An alternative NURF complex sustains acute myeloid leukemia by regulating the accessibility of insulator regions.

Efficient treatment of acute myeloid leukemia (AML) patients remains a challenge despite recent therapeutic advances. Here, using a CRISPRi screen targeting chromatin factors, we identified the nucleosome-remodeling factor (NURF) subunit BPTF as an essential regulator of AML cell survival. We demonstrate that BPTF forms an alternative NURF chromatin remodeling complex with SMARCA5 and BAP18, which regulates the accessibility of a large set of insulator regions in leukemic cells. This ensures efficient CTCF binding and boundary formation between topologically associated domains that is essential for maintaining the leukemic transcriptional programs. We also demonstrate that the well-studied PHD2-BROMO chromatin reader domains of BPTF, while contributing to complex recruitment to chromatin, are dispensable for leukemic cell growth. Taken together, our results uncover how the alternative NURF complex contributes to leukemia and provide a rationale for its targeting in AML.

BRD4 and Cancer: going beyond transcriptional regulation.

BRD4, member of the Bromodomain and Extraterminal (BET) protein family, is largely acknowledged in cancer for its role in super-enhancers (SEs) organization and oncogenes expression regulation. Inhibition of BRD4 shortcuts the communication between SEs and target promoters with a subsequent cell-specific repression of oncogenes to which cancer cells are addicted and cell death. To date, this is the most credited mechanism of action of BET inhibitors, a class of small molecules targeting BET proteins which are currently in clinical trials in several cancer settings.However, recent evidence indicates that BRD4 relevance in cancer goes beyond its role in transcription regulation and identifies this protein as a keeper of genome stability.Indeed, a non-transcriptional role of BRD4 in controlling DNA damage checkpoint activation and repair as well as telomere maintenance has been proposed, throwing new lights into the multiple functions of this protein and opening new perspectives on the use of BETi in cancer. Here we discuss the current available information on non-canonical, non-transcriptional functions of BRD4 and on their implications in cancer biology. Integrating this information with the already known BRD4 role in gene expression regulation, we propose a "common" model to explain BRD4 genomic function. Furthermore, in light of the transversal function of BRD4, we provide new interpretation for the cytotoxic activity of BETi and we discuss new possibilities for a wide and focused employment of these drugs in clinical settings.

Linc00941 fuels ribogenesis and protein synthesis by supporting robust cMYC translation in malignant pleural mesothelioma.

Malignant pleural mesothelioma is a rare and lethal cancer caused by exposure to asbestos. The highly inflammatory environment caused by fibers accumulation forces cells to undergo profound adaptation to gain survival advantages. Prioritizing the synthesis of essential transcripts is an efficient mechanism coordinated by multiple molecules, including long non-coding RNAs. Enhancing the knowledge about these mechanisms is an essential weapon in combating mesothelioma. Linc00941 correlates to bad prognosis in various cancers, but it is reported to partake in distinct and apparently irreconcilable processes. In this work, we report that linc00941 supports the survival and aggressiveness of mesothelioma cells by influencing protein synthesis and ribosome biogenesis. Linc00941 binds to the translation initiation factor eIF4G, promoting the selective protein synthesis of cMYC, which, in turn, enhances the expression of key genes involved in translation. We analyzed a retrospective cohort of 97 mesothelioma patients' samples from our institution, revealing that linc00941 expression strongly correlates with reduced survival probability. This discovery clarifies linc00941's role in mesothelioma and proposes a unified mechanism of action for this lncRNA involving the selective translation of essential oncogenes, reconciling the discrepancies about its function.

Adding pieces to the puzzle of differentiated-to-anaplastic thyroid cancer evolution: the oncogene E2F7.

Anaplastic Thyroid Cancer (ATC) is the most aggressive and de-differentiated subtype of thyroid cancer. Many studies hypothesized that ATC derives from Differentiated Thyroid Carcinoma (DTC) through a de-differentiation process triggered by specific molecular events still largely unknown. E2F7 is an atypical member of the E2F family. Known as cell cycle inhibitor and keeper of genomic stability, in specific contexts its function is oncogenic, guiding cancer progression. We performed a meta-analysis on 279 gene expression profiles, from 8 Gene Expression Omnibus patient samples datasets, to explore the causal relationship between DTC and ATC. We defined 3 specific gene signatures describing the evolution from normal thyroid tissue to DTC and ATC and validated them in a cohort of human surgically resected ATCs collected in our Institution. We identified E2F7 as a key player in the DTC-ATC transition and showed in vitro that its down-regulation reduced ATC cells' aggressiveness features. RNA-seq and ChIP-seq profiling allowed the identification of the E2F7 specific gene program, which is mainly related to cell cycle progression and DNA repair ability. Overall, this study identified a signature describing DTC de-differentiation toward ATC subtype and unveiled an E2F7-dependent transcriptional program supporting this process.

KAP1 is a new non-genetic vulnerability of malignant pleural mesothelioma (MPM).

