Platelet-activating factor induction of secreted phosphatase activity in Trypanosoma cruzi

Elevated extracellular inorganic phosphate inhibits ecto-phosphatase activity in breast cancer cells: Regulation by hydrogen peroxide

For cells to obtain inorganic phosphate, ectoenzymes in the plasma membrane, which contain a catalytic site facing the extracellular environment, hydrolyze phosphorylated molecules. In this study, we show that increased Pi levels in the extracellular environment promote a decrease in ecto-phosphatase activity, which is associated with Pi-induced oxidative stress. High levels of Pi inhibit ecto-phosphatase because Pi generates H2 O2 . Ecto-phosphatase activity is inhibited by H2 O2 , and this inhibition is selective for phospho-tyrosine hydrolysis. Additionally, it is shown that the mechanism of inhibition of ecto-phosphatase activity involves lipid peroxidation. In addition, the inhibition of ecto-phosphatase activity by H2 O2 is irreversible. These findings have new implications for understanding ecto-phosphatase regulation in the tumor microenvironment. H2 O2 stimulated by high Pi inhibits ecto-phosphatase activity to prevent excessive accumulation of extracellular Pi, functioning as a regulatory mechanism of Pi variations in the tumor microenvironment.

Functional characterization of maternally accumulated hydrolases in the mature oocytes of the vector Rhodnius prolixus reveals a new protein phosphatase essential for the activation of the yolk mobilization and embryo development

Yolk biogenesis and consumption have been well conserved in oviparous animals throughout evolution. Most egg-laying animals store yolk proteins within the oocytes' yolk granules (Ygs). Following fertilization, the Ygs participate in controlled pathways of yolk breakdown to support the developing embryo's anabolic metabolism. While the unfolding of the yolk degradation program is a crucial process for successful development in many species, the molecular mechanisms responsible for yolk mobilization are still mysterious and have mostly not been explored. Here, we investigate the functional role of the oocyte maternally accumulated mRNAs of a protein phosphatase (PP501) and two aspartic proteases (cathepsin-D 405, CD405 and cathepsin-D 352, CD352) in the yolk degradation and reproduction of the insect vector of Chagas disease Rhodnius prolixus. We found that PP501 and CD352 are highly expressed in the vitellogenic ovary when compared to the other organs of the adult insect. Parental RNAi silencing of PP501 resulted in a drastic reduction in oviposition and increased embryo lethality whereas the silencing of CD352 resulted only in a slight decrease in oviposition and embryo viability. To further investigate the PP501-caused high reproduction impairment, we investigated the Ygs biogenesis during oocyte maturation and the activation of the yolk degradation program at early development. We found that the Ygs biogenesis was deficient during oogenesis, as seen by flow cytometry, and that, although the PP501-silenced unviable eggs were fertilized, the Ygs acidification and acid phosphatase activity were affected, culminating in a full impairment of the yolk proteins degradation at early embryogenesis. Altogether we found that PP501 is required for the oocyte maturation and the activation of the yolk degradation, being, therefore, essential for this vector reproduction.

A novel receptor for platelet-activating factor and lysophosphatidylcholine in Trypanosoma cruzi

The lipid mediators, platelet-activating factor (PAF) and lysophosphatidylcholine (LPC), play relevant pathophysiological roles in Trypanosoma cruzi infection. Several species of LPC, including C18:1 LPC, which mimics the effects of PAF, are synthesized by T. cruzi. The present study identified a receptor in T. cruzi, which was predicted to bind to PAF, and found it to be homologous to members of the progestin and adiponectin family of receptors (PAQRs). We constructed a three-dimensional model of the T. cruzi PAQR (TcPAQR) and performed molecular docking to predict the interactions of the TcPAQR model with C16:0 PAF and C18:1 LPC. We knocked out T. cruzi PAQR (TcPAQR) gene and confirmed the identity of the expressed protein through immunoblotting and immunofluorescence assays using an anti-human PAQR antibody. Wild-type and knockout (KO) parasites were also used to investigate the in vitro cell differentiation and interactions with peritoneal mouse macrophages; TcPAQR KO parasites were unable to react to C16:0 PAF or C18:1 LPC. Our data are highly suggestive that PAF and LPC act through TcPAQR in T. cruzi, triggering its cellular differentiation and ability to infect macrophages.

