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Alternative RNA splicing plays an important role in cancer. To determine which factors involved in RNA processing are essential in prostate cancer, we performed a genome-wide CRISPR/Cas9 knockout screen to identify the genes that are required for prostate cancer growth. Functional annotation defined a set of essential spliceosome and RNA binding protein (RBP) genes, including most notably heterogeneous nuclear ribonucleoprotein L (HNRNPL). We defined the HNRNPL-bound RNA landscape by RNA immunoprecipitation coupled with next-generation sequencing and linked these RBP–RNA interactions to changes in RNA processing. HNRNPL directly regulates the alternative splicing of a set of RNAs, including those encoding the androgen receptor, the key lineage-specific prostate cancer oncogene. HNRNPL also regulates circular RNA formation via back splicing. Importantly, both HNRNPL and its RNA targets are aberrantly expressed in human prostate tumors, supporting their clinical relevance. Collectively, our data reveal HNRNPL and its RNA clients as players in prostate cancer growth and potential therapeutic targets.

Epigenetic regulators represent a promising new class of therapeutic targets for cancer. Enhancer of zeste homolog 2 (EZH2), a subunit of Polycomb repressive complex 2 (PRC2), silences gene expression via its histone methyltransferase activity. We found that the oncogenic function of EZH2 in cells of castration-resistant prostate cancer is independent of its role as a transcriptional repressor. Instead, it involves the ability of EZH2 to act as a coactivator for critical transcription factors including the androgen receptor. This functional switch is dependent on phosphorylation of EZH2 and requires an intact methyltransferase domain. Hence, targeting the non-PRC2 function of EZH2 may have therapeutic efficacy for treating metastatic, hormone-refractory prostate cancer.

Localized prostate cancers are genetically variable and frequently multifocal, comprising spatially distinct regions with multiple independently-evolving clones. To date there is no understanding of whether this variability can influence management decisions for patients with prostate tumors. Here, we present a single case from a clinical trial of neoadjuvant intense androgen deprivation therapy. A patient was diagnosed with a large semi-contiguous tumor by imaging, histologically composed of a large Gleason score 9 tumor with an adjacent Gleason score 7 nodule. DNA sequencing demonstrates these are two independent tumors, as only the Gleason 9 tumor harbors single-copy losses of PTEN and TP53 . The PTEN / TP53 -deficient tumor demonstrates treatment resistance, selecting for subclones with mutations to the remaining copies of PTEN and TP53 , while the Gleason 7 PTEN -intact tumor is almost entirely ablated. These findings indicate that spatiogenetic variability is a major confounder for personalized treatment of patients with prostate cancer. Prostate cancer is often a multifocal disease but how best to manage this clinically remains unclear. Here, the authors report a single case study of a patient with two genetically diverse tumours which showed differential response to therapy.

Whole-exome sequencing of circulating tumor cells enables accurate and powered calling of somatic point mutations. Comprehensive analyses of cancer genomes promise to inform prognoses and precise cancer treatments. A major barrier, however, is inaccessibility of metastatic tissue. A potential solution is to characterize circulating tumor cells (CTCs), but this requires overcoming the challenges of isolating rare cells and sequencing low-input material. Here we report an integrated process to isolate, qualify and sequence whole exomes of CTCs with high fidelity using a census-based sequencing strategy. Power calculations suggest that mapping of >99.995% of the standard exome is possible in CTCs. We validated our process in two patients with prostate cancer, including one for whom we sequenced CTCs, a lymph node metastasis and nine cores of the primary tumor. Fifty-one of 73 CTC mutations (70%) were present in matched tissue. Moreover, we identified 10 early trunk and 56 metastatic trunk mutations in the non-CTC tumor samples and found 90% and 73% of these mutations, respectively, in CTC exomes. This study establishes a foundation for CTC genomics in the clinic.

