Pbx1 is a downstream target of Evi-1 in hematopoietic stem/progenitors and leukemic cells

A novel mutation in MECOM affects MPL regulation in vitro and results in thrombocytopenia and bone marrow failure

MECOM-associated syndrome (MECOM-AS) is a rare disease characterized by amegakaryocytic thrombocytopenia, progressive bone marrow failure, pancytopenia and radioulnar synostosis with high penetrance. The clinical phenotype may also include finger malformations, cardiac and renal alterations, hearing loss, B-cell deficiency and predisposition to infections. The syndrome, usually diagnosed in the neonatal period because of severe thrombocytopenia, is caused by mutations in the MECOM gene, encoding for the transcription factor EVI1. The mechanism linking the alteration of EVI1 function and thrombocytopenia is poorly understood. In a paediatric patient affected by severe thrombocytopenia, we identified a novel variant of the MECOM gene (p.P634L), whose effect was tested on pAP-1 enhancer element and promoters of targeted genes showing that the mutation impairs the repressive activity of the transcription factor. Moreover, we demonstrated that EVI1 controls the transcriptional regulation of MPL, a gene whose mutations are responsible for congenital amegakaryocytic thrombocytopenia (CAMT), potentially explaining the partial overlap between MECOM-AS and CAMT.

Regulation and signaling pathways in cancer stem cells: implications for targeted therapy for cancer

Cancer stem cells (CSCs), initially identified in leukemia in 1994, constitute a distinct subset of tumor cells characterized by surface markers such as CD133, CD44, and ALDH. Their behavior is regulated through a complex interplay of networks, including transcriptional, post-transcriptional, epigenetic, tumor microenvironment (TME), and epithelial-mesenchymal transition (EMT) factors. Numerous signaling pathways were found to be involved in the regulatory network of CSCs. The maintenance of CSC characteristics plays a pivotal role in driving CSC-associated tumor metastasis and conferring resistance to therapy. Consequently, CSCs have emerged as promising targets in cancer treatment. To date, researchers have developed several anticancer agents tailored to specifically target CSCs, with some of these treatment strategies currently undergoing preclinical or clinical trials. In this review, we outline the origin and biological characteristics of CSCs, explore the regulatory networks governing CSCs, discuss the signaling pathways implicated in these networks, and investigate the influential factors contributing to therapy resistance in CSCs. Finally, we offer insights into preclinical and clinical agents designed to eliminate CSCs.

EVI1-mediated Programming of Normal and Malignant Hematopoiesis

Ecotropic viral integration site 1 (EVI1), encoded at the MECOM locus, is an oncogenic zinc finger transcription factor with diverse roles in normal and malignant cells, most extensively studied in the context of hematopoiesis. EVI1 interacts with other transcription factors in a context-dependent manner and regulates transcription and chromatin remodeling, thereby influencing the proliferation, differentiation, and survival of cells. Interestingly, it can act both as a transcriptional activator as well as a transcriptional repressor. EVI1 is expressed, and fulfills important functions, during the development of different tissues, including the nervous system and hematopoiesis, demonstrating a rigid spatial and temporal expression pattern. However, EVI1 is regularly overexpressed in a variety of cancer entities, including epithelial cancers such as ovarian and pancreatic cancer, as well as in hematologic malignancies like myeloid leukemias. Importantly, EVI1 overexpression is generally associated with a very poor clinical outcome and therapy-resistance. Thus, EVI1 is an interesting candidate to study to improve the prognosis and treatment of high-risk patients with "EVI1high" hematopoietic malignancies.

Mosaic Chromosomal Alterations Are Associated With Increased Lung Cancer Risk: Insight From the INTEGRAL-ILCCO Cohort Analysis

INTRODUCTION

Mosaic chromosomal alterations (mCAs) detected in white blood cells represent a type of clonal hematopoiesis (CH) that is understudied compared with CH-related somatic mutations. A few recent studies indicated their potential link with nonhematological cancers, especially lung cancer.

METHODS

In this study, we investigated the association between mCAs and lung cancer using the high-density genotyping data from the OncoArray study of INTEGRAL-ILCCO, the largest single genetic study of lung cancer with 18,221 lung cancer cases and 14,825 cancer-free controls.

RESULTS

We identified a comprehensive list of autosomal mCAs, ChrX mCAs, and mosaic ChrY (mChrY) losses from these samples. Autosomal mCAs were detected in 4.3% of subjects, in addition to ChrX mCAs in 3.6% of females and mChrY losses in 9.6% of males. Multivariable logistic regression analysis indicated that the presence of autosomal mCAs in white blood cells was associated with an increased lung cancer risk after adjusting for key confounding factors, including age, sex, smoking status, and race. This association was mainly driven by a specific type of mCAs: copy-neutral loss of heterozygosity on autosomal chromosomes. The association between autosome copy-neutral loss of heterozygosity and increased risk of lung cancer was further confirmed in two major histologic subtypes, lung adenocarcinoma and squamous cell carcinoma. In addition, we observed a significant increase of ChrX mCAs and mChrY losses in smokers compared with nonsmokers and racial differences in certain types of mCA events.

CONCLUSIONS

Our study established a link between mCAs in white blood cells and increased risk of lung cancer.

Comprehensive overview of the role of PBX1 in mammalian kidneys

Pre-B-cell leukemia homeobox transcription factor 1 (PBX1) is a member of the TALE (three-amino acid loop extension) family and functions as a homeodomain transcription factor (TF). When dimerized with other TALE proteins, it can act as a pioneer factor and provide regulatory sequences via interaction with partners. In vertebrates, PBX1 is expressed during the blastula stage, and its germline variations in humans are interrelated with syndromic anomalies of the kidney, which plays an important role in hematopoiesis and immunity among vertebrates. Herein, we summarize the existing data on PBX1 functions and the impact of PBX1 on renal tumors, PBX1-deficient animal models, and blood vessels in mammalian kidneys. The data indicated that the interaction of PBX1 with different partners such as the HOX genes is responsible for abnormal proliferation and variation of the embryonic mesenchyme, while truncating variants were shown to cause milder phenotypes (mostly cryptorchidism and deafness). Although such interactions have been identified to be the cause of many defects in mammals, some phenotypic variations are yet to be understood. Thus, further research on the TALE family is required.

CRISPR-mediated MECOM depletion retards tumor growth by reducing cancer stem cell properties in lung squamous cell carcinoma

Targeted therapy for lung squamous cell carcinoma (LUSC) remains a challenge due to the lack of robust targets. Here, we identified MECOM as a candidate of therapeutic target for LUSC by screening 38 genes that were commonly amplified in three pairs of primary tumors and patient-derived xenografts (PDXs) using a clustered regularly interspaced short palindromic repeats (CRISPR)-mediated approach. High MECOM expression levels were associated with poor prognosis. Forced expression of MECOM in LUSC cell lines promoted cancer stem cell (CSC) properties, and its knockout inhibited CSC phenotypes. Furthermore, systemic delivery of CRISPR-mediated MECOM depletion cassette using adenovirus with an adaptor, which is composed of a single-chain fragment variable (scFv) against epithelial cell adhesion molecules (EpCAM) fused to the ectodomain of coxsackievirus and adenovirus receptor, and a protector, which consists of the scFv connected to the hexon symmetry of the adenovirus, could specifically target subcutaneous and orthotopic LUSC and retard tumor growth. This study could provide a novel therapeutic strategy for LUSC with high efficacy and specificity.

