Rapamycin inhibits F-actin reorganization and phosphorylation of focal adhesion proteins.
An early event of cell migration is characterized as the rapid reorganization of the actin cytoskeleton. Recently, we have demonstrated that rapamycin inhibits tumor cell motility. To understand the underlying mechanism, this study was set to determine whether rapamycin inhibition of cell motility is related to its prevention of F-actin reorganization. We found that rapamycin prevented type I insulin-like growth factor (IGF-I)-stimulated F-actin reorganization in human rhabdomyosarcoma (Rh30), Ewing sarcoma (Rh1), glioblastoma (U-373) and prostate carcinoma (PC-3) cells, and concurrently inhibited phosphorylation of focal adhesion proteins, including focal adhesion kinase (FAK), paxillin and p130(Cas) in the cells. The effect of rapamycin was blocked by expression of a rapamycin-resistant mutant of mTOR (mTORrr), but not a kinase-dead mTORrr. Downregulation of raptor mimicked the effect of rapamycin. Cells infected with a recombinant adenovirus expressing constitutively active and rapamycin-resistant mutant of p70 S6 kinase 1 (S6K1) conferred to resistance to rapamycin. Further, IGF-I failed to stimulate F-actin reorganization and phosphorylation of the focal adhesion proteins in the S6K1-downregulated cells. Expression of constitutively hypophosphorylated eukaryotic initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1-5A) inhibited IGF-I-stimulated F-actin reorganization, but did not alter the cellular protein or phosphorylation levels of the focal adhesion proteins. The results suggest that rapamycin inhibits IGF-I-induced F-actin reorganization and phosphorylation of the focal adhesion proteins by disruption of mTOR-raptor complex. Both S6K1 and 4E-BP1 pathways, mediated by the mTOR-raptor complex, are involved in the regulation of IGF-I-stimulated F-actin reorganization, but only the former controls IGF-I-stimulated phosphorylation of the focal adhesion proteins.
Liu
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Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, L71130-3932, USA.
Chen
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L
Chung
J
J
Huang
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S
D000199:Actins / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins / Q000378:metabolism; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002478:Cells, Cultured; D019281:Dimerization; D022001:Focal Adhesions / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism / Q000502:physiology; D011506:Proteins / Q000378:metabolism; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D000076223:Regulatory-Associated Protein of mTOR; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism / Q000502:physiology; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000502:physiology
D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; C500984:CRTC1 protein, human; D002352:Carrier Proteins; D015815:Cell Adhesion Molecules; D011506:Proteins; C492571:RICTOR protein, human; C463659:RPTOR protein, human; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D000076223:Regulatory-Associated Protein of mTOR; D014157:Transcription Factors; D007334:Insulin-Like Growth Factor I; D011494:Protein Kinases; C546842:MTOR protein, human; C069329:RPS6KA1 protein, human; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus