Induction of the AP-1 members c-Jun and JunB by TGF-beta/Smad suppresses early Smad-driven gene activation.
Smad proteins transduce signals from TGF-beta receptors and regulate transcription of target genes. Among the latter are c-jun and junB, which encode members of the AP-1 family of transcription factors. In this study, we have investigated the functional interactions of the Smad and AP-1 transcription factors in the context of Smad-specific gene transactivation in both fibroblasts and keratinocytes. We demonstrate that overexpression of either junB or c-jun prevents TGF-beta- or Smad3-induced transactivation of the Smad-specific promoter construct (SBE)(4)-Lux. Inversely, Smad-driven promoter transactivation by TGF-beta/Smad is significantly enhanced when c-jun expression is abolished in HaCaT keratinocytes, and when junB expression is prevented in fibroblasts, consistent with the cell-type specific induction of jun members by TGF-beta. We also demonstrate that Smad-specific gene transactivation in junB(-/-) mouse embryonic fibroblasts is significantly higher than in embryonic fibroblasts from the control parental mouse line, and that this difference is abolished by rescuing junB expression in junB(-/-) cells. Finally, we have determined that off-DNA interactions between Smad3 and both c-Jun and JunB result in the reduction of Smad3/DNA interactions. From these results, we provide a model in which jun expression in response to the initial Smad cascade represents a negative feed-back mechanism counteracting Smad-driven gene transactivation.
Verrecchia
F
F
INSERM U532, Hôpital Saint-Louis, F-75010 Paris, France.
Tacheau
C
C
Schorpp-Kistner
M
M
Angel
P
P
Mauviel
A
A
D000818:Animals; D019556:COS Cells; D004247:DNA / Q000235:genetics / Q000378:metabolism; D016373:DNA, Antisense / Q000235:genetics; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D005347:Fibroblasts / Q000502:physiology; D016758:Genes, jun / Q000235:genetics; D006801:Humans; D015603:Keratinocytes / Q000502:physiology; D051379:Mice; D016755:Proto-Oncogene Proteins c-jun / Q000096:biosynthesis* / Q000235:genetics; D051900:Smad3 Protein; D015534:Trans-Activators / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D018808:Transcription Factor AP-1 / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D015533:Transcriptional Activation / Q000502:physiology*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000502:physiology*
D016373:DNA, Antisense; D004268:DNA-Binding Proteins; D016755:Proto-Oncogene Proteins c-jun; C497790:SMAD3 protein, human; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta; D004247:DNA