Targeting histone methylation to reprogram the transcriptional state that drives survival of drug-tolerant myeloid leukemia persisters

Although chemotherapy induces complete remission in the majority of acute myeloid leukemia (AML) patients, many face a relapse. This relapse is caused by survival of chemotherapy-resistant leukemia (stem) cells (measurable residual disease; MRD). Here, we demonstrate that the anthracycline doxorubicin epigenetically reprograms leukemia cells by inducing histone 3 lysine 27 (H3K27) and H3K4 tri-methylation. Within a doxorubicin-sensitive leukemia cell population, we identified a subpopulation of reversible anthracycline-tolerant cells (ATCs) with leukemic stem cell (LSC) features lacking doxorubicin-induced H3K27me3 or H3K4me3 upregulation. These ATCs have a distinct transcriptional landscape than the leukemia bulk and could be eradicated by KDM6 inhibition. In primary AML, reprogramming the transcriptional state by targeting KDM6 reduced MRD load and survival of LSCs residing within MRD, and enhanced chemotherapy response in vivo. Our results reveal plasticity of anthracycline resistance in AML cells and highlight the potential of transcriptional reprogramming by epigenetic-based therapeutics to target chemotherapy-resistant AML cells.

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Reversible anthracycline-tolerant leukemia cells (ATCs) have low H3K27me3 or H3K4me3

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ATCs exhibit stem cell features similar to leukemic stem cells

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Reprogramming the transcriptional state by inhibition of KDM6 depletes ATCs

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Inhibiting KDM6 adds to doxorubicin treatment and eradicates AML MRD (stem) cells

Hematopoietic Stem Cell Factors: Their Functional Role in Self-Renewal and Clinical Aspects

Hematopoietic stem cells (HSCs) possess two important properties such as self-renewal and differentiation. These properties of HSCs are maintained through hematopoiesis. This process gives rise to two subpopulations, long-term and short-term HSCs, which have become a popular convention for treating various hematological disorders. The clinical application of HSCs is bone marrow transplant in patients with aplastic anemia, congenital neutropenia, sickle cell anemia, thalassemia, or replacement of damaged bone marrow in case of chemotherapy. The self-renewal attribute of HSCs ensures long-term hematopoiesis post-transplantation. However, HSCs need to be infused in large numbers to reach their target site and meet the demands since they lose their self-renewal capacity after a few passages. Therefore, a more in-depth understanding of ex vivo HSCs expansion needs to be developed to delineate ways to enhance the self-renewability of isolated HSCs. The multifaceted self-renewal process is regulated by factors, including transcription factors, miRNAs, and the bone marrow niche. A developed classical hierarchical model that outlines the hematopoiesis in a lineage-specific manner through in vivo fate mapping, barcoding, and determination of self-renewal regulatory factors are still to be explored in more detail. Thus, an in-depth study of the self-renewal property of HSCs is essentially required to be utilized for ex vivo expansion. This review primarily focuses on the Hematopoietic stem cell self-renewal pathway and evaluates the regulatory molecular factors involved in considering a targeted clinical approach in numerous malignancies and outlining gaps in the current knowledge.

PBX1: a key character of the hallmarks of cancer

Pre-B-cell leukemia homeobox transcription factor 1 (PBX1) was first identified as part of a fusion protein resulting from the chromosomal translocation t(1;19) in pre-B cell acute lymphoblastic leukemias. Since then, PBX1 has been associated with important developmental programs, and its expression dysregulation has been related to multifactorial disorders, including cancer. As PBX1 overexpression in many cancers is correlated to poor prognosis, we sought to understand how this transcription factor contributes to carcinogenesis, and to organize PBX1's roles in the hallmarks of cancer. There is enough evidence to associate PBX1 with at least five hallmarks: sustaining proliferative signaling, activating invasion and metastasis, inducing angiogenesis, resisting cell death, and deregulating cellular energetics. The lack of studies investigating a possible role for PBX1 on the remaining hallmarks made it impossible to defend or refute its contribution on them. However, the functions of some of the PBX1's transcription targets indicate a potential engagement of PBX1 in the avoidance of immune destruction and in the tumor-promoting inflammation hallmarks. Interestingly, PBX1 might be a player in tumor suppression by activating the transcription of some DNA damage response genes. This is the first review organizing PBX1 roles into the hallmarks of cancer. Thus, we encourage future studies to uncover the PBX1's underlying mechanisms to promote carcinogenesis, for it is a promising diagnostic and prognostic biomarker, as well as a potential target in cancer treatment.

EVI1 overexpression promotes ovarian cancer progression by regulating estrogen signaling

High-grade serous ovarian cancer (HGSOC) is characterized by TP53 mutation and somatic copy number alterations (SCNAs). Here we show that the oncogenic transcription factor EVI1 (ecotropic viral integration site-1) is amplified and overexpressed up to 30% of 1640 HGSOC cases in The Cancer Genome Atlas (TCGA). Functionally, EVI1 promotes proliferation/invasion in vitro and tumor growth of xenograft model in vivo. Importantly, we discover that EVI1 regulates estrogen signaling by directly activating ESR1 (estrogen receptor 1) transcription determined by the ChIP and luciferase assay. Interestingly, EVI1 and ESR1 share common regulatory targets as indicated by the analysis of ChIP-Seq data. EVI1 and ESR1 collaborate in the regulation of some estrogen receptor-regulated genes. Furthermore, EVI1 drives tumor aggressiveness partially by regulating estrogen signaling. Estrogen enhances the proliferation, invasion and xenograft growth of ovarian cancer cells. Importantly, estrogen can rescue the inhibition of proliferation, invasion and xenograft growth induced by silencing EVI1. These findings suggest that EVI1 functions as a novel regulator of the estrogen signaling network in ovarian cancer.

EVI1 dysregulation: impact on biology and therapy of myeloid malignancies

Ecotropic viral integration site 1 (Evi1) was discovered in 1988 as a common site of ecotropic viral integration resulting in myeloid malignancies in mice. EVI1 is an oncogenic zinc-finger transcription factor whose overexpression contributes to disease progression and an aggressive phenotype, correlating with poor clinical outcome in myeloid malignancies. Despite progress in understanding the biology of EVI1 dysregulation, significant improvements in therapeutic outcome remain elusive. Here, we highlight advances in understanding EVI1 biology and discuss how this new knowledge informs development of novel therapeutic interventions. EVI1 is overexpression is correlated with poor outcome in some epithelial cancers. However, the focus of this review is the genetic lesions, biology, and current therapeutics of myeloid malignancies overexpressing EVI1.

