Retroviral activation of a novel gene encoding a zinc finger protein in IL-3-dependent myeloid leukemia cell lines

Enhanced sensitivity to hydrogen peroxide-induced apoptosis in Evi1 transformed Rat1 fibroblasts due to repression of carbonic anhydrase III

EVI1 is a nuclear zinc finger protein essential to normal development, which participates in acute myeloid leukaemia progression and transforms Rat1 fibroblasts. In this study we show that enforced expression of Evi1 in Rat1 fibroblasts protects from paclitaxel-induced apoptosis, consistent with previously published studies. Surprisingly, however, these cells show increased sensitivity to hydrogen peroxide (H(2)O(2))-induced apoptosis, demonstrated by elevated caspase 3 catalytic activity. This effect is caused by a reduction in carbonic anhydrase III (caIII) production. caIII transcripts are repressed by 92-97% by Evi1 expression, accompanied by a similar reduction in caIII protein. Reporter assays with the rat caIII gene promoter show repressed activity, demonstrating that Evi1 either directly or indirectly modulates transcription of this gene in Rat1 cells. Targeted knockdown of caIII alone, with Dicer-substrate short inhibitory RNAs, also increases the sensitivity of Rat1 fibroblasts to H(2)O(2), which occurs in the absence of any other changes mediated by Evi1 expression. Enforced expression of caIII in Evi1-expressing Rat1 cells reverts the phenotype, restoring H(2)O(2) resistance. Together these data show that Evi1 represses transcription of caIII gene expression, leading to increased sensitivity to H(2)O(2)-induced apoptosis in Rat1 cells and might suggest the basis for the development of a novel therapeutic strategy for the treatment of leukaemias and solid tumours where EVI1 is overexpressed.

EVI-1 interacts with histone methyltransferases SUV39H1 and G9a for transcriptional repression and bone marrow immortalization

The ecotropic viral integration site-1 (EVI-1) is a nuclear transcription factor and has an essential function in the proliferation/maintenance of haematopoietic stem cells. Aberrant expression of EVI-1 has been frequently found in myeloid leukaemia as well as in several solid tumours, and is associated with a poor patient survival. It was recently shown that EVI-1 associates with two different histone methyltransferases (HMTs), SUV39H1 and G9a. However, the functional roles of these HMTs in EVI-1-mediated leukemogenesis remain unclear. In this study, we showed that EVI-1 physically interacts with SUV39H1 and G9a, but not with Set9. Immunofluorescence analysis revealed that EVI-1 colocalizes with these HMTs in nuclei. We also found that the catalytically inactive form of SUV39H1 abrogates the transcriptional repression mediated by EVI-1, suggesting that SUV39H1 is actively involved in EVI-1-mediated transcriptional repression. Furthermore, RNAi-based knockdown of SUV39H1 or G9a in Evi-1-expressing progenitors significantly reduced their colony-forming activity. In contrast, knockdown of these HMTs did not impair bone marrow immortalization by E2A/HLF. These results indicate that EVI-1 forms higher-order complexes with HMTs, and this association has a role in the transcription repression and bone marrow immortalization. Targeting these HMTs may be of therapeutic benefit in the treatment for EVI-1-related haematological malignancies.

A combination of transposable elements and magnetic cell sorting provides a very efficient transgenesis system for chicken primary erythroid progenitors

Background

Stable transgenesis is an undeniable key to understanding any genetic system. Retrovirus-based insertional strategies, which feature several technical challenges when they are used, are often limited to one particular species, and even sometimes to a particular cell type as the infection depends on certain cellular receptors. A universal-like system, which would allow both stable transgene expression independent of the cell type and an efficient sorting of transfected cells, is required when handling cellular models that are incompatible with retroviral strategies.

Results

We report here on the combination of a stable insertional transgenesis technique, based on the Tol2 transposon system together with the magnetic cell sorting (MACS) technique, which allows specific selection of cells carrying the transgene in an efficient, reliable and rapid way.

Conclusion

This new Tol2/MACS system leads to stable expression in a culture of primary chicken erythroid cells highly enriched in cells expressing the transgene of interest. This system could be used in a wide variety of vertebrate species.

