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Changes in chromatin structure mediated by ATP-dependent nucleosome remodelers and histone modifying enzymes are integral to the process of gene regulation. Here, we review the roles of the SWI/SNF (switch/sucrose nonfermenting) and NuRD (nucleosome remodeling and deacetylase) and the Polycomb system in chromatin regulation and cancer. First, we discuss the basic molecular mechanism of nucleosome remodeling, and how this controls gene transcription. Next, we provide an overview of the functional organization and biochemical activities of SWI/SNF, NuRD, and Polycomb complexes. We describe how, in metazoans, the balance of these activities is central to the proper regulation of gene expression and cellular identity during development. Whereas SWI/SNF counteracts Polycomb, NuRD facilitates Polycomb repression on chromatin. Finally, we discuss how disruptions of this regulatory equilibrium contribute to oncogenesis, and how new insights into the biological functions of remodelers and Polycombs are opening avenues for therapeutic interventions on a broad range of cancer types.

EZH2 is an oncogene in non-Hodgkin lymphoma. Understanding the underlying pathogenic mechanisms will be essential to improve treatments for patients with EZH2 mutant lymphomas. Recently Donaldson-Collier and colleagues (Nat. Genet. 2019; published online January 28, https://doi.org/10.1038/s41588-018-0338-y) examined the effects of mutant EZH2 on the 3D architecture of the lymphoma genome, highlighting the potential relevance of chromatin folding dynamics.

This abstract was withdrawn by the authors. Citation Format: Loughman T, Wang C-JA, Dynoodt P, Fender B, Lopez-Ruiz C, Barron S, Stapleton S, O'Leary D, Fabre A, Quinn C, Nodin B, Jirström K, Bracken A, Gallagher WM. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-08-31.

The aim of the study was to assess the prognostic performance of a 6-gene molecular score (OncoMasTR Molecular Score [OMm]) and a composite risk score (OncoMasTR Risk Score [OM]) and to conduct a within-patient comparison against four routinely used molecular and clinicopathological risk assessment tools: Oncotype DX Recurrence Score, Ki67, Nottingham Prognostic Index and Clinical Risk Category, based on the modified Adjuvant! Online definition and three risk factors: patient age, tumour size and grade.Biospecimens and clinicopathological information for 404 Irish women also previously enrolled in the Trial Assigning Individualized Options for Treatment [Rx] were provided by 11 participating hospitals, as the primary objective of an independent translational study. Gene expression measured via RT-qPCR was used to calculate OMm and OM. The prognostic value for distant recurrence-free survival (DRFS) and invasive disease-free survival (IDFS) was assessed using Cox proportional hazards models and Kaplan-Meier analysis. All statistical tests were two-sided ones.OMm and OM (both with likelihood ratio statistic [LRS] P 0.001; C indexes = 0.84 and 0.85, respectively) were more prognostic for DRFS and provided significant additional prognostic information to all other assessment tools/factors assessed (all LRS P ≤ 0.002). In addition, the OM correctly classified more patients with distant recurrences (DRs) into the high-risk category than other risk classification tools. Similar results were observed for IDFS.Both OncoMasTR scores were significantly prognostic for DRFS and IDFS and provided additional prognostic information to the molecular and clinicopathological risk factors/tools assessed. OM was also the most accurate risk classification tool for identifying DR. A concise 6-gene signature with superior risk stratification was shown to increase prognosis reliability, which may help clinicians optimise treatment decisions.