Myeloid neoplasms associated with t(3;12)(q26.2;p13) are clinically aggressive, show myelodysplasia, and frequently harbor chromosome 7 abnormalities

Sporadic reports of t(3;12)(q26.2;p13) indicate that this abnormality is associated with myeloid neoplasms, myelodysplasia, and a poor prognosis. To better characterize neoplasms with this abnormality, we assessed 20 patients utilizing clinicopathological data, cytogenetic, and targeted next-generation sequencing analysis. We also performed literature review of 58 prior reported cases. Patients included ten men and ten women with median age 55.8 years (range, 27.8-78.8). Diagnoses included 11 acute myeloid leukemia (AML, 5 de novo and 6 secondary), 5 myelodysplastic syndromes (MDS, 3 de novo excess blasts-2 and 2 therapy-related), 2 chronic myeloid leukemia BCR-ABL1-positive blast phase (1 de novo and 1 secondary), 1 primary myelofibrosis (secondary), and 1 mixed-phenotype acute leukemia T/myeloid (MPAL, secondary). Morphologic dysplasia was identified in all AML cases (5/5), MDS cases (4/4), therapy-related cases (3/3), half of myeloproliferative neoplasm cases (1/2), and one MPAL case assessed. The t(3;12) was detected de novo and in subsequent workups in 9 and 11 patients, respectively. Seven patients had t(3;12) only and eight patients had additional chromosome 7 abnormalities. Fluorescence in-situ hybridization detected MECOM (n = 11) and ETV6 (n = 7) rearrangements in all cases assessed. FLT3 internal tandem duplication was identified in five (25%) patients. We identified 13 genetic abnormalities in the de novo group (n = 9), and 25 in the secondary disease group (n = 11). All patients received chemotherapy, with seven allogeneic and two autologous stem cell transplantations. At last follow-up, 14 (70%) patients died with median survival of 6.3 months (range, 0.1-17.3) after detection of t(3;12). In summary, t(3;12)(q26.2;p13) is a rare cytogenetic abnormality in myeloid neoplasms. Myelodysplasia, chromosome 7 abnormalities, and high blast counts are common, and the prognosis is poor. Given the close relationship between the presence of this cytogenetic abnormality and the MDS-related changes, we recommend adding t(3;12)(q26.2;p13) to the list of AML with myelodysplasia-related changes defining abnormalities of the World Health Organization 2017 classification of myeloid neoplasms.

Two effects of GATA2 enhancer repositioning by 3q chromosomal rearrangements

Chromosomal inversion and translocation between 3q21 and 3q26 [inv (3)(q21.3q26.2) and t(3;3)(q21.3;q26.2), respectively] give rise to acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS), which have poor prognoses. The chromosomal rearrangements reposition a GATA2 distal hematopoietic enhancer from the original 3q21 locus to the EVI1 (also known as MECOM) locus on 3q26. Therefore, the GATA2 enhancer from one of two GATA2 alleles drives EVI1 gene expression in hematopoietic stem and progenitor cells, which promotes the accumulation of abnormal progenitors and induces leukemogenesis. On the other hand, one allele of the GATA2 gene loses its enhancer, which results in reduced GATA2 expression. The GATA2 gene encodes a transcription factor critical for the generation and maintenance of hematopoietic stem and progenitor cells. GATA2 haploinsufficiency has been known to cause immunodeficiency and myeloid leukemia. Notably, reduced GATA2 expression suppresses the differentiation but promotes the proliferation of EVI1-expressing leukemic cells, which accelerates EVI1-driven leukemogenesis. A series of studies have shown that the GATA2 enhancer repositioning caused by the chromosomal rearrangements between 3q21 and 3q26 provokes misexpression of both the EVI1 and GATA2 genes and that these two effects coordinately elicit high-risk leukemia.

Oncogenic heterogeneous nuclear ribonucleoprotein D-like modulates the growth and imatinib response of human chronic myeloid leukemia CD34+ cells via pre-B-cell leukemia homeobox 1

Chronic myeloid leukemia (CML) originates from normal hematopoietic stem cells acquiring BCR-ABL fusion gene, specific BCR-ABL inhibitors (e.g., imatinib mesylate, IM) have greatly improved patient management. However, some patients are still suffering from relapse and drug resistance, which urges better understanding of the growth/survival mechanisms of CML stem/progenitor cells. In the present study, the role and its underlying mechanism of heterogeneous nuclear ribonucleoprotein D-like (HNRPDL) in CML cells were investigated. Firstly, overexpression of HNRPDL promoted the growth of murine BaF3 cells in vitro and induced leukemia in vivo, which was enhanced by co-expression of BCR-ABL. Conversely, HNRPDL silencing inhibited colony-forming cell (CFC) production of CML CD34⁺ cells and attenuated BCR-ABL induced leukemia. In addition, HNRPDL modulated imatinib response of K562 cells and HNRPDL silencing sensitized CML CD34⁺ cells to imatinib treatment. Mechanistically, we found the stability of pre-B-cell leukemia homeobox 1 (PBX1) mRNA was sustained by HNRPDL through its binding to a specific motif (ACUAGC) in 3'-untranslated region (3'-UTR) of PBX1. The expression of PBX1 was significantly higher in CML CD34⁺ cells than that in control cells and PBX silencing inhibited the growth of CML cells and sensitized them to imatinib treatment. In contrast, overexpression of PBX1 elevated the CFC production of normal hematopoietic CD34⁺ cells and "rescued" HNRPDL silencing induced growth inhibition and imatinib sensitization. Taken together, our data have demonstrated that HNRPDL transforms hematopoietic cells and a novel HNRPDL/PBX1 axis plays an important role in human CML CD34⁺ cells.

EVI1 overexpression reprograms hematopoiesis via upregulation of Spi1 transcription

Inv(3q26) and t(3:3)(q21;q26) are specific to poor-prognosis myeloid malignancies, and result in marked overexpression of EVI1, a zinc-finger transcription factor and myeloid-specific oncoprotein. Despite extensive study, the mechanism by which EVI1 contributes to myeloid malignancy remains unclear. Here we describe a new mouse model that mimics the transcriptional effects of 3q26 rearrangement. We show that EVI1 overexpression causes global distortion of hematopoiesis, with suppression of erythropoiesis and lymphopoiesis, and marked premalignant expansion of myelopoiesis that eventually results in leukemic transformation. We show that myeloid skewing is dependent on DNA binding by EVI1, which upregulates Spi1, encoding master myeloid regulator PU.1. We show that EVI1 binds to the -14 kb upstream regulatory element (-14kbURE) at Spi1; knockdown of Spi1 dampens the myeloid skewing. Furthermore, deletion of the -14kbURE at Spi1 abrogates the effects of EVI1 on hematopoietic stem cells. These findings support a novel mechanism of leukemogenesis through EVI1 overexpression.

Reprogramming acute myeloid leukemia into sensitivity for retinoic-acid-driven differentiation

The success of all-trans retinoic acid (ATRA) therapy for acute promyelocytic leukemia (APL) provides a rationale for using retinoic acid (RA)-based therapy for other subtypes of acute myeloid leukemia (AML). Recently, several studies showed that ATRA may drive leukemic cells efficiently into differentiation and/or apoptosis in a subset of AML patients with an NPM1 mutation, a FLT3-ITD, an IDH1 mutation, and patients overexpressing EVI-1. Because not all patients within these molecular subgroups respond to ATRA and clinical trials that tested ATRA response in non-APL AML patients have had disappointing results, the identification of additional biomarkers may help to identify patients who strongly respond to ATRA-based therapy. Searching for response biomarkers might also reveal novel RA-based combination therapies with an efficient differentiation/apoptosis-inducing effect in non-APL AML patients. Preliminary studies suggest that the epigenetic or transcriptional state of leukemia cells determines their susceptibility to ATRA. We hypothesize that reprogramming by inhibitors of epigenetic-modifying enzymes or by modulation of microRNA expression might sensitize non-APL AML cells for RA-based therapy. AML relapse is caused by a subpopulation of leukemia cells, named leukemic stem cells (LSCs), which are in a different epigenetic state than the total bulk of the AML. The survival of LSCs after therapy is the main cause of the poor prognosis of AML patients, and novel differentiation therapies should drive these LSCs into maturity. In this review, we summarize the current knowledge on the epigenetic aspects of susceptibility to RA-induced differentiation in APL and non-APL AML.

