Dysregulated heparan sulfate proteoglycan metabolism promotes Ewing sarcoma tumor growth

Human EWS-FLI protein levels and neomorphic functions show a complex, function-specific dose-response relationship in Drosophila

Ewing sarcoma (EwS) is a cancer that arises in the bones and soft tissues, typically driven by the Ewing's sarcoma breakpoint region 1-Friend leukemia virus integration 1 (EWS-FLI) oncogene. Implementation of genetically modified animal models of EwS has proved difficult largely owing to EWS-FLI's high toxicity. The EWS-FLI1FS frameshift variant that circumvents toxicity but is still able to perform key oncogenic functions provided the first study model in Drosophila. However, the quest for Drosophila lines expressing full-length, unmodified EWS-FLI remained open. Here, we show that EWS-FLI1FS's lower toxicity is owed to reduced protein levels caused by its frameshifted C-terminal peptide, and report new strategies through which we have generated Drosophila lines that express full-length, unmodified EWS-FLI. Using these lines, we have found that the upregulation of transcription from GGAA-microsatellites (GGAAμSats) presents a positive linear correlation within a wide range of EWS-FLI protein concentrations. In contrast, rather counterintuitively, GGAAμSats-independent transcriptomic dysregulation presents relatively minor differences across the same range, suggesting that GGAAμSat-dependent and -independent transcriptional upregulation present different kinetics of response with regards to changing EWS-FLI protein concentration. Our results underpin the functional relevance of varying EWS-FLI expression levels and provide experimental tools to investigate, in Drosophila, the effect of the EWS-FLI 'high' and 'low' states that have been reported and are suspected to be important for EwS in humans.

Immunocompetent murine model of Ewing sarcoma reveals role for TGFβ inhibition to enhance immune infiltrates in Ewing tumors during radiation

Ewing sarcoma (ES) is an aggressive cancer diagnosed in adolescents and young adults. The fusion oncoprotein (EWSR1::FLI1) that drives Ewing sarcoma is known to downregulate TGFBR2 expression (part of the TGFβ receptor). Because TGFBR2 is downregulated, it was thought that TGFβ likely plays an inconsequential role in Ewing biology. However, the expression of TGFβ in the Ewing tumor immune microenvironment (TIME) and functional impact of TGFβ in the TIME remains largely unknown given the historical lack of immunocompetent preclinical models. Here, we use single-cell RNAseq analysis of human Ewing tumors to show that immune cells, such as NK cells, are the largest source of TGFβ production in human Ewing tumors. We develop a humanized (immunocompetent) mouse model of ES and demonstrate distinct TME signatures and metastatic potential in these models as compared to tumors developed in immunodeficient mice. Using this humanized model, we study the effect of TGFβ inhibition on the Ewing TME during radiation therapy, a treatment that both enhances TGFβ activation and is used to treat aggressive ES. Utilizing a trivalent ligand TGFβ TRAP to inhibit TGFβ, we demonstrate that in combination with radiation, TGFβ inhibition both increases ES immune cell infiltration and decreases lung metastatic burden in vivo . The culmination of these data demonstrates the value of humanized models to address immunobiologic preclinical questions in Ewing sarcoma and suggests TGFβ inhibition as a promising intervention during radiation therapy to promote metastatic tumor control.

Trabectedin Enhances Oncolytic Virotherapy by Reducing Barriers to Virus Spread and Cytotoxic Immunity in Preclinical Pediatric Bone Sarcoma

We previously reported that the DNA alkylator and transcriptional-blocking chemotherapeutic agent trabectedin enhances oncolytic herpes simplex viroimmunotherapy in human sarcoma xenograft models, though the mechanism remained to be elucidated. Here we report trabectedin disrupts the intrinsic cellular anti-viral response which increases viral transcript spread throughout the human tumor cells. We also extended our synergy findings to syngeneic murine sarcoma models, which are poorly susceptible to virus infection. In the absence of robust virus replication, we found trabectedin enhanced viroimmunotherapy efficacy by reducing immunosuppressive macrophages and stimulating granzyme expression in infiltrating T and NK cells to cause immune-mediated tumor regressions. Thus, trabectedin enhances both the direct virus-mediated killing of tumor cells and the viral-induced activation of cytotoxic effector lymphocytes to cause tumor regressions across models. Our data provide a strong rationale for clinical translation as both mechanisms should be simultaneously active in human patients.

