Author Correction: EWS-FLI1 increases transcription to cause R-loops and block BRCA1 repair in Ewing sarcoma.

In this Letter, the sentence beginning "This work was funded…." in the Acknowledgements should have read "CPRIT (RP140105) to J.C.R." rather than "CPRIT (RP150445) to J.C.R." This error has been corrected online.

EWS-FLI1 increases transcription to cause R-loops and block BRCA1 repair in Ewing sarcoma.

Ewing sarcoma is an aggressive paediatric cancer of the bone and soft tissue. It results from a chromosomal translocation, predominantly t(11;22)(q24:q12), that fuses the N-terminal transactivation domain of the constitutively expressed EWSR1 protein with the C-terminal DNA binding domain of the rarely expressed FLI1 protein. Ewing sarcoma is highly sensitive to genotoxic agents such as etoposide, but the underlying molecular basis of this sensitivity is unclear. Here we show that Ewing sarcoma cells display alterations in regulation of damage-induced transcription, accumulation of R-loops and increased replication stress. In addition, homologous recombination is impaired in Ewing sarcoma owing to an enriched interaction between BRCA1 and the elongating transcription machinery. Finally, we uncover a role for EWSR1 in the transcriptional response to damage, suppressing R-loops and promoting homologous recombination. Our findings improve the current understanding of EWSR1 function, elucidate the mechanistic basis of the sensitivity of Ewing sarcoma to chemotherapy (including PARP1 inhibitors) and highlight a class of BRCA-deficient-like tumours.

A qualitative study exploring personal recovery meaning and the potential influence of clinical recovery status on this meaning 20 years after a first-episode psychosis.

PURPOSE: Long-term data on recovery conceptualisation in psychotic illness are needed to support mental health services to organise themselves according to recovery-oriented frameworks. To our knowledge, no previous research has investigated how first-episode psychosis (FEP) service users (sampled across psychotic illness type) perceive recovery beyond 5 years after diagnosis. We aimed to explore personal recovery meaning with individuals 20 years after their FEP and examine the potential influence of clinical recovery status on how they defined recovery (i.e. personal recovery). METHODS: Twenty participants were purposefully sampled from an epidemiologically representative FEP incidence cohort. At 20-year follow-up, semi-structured interviews were conducted with 10 cohort members who met full 'functional recovery criteria' (Clinically Recovered Group) and 10 who did not (Not Clinically Recovered Group). A thematic analysis was performed to develop shared themes and group-specific sub-themes to capture agreement and divergence between groups. RESULTS: Five shared themes were produced: pursuing balance in conflict, generating meaning in life, experiencing a dynamic personal relationship with time, redressing inequality while managing added challenges/vulnerability, and directing life from resilience to flourishing. The five group-specific sub-themes developed illuminate differences in the meaning ascribed to personal recovery by each group. CONCLUSION: Findings emphasise the role of time in how personal recovery is conceptualised by service users and identify ways clinical recovery may influence personal recovery meaning in FEP at mid-later life. Mental health services failing to consider temporal changes in meaning-making and discounting clinical recovery risk ignoring key factors affecting personal recovery.

The Ewing Sarcoma Secretome and Its Response to Activation of Wnt/beta-catenin Signaling.