The MDS and EVI1 complex locus (MECOM) isoforms regulate their own transcription and have different roles in the transformation of hematopoietic stem and progenitor cells

Transcriptional activation of the EVI1 oncogene (3q26) leads to aggressive forms of human acute myeloid leukemia (AML). However, the mechanism of EVI1-mediated leukemogenesis has not been fully elucidated. Previously, by characterizing the EVI1 promoter, we have shown that RUNX1 and ELK1 directly regulate EVI1 transcription. Intriguingly, bioinformatic analysis of the EVI1 promoter region identified the presence of several EVI1 potential binding sites. Thus, we hypothesized that EVI1 could bind to these sites regulating its own transcription. In this study, we show that there is a functional interaction between EVI1 and its promoter, and that the different EVI1 isoforms (EVI1-145kDa, EVI1-Δ324 and MDS1-EVI1) regulate the transcription of EVI1 transcripts through distinct promoter regions. Moreover, we determine that the EVI1-145kDa isoform activates EVI1 transcription, whereas EVI1-Δ324 and MDS1-EVI1 act as repressors. Finally, we demonstrate that these EVI1 isoforms are involved in cell transformation; functional experiments show that EVI1-145kDa prolongs the maintenance of hematopoietic stem and progenitor cells; conversely, MDS1-EVI1 repressed hematopoietic stem and progenitor colony replating capacity. We demonstrate for the first time that EVI1 acts as a regulator of its own expression, highlighting the complex regulation of EVI1, and open new directions to better understand the mechanisms of EVI1 overexpressing leukemias.

Loss of p53 induces leukemic transformation in a murine model of Jak2 V617F-driven polycythemia vera

As leukemic transformation of myeloproliferative neoplasms (MPNs) worsens the clinical outcome, reducing the inherent risk of the critical event in MPN cases could be beneficial. Among genetic alterations concerning the transformation, the frequent one is TP53 mutation. Here we show that retroviral overexpression of Jak2 V617F mutant into wild-type p53 murine bone marrow cells induced polycythemia vera (PV) in the recipient mice, whereas Jak2 V617F-transduced p53-null mice developed lethal leukemia after the preceding PV phase. The leukemic mice had severe anemia, hepatosplenomegaly, pulmonary hemorrhage and expansion of dysplastic erythroid progenitors. Primitive leukemia cells (c-kit⁺Sca1⁺Lin^- (KSL) and CD34^-CD16/32^-c-kit⁺Sca1^-Lin^- (megakaryocyte-erythroid progenitor; MEP)) and erythroid progenitors (CD71⁺) from Jak2 V617F-transduced p53-null leukemic mice had leukemia-initiating capacity, however, myeloid differentiated populations (Mac-1⁺) could not recapitulate the disease. Interestingly, recipients transplanted with CD71⁺ cells rapidly developed erythroid leukemia, which was in sharp contrast to leukemic KSL cells to cause lethal leukemia after the polycythemic state. The leukemic CD71⁺ cells were more sensitive to INCB18424, a potent JAK inhibitor, than KSL cells. p53 restoration could ameliorate Jak2 V617F-transduced p53-null erythroleukemia. Taken together, our results show that p53 loss is sufficient for inducing leukemic transformation in Jak2 V617F-positive MPN.

Internal Tandem Duplication in FLT3 Attenuates Proliferation and Regulates Resistance to the FLT3 Inhibitor AC220 by Modulating p21Cdkn1a and Pbx1 in Hematopoietic Cells

Internal tandem duplication (ITD) mutations in the Fms-related tyrosine kinase 3 (FLT3) gene (FLT3-ITD) are associated with poor prognosis in patients with acute myeloid leukemia (AML). Due to the development of drug resistance, few FLT3-ITD inhibitors are effective against FLT3-ITD⁺ AML. In this study, we show that FLT3-ITD activates a novel pathway involving p21^Cdkn1a (p21) and pre-B cell leukemia transcription factor 1 (Pbx1) that attenuates FLT3-ITD cell proliferation and is involved in the development of drug resistance. FLT3-ITD up-regulated p21 expression in both mouse bone marrow c-kit⁺-Sca-1⁺-Lin^- (KSL) cells and Ba/F3 cells. The loss of p21 expression enhanced growth factor-independent proliferation and sensitivity to cytarabine as a consequence of concomitantly enriching the S+G₂/M phase population and significantly increasing the expression of Pbx1, but not Evi-1, in FLT3-ITD⁺ cells. This enhanced cell proliferation following the loss of p21 was partially abrogated when Pbx1 expression was silenced in FLT3-ITD⁺ primary bone marrow colony-forming cells and Ba/F3 cells. When FLT3-ITD was antagonized with AC220, a selective inhibitor of FLT3-ITD, p21 expression was decreased coincident with Pbx1 mRNA up-regulation and a rapid decline in the number of viable FLT3-ITD⁺ Ba/F3 cells; however, the cells eventually became refractory to AC220. Overexpressing p21 in FLT3-ITD⁺ Ba/F3 cells delayed the emergence of cells that were refractory to AC220, whereas p21 silencing accelerated their development. These data indicate that FLT3-ITD is capable of inhibiting FLT3-ITD⁺ cell proliferation through the p21/Pbx1 axis and that treatments that antagonize FLT3-ITD contribute to the subsequent development of cells that are refractory to a FLT3-ITD inhibitor by disrupting p21 expression.

Reduction in Cell Viability and in Homeobox Protein Levels Following in Vitro Exposure to δ-tocopherol in Acute Myeloid Leukemia

δ-Tocopherol (δ-T), the least prevalent tocopherol in our diet, was described to have a more potent anticancer activity in solid tumors compared to the other tocopherols. δ-T induces tumor cell death through peroxisome proliferator-activated receptor γ (PPAR-γ) induction, cyclin-D1 inhibition, and modulation of redox balance. Nevertheless, the role of δ-T in preventing or treating hematologic malignancies has not been studied. In this study, we screened the efficacy of δ-T against six cell lines representing a wide spectrum of hematologic malignancies: Jurkat (acute T-cell leukemia), K-562 (chronic myeloid leukemia), KG-1 [acute myeloid leukemia (AML)], THP-1 (acute monocytic leukemia), TOM-1 (acute lymphoblastic leukemia), and UMCL01-101 (AIDS-associated diffuse large B-cell lymphoma). Interestingly, the AML cell line KG-1 was the only one to be significantly affected at concentrations of δ-T as low as 20 µM. The antileukemic activity of δ-T in AML was verified in a set of primary cells collected from patients newly diagnosed with AML. Apoptotic induction and cell cycle arrest explained the efficacy of δ-T against KG-1 cells. The mechanism of cell growth inhibition of δ-T was through downregulation of cyclin-D1 and a set of homeobox proteins (HOXA9, PBX1, and Cdx2) that have a well-documented role in the pathobiology of AML.

Expression of MECOM is associated with unfavorable prognosis in glioblastoma multiforme

Background

MDS1 and EVI1 complex locus protein EVI1 (MECOM) is an oncogenic transcription factor in several kinds of cancers. However, the clinical significance of MECOM in glioblastoma multiforme (GBM) has not been well elucidated.

