Contribution of mutant HSC clones to immature and mature cells in MDS and CMML, and variations with AZA therapy.

Myelodysplastic neoplasms (MDSs) and chronic myelomonocytic leukemia (CMML) are clonal disorders driven by progressively acquired somatic mutations in hematopoietic stem cells (HSCs). Hypomethylating agents (HMAs) can modify the clinical course of MDS and CMML. Clinical improvement does not require eradication of mutated cells and may be related to improved differentiation capacity of mutated HSCs. However, in patients with established disease it is unclear whether (1) HSCs with multiple mutations progress through differentiation with comparable frequency to their less mutated counterparts or (2) improvements in peripheral blood counts following HMA therapy are driven by residual wild-type HSCs or by clones with particular combinations of mutations. To address these questions, the somatic mutations of individual stem cells, progenitors (common myeloid progenitors, granulocyte monocyte progenitors, and megakaryocyte erythroid progenitors), and matched circulating hematopoietic cells (monocytes, neutrophils, and naïve B cells) in MDS and CMML were characterized via high-throughput single-cell genotyping, followed by bulk analysis in immature and mature cells before and after AZA treatment. The mutational burden was similar throughout differentiation, with even the most mutated stem and progenitor clones maintaining their capacity to differentiate to mature cell types in vivo. Increased contributions from productive mutant progenitors appear to underlie improved hematopoiesis in MDS following HMA therapy.

Inorganic nanoparticle-based advanced cancer therapies: Promising combination strategies.

Inorganic nanoparticles for drug delivery in cancer treatment offer many potential advantages because they can maximize therapeutic effect through targeting ligands while minimizing off-target side-effects through drug adsorption and infiltration. Although inorganic nanoparticles were introduced as drug carriers, they have emerged as having the capacity for combined therapeutic capabilities, including anticancer effects through cytotoxicity, suppression of oncogenes and cancer cell signaling pathway inhibition. The most promising advanced strategies for cancer therapy are as synergistic platforms for RNA interference (siRNA, miRNA, shRNA) and as synergistic drug delivery agents for the inhibition of cancer cell signaling pathways. The present work summarizes relevant current work, the promise of which is suggested by a projected compound annual growth rate of âˆ¼ 20% for drug delivery alone.

The splicing factor RBM17 drives leukemic stem cell maintenance by evading nonsense-mediated decay of pro-leukemic factors.

Chemo-resistance in acute myeloid leukemia (AML) patients is driven by leukemic stem cells (LSCs) resulting in high rates of relapse and low overall survival. Here, we demonstrate that upregulation of the splicing factor, RBM17 preferentially marks and sustains LSCs and directly correlates with shorten patient survival. RBM17 knockdown in primary AML cells leads to myeloid differentiation and impaired colony formation and in vivo engraftment. Integrative multi-omics analyses show that RBM17 repression leads to inclusion of poison exons and production of nonsense-mediated decay (NMD)-sensitive transcripts for pro-leukemic factors and the translation initiation factor, EIF4A2. We show that EIF4A2 is enriched in LSCs and its inhibition impairs primary AML progenitor activity. Proteomic analysis of EIF4A2-depleted AML cells shows recapitulation of the RBM17 knockdown biological effects, including pronounced suppression of proteins involved in ribosome biogenesis. Overall, these results provide a rationale to target RBM17 and/or its downstream NMD-sensitive splicing substrates for AML treatment.

Mesoderm-derived PDGFRA+ cells regulate the emergence of hematopoietic stem cells in the dorsal aorta.

Mouse haematopoietic stem cells (HSCs) first emerge at embryonic day 10.5 (E10.5), on the ventral surface of the dorsal aorta, by endothelial-to-haematopoietic transition. We investigated whether mesenchymal stem cells, which provide an essential niche for long-term HSCs (LT-HSCs) in the bone marrow, reside in the aorta-gonad-mesonephros and contribute to the development of the dorsal aorta and endothelial-to-haematopoietic transition. Here we show that mesoderm-derived PDGFRA+ stromal cells (Mesp1der PSCs) contribute to the haemogenic endothelium of the dorsal aorta and populate the E10.5-E11.5 aorta-gonad-mesonephros but by E13.5 were replaced by neural-crest-derived PSCs (Wnt1der PSCs). Co-aggregating non-haemogenic endothelial cells with Mesp1der PSCs but not Wnt1der PSCs resulted in activation of a haematopoietic transcriptional programme in endothelial cells and generation of LT-HSCs. Dose-dependent inhibition of PDGFRA or BMP, WNT and NOTCH signalling interrupted this reprogramming event. Together, aorta-gonad-mesonephros Mesp1der PSCs could potentially be harnessed to manufacture LT-HSCs from endothelium.

