Pbx3 and Meis1 cooperate through multiple mechanisms to support Hox-induced murine leukemia

Low expression of miR-182 caused by DNA hypermethylation accelerates acute lymphocyte leukemia development by targeting PBX3 and BCL2: miR-182 promoter methylation is a predictive marker for hypomethylation agents + BCL2 inhibitor venetoclax

BACKGROUND

miR-182 promoter hypermethylation frequently occurs in various tumors, including acute myeloid leukemia, and leads to low expression of miR-182. However, whether adult acute lymphocyte leukemia (ALL) cells have high miR-182 promoter methylation has not been determined.

METHODS

To assess the methylation status of the miR-182 promoter, methylation and unmethylation-specific PCR analysis, bisulfite-sequencing analysis, and MethylTarget™ assays were performed to measure the frequency of methylation at the miR-182 promoter. Bone marrow cells were isolated from miR-182 knockout (182KO) and 182 wild type (182WT) mice to construct BCR-ABL (P190) and Notch-induced murine B-ALL and T-ALL models, respectively. Primary ALL samples were performed to investigate synergistic effects of the hypomethylation agents (HMAs) and the BCL2 inhibitor venetoclax (Ven) in vitro.

RESULTS

miR-182 (miR-182-5P) expression was substantially lower in ALL blasts than in normal controls (NCs) because of DNA hypermethylation at the miR-182 promoter in ALL blasts but not in normal controls (NCs). Knockout of miR-182 (182KO) markedly accelerated ALL development, facilitated the infiltration, and shortened the OS in a BCR-ABL (P190)-induced murine B-ALL model. Furthermore, the 182KO ALL cell population was enriched with more leukemia-initiating cells (CD43+B220+ cells, LICs) and presented higher leukemogenic activity than the 182WT ALL population. Furthermore, depletion of miR-182 reduced the OS in a Notch-induced murine T-ALL model, suggesting that miR-182 knockout accelerates ALL development. Mechanistically, overexpression of miR-182 inhibited proliferation and induced apoptosis by directly targeting PBX3 and BCL2, two well-known oncogenes, that are key targets of miR-182. Most importantly, DAC in combination with Ven had synergistic effects on ALL cells with miR-182 promoter hypermethylation, but not on ALL cells with miR-182 promoter hypomethylation.

CONCLUSIONS

Collectively, we identified miR-182 as a tumor suppressor gene in ALL cells and low expression of miR-182 because of hypermethylation facilitates the malignant phenotype of ALL cells. DAC + Ven cotreatment might has been applied in the clinical try for ALL patients with miR-182 promoter hypermethylation. Furthermore, the methylation frequency at the miR-182 promoter should be a potential biomarker for DAC + Ven treatment in ALL patients.

Single-cell analysis of shared signatures and transcriptional diversity during zebrafish development

During development, animals generate distinct cell populations with specific identities, functions, and morphologies. We mapped transcriptionally distinct populations across 489,686 cells from 62 stages during wild-type zebrafish embryogenesis and early larval development (3-120 h post-fertilization). Using these data, we identified the limited catalog of gene expression programs reused across multiple tissues and their cell-type-specific adaptations. We also determined the duration each transcriptional state is present during development and identify unexpected long-term cycling populations. Focused clustering and transcriptional trajectory analyses of non-skeletal muscle and endoderm identified transcriptional profiles and candidate transcriptional regulators of understudied cell types and subpopulations, including the pneumatic duct, individual intestinal smooth muscle layers, spatially distinct pericyte subpopulations, and recently discovered best4+ cells. To enable additional discoveries, we make this comprehensive transcriptional atlas of early zebrafish development available through our website, Daniocell.

The MLL-Menin Interaction is a Therapeutic Vulnerability in NUP98-rearranged AML

Chromosomal translocations involving the NUP98 locus are among the most prevalent rearrangements in pediatric acute myeloid leukemia (AML). AML with NUP98 fusions is characterized by high expression of HOXA and MEIS1 genes and is associated with poor clinical outcome. NUP98 fusion proteins are recruited to their target genes by the mixed lineage leukemia (MLL) complex, which involves a direct interaction between MLL and Menin. Here, we show that therapeutic targeting of the Menin-MLL interaction inhibits the propagation of NUP98-rearrranged AML both ex vivo and in vivo. Treatment of primary AML cells with the Menin inhibitor revumenib (SNDX-5613) impairs proliferation and clonogenicity ex vivo in long-term coculture and drives myeloid differentiation. These phenotypic effects are associated with global gene expression changes in primary AML samples that involve the downregulation of many critical NUP98 fusion protein-target genes, such as MEIS1 and CDK6. In addition, Menin inhibition reduces the expression of both wild-type FLT3 and mutated FLT3-ITD, and in combination with FLT3 inhibitor, suppresses patient-derived NUP98-r AML cells in a synergistic manner. Revumenib treatment blocks leukemic engraftment and prevents leukemia-associated death of immunodeficient mice transplanted with NUP98::NSD1 FLT3-ITD-positive patient-derived AML cells. These results demonstrate that NUP98-rearranged AMLs are highly susceptible to inhibition of the MLL-Menin interaction and suggest the inclusion of AML patients harboring NUP98 fusions into the clinical evaluation of Menin inhibitors.

Developmentally regulated expression of integrin alpha-6 distinguishes neural crest derivatives in the skin

Neural crest-derived cells play essential roles in skin function and homeostasis. However, how they interact with environmental cues and differentiate into functional skin cells remains unclear. Using a combination of single-cell data analysis, neural crest lineage tracing, and flow cytometry, we found that the expression of integrin α6 (ITGA6) in neural crest and its derivatives was developmentally regulated and that ITGA6 could serve as a functional surface marker for distinguishing neural crest derivatives in the skin. Based on the expression of ITGA6, Wnt1-Cre lineage neural crest derivatives in the skin could be categorized into three subpopulations, namely, ITGA6^bright, ITGA6^dim, and ITGA6^neg, which were found to be Schwann cells, melanocytes, and fibroblasts, respectively. We further analyzed the signature genes and transcription factors that specifically enriched in each cell subpopulation, as well as the ligand or receptor molecules, mediating the potential interaction with other cells of the skin. Additionally, we found that Hmx1 and Lhx8 are specifically expressed in neural crest-derived fibroblasts, while Zic1 and homeobox family genes are expressed in mesoderm-derived fibroblasts, indicating the distinct development pathways of fibroblasts of different origins. Our study provides insights into the regulatory landscape of neural crest cell development and identifies potential markers that facilitate the isolation of different neural crest derivatives in the skin.

Single-cell analysis of shared signatures and transcriptional diversity during zebrafish development

During development, animals generate distinct cell populations with specific identities, functions, and morphologies. We mapped transcriptionally distinct populations across 489,686 cells from 62 stages during wild-type zebrafish embryogenesis and early larval development (3-120 hours post-fertilization). Using these data, we identified the limited catalog of gene expression programs reused across multiple tissues and their cell-type-specific adaptations. We also determined the duration each transcriptional state is present during development and suggest new long-term cycling populations. Focused analyses of non-skeletal muscle and the endoderm identified transcriptional profiles of understudied cell types and subpopulations, including the pneumatic duct, individual intestinal smooth muscle layers, spatially distinct pericyte subpopulations, and homologs of recently discovered human best4+ enterocytes. The transcriptional regulators of these populations remain unknown, so we reconstructed gene expression trajectories to suggest candidates. To enable additional discoveries, we make this comprehensive transcriptional atlas of early zebrafish development available through our website, Daniocell.