BACKGROUNDLocalized high-risk prostate cancer (PCa) often recurs despite neoadjuvant androgen deprivation therapy (ADT). We sought to identify baseline molecular programs that predict pathologic response and reveal targetable vulnerabilities.METHODSWe profiled 147 biopsy foci from 48 MRI-visible lesions in 37 patients before 6 months of ADT plus enzalutamide and radical prostatectomy. Residual cancer burden (RCB) at prostatectomy was the primary outcome. Analyses incorporated PTEN loss, TMPRSS2:ERG status, and HER2/androgen receptor (AR) immunohistochemistry on baseline and posttreatment tissues. Findings were evaluated in an external transcriptional cohort (n = 121) and by multiplex immunostaining in an independent cohort (n = 61). Functional assays tested enzalutamide-responsive enhancers near ERBB2 and sensitivity to HER2 inhibition.RESULTSA baseline, HER2-associated transcriptional program correlated with higher RCB and inversely with AR activity, independent of PTEN and ERG. Exceptional responders had lower HER2 protein levels in pretreatment biopsy specimens. The inverse AR-HER2 relationship recurred across data sets and multiplex immunostaining, which revealed coexisting AR-high/HER2-low and HER2-high/AR-low subpopulations. Enzalutamide inhibited AR-mediated repression of ERBB2. HER2-high/AR-low cells present before therapy resisted ADT yet were sensitive to HER2 inhibitors; combining HER2 inhibitors with enzalutamide increased tumor cell killing. These findings were reproduced in the external cohort and orthogonal assays.CONCLUSIONBaseline HER2 activity marks intrinsic resistance to neoadjuvant ADT in localized high-risk PCa and identifies a preexisting, targetable AR-low subpopulation. HER2-directed therapy, alone or with AR blockade, warrants clinical evaluation.TRIAL REGISTRATIONClinicalTrials.gov registration: NCT02430480.FUNDINGProstate Cancer Foundation; Department of Defense Prostate Cancer Research Program; National Institutes of Health.

In prostate cancer, the oncogenicity of transcription factor ERG is mediated, in part, by competition with another member of the ETS family, ERF. Opposing protein actions in tumour growth In prostate cancer, TMPRSS2 – ERG translocations are very frequent and lead to overexpression of ERG, which can trigger tumour growth. Rohit Bose and colleagues now show that another member of the ETS family, ERF, functions as a tumour suppressor in prostate cancer. ERF is lost in many tumours without TMPRSS2 – ERG translocations. ERF normally competes with other members of the ETS family for binding to DNA, and this function is disabled either by loss of ERF or increased levels of ERG. These findings shed further light on the opposing functions of ETS family proteins in tumorigenesis. Half of all prostate cancers are caused by the TMPRSS2–ERG gene-fusion, which enables androgens to drive expression of the normally silent E26 transformation-specific (ETS) transcription factor ERG in prostate cells 1 , 2 . Recent genomic landscape studies of such cancers 3 , 4 , 5 , 6 , 7 , 8 have reported recurrent point mutations and focal deletions of another ETS member, the ETS2 repressor factor ERF 9 . Here we show these ERF mutations cause decreased protein stability and mostly occur in tumours without ERG upregulation. ERF loss recapitulates the morphological and phenotypic features of ERG gain in normal mouse prostate cells, including expansion of the androgen receptor transcriptional repertoire, and ERF has tumour suppressor activity in the same genetic background of Pten loss that yields oncogenic activity by ERG . In the more common scenario of ERG upregulation, chromatin immunoprecipitation followed by sequencing indicates that ERG inhibits the ability of ERF to bind DNA at consensus ETS sites both in normal and in cancerous prostate cells. Consistent with a competition model, ERF overexpression blocks ERG-dependent tumour growth, and ERF loss rescues TMPRSS2–ERG -positive prostate cancer cells from ERG dependency. Collectively, these data provide evidence that the oncogenicity of ERG is mediated, in part, by competition with ERF and they raise the larger question of whether other gain-of-function oncogenic transcription factors might also inactivate endogenous tumour suppressors.

Approximately 50% of prostate cancer (PCa) patients harbor fusions involving the and genes. Despite this, tailored therapies targeting the fused gene, , remain undeveloped. Our study analyzed biopsy samples from two clinical trials assessing the efficacies of androgen receptor (AR) signaling inhibitors (ARSIs). The results revealed that promotes resistance to ARSIs and is associated with elevated levels of the glucocorticoid receptor (GR). Subsequent assays showed that GR directly interacts with tERG, alleviates allosteric autoinhibition and prevents chemotherapy-induced tERG degradation. In PCa models, either inhibiting GR or lowering cortisol levels suppressed tumor growth in tERG-positive models, but not in fusion-negative models. In addition, patient-derived fusion-positive xenografts displayed enhanced sensitivity to combined GR and AR inhibitors. Collectively, these findings highlight as a new biomarker and propose that simultaneous inhibition of GR and AR may specifically benefit -positine patients. However, GR stimulatory corticosteroid therapies may not be advisable for this patient subgroup.