Lysophosphatidylcholine triggers cell differentiation in the protozoan parasite Herpetomonas samuelpessoai through the CK2 pathway

BACKGROUND

Protozoa are distantly related to vertebrates but present some features of higher eukaryotes, making them good model systems for studying the evolution of basic processes such as the cell cycle. Herpetomonas samuelpessoai is a trypanosomatid parasite isolated from the hemipteran insect Zelus leucogrammus. Lysophosphatidylcholine (LPC) is implicated in the transmission and establishment of Chagas disease, whose etiological agent is Trypanosoma cruzi. LPC is synthesized by T. cruzi and its vectors, the hemipteran Rhodnius prolixus and Triatoma infestans. Platelet-activating factor (PAF), a phospholipid with potent and diverse physiological and pathophysiological actions, is a powerful inducer of cell differentiation in Herpetomonas muscarum muscarum and T. cruzi. The enzyme phospholipase A₂ (PLA₂) catalyzes the hydrolysis of the 2-ester bond of 3-sn-phosphoglyceride, transforming phosphatidylcholine (PC) into LPC.

METHODS

In this study, we evaluated cellular differentiation, PLA₂ activity and protein kinase CK2 activity of H. samuelpessoai in the absence and in the presence of LPC and PAF.

RESULTS

We demonstrate that both PC and LPC promoted a twofold increase in the cellular differentiation of H. samuelpessoai, through CK2, with a concomitant inhibition of its cell growth. Intrinsic PLA₂ most likely directs this process by converting PC into LPC.

CONCLUSIONS

Our results suggest that the actions of LPC on H. samuelpessoai occur upon binding to a putative PAF receptor and that the protein kinase CK2 plays a major role in this process. Cartoon depicting a model for the synthesis and functions of LPC in Herpetomonas samuelpessoai, based upon our results regarding the role of LPC on the cell biology of Trypanosoma cruzi [28-32]. N nucleus, k kinetoplast, PC phosphatidylcholine, LPC lysophosphatidylcholine, PLA₂ phospholipase A₂, PAFR putative PAF receptor in trypanosomatids [65], CK2 protein kinase CK2 [16].

Biochemical properties and possible roles of ectophosphatase activities in fungi

Ectophosphatases are surface membrane-bound proteins whose active sites face the extracellular medium. These enzymes have been reported in several microorganisms including a large number of medically relevant fungal species. An effective technique for identifying ectophosphatases is performing phosphatase activity assays using living intact cells. Biochemical characterization of these activities has shown their differential modulation by classical phosphatase inhibitors, divalent metals and pH range. The physiological roles of ectophosphatases are not well established; however, it has been suggested that these enzymes play important roles in nutrition, proliferation, differentiation, adhesion, virulence and infection. Adhesion to host cells is the first step in establishing a fungal infection and ectophosphatases may be one of the first parasite proteins that come into contact with the host cells. Several results indicate that ectophosphatase activities increase the capacity of fungi to adhere to the host cells. In this context, the present review provides an overview of recent discoveries related to the occurrence and possible roles of ectophosphatase activities in fungal cells.

Ecto-nucleotidases and Ecto-phosphatases from Leishmania and Trypanosoma parasites

Ecto-enzymes can be defined as membrane-bound proteins that have their active site facing the extracellular millieu. In trypanosomatids, the physiological roles of these enzymes remain to be completed elucidated; however, many important events have already been related to them, such as the survival of parasites during their complex life cycle and the successful establishment of host infection. This chapter focuses on two remarkable classes of ecto-enzymes: ecto-nucleotidases and ecto-phosphatases, summarizing their occurrence and possible physiological roles in Leishmania and Trypanosoma genera. Ecto-nucleotidases are characterized by their ability to hydrolyze extracellular nucleotides, playing an important role in purinergic signaling. By the action of these ecto-enzymes, parasites are capable of modulating the host immune system, which leads to a successful parasite infection. Furthermore, ecto-nucleotidases are also involved in the purine salvage pathway, acting in the generation of nucleosides that are able to cross plasma membrane via specialized transporters. Another important ecto-enzyme present in a vast number of pathogenic organisms is the ecto-phosphatase. These enzymes are able to hydrolyze extracellular phosphorylated substrates, releasing free inorganic phosphate that can be internalized by the cell, crossing the plasma membrane through a Pi-transporter. Ecto-phosphatases are also involved in the invasion and survival of parasite in the host cells. Several alternative functions have been suggested for these enzymes in parasites, such as participation in their proliferation, differentiation, nutrition and protection. In this context, the present chapter provides an overview of recent discoveries related to the occurrence of ecto-nucleotidase and ecto-phosphatase activities in Leishmania and Trypanosoma parasites.

