Phospholipid signalling pathways in Trypanosoma cruzi growth control

The role of phospholipids (PLs) in the signal transduction pathways that ar e activated by a mitogenic stimulus (foetal calf serum) in Trypanosoma cruz i epimastigotes (EPI) was investigated. Only phosphatidylinositol-bis-phosp hate was significantly altered in this process. Other phosphoinositides, in cluding major PLs such as phosphatidylcholine and phosphatidylethanolamine, were unaltered. Lysophosphatidic acid, reported to be the primary active s ubstance in effects of serum in other systems, had no mitogenic activity wh en added to epimastigote cultures. Involvement of phosphoinositide-specific phospholipase C was established using the inhibitors ET-18-OCH3 and U73122 , which prevented phosphatidylinositol-bis-phosphate hydrolysis; the latter compound decreased T. cruz proliferation. The intracellular signalling dow nstream to the phospholipase C was mediated by Ca2+/PL-dependent protein ki nase and Ca2+/calmodulin-dependent protein kinase II, judging from the mark ed decrease in replication caused by the specific inhibitors staurosporine, derythro-sphingosine and KN-93. Previous reports have demonstrated a dual control of cell growth in EPI, whose proliferation is stimulated by the act ivation of a phospholipase C system and inhibited by activation of an adeny late cyclase system. Investigating this 'cross-talk' phenomenon, we observe d that an increase in intracellular cAMP inhibited growth mediated by a cAM P-dependent protein kinase, but did not cause PL alterations, and also did not prevent the effect of serum on them. (C) 1999 Elsevier Science B.V. All rights reserved.