β-Catenin and Yes-Associated Protein 1 Cooperate in Hepatoblastoma Pathogenesis.

Hepatoblastoma (HB), the most common pediatric primary liver neoplasm, shows nuclear localization of β-catenin and yes-associated protein 1 (YAP1) in almost 80% of the cases. Co-expression of constitutively active S127A-YAP1 and ΔN90 deletion-mutant β-catenin (YAP1-ΔN90-β-catenin) causes HB in mice. Because heterogeneity in downstream signaling is being identified owing to mutational differences even in the β-catenin gene alone, we investigated if co-expression of point mutants of β-catenin (S33Y or S45Y) with S127A-YAP1 led to similar tumors as YAP1-ΔN90-β-catenin. Co-expression of S33Y/S45Y-β-catenin and S127A-YAP1 led to activation of Yap and Wnt signaling and development of HB, with 100% mortality by 13 to 14 weeks. Co-expression with YAP1-S45Y/S33Y-β-catenin of the dominant-negative T-cell factor 4 or dominant-negative transcriptional enhanced associate domain 2, the respective surrogate transcription factors, prevented HB development. Although histologically similar, HB in YAP1-S45Y/S33Y-β-catenin, unlike YAP1-ΔN90-β-catenin HB, was glutamine synthetase (GS) positive. However, both ΔN90-β-catenin and point-mutant β-catenin comparably induced GS-luciferase reporter in vitro. Finally, using a previously reported 16-gene signature, it was shown that YAP1-ΔN90-β-catenin HB tumors exhibited genetic similarities with more proliferative, less differentiated, GS-negative HB patient tumors, whereas YAP1-S33Y/S45Y-β-catenin HB exhibited heterogeneity and clustered with both well-differentiated GS-positive and proliferative GS-negative patient tumors. Thus, we demonstrate that β-catenin point mutants can also collaborate with YAP1 in HB development, albeit with a distinct molecular profile from the deletion mutant, which may have implications in both biology and therapy.

Min Q ，Molina L ，Li J ，Adebayo Michael AO ，Russell JO ，Preziosi ME ，Singh S ，Poddar M ，Matz-Soja M ，Ranganathan S ，Bell AW ，Gebhardt R ，Gaunitz F ，Yu J ，Tao J ，Monga SP ... -  《-》

Activation of β-catenin and Yap1 in human hepatoblastoma and induction of hepatocarcinogenesis in mice.

Aberrant activation of β-catenin and Yes-associated protein 1 (Yap1) signaling pathways have been associated with the development of multiple tumor types. Yap functions as a transcriptional coactivator by interacting with TEA domain DNA binding proteins. We investigated the interactions among these pathways during hepatic tumorigenesis. We used immunohistochemical analysis to determine expression of β-catenin and Yap1 in liver cancer specimens collected from patients in Europe and the United States, consisting of 104 hepatocellular carcinoma, 62 intrahepatic cholangiocarcinoma, and 94 hepatoblastoma samples. We assessed β-catenin and Yap1 signaling and interactions in hepatoblastoma cell lines ((HuH6, HepG2, HepT1, HC-AFW1, HepG2, and HC-AFW1); proteins were knocked down with small interfering RNAs, and effects on proliferation and cell death were measured. Sleeping beauty-mediated hydrodynamic transfection was used to overexpress constitutively active forms of β-catenin (ΔN90/β-catenin) and Yap1 (YapS127A) in livers of mice; tissues were collected, and histological and immunohistochemical analyses were performed. We observed nuclear localization of β-catenin and Yap1 in 79% of hepatoblastoma samples but not in most hepatocellular carcinoma or intrahepatic cholangiocarcinoma samples. Yap1 and β-catenin coprecipitated in hepatoblastoma but not hepatocellular carcinoma cells. Small interfering RNA-mediated knockdown of Yap1 or β-catenin in hepatoblastoma cells reduced proliferation in an additive manner. Knockdown of Yap1 reduced its ability to coactivate transcription with β-catenin; β-catenin inhibitors inactivated Yap1. Overexpression of constitutively active forms of Yap1 and β-catenin in mouse liver led to rapid tumorigenesis, with 100% mortality by 11 weeks. Tumor cells expressed both proteins, and human hepatoblastoma cells expressed common targets of their 2 signaling pathways. Yap1 binding of TEA domain factors was required for tumorigenesis in mice. β-catenin and the transcriptional regulator Yap1 interact physically and are activated in most human hepatoblastoma tissues; overexpression of activated forms of these proteins in livers of mice leads to rapid tumor development. Further analysis of these mice will allow further studies of these pathways in hepatoblastoma pathogenesis and could lead to the identification of new therapeutic targets.

Tao J ，Calvisi DF ，Ranganathan S ，Cigliano A ，Zhou L ，Singh S ，Jiang L ，Fan B ，Terracciano L ，Armeanu-Ebinger S ，Ribback S ，Dombrowski F ，Evert M ，Chen X ，Monga SPS ... -  《-》

TEA Domain Transcription Factor 4 Is the Major Mediator of Yes-Associated Protein Oncogenic Activity in Mouse and Human Hepatoblastoma.