Evaluation of the HOXA9 and MEIS1 genes as a potential biomarker in adult acute myeloid leukemia

Background

Acute myeloid leukemia (AML) is a heterogeneous disorder encompassing a set of hematopoietic tumors that develop when the myeloid precursor cells undergo disproportionate clonal proliferation. Homeobox A 9 (HOXA9) is a pioneer transcription factor in AML pathogenesis along with its cofactor myeloid ecotropic integration site 1 (MEIS1). Our work aimed to evaluate the different expression levels of HOXA9 and MEIS1 genes and their diagnostic and prognostic significance in adult Egyptian patients with de novo AML. The study was carried out on 91 de novo AML Egyptian patients and 41 healthy individuals. Bone marrow samples were obtained from both patients and controls and then tested by reverse transcription-quantitative polymerase chain reaction to assess the mRNA expression in the studied genes.

Results

HOXA9 and MEIS1 gene expression levels were significantly elevated in AML patients compared to controls (p < 0.001). There was a statistically significant positive correlation between HOXA9 and MEIS1 gene expression in AML patients. However, there was no association between HOXA9 and MEIS1 gene expression levels and disease-free survival (DFS) and overall survival (OS) (p = 0.264 and 0.351, respectively).

Conclusion

HOXA9 and MEIS1 genes are highly expressed in Egyptian AML patients, suggesting their interesting pathogenic role in AML. They could be used as markers for the diagnosis of AML, but not for the disease prognosis.

In toto imaging of early enteric nervous system development reveals that gut colonization is tied to proliferation downstream of Ret

The enteric nervous system is a vast intrinsic network of neurons and glia within the gastrointestinal tract and is largely derived from enteric neural crest cells (ENCCs) that emigrate into the gut during vertebrate embryonic development. Study of ENCC migration dynamics and their genetic regulators provides great insights into fundamentals of collective cell migration and nervous system formation, and these are pertinent subjects for study due to their relevance to the human congenital disease Hirschsprung disease (HSCR). For the first time, we performed in toto gut imaging and single-cell generation tracing of ENCC migration in wild type and a novel ret heterozygous background zebrafish (retwmr1/+) to gain insight into ENCC dynamics in vivo. We observed that retwmr1/+ zebrafish produced fewer ENCCs localized along the gut, and these ENCCs failed to reach the hindgut, resulting in HSCR-like phenotypes. Specifically, we observed a proliferation-dependent migration mechanism, where cell divisions were associated with inter-cell distances and migration speed. Lastly, we detected a premature neuronal differentiation gene expression signature in retwmr1/+ ENCCs. These results suggest that Ret signaling may regulate maintenance of a stem state in ENCCs.

Menin-MLL protein-protein interaction inhibitors: a patent review (2014-2021)

INTRODUCTION

Chromosomal translocations involving the mixed-lineage leukemia (MLL, KMT2A, MLL1) genes result in the production of MLL fusion proteins, which cause abnormal transcriptional regulation leading to acute leukemia (AL). Menin (MEN1) protein is essential for MLL to regulate the expression of related target genes. High affinity interactions between the amino terminus of MLL proteins and Menin proteins are required to mediate the oncogenic transformation of MLL fusion proteins. Therefore, inhibition of Menin and MLL interaction is a potential therapeutic strategy for MLL rearrangement (MLL-r) leukemia and can provide a new choice for treatment of other diseases. Therefore, researchers have made great efforts to explore small molecule Menin-MLL interaction inhibitors.

AREAS COVERED

This review is to provide an overview of the patented Menin-MLL protein protein interaction inhibitors from 2014 to 2021.

EXPERT OPINION

Menin-MLL interaction inhibitors have therapeutic potential in the treatment of acute leukemia, such as acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). Nowadays, SNDX-5613 and KO-539 have been granted orphan drug designation by the FDA for treatment of refractory/relapsed leukemia and AML, respectively. In addition, they are undergoing clinical evaluation for other indications. It is clear that Menin-MLL interaction inhibitors have promising benefits in the clinical treatment of acute leukemia and other diseases.

Recent Progress of Small Molecule Menin-MLL Interaction Inhibitors as Therapeutic Agents for Acute Leukemia

Mixed lineage leukemia (MLL) gene rearrangements are associated with acute leukemia. The protein menin is regarded as a critical oncogenic cofactor of the resulting MLL fusion proteins in acute leukemia. A direct interaction between menin and the MLL amino terminal sequences is necessary for MLL fusion protein-mediated leukemogenesis. Thus, inhibition of the interaction between menin and MLL has emerged as a novel therapeutic strategy. Recent improvements in structural biology and chemical reactivity have promoted the design and development of selective and potent menin-MLL interaction inhibitors. In this Perspective, different classes of menin-MLL interaction inhibitors are comprehensively summarized. Further research potential, challenges, and opportunities in the field are also discussed.

Transcription factor Meis1 act as a new regulator of ischemic arrhythmias in mice

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The reduction of Meis1 after MI leads to an increased susceptibility to arrhythmia.

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Meis1 deficiency is related to ubiquitination proteasome pathway mediated by CDC20.

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Meis1 acts as a new transcription activator for SCN5A in cardiomyocytes.

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After Meis1 recovery, the electrophysiological function in cardiomyocytes are improved.

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Meis1 is a new target for the treatment of arrhythmia after myocardial infarction.

Introduction

Objectives

Methods

Results

Conclusion

MEIS1 in Hematopoiesis and Cancer. How MEIS1-PBX Interaction Can Be Used in Therapy

Recently MEIS1 emerged as a major determinant of the MLL-r leukemic phenotype. The latest and most efficient drugs effectively decrease the levels of MEIS1 in cancer cells. Together with an overview of the latest drugs developed to target MEIS1 in MLL-r leukemia, we review, in detail, the role of MEIS1 in embryonic and adult hematopoiesis and suggest how a more profound knowledge of MEIS1 biochemistry can be used to design potent and effective drugs against MLL-r leukemia. In addition, we present data showing that the interaction between MEIS1 and PBX1 can be blocked efficiently and might represent a new avenue in anti-MLL-r and anti-leukemic therapy.

A genetic screen in Drosophila uncovers the multifaceted properties of the NUP98-HOXA9 oncogene

Acute myeloid leukemia (AML) underlies the uncontrolled accumulation of immature myeloid blasts. Several cytogenetic abnormalities have been associated with AML. Among these is the NUP98-HOXA9 (NA9) translocation that fuses the Phe-Gly repeats of nucleoporin NUP98 to the homeodomain of the transcription factor HOXA9. The mechanisms enabling NA9-induced leukemia are poorly understood. Here, we conducted a genetic screen in Drosophila for modifiers of NA9. The screen uncovered 29 complementation groups, including genes with mammalian homologs known to impinge on NA9 activity. Markedly, the modifiers encompassed a diversity of functional categories, suggesting that NA9 perturbs multiple intracellular events. Unexpectedly, we discovered that NA9 promotes cell fate transdetermination and that this phenomenon is greatly influenced by NA9 modifiers involved in epigenetic regulation. Together, our work reveals a network of genes functionally connected to NA9 that not only provides insights into its mechanism of action, but also represents potential therapeutic targets.

