Rapamycin Inhibits Cytoskeleton Reorganization and Cell Motility by Suppressing RhoA Expression and Activity

• DOI: 10.1074/jbc.m110.141168
• Publication Date: 2010-10-12T05:25:21Z
• Authors: Lei Liu; Yan Luo; Long Chen; Tao Shen; Baoshan Xu; Wenxing Chen; Hongyu Zhou; Xiuzhen Han; Shile Huang
• Keywords: Sirolimus; 0301 basic medicine; Antibiotics, Antineoplastic; Cell Survival; TOR Serine-Threonine Kinases; Proteins; Ribosomal Protein S6 Kinases, 70-kDa; Cell Cycle Proteins; Mechanistic Target of Rapamycin Complex 1; Phosphoproteins; 03 medical and health sciences; Gene Expression Regulation; Cell Movement; Multiprotein Complexes; Protein Biosynthesis; Humans; Insulin-Like Growth Factor I; Phosphorylation; Cytoskeleton; Adaptor Proteins, Signal Transducing; HeLa Cells; Signal Transduction

The mammalian target of rapamycin (mTOR) functions in cells at least as two complexes, mTORC1 and mTORC2. Intensive studies have focused on the roles of mTOR in the regulation of cell proliferation, growth, and survival. Recently we found that rapamycin inhibits type I insulin-like growth factor (IGF-1)-stimulated lamellipodia formation and cell motility, indicating involvement of mTOR in regulating cell motility. This study was set to further elucidate the underlying mechanism. Here we show that rapamycin inhibited protein synthesis and activities of small GTPases (RhoA, Cdc42, and Rac1), crucial regulatory proteins for cell migration. Disruption of mTORC1 or mTORC2 by down-regulation of raptor or rictor, respectively, inhibited the activities of these proteins. However, only disruption of mTORC1 mimicked the effect of rapamycin, inhibiting their protein expression. Ectopic expression of rapamycin-resistant and constitutively active S6K1 partially prevented rapamycin inhibition of RhoA, Rac1, and Cdc42 expression, whereas expression of constitutively hypophosphorylated 4E-BP1 (4EBP1-5A) or down-regulation of S6K1 by RNA interference suppressed expression of the GTPases, suggesting that both mTORC1-mediated S6K1 and 4E-BP1 pathways are involved in protein synthesis of the GTPases. Expression of constitutively active RhoA, but not Cdc42 and Rac1, conferred resistance to rapamycin inhibition of IGF-1-stimulated lamellipodia formation and cell migration. The results suggest that rapamycin inhibits cell motility at least in part by down-regulation of RhoA protein expression and activity through mTORC1-mediated S6K1 and 4E-BP1-signaling pathways.