Entamoeba histolytica: PKC transduction pathway activation in the trophozoite-fibronectin interaction

Interaction of Entamoeba histolytica trophozoites with fibronectin (FN) induces reorganization of the actin cytoskeleton and an increase in proteolytic activities that results in the degradation of the bound protein. The binding is mediated by a 37-kDa FN "receptor" localized in the trophozoite surface and associated to the cytoskeleton. The intracellular signals triggered by the ligand-receptor interaction are not well understood but it is plausible that they drive the observed responses. To address this issue, the activation of protein kinase C (PKC) pathways by FN binding was explored. Stimulation with phorbol myristate acetate (PMA) or FN produced a rapid increase in the amebas adhesion to the substrate and local release of proteases. Two PKC inhibitors, H7 and staurosporine, reverted the PMA stimulus and inhibited the response induced by FN. Interaction with FN as well as treatment with PMA produced transient changes of F-actin levels susceptible to inhibition by H7. Furthermore, phosphorylation of amebic proteins was enhanced in response to FN binding and PMA, while the presence of the PKC inhibitor diminished their phosphorylation. Inositol triphosphate production was stimulated by the FN binding, and PKC activation and translation was registered in cell extracts obtained from the stimulated amebas. Our results suggest that PKC pathways are activated in amebas by information transduced as a result of trophozoite binding to FN.