Acute myeloid leukemia or AML is a cancer of blood cells. Despite significant progress in recent years, a majority of afflicted individuals still succumbs to the disease. A variety of genetic defects have been associated to AML. Among these are chromosomal translocations, which entail the fusion of two genes, leading to the production of cancer-inducing chimeric proteins. A representative example is the NUP98-HOXA9 oncoprotein, which results from the fusion of the NUP98 and HOXA9 genes. The mechanism of action of NUP98-HOXA9 remains poorly understood. Given the evolutionarily conservation of NUP98 and HOXA9 as well as basic cellular processes across multicellular organisms, we took advantage of Drosophila fruit flies as a genetic tool to identify genes that impinge on the activity of human NUP98-HOXA9. Surprisingly, this approach identified a relatively large spectrum of conserved genes that engaged in functional interplay with NUP98-HOXA9, which indicated the pervasive effects that this oncogene has on basic cellular events. While some genes have been previously linked to NUP98-HOXA9, thus validating our experimental approach, several others are novel and as such represent potentially new avenues for therapeutic intervention.

MEIS1 and its potential as a cancer therapeutic target (Review)

Meis homeobox 1 (Meis1) was initially discovered in 1995 as a factor involved in leukemia in an animal model. Subsequently, 2 years later, MEIS1, the human homolog, was cloned in the liver and cerebellum, and was found to be highly expressed in myeloid leukemia cells. The MEIS1 gene, located on chromosome 2p14, encodes a 390-amino acid protein with six domains. The expression of homeobox protein MEIS1 is affected by cell type, age and environmental conditions, as well as the pathological state. Certain types of modifications of MEIS1 and its protein interaction with homeobox or pre-B-cell leukemia homeobox proteins have been described. As a transcription factor, MEIS1 protein is involved in cell proliferation in leukemia and some solid tumors. The present review article discusses the molecular biology, modifications, protein-protein interactions, as well as the role of MEIS1 in cell proliferation of cancer cells and MEIS1 inhibitors. It is suggested by the available literature MEIS1 has potential to become a cancer therapeutic target.

LncRNA CD27-AS1 promotes acute myeloid leukemia progression through the miR-224-5p/PBX3 signaling circuit

Acute myeloid leukemia (AML) is a hematological malignancy with a low cure rate, especially in the elderly. Previous studies have shown that long non-coding RNA (lncRNA) may be an important factor in the pathogenesis of hematological malignancies, including acute myeloid leukemia (AML). However, the biological roles and clinical significances of most lncRNAs in AML are not fully understood. LncRNA CD27 Antisense RNA 1 (CD27-AS1), as a member of lncRNA family, has rare reports on its function. In present study, we found that the expression of CD27-AS1 examined by quantitative real-time PCR was markedly increased in the AML patients (N = 40) compared with healthy volunteers (N = 40). The overall survival time was significantly shorter in patients with higher CD27-AS1 expression than that in patients with lower CD27-AS1 (P < 0.01). Furthermore, downregulation of CD27-AS1 in AML cells suppressed proliferative ability, arrested cell cycle in G0/G1 phase, and induced apoptosis. However, CD27-AS1 overexpression further enhanced the malignant phenotype of AML cells. Additionally, CD27-AS1 was proved to increase PBX3 expression through sponging miR-224-5p. CD27-AS1 knockdown blocked the MAPK signaling through PBX3 silencing and further inhibited the cell growth of AML cells. Taken together, we demonstrate that CD27-AS1 may be a potential prognostic biomarker of AML, and our finding also provides a new insight for non-coding RNA-based therapeutic intervention of AML.

Synergistic targeting of FLT3 mutations in AML via combined menin-MLL and FLT3 inhibition

The interaction of menin (MEN1) and MLL (MLL1, KMT2A) is a dependency and provides a potential opportunity for treatment of NPM1-mutant (NPM1mut) and MLL-rearranged (MLL-r) leukemias. Concomitant activating driver mutations in the gene encoding the tyrosine kinase FLT3 occur in both leukemias and are particularly common in the NPM1mut subtype. In this study, transcriptional profiling after pharmacological inhibition of the menin-MLL complex revealed specific changes in gene expression, with downregulation of the MEIS1 transcription factor and its transcriptional target gene FLT3 being the most pronounced. Combining menin-MLL inhibition with specific small-molecule kinase inhibitors of FLT3 phosphorylation resulted in a significantly superior reduction of phosphorylated FLT3 and transcriptional suppression of genes downstream of FLT3 signaling. The drug combination induced synergistic inhibition of proliferation, as well as enhanced apoptosis, compared with single-drug treatment in models of human and murine NPM1mut and MLL-r leukemias harboring an FLT3 mutation. Primary acute myeloid leukemia (AML) cells harvested from patients with NPM1mutFLT3mut AML showed significantly better responses to combined menin and FLT3 inhibition than to single-drug or vehicle control treatment, whereas AML cells with wild-type NPM1, MLL, and FLT3 were not affected by either of the 2 drugs. In vivo treatment of leukemic animals with MLL-r FLT3mut leukemia reduced leukemia burden significantly and prolonged survival compared with results in the single-drug and vehicle control groups. Our data suggest that combined menin-MLL and FLT3 inhibition represents a novel and promising therapeutic strategy for patients with NPM1mut or MLL-r leukemia and concurrent FLT3 mutation.

LncRNA HOXA-AS2 promotes the progression of prostate cancer via targeting miR-509-3p/PBX3 axis

Long non-coding RNAs (lncRNAs) act as crucial modulators during the development of diverse cancers. Although various types of lncRNAs in prostate cancer (PCa) have been explored, quantities of lncRNAs still wait to be exploited. The present study is to probe the functions and mechanism of lncRNA HOXA cluster antisense RNA 2 (HOXA-AS2) in PCa. In the present study, we discovered that HOXA-AS2 was highly expressed in PCa tissues and cells. HOXA-AS2 depletion obviously influenced cell proliferation, migration, invasion, as well as epithelial-to-mesenchymal transition (EMT) progression. In addition, miR-509-3p had low expression in PCa cells and inversely modulated by HOXA-AS2. Cutting down HOXA-AS2 expression was capable of up-regulating miR-509-3p expression. In addition, HOXA-AS2 served as a competing endogenous RNA (ceRNA) through sponging miR-509-3p to release pre-B-cell leukemia homeobox 3 (PBX3) expression. The expression of PBX3 was noticeably high in tumor tissues. And PBX3 expression level was down-regulated markedly with the knockdown of HOXA-AS2. Rescue experiments certified the facilitated role of HOXA-AS2-miR-509-3p-PBX3 axis in regulating the progress of PCa. The present study may provide clues for exploration of novel therapeutic targets for PCa patients.

Oncogenic and tumor suppressor function of MEIS and associated factors

MEIS proteins are historically associated with tumorigenesis, metastasis, and invasion in cancer. MEIS and associated PBX-HOX proteins may act as tumor suppressors or oncogenes in different cellular settings. Their expressions tend to be misregulated in various cancers. Bioinformatic analyses have suggested their upregulation in leukemia/lymphoma, thymoma, pancreas, glioma, and glioblastoma, and downregulation in cervical, uterine, rectum, and colon cancers. However, every cancer type includes, at least, a subtype with high MEIS expression. In addition, studies have highlighted that MEIS proteins and associated factors may function as diagnostic or therapeutic biomarkers for various diseases. Herein, MEIS proteins and associated factors in tumorigenesis are discussed with recent discoveries in addition to how they could be modulated by noncoding RNAs or newly developed small-molecule MEIS inhibitors.

