The binding of PRAS40 to 14-3-3 proteins is not required for activation of mTORC1 signalling by phorbol esters/ERK

Bruno D. Fonseca, Vivian H.Y. Lee, Christopher G. Proud

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26 Citations (Scopus)


PRAS40 binds to the mTORC1 (mammalian target of rapamycin complex 1) and is released in response to insulin. It has been suggested that this effect is due to 14-3-3 binding and leads to activation of mTORC1 signalling. In a similar manner to insulin, phorbol esters also activate mTORC1 signalling, in this case via PKC (protein kinase C) and ERK (extracellular-signal-regulated kinase). However, phorbol esters do not induce phosphorylation of PRAS40 at Thr 246, binding of 14-3-3 proteins to PRAS40 or its release from mTORC1. Mutation of Thr246 to a serine residue permits phorbol esters to induce phosphorylation and binding to 14-3-3 proteins. Such phosphorylation is apparently mediated by RSKs (ribosomal S6 kinases), which lie downstream of ERK. However, although the PRAS40(T246S) mutant binds to 14-3-3 better than wild-type PRAS40, each inhibits mTORC1 signalling to a similar extent. Our results show that activation of mTORC1 signalling by phorbol esters does not require PRAS40 to be phosphorylated at Thr246, bind to 14-3-3 or be released from mTORC1. It is conceivable that phorbol esters activate mTORC1 by a distinct mechanism not involving PRAS40. Indeed, our results suggest that PRAS40 may not actually be involved in controlling mTORC1, but rather be a downstream target of mTORC1 that is regulated in response only to specific stimuli, such as insulin.

Original languageEnglish
Pages (from-to)141-149
Number of pages9
JournalBiochemical Journal
Issue number1
Publication statusPublished or Issued - 1 Apr 2008
Externally publishedYes


  • 14-3-3 protein
  • MAPK (mitogen-activated protein kinase)
  • Mammalian target of rapamycin (mTOR)
  • Mammalian target of rapamycin complex 1 (mTORC1)
  • Phosphorylation
  • Proline-rich Akt substrate of 40 kDa (PRAS40)

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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