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PKB/Akt modulates TGF-β signalling through a direct interaction with Smad3

Nature Cell Biology volume 6, pages 358–365 (2004)Cite this article

Abstract

Transforming growth factor β (TGF-β) has a major role in cell proliferation, differentiation and apoptosis in many cell types. Integration of the TGF-β pathway with other signalling cascades that control the same cellular processes may modulate TGF-β responses. Here we report the discovery of a new functional link between TGF-β and growth factor signalling pathways, mediated by a physical interaction between the serine-threonine kinase PKB (protein kinase B)/Akt and the transcriptional activator Smad3. Formation of the complex is induced by insulin, but inhibited by TGF-β stimulation, placing PKB–Smad3 at a point of convergence between these two pathways. PKB inhibits Smad3 by preventing its phosphorylation, binding to Smad4 and nuclear translocation. In contrast, Smad3 does not inhibit PKB. Inhibition of Smad3 by PKB occurs through a kinase-activity-independent mechanism, resulting in a decrease in Smad3-mediated transcription and protection of cells against TGF-β-induced apoptosis. Consistently, knockdown of the endogenous PKB gene with small-interfering RNA (siRNA) has the opposite effect. Our results suggest a very simple mechanism for the integration of signals arising from growth-factor- and TGF-β-mediated pathways.

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Figure 1: Identification and characterization of the PKB–Smad3 interaction.
Figure 2: PKB inhibits Smad3 function.
Figure 3: PKB inhibits the Smad3-induced activation of transcription.
Figure 4: Wild-type and kinase-dead PKB protect cells against TGF-β-induced apoptosis.
Figure 5: The binding of Smad3 to PKB does not prevent phosphorylation-mediated activation of PKB.

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Acknowledgements

We gratefully acknowledge S. Sénéchal for his technical assistance in FACS analysis. We also thank M. Primeau, G. Ghaddar and J. Lamerdin for DNA constructs; K. Luo, A. Conery and A. Moustakas for Smad cDNAs, TBRI, TBRII, cell lines and vectors; D. Billadeau for the pSuppress vector; J. Jin and J. Woodgett for PKB and GSK3β; M. Scheid for PDK1; and M. E. Greenberg for FKHRL1 and BAD. This work was supported by the Human Frontiers Science Program (HFSP) and the Canadian Institutes for Health Research.

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  1. Département de Biochimie, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal, H3C 3J7, Québec, Canada

    Ingrid Remy, Annie Montmarquette & Stephen W. Michnick

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Correspondence to Stephen W. Michnick.

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Remy, I., Montmarquette, A. & Michnick, S. PKB/Akt modulates TGF-β signalling through a direct interaction with Smad3. Nat Cell Biol 6, 358–365 (2004). https://doi.org/10.1038/ncb1113

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