Hyperoxia-induced acute lung injury (HALI) is a key contributor to the pathogenesis of bronchopulmonary dysplasia (BPD) in neonates, for which no specific preventive or therapeutic agent is available. Here we show that lung micro-RNA (miR)-34a levels are significantly increased in lungs of neonatal mice exposed to hyperoxia. Deletion or inhibition of miR-34a improves the pulmonary phenotype and BPD-associated pulmonary arterial hypertension (PAH) in BPD mouse models, which, conversely, is worsened by miR-34a overexpression. Administration of angiopoietin-1, which is one of the downstream targets of miR34a, is able to ameliorate the BPD pulmonary and PAH phenotypes. Using three independent cohorts of human samples, we show that miR-34a expression is increased in type 2 alveolar epithelial cells in neonates with respiratory distress syndrome and BPD. Our data suggest that pharmacologic miR-34a inhibition may be a therapeutic option to prevent or ameliorate HALI/BPD in neonates.

The EWS/ETS fusion transcription factors drive Ewing sarcoma (EWS) by orchestrating an oncogenic transcription program. Therapeutic targeting of EWS/ETS has been unsuccessful; however, identifying mediators of the EWS/ETS function could offer new therapeutic options. Here, we describe the dependency of EWS/ETS-driven transcription upon chromatin reader BET bromdomain proteins and investigate the potential of BET inhibitors in treating EWS. EWS/FLI1 and EWS/ERG were found in a transcriptional complex with BRD4, and knockdown of BRD2/3/4 significantly impaired the oncogenic phenotype of EWS cells. RNA-seq analysis following BRD4 knockdown or inhibition with JQ1 revealed an attenuated EWS/ETS transcriptional signature. In contrast to previous reports, JQ1 reduced proliferation and induced apoptosis through MYC-independent mechanisms without affecting EWS/ETS protein levels; this was confirmed by depleting BET proteins using PROTAC-BET degrader (BETd). Polycomb repressive complex 2 (PRC2)-associated factor PHF19 was downregulated by JQ1/BETd or BRD4 knockdown in multiple EWS lines. EWS/FLI1 bound a distal regulatory element of PHF19, and EWS/FLI1 knockdown resulted in downregulation of PHF19 expression. Deletion of PHF19 via CRISPR-Cas9 resulted in a decreased tumorigenic phenotype, a transcriptional signature that overlapped with JQ1 treatment, and increased sensitivity to JQ1. PHF19 expression was also associated with worse prognosis in patients with EWS. , JQ1 demonstrated antitumor efficacy in multiple mouse xenograft models of EWS. Together these results indicate that EWS/ETS requires BET epigenetic reader proteins for its transcriptional program and can be mitigated by BET inhibitors. This study provides a clear rationale for the clinical utility of BET inhibitors in treating EWS. These findings reveal the dependency of EWS/ETS transcription factors on BET epigenetic reader proteins and demonstrate the potential of BET inhibitors for the treatment of EWS. .

BRD4 plays a major role in the transcription networks orchestrated by androgen receptor (AR) in castration-resistant prostate cancer (CRPC). Several BET inhibitors (BETi) that displace BRD4 from chromatin are being evaluated in clinical trials for CRPC. Here, we describe mechanisms of acquired resistance to BETi that are amenable to targeted therapies in CRPC. BETi-resistant CRPC cells displayed cross-resistance to a variety of BETi in the absence of gatekeeper mutations, exhibited reduced chromatin-bound BRD4, and were less sensitive to BRD4 degraders/knockdown, suggesting a BRD4-independent transcription program. Transcriptomic analysis revealed reactivation of AR signaling due to CDK9-mediated phosphorylation of AR, resulting in sensitivity to CDK9 inhibitors and enzalutamide. Additionally, increased DNA damage associated with PRC2-mediated transcriptional silencing of DDR genes was observed, leading to PARP inhibitor sensitivity. Collectively, our results identify the therapeutic limitation of BETi as a monotherapy; however, our BETi resistance data suggest unique opportunities for combination therapies in treating CRPC.

