Clear Cell Sarcoma (CCS) is a deadly malignancy affecting adolescents and young adults. It is characterized by reciprocal translocations resulting in the expression of the chimeric EWSR1-ATF1 or EWSR1-CREB1 fusion proteins, driving sarcomagenesis. Besides these characteristics, CCS has remained genomically uncharacterized. Copy number analysis of human CCSs showed frequent amplifications of the MITF locus and chromosomes 7 and 8. Few alterations were shared with Ewing sarcoma or desmoplastic small round cell tumors, other EWSR1-rearranged tumors. Exome sequencing in mouse tumors generated by expressing EWSR1-ATF1 from the Rosa26 locus demonstrated no other repeated pathogenic variants. Additionally, we generated a new CCS mouse by Cre-loxP-induced chromosomal translocation between Ewsr1 and Atf1, resulting in copy number loss of chromosome 6 and chromosome 15 instability, including amplification of a portion syntenic with human chromosome 8, surrounding Myc. Additional experiments in the Rosa26 conditional model demonstrated that Mitf or Myc can contribute to sarcomagenesis. Copy number observations in human tumors and genetic experiments in mice render, for the first time, a functional landscape of the CCS genome. These data advance efforts to understand the biology of CCS with innovative models, in which we can eventually validate preclinical therapies, necessary to move toward longer and better survival of the young victims of this disease.
Emanuele Panza, Benjamin B. Ozenberger, Krystal M. Straessler, Jared J. Barrott, Li Li, Yanliang Wang, Mingchao Xie, Anne Boulet, Simon W. A. Titen, Clinton C. Mason, Alexander J. Lazar, Li Ding, Mario R. Capecchi, Kevin B. Jones