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.
MeSH terms
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Adaptor Proteins, Signal Transducing
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Animals
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Bone Neoplasms / genetics
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Bone Neoplasms / pathology*
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Carrier Proteins / antagonists & inhibitors
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Carrier Proteins / metabolism
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Cell Cycle Proteins
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Cytoskeletal Proteins
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Eukaryotic Initiation Factors
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Female
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Mice
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Mice, SCID
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Osteosarcoma / genetics
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Osteosarcoma / pathology*
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Phosphoproteins / antagonists & inhibitors*
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Phosphoproteins / genetics
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Phosphoproteins / metabolism
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Phosphorylation / drug effects
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Protein Serine-Threonine Kinases / antagonists & inhibitors
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Protein Serine-Threonine Kinases / metabolism
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Proto-Oncogene Proteins / antagonists & inhibitors
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins c-akt
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RNA, Antisense / genetics
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RNA, Small Interfering / genetics
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Ribosomal Protein S6 Kinases, 70-kDa / antagonists & inhibitors
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Ribosomal Protein S6 Kinases, 70-kDa / metabolism
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Sirolimus / analogs & derivatives*
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Sirolimus / pharmacology*
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Transfection
Substances
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Adaptor Proteins, Signal Transducing
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Carrier Proteins
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Cell Cycle Proteins
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Cytoskeletal Proteins
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Eif4ebp1 protein, mouse
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Eukaryotic Initiation Factors
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Phosphoproteins
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Proto-Oncogene Proteins
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RNA, Antisense
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RNA, Small Interfering
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ezrin
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temsirolimus
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-akt
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Ribosomal Protein S6 Kinases, 70-kDa
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Sirolimus