Activation of host cell phosphatidylinositol 3-kinases by Trypanosoma cruzi infection

Novel diamides inspired by protein kinase inhibitors as anti-Trypanosoma cruzi agents: in vitro and in vivo evaluations

Background: Chagas disease is a life-threatening illness caused by Trypanosoma cruzi. The involvement of serine-/arginine-rich protein kinase in the T. cruzi life cycle is significant. Aims: To synthesize, characterize and evaluate the trypanocidal activity of diamides inspired by kinase inhibitor, SRPIN340. Material & Methods: Synthesis using a three-step process and characterization by infrared, nuclear magnetic resonance and high-resolution mass spectrometry were conducted. The selectivity index was obtained by the ratio of CC50/IC50 in two in vitro models. The most active compound, 3j, was evaluated using in vitro cytokine assays and assessing in vivo trypanocidal activity. Results: 3j activity in the macrophage J774 lineage showed an anti-inflammatory profile, and mice showed significantly reduced parasitemia and morbidity at low compound dosages. Conclusion: Novel diamide is active against T. cruzi in vitro and in vivo.

Anti-Trypanosoma cruzi activity of Coptis rhizome extract and its constituents

BACKGROUND

Current therapeutic agents, including nifurtimox and benznidazole, are not sufficiently effective in the chronic phase of Trypanosoma cruzi infection and are accompanied by various side effects. In this study, 120 kinds of extracts from medicinal herbs used for Kampo formulations and 94 kinds of compounds isolated from medicinal herbs for Kampo formulations were screened for anti-T. cruzi activity in vitro and in vivo.

METHODS

As an experimental method, a recombinant protozoan cloned strain expressing luciferase, namely Luc2-Tulahuen, was used in the experiments. The in vitro anti-T. cruzi activity on epimastigote, trypomastigote, and amastigote forms was assessed by measuring luminescence intensity after treatment with the Kampo extracts or compounds. In addition, the cytotoxicity of compounds was tested using mouse and human feeder cell lines. The in vivo anti-T. cruzi activity was measured by a murine acute infection model using intraperitoneal injection of trypomastigotes followed by live bioluminescence imaging.

RESULTS

As a result, three protoberberine-type alkaloids, namely coptisine chloride, dehydrocorydaline nitrate, and palmatine chloride, showed strong anti-T. cruzi activities with low cytotoxicity. The IC₅₀ values of these compounds differed depending on the side chain, and the most effective compound, coptisine chloride, showed a significant effect in the acute infection model.

CONCLUSIONS

For these reasons, coptisine chloride is a hit compound that can be a potential candidate for anti-Chagas disease drugs. In addition, it was expected that there would be room for further improvement by modifying the side chains of the basic skeleton.

Common Signal Transduction Molecules Activated by Bacterial Entry into a Host Cell and by Reactive Oxygen Species

Significance: An increasing number of pathogens are acquiring resistance to antibiotics. Efficient antimicrobial drug regimens are important even for the most advanced therapies, which range from cutting-edge invasive clinical protocols, such as robotic surgeries, to the treatment of harmless bacterial diseases and to minor scratches to the skin. Therefore, there is an urgent need to survey alternative antimicrobial drugs that can reinforce or replace existing antibiotics. Recent Advances: Bacterial proteins that are critical for energy metabolism, promising novel anticancer thiourea derivatives, and the use of synthetic molecules that increase the sensitivity of currently used antibiotics are among the recently discovered antimicrobial drugs. Critical Issues: In the development of new drugs, serious consideration should be given to the previous bacterial evolutionary selection caused by antibiotics, by the high proliferation rate of bacteria, and by the simple prokaryotic structure of bacteria. Future Directions: The survey of drug targets has mainly focused on bacterial proteins, although host signaling molecules involved in the treatment of various pathologies may have unknown antimicrobial characteristics. Recent data have suggested that small molecule inhibitors might enhance the effect of antibiotics, for example, by limiting bacterial entry into host cells. Phagocytosis, the mechanism by which host cells internalize pathogens through β-actin cytoskeletal rearrangement, induces calcium signaling, small GTPase activation, and phosphorylation of the phosphatidylinositol 3-kinase-serine/threonine-specific protein kinase B pathway. Antioxid. Redox Signal. 34, 486-503.

Transcriptional Studies on Trypanosoma cruzi - Host Cell Interactions: A Complex Puzzle of Variables

Chagas Disease, caused by the protozoan parasite Trypanosoma cruzi, affects nearly eight million people in the world. T. cruzi is a complex taxon represented by different strains with particular characteristics, and it has the ability to infect and interact with almost any nucleated cell. The T. cruzi-host cell interactions will trigger molecular signaling cascades in the host cell that will depend on the particular cell type and T. cruzi strain, and also on many different experimental variables. In this review we collect data from multiple transcriptomic and functional studies performed in different infection models, in order to highlight key differences between works that in our opinion should be addressed when comparing and discussing results. In particular, we focus on changes in the respiratory chain and oxidative phosphorylation of host cells in response to infection, which depends on the experimental model of T. cruzi infection. Finally, we also discuss host cell responses which reiterate independently of the strain, cell type and experimental conditions.

Effect of Ginsenoside-Rh2 and Curcurbitacin-B on Cryptosporidium parvum in vitro

Ginsenoside-Rh2 and cucurbitacin-B (CuB) are secondary metabolites of Ginseng (Panax ginseng) and Cucurbitaceae plants respectively. We assessed the anticryptosporidial activity of these two functional compounds in a cell culture model of cryptosporidiosis. The highest concentration of each compound that was not toxic to the host cells was used to assess the activity against C. parvum during infection/invasion and growth in HCT-8 cell monolayers. Monolayers were infected with pre-excysted C. parvum oocysts. Infected monolayers were incubated at 37 °C for 24 h and 48 h in the presence of different concentrations of each test compound. A growth resumption assay was performed by incubating infected monolayers in the presence of compounds for 24 h followed by a second 24-h incubation in the absence of compound. To screen for invasion inhibiting activity, freshly excysted C. parvum sporozoites were pre-treated with different concentrations of compounds prior to adding them to the cell monolayers. Paromomycin, a known inhibitor of C. parvum, and DMSO were used as positive and negative control, respectively. The level of infection was initially assessed using an immunofluorescent assay and quantified by real-time PCR. Both compounds were found to strongly inhibit C. parvum intracellular development in a dose-dependent manner. IC₅₀ values of 25 μM for a 24 h development period and 5.52 μM after 48 h development were measured for Rh2, whereas for CuB an IC₅₀ value of 0.169 μg/ml and 0.118 μg/ml were obtained for the same incubation periods. CuB also effectively inhibited resumption of growth, an activity that was not observed with Rh2. CuB was more effective at inhibiting excystation and/or host cell invasion, indicating that this compound also targets extracellular stages of the parasite.

