Entamoeba histolytica trophozoites activated by collagen type I and Ca2+ have a structured cytoskeleton during collagenase secretion

A peculiar characteristic of Entamoeba histolytica trophozoites is their ca pacity to invade human tissues. One of the cellular determinants of invasio n may include adhesion to extracellular matrix components such as collagen, induction, and secretion of electron-dense granules (EDG) and tissue diges tion. The mechanism and receptors involved in this process are not well und erstood. Previous results suggested that cytoskeleton plays a very importan t role during EDG secretion. We present evidence suggesting that adhesion t o collagen and activation of EDG secretion are integrin-dependent events, s ince (31 subunits detected by antibodies are concentrated at membrane sites where collagen and actin were colocalized. Furthermore, the involvement of actin, vimentin, and tubulin in restructuring cytoskeleton during EDG secr etion was evident, since cytoskeleton isolation was possible exclusively in activated cells. Studies of immunolocalization of tubulin, actin, and vime ntin by immunofluorescence and transmission electron microscopy suggest a r ole for cytoskeleton in EDG secretion. (C) 2001 Wiley-Liss, Inc.