title: Rapamycin blocks the phosphorylation of 4E-BP1 and inhibits cap-dependent initiation of translation.
abstract: The immunosuppressant drug rapamycin blocks progression of the cell cycle at the G1 phase in mammalian cells and yeast. Here we show that rapamycin inhibits cap-dependent, but not cap-independent, translation in NIH 3T3 cells. Cap-dependent translation is also specifically reduced in extracts from rapamycin-treated cells, as determined by in vitro translation experiments. This inhibition is causally related to the dephosphorylation and consequent activation of 4E-BP1, a protein recently identified as a repressor of the cap-binding protein, eIF-4E, function. These effects of rapamycin are specific as FK506, a structural analogue of rapamycin, had no effect on either cap-dependent translation or 4E-BP1 phosphorylation. The rapamycin-FK506 binding protein complex is the effector of the inhibition of 4E-BP1 phosphorylation as excess of FK506 over rapamycin reversed the rapamycin-mediated inhibition of 4E-BP1 phosphorylation. Thus, inactivation of eIF-4E is, at least in part, responsible for inhibition of cap-dependent translation in rapamycin-treated cells. Furthermore, these results suggest that 4E-BP1 phosphorylation is mediated by the FRAP/TOR signalling pathway.
authors.affiliation: Department of Biochemistry, McGill University, Montreal, Quebec H3G1Y6, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Beretta
authors.forename: A C
authors.initials: AC
authors.lastname: Gingras
authors.forename: Y V
authors.initials: YV
authors.lastname: Svitkin
authors.forename: M N
authors.initials: MN
authors.lastname: Hall
authors.forename: N
authors.initials: N
authors.lastname: Sonenberg
mesh_terms: D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D039561:Eukaryotic Initiation Factor-4E; D039642:Eukaryotic Initiation Factors; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D066298:In Vitro Techniques; D051379:Mice; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects; D010448:Peptide Initiation Factors / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011090:Polyenes / Q000494:pharmacology*; D012315:RNA Caps / Q000235:genetics / Q000378:metabolism; D020123:Sirolimus; D014407:Tumor Cells, Cultured
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C499527:Eif4ebp1 protein, mouse; D039561:Eukaryotic Initiation Factor-4E; D039642:Eukaryotic Initiation Factors; D007166:Immunosuppressive Agents; D010448:Peptide Initiation Factors; D010750:Phosphoproteins; D011090:Polyenes; D012315:RNA Caps; D020123:Sirolimus