Pathogenetic significance of ecotropic viral integration site-1 in hematological malignancies

The ecotropic viral integration site-1 (Evi-1) gene was first identified as a common locus of retroviral integration in murine leukemia models. In humans, EVI-1 is located on chromosome 3q26, and rearrangements on chromosome 3q26 often activate EVI-1 expression in hematological malignancies. Overexpression of EVI-1 also occurs with high frequency in leukemia patients without 3q26 abnormalities, and importantly, high EVI-1 expression is an independent negative prognostic indicator irrespective of the presence of 3q26 rearrangements. Recent gene targeting studies in mice revealed that Evi-1 is preferentially expressed in hematopoietic stem cells and plays an essential role in proliferation and maintenance of hematopoietic stem cells. In addition, intense attention has been focused on the EVI-1 gene complex as retrovirus integration sites because transcription-activating integrations into the EVI-1 locus confer survival and self-renewing ability to hematopoietic cells. The experimental results using animal models suggest that activation of Evi-1 in hematopoietic cells leads to clonal expansion or dysplastic hematopoiesis, whereas onset of full-blown leukemia requires cooperative genetic events. EVI-1 possesses diverse functions as an oncoprotein, including suppression of transforming growth factor-beta-mediated growth inhibition, upregulation of GATA2, inhibition of the Jun kinase pathway, and stimulation of cell growth via activator protein-1. In this article, we summarize current knowledge regarding the biochemical properties and biological functions of EVI-1 in normal and malignant hematopoiesis, with specific focus on its pathogenetic significance in hematological malignancies.

EVI1 recruits the histone methyltransferase SUV39H1 for transcription repression

EVI1 is an oncoprotein inappropriately expressed in acute myeloid leukemia and myelodysplastic syndrome cells. In vitro studies indicate that diverse biological properties can be attributed to this protein. Its role in leukemogenesis is still unclear but it is thought that overall EVI1 can act mostly as a transcription repressor through its interaction with a subset of histone deacetylases. Studies with histone deacetylase inhibitors have however indicated that EVI1-mediated repression can be only partially rescued by deacetylase inhibitor drugs, suggesting that additional chromosomal modifications might occur to induce gene repression by EVI1. To investigate whether histone methylation contributes to the repressive potential of EVI1, we examined a potential association between EVI1, the histone methyltransferase (HMT) SUV39H1, and methyltransferase activity in vitro. We find that EVI1 directly interacts with SUV39H1 and that the proteins form an active complex with methyltransferase activity in vitro. Our data indicate that SUV39H1 enhances the transcription repressive potential of EVI1 in vivo. We suggest that EVI1 affects promoters' activity in two different pathways, by association with histone deacetylases and by recruiting chromatin-modifying enzymes to impose a heterochromatin-like structure establishing a lasting transcription repression.

Combinatorial incorporation of enhancer-blocking components of the chicken beta-globin 5'HS4 and human T-cell receptor alpha/delta BEAD-1 insulators in self-inactivating retroviral vectors reduces their genotoxic potential

Insertional mutagenesis by retroviral vectors has emerged as a serious impediment to the widespread application of hematopoietic stem cell gene transfer for the treatment of hematologic diseases. Here we report the development of a 77-base pair element, FII/BEAD-A (FB), which contains the minimal enhancer-blocking components of the chicken beta-globin 5'HS4 insulator and a homologous region from the human T-cell receptor alpha/delta BEAD-1 insulator. With a new flow cytometry-based assay, we show that the FB element is as effective in enhancer-blocking activity as the prototypical 1.2-kilobase 5'HS4 insulator fragment. When incorporated into the residual U3 region of the 3' long terminal repeat (LTR) of a self-inactivating (SIN) gammaretroviral vector, the FB element was stably transferred to the 5' LTR during reverse transcription, flanking the integrated transgene expression cassette. Notably, using a recently established in vitro insertional mutagenesis assay involving primary murine hematopoietic cells, we found that SIN gammaretroviral vectors, as well as SIN lentiviral vectors, containing the FB element exhibited greatly reduced transforming potential-to background levels under the experimental conditions used-compared with their unshielded counterparts. These results suggest that the FB element-mediated enhancer-blocking modification is a promising approach to dramatically improve the safety of retroviral vectors for therapeutic gene transfer.