Possible roles of ectophosphatases in host-parasite interactions

The interaction and survival of pathogens in hostile environments and in confrontation with host immune responses are important mechanisms for the establishment of infection. Ectophosphatases are enzymes localized at the plasma membrane of cells, and their active sites face the external medium rather than the cytoplasm. Once activated, these enzymes are able to hydrolyze phosphorylated substrates in the extracellular milieu. Several studies demonstrated the presence of surface-located ecto-phosphatases in a vast number of pathogenic organisms, including bacteria, protozoa, and fungi. Little is known about the role of ecto-phosphatases in host-pathogen interactions. The present paper provides an overview of recent findings related to the virulence induced by these surface molecules in protozoa and fungi.

Characterization of an ecto-5'-nucleotidase activity present on the cell surface of Tritrichomonas foetus

Tritrichomonas foetus is the causative agent of sexually transmitted trichomoniasis in cattle. In females, the infection can be associated with infertility, vaginitis, endometritis, abortion or pyometra, leading to significant economic losses in cattle raising. T. foetus is devoid of the ability to synthesize purine nucleotides de novo, depending instead on salvaging purines from the host environment. Ecto-5'-nucleotidase catalyzes the final step of extracellular nucleotide degradation, the hydrolysis of nucleoside 5'-monophosphates to the corresponding nucleosides and Pi. In this work we show that living, intact cells of T. foetus were able to hydrolyze 5'AMP at a rate of 12.57 ± 1.23 nmol Pi × h(-1) × 10(-7) cells at pH 7.2 and the 5'AMP hydrolysis is due to a plasma membrane-bound ecto-enzyme activity. The apparent K(m) for 5'AMP was 0.49 ± 0.06 mM. In addition to 5'AMP, the enzyme hydrolyzed all substrate monophosphates tested except 3'AMP. No divalent metals or metal chelators were able to modulate enzyme activity. Phosphatase inhibitors did not have an effect on ecto-5'-nucleotidase activity while ammonium molybdate did inhibit the activity in a dose dependent manner. The presence of adenosine in the culture medium negatively modulated the enzyme. These results indicate the existence of an ecto-5'-nucleotidase that may play a role in the salvage of purines.

Inflammation and Chagas disease some mechanisms and relevance

Chagas cardiomyopathy is caused by infection with flagellated protozoan Trypanosoma cruzi. In patients, there is a fine balance between control of the replication and the intensity of the inflammatory response so that the host is unable to eliminate the parasite resulting in the parasite persisting as a lifelong infection in most individuals. However, the parasite persists in such a way that it causes no or little disease. This chapter reviews our understanding of many of the mediators of inflammation and cells which are involved in the inflammatory response of mammals to T. cruzi infection. Particular emphasis is given to the role of chemokines, endothelin and lipid mediators. Understanding the full range of mediators and cells present and how they interact with each other in Chagas disease may shed light on how we modulate disease pathogenesis and define new approaches to treat or prevent the disease.

Stimulation of Leishmania tropica protein kinase CK2 activities by platelet-activating factor (PAF)

Leishmania tropica is one of the causative agents of cutaneous leishmaniasis. Platelet-activating factor (PAF) is a phospholipid mediator in diverse biological and pathophysiological processes. Here we show that PAF promoted a three-fold increase on ecto-protein kinase and a three-fold increase on the secreted kinase activity of L. tropica live promastigotes. When casein was added to the reaction medium, along with PAF, there was a four-fold increase on the ecto-kinase activity. When live L. tropica promastigotes were pre-incubated for 30 min in the presence of PAF-plus casein, a six-fold increase on the secreted kinase activity was observed. Also, a protein released from L. tropica promastigotes reacted with polyclonal antibodies for the mammalian CK2 alpha catalytic subunit. Furthermore, in vitro mouse macrophage infection by L. tropica was doubled when promastigotes were pre-treated for 2 h with PAF. Similar results were obtained when the interaction was performed in the presence of purified CK2 or casein. TBB and DRB, CK2 inhibitors, reversed PAF enhancement of macrophage infection by L. tropica. WEB 2086, a competitive PAF antagonist, reversed all PAF effects here described. This study shows for the first time that PAF promotes the activation of two isoforms of CK2, secreted and membrane-bound, correlating these activities to infection of mouse macrophages.

