Biphenotypic sinonasal sarcoma (SNS) is a newly described tumor of the nasal and paranasal areas. Herein, we report the novel recurring chromosomal translocation t(2;4)(q35;q31.1) in SNS. The translocation results in the formation of the fusion protein PAX3-MAML3, which is a potent transcriptional activator of PAX3 response elements. The SNS phenotype is characterized by aberrant expression of genes involved in neuroectodermal and myogenic differentiation, which closely simulates the developmental roles of PAX3.

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Ewing sarcoma is an aggressive pediatric small round cell tumor that predominantly occurs in bone. Approximately 85% of Ewing sarcomas harbor the EWS/FLI fusion protein, which arises from a chromosomal translocation, t(11:22)(q24:q12). EWS/FLI interacts with numerous lineage-essential transcription factors to maintain mesenchymal progenitors in an undifferentiated state. We previously showed that EWS/FLI binds the osteogenic transcription factor RUNX2 and prevents osteoblast differentiation. In this study, we investigated the role of another Runt-domain protein, RUNX3, in Ewing sarcoma. RUNX3 participates in mesenchymal-derived bone formation and is a context dependent tumor suppressor and oncogene. RUNX3 was detected in all Ewing sarcoma cells examined, whereas RUNX2 was detected in only 73% of specimens. Like RUNX2, RUNX3 binds to EWS/FLI via its Runt domain. EWS/FLI prevented RUNX3 from activating the transcription of a RUNX-responsive reporter, p6OSE2. Stable suppression of RUNX3 expression in the Ewing sarcoma cell line A673 delayed colony growth in anchorage independent soft agar assays and reversed expression of EWS/FLI-responsive genes. These results demonstrate an important role for RUNX3 in Ewing sarcoma.

Basic molecular mechanisms take on new meaning in the context of diseases like cancer. In this cancer special issue, we want to highlight and celebrate the basic discoveries that have paved the way for the incredible progress that has been made in diagnosing and treating patients with cancer. We assume that most of our readers tend to focus on basic science, and for these readers, we hope to provide some context for the molecular mechanisms involved in the rapidly evolving cancer research field. That said, many scientists in our community are also focused on treating patients with cancer more directly, and for these readers, we aim to connect the disease biology back to the underlying mechanisms.More basic studies can inform the selection of therapeutic targets, support drug design, explain the acquisition of drug resistance, and suggest rational combination therapies (reviewed in Boshuizen et al., 1002Boshuizen et al., -1018, all ultimately improving the lives of patients with cancer, sometimes in unexpected and fortuitous ways. These basic discoveries provide the foundation upon which progress in translational and clinical research depends.Recent years have brought rapid progress in cancer research, from the sequencing of tumor genomes to the development of targeted therapies and immunotherapies. We now understand a variety of genetic and epigenetic mechanisms that drive tumorigenesis, and this knowledge has spurred breakthroughs in cancer research. Decades of basic research dedicated to understanding the function of KRAS (and oncogenes more broadly) culminated in the recent development of the first KRAS G12C inhibitors. Similarly, discoveries aimed at understanding DNA repair yielded information that led to the development of PARP inhibitors and other strategies to target the DNA damage response in cancer (reviewed in Cleary et al., 1070Cleary et al., -1085.Of course, this process works in reverse as well, as molecular biologists seek to understand the underlying biology to explain the successes and failures observed in the clinic, going back to the bench to unravel resistance mechanisms, improve therapeutic selection, and optimize drug design. In addition, drugs can make their way back to the lab as molecular tools. A notable example is the multiple myeloma drug thalidomide, also infamous for causing birth defects. The finding that thalidomide binds to and inhibits cereblon, a component of an E3 ubiquitin ligase complex, enabled development of PROTACs for targeted protein degradation.Another example of this cycle between basic and clinical work is how our understanding of transcription regulation has driven our ability to exploit this process to target cancer cells. Epigenomic dependencies in cancer have led to the development of a variety of promising compounds with therapeutic potential (reviewed in Wimalasena et al., 1086Wimalasena et al., -1095. These include inhibitors of the bromodomain and extraterminal domain-containing (BET) proteins, which have also found their way back to basic labs studying gen...

Bone and soft tissue tumors (BSTT) are a group of neoplasms most commonly found in children. The TRE17/ ubiquitin‐specific protease 6 (USP6) oncogene is intimately involved in several BSTTs, including alveolar rhabdomyosarcoma (ARMS). The molecular functions of TRE17 in ARMS pathogenesis are unknown. However, recent unpublished data from our lab has identified the Jak1‐STAT1/3 pathway as a key effector of TRE17.Type I Interferon (IFN) has been used previously to treat sarcomas. IFN functions through Jak1/STAT1. Interestingly, we found that TRE17 renders ARMS hypersensitive to IFN‐induced apoptosis in vitro. TRE17‐expressing ARMS, but not control ARMS, underwent apoptosis after 24h of IFN treatment. In addition to inducing apoptosis, IFN also resulted in the degradation of TRE17. The exact mechanisms behind the sensitization and subsequent downregulation of TRE17 in ARMS remain to be uncovered. The degradation of TRE17 appears to require its ubiquitin‐specific protease activity. Currently, work is being done to find the mechanism of TRE17 degradation upon exposure to IFN; preliminary data suggest that the proteosomal pathway is responsible. These studies may identify methods to sustain or induce TRE17 expression, which would render ARMS susceptible to killing by IFN, and ultimately allow exploration of IFN as a therapeutic agent for ARMS treatment.