Tumor: tumor microenvironment (TME) interactions are critical for tumor progression and the composition and structure of the local extracellular matrix (ECM) are key determinants of tumor metastasis. We recently reported that activation of Wnt/beta-catenin signaling in Ewing sarcoma cells induces widespread transcriptional changes that are associated with acquisition of a metastatic tumor phenotype. Significantly, ECM protein-encoding genes were found to be enriched among Wnt/beta-catenin induced transcripts, leading us to hypothesize that activation of canonical Wnt signaling might induce changes in the Ewing sarcoma secretome. To address this hypothesis, conditioned media from Ewing sarcoma cell lines cultured in the presence or absence of Wnt3a was collected for proteomic analysis. Label-free mass spectrometry was used to identify and quantify differentially secreted proteins. We then used in silico databases to identify only proteins annotated as secreted. Comparison of the secretomes of two Ewing sarcoma cell lines revealed numerous shared proteins, as well as a degree of heterogeneity, in both basal and Wnt-stimulated conditions. Gene set enrichment analysis of secreted proteins revealed that Wnt stimulation reproducibly resulted in increased secretion of proteins involved in ECM organization, ECM receptor interactions, and collagen formation. In particular, Wnt-stimulated Ewing sarcoma cells up-regulated secretion of structural collagens, as well as matricellular proteins, such as the metastasis-associated protein, tenascin C (TNC). Interrogation of published databases confirmed reproducible correlations between Wnt/beta-catenin activation and TNC and COL1A1 expression in patient tumors. In summary, this first study of the Ewing sarcoma secretome reveals that Wnt/beta-catenin activated tumor cells upregulate secretion of ECM proteins. Such Wnt/beta-catenin mediated changes are likely to impact on tumor: TME interactions that contribute to metastatic progression.

Menin regulates the serine biosynthetic pathway in Ewing sarcoma.

Developmental transcription programs are epigenetically regulated by multi-protein complexes, including the menin- and MLL-containing trithorax (TrxG) complexes, which promote gene transcription by depositing the H3K4me3 activating mark at target gene promoters. We recently reported that in Ewing sarcoma, MLL1 (lysine methyltransferase 2A, KMT2A) and menin are overexpressed and function as oncogenes. Small molecule inhibition of the menin-MLL interaction leads to loss of menin and MLL1 protein expression, and to inhibition of growth and tumorigenicity. Here, we have investigated the mechanistic basis of menin-MLL-mediated oncogenic activity in Ewing sarcoma. Bromouridine sequencing (Bru-seq) was performed to identify changes in nascent gene transcription in Ewing sarcoma cells, following exposure to the menin-MLL interaction inhibitor MI-503. Menin-MLL inhibition resulted in early and widespread reprogramming of metabolic processes. In particular, the serine biosynthetic pathway (SSP) was the pathway most significantly affected by MI-503 treatment. Baseline expression of SSP genes and proteins (PHGDH, PSAT1, and PSPH), and metabolic flux through the SSP were confirmed to be high in Ewing sarcoma. In addition, inhibition of PHGDH resulted in reduced cell proliferation, viability, and tumor growth in vivo, revealing a key dependency of Ewing sarcoma on the SSP. Loss of function studies validated a mechanistic link between menin and the SSP. Specifically, inhibition of menin resulted in diminished expression of SSP genes, reduced H3K4me3 enrichment at the PHGDH promoter, and complete abrogation of de novo serine and glycine biosynthesis, as demonstrated by metabolic tracing studies with 13 C-labeled glucose. These data demonstrate that the SSP is highly active in Ewing sarcoma and that its oncogenic activation is maintained, at least in part, by menin-dependent epigenetic mechanisms involving trithorax complexes. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The iHOPE-20 study: Relationships between and prospective predictors of remission, clinical recovery, personal recovery and resilience 20 years on from a first episode psychosis.

OBJECTIVE: Knowledge of outcome in psychotic illness is limited by the paucity of very long-term epidemiologically representative studies of incidence first episode psychosis (FEP) cohorts that measure and compare outcomes reflecting modern clinical practice, mental health policy and research agendas. Our study aimed to address this gap. METHOD: iHOPE-20 is a prospective 20-year follow-up study of a FEP incidence cohort (N = 171) conducted between 2014 and 2017 in Ireland. Data from previous studies and medical records were used to recruit cohort members. We assessed remission, clinical recovery, personal recovery and resilience at 20 years; explored the relationships between these outcomes and examined the predictive value of baseline characteristics in determining them. RESULTS: At follow-up, 20 out of 171 cohort members (11.70%) were deceased. We assessed 80 out of 151 alive cohort members (53% recruitment rate); 65% were in remission; 35.2% were in Full Functional Recovery and 53.7% confirmed they were fully recovered according to their personal definition of recovery. A complex array of relationships between outcomes was found. Outcomes were better for people who had a short duration of untreated psychosis, displayed higher premorbid social adjustment (between the ages of 5-11) and at baseline, were older, not living alone, in full-time employment, given a non-affective diagnosis, and had lower Global Assessment of Functioning scores. CONCLUSION: Among participants, full remission of psychotic symptoms and personally defined recovery was not just possible but likely in the very long term. However, attaining positive functional outcomes and building resilience in FEP remain key challenges for mental health services.