Pyridinecarboxylic Acid Derivative Stimulates Pro-Angiogenic Mediators by PI3K/AKT/mTOR and Inhibits Reactive Nitrogen and Oxygen Species and NF-κB Activation Through a PPARγ-Dependent Pathway in T. cruzi-Infected Macrophages

Chagas disease is caused by Trypanosoma cruzi infection and represents an important public health concern in Latin America. Macrophages are one of the main infiltrating leukocytes in response to infection. Parasite persistence could trigger a sustained activation of these cells, contributing to the damage observed in this pathology, particularly in the heart. HP₂₄, a pyridinecarboxylic acid derivative, is a new PPARγ ligand that exerts anti-inflammatory and pro-angiogenic effects. The aim of this work was to deepen the study of the mechanisms involved in the pro-angiogenic and anti-inflammatory effects of HP₂₄ in T. cruzi-infected macrophages, which have not yet been elucidated. We show for the first time that HP₂₄ increases expression of VEGF-A and eNOS through PI3K/AKT/mTOR and PPARγ pathways and that HP₂₄ inhibits iNOS expression and NO release, a pro-inflammatory mediator, through PPARγ-dependent mechanisms. Furthermore, this study shows that HP₂₄ modulates H₂O₂ production in a PPARγ-dependent manner. It is also demonstrated that this new PPARγ ligand inhibits the NF-κB pathway. HP₂₄ inhibits IKK phosphorylation and IκB-α degradation, as well as p65 translocation to the nucleus in a PPARγ-dependent manner. In Chagas disease, both the sustained increment in pro-inflammatory mediators and microvascular abnormalities are crucial aspects for the generation of cardiac damage. Elucidating the mechanism of action of new PPARγ ligands is highly attractive, given the fact that it can be used as an adjuvant therapy, particularly in the case of Chagas disease in which inflammation and tissue remodeling play an important role in the pathophysiology of this disease.

Canonical PI3Kγ signaling in myeloid cells restricts Trypanosoma cruzi infection and dampens chagasic myocarditis

Chagas disease is caused by infection with the protozoan Trypanosoma cruzi (T. cruzi) and is an important cause of severe inflammatory heart disease. However, the mechanisms driving Chagas disease cardiomyopathy have not been completely elucidated. Here, we show that the canonical PI3Kγ pathway is upregulated in both human chagasic hearts and hearts of acutely infected mice. PI3Kγ-deficient mice and mutant mice carrying catalytically inactive PI3Kγ are more susceptible to T. cruzi infection. The canonical PI3Kγ signaling in myeloid cells is essential to restrict T. cruzi heart parasitism and ultimately to avoid myocarditis, heart damage, and death of mice. Furthermore, high PIK3CG expression correlates with low parasitism in human Chagas’ hearts. In conclusion, these results indicate an essential role of the canonical PI3Kγ signaling pathway in the control of T. cruzi infection, providing further insight into the molecular mechanisms involved in the pathophysiology of chagasic heart disease.

Trypanosoma cruzi infection causes Chagas disease, but mechanisms underlying pathogenesis are unclear. Here, Silva et al. show that canonical PI3Kγ signaling in myeloid cells restricts T. cruzi infection in mice and that high PIK3CG expression correlates with low parasite levels in human Chagas’ hearts.

Role of Host Type IA Phosphoinositide 3-Kinase Pathway Components in Invasin-Mediated Internalization of Yersinia enterocolitica

Many bacterial pathogens subvert mammalian type IA phosphoinositide 3-kinase (PI3K) in order to induce their internalization into host cells. How PI3K promotes internalization is not well understood. Also unclear is whether type IA PI3K affects different pathogens through similar or distinct mechanisms. Here, we performed an RNA interference (RNAi)-based screen to identify components of the type IA PI3K pathway involved in invasin-mediated entry of Yersinia enterocolitica, an enteropathogen that causes enteritis and lymphadenitis. The 69 genes targeted encode known upstream regulators or downstream effectors of PI3K. A similar RNAi screen was previously performed with the food-borne bacterium Listeria monocytogenes The results of the screen with Y. enterocolitica indicate that at least nine members of the PI3K pathway are needed for invasin-mediated entry. Several of these proteins, including centaurin-α1, Dock180, focal adhesion kinase (FAK), Grp1, LL5α, LL5β, and PLD2 (phospholipase D2), were recruited to sites of entry. In addition, centaurin-α1, FAK, PLD2, and mTOR were required for remodeling of the actin cytoskeleton during entry. Six of the human proteins affecting invasin-dependent internalization also promote InlB-mediated entry of L. monocytogenes Our results identify several host proteins that mediate invasin-induced effects on the actin cytoskeleton and indicate that a subset of PI3K pathway components promote internalization of both Y. enterocolitica and L. monocytogenes.

Trans-sialidase stimulates eat me response from epithelial cells

Epithelial cell invasion by the protozoan parasite Trypanosoma cruzi is enhanced by the presence of an enzyme expressed on its cell surface during the trypomastigote life cycle stage. The enzyme, trans-sialidase (TS), is a member of one of the largest gene families expressed by the parasite and the role of its activity in mediating epithelial cell entry has not hitherto been understood. Here we show that the T. cruzi TS generates an eat me signal which is capable of enabling epithelial cell entry. We have utilized purified, recombinant, active (TcTS) and inactive (TcTS2V0) TS coated onto beads to challenge an epithelial cell line. We find that TS activity acts upon G protein coupled receptors present at the epithelial cell synapse with the coated bead, thereby enhancing cell entry. By so doing, we provide evidence that TS proteins bind glycans, mediate the formation of distinct synaptic domains and promote macropinocytotic uptake of microparticles into a perinuclear compartment in a manner which may emulate entosis.

Cell signaling during Trypanosoma cruzi invasion

Cell signaling is an essential requirement for mammalian cell invasion by Trypanosoma cruzi. Depending on the parasite strain and the parasite developmental form, distinct signaling pathways may be induced. In this short review, we focus on the data coming from studies with metacyclic trypomastigotes (MT) generated in vitro and tissue culture-derived trypomastigotes (TCT), used as counterparts of insect-borne and bloodstream parasites, respectively. During invasion of host cells by MT or TCT, intracellular Ca²⁺ mobilization and host cell lysosomal exocytosis are triggered. Invasion mediated by MT surface molecule gp82 requires the activation of mammalian target of rapamycin (mTOR), phosphatidylinositol 3-kinase (PI3K), and protein kinase C (PKC) in the host cell, associated with Ca²⁺-dependent disruption of the actin cytoskeleton. In MT, protein tyrosine kinase, PI3K, phospholipase C, and PKC appear to be activated. TCT invasion, on the other hand, does not rely on mTOR activation, rather on target cell PI3K, and may involve the host cell autophagy for parasite internalization. Enzymes, such as oligopeptidase B and the major T. cruzi cysteine proteinase cruzipain, have been shown to generate molecules that induce target cell Ca²⁺ signal. In addition, TCT may trigger host cell responses mediated by transforming growth factor β receptor or integrin family member. Further investigations are needed for a more complete and detailed picture of T. cruzi invasion.

Current understanding of the Trypanosoma cruzi-cardiomyocyte interaction

Trypanosoma cruzi, the etiological agent of Chagas disease, exhibits multiple strategies to ensure its establishment and persistence in the host. Although this parasite has the ability to infect different organs, heart impairment is the most frequent clinical manifestation of the disease. Advances in knowledge of T. cruzi-cardiomyocyte interactions have contributed to a better understanding of the biological events involved in the pathogenesis of Chagas disease. This brief review focuses on the current understanding of molecules involved in T. cruzi-cardiomyocyte recognition, the mechanism of invasion, and on the effect of intracellular development of T. cruzi on the structural organization and molecular response of the target cell.

