Role Of TAZ Research Articles

Abstract 3520: TAZ (WWTR1), a key transcription co-activator of hippo-pathway, promotes hepatocellular carcinoma progression via PI3K/Akt/mTOR pathway

Abstract Introduction: The contact inhibition of proliferation is crucial for well-controlled organogenesis. Its disruption results in sustained cell proliferation, which is a hallmark of solid tumors. The Hippo signaling pathway has been implicated in contact inhibition of proliferation. Here, we investigated the role of TAZ (WWTR1), a key transcription co-activator of hippo-pathway, in HCC progression. Methods and Results: In HCC patients, the high TAZmRNA expression examined by real time PCR showed worsen survival outcomes compared with low expression group. Additionally, the tumor size in High TAZmRNA expression group was significantly larger than that in low expression group, and its high protein expression in HCC was deeply associated with the cell proliferative activity. A knockdown of TAZ expression in HCC cell lines attenuated the cell growth accompanying the downstream gene expressions (CTGF and CYR61). As the TAZ-mediated signaling pathway in cell growth, a knockdown of TAZ expression using RNAi inactivated the PI3K/Akt/mTOR pathway. Conclusion: Thus, TAZ plays a crucial role in tumor progression by accelerating cell growth via a PI3K/Akt/mTOR pathway, and tumoral TAZmRNA expression level may be a useful prognostic biomarker in HCC. Citation Format: Hiromitsu Hayashi, Hideyuki Kuroki, Shigeki Nakagawa, Takaaki Higashi, Keita Sakamoto, Naomi Yokoyama, Takatoshi Ishiko, Toru Beppu, Hideo Baba. TAZ (WWTR1), a key transcription co-activator of hippo-pathway, promotes hepatocellular carcinoma progression via PI3K/Akt/mTOR pathway. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3520. doi:10.1158/1538-7445.AM2014-3520

Role of TAZ as Mediator of Wnt Signaling

Wnt growth factors are fundamental regulators of cell fate, but how the Wnt signal is translated into biological responses is incompletely understood. Here, we report that TAZ, a biologically potent transcriptional coactivator, serves as a downstream element of the Wnt/β-catenin cascade. This function of TAZ is independent from its well-established role as mediator of Hippo signaling. In the absence of Wnt activity, the components of the β-catenin destruction complex--APC, Axin, and GSK3--are also required to keep TAZ at low levels. TAZ degradation depends on phosphorylated β-catenin that bridges TAZ to its ubiquitin ligase β-TrCP. Upon Wnt signaling, escape of β-catenin from the destruction complex impairs TAZ degradation and leads to concomitant accumulation of β-catenin and TAZ. At the genome-wide level, a substantial portion of Wnt transcriptional responses is mediated by TAZ. TAZ activation is a general feature of Wnt signaling and is functionally relevant to mediate Wnt biological effects.

The ciliopathy disease protein NPHP9 promotes nuclear delivery and activation of the oncogenic transcriptional regulator TAZ

Nephronophthisis (NPH) is a genetically heterogenous kidney disease and represents the most common genetic cause for end-stage renal disease in children. It is caused by the mutation of genes encoding for the nephrocystin proteins (NPHPs) which localize to primary cilia or centrosomes, classifying this disease as a 'ciliopathy'. Recently, it has been shown that NPHP4 acts as a potent negative regulator of mammalian Hippo signalling by interacting with the Lats protein kinase and controlling the phosphorylation of the oncogenic transcriptional activator TAZ. Here, we demonstrate that NPHP9, another NPH family member, also controls TAZ activity by a distinct mechanism. NPHP9, which is also called NEK8, directly interacted with TAZ and induced nuclear translocation of the TAZ/NPHP9 protein complex. Binding of NPHP9 to TAZ was enhanced in a TAZ mutant that lost its ability to bind 14-3-3, suggesting that 14-3-3 and NPHP9 may compete for TAZ binding, with 14-3-3 favouring cytoplasmic retention and NPHP9 mediating nuclear delivery. Consistently, co-expression of NPHP4, which inhibits TAZ phosphorylation at the 14-3-3 binding site through the inhibition of Lats kinase activity, induced efficient nuclear delivery of the TAZ/NPHP9 protein pair. Consistent with a role for TAZ in controlling proliferation and tumorigenesis, the downregulation of NPHP9 inhibited the TAZ-dependent proliferation of hippo-responsive normal epithelial and also breast cancer cells. As NPHP9 has been shown to be upregulated in breast cancer, these data do not only support a critical role for TAZ/hippo signalling in the pathogenesis of NPH but may also imply a possible role for NPHP9 in TAZ-mediated tumorigenesis.

