Platelet-activating factor induction of secreted phosphatase activity in Trypanosoma cruzi

The effects of platelet-activating factor (PAP) on the ecto-phosphatase act ivity of Trypanosoma cruzi were investigated. Living parasites hydrolyzed p -nitro-phenyl phosphate (p-NPP) at a rate of 5.71 +/- 0.37 nmol P-i mg(-1) min(-1). This ecto-phosphatase activity increased to 8.70 +/- 1.12 nmol P-i mg(-1) min(-1) when the cells were grown in the presence of 10(-9) M PAF. This effect was probably due to stimulation of the release of the ecto-phos phatase and/or the secretion of an intracellular phosphatase to the extrace llular medium, as suggested by cytochemical analysis. Modulation of the ect o-phosphatase activity was also observed when PAF was added during the time course of the reaction. WEB 2086, a competitive PAF antagonist, was able t o revert PAF effects when both were used at the same concentration. When PA F was added to a membrane enriched fraction preparation of T. cruzi no alte ration on the phosphatase activity was observed. This result suggests an in volvement of intracellular signaling, as PAF was only effective on intact c ells. Sphingosine and phorbol-12-myristate-13-acetate (PMA) were then used to investigate a possible involvement of protein kinase C (PKC) with PAF-in duced phosphatase secretion. Sphingosine by itself stimulated the secretion of a phosphatase but did not significantly interfere with PAF effects on t his enzyme. On the other hand, PMA was able to abrogate PAF-induced release of this phosphatase. These data are highly suggestive of a putative involv ement of signal transduction mediated by a ligand of mammalian origin (PAF) , through PKC and a specific receptor located on the cell surface of the hu man parasite Trypanosoma cruzi. (C) 1999 Academic Press.