High-risk localized prostate cancer (HRLPC) is associated with a substantial risk of recurrence and prostate cancer-specific mortality1. Recent clinical trials have shown that intensifying anti-androgen therapies administered prior to prostatectomy can induce pathologic complete responses (pCR) or minimal residual disease (MRD) (<5 mm), together termed exceptional response, although the molecular determinants of these clinical outcomes are largely unknown. Here, we performed whole exome (WES) and whole transcriptome sequencing (RNA-seq) on pre-treatment multi-regional tumor biopsies from exceptional responders (ER: pCR and MRD patients) and non-responders (NR: pathologic T3 or lymph node positive disease) treated with intensive anti-androgen therapies prior to prostatectomy. SPOP mutation and SPOPL copy number loss were exclusively observed in ER, while TP53 mutation and PTEN copy number loss were exclusively observed in NR. These alterations were clonal in all tumor phylogenies per patient. Additionally, transcriptional programs involving androgen signaling and TGFβ signaling were enriched in ER and NR, respectively. The presence of these alterations in routine biopsies from patients with HRLPC may inform the prospective identification of responders to neoadjuvant anti-androgen therapies to improve clinical outcomes and stratify other patients to alternative biologically informed treatment strategies.

Matthew Freedman and colleagues show that androgen receptor (AR) binding sites undergo extensive reprogramming during prostate epithelial transformation. They further show that FOXA1 and HOXB13 colocalize at reprogrammed AR binding sites in human tumor tissue and are able to reprogram the AR cistrome of an immortalized prostate cell line to resemble that of prostate tumors. Master transcription factors interact with DNA to establish cell type identity and to regulate gene expression in mammalian cells 1 , 2 . The genome-wide map of these transcription factor binding sites has been termed the cistrome 3 . Here we show that the androgen receptor (AR) cistrome undergoes extensive reprogramming during prostate epithelial transformation in man. Using human prostate tissue, we observed a core set of AR binding sites that are consistently reprogrammed in tumors. FOXA1 and HOXB13 colocalized at the reprogrammed AR binding sites in human tumor tissue. Introduction of FOXA1 and HOXB13 into an immortalized prostate cell line reprogrammed the AR cistrome to resemble that of a prostate tumor, functionally linking these specific factors to AR cistrome reprogramming. These findings offer mechanistic insights into a key set of events that drive normal prostate epithelium toward transformation and establish the centrality of epigenetic reprogramming in human prostate tumorigenesis.

Epigenetic processes govern prostate cancer (PCa) biology, as evidenced by the dependency of PCa cells on the androgen receptor (AR), a prostate master transcription factor. We generated 268 epigenomic datasets spanning two state transitions—from normal prostate epithelium to localized PCa to metastases—in specimens derived from human tissue. We discovered that reprogrammed AR sites in metastatic PCa are not created de novo; rather, they are prepopulated by the transcription factors FOXA1 and HOXB13 in normal prostate epithelium. Reprogrammed regulatory elements commissioned in metastatic disease hijack latent developmental programs, accessing sites that are implicated in prostate organogenesis. Analysis of reactivated regulatory elements enabled the identification and functional validation of previously unknown metastasis-specific enhancers at HOXB13 , FOXA1 and NKX3-1 . Finally, we observed that prostate lineage-specific regulatory elements were strongly associated with PCa risk heritability and somatic mutation density. Examining prostate biology through an epigenomic lens is fundamental for understanding the mechanisms underlying tumor progression. Analyses of epigenomic datasets spanning transitions from normal prostate epithelium to localized prostate cancer to metastases show that latent developmental programs are reactivated in metastatic disease and that prostate lineage-specific regulatory elements are strongly enriched for prostate cancer risk heritability.