Rapamycin differentially inhibits S6Ks and 4E-BP1 to mediate cell-type-specific repression of mRNA translation

• Published in: Proceedings of the National Academy of Sciences - PNAS 2008-11, Vol.105 (45), p.17414-17419
• Main Authors: Choo, Andrew Y, Yoon, Sang-Oh, Kim, Sang Gyun, Roux, Philippe P, Blenis, John
• Format: Article
• Language: English
• Subjects: Animals; Biological Sciences; Birds of prey; Carrier Proteins - antagonists & inhibitors; Carrier Proteins - metabolism; Cells; Drug resistance; Gene expression regulation; Gene Expression Regulation - drug effects; HEK293 cells; Kidney cells; Mammals; Messenger RNA; Mice; Phosphoproteins - antagonists & inhibitors; Phosphoproteins - metabolism; Phosphorylation; Physiological regulation; Protein Biosynthesis - drug effects; Protein Biosynthesis - physiology; Protein synthesis; Ribonucleic acid; Ribosomal Protein S6 Kinases - antagonists & inhibitors; Ribosomal Protein S6 Kinases - metabolism; RNA; Sirolimus - pharmacology; Small interfering RNA; Transcription Factors - antagonists & inhibitors; Transcription Factors - metabolism; Untranslated regions
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0809136105

The mammalian translational initiation machinery is a tightly controlled system that is composed of eukaryotic initiation factors, and which controls the recruitment of ribosomes to mediate cap-dependent translation. Accordingly, the mTORC1 complex functionally controls this cap-dependent translation machinery through the phosphorylation of its downstream substrates 4E-BPs and S6Ks. It is generally accepted that rapamycin, a specific inhibitor of mTORC1, is a potent translational repressor. Here we report the unexpected discovery that rapamycin's ability to regulate cap-dependent translation varies significantly among cell types. We show that this effect is mechanistically caused by rapamycin's differential effect on 4E-BP1 versus S6Ks. While rapamycin potently inhibits S6K activity throughout the duration of treatment, 4E-BP1 recovers in phosphorylation within 6 h despite initial inhibition (1-3 h). This reemerged 4E-BP1 phosphorylation is rapamycin-resistant but still requires mTOR, Raptor, and mTORC1's activity. Therefore, these results explain how cap-dependent translation can be maintained in the presence of rapamycin. In addition, we have also defined the condition by which rapamycin can control cap-dependent translation in various cell types. Finally, we show that mTOR catalytic inhibitors are effective inhibitors of the rapamycin-resistant phenotype.