Disruption of CTCF Boundary at HOXA Locus Promote BET Inhibitors' Therapeutic Sensitivity in Acute Myeloid Leukemia

Both HOX gene expression and CTCF regulation have been well demonstrated to play a critical role in regulating maintenance of leukemic stem cells (LSCs) that are known to be resistant to BET inhibitor (BETi). To investigate the regulatory role of CTCF boundary in aberrant HOX gene expression and the therapeutic sensitivity of BETi in AML, we employed CRISPR-Cas9 genome editing technology to delete 47 base pairs of the CTCF binding motif which is located between HOXA7 and HOXA9 genes (CBS7/9) in different subtypes of AML with either MLL-rearrangement or NPM1 mutation. Our results revealed that HOXA9 is significantly downregulated in response to the CBS7/9 deletion. Moreover, CBS7/9 boundary deletion sensitized the BETi treatment reaction in both MOLM-13 and OCI-AML3 cells. To further examine whether BETi therapeutic sensitivity in AML is depended on the expression level of the HOXA9 gene, we overexpressed the HOXA9 in the CBS7/9 deleted AML cell lines, which can rescue and restore the resistance to BETi treatment of the CBS7/9 KO cells by activating MAPK signaling pathway. Deletion of CBS7/9 specifically decreased the recruitment of BRD4 and RNA pol II to the posterior HOXA genes, in which, a transcription elongation factor ELL3 is the key factor in regulating HOXA gene transcription monitored by CBS7/9 chromatin boundary. Thus, disruption of CBS7/9 boundary perturbs HOXA9 transcription and regulates BETi sensitivity in AML treatment. Moreover, alteration of CTCF boundaries in the oncogene loci may provide a novel strategy to overcome the drug resistance of LSCs. Graphical abstract.

Mapping the native interaction surfaces of PREP1 with PBX1 by cross-linking mass-spectrometry and mutagenesis

Both onco-suppressor PREP1 and the oncogene MEIS1 bind to PBX1. This interaction stabilizes the two proteins and allows their translocation into the nucleus and thus their transcriptional activity. Here, we have combined cross-linking mass-spectrometry and systematic mutagenesis to detail the binding geometry of the PBX1-PREP1 (and PBX1-MEIS1) complexes, under native in vivo conditions. The data confirm the existence of two distinct interaction sites within the PBC domain of PBX1 and unravel differences among the highly similar binding sites of MEIS1 and PREP1. The HR2 domain has a fundamental role in binding the PBC-B domain of PBX1 in both PREP1 and MEIS1. The HR1 domain of MEIS1, however, seem to play a less stringent role in PBX1 interaction with respect to that of PREP1. This difference is also reflected by the different binding affinity of the two proteins to PBX1. Although partial, this analysis provides for the first time some ideas on the tertiary structure of the complexes not available before. Moreover, the extensive mutagenic analysis of PREP1 identifies the role of individual hydrophobic HR1 and HR2 residues, both in vitro and in vivo.

Alpha lipoic acid promotes development of hematopoietic progenitors derived from human embryonic stem cells by antagonizing ROS signals

Antagonism of ROS signaling can inhibit cell apoptosis and autophagy, thus favoring the maintenance and expansion of hematopoietic stem cells. Alpha lipoic acid (ALA), a small antioxidant molecule, affects cell apoptosis by lowering the ROS level. In this study, we show that ALA promoted production of human pluripotent stem cells (hPSCs) derived hemogenic endothelial cells and hematopoietic stem/progenitor cells in vitro. Transcriptome analysis of hPSCs derived hemogenic endothelial cells showed that ALA promoted endothelial‐to‐hematopoietic transition by up‐regulating RUNX1, GFI1, GFI1B, MEIS2, and HIF1A and down‐regulating SOX17, TGFB1, TGFB2, TGFB3, TGFBR1, and TGFBR2. ALA also up‐regulated sensor genes of ROS signals, including HIF1A, FOXO1, FOXO3, ATM, PETEN, SIRT1, and SIRT3, during the process of hPSCs derived hemogenic endothelial cells generation. However, in more mature hPSC‐derived hematopoietic stem/progenitor cells, ALA reduced ROS levels and inhibited apoptosis. In particular, ALA enhanced development of hPSCs derived hematopoietic stem/progenitor cells by up‐regulating HIF1A in response to a hypoxic environment. Furthermore, addition of ALA in ex vivo culture greatly improved the maintenance of functional cord blood HSCs by in vivo transplantation assay. Our findings support the conjecture that ALA plays an important role in efficient regeneration of hematopoietic stem/progenitor cells from hPSCs and maintenance of functional HSCs, providing insight into understanding of regeneration of early hematopoiesis for engineering clinically useful hPSCs derived hematopoietic stem/progenitor cells transplantation. Thus, ALA can be used in the study of hPSCs derived HSCs.

PBX1 is a valuable prognostic biomarker for patients with breast cancer

Pre-B-cell leukemia transcription factor (PBX) proteins have important roles in the development of numerous organs. To date, four members of the PBX family have been identified to be involved in human cancer but little is known about their expression patterns and precise functions in breast cancer (BC) progression. The aim of the present study was to determine whether they have the potential to be prognostic biomarkers in patients with BC. The expression patterns of PBXs were evaluated using Oncomine, Cancer Cell Line Encyclopedia and Gene expression-based Outcome for Breast cancer Online algorithm analyses. The prognostic value of PBX1 was determined by Kaplan-Meier plotter analysis. It was observed that, among all PBX family members, only PBX1 was significantly upregulated in BC vs. normal tissues. Meta-analysis in the Oncomine database revealed that PBX1 was significantly upregulated in invasive breast carcinoma stroma, ductal breast carcinoma, invasive lobular breast carcinoma, invasive mixed breast carcinoma and male breast carcinoma compared with normal tissues. In addition, PBX1 was significantly correlated with forkhead box protein A1. Subtype analysis indicated that PBX1 overexpression was associated with luminal-like and hormone receptor-sensitive subtypes. In the survival analysis, a high expression level of PBX1 was associated with poor prognosis of patients with estrogen receptor (ER)-positive, luminal A and luminal B subtypes of BC. The results of the present study indicate that PBX1 may serve as a specific biomarker and essential prognostic factor for ER-positive, luminal A and luminal B subtypes of BC.

PBX1 acts as terminal selector for olfactory bulb dopaminergic neurons

Neuronal specification is a protracted process that begins with the commitment of progenitor cells and culminates with the generation of mature neurons. Many transcription factors are continuously expressed during this process but it is presently unclear how these factors modify their targets as cells transition through different stages of specification. In olfactory bulb adult neurogenesis, the transcription factor PBX1 controls neurogenesis in progenitor cells and the survival of migrating neuroblasts. Here, we show that, at later differentiation stages, PBX1 also acts as a terminal selector for the dopaminergic neuron fate. PBX1 is also required for the morphological maturation of dopaminergic neurons and to repress alternative interneuron fates, findings that expand the known repertoire of terminal-selector actions. Finally, we reveal that the temporal diversification of PBX1 functions in neuronal specification is achieved, at least in part, through the dynamic regulation of alternative splicing. In Caenorhabditis elegans, PBX/CEH-20 also acts as a dopaminergic neuron terminal selector, which suggests an ancient role for PBX factors in the regulation of terminal differentiation of dopaminergic neurons.

