Schistosoma mansoni TGF-β receptor II:: Role in host ligand- induced regulation of a schistosome target gene

Members of transforming growth factor-beta (TGF-beta) superfamily play pivotal roles in development in multicellular organisms. We report the functional characterization of the Schistosoma mansoni type II receptor (SmT beta RII). Mining of the S. mansoni expressed sequence tag (EST) database identified an EST clone that shows homology to the kinase domain of type II receptors from different species. The amplified EST sequence was used as a probe to isolate a cDNA clone spanning the entire coding region of a type II serine/threonine kinase receptor. The interaction of SmTbRII with SmT beta RI was elucidated and shown to be dependent on TGF-beta ligand binding. Furthermore, in the presence of human TGF-beta 1, SmT beta RII was able to activate SmT beta RI, which in turn activated SmSmad2 and promoted its interaction with SmSmad4, proving the transfer of the signal from the receptor complex to the Smad proteins. Gynaecophoral canal protein (GCP), whose expression in male worms is limited to the gynaecophoric canal, was identified as a potential TGF-beta target gene in schistosomes. Knocking down the expression of SmTbRII using short interfering RNA molecules (siRNA) resulted in a concomitant reduction in the expression of GCP. These data provide evidence for the direct involvement of SmT beta RII in mediating TGF-beta-induced activation of the TGF-beta target gene, SmGCP, within schistosome parasites. The results also provide additional evidence for a role for the TGF-beta signaling pathway in male-induced female reproductive development.