Mycelial forms of Pseudallescheria boydii present ectophosphatase activities

Phosphatase activities were characterized in intact mycelial forms of Pseudallescheria boydii, which are able to hydrolyze the artificial substrate p-nitrophenylphosphate (p-NPP) to p-nitrophenol (p-NP) at a rate of 41.41+/-2.33 nmol p-NP per h per mg dry weight, linearly with increasing time and with increasing cell density. MgCl2, MnCl2 and ZnCl2 were able to increase the (p-NPP) hydrolysis while CdCl2 and CuCl2 inhibited it. The (p-NPP) hydrolysis was enhanced by increasing pH values (2.5-8.5) over an approximately 5-fold range. High sensitivity to specific inhibitors of alkaline and acid phosphatases suggests the presence of both acid and alkaline phosphatase activities on P. boydii mycelia surface. Cytochemical localization of the acid and alkaline phosphatase showed electron-dense cerium phosphate deposits on the cell wall, as visualized by electron microscopy. The product of p-NPP hydrolysis, inorganic phosphate (Pi), and different inhibitors for phosphatase activities inhibited p-NPP hydrolysis in a dose-dependent manner, but only the inhibition promoted by sodium orthovanadate and ammonium molybdate is irreversible. Intact mycelial forms of P. boydii are also able to hydrolyze phosphoaminoacids with different specificity.

Entamoeba histolytica: An ecto-phosphatase activity regulated by oxidation–reduction reactions

In this work, an ecto-phosphatase activity of Entamoeba histolytica was characterized using intact cells. This activity presented the following biochemical characteristics: (i) it hydrolyzes p-NPP with V(max) of 8.00+/-0.22 nmol p-NP x h(-1) x 10(-5) cells and K(m) of 2.68+/-0.25 mM; (ii) it is inhibited by acid phosphatase inhibitors, such as sodium molybdate (K(i)=1.70+/-0.24 microM) and sodium fluoride (K(i)=0.25+/-0.02 mM); (iii) it also showed high sensitivity to phosphotyrosine phosphatase inhibitors, such as sodium orthovanadate (K(i)=1.07+/-0.14 microM), bpV-PHEN (K(i)=0.38+/-0.02 microM) and mpV-PIC (K(i)=0.39+/-0.04 microM). Zn(2+), an oxidizing agent, decreased the enzymatic activity in 50%. DTT and GSH, two reducing agents, enhanced the activity twofold. The non-invasive E. histolytica and free-living E. moshkovskii were less efficient in hydrolyzing p-NPP than the pathogenic E. histolytica suggesting that this enzyme could represent a virulence marker for this cell.

Iron modulates ecto-phosphohydrolase activities in pathogenic trichomonads

The presence of iron in the extracellular medium is essential for both in vivo and in vitro survival of pathogenic microorganisms, including Trichomonas vaginalis and Tritrichomonas foetus. In these parasites, iron is directly involved in the proliferation, protein expression and activation of critical enzymes. The purpose of this study was to investigate the role of iron in ecto-ATPase, ecto-phophatase and secreted phosphatase activities of these trichomonads. We observed that trichomonads grown in iron-depleted medium exhibited a remarkable decrease in both ecto-ATPase and ecto-phosphatase activities, when compared to those cultivated under control conditions (iron-rich medium). Furthermore, parasites grown in iron-depleted medium restored their enzyme activities when they were re-inoculated into fresh iron-rich medium. We demonstrated that modulation of ecto-phosphohydrolase activities is due neither to enzyme-iron nor to substrate-iron complex formation, since iron addition directly to the medium where the enzymatic reactions occurred did not alter their activities. Previously, we had reported that a fresh clinical isolate of T. vaginalis was much more cytotoxic to epithelial cell monolayers than a long-term cultured one. In this study we witnessed that the fresh isolate of T. vaginalis presented higher activities to all herein investigated enzymes than the long-term cultured one. Altogether, our data clearly point out that iron has a pivotal role in the expression of phosphohydrolases in both trichomonads.