Patients and methods

Our study enrolled 86 resected samples of GBM in three medical centers. We detected the expression of MECOM in all the 86 samples by immunohistochemistry and compared the difference of MECOM mRNA between tumor tissues and adjacent tissues with real-time polymerase chain reaction. With immunoblotting, we detected the MECOM expression in different GBM cell lines. Moreover, we analyzed the correlation between MECOM expression and clinicopathologic factors with chi-square test, and evaluated the prognostic value of MECOM with univariate and multivariate analysis.

Results

In GBM tissue, the percentage of MECOM high expression is 41.9% (36/86). The mRNA of MECOM in tumor tissues is remarkably higher than that in adjacent tissues, indicating the oncogenic role of MECOM in GBM. MECOM exists in all the detected cell lines with different abundance. Moreover, MECOM is correlated with poorer overall survival rate (P=0.033) and can be identified as an independent prognostic factor in GBM (P=0.042).

Conclusion

MECOM could be considered as an independent prognostic factor in GBM, predicting it as a potential and promising molecular drug target.

Review: Aberrant EVI1 expression in acute myeloid leukaemia

Deregulated expression of the ecotropic virus integration site 1 (EVI1) gene is the molecular hallmark of therapy-resistant myeloid malignancies bearing chromosomal inv(3)(q21q26·2) or t(3;3)(q21;q26·2) [hereafter referred to as inv(3)/t(3;3)] abnormalities. EVI1 is a haematopoietic stemness and transcription factor with chromatin remodelling activity. Interestingly, the EVI1 gene also shows overexpression in 6-11% of adult acute myeloid leukaemia (AML) cases that do not carry any 3q aberrations. Deregulated expression of EVI1 is strongly associated with monosomy 7 and 11q23 abnormalities, which are known to be associated with poor response to treatment. However, EVI1 overexpression has been revealed as an important independent adverse prognostic marker in adult AML and defines distinct risk categories in 11q23-rearranged AML. Recently, important progress has been made in the delineation of the mechanism by which EVI1 becomes deregulated in inv(3)/t(3;3) as well as the cooperating mutations in this specific subset of AML with dismal prognosis.

3q26/EVI1 rearrangements in myeloid hemopathies: a cytogenetic review

ABSTRACT 

The EVI1 gene, located in chromosomal band 3q26, is a transcription factor that has stem cell-specific expression pattern and is essential for the regulation of self-renewal of hematopoietic stem cells. It is now recognized as one of the dominant oncogenes associated with myeloid leukemia. EVI1 overexpression is associated with minimal to no response to chemotherapy and poor clinical outcome. Several chromosomal rearrangements involving band 3q26 are known to induce EVI1 overexpression. They are mainly found in acute myeloid leukemia and blastic phase of Philadelphia chromosome-positive chronic myeloid leukemia, more rarely in myelodysplastic syndromes. They include inv(3)(q21q26), t(3;3)(q21;q26), t(3;21)(q26;q22), t(3;12)(q26;p13) and t(2;3)(p15–23;q26). However, many other chromosomal rearrangements involving 3q26/EVI1 have been identified. The precise molecular event has not been elucidated in the majority of these chromosomal abnormalities and most gene partners remain unknown.

EVI1 promotes tumor growth via transcriptional repression of MS4A3

Background

The transcription factor Ecotropic Virus Integration site 1 (EVI1) regulates cellular proliferation, differentiation, and apoptosis, and its overexpression contributes to an aggressive course of disease in myeloid leukemias and other malignancies. Notwithstanding, knowledge about the target genes mediating its biological and pathological functions remains limited. We therefore aimed to identify and characterize novel EVI1 target genes in human myeloid cells.

Methods

U937T_EVI1, a human myeloid cell line expressing EVI1 in a tetracycline regulable manner, was subjected to gene expression profiling. qRT-PCR was used to confirm the regulation of membrane-spanning-4-domains subfamily-A member-3 (MS4A3) by EVI1. Reporter constructs containing various parts of the MS4A3 upstream region were employed in luciferase assays, and binding of EVI1 to the MS4A3 promoter was investigated by chromatin immunoprecipitation. U937 derivative cell lines experimentally expressing EVI1 and/or MS4A3 were generated by retroviral transduction, and tested for their tumorigenicity by subcutaneous injection into severe combined immunodeficient mice.

Results

Gene expression microarray analysis identified 27 unique genes that were up-regulated, and 29 unique genes that were down-regulated, in response to EVI1 induction in the human myeloid cell line U937T. The most strongly repressed gene was MS4A3, and its down-regulation by EVI1 was confirmed by qRT-PCR in additional, independent experimental model systems. MS4A3 mRNA levels were also negatively correlated with those of EVI1 in several published AML data sets. Reporter gene assays and chromatin immunoprecipitation showed that EVI1 regulated MS4A3 via direct binding to a promoter proximal region. Experimental re-expression of MS4A3 in an EVI1 overexpressing cell line counteracted the tumor promoting effect of EVI1 in a murine xenograft model by increasing the rate of apoptosis.

Conclusions

Our data reveal MS4A3 as a novel direct target of EVI1 in human myeloid cells, and show that its repression plays a role in EVI1 mediated tumor aggressiveness.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-015-0124-6) contains supplementary material, which is available to authorized users.

Survivin modulates genes with divergent molecular functions and regulates proliferation of hematopoietic stem cells through Evi-1

The inhibitor of apoptosis protein Survivin regulates hematopoiesis, although its mechanisms of regulation of hematopoietic stem cells (HSCs) remain largely unknown. While investigating conditional Survivin deletion in mice, we found that Survivin was highly expressed in phenotypically defined HSCs and Survivin deletion in mice resulted in significantly reduced total marrow HSC and progenitor cells (HPC). Transcriptional analysis of Survivin^−/− HSCs revealed altered expression of multiple genes not previously linked to Survivin activity. In particular, Survivin deletion significantly reduced expression of the Evi-1 transcription factor indispensable for HSC function, and the downstream Evi-1 target genes Gata2, Pbx1 and Sall2. The loss of HSCs following Survivin deletion and impaired long-term HSC repopulating function could be partially rescued by ectopic Evi-1 expression in Survivin −/− HSCs. These data demonstrate that Survivin partially regulates HSC function by modulating the Evi-1transcription factor and its downstream targets and identify new genetic pathways in HSCs regulated by Survivin.

Physical and functional interaction of the proto-oncogene EVI1 and tumor suppressor gene HIC1 deregulates Bcl-xL mediated block in apoptosis

Ecotropic viral integration site 1 was originally identified as a retroviral integration site in murine leukemias. Several studies have established ecotropic viral integration site 1 as both a transcription factor and an interacting partner that presumably regulates gene expression. Using coimmunoprecipitation and fluorescence resonance energy transfer analysis, we found that the N-terminal domain of hypermethylated in cancer 1 interacts with the proximal set of zinc fingers of ecotropic viral integration site 1. This interaction not only abolishes the DNA binding activity of ecotropic viral integration site 1 but also disrupts the transcriptional activity of an anti-apoptotic gene promoter selectively targeted by ecotropic viral integration site 1. By using flow cytometry and western blotting, here we show that hypermethylated in cancer 1 can deregulate ecotropic viral integration site 1-mediated blockage of apoptosis. We hypothesize that therapeutic upregulation of hypermethylated in cancer 1 may provide an important means of targeting ecotropic viral integration site 1-positive cancers.