Abstract 3247: Identification of a novel TAZ/TEAD/BMP4/Smad1,5 signaling axis

Abstract TAZ functions as a transcriptional co-activator critical for tissue development, mesenchymal stem cell differentiation, and embryonic stem cell renewal. Recently, TAZ has been identified as a major downstream component of the novel Hippo-LATS tumor suppressor pathway, where TAZ over-expression in immortalized mammary epithelial cells, MCF10A, leads to enhanced cell proliferation and migration, transformation, EMT, and resistance to the chemotherapeutic paclitaxel. However, the molecular mechanisms underlying these TAZ-induced phenotypes are largely unknown. In this study, we aimed to identify downstream targets responsible for TAZ-induced phenotypes. Through screening a 44K human genome microarray we have identified many potential targets, one of which is bone morphogenetic protein 4 (BMP4), a cytokine that regulates important processes such as cell proliferation, migration, and EMT. By qRT-PCR, western blotting, and an ELISA assay we verified that BMP4 is upregulated at the mRNA, protein, and secreted levels, respectively, in TAZ overexpressing MCF10A cells (MCF10A-TAZ) compared to control cells (MCF10A-WPI). To investigate whether BMP4 is a direct transcriptional target of TAZ, we used a dual luciferase assay to measure BMP4 promoter activity. When co-transfected with TAZ and TEAD4, a transcription factor mediating TAZ transactivation, BMP4 promoter activity was significantly increased. This TAZ/TEAD interaction is critical for BMP4 transcriptional activation as interaction mutants of TAZ and TEAD4 (TAZα72 and TEAD4-Y429H) both fail to activate BMP4 promotor activity. Significantly, we have identified two TEAD Response Elements (TRE) located in the BMP4 promoter where mutation of TRE1 alone completely abolished activation of BMP4 promoter activity by TAZ/TEAD4 and mutation of TRE2 had no effect. This suggests that TRE1 is responsible for TAZ/TEAD activation of BMP4. Through microarray analysis, we have identified many secreted cytokines leading us to suspect that they may promote EMT. Strikingly, MCF10A cells continuously treated with conditioned media from MCF10A-TAZ or exogenous BMP4 induced an obvious EMT phenotype, suggesting that BMP4 may be responsible for TAZ-induced EMT. Moreover, phosphorylation of Smad1,5 (pSmad1,5), two major mediators of BMP4 function, was also significantly increased in MCF10A-TAZ, but was completely abolished when MCF10A-TAZ cells were treated with Noggin, a BMP4 specific inhibitor, demonstrating that activation of Smad is specifically due to BMP4. Our results provide convincing evidence that BMP4 is a novel transcriptional target of TAZ, which may mediate the TAZ-induced EMT phenotype and thereby identify a novel TAZ/TEAD/BMP4/Smad1,5 signaling axis. Further functional characterization of this pathway will greatly facilitate our understanding of the roles of TAZ in the metastatic progression of breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3247. doi:1538-7445.AM2012-3247

Abstract 978: A regulatory role for TAZ in mesenchymal differentiation of glioblastoma