Malignant pleural mesothelioma (MPM) is a rare and incurable cancer, which incidence is increasing in many countries. MPM escapes the classical genetic model of cancer evolution, lacking a distinctive genetic fingerprint. Omics profiling revealed extensive heterogeneity failing to identify major vulnerabilities and restraining development of MPM-oriented therapies. Here, we performed a multilayered analysis based on a functional genome-wide CRISPR/Cas9 screening integrated with patients molecular and clinical data, to identify new non-genetic vulnerabilities of MPM. We identified a core of 18 functionally-related genes as essential for MPM cells. The chromatin reader KAP1 emerged as a dependency of MPM. We showed that KAP1 supports cell growth by orchestrating the expression of a G2/M-specific program, ensuring mitosis correct execution. Targeting KAP1 transcriptional function, by using CDK9 inhibitors resulted in a dramatic loss of MPM cells viability and shutdown of the KAP1-mediated program. Validation analysis on two independent MPM-patients sets, including a consecutive, retrospective cohort of 97 MPM, confirmed KAP1 as new non-genetic dependency of MPM and proved the association of its dependent gene program with reduced patients' survival probability. Overall these data: provided new insights into the biology of MPM delineating KAP1 and its target genes as building blocks of its clinical aggressiveness.

Molecular Fingerprints of Malignant Pleural Mesothelioma: Not Just a Matter of Genetic Alterations.

Malignant pleural mesothelioma (MPM) is a clinical emergency of our time. Being strongly associated with asbestos exposure, incidence of this cancer is ramping up these days in many industrialized countries and it will soon start to increase in many developing areas where the use of this silicate derivate is still largely in use. Deficiency of reliable markers for the early identification of these tumors and the limited efficacy of the currently available therapeutic options are the basis of the impressive mortality rate of MPM. These shortcomings reflect the very poor information available about the molecular basis of this disease. Results of the recently released deep profiling studies point to the epigenome as a central element in MPM development and progression. First, MPM is characterized by a low mutational burden and a highly peculiar set of mutations that hits almost exclusively epigenetic keepers or proteins controlling chromatin organization and function. Furthermore, asbestos does not seem to be associated with a distinctive mutational signature, while the precise mapping of epigenetic changes caused by this carcinogen has been defined, suggesting that alterations in epigenetic features are the driving force in the development of this disease. Last but not least, consistent evidence also indicates that, in the setting of MPM, chromatin rewiring and epigenetic alterations of cancer cells heavily condition the microenvironment, including the immune response. In this review we aim to point to the relevance of the epigenome in MPM and to highlight the dependency of this tumor on chromatin organization and function. We also intend to discuss the opportunity of targeting these mechanisms as potential therapeutic options for MPM.

Deep Sequencing Analysis Identified a Specific Subset of Mutations Distinctive of Biphasic Malignant Pleural Mesothelioma.

Malignant Pleural Mesothelioma (MPM) is a heterogeneous disease. Morphologically, three different phenotypes are distinguishable: epithelioid (e-), sarcomatoid (s-) and biphasic (biph-) MPM, the latest, being a mixture of e- and s-MPM cells. Being an intermediate entity, management of biph-MPM, remains debatable and controversial, with different guidelines recommending distinct approaches. Identification of biph-MPM associated genetic alterations, through deep sequencing analysis, may provide useful tools to understand these lesions. A retrospective cohort of 69 surgically resected MPMs, 39 biph-MPMs (56.5%) and 30 e-MPMs (43.5%) was selected. A separate set of 16 biph-MPM was used as validation set. Deep sequencing analysis on an MPM-specific custom panel (MPM_geneset) comprising 1041 amplicons spanning 34 genes was performed. A total of 588 variants and 5309 mutational events were detected. In total, 91.3% of MPMs showed at least one mutation and 76.8% showed co-occurrence of more than one alteration. Mutations in MXRA5 (p = 0.05) and NOD2 (p = 0.018) were significantly associated with biph-MPM both in the training and validation cohort and correlated with the extent of the sarcomatoid component. Mutations in NOD2 and XRCC6 correlated with patients' survival. We demonstrated that biph-MPM are associated with a specific mutation set, and that genetic analysis at diagnosis may improve patients' risk stratification.

PRMT5 methylome profiling uncovers a direct link to splicing regulation in acute myeloid leukemia.

Protein arginine methyltransferase 5 (PRMT5) has emerged as a promising cancer drug target, and three PRMT5 inhibitors are currently in clinical trials for multiple malignancies. In this study, we investigated the role of PRMT5 in human acute myeloid leukemia (AML). Using an enzymatic dead version of PRMT5 and a PRMT5-specific inhibitor, we demonstrated the requirement of the catalytic activity of PRMT5 for the survival of AML cells. We then identified PRMT5 substrates using multiplexed quantitative proteomics and investigated their role in the survival of AML cells. We found that the function of the splicing regulator SRSF1 relies on its methylation by PRMT5 and that loss of PRMT5 leads to changes in alternative splicing of multiple essential genes. Our study proposes a mechanism for the requirement of PRMT5 for leukemia cell survival and provides potential biomarkers for the treatment response to PRMT5 inhibitors.