Anticancer therapeutic effect of cerium-based nanoparticles: known and unknown molecular mechanisms.

Cerium-based nanoparticles (CeNPs), particularly cerium oxide (CeO2), have been studied extensively for their antioxidant and prooxidant properties. However, their complete redox and enzyme-mimetic mechanisms of therapeutic action at the molecular level remain elusive, constraining their potential for clinical translation. Although the therapeutic effects of both antioxidant and prooxidant mechanisms generally are attributed to Ce3+ ↔ Ce4+ redox switching mediation, some studies have hinted at the involvement of unknown pathways in therapeutic effects. While redox switching is recognised increasingly as playing a key role in ROS-dependent cancer therapy, ROS-independent cytotoxicity mechanisms, such as Ce4+ dissolution and autophagy, also are emerging as being of importance. Although ROS-mediated prooxidant therapies are the most intensively studied, particularly in the context of cancer, the antioxidant activity deriving from the redox switching, particularly during radiation therapy, also plays an important role in the protection of normal cells during radiation therapy, hence reducing adverse effects. Since cancer cell proliferation results in aberrant behaviour of the tumour microenvironment (TME), then CeNP-based therapies are being used to address a multiplicity of known and unknown factors that aim to normalise the TME and thus prevent this aberrant behaviour. Although it is perceived that the pH plays a key role in the therapeutic performance of cerium-based nanoparticles, this is not conclusive because the relative importances of other factors, particularly Ce dissolution, Ce3+/Ce4+ ratio, cellular H2O2 level, and the role of anions, remain poorly understood. Consequently, the present work explores these multiple chemistry-driven mechanisms, which are both ROS-dependent and ROS-independent, in cancer therapy.

Demethylation and Up-Regulation of an Oncogene after Hypomethylating Therapy.

BACKGROUND: Although hypomethylating agents are currently used to treat patients with cancer, whether they can also reactivate and up-regulate oncogenes is not well elucidated. METHODS: We examined the effect of hypomethylating agents on SALL4, a known oncogene that plays an important role in myelodysplastic syndrome and other cancers. Paired bone marrow samples that were obtained from two cohorts of patients with myelodysplastic syndrome before and after treatment with a hypomethylating agent were used to explore the relationships among changes in SALL4 expression, treatment response, and clinical outcome. Leukemic cell lines with low or undetectable SALL4 expression were used to study the relationship between SALL4 methylation and expression. A locus-specific demethylation technology, CRISPR-DNMT1-interacting RNA (CRISPR-DiR), was used to identify the CpG island that is critical for SALL4 expression. RESULTS: SALL4 up-regulation after treatment with hypomethylating agents was observed in 10 of 25 patients (40%) in cohort 1 and in 13 of 43 patients (30%) in cohort 2 and was associated with a worse outcome. Using CRISPR-DiR, we discovered that demethylation of a CpG island within the 5' untranslated region was critical for SALL4 expression. In cell lines and patients, we confirmed that treatment with a hypomethylating agent led to demethylation of the same CpG region and up-regulation of SALL4 expression. CONCLUSIONS: By combining analysis of patient samples with CRISPR-DiR technology, we found that demethylation and up-regulation of an oncogene after treatment with a hypomethylating agent can indeed occur and should be further studied. (Funded by Associazione Italiana per la Ricerca sul Cancro and others.).

Targeting an Inducible SALL4-Mediated Cancer Vulnerability with Sequential Therapy.

