 production and phospholipase A2 activity in the rat gastric mucosa are, here, extended. In the present investigations, fatty acid and prostaglandin E2 catabolizing enzymes were assayed in gastric mucosa from rats fed either a low fat diet (corn oil: 4.4% w/w) (referred as control group), a corn oil-enriched diet (17%) or a salmon oil-enriched diet (12.5%) supplemented with corn oil (4.5%) (referred as groups of treated animals) for eight weeks.Peroxisomal fatty acyl-CoA β-oxidation was induced in the treated animals whereas the activities of catalase and mitochondrial tyramine oxidase were increased and normal, respectively. Mitochondrial acyl-CoA dehydrogenations occured at higher rates and carnitine acyltransferase activities were enhanced. In addition, the induction of peroxisomal but not mitochondrial prostaglandoyl-E2-CoA β-oxidation could be demonstrated. Induction of peroxisomal oxidation of fatty acids and prostaglandins is suggested to contribute to the decrease of prostaglandin E2 production in the treated animals, especially those receiving the salmon oil diet, that the above mentioned authors originally reported.     

Cell cycle dependent distribution of a centrosomal antigen at the perinuclear MTOC or at the kinetochores of higher plant cells

Compelling evidence has been obtained in favour of the idea that the nuclear surface of higher plant cells is a microtubule-nucleating and/or organizing site (MTOC), in the absence of defined centrosomes. How these plant MTOC proteins are redistributed and function during the progression of the cell cycle remains entirely unknown. Using a monoclonal antibody (mAb 6C6) raised against isolated calf thymus centrosomes and showing apparent reaction with the plant nuclear surface, we followed the targeted antigen distribution during mitosis and meiosis of higher plants. Immunoblot analysis of protein fractions from Allium root meristematic cell extracts probed with mAb 6C6 reveals a polypeptide of an apparent Mr of 78000. In calf centrosome extracts, a polypeptide of comparable molecular mass is found in addition to a major antigen of Mr 180000 after mAb 6C6 immunoblotting. During mitotic initiation, the plant antigen is prominent on the periphery of the prophase nucleus. When the nuclear envelope breaks down, the antigen suddenly becomes associated with the centromere-kinetochores until late anaphase. In telophase, when the nuclear envelope is being reconstructed, it is no longer detected at the kinetochores but is solely associated again with the nuclear surface. This antigen displays a unique spatial and temporal distribution, which may reflect the pathway of plant protein(s) between the nuclear surface and the kinetochores under cell cycle control. So far, such processes have not been described in higher plant cells. These observations shed light on the putative activity of the plant kinetochore as a protein transporter. They also suggest that a plant centrosome-like antigen may have different cytoskeletal related functions depending on cell cycle regulated changes in its subcellular distribution.Abbreviations mAb monoclonal antibody - MSB microtubule stabilizing buffer - TBS Tris buffered saline - MTOC microtubule organizing centre