Rapid turnover of the mTOR complex 1 (mTORC1) repressor REDD1 and activation of mTORC1 signaling following inhibition of protein synthesis.
mTORC1 is a complex of proteins that includes the mammalian target of rapamycin (mTOR) and several regulatory proteins. It is activated by a variety of hormones (e.g. insulin) and nutrients (e.g. amino acids) that act to stimulate cell growth and proliferation and repressed by hormones (e.g. glucocorticoids) that act to reduce cell growth. Curiously, mTORC1 signaling is reported to be rapidly (e.g. within 1-2 h) activated by inhibitors of protein synthesis that act on either mRNA translation elongation or gene transcription. However, the basis for the mTORC1 activation has not been satisfactorily delineated. In the present study, mTORC1 signaling was found to be activated in response to inhibition of either the initiation or elongation phases of mRNA translation. Changes in mTORC1 signaling were inversely proportional to alterations in the expression of the mTORC1 repressor, REDD1, but not the expression of TRB3 or TSC2. Moreover the cycloheximide-induced increase in mTORC1 signaling was significantly attenuated in cells lacking REDD1, showing that REDD1 plays an integral role in the response. Finally, the half-life of REDD1 was estimated to be 5 min or less. Overall, the results are consistent with a model in which inhibition of protein synthesis leads to a loss of REDD1 protein because of its rapid degradation, and in part reduced REDD1 expression subsequently leads to de-repression of mTORC1 activity.
Kimball
Scot R
SR
Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and the. Electronic address: skimball@psu.edu.
Do
A N Dang
AND
Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and the.
Kutzler
Lydia
L
Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and the.
Cavener
Douglas R
DR
Department of Biology, The Pennsylvania State University, University Park, Pennsylvania 16802.
Jefferson
Leonard S
LS
Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and the.
D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D005786:Gene Expression Regulation; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D009479:Neuropeptides / Q000378:metabolism / Q000502:physiology*; D010750:Phosphoproteins / Q000378:metabolism / Q000502:physiology*; D014176:Protein Biosynthesis; D011494:Protein Kinases / Q000378:metabolism / Q000502:physiology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D000076205:Ras Homolog Enriched in Brain Protein; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000502:physiology*; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins
D018797:Cell Cycle Proteins; C469992:Ddit4 protein, mouse; D009479:Neuropeptides; D010750:Phosphoproteins; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D000076205:Ras Homolog Enriched in Brain Protein; C490213:Rheb protein, mouse; C474830:TRB3 protein, mouse; D014157:Transcription Factors; C000624654:Tsc2 protein, mouse; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C508191:proline-rich Akt substrate, 40 kDa protein, mouse; D003513:Cycloheximide; D011494:Protein Kinases; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins