Interaction between pathogenic amebas and fibronectin: substrate degradation and changes in cytoskeleton organization.

Abstract

Abstract. Invasion of human tissues by the parasitic protozoan Entamoeba histolytica is a multistep process involving, as a first step, the recognition of surface molecules on target tissues by the amebas or trophozoites. This initial contact is followed by the release of proteolytic and other activities that lyse target cells and degrade the extracellular matrix.In other parasitic diseases, as well as in certain cancers, the interaction of invasive organisms or cells with fibronectin (FN) through specific receptors has been shown to be the initial step in target cell recognition. Interaction with FN triggers the release of proteolytic activities necessary for the effector cell migration and invasion. Here, we describe the specific interaction of Entamoeba histolytica trophozoites with FN, and identify a 37-kD membrane poptide as the putative receptor for FN. The interaction between the parasite and FN leads to a response reaction that includes the secretion of proteases that degrade the bound FN and the rearrangement of amebic actin into "adhesion plates" at sites of contact with FN-coated surfaces. The kinetics of the interaction was determined by measuring the binding of soluble ~25I-FN to the trophozoites and visualization of the bound protein using specific antibodies. Degradation of FN was measured by gel electrophoresis and the release of radioactivity into the incubation medium. Focal degradation of FN was visualized as black spots under the trophozoites at contact sites with fluorescent FN.We conclude that the interaction of E. histolytica with FN occurs through a specific surface receptor. The interaction promotes amebic cytoskeleton changes and release of proteases from the parasite. The binding and degradation of extracellular matrix components may facilitate the migration and penetration of amebas into tissues, causing the lesions seen in human hosts.

Involvement of the actin cytoskeleton and p21rho-family GTPases in the pathogenesis of the human protozoan parasite Entamoeba histolytica

“…Pharmacological inhibitors of PKC can block the phosphorylation of adhesion plate proteins that normally follows interaction with fibronectin (49). The interaction of amebae with proteins of the ECM results in local degradation at the site of contact between trophozoites and the substrate (13). This degradation has been correlated with the formation of adhesion plates (56) and it is thought that the formation of the plates may orient the secretion of proteases.…”

“…The binding of trophozoites to molecules of the ECM leads to the formation of amebic adhesion plates (13). Amebic adhesion plates contain several proteins similar to those found in mammalian focal adhesions or focal contacts including actin, the actin binding proteins α-actinin, vinculin and tropomyosin, myosins I and II and a protein similar to pp125 focal adhesion kinase (FAK) (50).…”

“…Amebic adhesion plates contain several proteins similar to those found in mammalian focal adhesions or focal contacts including actin, the actin binding proteins α-actinin, vinculin and tropomyosin, myosins I and II and a protein similar to pp125 focal adhesion kinase (FAK) (50). Binding of amebae to the ECM can be mediated by a 37-kDa receptor protein specific for fibronectin (13,56). A 140-kDa protein that is similar to the mammalian fibronectinbinding protein, ß 1 integrin, has also been found in the ameba (57).…”

“…This adherence is mediated by surface receptors on the invading cell, and their ligation is thought to trigger rearrangement of the cytoskeleton and the secretion of proteases. Trophozoites of E. histolytica have been shown to preferentially recognize and degrade ECM both in vitro and in vivo (13,(53)(54)(55). This recognition and attachment has been specifically demonstrated in the case of amebic fibronectin receptors, some of which resemble metazoan ß-integrins (56,57).…”

“…Binding of amebae to the ECM is accompanied by the directed secretion of proteases into the matrix in vitro (13). The molecular events involved in the initial recognition of host target cells and ECM by the ameba are just beginning to be characterized, though many of the proteins involved in adherence are known to some extent.…”