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c-Jun associates with the oncoprotein Ski and suppresses Smad2 transcriptional activity
Marcia Pessah1, Jacqueline Marais, Celine Prunier
1INSERM U 482, Hôpital Saint-Antoine, 184 Rue du Faubourg Saint-Antoine, 75571, Paris Cedex 12, France.
Abstract:
The Smad proteins are key intracellular effectors of transforming growth factor-beta (TGF-beta) cytokines. The ability of Smads to modulate transcription results from a functional cooperativity with the coactivators p300/cAMP-response element-binding protein-binding protein (CBP), or the corepressors TGIF and Ski. The c-Jun N-terminal kinase (JNK) pathway, another downstream target activated by TGF-beta receptors, has also been suggested to inhibit TGF-beta signaling through interaction of c-Jun with Smad2 and Smad3. Here we show that c-Jun directly interacts with Ski to enhance the association of Ski with Smad2 in the basal state. Interestingly, TGF-beta signaling induces dissociation of c-Jun from Ski, thereby relieving active repression by c-Jun. Moreover, activation of JNK pathway suppressed the ability of TGF-beta to induce dissociation of c-Jun from ski. Thus, the formation of a c-Jun/Ski complex maintains the repressed state of Smad2-responsive genes in the absence of ligand and participates in negative feedback regulation of TGF-beta signaling by the JNK cascade.
Insights
Smad proteins mediate transforming growth factor-beta (TGF-beta) signaling. We found c-Jun interacts with Ski to repress Smad2, a mechanism regulated by TGF-beta and JNK pathways.
Area of Science:
- Molecular Biology
- Cell Signaling
- Gene Regulation
Background:
- Smad proteins are crucial intracellular mediators of TGF-beta cytokine signaling.
- Transcriptional modulation by Smads involves cooperation with coactivators (p300/CBP) or corepressors (TGIF, Ski).
- The c-Jun N-terminal kinase (JNK) pathway, activated by TGF-beta, may inhibit TGF-beta signaling via c-Jun interaction with Smad2/Smad3.
Purpose of the Study:
- To investigate the interaction between c-Jun, Ski, and Smad2 in TGF-beta signaling.
- To elucidate the role of the c-Jun/Ski complex in regulating Smad2-mediated gene expression.
- To determine how JNK pathway activation influences the TGF-beta/c-Jun/Ski/Smad2 regulatory axis.
Main Methods:
- Co-immunoprecipitation assays to detect protein-protein interactions.
- Western blotting to analyze protein levels and modifications.
- Reporter gene assays to assess transcriptional activity of Smad2-responsive genes.
Main Results:
- c-Jun directly interacts with Ski, enhancing Ski's association with Smad2 in unstimulated cells.
- TGF-beta signaling triggers the dissociation of c-Jun from Ski, relieving repression.
- JNK pathway activation inhibits TGF-beta-induced dissociation of c-Jun from Ski, maintaining repression.
Conclusions:
- The c-Jun/Ski complex maintains Smad2-responsive genes in a repressed state without ligand.
- The JNK cascade negatively regulates TGF-beta signaling through modulation of the c-Jun/Ski/Smad2 complex.
- This interaction provides a feedback mechanism for controlling TGF-beta pathway activity.