GDF6-CD99 Signaling Regulates Src and Ewing Sarcoma Growth

Roles of USP1 in Ewing sarcoma

Ewing sarcoma is a cancer of bone and soft tissue in children and young adults that is driven by the EWS-ETS fusion transcription factor, most commonly EWS-FLI1. We previously reported that Ewing sarcoma harbors two populations of cells, the CD133high population displaying higher growth rate and the CD133low population displaying chemotherapy resistance. We now find that the ubiquitin-specific protease 1 (USP1) is a transcriptional target of the EWS-FLI1 fusion oncoprotein, expressed at high and low levels in the CD133high and the CD133low populations, respectively, and determines chemo-sensitivity. We also find that USP1 inhibits cdc42, increases EWS-FLI1 transcriptional output, and simulates Ewing sarcoma growth. We show that chemo-sensitization by USP1 is independent of cdc42. A pharmacological inhibitor of USP1 was able to activate cdc42 and inhibit Ewing sarcoma growth. These results uncover critical roles for USP1 in Ewing sarcoma, which regulates growth and chemo-sensitivity via distinct mechanisms.

Nanotoxicity of tungsten trioxide nanosheets containing oxygen vacancy to human umbilical vein endothelial cells

Because of the excellent performance in photochemistry, WO3 is increasingly applied in the field of biology and medicine. However, little is known about the mechanism of WO3 cytotoxicity. In this work, WO3 nanosheets with oxygen vacancy are synthesized by solvothermal method, then characterized and added to culture medium of human umbilical vein endothelial cells (HUVECs) with different concentrations. We characterized and analyzed the morphology of nano-WO3 by transmission electron microscopy and calculated the specific data of oxygen vacancy by XPS. It is the first time the effect of WO3-x on cells that WO3-x can cause oxidative stress in HUVEC cells, resulting in DNA damage and thus promoting apoptosis. Transcriptome sequencing is performed on cells treated with low and high concentrations of WO3-x, and a series of key signals affecting cell proliferation and apoptosis are detected in differentially expressed genes, which indicates the research direction of nanotoxicity. The expression levels of key genes are also verified by quantitative PCR after cell treatment with different concentrations of WO3-x. This work fills the gap between the biocompatibility of nano WO3-x materials and molecular cytology and paves the way for investigating the mechanism and risks of oxygen vacancy in cancer therapy.

CD99 Modulates the Proteomic Landscape of Ewing Sarcoma Cells and Related Extracellular Vesicles

Ewing sarcoma (EWS) is an aggressive pediatric bone tumor characterized by unmet clinical needs and an incompletely understood epigenetic heterogeneity. Here, we considered CD99, a major surface molecule hallmark of EWS malignancy. Fluctuations in CD99 expression strongly impair cell dissemination, differentiation, and death. CD99 is also loaded within extracellular vesicles (EVs), and the delivery of CD99-positive or CD99-negative EVs dynamically exerts oncogenic or oncosuppressive functions to recipient cells, respectively. We undertook mass spectrometry and functional annotation analysis to investigate the consequences of CD99 silencing on the proteomic landscape of EWS cells and related EVs. Our data demonstrate that (i) the decrease in CD99 leads to major changes in the proteomic profile of EWS cells and EVs; (ii) intracellular and extracellular compartments display two distinct signatures of differentially expressed proteins; (iii) proteomic changes converge to the modulation of cell migration and immune-modulation biological processes; and (iv) CD99-silenced cells and related EVs are characterized by a migration-suppressive, pro-immunostimulatory proteomic profile. Overall, our data provide a novel source of CD99-associated protein biomarkers to be considered for further validation as mediators of EWS malignancy and as EWS disease liquid biopsy markers.

Hypoxia and HIFs in Ewing sarcoma: new perspectives on a multi-facetted relationship

Hypoxia develops during the growth of solid tumors and influences tumoral activity in multiple ways. Low oxygen tension is also present in the bone microenvironment where Ewing sarcoma (EwS) - a highly aggressive pediatric cancer - mainly arises. Hypoxia inducible factor 1 subunit alpha (HIF-1-a) is the principal molecular mediator of the hypoxic response in cancer whereas EWSR1::FLI1 constitutes the oncogenic driver of EwS. Interaction of the two proteins has been shown in EwS. Although a growing body of studies investigated hypoxia and HIFs in EwS, their precise role for EwS pathophysiology is not clarified to date. This review summarizes and structures recent findings demonstrating that hypoxia and HIFs play a role in EwS at multiple levels. We propose to view hypoxia and HIFs as independent protagonists in the story of EwS and give a perspective on their potential clinical relevance as prognostic markers and therapeutic targets in EwS treatment.