High WBP5 expression correlates with elevation of HOX genes levels and is associated with inferior survival in patients with acute myeloid leukaemia

WW domain binding protein 5 (WBP5), also known as Transcriptional Elongation Factor A like 9 (TCEAL9) has been proposed as a candidate oncogene for human colorectal cancers with microsatellite instability and as a predictive indicator of small cell lung cancers. Furthermore, several independent studies have proposed WBP5, and its association with Wilms Tumor-1 (WT1) expression, as part of a gene expression-based risk score for predicting survival and clinical outcome in patients with Acute Myeloid Leukaemia (AML). To date, the prognostic significance of the sole WBP5 expression and its impact on the survival outcome in AML patients remains largely understudied. In the present study, we have made use of publicly available patient expression arrays and have developed an unbiased approach to classify AML patients into low versus high WBP5 expressers and to balance them for known mutations and cytogenetic findings. Interestingly, we found that patients characterized by high WBP5 expression displayed inferior overall and event-free survival rates. Notably, gene expression profiling showed that patients with high WBP5 had elevated expression of several HOX cluster genes, such as HOXA5, HOXA7, HOXA9 and HOXA10, and several of their partner proteins, such as MEIS1 and FOXC1, which have been demonstrated to be causative for AML. Taken together, our data suggest that WBP5 expression level could serve as an indicator for prognosis and survival outcome in patients with AML.

PBX3 in Cancer

PBX3 is a homeodomain-containing transcription factor of the pre-B cell leukemia (PBX) family, members of which have extensive roles in early development and some adult processes. A number of features distinguish PBX3 from other PBX proteins, including the ability to form specific and stable interactions with DNA in the absence of cofactors. PBX3 has frequently been reported as having a role in the development and maintenance of a malignant phenotype, and high levels of PBX3 tumor expression have been linked to shorter overall survival in cancer. In this review we consider the similarities and differences in the function of PBX3 in different cancer types and draw together the core signaling pathways involved to help provide a better insight into its potential as a therapeutic target.

PBX3 Promotes Tumor Growth and Angiogenesis via Activation of AT1R/VEGFR2 Pathway in Papillary Thyroid Carcinoma

PBX3 (Pre-B-cell leukemia homeobox 3) had been considered to be a multifunctional oncogene which involved in tumor growth, invasion, and metastasis in leukemia and some solid tumors. However, the contribution of PBX3 to papillary thyroid carcinoma (PTC) remains unclear. In this study, we found that PBX3 expression was significantly upregulated in PTC tissues compared to adjacent normal tissues, and high levels of PBX3 were correlated with tumor size, lymphatic metastasis, TMN stage, and poor prognosis of PTC patients. Overexpression of PBX3 in PTC cell lines promoted cell proliferation. Consistently, knockdown of PBX3 by shRNA induced cell cycle arrest at G0/G1 phase, and inhibited angiogenesis and tumor growth in vitro and in vivo. Furthermore, PBX3 promoted PTC cell proliferation and angiogenesis through activation of AT1R/VEGFR2 pathway while overexpression of AT1R and treatment with VEGFA reversed PBX3-shRNA-induced decreased phosphorylation of VEGFR2 and its downstream (ERK1/2, AKT and Src). It demonstrated that PBX3 could be used as a potential prognostic biomarker and therapeutic target for PTC.

FMS-like Tyrosine Kinase 3/FLT3: From Basic Science to Clinical Implications

FMS-like tyrosine kinase 3 (FLT3) is a receptor tyrosine kinase that is expressed almost exclusively in the hematopoietic compartment. Its ligand, FLT3 ligand (FL), induces dimerization and activation of its intrinsic tyrosine kinase activity. Activation of FLT3 leads to its autophosphorylation and initiation of several signal transduction cascades. Signaling is initiated by the recruitment of signal transduction molecules to activated FLT3 through binding to specific phosphorylated tyrosine residues in the intracellular region of FLT3. Activation of FLT3 mediates cell survival, cell proliferation, and differentiation of hematopoietic progenitor cells. It acts in synergy with several other cytokines to promote its biological effects. Deregulated FLT3 activity has been implicated in several diseases, most prominently in acute myeloid leukemia where around one-third of patients carry an activating mutant of FLT3 which drives the disease and is correlated with poor prognosis. Overactivity of FLT3 has also been implicated in autoimmune diseases, such as rheumatoid arthritis. The observation that gain-of-function mutations of FLT3 can promote leukemogenesis has stimulated the development of inhibitors that target this receptor. Many of these are in clinical trials, and some have been approved for clinical use. However, problems with acquired resistance to these inhibitors are common and, furthermore, only a fraction of patients respond to these selective treatments. This review provides a summary of our current knowledge regarding structural and functional aspects of FLT3 signaling, both under normal and pathological conditions, and discusses challenges for the future regarding the use of targeted inhibition of these pathways for the treatment of patients.

HoxA9 transforms murine myeloid cells by a feedback loop driving expression of key oncogenes and cell cycle control genes

Ectopic expression of the oncogenic transcription factor HoxA9 is a major cause of acute myeloid leukemia (AML). Here, we demonstrate that HoxA9 is a specific substrate of granule proteases. Protease knockout allowed the comprehensive determination of genome-wide HoxA9 binding sites by chromatin immunoprecipitation sequencing in primary murine cells and a human AML cell line. The kinetics of enhancer activity and transcription rates in response to alterations of an inducible HoxA9 were determined. This permitted identification of HoxA9-controlled enhancers and promoters, allocation to their respective transcription units, and discrimination against HoxA9-bound, but unresponsive, elements. HoxA9 triggered an elaborate positive-feedback loop that drove expression of the complete Hox-A locus. In addition, it controlled key oncogenic transcription factors Myc and Myb and directly induced the cell cycle regulators Cdk6 and CyclinD1, as well as telomerase, drawing the essential blueprint for perturbation of proliferation by leukemogenic HoxA9 expression.

Six1 regulates leukemia stem cell maintenance in acute myeloid leukemia

Molecular genetic changes in acute myeloid leukemia (AML) play crucial roles in leukemogenesis, including recurrent chromosome translocations, epigenetic/spliceosome mutations and transcription factor aberrations. Six1, a transcription factor of the Sine oculis homeobox (Six) family, has been shown to transform normal hematopoietic progenitors into leukemia in cooperation with Eya. However, the specific role and the underlying mechanism of Six1 in leukemia maintenance remain unexplored. Here, we showed increased expression of SIX1 in AML patients and murine leukemia stem cells (c‐Kit⁺ cells, LSCs). Importantly, we also observed that a higher level of Six1 in human patients predicts a worse prognosis. Notably, knockdown of Six1 significantly prolonged the survival of MLL‐AF9‐induced AML mice with reduced peripheral infiltration and tumor burden. AML cells from Six1‐knockdown (KD) mice displayed a significantly decreased number and function of LSC, as assessed by the immunophenotype, colony‐forming ability and limiting dilution assay. Further analysis revealed the augmented apoptosis of LSC and decreased expression of glycolytic genes in Six1 KD mice. Overall, our data showed that Six1 is essential for the progression of MLL‐AF9‐induced AML via maintaining the pool of LSC.

Inactivation of PBX3 and HOXA9 by down-regulating H3K79 methylation represses NPM1-mutated leukemic cell survival

Acute myeloid leukemia (AML) with an NPM1 mutation (NPMc+) has a distinct gene expression signature and displays molecular abnormalities similar to mixed lineage leukemia (MLL), including aberrant expression of the PBX3 and HOXA gene cluster. However, it is unclear if the aberrant expression of PBX3 and HOXA is essential for the survival of NPM1-mutated leukemic cells.

