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Gastroenterology. 2014 Sep;147(3):690-701. doi: 10.1053/j.gastro.2014.05.004. Epub 2014 May 14.

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

Author information

1
Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, California.
2
Institute of Pathology, University of Greifswald, Greifswald, Germany.
3
Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.
4
Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania; The Second Affiliated Hospital, School of Medicine, Xi'an Jiaotong University, Xi'an, China.
5
Institute of Pathology, University Hospital Basel, Basel, Switzerland.
6
Department of Pediatric Surgery and Pediatric Urology, Children's University Hospital Tuebingen, Tuebingen, Germany.
7
Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, San Francisco, California; Liver Center, University of California, San Francisco, San Francisco, California. Electronic address: xin.chen@ucsf.edu.
8
Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania. Electronic address: smonga@pitt.edu.

Abstract

BACKGROUND & AIMS:

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.

METHODS:

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.

RESULTS:

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.

CONCLUSIONS:

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.

KEYWORDS:

Gene Regulation; Liver Cancer; Oncogene; Tumor Formation

PMID:
24837480
PMCID:
PMC4143445
DOI:
10.1053/j.gastro.2014.05.004
[Indexed for MEDLINE]
Free PMC Article

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