title: Mammalian cell size is controlled by mTOR and its downstream targets S6K1 and 4EBP1/eIF4E.
abstract: The coordinated action of cell cycle progression and cell growth (an increase in cell size and cell mass) is critical for sustained cellular proliferation, yet the biochemical signals that control cell growth are poorly defined, particularly in mammalian systems. We find that cell growth and cell cycle progression are separable processes in mammalian cells and that growth to appropriate cell size requires mTOR- and PI3K-dependent signals. Expression of a rapamycin-resistant mutant of mTOR rescues the reduced cell size phenotype induced by rapamycin in a kinase-dependent manner, showing the evolutionarily conserved role of mTOR in control of cell growth. Expression of S6K1 mutants that possess partial rapamycin-resistant activity or overexpression of eIF4E individually and additively partially rescues the rapamycin-induced decrease in cell size. In the absence of rapamycin, overexpression of S6K1 or eIF4E increases cell size, and, when coexpressed, they cooperate to increase cell size further. Expression of a phosphorylation site-defective mutant of 4EBP1 that constitutively binds the eIF4E-Cap complex to inhibit translation initiation reduces cell size and blocks eIF4E effects on cell size. These data show that mTOR signals downstream to at least two independent targets, S6K1 and 4EBP1/eIF4E, that function in translational control to regulate mammalian cell size.
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Diane C
authors.initials: DC
authors.lastname: Fingar
authors.forename: Sofie
authors.initials: S
authors.lastname: Salama
authors.forename: Christina
authors.initials: C
authors.lastname: Tsou
authors.forename: Ed
authors.initials: E
authors.lastname: Harlow
authors.forename: John
authors.initials: J
authors.lastname: Blenis
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D018951:Antigens, CD20 / Q000096:biosynthesis; D002352:Carrier Proteins / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D002455:Cell Division; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D039561:Eukaryotic Initiation Factor-4E; D005434:Flow Cytometry; D016193:G1 Phase; D016195:G2 Phase; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D047908:Intracellular Signaling Peptides and Proteins; D008934:Mitogens / Q000378:metabolism; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D009154:Mutation; D010448:Peptide Initiation Factors / Q000378:metabolism; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D014176:Protein Biosynthesis; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D016196:S Phase; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018951:Antigens, CD20; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002867:Chromones; D039561:Eukaryotic Initiation Factor-4E; D047908:Intracellular Signaling Peptides and Proteins; D008934:Mitogens; D009025:Morpholines; D010448:Peptide Initiation Factors; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011494:Protein Kinases; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C087000:EIF4EBP1 protein, human; C499526:Eif4ebp1 protein, rat; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546842:MTOR protein, human; C546845:mTOR protein, rat