Methods: Using the gene expression profiling of TCGA and E-MTAB-3444 datasets, we screened for high co-expression of PBX3 and HOXA9 in NPMc+ leukemia patients. We performed NPMc+ depletion and overexpression experiments to examine aberrant H3K79 methylation through epigenetic regulation. Through RNA interference technology and small-molecule inhibitor treatment, we evaluated the effect of methyl-modified H3K79 on cell survival and explored the possible underlying mechanism.

Results: We showed that NPMc+ increased the expression of PBX3 and HOXA9, which are both poor prognosis indicators in AML. High PBX3 and HOXA9 expression was accompanied by increased dimethylated and trimethylated H3K79 in transgenic murine Lin^-Sca-1⁺c-Kit⁺ cells and human NPMc+ leukemia cells. Using chromatin immunoprecipitation sequencing (ChIP-seq) assays of NPMc+ cells, we determined that hypermethylated H3K79 was present at the expressed HOXA9 gene but not the PBX3 gene. PBX3 expression was positively regulated by HOXA9, and a reduction in either PBX3 or HOXA9 resulted in NPMc+ cell apoptosis. Importantly, an inhibitor of DOT1L, EPZ5676, effectively and selectively promoted NPMc+ human leukemic cell apoptosis by reducing HOXA9 and PBX3 expression.

Conclusion: Our data indicate that NPMc+ leukemic cell survival requires upregulation of PBX3 and HOXA9, and this action can be largely attenuated by a DOT1L inhibitor.

Combining Whispering-Gallery Mode Optical Biosensors with Microfluidics for Real-Time Detection of Protein Secretion from Living Cells in Complex Media

The noninvasive monitoring of protein secretion of cells responding to drug treatment is an effective and essential tool in latest drug development and for cytotoxicity assays. In this work, a surface functionalization method is demonstrated for specific detection of protein released from cells and a platform that integrates highly sensitive optical devices, called whispering-gallery mode biosensors, with precise microfluidics control to achieve label-free and real-time detection. Cell biomarker release is measured in real time and with nanomolar sensitivity. The surface functionalization method allows for antibodies to be immobilized on the surface for specific detection, while the microfluidics system enables detection in a continuous flow with a negligible compromise between sensitivity and flow control over stabilization and mixing. Cytochrome c detection is used to illustrate the merits of the system. Jurkat cells are treated with the toxin staurosporine to trigger cell apoptosis and cytochrome c released into the cell culture medium is monitored via the newly invented optical microfluidic platform.

A Trib2-p38 axis controls myeloid leukaemia cell cycle and stress response signalling

Trib2 pseudokinase is involved in the etiology of a number of cancers including leukaemia, melanoma, ovarian, lung and liver cancer. Both high and low Trib2 expression levels correlate with different types of cancer. Elevated Trib2 expression has oncogenic properties in both leukaemia and lung cancer dependent on interactions with proteasome machinery proteins and degradation of transcription factors. Here, we demonstrated that Trib2 deficiency conferred a growth and survival advantage both at steady state and in stress conditions in leukaemia cells. In response to stress, wild type leukaemia cells exited the cell cycle and underwent apoptosis. In contrast, Trib2 deficient leukaemia cells continued to enter mitosis and survive. We showed that Trib2 deficient leukaemia cells had defective MAPK p38 signalling, which associated with a reduced γ-H2Ax and Chk1 stress signalling response, and continued proliferation following stress, associated with inefficient activation of cell cycle inhibitors p21, p16 and p19. Furthermore, Trib2 deficient leukaemia cells were more resistant to chemotherapy than wild type leukaemia cells, having less apoptosis and continued propagation. Trib2 re-expression or pharmacological activation of p38 in Trib2 deficient leukaemia cells sensitised the cells to chemotherapy-induced apoptosis comparable with wild type leukaemia cells. Our data provide evidence for a tumour suppressor role of Trib2 in myeloid leukaemia via activation of p38 stress signalling. This newly identified role indicates that Trib2 may counteract the propagation and chemotherapy resistance of leukaemia cells.

Fbxw11 promotes the proliferation of lymphocytic leukemia cells through the concomitant activation of NF-κB and β-catenin/TCF signaling pathways

The ubiquitin–proteasome system (UPS) participates in both physiological and pathological processes through the posttranslational regulation of intracellular signal transduction pathways. F-box and WD-40 domain protein 11 (Fbxw11) is a component of the SCF (Skp1–Cul1–F-box) E3 ubiquitin ligase complex. Fbxw11 regulates various signal transduction pathways, and it may have pathological roles in tumorigenesis. However, the role of Fbxw11 in the development of leukemia and the underlying mechanisms remain largely unknown. In this study, Fbxw11 expression was aberrantly upregulated in patients with lymphocytic leukemia. Its expression was dramatically decreased in patients who achieved complete remission (CR) after chemotherapy. The high level of Fbxw11 expression in L1210 lymphocytic leukemia cells stimulated cell proliferation in vitro and tumor formation in vivo. The effects were mediated by the stimulation of cell cycle progression rather than the induction of apoptosis. Furthermore, a bioinformatics analysis suggested concomitant activation of the NF-κB and β-catenin/TCF signaling pathways, which were confirmed by reporter gene assays. Moreover, blocking experiments suggested the involvement of both pathways in the growth-promoting effects of Fbxw11. Our results reveal the role of Fbxw11 in lymphocytic leukemia cells and imply that Fbxw11 may serve as a potential molecular target for the treatment of lymphocytic leukemia.

Targeting HOX/PBX dimers in cancer

The HOX and PBX gene families encode transcription factors that have key roles in establishing the identity of cells and tissues in early development. Over the last 20 years it has become apparent that they are also dysregulated in a wide range of solid and haematological malignancies and have a predominantly pro-oncogenic function. A key mode of transcriptional regulation by HOX and PBX proteins is through their interaction as a heterodimer or larger complex that enhances their binding affinity and specificity for DNA, and there is growing evidence that this interaction is a potential therapeutic target in malignancies that include prostate, breast, renal, ovarian and lung cancer, melanoma, myeloma, and acute myeloid leukaemia. This review summarizes the roles of HOX and PBX genes in cancer and assesses the therapeutic potential of HOX/PBX dimer inhibition, including the availability of biomarkers for its application in precision medicine.

Trib2 expression in granulocyte-monocyte progenitors drives a highly drug resistant acute myeloid leukaemia linked to elevated Bcl2

Trib2 pseudokinase has oncogenic and tumour suppressive functions depending on the cellular context. We investigated the ability of Trib2 to transform different haemopoietic stem and progenitor cells (HSPCs). Our study identified the granulocyte-macrophage progenitor (GMP) subpopulation as a potent leukaemia initiating cell of Trib2-driven AML in vivo. Trib2 transformed GMPs generated a fully penetrant and short latency AML. AML cells expressing elevated Trib2 led to a chemoresistant phenotype following chemotherapy treatment. We show that Trib2 overexpression results in an increase in BCL2 expression, and high Trib2 expressing cells are highly sensitive to cell killing by BCL2 inhibition (ABT199). Combined treatment with chemotherapeutic agents and BCL2 inhibition resulted in synergistic killing of Trib2+ AML cells. Trib2 transformed GMP AML cells showed more chemoresistance compared with HSPC derived Trib2 AML cells associated with higher Bcl2 expression. There is significant correlation of high TRIB2 and BCL2 expression in patient derived human AML cells. These data demonstrate that the cell of origin influences the leukaemic profile and chemotherapeutic response of Trib2+ AML. Combined TRIB2 and BCL2 expression in AML cells may have clinical utility relevant for monitoring drug resistance and disease relapse.

