The epidermal growth factor receptor (EGF-R) plays an important role in development and cell differentiation, and homologues of EGF-R have been identified in a broad range of vertebrate and invertebrate organisms. This work concerns the functional characterization of SER, the EGF-R-like molecule previously identified in the helminth parasite Schistosoma mansoni The epidermal growth factor receptor (EGF-R) 1 is a major key mediator of cell communication during animal development and homeostasis. EGF-R was the first receptor tyrosine kinase to be cloned (1), and its structure and activation pathways have been studied extensively. EGF-R represents the archetype of receptor tyrosine kinase with an extracellular ligand-binding part with two cysteine-rich repeats and an intracellular domain containing tyrosine kinase activity (2). In mammals, four isoforms of EGF-R have been characterized (EGF-R/ErbB-1, HER2/ErbB-2, HER3/ErbB-3, and HER4/ ErbB-4), and a number of different ligands, including epidermal growth factor (EGF)-like molecules, can selectively bind each isoform (3). Ligand binding activates the receptor by inducing the formation of homo-heterodimers. Dimerization triggers trans-phosphorylation and subsequent autophosphorylation of receptor molecules on tyrosine residues that provide docking sites for diverse effector and adaptor proteins. These partners (Grb2/Sos, p85-PI3K, PLC␥, and JAK) are active in different signal transduction cascades, such as the mitogenactivated protein kinase (MAPK), phosphoinositol 3-kinase, antiapoptotic kinase Akt, and several transcriptional regulatory pathways (reviewed in Ref. 4). Different homodimer-heterodimer combinations formed by EGF-R family members drive a complex signaling network within the MAPK pathway. The ERK pathway is the most recurrent and is mainly responsible for the mitogenic action of EGF receptors. Dysregulation of EGF-R signaling is therefore strongly oncogenic, and the direct implication of EGF-R isoforms in various cancers has been widely demonstrated. For this reason, EGF-R currently represents one of the major drug targets in human cancer therapy (5).In invertebrates, EGF-R isoforms appeared to be expressed in more limited numbers. A single isoform has been characterized in Caenorhabditis elegans (LET-23) (6) as well as in Drosophila melanogaster (DER) (7,8). A single cognate ligand (LIN-3) would be present in the worm (9), and four distinct cognate ligands (Vein, Gurken, Spitz, and Argos) would be present in the fly (10). These observations indicated that the EGF-R signaling module has grown in complexity from invertebrates to mammals. However, except for C. elegans and D. melanogaster models, few data are available at present about the role of the EGF-R family in invertebrate development.SER, the Schistosoma mansoni EGF-R homologue, is one of the three receptor tyrosine kinases that have been characterized in this trematode parasite (11,12). SER is present predominantly in schistosome muscles, suggesting that it could

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The Venus Kinase Receptor (VKR) is a single transmembrane molecule composed of an intracellular tyrosine kinase domain close to that of insulin receptor and an extracellular Venus Flytrap (VFT) structure similar to the ligand binding domain of many class C G Protein Coupled Receptors. This receptor tyrosine kinase (RTK) was first discovered in the platyhelminth parasite Schistosoma mansoni, then in a large variety of invertebrates. A single vkr gene is found in most genomes, except in S. mansoni in which two genes Smvkr1 and Smvkr2 exist. VKRs form a unique family of RTKs present only in invertebrates and their biological functions are still to be discovered. In this work, we show that SmVKRs are expressed in the reproductive organs of S. mansoni, particularly in the ovaries of female worms. By transcriptional analyses evidence was obtained that both SmVKRs fulfill different roles during oocyte maturation. Suppression of Smvkr expression by RNA interference induced spectacular morphological changes in female worms with a strong disorganization of the ovary, which was dominated by the presence of primary oocytes, and a defect of egg formation. Following expression in Xenopus oocytes, SmVKR1 and SmVKR2 receptors were shown to be activated by distinct ligands which are L-Arginine and calcium ions, respectively. Signalling analysis in Xenopus oocytes revealed the capacity of SmVKRs to activate the PI3K/Akt/p70S6K and Erk MAPK pathways involved in cellular growth and proliferation. Additionally, SmVKR1 induced phosphorylation of JNK (c-Jun N-terminal kinase). Activation of JNK by SmVKR1 was supported by the results of yeast two-hybrid experiments identifying several components of the JNK pathway as specific interacting partners of SmVKR1. In conclusion, these results demonstrate the functions of SmVKR in gametogenesis, and particularly in oogenesis and egg formation. By eliciting signalling pathways potentially involved in oocyte proliferation, growth and migration, these receptors control parasite reproduction and can therefore be considered as potential targets for anti-schistosome therapies.

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Grb14 is a member of the Grb7 family of adapters and acts as a negative regulator of insulin-mediated signaling. Here we found that the protein kinase C (PKC) interacting protein, ZIP, interacted with Grb14. Coimmunoprecipitation experiments demonstrated that ZIP bound to both Grb14 and PKC, thereby acting as a link in the assembly of a PKC-ZIP-Grb14 heterotrimeric complex. Mapping studies indicated that ZIP interacted through its ZZ zinc finger domain with the phosphorylated insulin receptor interacting region (PIR) of Grb14. PKC phosphorylated Grb14 under in vitro conditions and in CHO-IR cells as demonstrated by in vivo labeling experiments. Furthermore, Grb14 phosphorylation was increased under insulin stimulation, suggesting that the PKC-ZIP-Grb14 complex is involved in insulin signaling. The PIR of Grb14, which also interacts with the catalytic domain of the insulin receptor (IR) and inhibits its activity, was preferentially phosphorylated by PKC. Interestingly, the phosphorylation of Grb14 by PKC increased its inhibitory effect on IR tyrosine kinase activity in vitro. The role of ZIP and Grb14 in insulin signaling was further investigated in vivo in Xenopus laevis oocytes. In this model, ZIP potentiated the inhibitory action of Grb14 on insulininduced oocyte maturation. Importantly, this effect required the recruitment of PKC and the phosphorylation of Grb14, providing in vivo evidences for a regulation of Grb14-inhibitory action by ZIP and PKC. Together, these results suggest that Grb14, ZIP, and PKC participate in a new feedback pathway of insulin signaling.