The Ninth Annual Conference of “Anticancer Innovative Therapy”, organized by Fondazione IRCCS Istituto Nazionale dei Tumori di Milano (Fondazione IRCCS INT) and hosted by Hotel Michelangelo, was held in Milan on 25 January 2019. Cutting-edge science was presented in two main scientific sessions: i) pre-clinical evidences and new targets, and ii) clinical translation. The Keynote lecture entitled “Cancer stem cells (CSCs): metabolic strategies for their identification and eradication” presented by M. Lisanti, was one of the highlights of the conference.\ud \ud One key concept of the meeting was how the continuous advances in our knowledge about molecular mechanisms in various fields of research (cancer metabolism reprogramming, epigenetic regulation, transformation/invasiveness, and immunology, among others) are driving cancer research towards more effective personalized antineoplastic strategies. Specifically, recent preclinical data on the following topics were discussed: 1. Polycomb group proteins in cancer; 2. A d16HER2 splice variant is a flag of HER2 addiction across HER2-positive cancers; 3. Studying chromatin as a nexus between translational and basic research; 4. Metabolomic analysis in cancer patients; 5. CDK4-6 cyclin inhibitors: clinical activity and future perspectives as immunotherapy adjuvant; and 6. Cancer stem cells (CSCs): metabolic strategies for their identification and eradication. In terms of clinical translation, several novel approaches were presented: 1. Developing CAR-T cell therapies: an update of preclinical and clinical development at University of North Carolina; 2. Vγ9Vδ2 T-cell activation and immune suppression in multiple myeloma; 3. Predictive biomarkers for real-world immunotherapy: the cancer immunogram model in the clinical arena; and 4. Mechanisms of resistance to immune checkpoint blockade in solid tumors.\ud \ud Overall, the pre-clinical and clinical findings presented could pave the way to identify novel actionable therapeutic targets to significantly enhance the care of persons with cancer.

Developmental gene expression is tightly regulated through enhancer elements, which initiate dynamic spatio–temporal expression, and Polycomb response elements (PREs), which maintain stable gene silencing. These two cis-regulatory functions are thought to operate through distinct dedicated elements. By examining the occupancy of the Drosophila pleiohomeotic repressive complex (PhoRC) during embryogenesis, we revealed extensive co-occupancy at developmental enhancers. Using an established in vivo assay for PRE activity, we demonstrated that a subset of characterized developmental enhancers can function as PREs, silencing transcription in a Polycomb-dependent manner. Conversely, some classic Drosophila PREs can function as developmental enhancers in vivo, activating spatio–temporal expression. This study therefore uncovers elements with dual function: activating transcription in some cells (enhancers) while stably maintaining transcriptional silencing in others (PREs). Given that enhancers initiate spatio–temporal gene expression, reuse of the same elements by the Polycomb group (PcG) system may help fine-tune gene expression and ensure the timely maintenance of cell identities.

Several "moderate-risk breast cancer susceptibility genes" have been conclusively identified. Pathogenic mutations in these genes are thought to cause a two to fivefold increased risk of breast cancer. In light of the current development and use of multigene panel testing, the authors wanted to systematically obtain robust estimates of the cancer risk associated with loss-of-function mutations within these genes. An electronic search was conducted to identify studies that sequenced the full coding regions of ATM , CHEK2 , BRIP1 , PALB2 , NBS1 , and RAD50 in a general and gene-targeted approach. Inclusion was restricted to studies that sequenced the germline DNA in both high-risk cases and geographically matched controls. A meta-analysis was then performed on protein-truncating variants (PTVs) identified in the studies for an association with breast cancer risk. A total of 10,209 publications were identified, of which 64 studies comprising a total of 25,418 cases and 52,322 controls in the 6 interrogated genes were eligible under our selection criteria. The pooled odds ratios for PTVs in the susceptibility genes were at least >2.6. Additionally, mutations in these genes have shown geographic and ethnic variation. This comprehensive study emphasizes the fact that caution should be taken when identifying certain genes as moderate susceptibility with the lack of sufficient data, especially with regard to the NBS1 , RAD50 , and BRIP1 genes. Further data from case-control sequencing studies, and especially family studies, are warranted.

