BCL9-2 binds Arm/ beta-catenin in a Tyr142-independent manner and requires Pygopus for its function in Wg/ Wnt signaling.
The Wingless (Wg)/Wnt signal transduction pathway controls fundamental processes during animal development. Deregulation of the Wg/ Wnt pathway has been causally linked to several forms of cancer, most notably to colorectal cancer. In response to Wg/ Wnt signaling, Armadillo/ beta-catenin associates in the nucleus with DNA bound TCF and several co-factors, among them Legless/ BCL9, which provides a link to Pygopus. Recently, the second vertebrate homologue of Legless, BCL9-2 (or B9L), was characterized and proposed to mediate Wnt signaling in a Pygopus-independent manner, by binding to a Tyrosine-142-phosphorylated form of beta-catenin. Here we examine the role of Tyrosine-142 phosphorylation in several assays and find that it is neither important for the recruitment of BCL9-2, nor for the transcriptional activity of beta-catenin in cultured mammalian cells, nor in Drosophila for Wg signaling activity in vivo. Furthermore, we demonstrate that BCL9-2 can functionally replace Lgs both in cultured cells as well as in vivo and that this rescue activity depends on the ability of BCL9-2 to bind Pygo. Our results do not show a significant functional difference between BCL9-2 and BCL9 but rather suggest that the two proteins represent evolutionary duplicates of Legless, which have acquired distinct expression patterns while acting in a largely redundant manner.[1]References
- BCL9-2 binds Arm/beta-catenin in a Tyr142-independent manner and requires Pygopus for its function in Wg/Wnt signaling. Hoffmans, R., Basler, K. Mech. Dev. (2007) [Pubmed]
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