The iHOPE-20 study: mortality in first episode psychosis-a 20-year follow-up of the Dublin first episode cohort.

PURPOSE: Increased mortality rates have been found in those with a diagnosis of psychosis; studies suggest a shortened life expectancy of up to 20 years less than that of the general population. This study aimed to investigate the mortality of a first episode psychosis cohort at 20-year follow-up, compare it to that of the general Irish population, and explore whether the mortality gap has changed over time. METHODS: 171 individuals diagnosed with a first episode psychosis identified between 1995 and 1999 in a community mental health service were traced. Mortality was established by matching death certificates to deceased cohort members (using name, age at date of death, and address at date of death). Date of first presentation to service was used as date of entry point and date of death or end of follow-up as the end point. RESULTS: Of the 171 cases there were 20 deaths during follow-up. Nine deaths were attributed to natural causes; 7 to unnatural causes; and 4 were unknown. Comparing standardised mortality rates at 20-year follow-up to those at 12 year showed a reduction in rates over time. CONCLUSION: Findings suggest that the mortality gap in people with schizophrenia and other psychoses remains high, especially in young males.

Oncogenic fusion protein EWS-FLI1 is a network hub that regulates alternative splicing.

The synthesis and processing of mRNA, from transcription to translation initiation, often requires splicing of intragenic material. The final mRNA composition varies based on proteins that modulate splice site selection. EWS-FLI1 is an Ewing sarcoma (ES) oncoprotein with an interactome that we demonstrate to have multiple partners in spliceosomal complexes. We evaluate the effect of EWS-FLI1 on posttranscriptional gene regulation using both exon array and RNA-seq. Genes that potentially regulate oncogenesis, including CLK1, CASP3, PPFIBP1, and TERT, validate as alternatively spliced by EWS-FLI1. In a CLIP-seq experiment, we find that EWS-FLI1 RNA-binding motifs most frequently occur adjacent to intron-exon boundaries. EWS-FLI1 also alters splicing by directly binding to known splicing factors including DDX5, hnRNP K, and PRPF6. Reduction of EWS-FLI1 produces an isoform of γ-TERT that has increased telomerase activity compared with wild-type (WT) TERT. The small molecule YK-4-279 is an inhibitor of EWS-FLI1 oncogenic function that disrupts specific protein interactions, including helicases DDX5 and RNA helicase A (RHA) that alters RNA-splicing ratios. As such, YK-4-279 validates the splicing mechanism of EWS-FLI1, showing alternatively spliced gene patterns that significantly overlap with EWS-FLI1 reduction and WT human mesenchymal stem cells (hMSC). Exon array analysis of 75 ES patient samples shows similar isoform expression patterns to cell line models expressing EWS-FLI1, supporting the clinical relevance of our findings. These experiments establish systemic alternative splicing as an oncogenic process modulated by EWS-FLI1. EWS-FLI1 modulation of mRNA splicing may provide insight into the contribution of splicing toward oncogenesis, and, reciprocally, EWS-FLI1 interactions with splicing proteins may inform the splicing code.

'Recovery' in the Real World: Service User Experiences of Mental Health Service Use and Recommendations for Change 20 Years on from a First Episode Psychosis.