The identification of the breast cancer susceptibility genes BRCA1 and BRCA2 enhanced clinicians' ability to select high-risk individuals for aggressive surveillance and prevention, and led to the development of targeted therapies. However, BRCA1/2 mutations account for only 25% of familial breast cancer cases. To systematically identify rare, probably pathogenic variants in familial cases of breast cancer without BRCA1/2 mutations, we developed a list of 312 genes, and performed targeted DNA enrichment coupled to multiplex next-generation sequencing on 104 'BRCAx' patients and 101 geographically matched controls in Ireland. As expected, this strategy allowed us to identify mutations in several well-known high-susceptibility and moderate-susceptibility genes, including ATM (~ 5%), RAD50 (~ 3%), CHEK2 (~ 2%), TP53 (~ 1%), PALB2 (~ 1%), and MRE11A (~ 1%). However, we also identified novel pathogenic variants in 30 other genes, which, when taken together, potentially explain the etiology of the missing heritability in up to 35% of BRCAx patients. These included novel potential pathogenic mutations in MAP3K1, CASP8, RAD51B, ZNF217, CDKN2B-AS1, and ERBB2, including a splice site mutation, which we predict would generate a constitutively active HER2 protein. Taken together, this work extends our understanding of the genetics of familial breast cancer, and supports the need to implement hereditary multigene panel testing to more appropriately orientate clinical management.

Aims Women with inherited pathogenic mutations in the BRCA1 or BRCA2 genes have up to an 85% risk of developing breast cancer in their lifetime. However, only about 20% of familial breast cancer is attributed to mutations in BRCA1 and BRCA2, while a further 5–10% are attributed to mutations in other rare susceptibility genes such as TP53, STK11, PTEN, ATM and CHEK2. Despite extensive efforts to explain the missing heritability of this disease, the majority of familial clustering in breast cancer remains largely unexplained. We aim to analyze the pathology of familial cases of which no pathogenic mutation is yet identified. Methods We compared the pathological phenotype of BRCA1/BRCA2 negative familial breast cancer (BRCAx) to BRCA1-positive, BRCA2-positive and sporadic cases without a family history. Age-adjusted analysis is summarized in odd's ratios and confidence intervals for tumor type, grade, lymph node, ER and HER2 status. Results We found non-familial cases to be more likely to be ER positive ( P = 0.041) as compared with BRCAx tumors. More cases of lobular carcinoma were found with BRCAx as compared to BRCA1 tumors ( P = 0.05). After multivariate logistic regression analysis, BRCAx tumors are more likely ER positive ( P = 0.001) and HER2 positive ( P = 0.047) in comparison to BRCA1. Conversely, BRCAx cases are less likely to be ER positive ( P = 0.02) but more likely to be HER2 positive ( P = 0.021) as compared with BRCA2 tumors. Conclusion Our findings suggest that BRCA1, BRCA2 and BRCAx tumors differ in phenotype from non-familial and familial BRCA1-positive and BRCA2-positive tumors. Further studies will need to be performed in this important population in order to develop strategies for early detection and prevention.

535 Background: Multigene prognostic signatures (MGPS) can identify early stage breast cancer patients who may require less aggressive treatment. To be clinically useful, MGPSs must provide additional prognostic information to clinicopathological information routinely used by clinicians. The OncoMasTR MGPS was discovered via a novel bioinformatic transcriptional network analysis. OncoMasTR consists of genes – Master Transcription Regulators (MTRs) – that regulate previously known prognostic genes and have identified functional roles in several hallmarks of cancer including proliferation, invasion and metastasis. The OncoMasTR Molecular Score (OM) consists of just 3 MTRs. The OncoMasTR Risk Score (OncoMasTR) combines OM with lymph node status and tumour size, and categorises patients as low or high risk. The OncoMasTR Test has been analytically and clinically validated. Methods: MTR expression was measured by RT-qPCR in tissue from 404 patients enrolled in an independent translational trial (NCT02050750) that collected tissue and clinical data from patients enrolled in TAILORx in Ireland. OM, OncoMasTR and Oncotype DX Recurrence Score (RS) were compared on the additional prognostic value they provided to Ki67, Nottingham Prognostic Index (NPI) and other clinicopathological information for distant recurrence (DR) and invasive disease (ID). Results: OM (LRχ2 = 20.3, p < 0.00001, c-index = 0.84) and OncoMasTR (LRχ2 = 22.6, p < 0.00001, c-index = 0.85) were significantly prognostic, and more prognostic than RS (LRχ2 = 8.4, p = 0.004, c-index = 0.73) for DR. OM and OncoMasTR provided more additional prognostic information than RS to Ki67, NPI, tumour size, tumour grade, and age for DR. Similar results were found when OM, OncoMasTR and RS were compared on prognostic performance for ID. Conclusions: OM and OncoMasTR were significantly prognostic for DR and ID and added significant prognostic value to Ki67, NPI, and other clinicopathological information. Furthermore, OM and OncoMasTR showed superior prognostic performance to RS.

