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https://hdl.handle.net/2440/82725
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Type: | Journal article |
Title: | Re-evaluating the roles of proposed modulators of mammalian target of rapamycin complex 1 (mTORC1) signaling |
Author: | Wang, X. Fonseca, B. Tang, H. Liu, R. Elia, A. Clemens, M. Bommer, U. Proud, C. |
Citation: | Journal of Biological Chemistry, 2008; 283(45):30482-30492 |
Publisher: | Amer Soc Biochemistry Molecular Biology Inc |
Issue Date: | 2008 |
ISSN: | 0021-9258 1083-351X |
Statement of Responsibility: | Xuemin Wang, Bruno D. Fonseca, Hua Tang, Rui Liu, Androulla Elia, Michael J. Clemens, Ulrich-Axel Bommer and Christopher G. Proud |
Abstract: | Signaling through mammalian target of rapamycin complex 1 (mTORC1) is stimulated by amino acids and insulin. Insulin inactivates TSC1/2, the GTPase-activator complex for Rheb, and Rheb·GTP activates mTORC1. It is not clear how amino acids regulate mTORC1. FKBP38 (immunophilin FK506-binding protein, 38 kDa), was recently reported to exert a negative effect on mTORC1 function that is relieved by its binding to Rheb·GTP. We confirm that Rheb binds wild type FKBP38, but inactive Rheb mutants showed contrasting abilities to bind FKBP38. We were unable to observe any regulation of FKBP38/mTOR binding by amino acids or insulin. Furthermore, FKBP38 did not inhibit mTORC1 signaling. The translationally controlled tumor protein (TCTP) in Drosophila was recently reported to act as the guanine nucleotide-exchange factor for Rheb. We have studied the role of TCTP in mammalian TORC1 signaling and its control by amino acids. Reducing TCTP levels did not reproducibly affect mTORC1 signaling in amino acid-replete/insulin-stimulated cells. Moreover, overexpressing TCTP did not rescue mTORC1 signaling in amino acid-starved cells. In addition, we were unable to see any stable interaction between TCTP and Rheb or mTORC1. Accumulation of uncharged tRNA has been previously proposed to be involved in the inhibition of mTORC1 signaling during amino acid starvation. To test this hypothesis, we used a Chinese hamster ovary cell line containing a temperature-sensitive mutation in leucyl-tRNA synthetase. Leucine deprivation markedly inhibited mTORC1 signaling in these cells, but shifting the cells to the nonpermissive temperature for the synthetase did not. These data indicate that uncharged tRNALeu does not switch off mTORC1 signaling and suggest that mTORC1 is controlled by a distinct pathway that senses the availability of amino acids. Our data also indicate that, in the mammalian cell lines tested here, neither TCTP nor FKBP38 regulates mTORC1 signaling. |
Keywords: | CHO Cells Animals Humans Cricetulus Multiprotein Complexes Insulin Monomeric GTP-Binding Proteins Tacrolimus Binding Proteins Leucine-tRNA Ligase Telomerase Amino Acids Neuropeptides Proteins Tumor Suppressor Proteins Transcription Factors RNA, Transfer Hypoglycemic Agents Signal Transduction Protein Binding Mutation Cricetinae TOR Serine-Threonine Kinases Biomarkers, Tumor Ras Homolog Enriched in Brain Protein Mechanistic Target of Rapamycin Complex 1 Tuberous Sclerosis Complex 2 Protein Tumor Protein, Translationally-Controlled 1 |
Rights: | © 2008 by The American Society for Biochemistry and Molecular Biology, Inc. |
DOI: | 10.1074/jbc.M803348200 |
Published version: | http://dx.doi.org/10.1074/jbc.m803348200 |
Appears in Collections: | Aurora harvest 4 Molecular and Biomedical Science publications |
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