Protein phosphorylation during the process of interaction of Toxoplasma gondii with host cells

Previous studies have shown that tachyzoites of Toxoplasma gondii were able to penetrate into macrophages using two mechanisms: phagocytosis and active penetration. We show here that previous incubation of the macrophages or the parasites with staurosporine, a wide range inhibitor of protein kinases, tyrfostin and genistein, specific inhibitors of tyrosine kinases, significantly interfered with the process of parasite-macrophage interaction. Staurosporine treatment induced the formation of many filopodium-like surface projections of the macrophages and markedly increased the attachment of the tachyzoites to the cell surface. Genistein inhibited about 50% penetration of T. gondii into macrophages. Previous incubation of tachyzoites with genistein also significantly inhibited their attachment to and penetration into the macrophages. Confocal laser scanning microscopy was used to locate phosphoproteins in macrophages interacting with tachyzoites. Antiphosphotyrosine antibodies labeled the surface of macrophages, but not L929 cells, incubated in presence of T. gondii, even those cells did not show associated parasites. Anti phosphotyrosine, phosphothreonine and phosphoserine antibodies labeled the region surrounding the parasitophorous vacuoles. These observations suggest that protein phosphorylation is a key event in the process of T. gondii-host cell interaction.