Abstract CIC-rearranged sarcoma (CRS) is an rare disease driven by a specific fusion protein involving the CIC gene. Occurrence in the brain is 3% in all CRS patients. The native CIC protein is a transcriptional repressor of the (RTK)/Ras/ERK signaling pathway, which is one of the most tumorigenic pathways in cancer. The most common rearrangement is with the double homeobox 4 (DUX4) transcription factor (CIC-DUX4), and others, such as CIC-NUTM1 fusions, have been identified in a subset of pediatric primitive neuroectodermal tumors. However, the molecular mechanisms by which CIC-fusions drive CRS remain unknown. Preliminary data shows that CIC-DUX4/NUTM1 fusions activate JAK and its downstream effector STAT1/3. We hypothesize that the JAK/STAT1/3 signal transduction pathway cooperates with CIC-fusions to induce the expression of oncogenic transcription factors ETV1/4/5 and drive these sarcomas. We show high levels of JAK1/STAT1/3 activation in patient-derived CRS cell lines (NCC-SCC-89/C) as compared to other sarcoma cell lines without the fusion. JAK1 inhibition using Solicitinib and Ruxolitinib reduced phosphorylation of STAT1/3 as well as protein and mRNA expression of ETV1/4/5, promoter activity of ETV5, cell proliferation and tumorgenicity. Interestingly DUX4 is involved in histone acetylation and STAT1 has been shown to activate p300/CBP complex which lead us to evaluating the role of STAT1 in the gene activation CRS. We elucidate mechanistically that the fusion proteins increase binding of STAT1/3 at the promoters of ETV 1/4/5. Importantly, JAK1 inhibition effectively reduces histone acetylation induced by CIC-fusions at the promoters of ETV1/4/5. To evaluate the pre-clinical effect of targeting the JAK1/STAT1/3 pathway, A CRS cell line (NCC-SCC-89/C) were grafted into NSG mice. Ruxolitinib treatment significantly reduced tumor volume, STAT activation, and ETV1/4/5. In conclusion, we show that the JAK1/STAT1/3 pathway plays a critical role in cooperating with CIC-fusions to drive CRS, providing insight into potential therapeutic avenues for these aggressive tumors.
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