Smad2 functions as a co-activator of canonical Wnt/beta-catenin signaling pathway independent of Smad4 through histone acetyltransferase activity of p300

Hirota, M.; Watanabe, K.; Hamada, S.; Sun, Y.; Strizzi, L.; Mancino, M.; Nagaoka, T.; Gonzales, M.; Seno, M.; Bianco, C.; Salomon, D. S.

Cell Signal. 2008 Jul 4; 20(9):1632-41

Abstract

Both canonical Wnt/beta-catenin and TGFbeta/Smad signaling pathways coordinately regulate pattern formation during embryogenesis as well as tumor progression. Evidence of cross-talk between these two pathways has been reported. Here we demonstrated that the Activin-like kinase 4 (Alk4)/Smad2 pathway facilitates the transcriptional activity of the oncogenic Wnt/beta-catenin/Tcf4 pathway through a novel Smad4-independent mechanism. Upon activation, Smad2 physically interacted with Tcf4, beta-catenin and the co-activator p300 to enhance transcriptional activity of beta-catenin/Tcf4 through the histone acetyltransferase activity of p300. Transactivation by Smad2 was independent of a Smad-binding element (SBE) and Smad4. Indeed, the enhancement of beta-catenin/Tcf4 transcriptional activity by activated Smad2 was negatively regulated by the presence of Smad4. Moreover, a tumor-derived missense mutant of Smad2, lacking the ability to bind to Smad4 was still able to enhance the Tcf4 transcriptional reporter in the presence of beta-catenin and Tcf4. Our findings suggest that Smad2 may function as an activator of canonical Wnt/beta-catenin/Tcf4 signaling through a SBE/Smad4-independent pathway.

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