title: Rapamycin inhibits ezrin-mediated metastatic behavior in a murine model of osteosarcoma.
abstract: Osteosarcoma is the most frequent primary malignant tumor of bone with a high propensity for metastasis. We have previously showed that ezrin expression is necessary for metastatic behavior in a murine model of osteosarcoma (K7M2). In this study, we found that a mechanism of ezrin-related metastatic behavior is linked to an Akt-dependent mammalian target of rapamycin (mTOR)/p70 ribosomal protein S6 kinase (S6K1)/eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) pathway. Suppression of ezrin expression either by antisense transfection or by small interfering RNAs or disruption of ezrin function by transfection of a dominant-negative ezrin-T567A mutant led to decreased expression and decreased phosphorylation of both S6K1 and 4E-BP1. Proteosomal inhibition by MG132 reversed antisense-mediated decrease of S6K1 and 4E-BP1 protein expression, but failed to affect the effect of ezrin on phosphorylation of S6K1 and 4E-BP1. Blockade of the mTOR pathway with rapamycin or its analog, cell cycle inhibitor-779 led to significant inhibition of experimental lung metastasis in vivo. These results suggest that blocking the mTOR/S6K1/4E-BP1 pathway may be an appropriate target for strategies to reduce tumor cell metastasis.
authors.affiliation: Molecular Oncology Section, Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892-1106, USA.
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Wan
authors.forename: Arnulfo
authors.initials: A
authors.lastname: Mendoza
authors.forename: Chand
authors.initials: C
authors.lastname: Khanna
authors.forename: Lee J
authors.initials: LJ
authors.lastname: Helman
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001859:Bone Neoplasms / Q000235:genetics / Q000473:pathology*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; D039642:Eukaryotic Initiation Factors; D005260:Female; D051379:Mice; D016513:Mice, SCID; D012516:Osteosarcoma / Q000235:genetics / Q000473:pathology*; D010750:Phosphoproteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D016372:RNA, Antisense / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors / Q000378:metabolism; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000494:pharmacology*; D014162:Transfection; D000099149:Ezrin
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; D039642:Eukaryotic Initiation Factors; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D016372:RNA, Antisense; D034741:RNA, Small Interfering; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; D000099149:Ezrin; C499527:Eif4ebp1 protein, mouse; C401859:temsirolimus