Trypanosoma cruzi uses macropinocytosis as an additional entry pathway into mammalian host cell

Several intracellular pathogens are internalized by host cells via multiple endocytic pathways. It is no different with Trypanosoma cruzi. Evidences indicate that T. cruzi entry may occur by endocytosis/phagocytosis or by an active manner. Although macropinocytosis is largely considered an endocytic process where cells internalize only large amounts of solutes, several pathogens use this pathway to enter into host cells. To investigate whether T. cruzi entry into peritoneal macrophages and LLC-MK2 epithelial cells can be also mediated through a macropinocytosis-like process, we used several experimental strategies presently available to characterize macropinocytosis such as the use of different inhibitors. These macropinocytosis' inhibitors blocked internalization of T. cruzi by host cells. To further support this, immunofluorescence microscopy and scanning electron microscopy techniques were used. Field emission scanning electron microscopy revealed that after treatment, parasites remained attached to the external side of host cell plasma membrane. Proteins such as Rabankyrin 5, tyrosine kinases, Pak1 and actin microfilaments, which participate in macropinosome formation, were localized at T. cruzi entry sites. We also observed co-localization between the parasite and an endocytic fluid phase marker. All together, these results indicate that T. cruzi is able to use multiple mechanisms of penetration into host cell, including macropinocytosis.

Critical role for phosphoinositide 3-kinase gamma in parasite invasion and disease progression of cutaneous leishmaniasis

Obligate intracellular pathogens such as Leishmania specifically target host phagocytes for survival and replication. Phosphoinositide 3-kinase γ (PI3Kγ), a member of the class I PI3Ks that is highly expressed by leukocytes, controls cell migration by initiating actin polymerization and cytoskeletal reorganization, which are processes also critical for phagocytosis. In this study, we demonstrate that class IB PI3K, PI3Kγ, plays a critical role in pathogenesis of chronic cutaneous leishmaniasis caused by L. mexicana. Using the isoform-selective PI3Kγ inhibitor, AS-605240 and PI3Kγ gene-deficient mice, we show that selective blockade or deficiency of PI3Kγ significantly enhances resistance against L. mexicana that is associated with a significant suppression of parasite entry into phagocytes and reduction in recruitment of host phagocytes as well as regulatory T cells to the site of infection. Furthermore, we demonstrate that AS-605240 is as effective as the standard antileishmanial drug sodium stibogluconate in treatment of cutaneous leishmaniasis caused by L. mexicana. These findings reveal a unique role for PI3Kγ in Leishmania invasion and establishment of chronic infection, and demonstrate that therapeutic targeting of host pathways involved in establishment of infection may be a viable strategy for treating infections caused by obligate intracellular pathogens such as Leishmania.

Identification of components of the host type IA phosphoinositide 3-kinase pathway that promote internalization of Listeria monocytogenes

The bacterial pathogen Listeria monocytogenes causes food-borne illnesses resulting in gastroenteritis, meningitis, or abortion. Listeria promotes its internalization into some human cells through binding of the bacterial surface protein InlB to the host receptor tyrosine kinase Met. The interaction of InlB with the Met receptor stimulates host signaling pathways that promote cell surface changes driving bacterial uptake. One human signaling protein that plays a critical role in Listeria entry is type IA phosphoinositide 3-kinase (PI 3-kinase). The molecular mechanism by which PI 3-kinase promotes bacterial internalization is not understood. Here we perform an RNA interference (RNAi)-based screen to identify components of the type IA PI 3-kinase pathway that control the entry of Listeria into the human cell line HeLa. The 64 genes targeted encode known upstream regulators or downstream effectors of type IA PI 3-kinase. The results of this screen indicate that at least 9 members of the PI 3-kinase pathway play important roles in Listeria uptake. These 9 human proteins include a Rab5 GTPase, several regulators of Arf or Rac1 GTPases, and the serine/threonine kinases phosphoinositide-dependent kinase 1 (PDK1), mammalian target of rapamycin (mTor), and protein kinase C-ζ. These findings represent a key first step toward understanding the mechanism by which type IA PI 3-kinase controls bacterial internalization.

In Vitro Infection of Trypanosoma cruzi Causes Decrease in Glucose Transporter Protein-1 (GLUT1) Expression in Explants of Human Placental Villi Cultured under Normal and High Glucose Concentrations

Trypanosoma cruzi, the etiologic Chagas' disease agent, induces changes in protein pattern of the human placenta syncytiotrophoblast. The glucose transporter protein-1 (GLUT1) is the primary isoform involved in transplacental glucose transport. We carried out in vitro assays to determine if T. cruzi infection would induce changes in placental GLUT1 protein expression under normal and high concentration of glucose. Using Western blot and immunohistological techniques, GLUT1 expression was determined in normal placental villi cultured under normal or high concentrations of glucose, with or without in vitro T. cruzi infection, for 24 and 48 hours. High glucose media or T. cruzi infection alone reduced GLUT1 expression. A yet more accentuated reduction was observed when infection and high glucose condition took place together. We inform, for the first time, that T. cruzi infection may induce reduction of GLUT1 expression under normal and high glucose concentrations, and this effect is synergic to high glucose concentrations.

Trypanosoma cruzi utilizes the host low density lipoprotein receptor in invasion

Background

Trypanosoma cruzi, an intracellular protozoan parasite that infects humans and other mammalian hosts, is the etiologic agent in Chagas disease. This parasite can invade a wide variety of mammalian cells. The mechanism(s) by which T. cruzi invades its host cell is not completely understood. The activation of many signaling receptors during invasion has been reported; however, the exact mechanism by which parasites cross the host cell membrane barrier and trigger fusion of the parasitophorous vacuole with lysosomes is not understood.

Methodology/Principal Findings

In order to explore the role of the Low Density Lipoprotein receptor (LDLr) in T. cruzi invasion, we evaluated LDLr parasite interactions using immunoblot and immunofluorescence (IFA) techniques. These experiments demonstrated that T. cruzi infection increases LDLr levels in infected host cells, inhibition or disruption of LDLr reduces parasite load in infected cells, T. cruzi directly binds recombinant LDLr, and LDLr-dependent T. cruzi invasion requires PIP2/3. qPCR analysis demonstrated a massive increase in LDLr mRNA (8000 fold) in the heart of T. cruzi infected mice, which is observed as early as 15 days after infection. IFA shows a co-localization of both LDL and LDLr with parasites in infected heart.

Conclusions/Significance

These data highlight, for the first time, that LDLr is involved in host cell invasion by this parasite and the subsequent fusion of the parasitophorous vacuole with the host cell lysosomal compartment. The model suggested by this study unifies previous models of host cell invasion for this pathogenic protozoon. Overall, these data indicate that T. cruzi targets LDLr and its family members during invasion. Binding to LDL likely facilitates parasite entry into host cells. The observations in this report suggest that therapeutic strategies based on the interaction of T. cruzi and the LDLr pathway should be pursued as possible targets to modify the pathogenesis of disease following infection.