Oncofetal protein SALL4 is critical for cancer cell survival. Targeting SALL4, however, is only applicable in a fraction of cancer patients who are positive for this gene. To overcome this limitation, we propose to induce a cancer vulnerability by engineering a partial dependency upon SALL4. Following exogenous expression of SALL4, SALL4-negative cancer cells became partially dependent on SALL4. Treatment of SALL4-negative cells with the FDA-approved hypomethylating agent 5-aza-2'-deoxycytidine (DAC) resulted in transient upregulation of SALL4. DAC pretreatment sensitized SALL4-negative cancer cells to entinostat, which negatively affected SALL4 expression through a microRNA, miRNA-205, both in culture and in vivo. Moreover, SALL4 was essential for the efficiency of sequential treatment of DAC and entinostat. Overall, this proof-of-concept study provides a framework whereby the targeting pathways such as SALL4-centered therapy can be expanded, sensitizing cancer cells to treatment by transient target induction and engineering a dependency. SIGNIFICANCE: These findings provide a therapeutic approach for patients harboring no suitable target by induction of a SALL4-mediated vulnerability.

The RNA Atlas expands the catalog of human non-coding RNAs.

Existing compendia of non-coding RNA (ncRNA) are incomplete, in part because they are derived almost exclusively from small and polyadenylated RNAs. Here we present a more comprehensive atlas of the human transcriptome, which includes small and polyA RNA as well as total RNA from 300 human tissues and cell lines. We report thousands of previously uncharacterized RNAs, increasing the number of documented ncRNAs by approximately 8%. To infer functional regulation by known and newly characterized ncRNAs, we exploited pre-mRNA abundance estimates from total RNA sequencing, revealing 316 microRNAs and 3,310 long non-coding RNAs with multiple lines of evidence for roles in regulating protein-coding genes and pathways. Our study both refines and expands the current catalog of human ncRNAs and their regulatory interactions. All data, analyses and results are available for download and interrogation in the R2 web portal, serving as a basis for future exploration of RNA biology and function.

Human endogenous retroviruses form a reservoir of T cell targets in hematological cancers.

Human endogenous retroviruses (HERV) form a substantial part of the human genome, but mostly remain transcriptionally silent under strict epigenetic regulation, yet can potentially be reactivated by malignant transformation or epigenetic therapies. Here, we evaluate the potential for T cell recognition of HERV elements in myeloid malignancies by mapping transcribed HERV genes and generating a library of 1169 potential antigenic HERV-derived peptides predicted for presentation by 4 HLA class I molecules. Using DNA barcode-labeled MHC-I multimers, we find CD8+ T cell populations recognizing 29 HERV-derived peptides representing 18 different HERV loci, of which HERVH-5, HERVW-1, and HERVE-3 have more profound responses; such HERV-specific T cells are present in 17 of the 34 patients, but less frequently in healthy donors. Transcriptomic analyses reveal enhanced transcription of the HERVs in patients; meanwhile DNA-demethylating therapy causes a small and heterogeneous enhancement in HERV transcription without altering T cell recognition. Our study thus uncovers T cell recognition of HERVs in myeloid malignancies, thereby implicating HERVs as potential targets for immunotherapeutic therapies.

RNA Splicing Alterations Induce a Cellular Stress Response Associated with Poor Prognosis in Acute Myeloid Leukemia.

PURPOSE: RNA splicing is a fundamental biological process that generates protein diversity from a finite set of genes. Recurrent somatic mutations of splicing factor genes are common in some hematologic cancers but are relatively uncommon in acute myeloid leukemia (AML, < 20% of patients). We examined whether RNA splicing differences exist in AML, even in the absence of splicing factor mutations. EXPERIMENTAL DESIGN: We developed a bioinformatics pipeline to study alternative RNA splicing in RNA-sequencing data from large cohorts of patients with AML. RESULTS: We have identified recurrent differential alternative splicing between patients with poor and good prognosis. These splicing events occurred even in patients without any discernible splicing factor mutations. Alternative splicing recurrently occurred in genes with specific molecular functions, primarily related to protein translation. Developing tools to predict the functional impact of alternative splicing on the translated protein, we discovered that approximately 45% of the splicing events directly affected highly conserved protein domains. Several splicing factors were themselves misspliced and the splicing of their target transcripts were altered. Studying differential gene expression in the same patients, we identified that alternative splicing of protein translation genes in ELNAdv patients resulted in the induction of an integrated stress response and upregulation of inflammation-related genes. Finally, using machine learning techniques, we identified a splicing signature of four genes which refine the accuracy of existing risk prognosis schemes and validated it in a completely independent cohort. CONCLUSIONS: Our discoveries therefore identify aberrant alternative splicing as a molecular feature of adverse AML with clinical relevance.See related commentary by Bowman, p. 3503.

