Characterization of adhesion plates induced by the interaction of Entamoeba histolytica trophozoites with fibronectin

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Abstract
Entamoeba histolytica trophozoites are pleiomorphic and highly motile cells. Although scarce fibrous material can be identified in the cytoplasm as elements of an organized cytoskeleton, clearly defined actin‐containing structures are formed at the sites of cell‐matrix contact upon the interaction of trophozoites with fibronectin (FN) and other extracellular matrix substrates. These structures are reminiscent of the adhesion plaques or focal contacts found in higher eukaryotic cells, where actin filament bundles insert into specialized regions of the plasma membrane and function as signal transduction organelles. Thus, the formation of adhesion plates in this parasitic ameba could be related to specific signaling responses involved in its invasive behavior. Here, we report the isolation of amebic adhesion plates and the results of their structural and molecular analyses. Filaments, with the characteristic diameter of F‐actin, radiating from an electrondense matrix, are the main feature. Actin is one of the main protein components of the plate; other proteins identified are a FN‐binding protein—previously reported as a “putative” FN receptor—the actin‐binding proteins myosin II, myosin I, α‐actinin, vinculin, and tropomyosin. The presence in the isolated plates of several proteases and protein kinases, in particular pp125FAK, is also demonstrated. Our results suggest that adhesion plates in amebas are dynamic membrane‐cytoskeletal complexes participating not only in the attachment to FN substrates but also providing the structural basis for their involvement in parasite locomotion and invasiveness.