Secretory Pathway Activation by Interaction of Entamoeba histolytica Trophozoites with Fibronectin

Abstract

Entamoeba histolytica has a peculiar subcellular organization. Although secretory activation is well defined and apparently necessary for cell lytic and invasive properties, typical organelles involved in the secretory pathway of eukaryotic cells, such as the endoplasmic reticulum (ER) and Golgi complex, are not easily distinguished. Instead, a lattice of fine tubules and numerous vacuoles can be observed (1,2). Very recently, protein components of both ER and Golgi apparatus were identified in some vacuoles during secretion of proteins specific for cyst wall formation (3). As trophozoites glycosylate some of their proteins, it is possible that these proteins transit through regular secretory pathways. We have used the in vitro model established in our laboratory, where interaction of trophozoites with fibronectin (FN) elicits active secretion of proteases to the medium (4) to monitor the presence and organization of ER and Golgi-like cellular organelles. Protease secretion induced by FN substrates is one of the trophozoite responses to the signal transduction processes known to occur during its interaction with FN. The activation of secretory functions could then, as in the case of cyst formation, trigger the organization of the secretory machinery in the trophozoites.