Abstract Gene expression profiling studies have revealed that the mesenchymal signature (MES) is a predictor for poor survival and treatment resistance in glioblastoma (GBM) patients, whereas patients with a proneural (PN) signature perform better in the clinic. We found that the HIPPO pathway transcription co-factor TAZ, but not YAP is epigenetically silenced by CpG island hypermethylation in lower grade/PN tumors whereas its promoter is hypomethylated in GBM/MES tumors. Treatment of a demethylation agent (2′-deoxy-5-azacytidine) increased TAZ mRNA levels in glioma stem cells lacking this protein. Using bioinformatic approaches we found TAZ to be significantly connected to the MES gene signature network that was distinct from recently reported regulators of MES transition in GBM, viz., STAT3 and CEBPβ. Approximately 60% of the in silico inferred targets were confirmed to be direct targets of TAZ by ChIP-PCR. Silencing TAZ in GSCs decreased invasion and blocked tumorigenesis when implanted intracranially into mice. Conversely, overexpression of TAZ in GSCs that lack this protein resulted in increased MES gene expression, suppressed PN gene expression, increased invasion, differentiation toward an osteogenic and chondrocytic lineage and reduced tumor latency in the xenograft model. In primary NSCs, forced TAZ resulted in increased expression of mesenchymal markers such as fibronectin, and smooth muscle actin, whereas astrocytic or neuronal differentiation was suppressed. All aforementioned phenotypes were abolished when overexpressing a single point mutant version of TAZ (S51A) that lacks binding to its bona fide transcription partner, TEAD. Finally overexpression of TAZ in a PGDF-RCAS transgenic mouse model caused increased tumor grade and incidence and shift toward a MES phenotype. Our study identifies TAZ as important master regulator of PN to MES transition in gliomas and presents as an attractive therapeutic target for this devastating disease. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 978. doi:10.1158/1538-7445.AM2011-978

Mutations in TAZ/WWTR1, a co-activator of NKX2.1 and PAX8 are not a frequent cause of thyroid dysgenesis

In 80-85% of cases, congenital hypothyroidism is associated with thyroid dysgenesis (TD), but only in a small percentage of cases mutations in thyroid transcription factors (NKX2.1, PAX8, FOXE1, and NKX2.5) have been associated with the disease. Several studies demonstrated that the activity of the transcription factors can be modulated by the interaction with other proteins, such as coactivators and co-repressors, and TAZ (transcriptional co-activator with PDZ-binding motif or WWTR1) is a co-activator interacting with both NKX2.1 and PAX8. In the present study we investigate the role of TAZ in the pathogenesis of TD. By Single Stranded Conformational Polymorphism, we screened the entire TAZ coding sequence for mutations in 96 patients with TD and in 96 normal controls. No mutations were found in patients and controls, but we found several polymorphisms in both groups. No significant differences could be demonstrated in the prevalence of the mutations between patients and controls. Our data indicate that TAZ mutations are not a cause of TD in the series of patients studied.

A Role for TAZ in Migration, Invasion, and Tumorigenesis of Breast Cancer Cells

TAZ (WWTR1), identified as a 14-3-3 binding protein with a PDZ binding motif, modulates mesenchymal stem cell differentiation. We now show that TAZ plays a critical role in the migration, invasion, and tumorigenesis of breast cancer cells. TAZ is conspicuously expressed in human breast cancer cell lines in which its expression levels generally correlate with the invasiveness of cancer cells. Overexpression of TAZ in low-expressing MCF10A cells causes morphologic changes characteristic of cell transformation and promotes cell migration and invasion. Conversely, RNA interference-mediated knockdown of TAZ expression in MCF7 and Hs578T cells reduces cell migration and invasion. TAZ knockdown in MCF7 cells also retards anchorage-independent growth in soft agar and tumorigenesis in nude mice. Significantly, TAZ is overexpressed in approximately 20% of breast cancer samples. These results indicate that TAZ plays a role in the migration, invasion, and tumorigenesis of breast cancer cells and thus presents a novel target for the detection and treatment of breast cancer.