Role of the RUNX1-EVI1 fusion gene in leukemogenesis

RUNX1-EVI1 is a chimeric gene generated by t(3;21)(q26;q22) observed in patients with aggressive transformation of myelodysplastic syndrome or chronic myelogenous leukemia. RUNX1-EVI1 has oncogenic potentials through dominant-negative effect over wild-type RUNX1, inhibition of Jun kinase (JNK) pathway, stimulation of cell growth via AP-1, suppression of TGF-beta-mediated growth inhibition and repression of C/EBPalpha. Runx1-EVI1 heterozygous knock-in mice die in uteri due to central nervous system (CNS) hemorrhage and severe defects in definitive hematopoiesis as Runx1-/- mice do, indicating that RUNX1-EVI1 dominantly suppresses functions of wild-type RUNX1 in vivo. Acute myelogenous leukemia is induced in mice transplanted with bone marrow cells expressing RUNX1-EVI1, and a Runx1-EVI1 knock-in chimera mouse developed acute megakaryoblastic leukemia. These results suggest that RUNX1-EVI1 plays indispensable roles in leukemogenesis of t(3;21)-positive leukemia. Major leukemogenic effect of RUNX1-EVI1 is mainly through histone deacetyltransferase recruitment via C-terminal binding protein. Histone deacetyltransferase could be a target in molecular therapy of RUNX1-EVI1-expressing leukemia.

Amplification of PRKCI, located in 3q26, is associated with lymph node metastasis in esophageal squamous cell carcinoma

DNA amplification is one of the mechanisms to activate genes that are implicated in neoplastic transformation and gain of chromosome band 3q26 is a common event in squamous cell carcinomas. The aim of the present work was to identify the specific target gene from four candidates (MDS1, PRKCI, ECT2, and PIK3CA) located on 3q26 amplification in esophageal squamous cell carcinomas (ESCCs). To assess the prevalence of copy number gains of putative genes, fluorescence in situ hybridization (FISH) was applied on 108 ESCCs and 9 ESCC cell lines. Our data showed that MDS1 and PRKCI were more frequently gained. Positive correlation was found only for PRKCI between amplification and tumor size (P = 0.043), lymph node metastasis (P = 0.015) and clinical stage (P = 0.002). PRKCI gene amplification was highly correlated with protein overexpression (P = 0.009), suggesting that gene amplification is one important mechanism involved in PRKCI overexpression. To investigate further the role of PRKCI alteration in esophageal tumors, a tissue microarray containing samples from 180 ESCCs was used for immunohistochemistry analysis. Statistical analysis revealed that PRKCI overexpression was correlated with lymph node metastasis (P = 0.002) and higher stage (P = 0.004). Performing multivariate logistic regression analysis, a significant association between PRKCI overexpression and presence of lymph node metastasis was found, which was independent of T-stage of the primary tumors (P = 0.004). Our results indicate that PRKCI is an attractive target in the 3q26 amplicon and that it may serve as a molecular marker for metastasis and occult advanced tumor stages in ESCC.

A novel interaction between the proto-oncogene Evi1 and histone methyltransferases, SUV39H1 and G9a

The transcription factor ecotropic viral integration site 1 (Evi1) is associated with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) in patients due to chromosomal aberration of chromosome 3. Here we show that Evi1 interacts with the histone methyltransferase SUV39H1. The interaction requires the N-terminal part of Evi1 and the H3-specific histone methyltransferase domain, SET, of SUV39H1 without Evi1 having an inhibitory effect on SUV39H1 methyltransferase activity. Presence of SUV39H1 enhances Evi1 transcriptional repression in a dose dependent manner. In addition, Evi1 also interacts with another histone methyltransferase, G9a, but not with SET9. Our data establish an epigenetic role of Evi1 in cell transformation by recruiting higher order chromatin remodeling complexes.

Large-scale mutagenesis in p19(ARF)- and p53-deficient mice identifies cancer genes and their collaborative networks

p53 and p19(ARF) are tumor suppressors frequently mutated in human tumors. In a high-throughput screen in mice for mutations collaborating with either p53 or p19(ARF) deficiency, we identified 10,806 retroviral insertion sites, implicating over 300 loci in tumorigenesis. This dataset reveals 20 genes that are specifically mutated in either p19(ARF)-deficient, p53-deficient or wild-type mice (including Flt3, mmu-mir-106a-363, Smg6, and Ccnd3), as well as networks of significant collaborative and mutually exclusive interactions between cancer genes. Furthermore, we found candidate tumor suppressor genes, as well as distinct clusters of insertions within genes like Flt3 and Notch1 that induce mutants with different spectra of genetic interactions. Cross species comparative analysis with aCGH data of human cancer cell lines revealed known and candidate oncogenes (Mmp13, Slamf6, and Rreb1) and tumor suppressors (Wwox and Arfrp2). This dataset should prove to be a rich resource for the study of genetic interactions that underlie tumorigenesis.

