Entamoeba histolytica trophozoites activated by collagen type I and Ca²⁺ have a structured cytoskeleton during collagenase secretion

Abstract

A peculiar characteristic of Entamoeba histolytica trophozoites is their capacity to invade human tissues. One of the cellular determinants of invasion may include adhesion to extracellular matrix components such as collagen, induction, and secretion of electron-dense granules (EDG) and tissue digestion. The mechanism and receptors involved in this process are not well understood. Previous results suggested that cytoskeleton plays a very important role during EDG secretion. We present evidence suggesting that adhesion to collagen and activation of EDG secretion are integrin-dependent events, since beta1 subunits detected by antibodies are concentrated at membrane sites where collagen and actin were colocalized. Furthermore, the involvement of actin, vimentin, and tubulin in restructuring cytoskeleton during EDG secretion was evident, since cytoskeleton isolation was possible exclusively in activated cells. Studies of immunolocalization of tubulin, actin, and vimentin by immunofluorescence and transmission electron microscopy suggest a role for cytoskeleton in EDG secretion.

Entamoeba histolytica: Lipid rafts are involved in adhesion of trophozoites to host extracellular matrix components

“…Hgl, the heavy subunit of the Gal/GalNAc lectin, exhibits homology to β2 and β7 mammalian integrins in its C-terminus (Vines et al, 1998). Indeed, many of E. histolytica homologs of mammalian focal adhesion proteins, including actin, pp125 FAK , paxillin and vinculin, are activated upon exposure to ECM components (de Lourdes et al, 2001;Perez et al, 1996;Perez et al, 1998;Flores-Robles et al, 2003;Franco et al, 2002). The results of the present study demonstrate that rafts may cooperate with or form a platform for focal adhesion-like structures utilized during interaction with collagen.…”

“…Several lines of evidence suggest that adhesion of E. histolytica to ECM may be likened to focal adhesions of higher eukaryotes [Talamas-Rohana and Meza, 1988;de Lourdes et al, 2001). This interaction is also believed to activate parasite signal transduction pathways and virulence (Talamas-Rohana and Meza, 1988;de Lourdes et al, 2001;Cruz-Vera et al, 2003;Debnath et al, 2004;Perez et al, 1996;Perez et al, 1998;Flores-Robles et al, 2003;Franco et al, 2002;Talamas-Rohana and Rios, 2000). For example, exposure of E. histolytica to collagen induces both actin reorganization within the trophozoites and phosphorylation of tyrosine residues on the E. histolytica homolog of pp125 FAK (de Lourdes et al, 2001;Perez et al, 1996).…”