Simultaneous knockdown of YAP and TAZ increases apoptosis of hepatocellular carcinoma cells under hypoxic condition.

Hepatocellular carcinoma (HCC) is one of the common malignant tumors of the digestive system and its five-year survival rate is low. Hypoxia is an important feature of HCC, which can promote cell death resistance. However, the key regulator of HCC cell survival remains elusive in the hypoxic condition. Emerging researches have showed that the Hippo signaling pathway is involved in the initiation and progression of HCC. Here, we provide evidence that key downstream effectors YAP and its paralog TAZ play vital role in apoptosis resistance of HCC cells under hypoxia. Knockdown of YAP or TAZ does not affect the survival of HCC cells in normoxic and hypoxic microenvironment. In addition, the rate of apoptosis by knockdown or inhibition of both YAP and TAZ under hypoxic condition is largely higher than which under normoxia. In conclusion, simultaneous knockdown or inhibition of YAP and TAZ promote apoptosis of HCC cells dramatically. To our knowledge, this is the first research to explore the role of both YAP and TAZ in HCC hypoxic microenvironment in vitro and in vivo. Therefore, it may be useful for establishing novel targeted therapies of HCC, especially subtypes with plenty of hypoxic areas.

Yan B ，Li T ，Shen L ，Zhou Z ，Liu X ，Wang X ，Sun X ... -  《-》

Nogo-B fosters HCC progression by enhancing Yap/Taz-mediated tumor-associated macrophages M2 polarization.

Zhao X ，Wang X ，You Y ，Wen D ，Feng Z ，Zhou Y ，Que K ，Gong J ，Liu Z ... -  《-》

An Imbalance in TAZ and YAP Expression in Hepatocellular Carcinoma Confers Cancer Stem Cell-like Behaviors Contributing to Disease Progression.

Transcriptional coactivator with PDZ-binding motif (TAZ) and yes-associated protein (YAP) are equivalently placed downstream effectors of the Hippo pathway with oncogenic roles in human cancers. However, the expression profiles of TAZ/YAP differ depending on the cancer cell type, suggesting that these proteins have different roles during cancer progression, yet no studies have examined the biologic significance of the balance between TAZ and YAP expression levels. Here we examined the functional roles of TAZ/YAP in hepatocellular carcinoma progression. We found that TAZ, but not YAP, was predominantly expressed in HCC. TAZ knockdown under normal conditions attenuated cell growth in HCC cells; however, TAZ knockdown combined with 5-fluorouracil treatment significantly increased chemoresistance compared with control cells. Notably, TAZ knockdown induced compensatory YAP expression and was accompanied by upregulation of CD90, a HCC-specific cancer stem cell marker. Continuous treatment with 5-fluorouracil also induced YAP expression and promoted tumor formation in vivo. Conversely, double knockdown of TAZ/YAP reduced chemoresistance and tumorigenicity. Moreover, YAP knockdown aggravated HCC cell growth to a greater degree than TAZ knockdown, and YAP overexpression was strongly associated with poor prognoses in patients with HCC. Collectively, these studies demonstrate that TAZ and YAP exhibit different functional roles in cancer progression, and a shift to predominant YAP expression upon TAZ depletion conferred cancer stem cell-like properties including chemoresistance and tumorigenicity in HCC. Therefore, targeting of both TAZ/YAP will be required for a complete antitumor response in HCC.

Hayashi H ，Higashi T ，Yokoyama N ，Kaida T ，Sakamoto K ，Fukushima Y ，Ishimoto T ，Kuroki H ，Nitta H ，Hashimoto D ，Chikamoto A ，Oki E ，Beppu T ，Baba H ... -  《-》

TAZ target gene ITGAV regulates invasion and feeds back positively on YAP and TAZ in liver cancer cells.

The Hippo pathway effectors yes-associated protein (YAP) and WW domain containing transcription regulator 1 (TAZ/WWTR1) support tumor initiation and progression in various cancer entities including hepatocellular carcinoma (HCC). However, to which extent YAP and TAZ contribute to liver tumorigenesis via common and exclusive molecular mechanisms is poorly understood. RNAinterference (RNAi) experiments illustrate that YAP and TAZ individually support HCC cell viability and migration, while for invasion additive effects were observed. Comprehensive expression profiling revealed partly overlapping YAP/TAZ target genes as well as exclusively regulated genes. Integrin-αV (ITGAV) is a novel TAZ-specific target gene, whose overexpression in human HCC patients correlates with poor clinical outcome, TAZ expression in HCCs, and the abundance of YAP/TAZ target genes. Functionally, ITGAV contributes to actin stress fiber assembly, tumor cell migration and invasion. Perturbation of ITGAV diminishes actin fiber formation and nuclear YAP/TAZ protein levels. We describe a novel Hippo downstream mechanism in HCC cells, which is regulated by TAZ and ITGAV and that feedbacks on YAP/TAZ activity. This mechanism may represent a therapeutic target structure since it contributes to signal amplification of oncogenic YAP/TAZ in hepatocarcinogenesis.

Weiler SME ，Lutz T ，Bissinger M ，Sticht C ，Knaub M ，Gretz N ，Schirmacher P ，Breuhahn K ... -  《-》

USP10 Promotes Proliferation of Hepatocellular Carcinoma by Deubiquitinating and Stabilizing YAP/TAZ.

Yes-associated protein (YAP) and its paralog, transcriptional coactivator with PDZ-binding motif (TAZ), play pivotal roles in promoting the progression of hepatocellular carcinoma. However, the regulatory mechanism underpinning aberrant activation of YAP/TAZ in hepatocellular carcinoma remains unclear. In this study, we globally profiled the contribution of deubiquitinating enzymes (DUB) to both transcriptional activity and protein abundance of YAP/TAZ in hepatocellular carcinoma models and identified ubiquitin-specific peptidase 10 (USP10) as a potent YAP/TAZ-activating DUB. Mechanistically, USP10 directly interacted with and stabilized YAP/TAZ by reverting their proteolytic ubiquitination. Depletion of USP10 enhanced polyubiquitination of YAP/TAZ, promoted their proteasomal degradation, and ultimately arrested the proliferation of hepatocellular carcinoma in vitro and in vivo. Expression levels of USP10 positively correlated with the abundance of YAP/TAZ in hepatocellular carcinoma patient samples as well as in N-nitrosodiethylamine (DEN)-induced liver cancer mice models. Collectively, this study establishes the causal link between USP10 and hyperactivated YAP/TAZ in hepatocellular carcinoma cells and provides a rationale for potential therapeutic interventions in the treatment of patients with hepatocellular carcinoma harboring a high level of YAP/TAZ. SIGNIFICANCE: These findings identify USP10 as a DUB of YAP/TAZ and its role in hepatocellular carcinoma progression, which may serve as a potential therapeutic target for hepatocellular carcinoma treatment.

Zhu H ，Yan F ，Yuan T ，Qian M ，Zhou T ，Dai X ，Cao J ，Ying M ，Dong X ，He Q ，Yang B ... -  《-》