title: Ezrin mediates growth and survival in Ewing's sarcoma through the AKT/mTOR, but not the MAPK, signaling pathway.
abstract: Recent reports on the role of the membrane-cytoskeleton linker protein ezrin in sarcomas showed an effect on the formation of metastases, dependent on the level of ezrin expression. In this study, we explore the role of ezrin in Ewing's sarcoma, a frequently fatal mesenchymal neoplasm of children and young adults. Through both immunohistochemistry and Western immunoblot studies we find ubiquitous, high-level expression of ezrin in Ewing's sarcoma. In contrast to the observations in osteosarcoma and rhabdomyosarcoma, we demonstrate that inhibition of ezrin-mediated signal transduction, through the expression of a non-phosphorylatable T567A mutant, slows primary growth of Ewing's sarcoma cells in vitro. This reduction in growth is a result of increased apoptosis in the mutant expressing cells. We further show that expression of this mutant reduces the ability of Ewing's sarcoma cells to form experimental metastases in vivo. Molecular examination reveals that the action of ezrin in Ewing's sarcoma is dependent on the AKT/mTOR signal transduction cascade, but not MAP Kinase. These results, therefore, demonstrate that, in Ewing's sarcoma, the biology of ezrin is distinct from that described in other sarcomas. This study further validates ezrin as a potential therapeutic target.
authors.affiliation: Molecular Oncology Section, Pediatric Oncology Branch, National Cancer Institute, National Institutes of Health, Building 10, Room 1-3816, 10 Center Drive, Bethesda, MD 20892, USA. krishhka@mail.nih.gov
authors.forename: Kartik
authors.initials: K
authors.lastname: Krishnan
authors.forename: Ben
authors.initials: B
authors.lastname: Bruce
authors.forename: Stephen
authors.initials: S
authors.lastname: Hewitt
authors.forename: Dafydd
authors.initials: D
authors.lastname: Thomas
authors.forename: Chand
authors.initials: C
authors.lastname: Khanna
authors.forename: Lee J
authors.initials: LJ
authors.lastname: Helman
mesh_terms: D000818:Animals; D017209:Apoptosis; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000502:physiology*; D006801:Humans; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009154:Mutation; D009362:Neoplasm Metastasis; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012512:Sarcoma, Ewing / Q000378:metabolism* / Q000473:pathology*; D015398:Signal Transduction; D014162:Transfection; D014407:Tumor Cells, Cultured; D000099149:Ezrin
chemical_list: D003598:Cytoskeletal Proteins; D020928:Mitogen-Activated Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; D000099149:Ezrin