Introduction Cocaine- and amphetamine-regulated transcript (CART) peptides are neuropeptides involved in regulating physiological processes, such as feeding and drug reward. Recent studies have associated high CART expression with worse overall survival in patients with small-bowel carcinoid tumours and estrogen receptor-positive (ER+), lymph node-negative breast cancer. CART was also shown to be associated with poor patient response to tamoxifen, suggesting CART may play a role in conferring tamoxifen resistance. Materials and methods We have previously demonstrated that CART can impact the transcriptional activity of ERα through the use of western blotting and qPCR for specific ERα gene targets. RNA sequencing was carried out using a stable CART-inducible cell line model to identify genes which are upregulated/downregulated in cells expressing CART. Further, using our stable CART-inducible cell line model, we preformed ERα-Immunoprecipitation followed by in-solution mass spectrometry to identify differentially recruited protein complexes +/- CART expression. Results and discussion RNA sequencing revealed 156 significantly downregulated, and 100 significantly upregulated, genes in cells expressing CART (p Conclusion In conclusion, we suggest that CART expression results in the recruitment of chromatin remodelling complexes to ERα in order to facilitate the regulation of receptor function and this impacts on patient outcome. Citation Format: O'Connor DP, Mooney B, Das S, Klinger R, Moran B, Ni Chonghaile T, Cagney G, Bracken A, Gallagher WM. Expression of the cocaine- and amphetamine-regulated transcript (CART) recruits SWI/SNF chromatin remodelling complexes to the estrogen receptor [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-05-07.

SummaryThe chromatin remodeler CHD5 is expressed in neural tissue and is frequently deleted in aggressive neuroblastoma. Very little is known about the function of CHD5 in the nervous system or its mechanism of action. Here we report that depletion of Chd5 in the developing neocortex blocks neuronal differentiation and leads to an accumulation of undifferentiated progenitors. CHD5 binds a large cohort of genes and is required for facilitating the activation of neuronal genes. It also binds a cohort of Polycomb targets and is required for the maintenance of H3K27me3 on these genes. Interestingly, the chromodomains of CHD5 directly bind H3K27me3 and are required for neuronal differentiation. In the absence of CHD5, a subgroup of Polycomb-repressed genes becomes aberrantly expressed. These findings provide insights into the regulatory role of CHD5 during neurogenesis and suggest how inactivation of this candidate tumor suppressor might contribute to neuroblastoma.

Retinoic acid attenuates colitis and is associated with increased IL-22 production from γδ T cells and innate lymphoid cells and enhanced antimicrobial peptide expression., Retinoic acid (RA), a vitamin A metabolite, modulates mucosal T helper cell responses. Here we examined the role of RA in regulating IL-22 production by γδ T cells and innate lymphoid cells in intestinal inflammation. RA significantly enhanced IL-22 production by γδ T cells stimulated in vitro with IL-1β or IL-18 and IL-23. In vivo RA attenuated colon inflammation induced by dextran sodium sulfate treatment or Citrobacter rodentium infection. This was associated with a significant increase in IL-22 secretion by γδ T cells and innate lymphoid cells. In addition, RA treatment enhanced production of the IL-22–responsive antimicrobial peptides Reg3β and Reg3γ in the colon. The attenuating effects of RA on colitis were reversed by treatment with an anti–IL-22 neutralizing antibody, demonstrating that RA mediates protection by enhancing IL-22 production. To define the molecular events involved, we used chromatin immunoprecipitation assays and found that RA promoted binding of RA receptor to the IL-22 promoter in γδ T cells. Our findings provide novel insights into the molecular events controlling IL-22 transcription and suggest that one key outcome of RA signaling may be to shape early intestinal immune responses by promoting IL-22 synthesis by γδ T cells and innate lymphoid cells.

