Potentiation of Smad transactivation by Jun proteins during a combined treatment with epidermal growth factor and transforming growth factor-beta in rat hepatocytes. role of phosphatidylinositol 3-kinase-induced AP-1 activation.
Cross-talk between Smad and mitogen-activated protein kinase pathways has been described recently, and evidence for Smad cooperation with AP-1 is emerging. Here we report that epidermal growth factor (EGF) potentializes transforming growth factor beta (TGF-beta)-induced Smad3 transactivation in rat hepatocytes, an effect abrogated by TAM-67, a dominant negative mutant of AP-1. Antisense transfection experiments indicated that c-Jun and JunB were involved in the synergistic effect, and endogenous c-Jun physically associated with Smad3 during a combined EGF/TGF-beta treatment. We next investigated which signaling pathway transduced by EGF was responsible for the Jun-induced synergism. Whereas inhibition of JNK had no effect, inhibition of the phosphatidylinositol-3' kinase (PI3-kinase) pathway by LY294002 or by expression of a dominant negative mutant of PI3-kinase reduced EGF/TGF-beta-induced Smad3 transcriptional activity. Transfection of an activated Ras with a mutation enabling the activation of the PI3-kinase pathway alone mimicked the EGF/TGF-beta potentiation of Smad3 transactivation, and TAM-67 abolished this effect, suggesting that the PI3-kinase pathway stimulates Smad3 via AP-1 stimulation. The EGF/TGF-beta-induced activation of Smad3 correlated with PI3-kinase and p38-dependent but not JNK-dependent phosphorylation of c-Jun. Since potentiation of a Smad-binding element-driven gene was also induced by EGF/TGF-beta treatment, this novel mechanism of Jun/Smad cooperation might be crucial for diversifying TGF-beta responses.
Peron
P
P
Laboratoire de Biologie Cellulaire, INSERM Unité 327, Faculté de Médecine Xavier Bichat, Université Paris 7 Denis Diderot, Paris 75018, France.
Rahmani
M
M
Zagar
Y
Y
Durand-Schneider
A M
AM
Lardeux
B
B
Bernuau
D
D
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000378:metabolism*; D005799:Genes, Dominant; D017930:Genes, Reporter; D022781:Hepatocytes / Q000378:metabolism*; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D009154:Mutation; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D051900:Smad3 Protein; D015534:Trans-Activators / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases
D002867:Chromones; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines; D016376:Oligonucleotides, Antisense; D019869:Phosphatidylinositol 3-Kinases; D016755:Proto-Oncogene Proteins c-jun; D051900:Smad3 Protein; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta; D048051:p38 Mitogen-Activated Protein Kinases; C497787:Smad3 protein, rat; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one