Myeloid transforming protein Evi1 interacts with methyl-CpG binding domain protein 3 and inhibits in vitro histone deacetylation by Mbd3/Mi-2/NuRD

The ecotropic viral integration site 1 ( Evi1) gene encodes a putative transcription regulator, which is aberrantly expressed in acute myeloid leukemias (AML) with chromosomal abnormalities involving the 3q26 locus. Repression and activation of transcriptional control have been reported, but it is currently unclear how Evi1 may evoke these opposing effects. Using a yeast two-hybrid screen, we identified a novel binding partner of Evi1, i.e., methyl binding domain 3b (Mbd3b) protein, a member of the Mi-2/NuRD histone deacetylase complex. Applying in vitro and in vivo assays, we found that Evi1 interacts with Mbd3b but not with other MBD family members Mbd1, -2, and -4 or MeCP2. We show that interaction of Evi1 with Mbd3 requires 40 amino acids that are adjacent and downstream of the methyl binding domain (MBD). We further demonstrate that the first three zinc fingers of Evi1 are needed for Mbd3 interaction. Evi1 acts as a transcriptional repressor when recruited to an active promoter, yet when present in the Mi-2/NuRD complex through Mbd3 interaction, it inhibits the histone deacetylation function of this multiprotein structure. Our data may in part explain how Evi1 could act as a repressor as well as an activator of transcription.

Evaluation of gene promoters for liver expression by hydrodynamic gene transfer

OBJECTIVE

Gene therapy represents a promising treatment for hepatic disease. Most approaches today use viral methods to target tissues. While nonviral gene therapy is less prominent, hydrodynamic gene delivery represents a promising approach to direct gene expression to the liver. The purpose of the present study was to evaluate promoters for efficient gene expression in hepatocytes in vivo by hydrodynamic delivery and to test the findings in a model of hemophilia A.

MATERIALS AND METHODS

Human cytomegalovirus (hCMV), chicken beta-actin/CMV enhancer (CAG), elongation factor-1 alpha (EF1alpha), and phosphoglycerokinase (PGK) promoters were subcloned into plasmids with a luciferase reporter gene. In vitro calcium phosphate-mediated transfection of 2 x 10(5) HEK 293 cells was followed by in vivo whole animal bioluminescence and luminometry after hydrodynamic tail vein injection of plasmid DNA. Six-month-old FVB factor VIII (FVIII)-deficient mice were similarly injected with CBA- or EF1alpha-promoted constructs containing the FVIII heavy and light chains and expression was examined.

RESULTS

In vitro transfection demonstrated a hierarchy of expression: hCMV-intron>CAG>EF1alpha>hCMV>>PGK. In vivo luminometry demonstrated that the CAG construct produced 2.6x, 3.0x, 3.4x, and >1000x the expression of the hCMV-intron, EF1alpha, hCMV, and PGK constructs respectively. FVIII plasmid injected hemophilic mice demonstrated higher levels of FVIII expression with CAG versus EF1alpha, confirming the reporter gene studies. All FVIII-deficient mice injected with EF1alpha-FVIII or CAG-FVIII plasmids survived after tail clipping.

CONCLUSIONS

The CAG promoter/enhancer combination is an excellent alternative to the human CMV promoter for hydrodynamic gene delivery to the liver.

Genome-wide survey and developmental expression mapping of zebrafish SET domain-containing genes

SET domain-containing proteins represent an evolutionarily conserved family of epigenetic regulators, which are responsible for most histone lysine methylation. Since some of these genes have been revealed to be essential for embryonic development, we propose that the zebrafish, a vertebrate model organism possessing many advantages for developmental studies, can be utilized to study the biological functions of these genes and the related epigenetic mechanisms during early development. To this end, we have performed a genome-wide survey of zebrafish SET domain genes. 58 genes total have been identified. Although gene duplication events give rise to several lineage-specific paralogs, clear reciprocal orthologous relationship reveals high conservation between zebrafish and human SET domain genes. These data were further subject to an evolutionary analysis ranging from yeast to human, leading to the identification of putative clusters of orthologous groups (COGs) of this gene family. By means of whole-mount mRNA in situ hybridization strategy, we have also carried out a developmental expression mapping of these genes. A group of maternal SET domain genes, which are implicated in the programming of histone modification states in early development, have been identified and predicted to be responsible for all known sites of SET domain-mediated histone methylation. Furthermore, some genes show specific expression patterns in certain tissues at certain stages, suggesting the involvement of epigenetic mechanisms in the development of these systems. These results provide a global view of zebrafish SET domain histone methyltransferases in evolutionary and developmental dimensions and pave the way for using zebrafish to systematically study the roles of these genes during development.

