Entamoeba histolytica:Identification of Functional Gsand GiProteins as Possible Signal Transduction Elements in the Interaction of Trophozoites with Fibronectin

Soid-Raggi, L. G., Torres-Maárquez, M. E., and Meza, I. 1998.Entamoeba histolytica:Identification of functional G_sand G_iproteins as possible signal transduction elements in the interaction of trophozoites with fibronectin.Experimental Parasitology90, 262–269. Trophozoites ofEntamoeba histolyticaadhere to several components of the extracellular matrix. Binding is mediated by specific receptors identified in the parasite surface. Interaction of trophozoites with FN induces the formation of special adhesion structures that are dynamic cytoskeleton membrane complexes and facilitate both adhesion and substrate degradation. The process requires activation of signaling pathways in which PLC, IP₃, Ca²⁻, and PKC participate. These observations, and recent experiments showing increments in cAMP in the trophozoites during the interaction with FN, suggest that FN receptors in the amebic surface could be coupled to G-proteins. We report here that trophozoite plasma membrane peptides of 92, 49, 42, 37, and 21 kDa are ADP-ribosylated byVibrio choleraeandBordetella pertussistoxins. Three of them are also recognized by antibodies prepared against the α-subunit of G_s-and G_i-proteins. Adenylyl cyclase activity detected in isolated membranes was strongly stimulated by treatment with the toxins. Forskolin (an agonist of the enzyme) and FN also induced increments in the enzymatic activity. Live amebas incubated with the toxins showed enhanced adhesion to FN substrates and a striking reorganization of polymerized actin. The actin rearrangement is reminiscent of the one induced by either forskolin or dibutyril cyclic AMP treatment. Our present data show the presence and the functionality of G_s- and G_i-like proteins and their apparent activation duringin vitrointeraction of amebas with FN and complement previous observations indicating the operation of signal transduction mechanisms inE. histolytica.