High expression of FLT3 is a risk factor in leukemia

Several studies have shown that internal tandem duplication (ITD) of FMS-like tyrosine kinase 3 (FLT3) can result in the failure of leukemia treatment and contribute to a poor prognosis. However, the role of the overexpression of FLT3 in leukemia remains to be fully elucidated. By mining public database, the present study first identified that the expression of FLT3 in leukemia was markedly higher, compared with that in other types of tumor and cell lines, indicating that FLT3 is important in leukemia. In leukemia, FLT3 was found to be significantly upregulated in acute myeloid leukemia and acute lymphoblastic leukemia, and a high expression of FLT3 contributed to reduced survival rates. By analyzing Gene Expression Omnibus and The Cancer Genome Atlas data, it was found that genetic alterations and modification of DNA methylation increased the expression of FLT3 in leukemia. FLT3-ITD and FLT3 tyrosine kinase domain point mutations increased the expression of FLT3 in four independent datasets. In addition, the status of FLT3 gene methylation was negatively correlated with the expression of FLT3, and haploinsufficiency of DNA methyltransferase 1 increased the expression of Flt3 in mouse leukemia cells. By analyzing the enrichment of differentially-expressed genes in chemical and genetic perturbation datasets, it was found that genes, which were upregulated in the FLT3 high expression group had myeloid lymphoid leukemia- and nucleophosmin 1-like signatures, indicating that the overexpression of FLT3 may use the same mechanism to promote leukemia. Collectively, the results of the present study showed that the overexpression of FLT3 is a potential risk factor in leukemia.

PBX3 is associated with proliferation and poor prognosis in patients with cervical cancer

Pre-B-cell leukemia homeobox 3 (PBX3) is upregulated in various malignancies; however, the role of PBX3 in cervical cancer (CC) is unknown. The purpose of this study was to explore the expression characteristics, clinicopathological significance, and molecular biological function of PBX3 in CC. The expression levels of PBX3 were analyzed in CC cell lines and tumor specimens by real-time polymerase chain reaction (RT-PCR), Western blotting, and immunohistochemical staining. The clinicopathological characteristics associated with PBX3 expression were evaluated. An RNA interference approach was employed to suppress PBX3 expression in CC in vitro and in vivo, determine its role in cell proliferation and analyze its molecular function. We found that PBX3 expression was significantly upregulated in CC cell lines and clinical specimens compared with normal cells and adjacent nontumorous cervical tissues. PBX3 was an independent predictive factor of poor prognosis, and its expression was correlated with tumor diameter, pathological grading, lymph node metastasis, invasion depth, vascular invasion, and clinical stage of CC. Multivariate analysis suggested that PBX3 expression may represent an independent prognostic indicator of the survival of CC patients. CC patients with high PBX3 expression exhibited reduced overall survival compared with those with low PBX3 expression. Additionally, stable downregulation of PBX3 expression in CC cell lines suppressed cell proliferation and decreased p-AKT protein expression levels in vitro. Similarly, in vivo assays demonstrated that PBX3 downregulation in CC cells markedly inhibited tumor size and weight. Overall, we demonstrated that PBX3 can promote CC cell proliferation via the AKT signaling pathway and that it may serve as a prognostic marker. Our data indicate that inactivation of PBX3 may be an effective clinical treatment for CC.

Deregulation of the HOXA9/MEIS1 axis in acute leukemia

PURPOSE OF REVIEW

HOXA9 is a homeodomain transcription factor that plays an essential role in normal hematopoiesis and acute leukemia, in which its overexpression is strongly correlated with poor prognosis. The present review highlights recent advances in the understanding of genetic alterations leading to deregulation of HOXA9 and the downstream mechanisms of HOXA9-mediated transformation.

RECENT FINDINGS

A variety of genetic alterations including MLL translocations, NUP98-fusions, NPM1 mutations, CDX deregulation, and MOZ-fusions lead to high-level HOXA9 expression in acute leukemias. The mechanisms resulting in HOXA9 overexpression are beginning to be defined and represent attractive therapeutic targets. Small molecules targeting MLL-fusion protein complex members, such as DOT1L and menin, have shown promising results in animal models, and a DOT1L inhibitor is currently being tested in clinical trials. Essential HOXA9 cofactors and collaborators are also being identified, including transcription factors PU.1 and C/EBPα, which are required for HOXA9-driven leukemia. HOXA9 targets including IGF1, CDX4, INK4A/INK4B/ARF, mir-21, and mir-196b and many others provide another avenue for potential drug development.

SUMMARY

HOXA9 deregulation underlies a large subset of aggressive acute leukemias. Understanding the mechanisms regulating the expression and activity of HOXA9, along with its critical downstream targets, shows promise for the development of more selective and effective leukemia therapies.

Superenhancer Analysis Defines Novel Epigenomic Subtypes of Non-APL AML, Including an RARα Dependency Targetable by SY-1425, a Potent and Selective RARα Agonist

We characterized the enhancer landscape of 66 patients with acute myeloid leukemia (AML), identifying 6 novel subgroups and their associated regulatory loci. These subgroups are defined by their superenhancer (SE) maps, orthogonal to somatic mutations, and are associated with distinct leukemic cell states. Examination of transcriptional drivers for these epigenomic subtypes uncovers a subset of patients with a particularly strong SE at the retinoic acid receptor alpha (RARA) gene locus. The presence of a RARA SE and concomitant high levels of RARA mRNA predisposes cell lines and ex vivo models to exquisite sensitivity to a selective agonist of RARα, SY-1425 (tamibarotene). Furthermore, only AML patient-derived xenograft (PDX) models with high RARA mRNA were found to respond to SY-1425. Mechanistically, we show that the response to SY-1425 in RARA-high AML cells is similar to that of acute promyelocytic leukemia treated with retinoids, characterized by the induction of known retinoic acid response genes, increased differentiation, and loss of proliferation.Significance: We use the SE landscape of primary human AML to elucidate transcriptional circuitry and identify novel cancer vulnerabilities. A subset of patients were found to have an SE at RARA, which is predictive for response to SY-1425, a potent and selective RARα agonist, in preclinical models, forming the rationale for its clinical investigation in biomarker-selected patients. Cancer Discov; 7(10); 1136-53. ©2017 AACR.See related commentary by Wang and Aifantis, p. 1065.This article is highlighted in the In This Issue feature, p. 1047.

Genome-wide association study identifies novel susceptible loci and highlights Wnt/beta-catenin pathway in the development of adolescent idiopathic scoliosis

The genetic architecture of adolescent idiopathic scoliosis (AIS) remains poorly understood. Here we present the result of a 4-stage genome-wide association study composed of 5,953 AIS patients and 8,137 controls. Overall, we identified three novel susceptible loci including rs7593846 at 2p14 near MEIS1 (Pcombined = 1.19 × 10-13, OR = 1.21, 95% CI = 1.10-1.32), rs7633294 at 3p14.1 near MAGI1 (Pcombined = 1.85 × 10-12, OR = 1.20, 95% CI = 1.09-1.32), and rs9810566 at 3q26.2 near TNIK (Pcombined = 1.14 × 10-11, OR = 1.19, 95% CI = 1.08-1.32). We also confirmed a recently reported region associated with AIS at 20p11.22 (Pcombined = 1.61 × 10-15, OR = 1.22, 95% CI = 1.12-1.34). Furthermore, we observed significantly asymmetric expression of Wnt/beta-catenin pathway in the bilateral paraspinal muscle of AIS patients, including beta-catenin, TNIK, and LBX1. This is the first study that unveils the potential role of Wnt/beta-catenin pathway in the development of AIS, and our findings may shed new light on the etiopathogenesis of AIS.

