ABSTRACT
We previously reported that Frizzled homologue 10 (FZD10), a member of the Wnt signal receptor family, was highly and specifically upregulated in synovial sarcoma and played critical roles in its cell survival and growth. We here report a possible molecular mechanism of the FZD10 signaling in synovial sarcoma cells. We found a significant enhancement of phosphorylation of the Dishevelled (Dvl)2/Dvl3 complex as well as activation of the Rac1-JNK cascade in synovial sarcoma cells in which FZD10 was overexpressed. Activation of the FZD10-Dvls-Rac1 pathway induced lamellipodia formation and enhanced anchorage-independent cell growth cells. FZD10 overexpression also caused the destruction of the actin cytoskeleton structure, probably through the downregulation of the RhoA activity. Our results have strongly implied that FZD10 transactivation causes the activation of the non-canonical Dvl-Rac1-JNK pathway and plays critical roles in the development/progression of synovial sarcomas.
Subject(s)
Adaptor Proteins, Signal Transducing/metabolism , Frizzled Receptors/genetics , JNK Mitogen-Activated Protein Kinases/metabolism , Phosphoproteins/metabolism , Receptors, G-Protein-Coupled/genetics , Sarcoma, Synovial/metabolism , Signal Transduction , rac1 GTP-Binding Protein/metabolism , Actins/metabolism , Adaptor Proteins, Signal Transducing/genetics , Animals , Blotting, Western , COS Cells , Cell Adhesion/physiology , Cells, Cultured , Chlorocebus aethiops , Cytoskeleton/metabolism , Dishevelled Proteins , Enzyme Activation , Frizzled Receptors/metabolism , Humans , Immunoenzyme Techniques , Immunoprecipitation , JNK Mitogen-Activated Protein Kinases/genetics , Mesenchymal Stem Cells/metabolism , Phosphoprotein Phosphatases/metabolism , Phosphoproteins/genetics , Phosphorylation , Pseudopodia/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , Receptors, G-Protein-Coupled/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Sarcoma, Synovial/genetics , Transcriptional Activation , rac1 GTP-Binding Protein/genetics , rhoA GTP-Binding Protein/antagonists & inhibitors , rhoA GTP-Binding Protein/metabolismABSTRACT
I-2(PP2A)/SET, an inhibitor of protein phosphatase 2A, is supposed to be one of the oncoproteins associated with human myeloid leukemia. The I-2(PP2A)/SET gene expression was observed ubiquitously among all the rat tissues examined, but low in liver. Of interest is that the expression in the rat primary hepatomas and hyperplastic nodules was significantly elevated. The experiments using regenerating livers after partial hepatectomy showed that the expression of I-2(PP2A)/SET mRNA was low at the quiescent hepatocytes, but up-regulated at 12-24 h after partial hepatectomy, which corresponds to the mid G1 to S transition in the cell cycle. These results suggested the importance of I-2(PP2A)/SET in the hepatocarcinogenesis and hepatic cell proliferation.
Subject(s)
Liver Neoplasms, Experimental/genetics , Liver Regeneration/genetics , Proteins/genetics , Amino Acid Sequence , Animals , Base Sequence , Chromosomal Proteins, Non-Histone , DNA, Complementary/genetics , DNA-Binding Proteins , Gene Expression Regulation, Neoplastic , Histone Chaperones , Liver/metabolism , Liver/physiology , Liver Neoplasms, Experimental/metabolism , Male , Mice , Molecular Sequence Data , Phosphoprotein Phosphatases/antagonists & inhibitors , Protein Biosynthesis , Protein Phosphatase 2 , RNA, Messenger/genetics , RNA, Messenger/metabolism , Rats , Rats, Sprague-Dawley , Rats, Wistar , Tissue Distribution , Transcription Factors , Up-RegulationABSTRACT
Porcine cardiac myosin monomers in equilibrium with filaments under physiological conditions were observed to have two conformations, extended and folded forms, upon electron microscopy and gel filtration HPLC. The conformational state was independent of ATP and the phosphorylation of regulatory light chain. The folded monomers of cardiac myosin were mainly in an open conformation with only one bend in the tail, and may not trap the hydrolysis products of ATP, as assessed by single turnover experiments. These properties are similar to those of the folded monomers of rabbit skeletal myosin [Katoh, T., Konishi, K., and Yazawa, M. (1998) J. Biol. Chem. 273, 11436-11439]. The conformational states of skeletal and cardiac myosin monomers were not affected by pH between 7.0 and 8.5. Although significant disassembly of filaments and thus an increase in the monomer concentration were observed with an increase in pH. The results indicate that the pH-dependent change in filament assembly is due to a shift of equilibrium between the filaments and extended monomers toward filament disassembly. The Mg2+-ATPase activity of these myosin monomers decreased with a decrease in the salt concentration below approximately 0.1 M, suggestive of the formation of a closed conformation similar to the conformation of 10S smooth myosin. The results suggest that the conformational change from the extended to the folded form is a common property of various myosin IIs.
