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, Ptdlns-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 pg/ml. A higher concentration of 1,2-dioctanoyl-sn-glycerol (70 pg/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. nzansoni.

Acetylcholinesterase from Schistosoma mansoni: interaction of globular species with heparin

“…We showed previously that approx. 50 % of the AChE of S. mansoni larval stages is a G # form, attached via a GPI anchor to the surface of the tegumental membrane, while the other 50 % is internal, and associated mainly with the musculature [25,29]. Our present data show that only this internal AChE interacts with heparin ; however, despite the evidence for its association with the musculature, the molecular form involved is a G form rather than an A form.…”

“…This indicates that, like many other parasite surface proteins [26], this surface AChE is a glycosylphosphatidylinositol (GPI)-anchored protein [27], analogous to the GPI-anchored G # form of AChE present in, for example, the Torpedo electric organ [28]. The removal of the surface AChE by PI-PLC in situ activates de no o biosynthesis of AChE to replenish the surface enzyme [29]. This phenomenon is specific for AChE, and is not observed for another GPI-anchored enzyme of the parasite, alkaline phosphatase.…”

“…In order to study separately the heparin-binding properties of the surface and internal AChE forms, schistosomula, cultured for 24 h, were treated with PI-PLC as described previously [27,29]. The AChE activity released from the surface of the intact schistosomula by PI-PLC treatment, and the residual enzyme extracted from the whole organism with detergent, were each fractionated on the heparin-Sepharose column.…”

“…The elution pattern on the heparin-Sepharose column for the detergent-solubilized material obtained from the schistosomula after PI-PLC treatment is shown in Figure 3(B). Part of the AChE activity (10-30 %) was not bound to the column, and may represent replenished surface enzyme synthesized subsequent to exposure to PI-PLC [29]. However, most of the AChE activity was bound to the column, and was only eluted at approx.…”

Distribution of acetylcholinesterase activity during the development of cysticercoids of Hymenolepis diminuta (Cestoda)

“…According to Nizami et al (1977) some mature trematodes also secrete AChE to their environment. Non-neural AChEs operate in the tegument, testes, and ovary of Fasciola hepatica (Probert and Durrani 1977), in the tegument of schistosomes (Levi-Schaffer et al 1984, Espinoza et al 1991, Jones et al 2002, and in the tegument of the mature tapeworms Echinococcus granulosus, Hydatigera taeniaformis (Shield 1969) and Raillietina johri (Roy 1980). However, the true role played by AChEs in these structures is generally unknown.…”