PBX3 is essential for leukemia stem cell maintenance in MLL-rearranged leukemia

Interaction of HOXA9/MEIS1/PBX3 is responsible for hematopoietic system transformation in MLL-rearranged (MLL-r) leukemia. Of these genes, HOXA9 has been shown to be critical for leukemia cell survival, while MEIS1 has been identified as an essential regulator for leukemia stem cell (LSC) maintenance. Although significantly high expression of PBX3 was observed in clinical acute myeloid leukemia (AML) samples, the individual role of PBX3 in leukemia development is still largely unknown. In this study, we explored the specific role of PBX3 and its associated regulatory network in leukemia progression. By analyzing the clinical database, we found that the high expression of PBX3 is significantly correlated with a poor prognosis in AML patients. ChIP-Seq/qPCR analysis in MLL-r mouse models revealed aberrant epigenetic modifications with increased H3K79me2, and decreased H3K9me3 and H3K27me3 levels in LSCs, which may account for the high expression levels of Pbx3. To further examine the role of Pbx3 in AML maintenance and progression, we used the CRISPR/Cas9 system to delete Pbx3 in leukemic cells in the MLL-AF9 induced AML mouse model. We found that Pbx3 deletion significantly prolonged the survival of leukemic mice and decreased the leukemia burden by decreasing the capacity of LSCs and promoting LSC apoptosis. In conclusion, we found that PBX3 is epigenetically aberrant in the LSCs of MLL-r AML and is essential for leukemia development. Significantly, the differential expression of PBX3 in normal and malignant hematopoietic cells suggests PBX3 as a potential prognostic marker and therapeutic target for MLL-r leukemia.

HOXB13 mutations and binding partners in prostate development and cancer: Function, clinical significance, and future directions

The recent and exciting discovery of germline HOXB13 mutations in familial prostate cancer has brought HOX signaling to the forefront of prostate cancer research. An enhanced understanding of HOX signaling, and the co-factors regulating HOX protein specificity and transcriptional regulation, has the high potential to elucidate novel approaches to prevent, diagnose, stage, and treat prostate cancer. Toward our understanding of HOX biology in prostate development and prostate cancer, basic research in developmental model systems as well as other tumor sites provides a mechanistic framework to inform future studies in prostate biology. Here we describe our current understanding of HOX signaling in genitourinary development and cancer, current clinical data of HOXB13 mutations in multiple cancers including prostate cancer, and the role of HOX protein co-factors in development and cancer. These data highlight numerous gaps in our understanding of HOX function in the prostate, and present numerous potentially impactful mechanistic and clinical opportunities for future investigation.

RNA binding protein MSI2 positively regulates FLT3 expression in myeloid leukemia

FLT3 is frequently mutated and overexpressed in acute myelogenous leukemia (AML) and other hematologic malignancies. Although signaling events downstream of FLT3 receptor tyrosine kinase have been studied in depth, molecular mechanisms of how FLT3 expression is regulated at the post-transcriptional level in particular remain elusive. In this study, we investigated the roles of an RNA binding protein MSI2 as a regulator of FLT3 expression. MSI2 and FLT3 are significantly co-regulated in human AML and chronic myelogenous leukemia in blast crisis (BC-CML). Genetic loss of MSI2 leads to down-regulation of the FLT3 receptor in both AML and BC-CML cells and concomitant impairment of clonogenic growth potential. Furthermore, we demonstrate that MSI2 protein is physically bound to FLT3 mRNA transcripts, suggesting post-transcriptional control of FLT3 expression. Collectively, these results reveal a novel mode of FLT3 regulation essential for leukemia growth, which may aid in designing a targeted therapy to treat human myeloid leukemia.

High expression of MAP7 predicts adverse prognosis in young patients with cytogenetically normal acute myeloid leukemia

Microtubule-associated protein 7 (MAP7) plays an important role in cancer cells. In this study, we identified the prognostic significance of MAP7 expression in cytogenetically normal acute myeloid leukemia (CN-AML) patients (aged <60 years) based on several microarray datasets. In the first group (n = 129), high MAP7 expression (MAP7^high) was associated with adverse overall survival (OS; P = 0.0441) and event-free survival (EFS; P = 0.0114) compared with low MAP7 expression (MAP7^low). In addition, the prognostic significance of MAP7 was confirmed by European Leukemia Net (ELN) intermediate-I genetic categories and multivariable analysis. In the second independent group of CN-AML patients (aged <60 years), MAP7^high was also associated with adverse OS (n = 88, OS; P = 0.00811). To understand the inherent mechanisms of MAP7's prognosis, we investigated genome-wide gene/microRNA expression signatures associated with MAP7 expression. Several known oncogenic genes/microRNAs and anti-oncogenic genes/microRNAs were disordered in MAP7^high CN-AML patients. In conclusion, MAP7^high is an adverse prognostic biomarker for CN-AML, which may be attributed to the distinctive genome-wide gene/microRNA expression and related cell signaling pathways.

The molecular mechanics of mixed lineage leukemia

Mixed lineage leukemia caused by MLL fusion proteins is still a mostly incurable disease. Research on novel treatment strategies has gained momentum in the last years with the elucidation of the molecular mechanisms underlying the transforming potential of these powerful oncoproteins. This review summarizes the recent developments in this area including new attempts to treat MLL in a rational way by exploiting the biochemical vulnerabilities of the leukemogenic process.

PBX3 and MEIS1 Cooperate in Hematopoietic Cells to Drive Acute Myeloid Leukemias Characterized by a Core Transcriptome of the MLL-Rearranged Disease

Overexpression of HOXA/MEIS1/PBX3 homeobox genes is the hallmark of mixed lineage leukemia (MLL)-rearranged acute myeloid leukemia (AML). HOXA9 and MEIS1 are considered to be the most critical targets of MLL fusions and their coexpression rapidly induces AML. MEIS1 and PBX3 are not individually able to transform cells and were therefore hypothesized to function as cofactors of HOXA9. However, in this study, we demonstrate that coexpression of PBX3 and MEIS1 (PBX3/MEIS1), without ectopic expression of a HOX gene, is sufficient for transformation of normal mouse hematopoietic stem/progenitor cells in vitro. Moreover, PBX3/MEIS1 overexpression also caused AML in vivo, with a leukemic latency similar to that caused by forced expression of MLL-AF9, the most common form of MLL fusions. Furthermore, gene expression profiling of hematopoietic cells demonstrated that PBX3/MEIS1 overexpression, but not HOXA9/MEIS1, HOXA9/PBX3, or HOXA9 overexpression, recapitulated the MLL-fusion-mediated core transcriptome, particularly upregulation of the endogenous Hoxa genes. Disruption of the binding between MEIS1 and PBX3 diminished PBX3/MEIS1-mediated cell transformation and HOX gene upregulation. Collectively, our studies strongly implicate the PBX3/MEIS1 interaction as a driver of cell transformation and leukemogenesis, and suggest that this axis may play a critical role in the regulation of the core transcriptional programs activated in MLL-rearranged and HOX-overexpressing AML. Therefore, targeting the MEIS1/PBX3 interaction may represent a promising therapeutic strategy to treat these AML subtypes.