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PKB/Akt modulates TGF-beta signalling through a direct interaction with Smad3
Ingrid Remy1, Annie Montmarquette, Stephen W Michnick
1Département de Biochimie, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal, Québec H3C 3J7, Canada.
Nature Cell Biology
|March 30, 2004
Summary
Protein kinase B (PKB)/Akt physically interacts with Smad3, integrating growth factor and TGF-beta signaling. PKB inhibits Smad3, decreasing TGF-beta-induced apoptosis and modulating cell responses.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Biochemistry
Background:
- Transforming growth factor beta (TGF-beta) regulates crucial cell processes like proliferation, differentiation, and apoptosis.
- Understanding how TGF-beta signaling integrates with other pathways is key to modulating cellular responses.
Purpose of the Study:
- To identify and characterize a novel functional link between TGF-beta and growth factor signaling pathways.
- To elucidate the mechanism of interaction between PKB/Akt and Smad3.
Main Methods:
- Investigated physical interaction between PKB/Akt and Smad3.
- Utilized insulin and TGF-beta stimulation to study complex formation.
- Employed small-interfering RNA (siRNA) for gene knockdown of PKB.
Main Results:
- Discovered a physical interaction between PKB/Akt and Smad3, forming a complex induced by insulin but inhibited by TGF-beta.
- PKB/Akt inhibits Smad3 by preventing phosphorylation, Smad4 binding, and nuclear translocation.
- PKB-mediated inhibition of Smad3 reduces Smad3-dependent transcription and protects cells from TGF-beta-induced apoptosis.
Conclusions:
- PKB/Akt and Smad3 act as a convergence point for growth factor and TGF-beta signaling pathways.
- PKB/Akt regulates TGF-beta responses through a kinase-activity-independent mechanism on Smad3.
- This interaction provides a simple mechanism for integrating signals from distinct cellular pathways.