Cellular senescence is an irreversible arrest of proliferation. It is activated when a cell encounters stress such as DNA damage, telomere shortening or oncogene activation. Like apoptosis, it impedes tumour progression and acts as a barrier that pre-neoplastic cells must overcome during their evolution toward the full tumourigenic state. This review focuses on the role of transcriptional regulators in the control of cellular senescence, explores how their function is perturbed in cancer and discusses the potential to harness this knowledge for future cancer therapies.

Background: OncoMasTR is a new multigene prognostic test that was discovered via a novel transcriptional network analysis method that identified upstream Master Transcription Regulators (MTRs), which regulate previously identified prognostic biomarkers. The optimised OncoMasTR signature incorporating clinicopathological information has been shown to be significantly prognostic for predicting distant recurrence in two independent cohorts (TransATAC & a subset of TAILORx from participating Irish centres). The analytical performance characteristics of the OncoMasTR test, comprising solely three prognostic MTRs, were determined. Methods: Relative gene expression levels were measured by RT-qPCR. Assay precision and input ranges were determined using a panel of samples representative of low and high recurrence risk tested across a number of runs incorporating different sources of variation. Serial dilutions of a pooled patient RNA sample was used to establish the linear range and efficiency of the individual gene assays. Results: The overall standard deviation of the OncoMasTR risk score was 0.15, which represents less than 2% of the 10-unit risk score range. The majority of the variability in OncoMasTR results was related to within-run variation (78.2%) with other between-run variation sources contributing relatively little (PCR instrument (0.6%), assay operator (5.2%), reagent lots (7.3%) or loading position (8.7%)). Consistent risk scores were measured for individual samples from 40ng down to 500-fold RNA input range corresponding to CT values of 23 – 36, demonstrating the ability of the test to reliably detect low level expression of the OncoMasTR panel. Importantly, PCR efficiencies were similar for the individual MTR and reference gene assays which ranged from 79 – 95%. Conclusions: The OncoMasTR prognostic test displays robust analytical and clinical performance and is being launched as a CE-marked test. The concise nature of the three gene signature and a simplified workflow that can be readily adopted using standard laboratory equipment will enable convenient qualification by local laboratories for decentralised use. (Less)

Introduction Traditionally, many women with lymph node-negative breast cancer (LN-BC) are unnecessarily treated with chemotherapy. This highlights the importance of accurately predicting patient prognosis. We previously identified a novel prognostic signature encompassing a set of master transcriptional regulators (MTRs), termed OncoMasTR. At the mRNA level, OncoMasTR predicted recurrence risk for LN-BC better than current prognostic signatures and accurately classifies >50% of patients as ‘low-risk', thus potentially reducing overtreatment. Here, we describe ongoing validation of the OncoMasTR biomarker signature at the protein level. Methods Commercially available antibodies targeted against markers were validated by Western blotting and immunohistochemistry (IHC) using CRISPR/Cas9 knockout cell-lines and full-face BC sections. IHC was performed on tissue microarrays (TMAs) containing multiple tumour cores from BC patients. Visiopharm's Oncotopix algorithm was used for image analysis, with stained sections verified manually by a pathologist. Image analysis data was obtained, and cut-off points optimised by maximum Chi-square values were used to differentiate low and high expression of individual markers. This was combined with clinical data to generate Kaplan-Meier survival curves. Multivariate analysis was used to determine the optimal combination of biomarkers. Results Antibodies against eight components of the OncoMasTR signature have been validated. IHC analysis demonstrated highly-specific nuclear staining for seven of the markers (UHRF1, ATAD2, HMGB2, E2F1, TCF19, MYBL2, PTTG1), whilst one showed both nuclear and cytoplasmic staining (p16). Image analysis for UHRF1, ATAD2 and HMGB2, using both manual and automated histological scores, showed that high expression of these biomarkers is linked with reduced survival. Additionally, UHRF1 was confirmed to have the same survival correlation in another independent cohort. Interestingly, high nuclear expression of p16 is linked with prolonged survival whilst high cytoplasmic expression of p16 is associated with poorer survival, aligning with previous reports. Conclusions The OncoMasTR signature offers a more accurate stratification of low-vs-high risk, thus showing promise in improving prognosis prediction for early-stage BC. This will translate to reduced overtreatment, decreased costs, improved survival rates and enhanced quality of life for patients. Citation Format: Arman Rahman, Seodhna Lynch, Nebras Alattar, Niamh Niamh, Charles Weige,, Romina Silva, Claudia Aura, Fiona Lanigan, Adrian Bracken, Björn Nodin, Karin Jirström, William Gallagher. Refining treatment recommendations for lymph node-negative breast cancer patients using a novel protein-based prognostic signature: The OncoMasTR assay [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-230.

