Abstract

Mammalian cell invasion by Trypanosoma cruzi requires the activation of signal transduction pathways that result in a Ca2+ response both in the parasite and the host cell. By using drugs that interfere with the signalling processes, we investigated if the difference in the ability of T. cruzi isolates to invade host cells was associated with the activation of distinct signalling routes in the parasites. Experiments were performed with metacyclic trypomastigotes, the developmental forms that initiate infection in the mammalian host, using the highly invasive isolate CL and the poorly infective isolate G, which belong to distinct phylogenetic lineages. Treatment of parasites with adenylyl cyclase activator forskolin increased the infectivity of the G but not of the CL isolate towards HeLa cells. On the other hand, a specific protein tyrosine kinase inhibitor genistein reduced by similar to75% the penetration of CL but not of G isolate into HeLa cells. In the CL but not in the G isolate, protein tyrosine kinase mediated the phosphorylation of a 175 kDa protein in a manner inducible by a HeLa cell extract. Upon treatment with the phospholipase C inhibitor U73122, or with drugs such as caffeine, which affects Ca2+ release from inositol-1,4,5-triphosphate-sensitive stores, or thapsigargin, an inhibitor of intracellular Ca2+ transport ATPases, the infectivity of the CL but not of the G isolate diminished significantly (P < 0.005). In both isolates, a combination of ionomycin plus NH4Cl or nigericin released Ca2+ from acidic vacuoles containing a Ca2+/H+, exchange system. This treatment reduced the infectivity of metacyclic forms of the G but not of the CL isolate. Taken together, these data suggest that, fur host cell invasion, distinct signalling pathways are activated in metacyclic trypomastigotes of the two isolates, leading to Ca2+ release from different intracellular compartments. (C) 2002 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.