Nitric oxide suppression by secreted frizzled-related protein 2 drives retinoblastoma

Retinoblastoma is a cancer of the infant retina primarily driven by loss of the Rb tumor suppressor gene, which is undruggable. Here, we report an autocrine signaling, mediated by secreted frizzled-related protein 2 (SFRP2), which suppresses nitric oxide and enables retinoblastoma growth. We show that coxsackievirus and adenovirus receptor (CXADR) is the cell-surface receptor for SFRP2 in retinoblastoma cells; that CXADR functions as a "dependence receptor," transmitting a growth-inhibitory signal in the absence of SFRP2; and that the balance between SFRP2 and CXADR determines nitric oxide production. Accordingly, high SFRP2 RNA expression correlates with high-risk histopathologic features in retinoblastoma. Targeting SFRP2 signaling by SFRP2-binding peptides or by a pharmacological inhibitor rapidly induces nitric oxide and profoundly inhibits retinoblastoma growth in orthotopic xenograft models. These results reveal a cytokine signaling pathway that regulates nitric oxide production and retinoblastoma cell proliferation and is amenable to therapeutic intervention.

Defective Joint Development and Maintenance in GDF6-Related Multiple Synostoses Syndrome

Multiple synostoses syndromes (SYNS) are a group of rare genetic bone disorders characterized by multiple joint fusions. We previously reported an SYNS4-causing GDF6 c.1330 T > A (p.Tyr444Asn) mutation, which reduced Noggin-induced GDF6 inhibition and enhanced SMAD1/5/8 signaling. However, the mechanisms by which GDF6 gain-of-function mutation alters joint formation and the comprehensive molecular portraits of SYNS4 remain unclear. Herein, we introduce the p.Tyr443Asn (orthologous to the human GDF6 p.Tyr444Asn) mutation into the mouse Gdf6 locus and report the results of extensive phenotype analysis, joint development investigation, and transcriptome profiling of Gdf6 p.Tyr443Asn limb buds. Gdf6 p.Tyr443Asn knock-in mice recapitulated the morphological features of human SYNS4, showing joint fusion in the wrists, ankles, phalanges, and auditory ossicles. Analysis of mouse embryonic forelimbs demonstrated joint interzone formation defects and excess chondrogenesis in Gdf6 p.Tyr443Asn knock-in mice. Further, RNA sequencing of forelimb buds revealed enhanced bone formation and upregulated bone morphogenetic protein (BMP) signaling in mice carrying the Gdf6 p.Tyr443Asn mutation. Because tightly regulated BMP signaling is critical for skeletal development and joint morphogenesis, our study shows that enhancing GDF6 activity has a significant impact on both prenatal joint development and postnatal joint maintenance. © 2023 American Society for Bone and Mineral Research (ASBMR).

Novel Targeted Therapeutic Strategies for Ewing Sarcoma

Simple Summary

Ewing sarcoma is an uncommon cancer that arises in mesenchymal tissues and represents the second most widespread malignant bone neoplasm after osteosarcoma in children. Therapy has increased the 5-year survival rate in the last 40 years, although the recurrence rate has remained high. There is an immediate and unmet need for the development of novel Ewing sarcoma therapies. We offer new prospective targets for the therapy of Ewing sarcoma. The EWSR1/FLI1 fusion protein, which is identified in 85–90% of Ewing sarcoma tumors, and its direct targets are given special focus in this study. Experimantal therapy that targets multiple signaling pathways activated during ES progression, alone or in combination with existing regimens, may become the new standard of care for Ewing sarcoma patients, improving patient survival.

