Canonical Wnt signalling activates TAZ through PP1A during osteogenic differentiation

Abstract

TAZ, a transcriptional modulator, has a key role in cell proliferation, differentiation and stem cell self-renewal. TAZ activity is regulated by several signalling pathways, including Hippo, GPCR and Wnt signalling, but the regulatory mechanisms of TAZ activation are not yet clearly understood. In this report, we show that TAZ is regulated by canonical Wnt signalling during osteogenic differentiation. Wnt3a increases TAZ expression and an inhibitor of GSK3b, a downstream effector of Wnt signalling, induces TAZ. Wnt3a facilitates the dephosphorylation of TAZ, which stabilises TAZ and prevents it from binding 14-3-3 proteins, thus inducing the nuclear localisation of TAZ. Dephosphorylation of TAZ occurs via PP1A, and depletion of PP1A blocks Wnt3a-induced TAZ stabilisation. Wnt3a-induced TAZ activates osteoblastic differentiation and siRNA-induced TAZ depletion decreases Wnt3a-induced osteoblast differentiation. Taken together, these results show that TAZ mediates Wnt3a-stimulated osteogenic differentiation through PP1A, suggesting that the Wnt signal regulates the Hippo pathway. Transcriptional co-activator with PDZ-binding motif (TAZ, also known as WWTR1) is a transcriptional modulator that has a key role in cell proliferation, differentiation and stem cell selfrenewal. TAZ interacts with several transcription factors including Runx2, PPARg, TEADS, TTF-1/Nkx2.1, Tbx5, Pax3, Smad2/3-4 complexes, MyoD and NFAT5. [1][2][3][4][5][6][7][8][9][10][11] This interaction regulates the transcription of target genes with diverse biological functions. For example, TAZ and its paralogue YAP interact with TEADs and stimulate their target genes, including CTGF and Cyr61, to promote cell proliferation and migration. This stimulation is inhibited by Hippo signalling, which regulates organ size, cell proliferation, differentiation and stem cell self-renewal.12-15 Several components are involved in the transduction of the signal. In Drosophila, Hippo and its regulatory protein Salvador stimulate Warts, which inactivates Yorkie. These components are highly evolutionarily conserved and their mammalian orthologues have been characterised. MST1/2 and its regulatory protein WW45 stimulate the downstream kinase Lats1/2, which inhibits nuclear localisation of TAZ/YAP and induces their proteolytic degradation.In cellular differentiation, TAZ modulates the cellular fate of mesenchymal stem cells (MSCs) via the activation of osteoblast and myoblast differentiation, and the inhibition of adipocytes differentiation. 2,10 The interaction between TAZ and Runx2 stimulates Runx2-mediated gene transcription. Wnts are a family of secreted glycoproteins that are involved in the regulation of cell proliferation, differentiation, axis formation, organ development and tissue homeostasis. 16-18b-Catenin is a transcriptional regulator in the canonical Wnt pathway, and, in the absence of Wnts, cytoplasmic b-catenin is phosphorylated by casein kinase I (CKI) and glycogen synthase kinase 3b (GSK3b). This phosphorylation facilitates its ubiquitination and pr...

Alternative Wnt Signaling Activates YAP/TAZ

“…Notably, recent unbiased proteomic studies have not identified the destruction complex as YAP/TAZ interacting proteins while these studies have validated many known YAP/TAZ binding partners (Couzens et al, 2013; Kohli et al, 2014; Kwon et al, 2013; Wang et al, 2014). Consistent with our results, Byun et al also showed that Wnt3a activates TAZ by dephosphorylating Lats1/2 target sites, demonstrating the link between Wnt3a and Hippo pathway (Byun et al, 2014). …”

Histone Deacetylase Inhibitors Target the Leukemic Microenvironment by Enhancing a Nherf1-Protein Phosphatase 1α-TAZ Signaling Pathway in Osteoblasts

“…TAZ activity is tightly regulated to maintain development and homeostasis because TAZ regulates the proliferation, differentiation, adhesion, and apoptosis of diverse cell types (50,51). Interestingly, TAZ phosphorylation on Ser-89 by the Hippo pathway kinase LATS promotes formation of a complex between TAZ and 14-3-3 that retains TAZ in the cytoplasm (20,26,52). Thus, LATS kinase inhibitor drugs, currently under development (35, 49 -51, 53) or natural compounds (54) shown to promote dephosphorylation of TAZ may, like HDACi, be useful for AML combination therapy.…”

“…8C). In these experiments, TAZ in the nuclear fraction consisted of multiple bands, likely reflecting posttranslational modifications, including phosphorylation at multiple residues, which occurs within the nucleus (20,26,35). As shown below (see Fig.…”

“…Inhibiting PP1␣ is not expected to be informative because PP1␣ is required for osteoblast differentiation (20,21), and we previously showed that MC3T3 differentiation is required for protection of KG1a-CXCR4 AML cells (8). Thus, we utilized the approach of overexpressing either wild-type (PP1␣WT) or constitutively active PP1␣ (PP1␣T320A) in MC3T3 cells and examining the effects on the AML cells.…”

A Transcriptome-Level Study Identifies Changing Expression Profiles for Ossification of the Ligamentum Flavum of the Spine

“…For instance, activated Wnt signaling through treatment with Wnt3a induces TAZ expression and increases its nuclear localization to stimulate osteogenic differentiation 36 . Activated mTOR signaling promotes expression of the transcription factor RUNX2 to induce osteogenesis 37 .…”