Phosphatidylinositol‐specific phospholipase C induces biosynthesis of acetylcholinesterase via diacylglycerol in Schistosoma mansoni

Abstract

We have previously shown that two ectoenzymes, acetylcholinesterase (AChE) and alkaline phosphatase, are released from the surface and from particulate fractions of the parasite Schistosoma mansoni, by a phosphatidylinositol-specific phospholipase C (PtdIns-PLC) of bacterial origin. Exposure to PtdIns-PLC not only removes large amounts of AChE from the surface of intact, viable Schistosoma in culture, but is accompanied by a concomitant increase in overall levels of AChE in the parasite. The same phenomenon is observed with PtdIns-PLC from two different bacterial sources; Staphylococcus aureus and Bacillus thuringiensis. The increase in AChE levels may be ascribed to de novo synthesis since exposure to PtdIns-PLC, in the presence of the protein-synthesis inhibitor cycloheximide, totally blocked the increase in AChE activity. Furthermore, PtdIns-PLC induced an increased incorporation of [35S]methionine into the AChE immunoprecipitated by a specific anti-AChE serum. This increase is selective for AChE, since total protein synthesis remained almost unchanged after PtdIns-PLC addition, and little or no effect was observed on the enzymatic activity of alkaline phosphatase, which is also glycophosphatidylinositol anchored. Since cleavage of the phosphatidylinositol anchor by PtdIns-PLC should liberate diacylglycerol, which may act as second messenger, we investigated the effect of exogenous diacylglycerols on the synthesis of AChE in S. mansoni. Three different diacylglycerols were tested as possible inducers of AChE activity in the parasite. Both 1-oleoyl-2-acetyl-sn-glycerol and 1,2-dimyristoyl-sn-glycerol were able to increase AChE activity by 35-40% at concentrations of 25 micrograms/ml. A higher concentration of 1,2-dioctanoyl-sn-glycerol (70 micrograms/ml) was needed to produce an equivalent effect. Moreover, addition of phorbol-12-myristate-13-acetate, together with the calcium ionophore A23187, produced a similar increase in AChE activity. Finally, polymixin B, a specific inhibitor of protein kinase C, partially blocked the increase in AChE activity induced by PtdIns-PLC. Our results suggest the involvement of glycophosphatidyl membrane-anchor breakdown products as putative second messengers in the parasite S. mansoni.