Abstract

Ewing sarcoma (ES) is an uncommon cancer that arises in mesenchymal tissues and represents the second most widespread malignant bone neoplasm after osteosarcoma in children. Amplifications in genomic, proteomic, and metabolism are characteristics of sarcoma, and targeting altered cancer cell molecular processes has been proposed as the latest promising strategy to fight cancer. Recent technological advancements have elucidated some of the underlying oncogenic characteristics of Ewing sarcoma. Offering new insights into the physiological basis for this phenomenon, our current review examines the dynamics of ES signaling as it related to both ES and the microenvironment by integrating genomic and proteomic analyses. An extensive survey of the literature was performed to compile the findings. We have also highlighted recent and ongoing studies integrating metabolomics and genomics aimed at better understanding the complex interactions as to how ES adapts to changing biochemical changes within the tumor microenvironment.

EZH2 suppresses endogenous retroviruses and an interferon response in cancers

Ewing sarcoma is an aggressive cancer of bone and soft tissue in children. It is characterized by the chromosomal translocation between EWS and an Ets family transcription factor, most commonly FLI1. We recently reported that Ewing sarcoma depends on the autocrine signaling mediated by a cytokine, NELL2. NELL2 signaling stimulates the transcriptional output of EWS-FLI1 through the BAF chromatin remodeling complexes. While studying the impact of NELL2 silencing on Ewing sarcoma, we found that suppression of NELL2 signaling induces the expression of endogenous retroviruses (ERVs) and LINE-1 retrotransposons, an interferon response, and growth arrest. We determined that a histone methyltransferase, EZH2, is the critical downstream target of NELL2 signaling in suppressing ERVs, LINE-1, an interferon response, and growth arrest. We show that EZH2 inhibitors induce ERVs, LINE-1, and an interferon response in a variety of cancer types. These results uncover the role for NELL2–EZH2 signaling in suppressing endogenous virus-like agents and an antiviral response, and suggest the potential utility of EZH2 inhibitors in enhancing anti-tumor immunity.

NELL2-cdc42 signaling regulates BAF complexes and Ewing sarcoma cell growth

BAF chromatin remodeling complexes play important roles in chromatin regulation and cancer. Here, we report that Ewing sarcoma cells are dependent on the autocrine signaling mediated by NELL2, a secreted glycoprotein that has been characterized as an axon guidance molecule. NELL2 uses Robo3 as the receptor to transmit critical growth signaling. NELL2 signaling inhibits cdc42 and upregulates BAF complexes and EWS-FLI1 transcriptional output. We demonstrate that cdc42 is a negative regulator of BAF complexes, inducing actin polymerization and complex disassembly. Furthermore, we identify NELL2highCD133highEWS-FLI1high and NELL2lowCD133lowEWS-FLI1low populations in Ewing sarcoma, which display phenotypes consistent with high and low NELL2 signaling, respectively. We show that NELL2, CD133, and EWS-FLI1 positively regulate each other and upregulate BAF complexes and cell proliferation in Ewing sarcoma. These results reveal a signaling pathway regulating critical chromatin remodeling complexes and cancer cell proliferation.

Clofarabine induces ERK/MSK/CREB activation through inhibiting CD99 on Ewing sarcoma cells

Clofarabine, an FDA approved purine analog, is used in the treatment of relapsed or refractory acute lymphoblastic leukemia. Clofarabine acts by inhibiting DNA synthesis. We demonstrated that clofarabine may have a novel function though inhibiting CD99, a transmembrane protein highly expressed on Ewing Sarcoma (ES) cells. CD99 is a validated target in ES whose inhibition may lead to a high therapeutic index for patients. Here we present additional data to support the hypothesis that clofarabine acts on CD99 and regulates key signaling pathways in ES. Cellular thermal shift assay indicated a direct interaction between clofarabine and CD99 in ES cell lysates. Clofarabine induced ES cell death does not require clofarabine's conversion to its active form by deoxycytidine kinase. A phosphokinase array screen with clofarabine and a CD99 blocking antibody identified alterations in signaling pathways. CD99 inhibition with clofarabine in ES cells caused rapid and sustained phosphorylation of ERK, MSK, and CREB. However, activation of this pathway did not correlate with clofarabine induced ES cell death. In summary, we demonstrated that clofarabine may activate ERK, MSK, and CREB phosphorylation through CD99 within minutes, however this paradoxical activation and subsequent ES cell death requires additional investigation.