mTOR inhibition affects Yap1-β-catenin-induced hepatoblastoma growth and development

Abstract

// Laura Molina 1, 2, * , Hong Yang 3, * , Adeola O. Adebayo Michael 4 , Michael Oertel 1, 5 , Aaron Bell 1 , Sucha Singh 1 , Xin Chen 6 , Junyan Tao 1 and Satdarshan P.S. Monga 1, 5, 7 1 Division of Experimental Pathology, Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA 2 Medical Scientist Training Program, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA 3 Department of Medical Ultrasonics, The First Affiliated Hospital of Guangxi Medical University, Guangxi, China 4 Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, USA 5 Pittsburgh Liver Research Center, University of Pittsburgh Medical Center and University of Pittsburgh School of Medicine, Pittsburgh PA, USA 6 Department of Bioengineering and Therapeutic Sciences and Liver Center, University of California, San Francisco, CA, USA 7 Division of Gastroenterology, Hepatology and Nutrition, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA * These authors have contributed equally to this work Correspondence to: Satdarshan P.S. Monga, email: smonga@pitt.edu Junyan Tao, email: junyantao2010@gmail.com Keywords: pediatric liver tumor; Wnt signaling; mTOR pathway; beta-catenin; YAP1 Received: December 20, 2018     Accepted: January 22, 2019     Published: February 19, 2019 ABSTRACT Hepatoblastoma (HB) is the most common pediatric liver malignancy. Around 80% of HB demonstrate simultaneous activation of β-catenin and Yes-associated protein 1 (Yap1). The mechanism by which these signaling pathways contribute to HB pathogenesis remain obscure. Recently, mTORC1 activation was reported in human HB cells and in a murine HB model driven by β-catenin and Yap1. Here, we directly investigate the therapeutic impact of mTOR inhibition following HB development in the Yap1-β-catenin model. HB were established by hydrodynamic tail vein injection of Sleeping Beauty transposase and plasmids coding for ΔN90-β-catenin and S127A-Yap1. Five weeks after injection, when HB were evident, mice were randomized into Rapamycin diet-fed or basal-diet-fed groups for 5-weeks. Tumor growth was monitored via ultrasound imaging and mice in both groups were euthanized after 5-weeks for molecular analysis. Transcriptomic analysis showed a strong correlation in gene expression between HB in the Yap1-β-catenin model and HB patient cohorts. Rapamycin treatment decreased HB burden, almost normalizing liver weight to body weight ratio. Ultrasound imaging showed reduction in tumor growth over the duration of Rapamycin treatment as compared to controls. Majority of HB in the controls exhibited crowded fetal or embryonal histology, while remnant tumors in the experimental group showed well-differentiated fetal morphology. Immunohistochemistry confirmed inhibition of mTORC1 in the Rapamycin group. Thus, Rapamycin reduces HB in a clinically relevant model driven by β-catenin and Yap1, supporting use of mTORC1 inhibitors in their therapy. We also show the utility of standard and 3D ultrasound imaging for monitoring liver tumors in mice.