Phosphatidylinositol 3-kinase-dependent transcriptional silencing of the translational repressor 4E-BP1

Cell Mol Life Sci. 2008 Oct;65(19):3110-7. doi: 10.1007/s00018-008-8418-2.

Abstract

The suppressor of translation initiation 4E-BP1 functions as a key regulator in cellular growth, differentiation, apoptosis and survival. While the control of 4E-BP1 activity via phosphorylation has been widely studied, the molecular mechanisms and the signaling pathways that govern 4E-BP1 gene expression are largely unknown. Here we show that inactivation of phosphatidylinositol 3-kinase (PI3K) consequent to stable expression of the antiproliferative somatostatin receptor 2 (sst2) in pancreatic cancer cells leads to transcriptional accumulation of the hypophosphorylated forms of 4E-BP1 protein. In cancer cells, while 4E-BP1 gene promoter is maintained repressed in a PI3K-dependent mechanism, sst2-dependent inactivation of the PI3K/Akt pathway releases 4E-BP1 gene transcription. Furthermore, the use of a pharmacological inhibitor and dominant-negative or -positive mutants of PI3K all affect 4E-BP1 protein expression and promoter activity in different cell lines. These data show that, in addition to inactivation of 4E-BP1 via hyperphosphorylation, signaling through the PI3K pathway silences 4E-BP1 gene transcription.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism*
  • Animals
  • Base Sequence
  • Cell Cycle Proteins
  • Cell Line
  • Enzyme Activation
  • Gene Silencing*
  • Genes, Reporter
  • Humans
  • Molecular Sequence Data
  • Ornithine Decarboxylase / metabolism
  • Phosphatidylinositol 3-Kinases / genetics
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoproteins / genetics
  • Phosphoproteins / metabolism*
  • Protein Biosynthesis
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Signal Transduction / physiology
  • Transcription, Genetic*

Substances

  • Adaptor Proteins, Signal Transducing
  • Cell Cycle Proteins
  • EIF4EBP1 protein, human
  • Phosphoproteins
  • Repressor Proteins
  • Ornithine Decarboxylase