Acute myeloid leukemia (AML) is a hematopoietic malignancy characterized by uncontrolled division, and differentiation arrest, of hematopoietic stem cells (HSCs) and myeloid progenitors. AML is a genetically heterogeneous disease, with mutations in genes belonging to multiple functional groups. Of these, chromatin regulators and transcriptional factors (TFs) are an important functional group to study because of a lack of targeted AML therapies against these factors. PHD Finger Protein 6 (PHF6) is one such chromatin-associated protein with a yet-unknown molecular mechanism of action. It is mutated in 3-5% of MDS, CMML, and AMLs and 20% of T- ALLs, and is considered a leukemia suppressor. To assess the effects of PHF6 on the AML transcriptome, we generated CRISPR-mediated knockout (KO) clones in THP-1 monocytic AML cell line, and integrated a Dox-inducible PHF6 construct into a PHF6 KO clone, enabling us to conditionally rescue PHF6 expression to parental levels (Fig A & B). RNA-Seq analysis of these knockout and rescue systems revealed that PHF6 expression upregulates genes related to myeloid differentiation and downregulates genes related to hematopoietic stem cells and cell division in myeloid cells. Additionally, loss of PHF6 increased THP-1 proliferation, and restoring PHF6 expression decreased proliferation. We also performed ChIP-Seq for PHF6 in the THP-1 cells and found that PHF6 binds to open and active enhancer regions. Unbiased motif analysis showed that PHF6-bound enhancers (compared to all enhancers genome-wide) were enriched for RUNX1, PU.1, and IRF8 motifs. Metagene plotting of PHF6 ChIP-Seq signal against ChIP-Seq for these TFs showed striking concordance in their binding patterns, indicating that PHF6 co-occupies chromatin with key hematopoietic transcription factors. (Fig C). PHF6 has two extended PHD (ePHD) domains with a similar structure to canonical PHD domains, but with unknown functions. Based on leukemia genome sequencing results from COSMIC, we observed that while nonsense and frameshift mutations of PHF6 (accounting for 2/3 rd of PHF6 mutations, and expected to produce no protein) are distributed throughout the gene body, missense mutations (accounting for 1/3 rd of PHF6 mutations and expected to produce a full-length protein with single amino acid substitution), are concentrated in the second ePHD domain (ePHD2). To assess the functional consequence of mutations in the ePHD2 domain, we generated from a PHF6 KO clone a clone expressing Dox-inducible PHF6 R274Q, the most common missense mutation of PHF6 seen in leukemia. RNA-Seq showed that PHF6 R274Q induction has no downstream effects on the cellular transcriptome, in striking contrast to the effects of wildtype PHF6 induction (Fig D). Additionally, the expression of PHF6 R274Q has no effect on cell growth. These results indicate that the ePHD2-domain mutant PHF6 R274Q is functionally dead (fully or partially), and the ePHD2 domain is critical for PHF6 function. Our results support an important transcriptional role of PHF6 in the myeloid system, involving co-occupancy with TFs at enhancers to promote the transcription of myeloid differentiation genes. This loss of this transcriptional regulation, either through complete PHF6 protein loss or point mutation of its ePHD2 domain, dysregulates myeloid differentiation and contributes to leukemogenesis. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Ewing sarcoma (EWS) is a lethal pediatric small, round, blue cell tumor defined by the characteristic fusion between EWSR1 and a member of the ETS family transcription factor, mostly FLI1 and ERG. Bromodomain and extra-terminal domain (BET) proteins play an essential role in transcription as an epigenetic reader of acetylated histones and transcription factors, and recent studies of inhibitors against these proteins have demonstrated therapeutic potential in various cancers. In this study, we investigated the importance of BET proteins BRD2, BRD3, and BRD4 in EWS-fusion driven transcription program required for maintenance and progression of EWS. Similar to EWS-FLI1 and EWS-ERG, knock-down of BET proteins severely impaired the proliferation and invasion of EWS cells. Gene expression profiling by RNA-Seq showed a common set of genes altered in EWS-FLI1 and BRD2/3/4 knockdown cells implicating a direct role of BET proteins in the transcriptional regulation of EWS-fusion targets. Importantly, BET inhibitor, JQ1, induces apoptosis in EWS cells through an MYC-independent mechanism, and without affecting the EWS-fusion levels. Rather, evidence suggested that BRD4 exists in a complex with EWS-ETS fusion proteins and that its inhibition abrogates the fusion transcriptional program. In vivo, JQ1 inhibited the metastases in chicken CAM model of EWS as well as displayed anti-tumor and anti-metastatic activity in mouse xenograft models of EWS. Together, these results indicate that BET proteins, especially BRD4 interacts with EWS-ETS fusion proteins and this interaction is necessary for the EWS-fusion mediated oncogenesis. Moreover, this study provides a clear rationale for the clinical utility of BET inhibitors in treating metastatic Ewing sarcoma patients. Citation Format: Paradesi N. Gollavilli, Aishwarya Pawar, Kari Wilder-Romans, Carl Engelke, Vijaya L. Dommeti, Pranathi M. Krishnamurthy, Archana Nallasivam, Ingrid A. Apel, Tianlei Xu, Zhaohui S. Qin, Felix Y. Feng, Irfan A. Asangani. BET bromodomain proteins are essential for the oncogenic EWS-fusion driven Ewing Sarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-099. doi:10.1158/1538-7445.AM2017-LB-099