Characterization of ecto-phosphatase activities of Trypanosoma cruzi: a comparative study between Colombiana and Y strains

The etiological agent of Chagas disease, Trypanosoma cruzi, is consisted of two phylogenetic lineages. Using live epimastigotes, in this study we have characterized ecto-phosphatase activities of two strains of T. cruzi, one (Y strain) is a member of group T. cruzi I and the other (Colombiana) is a member of group T. cruzi II. About one-third of the total ecto-phosphatase activity from the Y strain was Mg(2+)-dependent, but no such activity was observed with Colombiana. The level of Mg(2+)-independent activity was dramatically different in the two strains, with Colombiana showing more than 15-fold higher activity. Experiments using classical inhibitors of acid phosphatases, as well as inhibitors of phosphotyrosine phosphatase, showed a decrease in these phosphatase activities, with different patterns of inhibition. The Mg(2+)-independent activities of the Colombiana and Y strains decreased inversely with pH, varying from 6.5 to 8.0. On the other hand, the Mg(2+)-dependent activity of the Y strain increased concomitantly with the increase in pH in the same range.

Pho5p and newly identified nucleotide pyrophosphatases/ phosphodiesterases regulate extracellular nucleotide phosphate metabolism in Saccharomyces cerevisiae

Extracellular nucleotides play many biological roles, including intercellular communication and modulation of nucleotide receptor signaling, and are dependent on the phosphorylation state of the nucleotide. Regulation of nucleotide phosphorylation is necessary, and a specialized class of enzymes, nucleotide pyrophosphatases/phosphodiesterases (E-NPPs), has been identified in mammals to perform this function. Although the E-NPP class is conserved among complex eukaryotes, this system has not yet been identified in Saccharomyces cerevisiae. Using genetic and biochemical experiments, we show that two orthologs of the E-NPP family, referred to as Npp1p and Npp2p, exist in budding yeast and can perform nucleotide phosphate hydrolysis. This activity is enhanced during phosphate starvation, where hydrolyzed phosphates can be imported from extracellular sources and utilized to overcome phosphate starvation through the activity of the Pho5p acid phosphatase. The added compensatory effect by Pho5p is also a newly established role for Pho5p. This study demonstrates that extracellular nucleotide phosphate metabolism appears to be controlled by at least two independent regulatory mechanisms, uniting phosphate starvation with extracellular nucleotide regulation.

Platelet-activating factor-like activity isolated from Trypanosoma cruzi

Platelet-activating factor is a phospholipid mediator that exhibits a wide variety of physiological and pathophysiological effects, including induction of inflammatory response, chemotaxis and cellular differentiation. Trypanosoma cruzi, the etiological agent of Chagas' disease, is transmitted by triatomine insects and while in the triatomine midgut the parasite differentiates from a non-infective epimastigote stage into the pathogenic trypomastigote metacyclic form. We have previously demonstrated that platelet activating factor triggers in vitro cell differentiation of T. cruzi. Here we show a platelet activating factor-like activity isolated from lipid extract of T. cruzi epimastigotes incubated in the presence of [14C]acetate. Trypanosoma cruzi-platelet activating factor-like lipid induced the aggregation of rabbit platelets, which was prevented by platelet activating factor-acetylhydrolase. Mouse macrophage infection by T. cruzi was stimulated when epimastigotes were kept for 5 days in the presence of T. cruzi-platelet activating factor, before interacting with the macrophages. The differentiation of epimastigotes into metacyclic trypomastigotes was also triggered by T. cruzi-platelet activating factor. These effects were abrogated by a platelet activating factor antagonist, WEB 2086. Polyclonal antibody raised against mouse platelet activating factor receptor showed labelling for T. cruzi epimastigotes using immunoblotting and immunofluorescence assays. These data suggest that T. cruzi contain the components of an autocrine platelet activating factor-like ligand-receptor system that modulates cell differentiation towards the infectious stage.