Therapeutic Hope on the Surface of Ewing Sarcoma

A detailed analysis of the Ewing sarcoma surfacesome has arrived. Robust expression of surface CDH11 and ENPP1 was identified. This "comprehensive catalog" of the Ewing surfacesome serves as a fresh roadmap to development of new therapeutic approaches, including immunotherapies and multi-modality therapeutic combinations, to target aggressive Ewing tumor subpopulations. See related article by Mooney et al., p. 1022.

Seed Becoming Soil: A New Paradigm of the Ewing Sarcoma Tumor Microenvironment

Cells in the tumor microenvironment, including cancer-associated fibroblasts (CAF), contribute to tumor growth and immune evasion. A recent study of Ewing sarcoma identified "CAF-like" tumor cells that mimic the protumorigenic features of CAFs. These findings highlight the role of cell plasticity in tumor growth. See related article by Wrenn et al., p. 5140.

Carbonic Anhydrase Inhibitors Induce Ferroptosis through Inhibition of AKT/FTH1 Signaling in Ewing Sarcoma Tumor Cells

Ewing sarcoma (ES) is one of the most frequent types of malignant tumors among children. The active metabolic state of ES cells presents a new potential target for therapeutic interventions. As a primary regulator of cellular homeostasis, carbonic anhydrases (CAs; EC 4.2.1.1) have emerged as promising molecular targets for the development of anticancer drugs. Within the present study, we tested the commercial drug acetazolamide and our previously discovered inhibitors to target the CAII isoform, which was overexpressed and positively correlated with ES patient relapse. We employed molecular biology tests to identify effective inhibitors of CAII that can induce ferroptosis by downregulating FTH1 expression in ES cells. In vitro, we have also demonstrated their ability to reduce cell proliferation, decrease invasion, and induce apoptosis- or autophagy-related cell death. Using Western blotting, we confirmed the induction of cathepsin B in cells treated with CA inhibitors. It was found that the suppression of cathepsin B expression during the treatment reduces the anticancer efficacy of selected CAII inhibitors. These experiments highlighted profound antitumor activity of CAII inhibitors attributive to their remarkable ability to trigger ferroptosis in Ewing sarcoma cells without causing substantial host damage. The obtained results suggest that cytosolic CAII may be a prospective target for ES treatment, and CAII inhibitors can be considered as potential single-agent or combination antitumor agents to be used in the treatment of ES.

TATA-box-binding protein-associated factor 15 is a novel biomarker that promotes cell proliferation and migration in gastrointestinal stromal tumor

BACKGROUND

Gastrointestinal stromal tumor (GIST) is a common neoplasm with high rates of recurrence and metastasis, and its therapeutic efficacy is still not ideal. There is an unmet need to find new molecular therapeutic targets for GIST. TATA-box-binding protein-associated factor 15 (TAF15) contributes to the progress of various tumors, while the role and molecular mechanism of TAF15 in GIST progression are still unknown.

AIM

To explore new molecular therapeutic targets for GIST and understand the biological role and underlying mechanisms of TAF15 in GIST progression.

METHODS

Proteomic analysis was performed to explore the differentially expressed proteins in GIST. Western blotting and immunohistochemical analysis were used to verify the expression level of TAF15 in GIST tissues and cell lines. Cell counting kit-8, colony formation, wound-healing and transwell assay were executed to detect the ability of TAF15 on cell proliferation, migration and invasion. A xenograft mouse model was applied to explore the role of TAF15 in the progression of GIST. Western blotting was used to detect the phosphorylation level and total level of RAF1, MEK and ERK1/2.

