A molecular mechanism that links Hippo signalling to the inhibition of Wnt/β-catenin signalling

The Hippo signalling pathway has emerged as a key regulator of organ size, tissue homeostasis, and patterning. Recent studies have shown that two effectors in this pathway, YAP/TAZ, modulate Wnt/beta-catenin signalling through their interaction with beta-catenin or Dishevelled, depending on biological contexts. Here, we identify a novel mechanism through which Hippo signalling inhibits Wnt/beta-catenin signalling. We show that YAP and TAZ, the transcriptional co-activators in the Hippo pathway, suppress Wnt signalling without suppressing the stability of beta-catenin but through preventing its nuclear translocation. Our results show that YAP/TAZ binds to beta-catenin, thereby suppressing Wnt-target gene expression, and that the Hippo pathway-stimulated phosphorylation of YAP, which induces cytoplasmic translocation of YAP, is required for the YAP-mediated inhibition of Wnt/beta-catenin signalling. We also find that downregulation of Hippo signalling correlates with upregulation of beta-catenin signalling in colorectal cancers. Remarkably, our analysis demonstrates that phosphorylated YAP suppresses nuclear translocation of beta-catenin by directly binding to it in the cytoplasm. These results provide a novel mechanism, in which Hippo signalling antagonizes Wnt signalling by regulating nuclear translocation of b-catenin. The EMBO Journal ( 2012) 31, 1109-1122. doi: 10.1038/emboj.2011.487; Published online 10 January 2012