The MDS1-EVI1 gene complex as a retrovirus integration site: impact on behavior of hematopoietic cells and implications for gene therapy

Gene therapy trials have been performed with virus-based vectors that have the ability to integrate permanently into genomic DNA and thus allow prolonged expression of corrective genes after transduction of hematopoietic stem and progenitor cells. Adverse events observed during the X-linked severe combined immunodeficiency gene therapy trial revealed a significant risk of genotoxicity related to retrovirus vector integration and activation of adjacent proto-oncogenes, with several cases of T-cell leukemia linked to vector activation of the LMO2 gene. In patients with chronic granulomatous disease (CGD), rhesus macaques, and mice receiving hematopoietic stem and progenitor cells transduced with retrovirus vectors, a highly non-random pattern of vector integration has been reported. The most striking finding has been overrepresentation of integrations in one specific genomic locus, a complex containing the MDS1 and the EVI1 genes. Most evidence suggests that this overrepresentation is primarily due to a modification of primitive myeloid cell behavior by overexpression of EVI1 or MDS1-EVI1, as opposed to a specific predilection for integration at this site. Three different proteins can be produced from this complex locus: MDS1, MDS1-EVI1, and EVI1. This review will summarize current knowledge regarding this locus and its gene products, with specific focus on issues with relevance to gene therapy, leukemogenesis, and hematopoiesis. Insights into the mechanisms that result in altered hematopoiesis and leukemogenesis when this locus is dysregulated could improve the safety of gene therapy in the future.

Globin lentiviral vector insertions can perturb the expression of endogenous genes in beta-thalassemic hematopoietic cells

Although hematopoietic cell gene therapy using retroviral vectors has recently achieved success in clinical trials, safety issues regarding vector insertional mutagenesis have emerged. Vector insertion, resulting in transcriptional activation of proto-oncogenes, played a role in the development of lymphoid leukemia in an X-linked severe combined immunodeficiency trial, and caused myeloid clonal dominance in a trial for chronic granulomatous disease. These events have raised the question of whether gene therapy for other disorders such as beta-thalassemia and sickle cell disease may hold a similar risk. In this study, we prospectively evaluated whether gamma-globin lentiviral vectors containing enhancer elements from the beta-globin locus control region could alter the expression of genes near the vector insertion. We studied this question in primary, clonal murine beta-thalassemic erythroid cells, where globin regulatory elements are highly active. We found an overall incidence of perturbed expression in 28% of the transduced clones, with 11% of all genes contained within a 600-kilobase region surrounding the vector-insertion site demonstrating altered expression. This rate was higher than that observed for a lentiviral vector containing a viral long-terminal repeat (LTR). This is the first direct evidence that lentiviral vectors can cause insertional dysregulation of cellular genes at a frequent rate.

AML1 mutations induced MDS and MDS/AML in a mouse BMT model

Myelodysplastic syndrome (MDS) is a hematopoietic stem-cell disorder characterized by trilineage dysplasia and susceptibility to acute myelogenous leukemia (AML). Analysis of molecular basis of MDS has been hampered by the heterogeneity of the disease. Recently, mutations of the transcription factor AML1/RUNX1 have been identified in 15% to 40% of MDS-refractory anemia with excess of blasts (RAEB) and MDS/AML. We performed mouse bone marrow transplantation (BMT) using bone marrow cells transduced with the AML1 mutants. Most mice developed MDS and MDS/AML-like symptoms within 4 to 13 months after BMT. Interestingly, among integration sites identified, Evi1 seemed to collaborate with an AML1 mutant harboring a point mutation in the Runt homology domain (D171N) to induce MDS/AML with an identical phenotype characterized by marked hepatosplenomegaly, myeloid dysplasia, leukocytosis, and biphenotypic surface markers. Collaboration between AML1-D171N and Evi1 was confirmed by a BMT model where coexpression of AML1-D171N and Evi1 induced acute leukemia of the same phenotype with much shorter latencies. On the other hand, a C-terminal truncated AML1 mutant (S291fsX300) induced pancytopenia with erythroid dysplasia in transplanted mice, followed by progression to MDS-RAEB or MDS/AML. Thus, we have developed a useful mouse model of MDS/AML that should help in the understanding of the molecular basis of MDS and the progression of MDS to overt leukemia.