Trypanosoma cruzi, an intracellular protozoan parasite that causes Chagas disease in humans and results in the development of cardiomyopathy, is a major health problem in endemic areas. This parasite can invade a wide variety of mammalian cells. The mechanisms by which these parasites invade their host cells are not completely understood. Our study highlights, for the first time, that the Low Density Lipoprotein receptor (LDLr) is important in the invasion and the subsequent fusion of the parasitophorous vacuole with host lysosomes. We demonstrate that T. cruzi directly binds to LDLr, and inhibition or disruption of LDLr significantly decreases parasite entry. Additionally, we have determined that this cross-linking triggers the accumulation of LDLr and phosphotidylinositol phosphates in coated pits, which initiates a signaling cascade that results in the recruitment of lysosomes, possibly via the sorting motif in the cytoplasmic tail of LDLr, to the site of adhesion/invasion. Studies of infected CD1 mice demonstrate that LDLs accumulate in infected heart and that LDLr co-localize with internalized parasites. Overall, this study demonstrates that LDLr and its family members, engaged mainly in lipoprotein transportation, are also involved in T. cruzi entry into host cells and this interaction likely contributes to the progression of chronic cardiomyopathy.

Activation of phosphatidylinositol 3-kinase/Akt and impairment of nuclear factor-kappaB: molecular mechanisms behind the arrested maturation/activation state of Leishmania infantum-infected dendritic cells

Understanding the complex interactions between Leishmania and dendritic cells (DCs) is central to the modulation of the outcome of this infection, given that an effective immune response against Leishmania is dependent on the successful activation and maturation of DCs. We report here that Leishmania infantum promastigotes successfully infect mouse bone marrow-derived DCs without triggering maturation, as shown by a failure in the up-regulation of CD40 and CD86 expression, and that parasites strongly counteract the lipopolysaccharide-triggered maturation of DCs. A small increase in interleukin (IL)-12 and IL-10 transcription and secretion and a decrease in IL-6 were observed in infected cells. This arrested DC maturation state is actively promoted by parasites because heat-killed or fixed parasites increased cytokine and costimulatory molecule expression. At a molecular level, L. infantum rapidly induced activation of phosphatidylinositol 3-kinase/Akt and extracellular signal-regulated kinase 1/2, whereas no effect was observed in the c-Jun N-terminal kinase and p38 mitogen-activated protein kinase proinflammatory pathways. Moreover, parasites actively promoted cleavage of the nuclear factor-κB p65(RelA) subunit, causing its impairment. The blockade of phosphatidylinositol 3-kinase/Akt by either treatment of bone marrow-derived DCs with wortmannin or transfection with an Akt dominant-negative mutant resulted in a strong decrease in infection rates, revealing for the first time a crucial role of this pathway on Leishmania engulfment by DCs. Overall, our data indicate that activation of Akt and impairment of nuclear factor-κB are responsible for immunogenicity subversion of L. infantum-infected DCs.

Molecular mechanisms of host cell invasion by Trypanosoma cruzi

The protozoan parasite Trypanosoma cruzi, the etiologic agent of Chagas disease, is an obligate intracellular protozoan pathogen. Overlapping mechanisms ensure successful infection, yet the relationship between these cellular events and clinical disease remains obscure. This review explores the process of cell invasion from the perspective of cell surface interactions, intracellular signaling, modulation of the host cytoskeleton and endosomal compartment, and the intracellular innate immune response to infection.

Dynasore, a dynamin inhibitor, inhibits Trypanosoma cruzi entry into peritoneal macrophages

BACKGROUND

Trypanosoma cruzi is an intracellular parasite that, like some other intracellular pathogens, targets specific proteins of the host cell vesicular transport machinery, leading to a modulation of host cell processes that results in the generation of unique phagosomes. In mammalian cells, several molecules have been identified that selectively regulate the formation of endocytic transport vesicles and the fusion of such vesicles with appropriate acceptor membranes. Among these, the GTPase dynamin plays an important role in clathrin-mediated endocytosis, and it was recently found that dynamin can participate in a phagocytic process.

METHODOLOGY/PRINCIPAL FINDINGS

We used a compound called dynasore that has the ability to block the GTPase activity of dynamin. Dynasore acts as a potent inhibitor of endocytic pathways by blocking coated vesicle formation within seconds of its addition. Here, we investigated whether dynamin is involved in the entry process of T. cruzi in phagocytic and non-phagocytic cells by using dynasore. In this aim, peritoneal macrophages and LLC-MK2 cells were treated with increasing concentrations of dynasore before interaction with trypomastigotes, amastigotes or epimastigotes. We observed that, in both cell lines, the parasite internalization was drastically diminished (by greater than 90% in LLC-MK2 cells and 70% in peritoneal macrophages) when we used 100 microM dynasore. The T. cruzi adhesion index, however, was unaffected in either cell line. Analyzing these interactions by scanning electron microscopy and comparing peritoneal macrophages to LLC-MK2 cells revealed differences in the stage at which cell entry was blocked. In LLC-MK2 cells, this blockade is observed earlier than it is in peritoneal macrophages. In LLC-MK2 cells, the parasites were only associated with cellular microvilli, whereas in peritoneal macrophages, trypomastigotes were not completely engulfed by a host cell plasma membrane.

CONCLUSIONS/SIGNIFICANCE

Taken together our results demonstrate that dynamin is an essential molecule necessary for cell invasion and specifically parasitophorous vacuole formation by host cells during interaction with Trypanosoma cruzi.

Cytokine-dependent and-independent gene expression changes and cell cycle block revealed in Trypanosoma cruzi-infected host cells by comparative mRNA profiling

Background

The requirements for growth and survival of the intracellular pathogen Trypanosoma cruzi within mammalian host cells are poorly understood. Transcriptional profiling of the host cell response to infection serves as a rapid read-out for perturbation of host physiology that, in part, reflects adaptation to the infective process. Using Affymetrix oligonucleotide array analysis we identified common and disparate host cell responses triggered by T. cruzi infection of phenotypically diverse human cell types.

Results

We report significant changes in transcript abundance in T. cruzi-infected fibroblasts, endothelial cells and smooth muscle cells (2852, 2155 and 531 genes respectively; fold-change ≥ 2, p-value < 0.01) 24 hours post-invasion. A prominent type I interferon response was observed in each cell type, reflecting a secondary response to secreted cytokine in infected cultures. To identify a core cytokine-independent response in T. cruzi-infected fibroblasts and endothelial cells transwell plates were used to distinguish cytokine-dependent and -independent gene expression profiles. This approach revealed the induction of metabolic and signaling pathways involved in cell proliferation, amino acid catabolism and response to wounding as common themes in T. cruzi-infected cells. In addition, the downregulation of genes involved in mitotic cell cycle and cell division predicted that T. cruzi infection may impede host cell cycle progression. The observation of impaired cytokinesis in T. cruzi-infected cells, following nuclear replication, confirmed this prediction.

Conclusion

Metabolic pathways and cellular processes were identified as significantly altered at the transcriptional level in response to T. cruzi infection in a cytokine-independent manner. Several of these alterations are supported by previous studies of T. cruzi metabolic requirements or effects on the host. However, our methods also revealed a T. cruzi-dependent block in the host cell cycle, at the level of cytokinesis, previously unrecognized for this pathogen-host cell interaction.

Non-opsonic phagocytosis of Legionella pneumophila by macrophages is mediated by phosphatidylinositol 3-kinase

Background

Legionella pneumophila, is an intracellular pathogen that causes Legionnaires' disease in humans, a potentially lethal pneumonia. L. pneumophila has the ability to enter and replicate in the host and is essential for pathogenesis.

