Metacyclic trypomastigote forms of Trypanosoma cruzi strains from genetic group TcI are poorly invasive, this property being attributed to the expression. and release at high levels of gp90, the surfasse molecule that functions as a negative modulator of cell invasion. Expression of g90 at low levels is characteristic of invasive strains from genetic group TcVI that use the surface molecule gp82 for their internalization. Gp90 and gp82 bind to still non identified host cell receptors and exert opposite efffects: gp82 promotes the spreading of lysosomes culminating in exocytosis whereas gp90 acts in retaining lysosomes in the perinuclear area. As metacyclic forms of TcI and TcVI groups express high levels of gp82, the binding of gp90 possibly prevais over gp82 during parasite-host cell interaction. Opposite to what occurs in full nutrient medium, invasion by TcI strains in nutrietn-depleted médium reaches levels comparable to those of TcVI strains. Incubation of host cells for a short time (30-60 minutos) in PBS++, medium without macromolecules or amino acids, results in lysosome mobiliazation and exocytosis. Under this condition, the interaction of TcI metacyclic forms is probably mediated by gp82. Experiments with G strain (TcI) in PBS++ indicate that the host cell protein tyrosine kinase (PTK) is involved. The focal adhesion molecule FAK, which has kinase activitiy, is required for invasion of tissue culture-derived trypomastigotes into cardiomyocytes. There is no information about the participation of FAK in the internalization of metacyclic forms. For the increase in cell invasion by G strain in PBS++ may be also contributing the release of gp90 and gp82 in lower amounts as compared to complete medium. Differently from CL strain (TcVI), when incubated in complete medium with serum, G strain metacyclic forms release high amounts of gp90 and gp82, which interfere with the parasite-host cell interaction. In PBS++, the release of gp90 and gp82 is much lower. Recent observations have shown that the host cell invasion by G strain in PBS++ may be inhibited by some amino acids, which eventually would affect the secretion of gp90 and gp82 or the lysosome spreading. Another question to be clarified refers to gp90 and gp82 receptors. The specific objectives of this project are: i) to establish cell lines with depleted FAK expression. and examine their susceptibility to invasion by metacyclic forms, ii) to determine whether gp90 or gp82 has any effect on FAK phosphorylation, iii) to examine the effect of each amino acid present in the compostion of complete médium as concerns the release of gp90 and gp82 by the parasites in PBS++ and the capacity to affect the lysosome mobilization, iv) to identify the host cell component that binds to gp90.
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