Pathogenic risk of endogenous retrovirus infection in immunodeficient hosts

To investigate the pathogenic risk of endogenous retroviruses (ERVs) infection in immunodeficient hosts, the ERV of N-type ecotropic murine leukemia virus (MuLV) isolated from SL mice, a kind of mice containing considerable infectious ERV particles determined with SC-XC test and developing leukemia spontaneously with average of high frequency of 30% and incubation period of 315days, was inoculated intraperitoneally into newborn CBA nude mice. The distinct marker of splenomegaly for leukemia was observed in 33% of homozygous (nu/nu) and 17% of heterozygous (nu/+) of CBA nude mice with average incubation period of 310days and 432days post-inoculation, respectively. Furthermore, the ERV induced leukemia in both the SL mice and CBA nude mice was identified to be B lymphatic, transplantable and with rearrangement of the Evi-1 locus. The higher induction of leukemia and rearrangement of the Evi-1 locus in CBA nude mice are considered to be dependent on the lower immune status of the hosts. These findings indicate that the ERV could present the host immune dependent leukemogenesis in immunodeficient hosts through the Evi-1 gene rearrangement and suggest that screening of ERVs may be necessary in clinical transplantation or transfusion.

Promoter Choice for Retroviral Vectors: Transcriptional Strength Versus Trans-Activation Potential

Gene expression from retroviral vectors can be driven by either the retroviral long terminal repeat (LTR) promoter or by cellular or viral promoters located internally in an LTR-deleted self-inactivating vector design. Adverse events in a gene therapy clinical trial for X-linked severe combined immune deficiency have led to the realization that the enhancer/promoter elements contained within integrated vectors may also act outside the vector genome to trans-activate host genes. Ideally, the gene expression system chosen for a vector should possess a low probability of trans-activation while still being able to support adequate levels of transgene expression. However, the parameters that define these specific characteristics are unknown. To gain insight into the mechanism of trans-activation, we compared a panel of commonly used retroviral LTRs and cellular and viral promoters for their ability to drive gene expression and to trans-activate a nearby minimal promoter in three different cell lines. These studies identified two elements, the cytomegalovirus enhancer/chicken beta-actin (CAG) and elongation factor (EF)-1alpha promoters, as being of potential value for use in vectors targeting lymphoid cells, as these elements exhibited both high levels of reporter gene expression and relatively low levels of trans-activation in T cells.

Leukemogenesis of the EVI1/MEL1 gene family

Leukemia is a group of monoclonal diseases that arise from hematopoietic stem and progenitor cells in the bone marrow or other hematopoietic organs. Retroviral infections are one of the major events leading to leukemogenesis in mice, because retroviruses can induce hematopoietic disease via the insertional mutagenesis of oncogenes; therefore, the cloning of viral-integration sites in murine leukemia has provided valuable molecular tags for oncogene discovery. Transcription of the murine gene ecotropic viral-integration site 1 (Evi1) is activated by nearby viral integration. In humans, the Evi1 homologue EVI1 is activated by chromosomal translocations. This review discusses the roles of the overexpression of EVI1/MEL1 gene family members in leukemogenesis, the relationships of various translocations in EVI1 overexpression, and the importance of PR domains in tumor suppression and oncogenesis. The functions of EVI1/MEL1 members as transcription factors and the concept of EVI1-positive leukemia as a stem cell disease are also reviewed.

