title: Platelet-activating factor induction of secreted phosphatase activity in Trypanosoma cruzi.
abstract: The effects of platelet-activating factor (PAF) on the ecto-phosphatase activity of Trypanosoma cruzi were investigated. Living parasites hydrolyzed p-nitrophenyl 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-phosphatase and/or the secretion of an intracellular phosphatase to the extracellular medium, as suggested by cytochemical analysis. Modulation of the ecto-phosphatase activity was also observed when PAF was added during the time course of the reaction. WEB 2086, a competitive PAF antagonist, was able to revert PAF effects when both were used at the same concentration. When PAF was added to a membrane enriched fraction preparation of T. cruzi, no alteration on the phosphatase activity was observed. This result suggests an involvement of intracellular signaling, as PAF was only effective on intact cells. Sphingosine and phorbol-12-myristate-13-acetate (PMA) were then used to investigate a possible involvement of protein kinase C (PKC) with PAF-induced phosphatase secretion. Sphingosine by itself stimulated the secretion of a phosphatase but did not significantly interfere with PAF effects on this enzyme. On the other hand, PMA was able to abrogate PAF-induced release of this phosphatase. These data are highly suggestive of a putative involvement of signal transduction mediated by a ligand of mammalian origin (PAF), through PKC and a specific receptor located on the cell surface of the human parasite Trypanosoma cruzi.
authors.affiliation: Instituto de Microbiologia Prof. Paulo de Góes, UFRJ, Rio de Janeiro, RJ, 21941-590, Brazil.
authors.forename: C O
authors.initials: CO
authors.lastname: Rodrigues
authors.forename: P M
authors.initials: PM
authors.lastname: Dutra
authors.forename: F S
authors.initials: FS
authors.lastname: Barros
authors.forename: T
authors.initials: T
authors.lastname: Souto-Padrón
authors.forename: J R
authors.initials: JR
authors.lastname: Meyer-Fernandes
authors.forename: A H
authors.initials: AH
authors.lastname: Lopes
mesh_terms: D000818:Animals; D001381:Azepines / Q000494:pharmacology; D017077:Culture Media, Conditioned / Q000737:chemistry; D010749:Phosphoprotein Phosphatases / Q000032:analysis / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D010980:Platelet Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D015398:Signal Transduction / Q000187:drug effects; D013110:Sphingosine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors; D014230:Triazoles / Q000494:pharmacology; D014349:Trypanosoma cruzi / Q000187:drug effects* / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism
chemical_list: D001381:Azepines; D017077:Culture Media, Conditioned; D010972:Platelet Activating Factor; D010975:Platelet Aggregation Inhibitors; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D014230:Triazoles; C039351:platelet activating factor receptor; C052518:WEB 2086; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; D013110:Sphingosine; D013755:Tetradecanoylphorbol Acetate