Abstract 5115: Genetic signature of histiocytic sarcoma revealed by an unbiased genetic screen in mice
Authors: Allaei Raha , Starr Timothy K. , Sarver Aaron , O'Sullivan M. Gerard , Largaespada David A. 
Published: August 2012

Abstract
Histiocytic Sarcomas (HS) are rare neoplasms derived from hematopoietic or mesenchymal stem cells and are known to have a poor prognosis. Primary lesions of HS appear in the spleen, lymph nodes, lung, bone marrow, skin and hypodermis. The definitive cell of origin, genetic etiology, and critical drug targets for HS therapy are unknown. To address all three questions we have utilized a forward genetic screening method in mice that can identify mutations capable of causing cancer initiation and progression. The forward genetic screen uses the Sleeping Beauty (SB) DNA transposon as a random somatic mutagen, capable of both activating proto-oncogenes and inactivating tumor suppressor genes. The system relies on the use of a Cre/LoxP-regulated SB transposase transgene and mutagenic transposon vector transgenes that are mobilized by the transposase. Using Cre recombinase under the control of a tissue specific promoter allows for selective, tissue specific mutagenesis in particular cells of interest. Tumors generated in these mice are analyzed for recurrent transposon insertion sites (called common insertion sites or CIS) using ligation-mediated PCR in combination with high-throughput sequencing. As in human cancer, our results often reveal a small number of frequently mutated genes that cooperate with a greater number of rare mutant genes that drive formation of tumors. We hypothesized that SB-mediated transposition of an oncogenic transposon in myeloid lineage cells in mice could cause mutations in oncogenes and tumor suppressor genes leading to the initiation and progression of HS. We generated and aged 190 experimental and control transgenic mice. The triple transgenic, experimental mice express SB transposase in myeloid lineage cells containing an oncogenic transposon by virtue of a Cre recombinase transgene under the control of the Lysozyme M promoter, which is expressed in committed myeloid lineage cells. Remarkably, triple transgenic mice became moribund much faster than controls. Histopathology suggests 30% of the experimental mice developed HS. We have performed immunohistochemistry to confirm the tumor type using antibodies to Mac-2, F4/80 and PAX5. Tumors were analyzed by mapping transposon insertions to the mouse genome from many independently generated tumors. We mapped 1,177 non-redundant insertions and generated a list of 23 candidate HS genes comprised of known cancer genes as well as novel candidate genes. Our top 3 hits are Raf1 and Fli1, known oncogenes associated with hematological neoplasms, and Mitf, a transcription factor associated with melanoma. Our list also includes known tumor suppressors Trp53 and Nf1. Our results show that 1: A mature myeloid lineage cell can serve as a target cell for HS. 2: ETS and basic helix-loop-helix (hHLH)-leucine zipper transcription factor networks can induce HS with Raf-activated pathways And 3: RAF-MEK-ERK signaling is likely a useful target for HS treatment.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5115. doi:1538-7445.AM2012-5115