EXPERIMENTAL PARASITOLOGY 90, 262–269 (1998) ARTICLE NO. PR984333 Entamoeba histolytica: Identification of Functional G s and G i Proteins as Possible Signal Transduction Elements in the Interaction of Trophozoites with Fibronectin L. G. Soid-Raggi, M. E. Torres-Ma ´ rquez,* and I. Meza Departamento de Biologı ´ a Celular, CINVESTAV del IPN, Me ´ xico, D.F., Me ´ xico; and *Departamento de Bioquı ´ mica, Facultad de Medicina, UNAM, Mexico, D.F., Me ´ xico Soid-Raggi, L. G., Torres-Ma ´ rquez, M. E., and Meza, I. 1998. Enta- INTRODUCTION moeba histolytica: Identification of functional G s and G i proteins as possible signal transduction elements in the interaction of trophozoites with fibronectin. Experimental Parasitology 90, 262–269. Trophozoites Entamoeba histolytica is the etiological agent of invasive of Entamoeba histolytica adhere to several components of the extracel- amebiasis in humans. Clinical observations as well as experi- lular matrix. Binding is mediated by specific receptors identified in mental data have suggested that trophozoites, after intestinal the parasite surface. Interaction of trophozoites with FN induces the formation of special adhesion structures that are dynamic cytoskeleton colonization, display an ability to adhere to and degrade membrane complexes and facilitate both adhesion and substrate degra- several extracellular matrix (ECM) components, thus facili- dation. The process requires activation of signaling pathways in which tating the migration of the amebas to target tissues in the PLC, IP 3 , Ca 2+ , and PKC participate. These observations, and recent host (Pe ´ rez-Tamayo et al. 1990). It has been proposed that experiments showing increments in cAMP in the trophozoites during this phenomenon is mediated by specialized surface mole- the interaction with FN, suggest that FN receptors in the amebic surface could be coupled to G-proteins. We report here that trophozoite plasma cules with receptor activity for ECM proteins (Talama ´ s- membrane peptides of 92, 49, 42, 37, and 21 kDa are ADP-ribosylated Rohana and Meza 1988; Meza and Franco 1988; Va ´ zquez- by Vibrio cholerae and Bordetella pertussis toxins. Three of them are Prado and Meza 1992; Talama ´ s-Rohana et al. 1992; Rosales- also recognized by antibodies prepared against the -subunit of G s - Encina et al. 1992). Studies in our group (Talama ´ s-Rohana and G i -proteins. Adenylyl cyclase activity detected in isolated mem- and Meza 1988; Meza and Franco, 1988) demonstrated that branes was strongly stimulated by treatment with the toxins. Forskolin (an agonist of the enzyme) and FN also induced increments in the in vitro interaction of trophozoites with fibronectin (FN) and enzymatic activity. Live amebas incubated with the toxins showed laminin substrates elicits the formation of specific adhe- enhanced adhesion to FN substrates and a striking reorganization of sive structures—resulting from dynamic membrane– polymerized actin. The actin rearrangement is reminiscent of the one cytoskeleton interactions—structurally similar to the adhe- induced by either forskolin or dibutyril cyclic AMP treatment. Our sion plaques found in other types of eukaryotic cells present data show the presence and the functionality of G s - and G i -like proteins and their apparent activation during in vitro interaction (Burridge et al. 1988). Within these structures, whose main of amebas with FN and complement previous observations indicating component is F-actin, molecules such as a FN-binding pro- the operation of signal transduction mechanisms in E. histolytica. tein, protein kinase C (PKC), several actin-binding proteins,  1998 Academic Press and thiol proteases, were identified. Also present were Index Descriptors and Abbreviations: Entamoeba histolytica; fibro- pp125 FAK and vinculin that are phosphorylated proteins spe- nectin; trimeric G-proteins; signal transduction; adhesion; cytoskeleton; FN, fibronectin; PLC, phospholipase C; IP 3 , inositol triphosphate; PKC, cifically located in adhesion plaques (Va ´ zquez et al. 1995). protein kinase C; cAMP, cyclic adenosine monophosphate; G s , stim- Later on, it was demonstrated that the interaction of the ulatory G-protein; G i , inhibitory G-protein; CTX, Vibrio cholerae parasite with FN triggers increments in inositol triphosphate toxin; PTX, Bordetella pertussis toxin; ECM, extracellular matrix (IP 3 ), intracellular Ca 2+ (Ca 2+ i ), and cyclic adenosine mono- components. phosphate (cAMP)—all second messengers in signaling 262 0014-4894/98 $25.00 Copyright  1998 by Academic Press All rights of reproduction in any form reserved.