CHARACTERIZATION OF ADHESION PLATES INDUCED BY THE INTERACTION OF ENTAMOEBA-HISTOLYTICA TROPHOZOITES WITH FIBRONECTIN

Entamoeba histolytica trophozoites are pleiomorphic and highly motile cells. Although scarce fibrous material can be identified in the cytop lasm as elements of an organized cytoskeleton, clearly defined actin-c ontaining structures are formed at the sites of cell-matrix contact up on the interaction of trophozoites with fibronectin (FN) and other ext racellular matrix substrates. These structures are reminiscent of the adhesion plaques or focal contacts found in higher eukaryotic cells, w here actin filament bundles insert into specialized regions of the pla sma 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. He re, we report the isolation of amebic adhesion plates and the results of their structural and molecular analyses. Filaments, with the charac teristic diameter of F-actin, radiating from an electron-dense matrix, are the main feature. Actin is one of the main protein components of the plate; other proteins identified are a FN-binding protein-previous ly reported as a ''putative'' FN receptor-the actin-binding proteins m yosin II, myosin I, alpha cr-actinin, vinculin, and tropomyosin. The p resence in the isolated plates of several proteases and protein kinase s, in particular ppl25(FAK), is also demonstrated. Our results suggest that adhesion plates in amebas are dynamic membrane-cytoskeletal comp lexes participating not only in the attachment to FN substrates but al so providing the structural basis for their involvement in parasite lo comotion and invasiveness. (C) 1995 Wiley-Liss, Inc.