Dual Role of Signaling Pathways Leading to Ca²⁺and Cyclic AMP Elevation in Host Cell Invasion byTrypanosoma cruzi

Abstract

Cell invasion by the protozoan parasite Trypanosoma cruzi involves activation of host signaling pathways and the recruitment and fusion of lysosomes at the parasite entry site. A major signaling pathway regulating invasion of fibroblasts, epithelial cells, and myoblasts involves mobilization of Ca 2؉ from intracellular stores and requires the activity of a T. cruzi serine peptidase, oligopeptidase B (OPB). Deletion of the OPB gene results in a marked defect in trypomastigote virulence, consistent with a greatly reduced cell invasion capacity. Here we show that uptake by macrophages, on the other hand, is largely independent of OPB expression and sensitive to inhibition of by cytochalasin D. The residual invasion capacity of OPBnull trypomastigotes in fibroblasts still involves lysosome recruitment, although in a significantly delayed fashion. Transient elevations in intracellular Ca 2؉ concentrations were observed in host cells exposed to both wild-type and OPBnull trypomastigotes, but the signals triggered by the mutant parasites were less vigorous and delayed. The capacity of triggering elevation in host cell cyclic AMP (cAMP), however, was unaltered in OPBnull trypomastigotes. Modulation in cAMP levels preferentially affected the residual cell invasion capacity of OPBnull parasites, suggesting that this signaling pathway can play a dominant role in promoting cell invasion in the absence of the major OPB-dependent pathway.

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

“…Thus, our data do not support gross underrepresentation of lysosome-associated parasites. Moreover, the existence of a significant, lysosome-independent route for T. cruzi entry may offer an explanation for previous observations showing that interference with the function of synaptotagmin VII, an important component of Ca 2+ -regulated lysosome exocytosis machinery (Reddy et al, 2001), resulted in an ~90% inhibition of Ca 2+ -dependent lysosome exocytosis (Martinez et al, 2000), while the effect on T. cruzi invasion was considerably less profound (Caler et al, 2000).…”

Regulation of the expression of whiB1 in Mycobacterium tuberculosis: role of cAMP receptor protein

“…cAMP is an important signalling molecule regulating various cellular functions, including virulence factors from a diverse range of pathogens (Alspaugh et al, 2002;Caler et al, 2000;D'Souza & Heitman, 2001;Gross et al, 2003;Lee et al, 2003;Li et al, 2002). There is little information about the role of cAMP in mycobacteria, despite its presence in both fast-and slow-growing, as well as pathogenic and nonpathogenic, species (Padh & Venkitasubramanian, 1977).…”

Participation of Host Cell Actin Filaments during Interaction of Trypomastigote Forms of Trypanosoma cruzi with Host Cells.

“…In most of the studies such interference is negative, decreasing the rate of infection and increasing attachment (Barbosa et al, 1995;Meirelles et al, 1982). In other situations, however, it has been shown that cytochalasin treatment even enhances parasite penetration (Caler et al, 2000;Nogueira et al, 1976;Procopio et al, 1994;Schenkman et al, 1991;Sibley et al, 2000). We decided to re-investigate the problem using cytochalasin D in concentrations described for other systems and which proved to be highly effective at a concentration of 5 µg/ml.…”

“…Studies carried out by several groups have shown that involvement of host cell actin with cytochalasins interferes with the internalization of trypomastigote forms into vertebrate cells (Barbosa et al, 1995;Burleigh et al, 1995;Burleigh et al, 1998;Caler et al, 2000;Carvalho et al, 1999;Mortara et al, 1999;Nogueira et al, 1976;Procopio et al, 1994;Schenkman et al, 1991). In most of the studies such interference is negative, decreasing the rate of infection and increasing attachment (Barbosa et al, 1995;Meirelles et al, 1982).…”