Trypanosoma rangeli: Differential expression of cell surface polypeptides and ecto-phosphatase activity in short and long epimastigote forms

Trypanosoma rangeli is a parasite of a numerous wild and domestic animals, presenting wide geographical distribution and high immunological cross-reactivity with Trypanosoma cruzi, which may lead to misdiagnosis. T. rangeli has a complex life cycle, involving distinct morphological and functional forms in the vector. Here, we characterized the cell surface polypeptides and the phosphatase activities in short and long epimastigotes forms of T. rangeli, using intact living parasites. The surface protein profile revealed by the incubation of parasites with biotin showed a preferential expression of the 97, 70, 50, 45, 25-22, and 15 kDa biotinylated polypeptides in the long forms, in contrast to the 55 and 28 kDa biotinylated polypeptides synthesized by the short epimastigotes. Additionally, flow cytometry analysis showed that the short forms had relatively lower biotin surface binding than long ones. The involvement of phosphatases with the trypanosomatid differentiation has been proposed. In this sense, T. rangeli living parasites were able to hydrolyze the artificial substrate p-nitrophenylphosphate at a rate of 25.57+/-2.03 and 10.09+/-0.93 nmol p-NPP x h(-1) x 10(7) cells for the short and long epimastigotes, respectively. These phosphatase activities were linear with time for at least 60 min and the optimum pH lies in the acid range. Classical inhibitors of acid phosphatases, such as ammonium molybdate, sodium fluoride, and zinc chloride, showed a significant decrease in these phosphatase activities, with different patterns of inhibition. Additionally, these phosphatase activities presented different kinetic parameters (Km and Vmax) and distinct sensitivities to divalent cations. Both epimastigotes were unable to release phosphatase to the extracellular environment. Cytochemical analysis demonstrated the localization of these enzymes on the parasite surfaces (cell body and flagellum) and in intracellular vacuoles, resembling acidocalcisomes.

Secreted phosphatase activity induced by dimethyl sulfoxide in Herpetomonas samuelpessoai

A phosphatase activity of the trypanosomatid parasite Herpetomonas samuelpessoai was characterized using intact living cells. The effects of dimethyl sulfoxide (DMSO) on this activity were investigated. This phosphatase activity (2.53+/-0.01 nmol P(i)/mg protein x min) was linear with cell density and with time for at least 60 min. The optimum pH for the H. samuelpessoai phosphatase lies in the acid range. This phosphatase activity was inhibited by metal chelators and classical phosphatase inhibitors. A robust stimulation of the phosphatase activity was observed when the flagellates were grown in the presence of 4% DMSO, both when intact flagellates and when culture supernatant from those cells were assayed, as observed by biochemical and cytochemical analysis. We also demonstrate that DMSO induced the secretion and/or shedding of this phosphatase to the extracellular medium, with a possible involvement of protein kinase C in this process.

Platelet-activating factor (PAF) activates casein kinase 2 in the protozoan parasite Herpetomonas muscarum muscarum

Herpetomonas muscarum muscarum is a flagellate parasite of the family Trypanosomatidae, whose cell differentiation can be triggered by the lipid mediator, PAF. In this study we demonstrate for the first time that PAF effect relies on the activation of casein kinase 2 (CK2). The classical antagonist of PAF receptor, WEB 2086, abrogated PAF-enhanced CK2 activity. CK2 activation by PAF was also inhibited when parasite extracts were assayed in the presence of modulators of PKC, MAPK, and both Ser/Thr and Tyr phosphatases. Finally, a cell permeable inhibitor of CK2 (DRB) suppressed PAF-induced cell differentiation in a dose-dependent manner.

