Pediatric rhabdomyosarcoma (RMS) is a morphologically and genetically heterogeneous malignancy commonly classified into three histologic subtypes, namely, alveolar, embryonal, and anaplastic. An issue that continues to challenge effective RMS patient prognosis is the dearth of molecular markers predictive of disease stage irrespective of tumor subtype. Our study involving a panel of 70 RMS tumors has identified specific alternative splice variants of the oncogenes Murine Double Minute 2 (MDM2) and MDM4 as potential biomarkers for RMS. Our results have demonstrated the strong association of genotoxic-stress inducible splice forms MDM2-ALT1 (91.6% Intergroup Rhabdomyosarcoma Study Group stage 4 tumors) and MDM4-ALT2 (90.9% MDM4-ALT2-positive T2 stage tumors) with high-risk metastatic RMS. Moreover, MDM2-ALT1- positive metastatic tumors belonged to both the alveolar (50%) and embryonal (41.6%) subtypes, making this the first known molecular marker for high-grade metastatic disease across the most common RMS subtypes. Furthermore, our results show that MDM2-ALT1 expression can function by directly contribute to metastatic behavior and promote the invasion of RMS cells through a matrigel-coated membrane. Additionally, expression of both MDM2-ALT1 and MDM4-ALT2 increased anchorageindependent cell-growth in soft agar assays. Intriguingly, we observed a unique coordination in the splicing of MDM2-ALT1 and MDM4-ALT2 in approximately 24% of tumor samples in a manner similar to genotoxic stress response in cell lines. To further explore splicing network alterations with possible relevance to RMS disease, we used an exon microarray approach to examine stress-inducible splicing in an RMS cell line (Rh30) and observed striking parallels between stress-responsive alternative splicing and constitutive splicing in RMS tumors.
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Abbreviations: COG, Children’s Oncology Group; MDM2, murine double minute 2; MDM4, murine double minute 4; RMS, rhabdomyosarcoma; STS, soft tissue sarcoma Address all correspondence to: Dawn S. Chandler, PhD, Center for Childhood Cancer, Research Institute at Nationwide Children’s Hospital, Rm WA5023, 700 Children’s Drive, Columbus, OH 43205-2696. E-mail: Dawn.Chandler@nationwidechildrens.org 1This study was supported in part by Alex’s Lemonade Stand Foundation and the Sarcoma Foundation of America to D.S.C. We acknowledge the National Cancer Institute, National Institutes of Health (Bethesda, MD) for grant 1R01CA133571 to D.S.C. and grant RO1CA108882 to K.B.L. We also acknowledge the Chair’s grant U10 CA98543 and Human Specimen Banking grant U24 CA114766 of the Children’s Oncology Group from the National Cancer Institute, National Institutes of Health for research support. Additional support for this research is provided by a grant from the WWWW (QuadW) Foundation, Inc (www.QuadW.org) to the Children’s Oncology Group. 2This article refers to supplementary materials, which are designated by Tables W1 to W3 and Figures W1 to W4 and are available online at www.neoplasia.com. Received 20 January 2013; Revised 5 July 2013; Accepted 15 July 2013 Copyright © 2013 Neoplasia Press, Inc. All rights reserved 1522-8002/13/$25.00 DOI 10.1593/neo.13286