Little is known about how recovery oriented policy and legislative changes influence service users' perceptions of mental health care over time. Although the recovery approach is endorsed in many countries, qualitative research examining its impact on service use experiences has been lacking. This study aimed to explore this impact as well as experiences of service utilisation and suggestions for change with people diagnosed with a First Episode Psychosis between 1995 and 1999. Participants had used services during the 10 year period prior to, and 10 years post, policy and legislative shifts to the recovery approach. Semi-structured interviews were conducted with 10 participants who met criteria for 'full functional recovery' and 10 who did not. Data were analysed using Thematic Networks Analysis to develop Basic, Organising, and Global Themes. Over time, recovered participants perceived an improvement in service quality through the 'humanising' of treatment and non-recovered participants experienced their responsibility in recovery being recognised, but felt abandoned to the recovery approach. Findings suggest the importance of viewing service users as demonstrating personhood and having societal value; examining the personal meaning of psychotic experiences; and matching expectations with what services can feasibly provide. The implementation and the principal tenets of the recovery approach warrant further investigation.

Clozapine Use in a Cohort of First-Episode Psychosis.

PURPOSE/BACKGROUND: For approximately one third of individuals treated for psychosis or schizophrenia, antipsychotic medications will have little or no therapeutic benefit. Clozapine remains the sole medication approved for treatment-resistant schizophrenia, and studies have demonstrated its superior efficacy in reducing psychotic symptoms. METHODS/PROCEDURES: Data were collected from the medical records of people who originally presented with a first-episode psychosis between 1995 and 1999 (N = 171). Data were obtained from first presentation up to December 31, 2013 or until the patient was discharged or transferred. Information on service use and physical health was gathered using a data collection template designed specifically for this audit. FINDINGS/RESULTS: Twenty-eight (16.3%) of the cohort were prescribed clozapine. Data were available for 24 individuals. Of this clozapine subsample, the mean age at baseline was 23.11 (SD = 4.58); 82.14% (n = 23) were male; and 82.14% (n = 23) had a baseline diagnosis of schizophrenia. The mean time to first trial of clozapine was 6.7 years. The mean number of antipsychotics prescribed before clozapine trial was 4.85. After the initiation of clozapine, the mean number of hospital admissions reduced from 6.04 per year to 0.88 per year. IMPLICATIONS/CONCLUSIONS: Nearly 1 in 5 of the original cohort was considered to have a suboptimal response to trials of antipsychotic medication. The use of clozapine for treatment-resistant schizophrenia is underutilized, and better understanding of the barriers to prescribing clozapine is necessary given the implications for patient's quality of life and hospital admission rates. Physical health data further emphasizes the importance of physical health monitoring in this vulnerable population.

Comparison of clinical features and outcomes in patients with extraskeletal versus skeletal localized Ewing sarcoma: A report from the Children's Oncology Group.

BACKGROUND: The prognostic significance of having extraskeletal (EES) versus skeletal Ewing sarcoma (ES) in the setting of modern chemotherapy protocols is unknown. The purpose of this study was to compare the clinical characteristics, biologic features, and outcomes for patients with EES and skeletal ES. METHODS: Patients had localized ES and were treated on two consecutive protocols using five-drug chemotherapy (INT-0154 and AEWS0031). Patients were analyzed based on having an extraskeletal (n = 213) or skeletal (n = 826) site of tumor origin. Event-free survival (EFS) was estimated using the Kaplan-Meier method, compared using the log-rank test, and modeled using Cox multivariate regression. RESULTS: Patients with extraskeletal ES (EES) were more likely to have axial tumors (72% vs. 55%; P < 0.001), less likely to have tumors >8 cm (9% vs. 17%; P < 0.01), and less likely to be white (81% vs. 87%; P < 0.001) compared to patients with skeletal ES. There was no difference in key genomic features (type of EWSR1 translocation, TP53 mutation, CDKN2A mutation/loss) between groups. After controlling for age, race, and primary site, EES was associated with superior EFS (hazard ratio = 0.69; 95% confidence interval: 0.50-0.95; P = 0.02). Among patients with EES, age ≥18, nonwhite race, and elevated baseline erythrocyte sedimentation rate were independently associated with inferior EFS. CONCLUSION: Clinical characteristics, but not key tumor genomic features, differ between EES and skeletal ES. Extraskeletal origin is a favorable prognostic factor, independent of age, race, and primary site.