Methodology/Principal Findings

Phagocytosis was measured by cell invasion assays. Construction of PI3K mutant by PCR cloning and expression of dominant negative mutant was detected by Western blot. PI3K activity was measured by ³²P labeling and detection of phospholipids products by thin layer chromatography. Infection of macrophages with virulent L. pneumophila stimulated the formation of phosphatidylinositol 3-phosphate (PIP3), a phosphorylated lipid product of PI3K whereas two structurally distinct phosphatidylinositol 3 kinase (PI3K) inhibitors, wortmannin and LY294002, reduced L. pneumophila entry into macrophages in a dose-dependent fashion. Furthermore, PI3K activation led to Akt stimulation, a serine/threonine kinase, which was also inhibited by wortmannin and LY294002. In contrast, PI3K and protein kinase B (PKB/Akt) activities were lower in macrophages infected with an avirulent bacterial strain. Only virulent L. pneumophila increased lipid kinase activity present in immunoprecipitates of the p85α subunit of class I PI3K and tyrosine phosphorylated proteins. In addition, macrophages expressing a specific dominant negative mutant of PI3K reduced L. pneumophila entry into these cells.

Conclusion/Significance

Entry of L. pneumophila is mediated by PI3K/Akt signaling pathway. These results suggest an important role for PI3K and Akt in the L. pneumophila infection process. They point to possible novel strategies for undermining L. pneumophila host uptake and reducing pathogenesis of Legionnaires' disease.

Rab5 activation by Toll-like receptor 2 is required for Trypanosoma cruzi internalization and replication in macrophages

Trypanosoma cruzi can infect and replicate in macrophages. During invasion, T. cruzi interacts with different macrophage receptors to induce its own phagocytosis. However, the nature of those receptors and the molecular mechanisms involved are poorly understood. In this study, we demonstrate that T. cruzi metacyclic trypomastigotes but not epimastigotes were able to induce Rab5 activation and binding to the early endosomes in peritoneal macrophages. In this process, active Rab5 colocalized with parasites in the phagosome and with the Rab5A effector molecule early endosomal antigen 1. Phagosome formation and T. cruzi internalization were inhibited in Raw 264.7 macrophages expressing a dominant-negative form of Rab5 [(S34N)Rab5]. Using T. cruzi membrane extracts, we verified that the Rab5 activation depends on the interaction between parasite surface molecules and macrophages surface molecule. In addition, during infection of macrophages, phosphatidylinositol 3-kinase (PI3K) pathway was activated. Assays carried out using a selective PI3K inhibitor (LY294002) showed that the PI3K activation is essential for Rab5 activation by T. cruzi infection and for the entrance and intracellular replication of T. cruzi in macrophages. Moreover, using macrophages from knockout mice, we found that activation of Rab5, fusion of early endosomes and phagocytosis induced by T. cruzi infection involved Toll-like receptor (TLR)2 but were independent of TLR4 receptors.

Trypanosoma cruzi: parasite and host cell signaling during the invasion process

Mammalian cell invasion by Trypanosoma cruzi is a complex process in which various parasite and host cell components interact, triggering the activation of signaling cascades and Ca2+ mobilization in both cells. Using metacyclic trypomastigotes (MT) generated in vitro and tissue culture-derived trypomastigotes (TCT), as counterparts of insect-borne and bloodstream parasites, respectively, the mechanisms of host cell invasion by T. cruzi have been partially elucidated. Distinct sets of molecules are engaged by MT and TCT to enter target cells. MT make use of surface glycoproteins with dual Ca2+ signaling activity, in a manner dependent of T. cruzi isolate. In highly infective MT, the binding of gp82 to its receptor triggers a signaling cascade involving protein tyrosine kinase, phospholipase C and production of inositol 1,4,5-triphosphate, whereas in poorly invasive MT, the mucin-like gp35/50 induces the activation of a signaling route in which adenylate cyclase, generation of cAMP and Ca2+ mobilization from acidocalcisomes are implicated. The host cell signaling pathways activated by MT remain to be determined. Differently from MT, the TCT surface molecules that bind to host cells as a prelude to invasion, such as the glycoproteins of gp85 family, appear to be devoid of signaling properties, but they may induce TCT enzymes, such as oligopeptidase B and cruzipain, to generate Ca2+ signaling factors of parasite or host cell origin. Host cell responses mediated by TGF-beta receptor or integrin family member may also be triggered by TCT. A more complete and detailed picture of T. cruzi invasion needs further investigations.

Transcriptional analysis of three major putative phosphatidylinositol kinase genes in a parasitic protozoan, Giardia lamblia

The current investigation evaluates the expression of phosphatidylinositol kinase (PIK) genes in the parasitic protozoan, Giardia lamblia. The G. lamblia Genome Database revealed the presence of two putative phosphatidylinositol-3-kinase (gPI3K) and one phosphatidylinositol-4-kinase (gPI4K) genes resembling the catalytic subunit of eukaryotic PIKs. Primers, designed to amplify mRNA of these three genes, were used to measure transcription by quantitative reverse-transcriptase polymerase chain reactions. Results suggest that all three PIK genes are expressed in non-encysting and encysting trophozoites. The relative levels of the mRNA were highest in parasites cultured in pre-encysting medium that contained no bile. Two inhibitors of PI3K, LY 294002 and wortmannin were found to inhibit the growth of the trophozoite in culture. However, wortmannin was more effective than LY294002. Altogether, the present study indicates that Giardia is capable of expressing PIKs that are necessary for the growth and differentiation of this pathogen.

Evolution and pathology in chagas disease--a review

Trypanosoma cruzi acute infections often go unperceived, but one third of chronically infected individuals die of Chagas disease, showing diverse manifestations affecting the heart, intestines, and nervous systems. A common denominator of pathology in Chagas disease is the minimal rejection unit, whereby parasite-free target host cells are destroyed by immune system mononuclear effectors cells infiltrates. Another key feature stemming from T. cruzi infection is the integration of kDNA minicircles into the vertebrate host genome; horizontal transfer of the parasite DNA can undergo vertical transmission to the progeny of mammals and birds. kDNA integration-induced mutations can enter multiple loci in diverse chromosomes, generating new genes, pseudo genes and knock-outs, and resulting in genomic shuffling and remodeling over time. As a result of the juxtaposition of kDNA insertions with host open reading frames, novel chimeric products may be generated. Germ line transmission of kDNA-mutations determined the appearance of lesions in birds that are indistinguishable from those seen in Chagas disease patients. The production of tissue lesions showing typical minimal rejection units in birds' refractory to T. cruzi infection is consistent with the hypothesis that autoimmunity, likely triggered by integration-induced phenotypic alterations, plays a major role in the pathogenesis of Chagas disease.

