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

Proc Natl Acad Sci U S A. 2008 Nov 11;105(45):17414-9. doi: 10.1073/pnas.0809136105. Epub 2008 Oct 27.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adaptor Proteins, Signal Transducing
  • Animals
  • Carrier Proteins / antagonists & inhibitors*
  • Carrier Proteins / metabolism
  • Cell Cycle Proteins
  • Eukaryotic Initiation Factors
  • Gene Expression Regulation / drug effects*
  • Mice
  • Phosphoproteins / antagonists & inhibitors*
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Protein Biosynthesis / drug effects*
  • Protein Biosynthesis / physiology
  • Ribosomal Protein S6 Kinases / antagonists & inhibitors*
  • Ribosomal Protein S6 Kinases / metabolism
  • Sirolimus / pharmacology*
  • Transcription Factors / antagonists & inhibitors*
  • Transcription Factors / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins
  • Cell Cycle Proteins
  • Crtc1 protein, mouse
  • Eif4ebp1 protein, mouse
  • Eukaryotic Initiation Factors
  • Phosphoproteins
  • Transcription Factors
  • Ribosomal Protein S6 Kinases
  • Sirolimus