The relationship between mental health literacy regarding schizophrenia and psychiatric stigma in the Republic of Ireland.

BACKGROUND: There is an unclear relationship between mental health literacy (MHL) and psychiatric stigma. MHL is associated with both positive and negative attitudes to mental illness. To our knowledge, no published peer reviewed study has examined this relationship in the Republic of Ireland. AIMS: This study was conducted to assess MHL regarding schizophrenia and the degree of psychiatric stigma displayed by the general public in the Republic of Ireland. METHOD: A face-to-face in-home omnibus survey was conducted with a representative sample of residents of the Republic of Ireland. Participants (N = 1001) were presented with a vignette depicting schizophrenia and were asked questions to determine their ability to recognise the condition and to ascertain their attitudes towards schizophrenia and mental illness. RESULTS: Among the participants, 34.1% correctly identified schizophrenia. Higher age, higher socioeconomic status, and an urban geographic location predicted identification. Those who did not correctly identify schizophrenia were significantly more optimistic about recovery and perceived people with schizophrenia as less dangerous. However, only the relationship with perceived dangerousness was considered robust. CONCLUSIONS: Participants with higher MHL displayed more negative attitudes to mental illness. Findings have implications internationally for MHL and anti-stigma campaigns.

Systemic levels of neuropeptide Y and dipeptidyl peptidase activity in patients with Ewing sarcoma--associations with tumor phenotype and survival.

BACKGROUND: Ewing sarcoma (ES) is driven by fusion of the Ewing sarcoma breakpoint region 1 gene (EWSR1) with an E26 transformation-specific (ETS) transcription factor (EWS-ETS), most often the Friend leukemia integration 1 transcription factor (FLI1). Neuropeptide Y (NPY) is an EWS-FLI1 transcriptional target; it is highly expressed in ES and exerts opposing effects, ranging from ES cell death to angiogenesis and cancer stem cell propagation. The functions of NPY are regulated by dipeptidyl peptidase IV (DPPIV), a hypoxia-inducible enzyme that cleaves the peptide and activates its growth-promoting actions. The objective of this study was to determine the clinically relevant functions of NPY by identifying the associations between patients' ES phenotype and their NPY concentrations and DPP activity. METHODS: NPY concentrations and DPP activity were measured in serum samples from 223 patients with localized ES and 9 patients with metastatic ES provided by the Children's Oncology Group. RESULTS: Serum NPY levels were elevated in ES patients compared with the levels in a healthy control group and an osteosarcoma patient population, and the elevated levels were independent of EWS-ETS translocation type. Significantly higher NPY concentrations were detected in patients with ES who had tumors of pelvic and bone origin. A similar trend was observed in patients with metastatic ES. There was no effect of NPY on survival in patients with localized ES. DPP activity in sera from patients with ES did not differ significantly from that in healthy controls and patients with osteosarcoma. However, high DPP levels were associated with improved survival. CONCLUSIONS: Systemic NPY levels are elevated in patients with ES, and these high levels are associated with unfavorable disease features. DPPIV in serum samples from patients with ES is derived from nontumor sources, and its high activity is correlated with improved survival.

Mast cells are required for angiogenesis and macroscopic expansion of Myc-induced pancreatic islet tumors.

An association between inflammation and cancer has long been recognized, but the cause and effect relationship linking the two remains unclear. Myc is a pleiotropic transcription factor that is overexpressed in many human cancers and instructs many extracellular aspects of the tumor tissue phenotype, including remodeling of tumor stroma and angiogenesis. Here we show in a beta-cell tumor model that activation of Myc in vivo triggers rapid recruitment of mast cells to the tumor site-a recruitment that is absolutely required for macroscopic tumor expansion. In addition, treatment of established beta-cell tumors with a mast cell inhibitor rapidly triggers hypoxia and cell death of tumor and endothelial cells. Inhibitors of mast cell function may therefore prove therapeutically useful in restraining expansion and survival of pancreatic and other cancers.