Mycobacteria directly induce cytoskeletal rearrangements for macrophage spreading and polarization through TLR2-dependent PI3K signaling

Macrophage migration and adhesion are important for the control of mycobacterial infection and are critically dependent on the reorganization of the cytoskeleton. Mycobacteria elicit rapid morphological changes, such as cell spreading, a process relevant to in vivo changes of macrophage shape during extravasation and migration. In this study, we investigated the BCG mycobacteria-induced signaling events leading to macrophage cytoskeletal rearrangements employing specific pharmacological inhibitors to suppress distinct kinase pathways known to be elicited by infection. Viable or lysed mycobacteria, as well as purified cell wall lipoprotein p19, TLR2 agonist, induced RAW264.7 cells to extend actin-rich pseudopods, which impart radial spreading within 3 h, leading later to persistent cell polarization. BCG induced rapid activation of phosphatidylinositol 3-kinase, PI3K, activation that was recruited to the activated TLR2 receptor. TLR2- neutralizing antibody inhibited macrophage spreading and PI3K activation induced by p19. Additionally, BCG induced spreading and polarization of bone marrow-derived macrophages from TLR2- expressing mice in contrast to their TLR2-knockout counterparts. Neither MEK1/ERK, p38 MAPK, nor NF-kappaB activation were important for the early cytoskeletal rearrangements observed, although suppression of these pathways is known to inhibit chemokine secretion by activated macrophages. Beta2-integrins blockade with a corresponding antibody inhibited macrophage spreading and polarization but had no effect on pseudopodia protrusions demonstrating the downstream position of integrin-mediated adhesion in PI3K- dependent signaling pathway leading to the motility phenotype. The obtained data demonstrate that the direct effect of mycobacteria on macrophage shape might be mediated through TLR2-dependent PI3K activation.

Effects of protein kinase and phosphatidylinositol-3 kinase inhibitors on growth and ultrastructure of Trypanosoma cruzi

An increasing number of protein kinases (PKs) of parasitic protozoa are being evaluated as drug targets. Some PK inhibitors display antiproliferative effects on protozoa. We tested three PK inhibitors on the growth and ultrastructure of epimastigotes of Trypanosoma cruzi and the effect of these drugs on intracellular amastigotes. They were staurosporine (serine/threonine kinase inhibitor), genistein (tyrosine kinase inhibitor), and wortmannin (phosphatidylinositol 3' (PI3) kinase inhibitor). All drugs inhibited epimastigote growth at the concentrations tested. Wortmannin inhibited parasite growth at the lowest concentrations. However, staurosporine was the most effective after 24 h treatment and genistein caused the stronger inhibition during the whole treatment (60-70% inhibition). The IC50 were: staurosporine: 6.43+/-1.28 microM; genistein: 6.54+/-1.86 microM; and wortmannin: 0.056+/-0.014 microM. These PK inhibitors had strong ultrastructural effects on the epimastigotes: abnormal chromatin condensation of the nucleus; loose flagellar membrane with the formation of blebs; incomplete cell division; autophagosomes and myelin-like figures. These drugs did not interfere with the division of intracellular amastigotes or with its differentiation to trypomastigotes. However, as trypanosomes have kinomes that contain a large set of protein kinases and phosphatases, PKs should not be disregarded as an important target for chemotherapy of Chagas disease.

Molecular cloning of a Trypanosoma cruzi cell surface casein kinase II substrate, Tc-1, involved in cellular infection

In this work, we report the cloning and characterization of the first cell surface casein kinase II (CKII) substrate (Tc-1) of Trypanosoma cruzi, the causative agent of Chagas' disease. Analysis of the gene sequence revealed a 1,653-bp open reading frame coding for 550 amino acid residues. Northern blot analysis showed a 4.5-kb transcript that is expressed in invasive trypomastigotes but not in noninvasive epimastigote forms of T. cruzi. Southern blot analysis indicates that Tc-1 is a single-copy gene. At the amino acid level, Tc-1 displayed 95% and 99% identity to two hypothetical proteins recently reported by the T. cruzi genome project. Analysis of the translated amino acid sequence indicates that the Tc-1 gene has a putative transmembrane domain with multiple cytoplasmic and extracellular CKII phosphosites. Exogenous human CKII was able to phosphorylate serine residues on both recombinant Tc-1 and Tc-1 of intact trypomastigotes. This phosphorylation was inhibited by the CKII inhibitors heparin and 4,5,6,7,-tetrabromo-2-azabenzimidazole. Immunoblots of solubilized trypomastigotes, epimastigotes, and amastigotes probed with anti-recombinant Tc-1 immunoglobulin G revealed a 62-kDa protein that is expressed only in infective trypomastigotes. Immunoprecipitation of labeled surface proteins of trypomastigotes indicated that the 62-kDa protein is a surface protein, and we found that the protein is uniformly distributed on the surface of trypomastigotes by direct immunofluorescence. Antibodies to Tc-1 effectively blocked trypomastigote invasion of host cells and consequently reduced parasite load. Preincubation of either trypomastigotes or myoblasts with CKII inhibitors blocked T. cruzi infection. Thus, for the first time, we describe a cell surface CKII substrate of a protozoan parasite that is phosphorylated by human CKII and that is involved in cellular infection.

Cell invasion by Trypanosoma cruzi amastigotes of distinct infectivities: studies on signaling pathways

Trypanosoma cruzi metacyclic trypomastigotes of the major phylogenetic lineages use specific signaling pathways to invade host cells. Using a panel of drugs, we studied if the differences in the ability of extracellular amastigotes (EA) from G (T. cruzi I) and CL (T. cruzi II) strains to invade host cells could be associated to activation of specific signaling routes. Sonicated extracts from G or CL strain EA induced transient raises in HeLa cell intracellular Ca(2+) levels in a dose-dependent manner. Treatment of EA with drugs that affect Ca(2+) release from inositol-1,4,5-triphosphate-sensitive stores did not significantly affect the infectivity of either strain, whereas EA of both strains treated with ionomycin plus NH(4)Cl or nigericin that release Ca(2+) from acidocalcisomes had their infectivity reduced. Treatment of parasites with adenylate cyclase activator forskolin increased the infectivity of both strains towards HeLa cells. These data, taken together, suggest that, for host cell invasion, G and CL strain EA engage signaling pathways that lead to an increase of cyclic adenosine monophosphate and Ca(2+) mobilization from acidocalcisomes. Moreover, treatment of EA with genistein reduced by approximately 45% the invasion of HeLa cells by G but not by CL strain, implicating a protein tyrosine kinase in the process. In line with this, HeLa cell extracts contained a protein tyrosine kinase activity that mediated the phosphorylation of 87- and 175-kDa polypeptides of EA from G but not from CL strain. Regarding the target cell response, the activation of host PI3 kinase appears to be required for invasion by either strain as treatment of HeLa cells with wortmannin reduced EA infectivity. These data overall reinforce the concept that cell invasion by T. cruzi EA markedly differs from the process involving metacyclic trypomastigotes.

Molecular basis of mammalian cell invasion by Trypanosoma cruzi

Establishment of infection by Trypanosoma cruzi, the agent of Chagas' disease, depends on a series of events involving interactions of diverse parasite molecules with host components. Here we focus on the mechanisms of target cell invasion by metacyclic trypomastigotes (MT) and mammalian tissue culture trypomastigotes (TCT). During MT or TCT internalization, signal transduction pathways are activated both in the parasite and the target cell, leading to Ca2+ mobilization. For cell adhesion, MT engage surface glycoproteins, such as gp82 and gp35/50, which are Ca2+ signal-inducing molecules. In T. cruzi isolates that enter host cells in gp82-mediated manner, parasite protein tyrosine kinase as well as phospholipase C are activated, and Ca2+ is released from I P3-sensitive stores, whereas in T. cruzi isolates that attach to target cells mainly through gp35/50, the signaling pathway involving adenylate cyclase appears to be stimulated, with Ca2+ release from acidocalciosomes. In addition, T. cruzi isolate-dependent inhibitory signals, mediated by MT-specific gp90, may be triggered both in the host cell and the parasite. The repertoire of TCT molecules implicated in cell invasion includes surface glycoproteins of gp85 family, with members containing binding sites for laminin and cytokeratin 18, enzymes such as cruzipain, trans-sialidase, and an oligopeptidase B that generates a Ca2+-agonist from a precursor molecule.

