Vol. 9, Issue 6, 1537-1547, June 1998

Virulence and Functions of Myosin II Are Inhibited by Overexpression of Light Meromyosin in Entamoeba histolytica

Philippe Arhets,^* Jean-Christophe Olivo, Pierre Gounon, Philippe Sansonetti,^* and Nancy Guillén^*§

 ^*Unité de Pathogénie Microbienne Moléculaire, Institut National de la Santé et de la Recherche Médicale U389, and  Station Centrale de Microscopie Electronique, Institut Pasteur, 75724 Paris Cédex 15, France; and  European Molecular Biology Laboratory, Cell Biophysics Programme, D-69112 Heidelberg, Germany

Several changes in cell morphology take place during the capping of surface receptors in Entamoeba histolytica. The amoebae develop the uroid, an appendage formed by membrane invaginations, which accumulates ligand-receptor complexes resulting from the capping process. Membrane shedding is particularly active in the uroid region and leads to the elimination of accumulated ligands. This appendage has been postulated to participate in parasitic defense mechanisms against the host immune response, because it eliminates complement and specific antibodies bound to the amoeba surface. The involvement of myosin II in the capping process of surface receptors has been suggested by experiments showing that drugs that affect myosin II heavy-chain phosphorylation prevent this activity. To understand the role of this mechanoenzyme in surface receptor capping, a myosin II dominant negative strain was constructed. This mutant is the first genetically engineered cytoskeleton-deficient strain of E. histolytica. It was obtained by overexpressing the light meromyosin domain, which is essential for myosin II filament formation. E. histolytica overexpressing light meromyosin domain displayed a myosin II null phenotype characterized by abnormal movement, failure to form the uroid, and failure to undergo the capping process after treatment with concanavalin A. In addition, the amoebic cytotoxic capacities of the transfectants on human colon cells was dramatically reduced, indicating a role for cytoskeleton in parasite pathogenicity.