Kras activation in p53-deficient myoblasts results in high-grade sarcoma formation with impaired myogenic differentiation

// Timothy McKinnon 1 , Rosemarie Venier 1 , Brendan C. Dickson 4 , Leah Kabaroff 1 , Manon Alkema 1 , Li Chen 5 , Jack F. Shern 5 , Marielle E. Yohe 5 , Javed Khan 5 , Rebecca A. Gladdy 1, 2, 3 1 Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Canada 2 Ontario Institute for Cancer Research, Cancer Stem Cell Program, Toronto, Canada 3 Department of Surgery, University of Toronto, Toronto, Canada 4 Department of Pathology & Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada 5 Genetics Branch, Oncogenomics Section, Center for Cancer Research, National Institute of Health, Gaithersburg, MD, USA Correspondence to: Rebecca Gladdy, e-mail: gladdy@lunenfeld.ca Keywords: sarcoma, rhabdomyosarcoma, mouse models of cancer, Kras, myogenic differentiation Received: January 26, 2015      Accepted: May 04, 2015      Published: May 15, 2015 ABSTRACT While genomic studies have improved our ability to classify sarcomas, the molecular mechanisms involved in the formation and progression of many sarcoma subtypes are unknown. To better understand developmental origins and genetic drivers involved in rhabdomyosarcomagenesis, we describe a novel sarcoma model system employing primary murine p53-deficient myoblasts that were isolated and lentivirally transduced with Kras G12D . Myoblast cell lines were characterized and subjected to proliferation, anchorage-independent growth and differentiation assays to assess the effects of transgenic Kras G12D expression. Kras G12D overexpression transformed p53 −/− myoblasts as demonstrated by an increased anchorage-independent growth. Induction of differentiation in parental myoblasts resulted in activation of key myogenic regulators. In contrast, Kras-transduced myoblasts had impaired terminal differentiation. p53 −/− myoblasts transformed by Kras G12D overexpression resulted in rapid, reproducible tumor formation following orthotopic injection into syngeneic host hindlimbs. Pathological analysis revealed high-grade sarcomas with myogenic differentiation based on the expression of muscle-specific markers, such as Myod1 and Myog. Gene expression patterns of murine sarcomas shared biological pathways with RMS gene sets as determined by gene set enrichment analysis (GSEA) and were 61% similar to human RMS as determined by metagene analysis. Thus, our novel model system is an effective means to model high-grade sarcomas along the RMS spectrum.