Predicting uptake of group CBT in a first-episode psychosis cohort.

Many people with psychosis do not engage in psychological treatments when offered. We examined variables that predicted uptake of group cognitive behavioural therapy (CBT) in first-episode psychosis. We assessed all consenting consecutive referrals over a 2-year period. T-tests and logistic regressions examined factors which predicted uptake. The suitability for short-term CBT scale (SSCT) and negative symptoms successfully differentiated engagement and non-engagement. A model combining negative symptoms and the SSCT significantly predicted uptake of group CBT. Attention has not been paid to poor uptake of psychological treatments in psychosis. This may have a greater impact on outcomes than treatment effectiveness.

Temporal dissection of p53 function in vitro and in vivo.

To investigate the functions of the p53 tumor suppressor, we created a new knock-in gene replacement mouse model in which the endogenous Trp53 gene is substituted by one encoding p53ER(TAM), a p53 fusion protein whose function is completely dependent on ectopic provision of 4-hydroxytamoxifen. We show here that both tissues in vivo and cells in vitro derived from such mice can be rapidly toggled between wild-type and p53 knockout states. Using this rapid perturbation model, we define the kinetics, dependence, persistence and reversibility of p53-mediated responses to DNA damage in tissues in vivo and to activation of the Ras oncoprotein and stress in vitro. This is the first example to our knowledge of a new class of genetic model that allows the specific, rapid and reversible perturbation of the function of a single endogenous gene in vivo.

Lack of insight in psychosis: theoretical concepts and clinical aspects.

BACKGROUND: Different theories concerning pathways to insight have been proposed which underpin the numerous assessment measures. Cognitive behavioural therapy (CBT) is one treatment approach that has been used to improve insight. AIMS: The aim of this review was to promote a greater focus on developing effective CBT strategies to ameliorate insight in psychosis through the exploration of the concept of insight in psychosis and evaluation of research in the area. METHOD: A comprehensive search and review of published studies examining the impact of CBT on insight in psychosis was conducted. We searched the databases PubMed, Medline, PsychInfo, the Psychology and Behavioral Sciences Database, and CINAHL with limits set to 10 years, humans, and English language. We hand-searched reference lists of major studies on insight, and theoretical review papers. We filtered our results according to relevance and chose 50 papers for final consideration. RESULTS: The multidimensionality of insight is reflected in the variety of different insight measures in clinical use. Research findings on the impact of CBT on insight are conflicting. Cognitive insight and clinical insight appear to be different concepts that are not fully captured by existing measurement scales. CONCLUSIONS: The conflicting results found in research examining the impact of CBT on insight may be partially explained by the different theories underpinning insight in psychosis communicated through psychoeducation in CBT. Furthermore, the use of more than one insight assessment measure may capture the complexity of insight more effectively. Qualitative research with service users would enrich the knowledge in this area.

Cancer-Associated Fibroblast-Like Tumor Cells Remodel the Ewing Sarcoma Tumor Microenvironment.

PURPOSE: Despite limited genetic and histologic heterogeneity, Ewing sarcoma (EwS) tumor cells are transcriptionally heterogeneous and display varying degrees of mesenchymal lineage specification in vitro. In this study, we investigated if and how transcriptional heterogeneity of EwS cells contributes to heterogeneity of tumor phenotypes in vivo. EXPERIMENTAL DESIGN: Single-cell proteogenomic-sequencing of EwS cell lines was performed and integrated with patient tumor transcriptomic data. Cell subpopulations were isolated by FACS for assessment of gene expression and phenotype. Digital spatial profiling and human whole transcriptome analysis interrogated transcriptomic heterogeneity in EwS xenografts. Tumor cell subpopulations and matrix protein deposition were evaluated in xenografts and patient tumors using multiplex immunofluorescence staining. RESULTS: We identified CD73 as a biomarker of highly mesenchymal EwS cell subpopulations in tumor models and patient biopsies. CD73+ tumor cells displayed distinct transcriptional and phenotypic properties, including selective upregulation of genes that are repressed by EWS::FLI1, and increased migratory potential. CD73+ cells were distinguished in vitro and in vivo by increased expression of matrisomal genes and abundant deposition of extracellular matrix (ECM) proteins. In epithelial-derived malignancies, ECM is largely deposited by cancer-associated fibroblasts (CAF), and we thus labeled CD73+ EwS cells, CAF-like tumor cells. Marked heterogeneity of CD73+ EwS cell frequency and distribution was detected in tumors in situ, and CAF-like tumor cells and associated ECM were observed in peri-necrotic regions and invasive foci. CONCLUSIONS: EwS tumor cells can adopt CAF-like properties, and these distinct cell subpopulations contribute to tumor heterogeneity by remodeling the tumor microenvironment. See related commentary by Kuo and Amatruda, p. 5002.