Host cell signaling and Trypanosoma cruzi invasion: do all roads lead to lysosomes?

Trypanosoma cruzi, the protozoan parasite that causes Chagas' disease in humans, is capable of invading and replicating within a wide variety of nucleated mammalian cell types. Host cell invasion by infective T. cruzi trypomastigotes is governed by parasite-triggered activation of host cell signaling pathways. Recent studies highlighting a role for host cell phosphatidylinositol 3-kinases (PI3Ks) in the T. cruzi invasion process have revealed surprising new insights into the mechanism of host cell invasion by this pathogen. In this Perspective, we discuss these findings and propose alternative models of T. cruzi invasion that incorporate this new information.

Placental alkaline phosphatase (PLAP) study in diabetic human placental villi infected with Trypanosoma cruzi

Previous work has demonstrated that PLAP activity decreases in serum and placental villi from term chagasic and diabetic pregnant women. In vitro, T. cruzi induces changes in human syncytiotrophoblast's PLAP. Our aim was to determine if infection with T. cruzi induces changes in PLAP activity in diabetic and chagasic women's placenta, in order to elucidate if PLAP plays a role in the mechanisms of interaction between placenta and T. cruzi, and whether hyperglycemic conditions could worsen the placental infection. Using zymogrammes, Western blot, biochemical and immunohistological techniques, PLAP activity was determined in placental villi from diabetic and chagasic women, and in normal placentas cultured under hyperglycemic conditions with or without trypomastigotes. A significant reduction of PLAP expression was immunologically detected in infected diabetic and normal placental villi cultured under hyperglycemic conditions of 71 and 81%, respectively, compared with controls. A significant decrease of PLAP specific activity was registered in homogenates and in the culture media from both infected diabetic and normal placentas under hyperglycemic conditions (of about 50-70%), and in chagasic ones (of about 87%), when compared with controls. Thus, PLAP might be involved in parasite invasion and diabetic and hyperglycemic placentas could be more susceptible to T. cruzi infection.

Lysosomal fusion is essential for the retention of Trypanosoma cruzi inside host cells

Trypomastigotes, the highly motile infective forms of Trypanosoma cruzi, are capable of infecting several cell types. Invasion occurs either by direct recruitment and fusion of lysosomes at the plasma membrane, or through invagination of the plasma membrane followed by intracellular fusion with lysosomes. The lysosome-like parasitophorous vacuole is subsequently disrupted, releasing the parasites for replication in the cytosol. The role of this early residence within lysosomes in the intracellular cycle of T. cruzi has remained unclear. For several other cytosolic pathogens, survival inside host cells depends on an early escape from phagosomes before lysosomal fusion. Here, we show that when lysosome-mediated T. cruzi invasion is blocked through phosophoinositide 3-kinase inhibition, a significant fraction of the internalized parasites are not subsequently retained inside host cells for a productive infection. A direct correlation was observed between the lysosomal fusion rates after invasion and the intracellular retention of trypomastigotes. Thus, formation of a parasitophorous vacuole with lysosomal properties is essential for preventing these highly motile parasites from exiting host cells and for allowing completion of the intracellular life cycle.

Role of placental alkaline phosphatase in the internalization of trypomatigotes of Trypanosoma cruzi into HEp2 cells

BACKGROUND

In vitro, Trypanosoma cruzi invades a wide variety of mammalian cells by an unique process that is still poorly understood. Trypomastigotes adhere to specific receptors on the outer membrane of host cells before intracellular invasion, causing calcium ion mobilization and rearrangement of host cell microfilaments.

OBJECTIVE

To test if placental alkaline phosphatase (PLAP), a trophoblast plasma membrane protein anchored by a glycosylphosphatidylinositol molecule, is involved in the transplacental transmission of this parasite.

METHOD

We cultured HEp2 cells with the parasite and studied PLAP and actin microfilaments. The results were correlated with invasion rate.

RESULTS

Human HEp2 tumour cells express PLAP. HEp2 cells infected with trypomastigotes showed alteration in their alkaline phosphatase activity and a different pattern of actin organization, compared to control cells. Perturbation of PLAP from HEp2 cells before infection with T. cruzi trypomastigotes decreased the invasion rate.

CONCLUSION

Placental alkaline phosphatase could be involved in the internalization of T. cruzi into HEp2 cells, via activation of tyrosine kinase and rearrangement of actin microfilaments.

Novel PI 3-kinase-dependent mechanisms of trypanosome invasion and vacuole maturation

Mammalian cell invasion by the protozoan parasite, Trypanosoma cruzi, is facilitated by the activation of host cell phosphatidylinositol 3 (PI 3)-kinases. We demonstrate that the well-characterized Ca2+-regulated lysosome-mediated parasite entry pathway is abolished by wortmannin pretreatment. In addition, we have characterized a novel route of T. cruzi invasion unexpectedly revealed in the course of this study. For over a decade, targeted exocytosis of lysosomes at the host cell plasma membrane was considered as the primary mechanism for T. cruzi entry into non-professional phagocytic cells. We now provide evidence that a significant fraction (50% or greater) of invading T. cruzi trypomastigotes exploit an alternate actin-independent entry pathway that involves formation of a tightly associated host cell plasma membrane-derived vacuole enriched in the lipid products of class I PI 3-kinases, PtdInsP3/PtdIns(3,4)P2. Initially devoid of lysosomal markers, the resultant parasite-containing vacuoles gradually acquire lysosome associated membrane protein 1 (lamp-1) and fluid phase endocytic tracer from the lysosomal compartment. In striking contrast to latex bead phagosomes, few T. cruzi vacuoles associate with the early endosomal marker, EEA1 and the 'maturation' process becomes refractory to PI 3-kinase inhibition immediately following parasite internalization. Jointly, these data provide a new paradigm for T. cruzi invasion of non-professional phagocytic cells and reveal a novel vacuole maturation process that appears to bypass the requirement for EEA1.

Trypanosoma cruzi infection induces microfilament depletion in human placenta syncytiotrophoblast

Congenital Chagas disease, endemic in Latin America, is associated with premature labour, miscarriage, and placentitis. Metacyclic trypomastigotes adhere to specific receptors on the outer membrane of host cells as a prelude to intracellular invasion, causing calcium ion mobilization, rearrangement of host cell microfilaments, recruitment of lysosomes and parasite internalization. The actin cytoskeleton plays an important role in many cellular processes including the parasite invasion into mammalian cells. In order to observe if placental cytoskeleton is altered in the process of parasite invasion into placental villi, actin microfilaments were studied. Using immunohistochemical techniques, it was observed that the presence of actin in the syncytiotrophoblast was intense throughout the brush border in control placentae belonging to non-chagasic women. But after culture with the trypomastigote, this labelling disappeared, indicating that the parasite induced disassembly of the cortical actin cytoskeleton when the placenta was infected. As a control, placentae from chagasic women were studied, and no actin was found. The same results were obtained by the electron microscope. We confirmed that cortical actin rearrangements may be an early step in the Trypanosoma cruzi invasion mechanism into placental cells, in order to allow lysosomes access to the plasma membrane, and formation of the parasitophorous vacuole. The recruitment of lysosomes occurs directly beneath the invasion site, and this process is required for parasite internalization.