Constitutive CHK1 Expression Drives a pSTAT3-CIP2A Circuit that Promotes Glioblastoma Cell Survival and Growth.

High-constitutive activity of the DNA damage response protein checkpoint kinase 1 (CHK1) has been shown in glioblastoma (GBM) cell lines and in tissue sections. However, whether constitutive activation and overexpression of CHK1 in GBM plays a functional role in tumorigenesis or has prognostic significance is not known. We interrogated multiple glioma patient cohorts for expression levels of CHK1 and the oncogene cancerous inhibitor of protein phosphatase 2A (CIP2A), a known target of high-CHK1 activity, and examined the relationship between these two proteins in GBM. Expression levels of CHK1 and CIP2A were independent predictors for reduced overall survival across multiple glioma patient cohorts. Using siRNA and pharmacologic inhibitors we evaluated the impact of their depletion using both in vitro and in vivo models and sought a mechanistic explanation for high CIP2A in the presence of high-CHK1 levels in GBM and show that; (i) CHK1 and pSTAT3 positively regulate CIP2A gene expression; (ii) pSTAT3 and CIP2A form a recursively wired transcriptional circuit; and (iii) perturbing CIP2A expression induces GBM cell senescence and retards tumor growth in vitro and in vivo. Taken together, we have identified an oncogenic transcriptional circuit in GBM that can be destabilized by targeting CIP2A. IMPLICATIONS: High expression of CIP2A in gliomas is maintained by a CHK1-dependent pSTAT3-CIP2A recursive loop; interrupting CIP2A induces cell senescence and slows GBM growth adding impetus to the development of CIP2A as an anticancer drug target.

HMGA2 promotes long-term engraftment and myeloerythroid differentiation of human hematopoietic stem and progenitor cells.

Identification of determinants of fate choices in hematopoietic stem cells (HSCs) is essential to improve the clinical use of HSCs and to enhance our understanding of the biology of normal and malignant hematopoiesis. Here, we show that high-mobility group AT hook 2 (HMGA2), a nonhistone chromosomal-binding protein, is highly and preferentially expressed in HSCs and in the most immature progenitor cell subset of fetal, neonatal, and adult human hematopoiesis. Knockdown of HMGA2 by short hairpin RNA impaired the long-term hematopoietic reconstitution of cord blood (CB)-derived CB CD34+ cells. Conversely, overexpression of HMGA2 in CB CD34+ cells led to overall enhanced reconstitution in serial transplantation assays accompanied by a skewing toward the myeloerythroid lineages. RNA-sequencing analysis showed that enforced HMGA2 expression in CD34+ cells induced gene-expression signatures associated with differentiation toward megakaryocyte-erythroid and myeloid lineages, as well as signatures associated with growth and survival, which at the protein level were coupled with strong activation of AKT. Taken together, our findings demonstrate a key role of HMGA2 in regulation of both proliferation and differentiation of human HSPCs.

Srsf2P95H initiates myeloid bias and myelodysplastic/myeloproliferative syndrome from hemopoietic stem cells.

Mutations in SRSF2 occur in myelodysplastic syndromes (MDS) and MDS/myeloproliferative neoplasms (MPN). SRSF2 mutations cluster at proline 95, with the most frequent mutation being a histidine (P95H) substitution. They undergo positive selection, arise early in the course of disease, and have been identified in age-related clonal hemopoiesis. It is not clear how mutation of SRSF2 modifies hemopoiesis or contributes to the development of myeloid bias or MDS/MPN. Two prior mouse models of Srsf2P95H mutation have been reported; however, these models do not recapitulate many of the clinical features of SRSF2-mutant disease and relied on bone marrow (BM) transplantation stress to elicit the reported phenotypes. We describe a new conditional murine Srsf2P95H mutation model, where the P95H mutation is expressed physiologically and heterozygously from its endogenous locus after Cre activation. Using multiple Cre lines, we demonstrate that during native hemopoiesis (ie, no BM transplantation), the Srsf2P95H mutation needs to occur within the hemopoietic stem-cell-containing populations to promote myelomonocytic bias and expansion with corresponding transcriptional and RNA splicing changes. With age, nontransplanted Srsf2P95H animals developed a progressive, transplantable disease characterized by myeloid bias, morphological dysplasia, and monocytosis, hallmarks of MDS/MPN in humans. Analysis of cooccurring mutations within the BM demonstrated the acquisition of additional mutations that are recurrent in humans with SRSF2 mutations. The tractable Srsf2P95H/+ knock-in model we have generated is highly relevant to human disease and will serve to elucidate the effect of SRSF2 mutations on initiation and maintenance of MDS/MPN.