Carcinoma-associated fibroblast-like tumor cells remodel the Ewing sarcoma tumor microenvironment.

Tumor heterogeneity is a major driver of cancer progression. In epithelial-derived malignancies, carcinoma-associated fibroblasts (CAFs) contribute to tumor heterogeneity by depositing extracellular matrix (ECM) proteins that dynamically remodel the tumor microenvironment (TME). Ewing sarcomas (EwS) are histologically monomorphous, mesenchyme-derived tumors that are devoid of CAFs. Here we identify a previously uncharacterized subpopulation of transcriptionally distinct EwS tumor cells that deposit pro-tumorigenic ECM. Single cell analyses revealed that these CAF-like cells differ from bulk EwS cells by their upregulation of a matrisome-rich gene signature that is normally repressed by EWS::FLI1, the oncogenic fusion transcription factor that underlies EwS pathogenesis. Further, our studies showed that ECM-depositing tumor cells express the cell surface marker CD73, allowing for their isolation ex vivo and detection in situ. Spatial profiling of tumor xenografts and patient biopsies demonstrated that CD73 + EwS cells and tumor cell-derived ECM are prevalent along tumor borders and invasive fronts. Importantly, despite loss of EWS::FLI1-mediated gene repression, CD73 + EwS cells retain expression of EWS::FLI1 and the fusion-activated gene signature, as well as tumorigenic and proliferative capacities. Thus, EwS tumor cells can be reprogrammed to adopt CAF-like properties and these transcriptionally and phenotypically distinct cell subpopulations contribute to tumor heterogeneity by remodeling the TME.

ß-Catenin-Driven Differentiation Is a Tissue-Specific Epigenetic Vulnerability in Adrenal Cancer.

Adrenocortical carcinoma (ACC) is a rare cancer in which tissue-specific differentiation is paradoxically associated with dismal outcomes. The differentiated ACC subtype CIMP-high is prevalent, incurable, and routinely fatal. CIMP-high ACC possess abnormal DNA methylation and frequent ß-catenin-activating mutations. Here, we demonstrated that ACC differentiation is maintained by a balance between nuclear, tissue-specific ß-catenin-containing complexes, and the epigenome. On chromatin, ß-catenin bound master adrenal transcription factor SF1 and hijacked the adrenocortical super-enhancer landscape to maintain differentiation in CIMP-high ACC; off chromatin, ß-catenin bound histone methyltransferase EZH2. SF1/ß-catenin and EZH2/ß-catenin complexes present in normal adrenals persisted through all phases of ACC evolution. Pharmacologic EZH2 inhibition in CIMP-high ACC expelled SF1/ß-catenin from chromatin and favored EZH2/ß-catenin assembly, erasing differentiation and restraining cancer growth in vitro and in vivo. These studies illustrate how tissue-specific programs shape oncogene selection, surreptitiously encoding targetable therapeutic vulnerabilities. SIGNIFICANCE: Oncogenic ß-catenin can use tissue-specific partners to regulate cellular differentiation programs that can be reversed by epigenetic therapies, identifying epigenetic control of differentiation as a viable target for ß-catenin-driven cancers.