UXT interacts with the transcriptional repressor protein EVI1 and suppresses cell transformation

The EVI1 transcriptional repressor is critical to the normal development of a variety of tissues and participates in the progression of acute myeloid leukaemias. The repressor domain (Rp) was used to screen an adult human kidney yeast two-hybrid library and a novel binding partner designated ubiquitously expressed transcript (UXT) was isolated. Enforced expression of UXT in Evi1-expressing Rat1 fibroblasts suppresses cell transformation and UXT may therefore be a negative regulator of Evi1 biological activity. The Rp-binding site for UXT was determined and non-UXT-binding Evi1 mutants (Evi1Delta706-707) were developed which retain the ability to bind the corepressor mCtBP2. Evi1Delta706-707 transforms Rat1 fibroblasts, showing that the interaction is not essential for Evi1-mediated cell transformation. However, Evi1Delta706-707 produces an increased proportion of large colonies relative to wild-type, showing that endogenous UXT has an inhibitory effect on Evi1 biological activity. Exogenous UXT still suppresses Evi1Delta706-707-mediated cell transformation, indicating that it inhibits cell proliferation and/or survival by both Evi1-dependent and Evi1-independent mechanisms. These observations are consistent with the growth-suppressive function attributed to UXT in human prostate cancer. Our results show that UXT suppresses cell transformation and might mediate this function by interaction and inhibition of the biological activity of cell proliferation and survival stimulatory factors like Evi1.

The oncogene and developmental regulator EVI1: expression, biochemical properties, and biological functions

The EVI1 gene codes for a zinc finger transcription factor with important roles both in normal development and in leukemogenesis. Transcriptional activation of this gene through chromosome rearrangements or other, yet to be identified mechanisms leads to particularly aggressive forms of human myeloid leukemia. In vitro as well as in animal model systems, EVI1 affected cellular proliferation, differentiation, and apoptosis in cell type specific ways. Retroviral integrations into the EVI1 locus provided cells with increased abilities to engraft, survive, and proliferate in bone marrow transplantation experiments. Experimental overexpression of EVI1 by itself was insufficient to cause leukemia in animal model systems, but it cooperated with other genes in this process. This review summarizes the currently available experimental evidence for the proposed biochemical and biological functions of this important oncogene.

Mutation at the Evi1 locus in Junbo mice causes susceptibility to otitis media

Otitis media (OM), inflammation of the middle ear, remains the most common cause of hearing impairment in children. It is also the most common cause of surgery in children in the developed world. There is evidence from studies of the human population and mouse models that there is a significant genetic component predisposing to OM, yet nothing is known about the underlying genetic pathways involved in humans. We identified an N-ethyl-N-nitrosourea-induced dominant mouse mutant Junbo with hearing loss due to chronic suppurative OM and otorrhea. This develops from acute OM that arises spontaneously in the postnatal period, with the age of onset and early severity dependent on the microbiological status of the mice and their air quality. We have identified the causal mutation, a missense change in the C-terminal zinc finger region of the transcription factor Evi1. This protein is expressed in middle ear basal epithelial cells, fibroblasts, and neutrophil leukocytes at postnatal day 13 and 21 when inflammatory changes are underway. The identification and characterization of the Junbo mutant elaborates a novel role for Evi1 in mammalian disease and implicates a new pathway in genetic predisposition to OM.

Otitis media (OM), inflammation of the middle ear, is the most common cause of deafness in children. Although acute episodes of OM in children are associated with middle ear infections, in a substantial portion of cases recurrent episodes of OM, or a chronic suppurative OM, will develop. There is evidence from genetic studies of human families that there is a significant genetic component contributing to the development of recurrent and chronic forms of OM. However, the genes involved have not been identified. The authors have identified and characterized mouse mutants that demonstrate chronic OM as a route to identifying genes involved with OM. This study describes one mutant, Junbo, which shares many features with human OM. Junbo develops an acute OM following birth that subsequently develops into a chronic suppurative form of OM. Junbo carries a mutation in the transcription factor gene, Evi1. Evi1 is expressed in a variety of cell types in the middle ear lining when inflammatory changes are underway. The identification of the Junbo mutation implicates a new gene involved in predisposition to OM.

The Genetic Engineering of Hematopoietic Stem Cells: the Rise of Lentiviral Vectors, the Conundrum of the LTR, and the Promise of Lineage-restricted Vectors

Recent studies on the integration patterns of different categories of retroviral vectors, the genotoxicity of long-terminal repeats (LTRs) and other genetic elements, the rise of lentiviral technology and the emergence of regulated vector systems providing tissue-restricted transgene expression and RNA interference, are profoundly changing the landscape of stem cell-based therapies. New developments in vector design and an increasing understanding of the mechanisms underlying insertional oncogenesis are ushering in a new phase in hematopoietic stem cell (HSC) engineering, thus bringing the hitherto exclusive reliance on LTR-driven, gamma-retroviral vectors to an end. Based on their ability to transduce non-dividing cells and their genomic stability, lentiviral vectors offer new prospects for the manipulation of HSCs. Tissue-specific vectors, as exemplified by globin vectors, not only provide therapeutic efficacy, but may also enhance safety, insofar that they restrict transgene expression in stem cells, progenitor cells and blood cells in all but the transcriptionally targeted lineage. This review provides a survey of these advances as well as several remaining challenges, focusing in particular on the importance of achieving adequate levels of protein expression from a limited number of vector copies per cell-ideally one to two.