Evi1 defines leukemia-initiating capacity and tyrosine kinase inhibitor resistance in chronic myeloid leukemia

Relapse of chronic myeloid leukemia (CML) is triggered by stem cells with a reconstituting capacity similar to that of hematopoietic stem cells (HSCs) and CML stem cells are a source of resistance in drug therapy with tyrosine kinase inhibitors (TKIs). Ecotropic viral integration site 1 (EVI1), a key transcription factor in HSC regulation, is known to predict poor outcomes in myeloid malignancies, however, incapability of prospective isolation of EVI1-high leukemic cells precludes the functional evaluation of intraindividual EVI1-high cells. Introduction of CML into Evi1-internal ribosomal entry site (IRES)-green fluorescent protein (GFP) knock-in mice, a versatile HSC-reporter strain, enables us to separate Evi1-high CML cells from the individual. Evi1-IRES-GFP allele models of CML in chronic phase (CML-CP), by retroviral overexpression of BCR-ABL and by crossing BCR-ABL transgenic mice, revealed that Evi1 is predominantly enriched in the stem cell fraction and associated with an enhanced proliferative as well as a leukemia-initiating capacity and that Evi1-high CML-CP cells exhibit resistance to TKIs. Overexpressing BCR-ABL and NUP98-HOXA9 in Evi1-IRES-GFP knock-in mice to model CML in blast crisis (CML-BC), in which Evi1-high cells turned to be a major population as opposed to a minor population in CML-CP models, showed that Evi1-high CML-BC cells have a greater potential to recapitulate the disease and appear resistant to TKIs. Furthermore, given that Evi1 heterozygosity ameliorates CML-CP and CML-BC development and that the combination of Evi1 and BCR-ABL causes acute myeloid leukemia resembling CML-BC, Evi1 could regulate CML development as a potent driver. In addition, in human CML-CP cases, we show that EVI1 is highly expressed in stem cell-enriched CD34+CD38-CD90+ fraction at single-cell level. This is the first report to clarify directly that Evi1-high leukemic cells themselves possess the superior potential to Evi1-low cells in oncogenic self-renewal, which highlights the role of Evi1 as a valuable and a functional marker of CML stem cells.

A remote GATA2 hematopoietic enhancer drives leukemogenesis in inv(3)(q21;q26) by activating EVI1 expression

Chromosomal inversion between 3q21 and 3q26 results in high-risk acute myeloid leukemia (AML). In this study, we identified a mechanism whereby a GATA2 distal hematopoietic enhancer (G2DHE or -77-kb enhancer) is brought into close proximity to the EVI1 gene in inv(3)(q21;q26) inversions, leading to leukemogenesis. We examined the contribution of G2DHE to leukemogenesis by creating a bacterial artificial chromosome (BAC) transgenic model that recapitulates the inv(3)(q21;q26) allele. Transgenic mice harboring a linked BAC developed leukemia accompanied by EVI1 overexpression-neoplasia that was not detected in mice bearing the same transgene but that was missing the GATA2 enhancer. These results establish the mechanistic basis underlying the pathogenesis of a severe form of leukemia through aberrant expression of the EVI1 proto-oncogene.

The role of EVI1 in myeloid malignancies

The EVI1 oncogene at human chr 3q26 is rearranged and/or overexpressed in a subset of acute myeloid leukemias and myelodysplasias. The EVI1 protein is a 135 kDa transcriptional regulator with DNA-binding zinc finger domains. Here we provide a critical review of the current state of research into the molecular mechanisms by which this gene plays a role in myeloid malignancies. The major pertinent cellular effects are blocking myeloid differentiation and preventing cellular apoptosis, and several potential mechanisms for these phenomena have been identified. Evidence supports a role for EVI1 in inducing cellular quiescence, and this may contribute to the resistance to chemotherapy seen in patients with neoplasms that overexpress EVI1. Another isoform, MDS1-EVI1 (or PRDM3), encoded by the same locus as EVI1, harbors an N-terminal histone methyltransferase(HMT) domain; experimental findings indicate that this protein and its HMT activity are critical for the progression of a subset of AMLs, and this provides a potential target for therapeutic intervention.

Global Identification of EVI1 Target Genes in Acute Myeloid Leukemia

The ecotropic virus integration site 1 (EVI1) transcription factor is associated with human myeloid malignancy of poor prognosis and is overexpressed in 8-10% of adult AML and strikingly up to 27% of pediatric MLL-rearranged leukemias. For the first time, we report comprehensive genomewide EVI1 binding and whole transcriptome gene deregulation in leukemic cells using a combination of ChIP-Seq and RNA-Seq expression profiling. We found disruption of terminal myeloid differentiation and cell cycle regulation to be prominent in EVI-induced leukemogenesis. Specifically, we identified EVI1 directly binds to and downregulates the master myeloid differentiation gene Cebpe and several of its downstream gene targets critical for terminal myeloid differentiation. We also found EVI1 binds to and downregulates Serpinb2 as well as numerous genes involved in the Jak-Stat signaling pathway. Finally, we identified decreased expression of several ATP-dependent P2X purinoreceptors genes involved in apoptosis mechanisms. These findings provide a foundation for future study of potential therapeutic gene targets for EVI1-induced leukemia.

Phosphorylation of the leukemic oncoprotein EVI1 on serine 196 modulates DNA binding, transcriptional repression and transforming ability

The EVI1 (ecotropic viral integration site 1) gene at 3q26 codes for a transcriptional regulator with an essential role in haematopoiesis. Overexpression of EVI1 in acute myeloid leukaemia (AML) is frequently associated with 3q26 rearrangements and confers extremely poor prognosis. EVI1 mediates transcriptional regulation, signalling, and epigenetic modifications by interacting with DNA, proteins and protein complexes. To explore to what extent protein phosphorylation impacts on EVI1 functions, we analysed endogenous EVI1 protein from a high EVI1 expressing Fanconi anaemia (FA) derived AML cell line. Mass spectrometric analysis of immunoprecipitated EVI1 revealed phosphorylation at serine 196 (S196) in the sixth zinc finger of the N-terminal zinc finger domain. Mutated EVI1 with an aspartate substitution at serine 196 (S196D), which mimics serine phosphorylation of this site, exhibited reduced DNA-binding and transcriptional repression from a gene promotor selectively targeted by the N-terminal zinc finger domain. Forced expression of the S196D mutant significantly reduced EVI1 mediated transformation of Rat1 fibroblasts. While EVI1-mediated serial replating of murine haematopoietic progenitors was maintained by EVI1-S196D, this was associated with significantly higher Evi1-trancript levels compared with WT-EVI1 or EVI1-S196A, mimicking S196 non-phosphorylated EVI1. These data suggest that EVI1 function is modulated by phosphorylation of the first zinc finger domain.

An MLL-dependent network sustains hematopoiesis

The histone methyltransferase Mixed Lineage Leukemia (MLL) is essential to maintain hematopoietic stem cells and is a leukemia protooncogene. Although clustered homeobox genes are well-characterized targets of MLL and MLL fusion oncoproteins, the range of Mll-regulated genes in normal hematopoietic cells remains unknown. Here, we identify and characterize part of the Mll-dependent transcriptional network in hematopoietic stem cells with an integrated approach by using conditional loss-of-function models, genomewide expression analyses, chromatin immunoprecipitation, and functional rescue assays. The Mll-dependent transcriptional network extends well beyond the previously appreciated Hox targets, is comprised of many characterized regulators of self-renewal, and contains target genes that are both dependent and independent of the MLL cofactor, Menin. Interestingly, PR-domain containing 16 emerged as a target gene that is uniquely effective at partially rescuing Mll-deficient hematopoietic stem and progenitor cells. This work highlights the tissue-specific nature of regulatory networks under the control of MLL/Trithorax family members and provides insight into the distinctions between the participation of MLL in normal hematopoiesis and in leukemia.

