Entamoeba histolytica: FYVE-finger domains, phosphatidylinositol 3-phosphate biosensors, associate with phagosomes but not fluid filled endosomes

Endocytosis is an important virulence function for Entamoeba histolytica, the causative agent of amoebic dysentery. Although a number of E. histolytica proteins that regulate this process have been identified, less is known about the role of lipids. In other systems, phosphatidylinositol 3-phosphate (PI3P), a product of phosphatidylinositol 3-kinase (PI 3-kinase), has been shown to be required for endocytosis. FYVE-finger domains are protein motifs that bind specifically to PI3P. Using a PI3P biosensor consisting of glutathione-S-transferase (GST) fused to two tandem FYVE-finger domains, we have localized PI3P to phagosomes but not fluid-phase pinosomes in E. histolytica, suggesting a role for PI3P in phagocytosis. Treatment of cells with PI 3-kinase inhibitors impaired GST-2 x FYVE-phagosome association supporting the authenticity of the biosensor staining. However, treatment with PI 3-kinase inhibitors did not inhibit E. histolytica-particle interaction, indicating that PI3P is not required for the initial step, but is required for subsequent steps of phagocytosis.