4E-BP1 is a target of Smad4 essential for TGFbeta-mediated inhibition of cell proliferation.
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.
Azar
Rania
R
INSERM U858, Institut de Médecine Moléculaire de Rangueil (I2MR), Toulouse, France.
Alard
Amandine
A
Susini
Christiane
C
Bousquet
Corinne
C
Pyronnet
Stéphane
S
D048868:Adaptor Proteins, Signal Transducing / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000502:physiology*; D000818:Animals; D001483:Base Sequence; D018797:Cell Cycle Proteins; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D010750:Phosphoproteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000502:physiology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D020218:Response Elements; D051901:Smad4 Protein / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology* / Q000502:physiology
D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D010750:Phosphoproteins; D034741:RNA, Small Interfering; C497796:SMAD4 protein, human; D051901:Smad4 Protein; D016212:Transforming Growth Factor beta