Characterization of an ecto-ATPase of Tritrichomonas foetus

In this work, we describe the ability of living Tritrichomonas foetus to hydrolyze extracellular ATP. The addition of MgCl(2) to the assay medium increased the ecto-ATPase activity in a dose-dependent manner. At 5mM ATP, half maximal stimulation of ATP hydrolysis was obtained with 0.46mM MgCl(2). The ecto-ATPase activity was also stimulated by MnCl(2) and CaCl(2), but not by SrCl(2). The Mg(2+)-dependent ATPase presents two apparent K(m) values for Mg-ATP(2-) (K(m1)=0.03 mM and K(m2)=2.01 mM). ATP was the best substrate for this enzyme, although other nucleotides such as ITP, CTP, UTP also produced high reaction rates. GTP produced a low reaction rate and ADP was not a substrate for this enzyme. The Mg(2+)-dependent ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A(1), ouabain, furosemide, vanadate, molybdate, sodium fluoride and levamizole. The acid phosphatase inhibitors (vanadate and molybdate) inhibited about 60-70% of the Mg(2+)-independent ecto-ATPase activity, suggesting that the ATP hydrolysis measured in the absence of any metal divalent could, at least in part, also be catalyzed by an ecto-phosphatase present in this cell. In order to confirm the observed Mg(2+)-dependent activity as an ecto-ATPase, we used an impermeant inhibitor, 4,4'-diisothiocyanostylbene-2',2'-disulfonic acid (DIDS) as well as suramin, an antagonist of P(2) purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg(2+)-dependent ATPase activity in a dose-dependent manner. This ecto-ATPase was stimulated by more than 90% by 50mM D-galactose. Since previous results showed that D-galactose exposed on the surface of host cells is involved with T. foetus adhesion, the Mg(2+)-dependent ecto-ATPase may be involved with cellular adhesion and possible pathogenicity.

Secreted phosphatase activities in trypanosomatid parasites of plants modulated by platelet-activating factor

ABSTRACT The secreted phosphatase activities of two trypanosomatid parasites were characterized and compared with supernatants of living cells. The plant parasite Phytomonas françai and the phytophagous hemipteran parasite Herpetomonas sp. hydrolyzed p-nitrophenylphosphate at a rate of 15.54 and 6.51 nmol Pi/mg of protein per min, respectively. Sodium orthovanadate (N(a)VO(3)) and sodium fluoride (NaF) decreased the phosphatase activities. The phosphatase activity of P. françai was drastically diminished (73% inhibition) in the presence of sodium tartrate, whereas the phosphatase activity of Herpetomonas sp. was inhibited by 23%. Cytochemical analysis showed the localization of these enzymes on the external surface and in the flagellar pocket of the two trypanosomatids. Sodium tartrate inhibited this reaction, confirming the biochemical data. Platelet-activating factor modulated the phosphatase activities, inhibiting P. françai activity and stimulating Herpetomonas sp. phosphatase activity.

Effects of 4,4'-diisothyocyanatostilbene-2,2'-disulfonic acid on Trypanosoma cruzi proliferation and Ca(2+) homeostasis

Cell viability requires the perfect functioning of the processes controlling ATP and Ca(2+) homeostasis. It is known that cell death caused by a variety of toxins or pathological conditions is associated with a disruption of ATP and Ca(2+) homeostasis. This study shows that 4,4'-diisothyocyanatostilbene-2,2'-disulfonic acid (DIDS) inhibits Trypanosoma cruzi epimastigote cell growth. This thiol-reagent thiocyanate derivative was able to inhibit two ecto-enzymes present in this parasite. The ecto-ATPase and ecto-phosphatase activities were inhibited in a dose-dependent manner (K(i)=47.7 and 472.5 microM, respectively), but the 5'nucleotidase and 3'nucleotidase activities were not. DIDS uptake was approached by fluorescence microscopy. Pulse-chase experiments revealed the DIDS accumulation in compartments, presumably endocytic, in the posterior region of epimastigotes. In addition, we show that the T. cruzi mitochondria studied in permeabilized cells are able to accumulate and retain medium Ca(2+) in the absence of DIDS. However, in the presence of increasing concentrations of DIDS (50-200 microM), Ca(2+) transport was inhibited in a dose-dependent manner. DIDS also caused a disruption of the mitochondrial membrane potential, in the same concentration range, thus explaining its effect on Ca(2+) uptake. The presence of EGTA prevented the elimination of the mitochondrial membrane potential (DeltaPsi), supporting previous data suggesting that the binding of Ca(2+) to the mitochondrial membrane exposes buried thiols to react with DIDS. This thiocyanate derivative was also able to inhibit Ca(2+) uptake by the endoplasmic reticulum in a dose-dependent manner. Taken together, the data presented here provide further insights into the mechanisms underlying the antiproliferative actions of DIDS in T. cruzi.