Ewing sarcoma is the second most common bone cancer in children, with an estimated 5-year survival rate of 20% for metastatic cases. These tumors harbor the characteristic chromosomal translocation t(11;22)(q24;q12), which leads to expression of the oncogenic chimeric transcription factor, EWS-FLI1. EWS-FLI1 drives Ewing sarcoma tumorigenesis, and is an attractive therapeutic target because it is expressed exclusively in tumor cells. However, directly targeting EWS-FLI1 has proved difficult. Thus, despite advances in our understanding of EWS-FLI1 function, treatment options remain limited, and to date, no targeted therapeutics have been developed. In this study, we investigated the effects of the epigenetic modifier drug, JQ1, on Ewing sarcoma pathogenesis. JQ1 is a small molecule inhibitor of the BET family of bromodomain proteins, which bind to acetylated histones and transcription factors to regulate gene expression. JQ1 selectively inhibits these acetylation-dependent BET protein interactions. Recent studies reveal that JQ1 has potent anti-neoplastic activity against multiple cancers, with c-MYC downregulation being a key mechanism by which it induces cell death in several tumor types. Because Ewing sarcoma cells express high levels of c-MYC, we predicted that they would be sensitive to the cytotoxic effects of JQ1. Our results demonstrate that JQ1 indeed inhibits growth of Ewing sarcoma cells, but unexpectedly, it does not function through inhibition of c-MYC. Using multiple patient-derived Ewing sarcoma cell lines, we find that JQ1 induces apoptosis as measured by PARP cleavage. Preliminary data further indicate that JQ1 suppresses growth of Ewing sarcoma xenografts in vivo. Mechanistic studies and microarray analysis reveal that JQ1 inhibits EWS-FLI1 activity, with multiple targets of the oncogene being rapidly downregulated upon JQ1 treatment. Studies are currently underway to identify the specific BET family members required for EWS-FLI1 function, and to determine the mechanism by which they regulate EWS-FLI1 activity. Given the emergence of numerous JQ1-derivative compounds targeting specific BET proteins, it is hopeful that this class of compounds may ultimately be used as targeted therapies for the treatment of Ewing sarcoma. Citation Format: Krista L. Bledsoe, Aaron Stonestrom, Stephan Kadauke, Laura Quick, Robert Young, Gerd A. Blobel, Margaret M. Chou. BET protein inhibition by JQ1 blocks EWS-FLI1 activity in Ewing sarcoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 486. doi:10.1158/1538-7445.AM2015-486

Ewing sarcomas are aggressive, poorly differentiated pediatric tumors of bone and soft tissue. Ewing sarcoma affects one to three people per million every year and is the second most common pediatric bone malignancy after osteosarcoma. Approximately 85% of Ewing sarcomas harbor the EWS-FLI fusion protein, which arises from a chromosomal translocation, t(11:22)(q24:q12). EWS-FLI interacts with numerous lineage-essential transcription factors to maintain mesenchymal progenitors in an undifferentiated state. We previously showed that EWS-FLI binds the osteogenic transcription factor RUNX2, and prevents osteoblast differentiation. RUNX3 is highly homologous to RUNX2 and participates in the mesenchymal-derived bone formation. RUNX3 has been described as both a tumor suppressor and an oncogene in different tumor types. In this study, we investigated the role of RUNX3 in Ewing Sarcoma. RUNX3 was detected in all Ewing sarcoma cells examined (7/7 cell lines, and 4/4 primary tumors), whereas RUNX2 was detected in only 73% of these specimens. Immunoprecipitation experiments revealed that RUNX3 binds to EWS-FLI via its Runt domain, which is >91% identical to the Runt domain in RUNX2. The interaction between RUNX3 and EWS-FLI in cell nuclei was confirmed by immunofluorescence. Moreover, EWS-FLI interactions prevented RUNX3 from activating the transcription of a RUNX-responsive reporter, p6OSE2. To determine the role of RUNX3 in Ewing sarcoma cell growth, we stably suppressed RUNX3 expression in the Ewing sarcoma cell line A673 with shRNAs. In anchorage independent growth assays in soft agar, RUNX3-deficient A673 cells formed smaller colonies than cells expressing scrambled shRNAs. Consistent with the smaller colonies, RUNX3 suppressed cells had increased expression of the cyclin dependent kinase inhibitor p21. Taken together, these results suggest and oncogenic role for RUNX3 in Ewing sarcoma. Citation Format: Krista L. Bledsoe, Meghan E. McGee-Lawrence, Emily T. Camilleri, Andre M. Oliveira, Andre J. van Wijnen, Jennifer J. Westendorf. RUNX3 plays an oncogenic role in Ewing sarcoma cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1413. doi:10.1158/1538-7445.AM2014-1413