Integrative Genomics Identifies the Molecular Basis of Resistance to Azacitidine Therapy in Myelodysplastic Syndromes.

Myelodysplastic syndromes and chronic myelomonocytic leukemia are blood disorders characterized by ineffective hematopoiesis and progressive marrow failure that can transform into acute leukemia. The DNA methyltransferase inhibitor 5-azacytidine (AZA) is the most effective pharmacological option, but only ∼50% of patients respond. A response only manifests after many months of treatment and is transient. The reasons underlying AZA resistance are unknown, and few alternatives exist for non-responders. Here, we show that AZA responders have more hematopoietic progenitor cells (HPCs) in the cell cycle. Non-responder HPC quiescence is mediated by integrin α5 (ITGA5) signaling and their hematopoietic potential improved by combining AZA with an ITGA5 inhibitor. AZA response is associated with the induction of an inflammatory response in HPCs in vivo. By molecular bar coding and tracking individual clones, we found that, although AZA alters the sub-clonal contribution to different lineages, founder clones are not eliminated and continue to drive hematopoiesis even in complete responders.

Functional Mutations Form at CTCF-Cohesin Binding Sites in Melanoma Due to Uneven Nucleotide Excision Repair across the Motif.

CTCF binding sites are frequently mutated in cancer, but how these mutations accumulate and whether they broadly perturb CTCF binding are not well understood. Here, we report that skin cancers exhibit a highly specific asymmetric mutation pattern within CTCF motifs attributable to ultraviolet irradiation and differential nucleotide excision repair (NER). CTCF binding site mutations form independently of replication timing and are enriched at sites of CTCF/cohesin complex binding, suggesting a role for cohesin in stabilizing CTCF-DNA binding and impairing NER. Performing CTCF ChIP-seq in a melanoma cell line, we show CTCF binding site mutations to be functional by demonstrating allele-specific reduction of CTCF binding to mutant alleles. While topologically associating domains with mutated CTCF anchors in melanoma contain differentially expressed cancer-associated genes, CTCF motif mutations appear generally under neutral selection. However, the frequency and potential functional impact of such mutations in melanoma highlights the need to consider their impact on cellular phenotype in individual genomes.

A quantitative proteomics approach identifies ETV6 and IKZF1 as new regulators of an ERG-driven transcriptional network.

Aberrant stem cell-like gene regulatory networks are a feature of leukaemogenesis. The ETS-related gene (ERG), an important regulator of normal haematopoiesis, is also highly expressed in T-ALL and acute myeloid leukaemia (AML). However, the transcriptional regulation of ERG in leukaemic cells remains poorly understood. In order to discover transcriptional regulators of ERG, we employed a quantitative mass spectrometry-based method to identify factors binding the 321 bp ERG +85 stem cell enhancer region in MOLT-4 T-ALL and KG-1 AML cells. Using this approach, we identified a number of known binders of the +85 enhancer in leukaemic cells along with previously unknown binders, including ETV6 and IKZF1. We confirmed that ETV6 and IKZF1 were also bound at the +85 enhancer in both leukaemic cells and in healthy human CD34+ haematopoietic stem and progenitor cells. Knockdown experiments confirmed that ETV6 and IKZF1 are transcriptional regulators not just of ERG, but also of a number of genes regulated by a densely interconnected network of seven transcription factors. At last, we show that ETV6 and IKZF1 expression levels are positively correlated with expression of a number of heptad genes in AML and high expression of all nine genes confers poorer overall prognosis.