Dual role of signaling pathways leading to Ca(2+) and cyclic AMP elevation in host cell invasion by Trypanosoma cruzi

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.

Lysosomes and the plasma membrane: trypanosomes reveal a secret relationship

Studies of the cell invasion mechanism of the parasite Trypanosoma cruzi led to a series of novel findings, which revealed a previously unsuspected ability of conventional lysosomes to fuse with the plasma membrane. This regulated exocytic process, previously regarded mostly as a specialization of certain cell types, was recently shown to play an important role in the mechanism by which cells reseal their plasma membrane after injury.

Trypanosoma cruzi: in vitro phosphorylation of tubulin by a protein kinase CK2-like enzyme

One predominant 55-kDa polypeptide was phosphorylated in vitro in Trypanosoma cruzi homogenates prepared from three differentiation stages: epimastigotes, trypomastigotes, and spheromastigotes. Anti-alpha and anti-beta tubulin monoclonal antibodies immunoprecipitated the phosphorylated 55-kDa polypeptide from epimastigote extracts. Phosphoserine was the only residue phosphorylated in vitro in the 55-kDa polypeptide and in immunoprecipitated alpha tubulin. The phosphorylation of both the 55-kDa polypeptide and exogenously added casein was inhibited with GTP, heparin, and 2,3-bisphosphoglycerate in a dose-dependent manner, indicating the involvement of a CK2-like protein kinase. Moreover, when tubulin was isolated from an epimastigote homogenate by ultracentrifugation, followed by DEAE-Sephacel chromatography, a protein kinase that phosphorylated tubulin and casein co-purified with this cytoskeletal component. This result suggests an association between tubulin and its corresponding protein kinase in T. cruzi.

From the cell biology to the development of new chemotherapeutic approaches against trypanosomatids: dreams and reality

Members of the Trypanosomatidae family comprise a large number of species that are causative agents of important diseases such as sleeping sickness, Chagas' disease and Leishmaniasis. These organisms are also of biological interest since they are able to change the morphology according to the environment where they live, through a process of reversible cell transformation, and possess structures and organelles that are not found in mammalian cells. This review analyses the process of transformation, which takes place during the life cycle of Trypanosoma cruzi in the vertebrate and invertebrate hosts. Special attention is given to the interaction of the parasite with vertebrate cells. In addition, the present knowledge of structures and organelles such as the nucleus, the plasma membrane, the sub-pellicular microtubules, the flagellum, the kinetoplast-mitochondrion complex, the peroxisome (glycosome), the acidocalcisome and the structures and organelles involved in the endocytic pathway, is reviewed from a cell biology perspective. The possible use of available data for the development of new anti parasite drugs is also discussed.

Participation of host cell actin filaments during interaction of trypomastigote forms of Trypanosoma cruzi with host cells

The involvement of actin filaments from the host cell on the process of invasion of trypomastigote forms of Trypanosma cruzi was analyzed in seven different cell lines. Prior incubation of all cell lines with cytochalasin D, under conditions which interfere with actin filaments, markedly inhibited parasite internalization and increased parasite attachment. Attached parasites were readily ingested following washing of the drug-treated cells. Cytochalasin treatment interfered with the distribution of actin filaments of the host cell as evaluated by visualization of the filaments using confocal laser scanning microscopy of cells incubated in the presence of FITC-phalloidin. Concentration of actin filaments could be observed in most, but not all, parasites in the process of internalization. We also treated LLCMK 2 and macrophage cells with Jasplakinolide, a drug that stabilizes actin filaments, before interaction with the trypomastigote forms. This drug partially inhibits parasite invasion into the cells. Prior incubation of the host cells in the presence of colchicine, which interfere with microtubules, also inhibited parasite internalization into the cells.

Trypanosoma cruzi prolyl oligopeptidase Tc80 is involved in nonphagocytic mammalian cell invasion by trypomastigotes

Trypanosoma cruzi is an intracellular protozoan parasite able to invade a wide variety of mammalian cells. To have access to the target organs/cells, the parasite must cross the basal laminae and the extracellular matrix (ECM). We previously characterized an 80-kDa proteinase (Tc80) secreted by the infective trypomastigotes that hydrolyzes native collagens and might be involved in infection by degrading ECM components. Here, we present evidence indicating a role for Tc80 in the invasion of nonphagocytic cells. Tc80 was classified as a member of the prolyl oligopeptidase (POP) family of serine proteases and was also found to hydrolyze fibronectin. Selective inhibitors for POP Tc80 were synthesized that blocked parasite entry into cells. Blockage occurred when trypomastigotes were preincubated with irreversible inhibitors but not after host cell preincubation, and the blockage correlated with inhibition of POP Tc80 activity in treated parasites. These data and the enzyme location inside a vesicular compartment close to the flagellar pocket, a specialized domain in endocytosis/exocytosis, strongly suggest a role for POP Tc80 in the maturation of parasite protein(s) and/or, after secretion, in a local action on parasite or host cell/ECM components required for invasion.