Cellular signaling during the macrophage invasion by Trypanosoma cruzi

We have reported that protein tyrosine kinases play an important role in the invasion of Trypanosoma cruzi into primary resident macrophages. In the present study we carry out immunofluorescence assays, using monoclonal anti-phosphotyrosine antibodies, to reveal an accumulation of tyrosine-phosphorylated residues at the site of parasite association with the macrophage surface, colocalizing with host cell F-actin-rich domains. SDS-PAGE analysis of macrophage cell line IC-21 tyrosine phosphoproteins, labeled with [(35)S] L-methionine, revealed several peptides with increased levels of phosphorylation upon interaction with the parasite. Among them, were detected bands of 140, 120, 112, 94, 73, 67, and 56 kDa that match the molecular weights of proteins described as being tyrosine phosphorylated during events that lead to actin assembly in mononuclear phagocytes. The pretreatment of IC-21 macrophages with the tyrosine kinase inhibitor tyrphostin 23 inhibited trypomastigote uptake showing that tyrosine phosphorylation is important for the parasite penetration in this particular cell line. Immunofluorescence microscopy, using antibodies against p85, the regulatory subunit of phosphatidylinositol 3-kinase (PI 3-kinase), placed this enzyme also in the same sites, in accordance to what is reported for phagocytosis. We suggest that once the components of T. cruzi trypomastigotes surface are recognized by macrophage receptors, they trigger the activation of a tyrosine phosphorylation cascade, PI 3-kinase recruitment, and assembly of actin filaments at the site of initial cell-to-cell contact, resembling the events described during phagocytosis. These achievements support the model for a phagocytic-like actin-dependent invasion mechanism for T. cruzi trypomastigotes into macrophages.

Cell signalling and Trypanosoma cruzi invasion

Mammalian cell invasion by the protozoan pathogen Trypanosoma cruzi is critical to its survival in the host. To promote its entry into a wide variety of non-professional phagocytic cells, infective trypomastigotes exploit an arsenal of heterogenous surface glycoproteins, secreted proteases and signalling agonists to actively manipulate multiple host cell signalling pathways. Signals initiated in the parasite upon contact with mammalian cells also function as critical regulators of the invasion process. Whereas the full spectrum of cellular responses modulated by T. cruzi is not yet known, mounting evidence suggests that these pathways impinge on a number of cellular processes, in particular the ubiquitous wound-repair mechanism exploited for lysosome-mediated parasite entry. Furthermore, differential engagement of host cell signalling pathways in a cell type-specific manner and modulation of host cell gene expression by T. cruzi are becoming recognized as essential determinants of infectivity and intracellular survival by this pathogen.

Immediate/early response to Trypanosoma cruzi infection involves minimal modulation of host cell transcription

Host cell infection by the intracellular pathogen, Trypanosoma cruzi, involves activation of signaling pathways, cytoskeletal reorganization, and targeted recruitment of host cell lysosomes. To determine the consequences of T. cruzi invasion on host cell gene expression, high density microarrays consisting of approximately 27,000 human cDNAs were hybridized with fluorescent probes generated from T. cruzi-infected human fibroblasts (HFF) at early time points following infection (2-24 h). Surprisingly, no genes were induced > or =2-fold in HFF between 2 and 6 h post-infection (hpi) in repeated experiments while immediate repression of six host cell transcripts was observed. A significant increase in transcript abundance for 106 host cell genes was observed at 24 hpi. Among the most highly induced is a set of interferon-stimulated genes, indicative of a type I interferon (IFN) response to T. cruzi. In support of this, T. cruzi-infected fibroblasts begin to secrete IFNbeta at 18 hpi following the induction of IFNbeta transcripts. As compared with global transcriptional responses evoked by other intracellular pathogens, T. cruzi is a stealth parasite that elicits few changes in host cell transcription during the initiation of infection.

Trypanosoma cruzi trans-sialidase: a potent and specific survival factor for human Schwann cells by means of phosphatidylinositol 3-kinase/Akt signaling

Patients infected with Trypanosoma cruzi may remain asymptomatic for decades and show signs of neuroregeneration in the peripheral nervous system (PNS). In the absence of such neuroregeneration, patients may die in part by extensive neuronal destruction in the gastrointestinal tract. Thus, T. cruzi may, despite their invasion of the PNS, directly prevent cell death to keep nerve destruction in check. Indeed, T. cruzi invasion of Schwann cells, their prime target in PNS, suppressed host-cell apoptosis caused by growth-factor deprivation. The trans-sialidase (TS) of T. cruzi and the Cys-rich domain of TS reproduced the antiapoptotic activity of the parasites at doses (> or =3.0 nM) comparable or lower than those of bona fide mammalian growth factors. This effect was blocked by LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3K). TS also activated Akt, a downstream effector of PI3K. Ectopic expression of TS in an unrelated parasite, Leishmania major, turned those parasites into activators of Akt in Schwann cells. In contrast, the Cys-rich domain of TS did not block apoptosis in Schwann cells overexpressing dominant-negative Akt or constitutively active PTEN, a negative regulator of PI3K/Akt signaling. The results demonstrate that T. cruzi, through its TS, triggers the survival of host Schwann cells via the PI3K/Akt pathway, suggesting a role for PI3K/Akt in the pathogenesis of Chagas' disease.

Trypanosoma cruzi: phosphatidylinositol 3-kinase and protein kinase B activation is associated with parasite invasion

Multiple signal transduction events are triggered in the host cell during invasion by the protozoan parasite Trypanosoma cruzi. Here, we report the regulation of host cell phosphatydilinositol 3-kinase (PI3K) and protein kinase B (PKB/Akt) activities by T. cruzi during parasite-host cell interaction. Treatment of nonphagocytic cells (Vero, L(6)E(9), and NIH 3T3) and phagocytic cells (human and J774 murine macrophages) with the selective PI3K inhibitors Wortmannin and LY294002 significantly impaired parasite invasion in a dose-dependent fashion. A strong activation of PI3K and PKB/Akt activities in Vero cells was detected when these cells were incubated with trypomastigotes or their isolated membranes. Consistently, we were unable to detect activation of PI3K or PKB/Akt activities in host cells during epimastigote (noninfective) membrane-host cell interaction. Infection of transiently transfected cells containing an inactive mutant PKB showed a significant inhibition of invasion compared with the active mutant-transfected cells. T. cruzi PI3K-like activity was also required in host cell invasion since treatment of trypomastigotes with PI3K inhibitors prior to infection reduced parasite entry. Taken together, these results indicate that PI3K and PKB/Akt activation in parasites, as in host cells induced by T. cruzi, is an early invasion signal required for successful trypomastigote internalization.

Inositol metabolism in Trypanosoma cruzi: potential target for chemotherapy against Chagas' disease

Chagas' disease is a debilitating and often fatal disease caused by the protozoan parasite Trypanosoma cruzi. The great majority of surface molecules in trypanosomes are either inositol-containing phospholipids or glycoproteins that are anchored into the plasma membrane by glycosylphosphatidylinositol anchors. The polyalcohol myo-inositol is the precursor for the biosynthesis of these molecules. In this brief review, recent findings on some aspects of the molecular and cellular fate of inositol in T. cruzi life cycle are discussed and identified some points that could be targets for the development of parasite-specific therapeutic agents.