ECTO- AND EXO-PROTEIN KINASES IN SCHISTOSOMA MANSONI: REGULATION OF SURFACE PHOSPHORYLATION BY ACETYLCHOLINE AND IDENTIFICATION OF THE ALPHA SUBUNIT OF CKII AS A MAJOR SECRETED PROTEIN KINASE

The Schistosoma mansoni parasite life cycle involves complex developmental processes that enable it to cause severe hepatic damage. Protein phosphorylation has previously been implicated in the transformation of cercariae to schistosomula of S. mansoni. Here, we studied the possible involvement of surface (ecto) and shed (exo) protein kinases (PKs) in this developmental process. We found that ecto-PKs are indeed located on the surface of the schistosomula and can phosphorylate up to 5 distinct proteins at this location. Surface phosphorylation was sensitive to acetylcholine, which increased phosphorylation of 3 proteins and reduced phosphorylation of the other 2. The ecto-PKs can be shed from the surface into the incubation medium during parasite differentiation. The main exo-PK is CKII, as concluded from the substrate specificity of the PK, its inhibition by heparin, activation by spermin, and recognition by antibody directed to the anti–α-subunit of CKII in the incubation medium of the schistosomula. In spite of its similarity to the ecto-PKs, the activity of the exo-PK is not affected by addition of acetylcholine. These results indicate that ecto- and exo-PKs could be involved in the parasite's development or host–parasite interactions.