RESULTS

A total of 1669 proteins were identified as differentially expressed proteins with 762 upregulated and 907 downregulated in GIST. TAF15 was selected for the further study because of its important role in cell proliferation and migration. TAF15 was significantly over expressed in GIST tissues and cell lines. Overexpression of TAF15 was associated with larger tumor size and higher risk stage of GIST. TAF15 knockdown significantly inhibited the cell proliferation and migration of GIST in vitro and suppressed tumor growth in vivo. Moreover, the inhibition of TAF15 expression significantly decreased the phosphorylation level of RAF1, MEK and ERK1/2 in GIST cells and xenograft tissues, while the total RAF1, MEK and ERK1/2 had no significant change.

CONCLUSION

TAF15 is over expressed in GIST tissues and cell lines. Overexpression of TAF15 was associated with a poor prognosis of GIST patients. TAF15 promotes cell proliferation and migration in GIST via the activation of the RAF1/MEK/ERK signaling pathway. Thus, TAF15 is expected to be a novel latent molecular biomarker or therapeutic target of GIST.

TAF15 promotes cell proliferation, migration and invasion of gastric cancer via activation of the RAF1/MEK/ERK signalling pathway

TATA-box-binding protein-associated Factor 15 (TAF15), a member of the FUS/EWS/TAF15 (FET) family, contributes to the progression of various tumours. However, the role and molecular mechanism of TAF15 in gastric cancer (GC) progression are still unknown. In this study, we found that TAF15 was significantly upregulated in GC tumour tissues and cell lines. Overexpression of TAF15 was associated with a larger tumour size, high pathologic stage and high T stage of GC. TAF15 knockdown suppressed the proliferation, migration and invasion of GC cells in vitro and inhibited the tumour growth in vivo. Additionally, TAF15 knockdown led to the significant reductions in the phosphorylation levels of RAF1, MEK and ERK1/2, while total RAF1, MEK and ERK1/2 exhibited no significant change in GC cell lines. In summary, TAF15 is overexpressed in GC tumour tissues and cell lines, and promotes cell proliferation, migration and invasion in GC via the RAF1/MEK/ERK signaling pathway, which suggests that TAF15 might be a potential molecular diagnostic marker or therapeutic target for GC.

Fli1 and Tissue Fibrosis in Various Diseases

Being initially described as a factor of virally-induced leukemias, Fli1 (Friend leukemia integration 1) has attracted considerable interest lately due to its role in both healthy physiology and a variety of pathological conditions. Over the past few years, Fli1 has been found to be one of the crucial regulators of normal hematopoiesis, vasculogenesis, and immune response. However, abnormal expression of Fli1 due to genetic predisposition, epigenetic reprogramming (modifications), or environmental factors is associated with a few diseases of different etiology. Fli1 hyperexpression leads to malignant transformation of cells and progression of cancers such as Ewing's sarcoma. Deficiency in Fli1 is implicated in the development of systemic sclerosis and hypertensive disorders, which are often accompanied by pronounced fibrosis in different organs. This review summarizes the initial findings and the most recent advances in defining the role of Fli1 in diseases of different origin with emphasis on its pro-fibrotic potential.

Regulation of EWSR1-FLI1 Function by Post-Transcriptional and Post-Translational Modifications

Ewing sarcoma is the second most common bone tumor in childhood and adolescence. Currently, first-line therapy includes multidrug chemotherapy with surgery and/or radiation. Although most patients initially respond to chemotherapy, recurrent tumors become treatment refractory. Pathologically, Ewing sarcoma consists of small round basophilic cells with prominent nuclei marked by expression of surface protein CD99. Genetically, Ewing sarcoma is driven by a fusion oncoprotein that results from one of a small number of chromosomal translocations composed of a FET gene and a gene encoding an ETS family transcription factor, with ~85% of tumors expressing the EWSR1::FLI1 fusion. EWSR1::FLI1 regulates transcription, splicing, genome instability and other cellular functions. Although a tumor-specific target, EWSR1::FLI1-targeted therapy has yet to be developed, largely due to insufficient understanding of EWSR1::FLI1 upstream and downstream signaling, and the challenges in targeting transcription factors with small molecules. In this review, we summarize the contemporary molecular understanding of Ewing sarcoma, and the post-transcriptional and post-translational regulatory mechanisms that control EWSR1::FLI1 function.

