4E-BP1 is a target of Smad4 essential for TGFbeta-mediated inhibition of cell proliferation

EMBO J. 2009 Nov 18;28(22):3514-22. doi: 10.1038/emboj.2009.291. Epub 2009 Oct 15.

Abstract

Assembly of the multi-subunit eukaryotic translation initiation factor-4F (eIF4F) is critical for protein synthesis and cell growth and proliferation. eIF4F formation is regulated by the translation-inhibitory protein 4E-BP1. While proliferation factors and intracellular pathways that impinge upon 4E-BP1 phosphorylation have been extensively studied, how they control 4E-BP1 expression remains unknown. Here, we show that Smad4, a transcription factor normally required for TGFbeta-mediated inhibition of normal cell proliferation, enhances 4E-BP1 gene-promoter activity through binding to a conserved element. 4E-BP1 expression is specifically modulated by treatment with TGFbeta and by manipulations of the natural Smad4 regulators (co-Smads) in cells isolated from Smad4(+/+) human tumours, whereas no response is observed in cells isolated from Smad4(-/-) human tumours or in cells where Smad4 has been knocked down by specific siRNAs. In addition, cells where 4E-BP1 has been knocked down (inducible shRNAs in human pancreatic cancer cells or siRNAs in non-malignant human keratinocytes) or has been knocked out (mouse embryonic fibroblasts isolated from 4E-BP1(-/-) mice) proliferate faster and are resistant to the antiproliferative effect of TGFbeta. Thus, 4E-BP1 gene appears critical for TGFbeta/Smad4-mediated inhibition of cell proliferation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / antagonists & inhibitors
  • Adaptor Proteins, Signal Transducing / genetics*
  • Adaptor Proteins, Signal Transducing / physiology*
  • Animals
  • Base Sequence
  • Cell Cycle Proteins
  • Cell Proliferation / drug effects*
  • Cells, Cultured
  • Down-Regulation / drug effects
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Mice
  • Mice, Knockout
  • Phosphoproteins / antagonists & inhibitors
  • Phosphoproteins / genetics*
  • Phosphoproteins / physiology*
  • RNA, Small Interfering / pharmacology
  • Response Elements
  • Smad4 Protein / genetics
  • Smad4 Protein / metabolism
  • Smad4 Protein / physiology*
  • Transfection
  • Transforming Growth Factor beta / pharmacology*
  • Transforming Growth Factor beta / physiology

Substances

  • Adaptor Proteins, Signal Transducing
  • Cell Cycle Proteins
  • EIF4EBP1 protein, human
  • Phosphoproteins
  • RNA, Small Interfering
  • SMAD4 protein, human
  • Smad4 Protein
  • Transforming Growth Factor beta