© 2015 FEBS. The majority of women diagnosed with lymph node-negative breast cancer are unnecessarily treated with damaging chemotherapeutics after surgical resection. This highlights the importance of understanding and more accurately predicting patient prognosis. In the present study, we define the transcriptional networks regulating well-established prognostic gene expression signatures. We find that the same set of transcriptional regulators consistently lie upstream of both 'prognosis' and 'proliferation' gene signatures, suggesting that a central transcriptional network underpins a shared phenotype within these signatures. Strikingly, the master transcriptional regulators within this network predict recurrence risk for lymph node-negative breast cancer better than currently used multigene prognostic assays, particularly in estrogen receptor-positive patients. Simultaneous examination of p16INK4Aexpression, which predicts tumours that have bypassed cellular senescence, revealed that intermediate levels of p16INK4A correlate with an intact pRB pathway and improved survival. A combination of these master transcriptional regulators and p16INK4A, termed the OncoMasTR score, stratifies tumours based on their proliferative and senescence capacity, facilitating a clearer delineation of lymph node-negative breast cancer patients at high risk of recurrence, and thus requiring chemotherapy. Furthermore, OncoMasTR accurately classifies over 60% of patients as 'low risk', an improvement on existing prognostic assays, which has the potential to reduce overtreatment in early-stage patients. Taken together, the present study provides new insights into the transcriptional regulation of cellular proliferation in breast cancer and provides an opportunity to enhance and streamline methods of predicting breast cancer prognosis.

e23201 Background: Master transcriptional regulators (MTRs) are genes that are highly connected with many other genes and which can contribute to a specific cellular phenotype. The OncoMasTR panel, a set of 10 proliferation-linked MTRs and the key regulator of senescence CDKN2A, was identified in lymph node-negative breast cancer patients using publicly available data (Lanigan et al FEBS 2015 10.1111/febs.13354). Using two prognostic gene signatures and an experimentally defined ‘proliferative’ signature, highly concordant results for the top ranking sets of MTRs were found. One advantage of this process was the distillation of gene signatures into a discrete, mechanistically anchored biomarker set shown to be prognostically relevant, particularly in ER-positive patients, and with an ability to discriminate patients into low versus high risk of recurrence. Our aim here was to determine if the OncoMasTR panel was similarly useful in multiple other cancer types using publicly available transcriptomic data. Methods: The Gene Expression Omnibus was queried for datasets with relevant overall-, disease free- and/or recurrence free-survival information alongside microarray gene expression data. Survival analysis was conducted on 34 datasets using the R statistical environment package ‘survival’. Patient samples were scored based on median or tertile expression which were summed to give a final OncoMasTR RNA score, used to divide the patient samples into two groups (low and high risk) for analysis. Results: Using all 2,047 possible combinations of genes, a total of 23 datasets had significant prognostic associations. Following appropriate correction via multiple testing, this was reduced to 4 datasets representing bladder, lung and colorectal cancers, and multiple myeloma. Hazard ratios for the top 100 combinations in each data set were 1.8 – 2.1, 1.6 – 1.9, 1.1 – 1.3, 1.3 – 1.5 (standard error ±0.2, 0.1, 0.2, 0.1) respectively. All genes were found in the top ten combinations in all 4 datasets, and no specific combination was found to be prevalent across datasets, indicating that every MTR in the OncoMasTR panel contributes to its utility. Conclusions: The OncoMasTR panel is potentially prognostically useful in multiple cancer types.