Heparan Sulfate Proteoglycans in Tauopathy

Tauopathies are a class of neurodegenerative diseases, including Alzheimer's disease, and are characterized by intraneuronal tau inclusion in the brain and the patient's cognitive decline with obscure pathogenesis. Heparan sulfate proteoglycans, a major type of extracellular matrix, have been believed to involve in tauopathies. The heparan sulfate proteoglycans co-deposit with tau in Alzheimer's patient brain, directly bind to tau and modulate tau secretion, internalization, and aggregation. This review summarizes the current understanding of the functions and the modulated molecular pathways of heparan sulfate proteoglycans in tauopathies, as well as the implication of dysregulated heparan sulfate proteoglycan expression in tau pathology and the potential of targeting heparan sulfate proteoglycan-tau interaction as a novel therapeutic option.

The importance of fusion protein activity in Ewing sarcoma and the cell intrinsic and extrinsic factors that regulate it: A review

Accumulating evidence shows that despite clonal origins tumors eventually become complex communities comprised of phenotypically distinct cell subpopulations. This heterogeneity arises from both tumor cell intrinsic programs and signals from spatially and temporally dynamic microenvironments. While pediatric cancers usually lack the mutational burden of adult cancers, they still exhibit high levels of cellular heterogeneity that are largely mediated by epigenetic mechanisms. Ewing sarcomas are aggressive bone and soft tissue malignancies with peak incidence in adolescence and the prognosis for patients with relapsed and metastatic disease is dismal. Ewing sarcomas are driven by a single pathognomonic fusion between a FET protein and an ETS family transcription factor, the most common of which is EWS::FLI1. Despite sharing a single driver mutation, Ewing sarcoma cells demonstrate a high degree of transcriptional heterogeneity both between and within tumors. Recent studies have identified differential fusion protein activity as a key source of this heterogeneity which leads to profoundly different cellular phenotypes. Paradoxically, increased invasive and metastatic potential is associated with lower EWS::FLI1 activity. Here, we review what is currently understood about EWS::FLI1 activity, the cell autonomous and tumor microenvironmental factors that regulate it, and the downstream consequences of these activity states on tumor progression. We specifically highlight how transcription factor regulation, signaling pathway modulation, and the extracellular matrix intersect to create a complex network of tumor cell phenotypes. We propose that elucidation of the mechanisms by which these essential elements interact will enable the development of novel therapeutic approaches that are designed to target this complexity and ultimately improve patient outcomes.

Harnessing immunomodulation during DNA damage in Ewing sarcoma

Ewing sarcoma is a fusion-oncoprotein-driven primary bone tumor most commonly diagnosed in adolescents. Given the continued poor outcomes for patients with metastatic and relapsed Ewing sarcoma, testing innovative therapeutic approaches is essential. Ewing sarcoma has been categorized as a 'BRCAness' tumor with emerging data characterizing a spectrum of DNA damage repair defects within individual Ewing tumors, including the presence of EWSR1::FLI1 itself, recurrent somatic mutations, and rare germline-based defects. It is critical to understand the cumulative impact of various DNA damage repair defects on an individual Ewing tumor's response to therapy. Further, in addition to DNA-damage-directed therapies, subsets of Ewing tumors may be more susceptible to DNA-damage/immunotherapy combinations given the significant cross-talk between DNA damage and inflammatory pathways in the tumor microenvironment. Here we review potential approaches utilizing DNA-damaging agents as modulators of the Ewing tumor immune microenvironment, with a focus on radiation and opportunities during disease metastasis and relapse.