The shortest isoform of C/EBPβ, liver inhibitory protein (LIP), collaborates with Evi1 to induce AML in a mouse BMT model

Ecotropic viral integration site 1 (Evi1) is one of the master regulators in the development of acute myeloid leukemia (AML) and myelodysplastic syndrome. High expression of Evi1 is found in 10% of patients with AML and indicates a poor outcome. Several recent studies have indicated that Evi1 requires collaborative factors to induce AML. Therefore, the search for candidate factors that collaborate with Evi1 in leukemogenesis is one of the key issues in uncovering the mechanism of Evi1-related leukemia. Previously, we succeeded in making a mouse model of Evi1-related leukemia using a bone marrow transplantation (BMT) system. In the Evi1-induced leukemic cells, we identified frequent retroviral integrations near the CCAAT/enhancer-binding protein β (C/EBPβ) gene and overexpression of its protein. These findings imply that C/EBPβ is a candidate gene that collaborates with Evi1 in leukemogenesis. Cotransduction of Evi1 and the shortest isoform of C/EBPβ, liver inhibitory protein (LIP), induced AML with short latencies in a mouse BMT model. Overexpression of LIP alone also induced AML with longer latencies. However, excision of all 3 isoforms of C/EBPβ (LAP*/LAP/LIP) did not inhibit the development of Evi1-induced leukemia. Therefore, isoform-specific intervention that targets LIP is required when we consider C/EBPβ as a therapeutic target.

The Prdm family: expanding roles in stem cells and development

Members of the Prdm family are characterized by an N-terminal PR domain that is related to the SET methyltransferase domain, and multiple zinc fingers that mediate sequence-specific DNA binding and protein-protein interactions. Prdm factors either act as direct histone methyltransferases or recruit a suite of histone-modifying enzymes to target promoters. In this way, they function in many developmental contexts to drive and maintain cell state transitions and to modify the activity of developmental signalling pathways. Here, we provide an overview of the structure and function of Prdm family members and discuss the roles played by these proteins in stem cells and throughout development.

Ecotropic viral integration site 1, stem cell self-renewal and leukemogenesis

It has become evident that acute myeloid leukemia (AML) is organized as a cellular hierarchy initiated and maintained by a subset of self-renewing leukemia stem cells. Recent gene expression profile analysis of human leukemia stem cells and hematopoietic stem cell (HSC) populations identified a key transcriptional program shared by leukemia stem cells and HSC, which is associated with adverse outcomes in AML patients. One molecule that has been established as a pivotal regulator in fine-tuning of stem cell properties as well as a potent oncogenic determinant is ecotropic viral integration site 1 (EVI1). EVI1 is a transcription factor that has stem cell-specific expression pattern and is essential for the regulation of HSC self-renewal. This gene is notorious for its involvement in AML, as its activation confers extremely poor prognosis in patients with AML. Molecular analysis has identified a variety of gene products that are involved in HSC regulation as downstream targets or interacting proteins of EVI1. Thus, exploration of the molecular pathogenesis underlying EVI1-related leukemogenesis provides insight into how shared stemness transcriptional programs contribute to leukemia progression and therapeutic resistance in AML. Here, we review the current knowledge regarding the role of EVI1 in HSC self-renewal and leukemogenesis and highlight the relationship between stem cell self-renewal properties and adverse outcome in myeloid malignancies.

Evi1 forms a bridge between the epigenetic machinery and signaling pathways

Recent studies have demonstrated the significance of the leukemia oncogene Evi1 as the regulator of hematopoietic stem cells and marker of poor clinical outcomes in myeloid malignancies. Evi1-mediated leukemogenic activities include a wide array of functions such as the induction of epigenetic modifications, transcriptional control, and regulation of signaling pathways. We have recently succeeded in comprehensively elucidating the oncogenic function of Evi1 in a model of the polycomb-Evi1-PTEN/AKT/mTOR axis. These results may provide us with novel therapeutic approaches to conquer the poor prognosis associated with Evi1-activated leukemia or other solid tumors with high Evi1 expression. Here, we review the current understanding of the role of Evi1 in controlling the development of leukemia and highlight potential modalities for targeting factors involved in Evi1-regulated signaling.

Evi1 is essential for hematopoietic stem cell self-renewal, and its expression marks hematopoietic cells with long-term multilineage repopulating activity

A new mouse in which an IRES-GFP cassette is knocked-in to the Evi1 locus reveals that HSC long-term multilineage repopulating activity specifically segregates with expression of the Evi1 transcription factor.

Ecotropic viral integration site 1 (Evi1), a transcription factor of the SET/PR domain protein family, is essential for the maintenance of hematopoietic stem cells (HSCs) in mice and is overexpressed in several myeloid malignancies. Here, we generate reporter mice in which an internal ribosome entry site (IRES)-GFP cassette is knocked-in to the Evi1 locus. Using these mice, we find that Evi1 is predominantly expressed in long-term HSCs (LT-HSCs) in adult bone marrow, and in the hematopoietic stem/progenitor fraction in the aorta-gonad-mesonephros, placenta, and fetal liver of embryos. In both fetal and adult hematopoietic systems, Evi1 expression marks cells with long-term multilineage repopulating activity. When combined with conventional HSC surface markers, sorting according to Evi1 expression markedly enhances purification of cells with HSC activity. Evi1 heterozygosity leads to marked impairment of the self-renewal capacity of LT-HSCs, whereas overexpression of Evi1 suppresses differentiation and boosts self-renewal activity. Reintroduction of Evi1, but not Mds1-Evi1, rescues the HSC defects caused by Evi1 heterozygosity. Thus, in addition to documenting a specific relationship between Evi1 expression and HSC self-renewal activity, these findings highlight the utility of Evi1-IRES-GFP reporter mice for the identification and sorting of functional HSCs.

Acetylation of the proto-oncogene EVI1 abrogates Bcl-xL promoter binding and induces apoptosis

EVI1 (Ecotropic Viral Integration site I), which was originally identified as a myeloid transforming gene by means of retroviral insertional mutagenesis in mouse leukemia, encodes a nuclear DNA binding zinc finger protein. The presence of zinc fingers that are able to bind to specific sequences of DNA suggests that EVI1 is a transcriptional regulator; however, except a few, target genes of EVI1 are poorly functionally identified thus far. In this study we provide evidence that EVI1 directly induces the expression of Bcl-xL through the first set of zinc finger and thereby inhibits apoptosis. ChIP analysis showed that EVI1 binds to the Bcl-xL promoter in HT-29 cells, a colon carcinoma cell line, which expresses EVI1. The observation is also supported by the fact that EVI1 siRNA treated HT-29 cells, shows a down regulation of Bcl-xL expression and that over expression of EVI1 results in the induction of the Bcl-xL reporter construct. A set of EVI1 positive chronic myeloid leukemia (CML) samples also showed higher Bcl-xL expression with respect to EVI1 negative samples. Interestingly, co-expression of EVI1 with wild type, but not with dominant-negative form of PCAF, abolishes the effect of EVI1 on Bcl-xL, indicating that acetylation of EVI1 abrogates its ability not only to bind Bcl-xL promoter but also alleviate Bcl-xL activity. Finally we have shown that EVI1 expression regulates apoptosis in HT-29 cells, which is abrogated when HT-29 cells are transfected with EVI1 siRNA or PCAF. The result for the first time shows a direct pathway by which EVI1 can protect cells from apoptosis and also demonstrates that the pathway can be reversed when EVI1 is acetylated.

