The TAZ Protein Interactome in Striated Muscle

Hippo signalling is a prominent regulator of cell proliferation, differentiation, and death. Previously, we characterized the Hippo transcriptional effector TAZ as a repressor of the myogenic differentiation program. Without DNA-binding ability, TAZ function exclusively depends on its protein:protein interaction network. This prompted us to undertake a proteomic-based study aimed at identifying the TAZ interactome in striated muscle cells. Using a novel GFP-Nanotrap based affinity purification approach coupled with LC-MS/MS protein identification, we document a comprehensive list of known and novel TAZ interactome components in myogenic cells. TAZ interacting proteins include components of Hippo signalling: TEAD1-4, LATS1, 14-3-3 proteins. Epigenetic regulators were also represented: NuRD complex, FACT complex, and SWI/SNF complex. We focused on characterizing the TAZ interaction with the Wnt co-repressor TLE3 in myogenic cells. In myogenic cells, TAZ and TLE3 interact and co-localize within the nucleus. Functionally, TAZ and TLE3 repress β-catenin activation, as indicated by the Wnt-responsive TOP FLASH reporter gene system. Depletion of TAZ reduced the degree of TLE3-mediated repression of β-catenin activation. TAZ and TLE3 repressed MyoD-driven activation of the myogenin promoter. Overall, these data demonstrate a role for a TAZ/TLE3 complex in repressing the myogenic differentiation machinery having implications for muscle development and regeneration.