The epithelial-to-mesenchymal transition (EMT) is a reversible process comprised of various subprograms via which epithelial cells reduce their intercellular adhesions and proliferative capacity while gaining a mesenchymal phenotype with increased migratory and invasive properties. This process has been well described in several carcinomas, which are cancers of epithelial origin, and is crucial to metastatic tumor cell dissemination and drug resistance. In contrast, the precise role of EMT-related processes in tumors originating from mesenchymal tissues, such as bone and soft-tissues sarcomas, is still largely unclear. In fact, although the existence of the EMT in sarcomas appears paradoxical because these cancers are, by definition, mesenchymal , accumulating evidence suggests that many sarcomas can undergo EMT-related processes, which may be associated with aggressive clinical behavior. These processes may be especially operative in certain sarcoma subtypes, such as carcinosarcomas displaying a biphenotypic morphology with characteristics of both mesenchymal and epithelial tumors. In this review, we discuss findings regarding the potential existence of EMT-related processes in sarcomas and propose that sarcomas can reside in a metastable state, enabling them to become either more mesenchymal or epithelial under specific conditions, which likely has important clinical implications..

Pediatric malignancies including Ewing sarcoma (EwS) feature a paucity of somatic alterations except for pathognomonic driver-mutations that cannot explain overt variations in clinical outcome. Here, we demonstrate in EwS how cooperation of dominant oncogenes and regulatory germline variants determine tumor growth, patient survival and drug response. Binding of the oncogenic EWSR1-FLI1 fusion transcription factor to a polymorphic enhancer-like DNA element controls expression of the transcription factor MYBL2 mediating these phenotypes. Whole-genome and RNA sequencing reveals that variability at this locus is inherited via the germline and is associated with variable inter-tumoral MYBL2 expression. High MYBL2 levels sensitize EwS cells for inhibition of its upstream activating kinase CDK2 in vitro and in vivo, suggesting MYBL2 as a putative biomarker for anti-CDK2-therapy. Collectively, we establish cooperation of somatic mutations and regulatory germline variants as a major determinant of tumor progression and highlight the importance of integrating the regulatory genome in precision medicine.

Ewing sarcoma is an undifferentiated small-round-cell sarcoma. Although molecular detection of pathognomonic EWSR1-ETS fusions such as EWSR1-FLI1 enables definitive diagnosis, substantial confusion can arise if molecular diagnostics are unavailable. Diagnosis based on the conventional immunohistochemical marker CD99 is unreliable due to its abundant expression in morphological mimics.To identify novel diagnostic immunohistochemical markers for Ewing sarcoma, we performed comparative expression analyses in 768 tumors representing 21 entities including Ewing-like sarcomas, which confirmed that CIC-DUX4-, BCOR-CCNB3-, EWSR1-NFATc2-, and EWSR1-ETS-translocated sarcomas are distinct entities, and revealed that ATP1A1, BCL11B, and GLG1 constitute specific markers for Ewing sarcoma. Their high expression was validated by immunohistochemistry and proved to depend on EWSR1-FLI1-binding to highly active proximal super-enhancers. Automated cut-off-finding and combination-testing in a tissue-microarray comprising 174 samples demonstrated that detection of high BCL11B and/or GLG1 expression is sufficient to reach 96% specificity for Ewing sarcoma. While 88% of tested Ewing-like sarcomas displayed strong CD99-immunoreactivity, none displayed combined strong BCL11B- and GLG1-immunoreactivity.Collectively, we show that ATP1A1, BCL11B, and GLG1 are EWSR1-FLI1 targets, of which BCL11B and GLG1 offer a fast, simple, and cost-efficient way to diagnose Ewing sarcoma by immunohistochemistry. These markers may significantly reduce the number of misdiagnosed patients, and thus improve patient care.

Ewing sarcoma (EwS) is an aggressive childhood cancer likely originating from mesenchymal stem cells or osteo-chondrogenic progenitors. It is characterized by fusion oncoproteins involving EWSR1 and variable members of the ETS-family of transcription factors (in 85% FLI1). EWSR1-FLI1 can induce target genes by using GGAA-microsatellites as enhancers. Here, we show that EWSR1-FLI1 hijacks the developmental transcription factor SOX6a physiological driver of proliferation of osteo-chondrogenic progenitorsby binding to an intronic GGAA-microsatellite, which promotes EwS growth in vitro and in vivo. Through integration of transcriptome-profiling, published drug-screening data, and functional in vitro and in vivo experiments including 3D and PDX models, we discover that constitutively high SOX6 expression promotes elevated levels of oxidative stress that create a therapeutic vulnerability toward the oxidative stress-inducing drug Elesclomol. Collectively, our results exemplify how aberrant activation of a developmental transcription factor by a dominant oncogene can promote malignancy, but provide opportunities for targeted therapy.

Pancreatic ductal adenocarcinoma (PDAC) has a low overall survival rate, which is approximately 20% during the first year and decreases to less than 6% within five years of the disease. This is due to premature dissemination accompanied by a lack of disease-specific symptoms during the initial stages. Additionally, to date there are no biomarkers for an early prognosis available.A growing number of studies indicate that epithelial to mesenchymal transition (EMT), triggered by WNT-, TGF-β- and other signaling pathways is crucial for the initiation of the metastatic process in PDAC. Here we show, that BCL9L is up-regulated in PDAC cell lines and patient tissue compared to non-cancer controls. RNAi-induced BCL9L knockdown negatively affected proliferation, migration and invasion of pancreatic cancer cells. On a molecular basis, BCL9L depletion provoked an increment of E-cadherin protein levels, with concomitant increase of β-catenin retention at the plasma membrane. This is linked to the induction of a strong epithelial phenotype in pancreatic cancer cells upon BCL9L knockdown even in the presence of the EMT-inducer TGF-β. Finally, xenograft mouse models of pancreatic cancer revealed a highly significant reduction in the number of liver metastases upon BCL9L knockdown. Taken together, our findings underline the key importance of BCL9L for EMT and thus progression and metastasis of pancreatic cancer cells. Direct targeting of this protein might be a valuable approach to effectively antagonize invasion and metastasis of PDAC.