Ewing Sarcoma and Osteosarcoma Have Distinct Immune Signatures and Intercellular Communication Networks

PURPOSE

Ewing sarcoma and osteosarcoma are primary bone sarcomas occurring most commonly in adolescents. Metastatic and relapsed disease are associated with dismal prognosis. Although effective for some soft tissue sarcomas, current immunotherapeutic approaches for the treatment of bone sarcomas have been largely ineffective, necessitating a deeper understanding of bone sarcoma immunobiology.

EXPERIMENTAL DESIGN

Multiplex immunofluorescence analysis of immune infiltration in relapsed versus primary disease was conducted. To better understand immune states and drivers of immune infiltration, especially during disease progression, we performed single-cell RNA sequencing (scRNAseq) of immune populations from paired blood and bone sarcoma tumor samples.

RESULTS

Our multiplex immunofluorescence analysis revealed increased immune infiltration in relapsed versus primary disease in both Ewing sarcoma and osteosarcoma. scRNAseq analyses revealed terminally exhausted CD8+ T cells expressing co-inhibitory receptors in osteosarcoma and an effector T-cell subpopulation in Ewing sarcoma. In addition, distinct subsets of CD14+CD16+ macrophages were present in Ewing sarcoma and osteosarcoma. To determine pathways driving tumor immune infiltration, we conducted intercellular communication analyses and uncovered shared mechanisms of immune infiltration driven by CD14+CD16+ macrophages and unique pathways of immune infiltration driven by CXCL10 and CXCL12 in osteosarcoma.

CONCLUSIONS

Our study provides preclinical rationale for future investigation of specific immunotherapeutic targets upon relapse and provides an invaluable resource of immunologic data from bone sarcomas.

In vivo 3D profiling of site-specific human cancer cell morphotypes in zebrafish

Tissue microenvironments affect the functional states of cancer cells, but determining these influences in vivo has remained a challenge. We present a quantitative high-resolution imaging assay of single cancer cells in zebrafish xenografts to probe functional adaptation to variable cell-extrinsic cues and molecular interventions. Using cell morphology as a surrogate readout of cell functional states, we examine environmental influences on the morphotype distribution of Ewing Sarcoma, a pediatric cancer associated with the oncogene EWSR1-FLI1 and whose plasticity is thought to determine disease outcome through non-genomic mechanisms. Computer vision analysis reveals systematic shifts in the distribution of 3D morphotypes as a function of cell type and seeding site, as well as tissue-specific cellular organizations that recapitulate those observed in human tumors. Reduced expression of the EWSR1-FLI1 protein product causes a shift to more protrusive cells and decreased tissue specificity of the morphotype distribution. Overall, this work establishes a framework for a statistically robust study of cancer cell plasticity in diverse tissue microenvironments.

Human EWS-FLI protein recapitulates in Drosophila the neomorphic functions that induce Ewing sarcoma tumorigenesis

Ewing sarcoma (EwS) is a human malignant tumor typically driven by the Ewing sarcoma-Friend leukemia integration (EWS-FLI) fusion protein. A paucity of genetically modified animal models, partially owed to the high toxicity of EWS-FLI, hinders research on EwS. Here, we report a spontaneous mutant variant, EWS-FLI_1FS, that circumvents the toxicity issue in Drosophila. Through proteomic and genomic analyses, we show that human EWS-FLI_1FS interacts with the Drosophila homologues of EWS-FLI human protein partners, including core subunits of chromatin remodeling complexes, the transcription machinery, and the spliceosome; brings about a massive dysregulation of transcription that affects a significant fraction of known targets of EWS-FLI in human cells; and modulates splicing. We also show that EWS-FLI_1FS performs in Drosophila the two major neomorphic activities that it is known to have in human cells: activation of transcription from GGAA microsatellites and out competition of ETS transcription factors. We conclude that EWS-FLI_1FS reproduces in Drosophila the known oncogenic activities of EWS-FLI that drive EwS tumorigenesis in humans. These results open up an unprecedented opportunity to investigate EWS-FLI's oncogenic pathways in vivo in a genetically tractable organism.