Loss of AML1/Runx1 accelerates the development of MLL-ENL leukemia through down-regulation of p19ARF

Dysfunction of AML1/Runx1, a transcription factor, plays a crucial role in the development of many types of leukemia. Additional events are often required for AML1 dysfunction to induce full-blown leukemia; however, a mechanistic basis of their cooperation is still elusive. Here, we investigated the effect of AML1 deficiency on the development of MLL-ENL leukemia in mice. Aml1 excised bone marrow cells lead to MLL-ENL leukemia with shorter duration than Aml1 intact cells in vivo. Although the number of MLL-ENL leukemia-initiating cells is not affected by loss of AML1, the proliferation of leukemic cells is enhanced in Aml1-excised MLL-ENL leukemic mice. We found that the enhanced proliferation is the result of repression of p19(ARF) that is directly regulated by AML1 in MLL-ENL leukemic cells. We also found that down-regulation of p19(ARF) induces the accelerated onset of MLL-ENL leukemia, suggesting that p19(ARF) is a major target of AML1 in MLL-ENL leukemia. These results provide a new insight into a role for AML1 in the progression of leukemia.

EVI1 up-regulates the stress responsive gene SIRT1 which triggers deacetylation and degradation of EVI1

EVI1 (Ecotropic Viral Integration site I), which was originally identified as a site of viral integration in murine myeloid tumors, encodes a complex protein required for embryogenesis. The gene is known to express inappropriately in many types of human myeloid leukemias and solid tumors. Forced expression of EVI1 in murine hematopoietic precursor cells lead to abnormal differentiation and increased proliferation. EVI1 encodes two sets of zinc finger domains due to which it behaves as a transcriptional factor. However, except a few, the targets of EVI1 are not well understood and hence also the mechanism by which it initiates oncogenesis is not very clear. In this report, we show that SIRT1, a histone deacetylase is a direct target of EVI1. In vivo chromatin immunoprecipitation assay revealed that EVI1 binds to the promoter region of SIRT1 approximately 1kb upstream of the transcription start site. The functionality of the site was deduced by luciferase assay which showed that EVI1 significantly increases the SIRT1 promoter activity. SIRT1 was also found to be up regulated in cell lines and in chronic myeloid leukemia patient samples where EVI1 was detected. Over expression of SIRT1 in cells shows that it interacts with EVI1 and this interaction lead to the deacetylation of the protein. Upon deacetylation the stability of EVI1 was found to be affected which was negatively regulated by nicotinamide (NAM). Our results thus identify an EVI1-SIRT1 axis in the regulation of EVI1 activity suggesting a possible role of SIRT1 in EVI1 positive neoplasms.

Evi1 represses PTEN expression and activates PI3K/AKT/mTOR via interactions with polycomb proteins

Evi1 (ecotropic viral integration site 1) is essential for proliferation of hematopoietic stem cells and implicated in the development of myeloid disorders. Particularly, high Evi1 expression defines one of the largest clusters in acute myeloid leukemia and is significantly associated with extremely poor prognosis. However, mechanistic basis of Evi1-mediated leukemogenesis has not been fully elucidated. Here, we show that Evi1 directly represses phosphatase and tensin homologue deleted on chromosome 10 (PTEN) transcription in the murine bone marrow, which leads to activation of AKT/mammalian target of rapamycin (mTOR) signaling. In a murine bone marrow transplantation model, Evi1 leukemia showed modestly increased sensitivity to an mTOR inhibitor rapamycin. Furthermore, we found that Evi1 binds to several polycomb group proteins and recruits polycomb repressive complexes for PTEN down-regulation, which shows a novel epigenetic mechanism of AKT/mTOR activation in leukemia. Expression analyses and ChIPassays with human samples indicate that our findings in mice models are recapitulated in human leukemic cells. Dependence of Evi1-expressing leukemic cells on AKT/mTOR signaling provides the first example of targeted therapeutic modalities that suppress the leukemogenic activity of Evi1. The PTEN/AKT/mTOR signaling pathway and the Evi1-polycomb interaction can be promising therapeutic targets for leukemia with activated Evi1.

Control of EVI-1 oncogene expression in metastatic breast cancer cells through microRNA miR-22

Metastasis in breast cancer carries a disproportionately worse prognosis than localized primary disease. To identify microRNAs (miRNA) involved in metastasis, the expression of 254 miRNAs was measured across the following cell lines using microarray analysis: MDA-MB-231 breast cancer cells, cells that grew as a tumor in the mammary fat pad of nude mice (TMD-231), metastatic disease to the lungs (LMD-231), bone (BMD-231) and adrenal gland (ADMD-231). A brain-seeking variant of this cell line (231-BR) was used additionally in validation studies. Twenty miRNAs were upregulated and seven were downregulated in metastatic cancer cells compared with TMD-231 cells. The expression of the tumor suppressor miRNAs let-7 and miR-22 was consistently downregulated in metastatic cancer cells. These metastatic cells expressed higher levels of putative/proven miR-22 target oncogenes ERBB3, CDC25C and EVI-1. Introduction of miR-22 into cancer cells reduced the levels of ERBB3 and EVI-1 as well as phospho-AKT, an EVI-1 downstream target. The miR-22 primary transcript is located in the 5'-untranslated region of an open reading frame C17orf91, and the promoter/enhancer of C17orf91 drives miR-22 expression. We observed elevated C17orf91 expression in non-basal subtype compared with basal subtype breast cancers. In contrast, elevated expression of EVI-1 was observed in basal subtype and was associated with poor outcome in estrogen receptor-negative breast cancer patients. These results suggest that metastatic cancer cells increase specific oncogenic signaling proteins through downregulation of miRNAs. Identifying such metastasis-specific oncogenic pathways may help to manipulate tumor behavior and aid in the design of more effective targeted therapies.

Unbiased, genome-wide in vivo mapping of transcriptional regulatory elements reveals sex differences in chromatin structure associated with sex-specific liver gene expression

We have used a simple and efficient method to identify condition-specific transcriptional regulatory sites in vivo to help elucidate the molecular basis of sex-related differences in transcription, which are widespread in mammalian tissues and affect normal physiology, drug response, inflammation, and disease. To systematically uncover transcriptional regulators responsible for these differences, we used DNase hypersensitivity analysis coupled with high-throughput sequencing to produce condition-specific maps of regulatory sites in male and female mouse livers and in livers of male mice feminized by continuous infusion of growth hormone (GH). We identified 71,264 hypersensitive sites, with 1,284 showing robust sex-related differences. Continuous GH infusion suppressed the vast majority of male-specific sites and induced a subset of female-specific sites in male livers. We also identified broad genomic regions (up to ∼100 kb) showing sex-dependent hypersensitivity and similar patterns of GH responses. We found a strong association of sex-specific sites with sex-specific transcription; however, a majority of sex-specific sites were >100 kb from sex-specific genes. By analyzing sequence motifs within regulatory regions, we identified two known regulators of liver sexual dimorphism and several new candidates for further investigation. This approach can readily be applied to mapping condition-specific regulatory sites in mammalian tissues under a wide variety of physiological conditions.