Newcomers to the WW Domain-Mediated Network of the Hippo Tumor Suppressor Pathway.

The Hippo tumor suppressor pathway regulates the size of organs by controlling 2 opposing processes: proliferation and apoptosis. The pathway was originally defined in Drosophila, but it is well conserved in mammals. One of the unique features of Hippo signaling is the unusually wide occurrence of WW domains and its cognate PPxY ligand motifs within components of this pathway. Recently, it was proposed that the prevalence of WW domain-mediated complexes in the Hippo signaling pathway should facilitate its molecular analysis and help in the identification of new components of the Hippo-centered network. Indeed, several new members of the Hippo pathway, which form functional complexes with WW domains of YAP and TAZ effectors, were recently described. We focus here on 2 families of such proteins, angiomotins and SMADs, plus 1 regulatory factor, WBP-2, which together shed new light on the rapidly expanding Hippo network. Since the Hippo pathway acts as a tumor suppressor pathway, the complexes described here, which assemble on WW domains of YAP and TAZ, represent potential targets of cancer therapy.