The Polycomb group (PcG) proteins are transcriptional repressors that regulate lineage choices during development and differentiation. Recent studies have advanced our understanding of how the PcG proteins regulate cell fate decisions and how their deregulation potentially contributes to cancer. In this Review we discuss the emerging roles of long non-coding RNAs (ncRNAs) and a subset of transcription factors, which we call cell fate transcription factors, in the regulation of PcG association with target genes. We also speculate about how their deregulation contributes to tumorigenesis.

43 Background: Predicting the risk of tumour recurrence, and thus the need for chemotherapy, for lymph node-negative breast cancer patients is a significant problem for clinicians and patients. Methods: We have identified a ‘core proliferation signature,’ which is consistently high in proliferating primary cultures, and is downregulated during cellular senescence. Using a reverse engineering approach on a breast cancer-specific regulatory network, and confirmed by ChIP-seq analysis, we have identified a hierarchy of several highly interconnected Master Transcriptional Regulators upstream of these core proliferation genes. Results: Further analysis of the expression of these factors in breast cancer cohorts at the mRNA and protein levels reveals a remarkable ability to reliably predict recurrence risk for early-stage breast cancer. Strikingly, in our analyses, a combination of just two of these factors outperforms the currently used clinical biomarkers for breast cancer recurrence risk, as well as recently developed multi-gene prognostic assays. Moreover, the addition of the senescence regulator p16INK4A to this panel further increases its prognostic capability. Conclusions: We propose that this novel approach has succeeded in identifying ‘drivers’ of breast cancer proliferation which, when combined with a marker of senescence such as p16INK4A, successfully identify actively proliferating tumours with an impaired senescence response pathway. Furthermore, we suggest that this gene combination has the potential to become an improved prognostic assay for early-stage breast cancer.

The chromatin remodeler CHD5 is expressed in neural tissues and is frequently deleted in aggressive neuroblastoma. Very little is known about the normal function of CHD5, its mechanism of action or how its deletion may contribute to neuroblastoma. Here we report that depletion of CHD5 in the developing murine neocortex blocks neuronal differentiation leading to an accumulation of undifferentiated progenitors. Consistent with this, ChIP-SEQ analysis of CHD5 shows it binds a large cohort of neuronal genes and is required for facilitating their activation during differentiation. However, CHD5 also binds a cohort of Polycomb target genes and is required for the maintenance of H3K27me3 on their promoters and their sustained repression during differentiation. Finally, we show that the chromodomains of CHD5 directly bind H3K27me3 and are essential for the function of CHD5 during neuronal differentiation. These findings provide new insights into the essential role of CHD5 during neurogenesis and show how the inactivation of this candidate tumor suppressor might contribute to the progression of neuroblastoma via a defect in differentiation. This abstract is also presented as Poster A05. Citation Format: Christopher M. Egan, Ulrika Nyman, Julie Skotte, Gundula Streubel, Siobhán Turner, David J. O'Connell, Vilma Rraklli, Michael J. Dolan, Naomi Chadderton, Hansen Klaus, Farrar Gwyneth Jane, Kristian Helin, Johan Holmberg, Adrian P. Bracken. CHD5 is required for neurogenesis and has a dual role in facilitating gene expression and Polycomb gene repression. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr PR12.

Epigenetic deregulation of gene expression is emerging as key mechanism in tumorigenesis. Deregulated activity of the chromatin remodeling Polycomb Repressive Complex 2 (PRC2) has recently been shown to be a frequent event in human tumors. Here we discuss these findings and speculate on the role of the PRC2 complex in controlling gene expression during normal cellular proliferation and cancer development.