Hepatoblastoma (HB) is the most common type of pediatric liver cancer. Activation of yes-associated protein (YAP) has been implicated in HB molecular pathogenesis. The transcriptional co-activator Yap regulates downstream gene expression through interaction with the TEA domain (TEAD) proteins. Nonetheless, YAP also displays functions that are independent of its transcriptional activity. The underlying molecular mechanisms by which Yap promotes HB development remain elusive. In the current study, we demonstrated that blocking TEAD function via the dominant-negative form of TEAD2 abolishes Yap-driven HB formation in mice and restrains human HB growth in vitro. When TEAD2 DNA-binding domain was fused with virus protein 16 transcriptional activation domain, it synergized with activated β-catenin to promote HB formation in vivo. Among TEAD genes, silencing of TEAD4 consistently inhibited tumor growth and Yap target gene expression in HB cell lines. Furthermore, TEAD4 mRNA expression was significantly higher in human HB lesions when compared with corresponding nontumorous liver tissues. Human HB specimens also exhibited strong nuclear immunoreactivity for TEAD4. Altogether, data demonstrate that TEAD-mediated transcriptional activity is both sufficient and necessary for Yap-driven HB development. TEAD4 is the major TEAD isoform and Yap partner in human HB. Targeting TEAD4 may represent an effective treatment option for human HB.

Zhang J ，Liu P ，Tao J ，Wang P ，Zhang Y ，Song X ，Che L ，Sumazin P ，Ribback S ，Kiss A ，Schaff Z ，Cigliano A ，Dombrowski F ，Cossu C ，Pascale RM ，Calvisi DF ，Monga SP ，Chen X ... -  《-》

YAP1 Withdrawal in Hepatoblastoma Drives Therapeutic Differentiation of Tumor Cells to Functional Hepatocyte-Like Cells.

Despite surgical and chemotherapeutic advances, the 5-year survival rate for stage IV hepatoblastoma (HB), the predominant pediatric liver tumor, remains at 27%. Yes-associated protein 1 (YAP1) and β-catenin co-activation occurs in 80% of children's HB; however, a lack of conditional genetic models precludes tumor maintenance exploration. Thus, the need for a targeted therapy remains unmet. Given the predominance of YAP1 and β-catenin activation in HB, we sought to evaluate YAP1 as a therapeutic target in HB. We engineered the conditional HB murine model using hydrodynamic injection to deliver transposon plasmids encoding inducible YAP1S127A , constitutive β-cateninDelN90 , and a luciferase reporter to murine liver. Tumor regression was evaluated using bioluminescent imaging, tumor landscape characterized using RNA and ATAC sequencing, and DNA footprinting. Here we show that YAP1S127A withdrawal mediates more than 90% tumor regression with survival for 230+ days in mice. YAP1S127A withdrawal promotes apoptosis in a subset of tumor cells, and in remaining cells induces a cell fate switch that drives therapeutic differentiation of HB tumors into Ki-67-negative hepatocyte-like HB cells ("HbHeps") with hepatocyte-like morphology and mature hepatocyte gene expression. YAP1S127A withdrawal drives the formation of hbHeps by modulating liver differentiation transcription factor occupancy. Indeed, tumor-derived hbHeps, consistent with their reprogrammed transcriptional landscape, regain partial hepatocyte function and rescue liver damage in mice. YAP1S127A withdrawal, without silencing oncogenic β-catenin, significantly regresses hepatoblastoma, providing in vivo data to support YAP1 as a therapeutic target for HB. YAP1S127A withdrawal alone sufficiently drives long-term regression in HB, as it promotes cell death in a subset of tumor cells and modulates transcription factor occupancy to reverse the fate of residual tumor cells to mimic functional hepatocytes.

Smith JL ，Rodríguez TC ，Mou H ，Kwan SY ，Pratt H ，Zhang XO ，Cao Y ，Liang S ，Ozata DM ，Yu T ，Yin Q ，Hazeltine M ，Weng Z ，Sontheimer EJ ，Xue W ... -  《-》

Long non-coding RNA muskelin 1 antisense RNA (MKLN1-AS) is a potential diagnostic and prognostic biomarker and therapeutic target for hepatocellular carcinoma.

Hepatocellular carcinoma is recognized as the most common subtype of hepatic cancer. Muskelin 1 antisense RNA (MKLN1-AS) shows prognostic value in hepatitis B virus-hepatocellular carcinoma. The aim of this study is to investigate the detailed biological role of MKLN1-AS and Yes-associated transcriptional regulator 1 (YAP1)-related mechanisms. Based on online databases (GEPIA, TCGA, and GEO), the expression of MKLN1-AS and YAP1 in patients with hepatocellular carcinoma was analyzed. The IntaRNA algorithm was used to predict complementary sites between MKLN1-AS and YAP1 mRNA. Hepatocellular carcinoma tumor tissues and cells were collected for the quantification of MKLN1-AS and YAP1. FISH was performed to explore the location of MKLN1-AS in cells. The effects of MKLN1-AS and YAP1 on proliferation, migration and invasionof hepatocellular carcinoma were determined in vitro and in vivo. Actinomycin D and RNA immunoprecipitation were resorted to confirm the regulatory role of MKLN1-AS in YAP1 expression. The up-regulation of MKLN1-AS contributed to the poor prognosis of patients with hepatocellular carcinoma. MKLN1-AS and YAP1 were overexpressed in hepatocellular carcinoma tissues and cells. MKLN1-AS positively modulated YAP1 expression through targeting and stabilizing YAP1 mRNA.MKLN1-AS was predominantly located in the cytoplasm of the cells. MKLN1-AS intensified proliferation, migration and invasion of hepatocellular carcinoma cells via YAP1. MKLN1-AS also caused hepatocarcinogenesis through inducing YAP1 expression in vivo. MKLN1-AS overexpression enhances the stability of YAP1 mRNA, which is necessary for the oncogenic activity of MKLN1-AS. MKLN1-AS can be utilized in the diagnosis and prognosis of hepatocellular carcinoma as an upstream factor of YAP1.

Guo C ，Zhou S ，Yi W ，Yang P ，Li O ，Liu J ，Peng C ... -  《-》