Trib1 and Evi1 cooperate with Hoxa and Meis1 in myeloid leukemogenesis

Cooperative activation of Meis1 and Hoxa9 perturbs myeloid differentiation and eventually leads myeloid progenitors to leukemia, yet it remains to be clarified what kinds of subsequent molecular processes are required for development of overt leukemia. To understand the molecular pathway in Hoxa9/Meis1-induced leukemogenesis, retroviral insertional mutagenesis was applied using retrovirus-mediated gene transfer. The mice that received Hoxa9/Meis1-transduced bone marrow cells developed acute myeloid leukemia (AML), and Trib1, Evi1, Ahi1, Raralpha, Pitpnb, and AK039950 were identified as candidate cooperative genes located near common retroviral integration sites. Trib1 and Evi1 were up-regulated due to retroviral insertions, and coexpression of these genes significantly accelerated the onset of Hoxa9/Meis1-induced AML, suggesting that Trib1 and Evi1 are the key collaborators. Furthermore, Trib1 by itself is a novel myeloid oncogene, enhancing phosphorylation of ERK, resulting in inhibition of apoptosis. These results demonstrate the importance of specific oncogene interaction in myeloid leukemogenesis.

Targeted degradation of the AML1/MDS1/EVI1 oncoprotein by arsenic trioxide

Arsenic trioxide (ATO) has been found to be an effective treatment for acute promyelocytic leukemia patients and is being tested for treating other hematologic malignancies. We have previously shown that AML1/MDS1/EVI1 (AME), a fusion gene generated by a t(3;21)(q26;q22) translocation found in patients with chronic myelogenous leukemia during blast phase, myelodysplastic syndrome, or acute myelogenous leukemia (AML), impairs hematopoiesis and eventually induces an AML in mice. Both fusion partners of AME, AML1 and MDS1/EVI1, encode transcription factors and are also targets of a variety of genetic abnormalities in human hematologic malignancies. In addition, aberrant expression of ectopic viral integration site 1 (EVI1) has also been found in solid tumors, such as ovarian and colon cancers. In this study, we examined whether ATO could target AME and related oncoproteins. We found that ATO used at therapeutic levels degrades AME. The ATO treatment induces differentiation and apoptosis in AME leukemic cells in vitro as well as reduces tumor load and increases the survival of mice transplanted with these cells. We further found that ATO targets AME via both myelodysplastic syndrome 1 (MDS1) and EVI1 moieties and degrades EVI1 via the ubiquitin-proteasome pathway and MDS1 in a proteasome-independent manner. Our results suggest that ATO could be used as a part of targeted therapy for AME-, AML1/MDS1-, MDS1/EVI1-, and EVI1-positive human cancers.

C. elegans EVI1 proto-oncogene, EGL-43, is necessary for Notch-mediated cell fate specification and regulates cell invasion

During C. elegans development, LIN-12 (Notch) signaling specifies the anchor cell (AC) and ventral uterine precursor cell (VU) fates from two equivalent pre-AC/pre-VU cells in the hermaphrodite gonad. Once specified, the AC induces patterned proliferation of vulva via expression of LIN-3 (EGF) and then invades into the vulval epithelium. Although these cellular processes are essential for the proper organogenesis of vulva and appear to be temporally regulated, the mechanisms that coordinate the processes are not well understood. We computationally identified egl-43 as a gene likely to be expressed in the pre-AC/pre-VU cells and the AC, based on the presence of an enhancer element similar to the one that transcribes lin-3 in the same cells. Genetic epistasis analyses reveal that egl-43 acts downstream of or parallel to lin-12 in AC/VU cell fate specification at an early developmental stage, and functions downstream of fos-1 as well as upstream of zmp-1 and him-4 to regulate AC invasion at a later developmental stage. Characterization of the egl-43 regulatory region suggests that EGL-43 is a direct target of LIN-12 and HLH-2 (E12/47), which is required for the specification of the VU fate during AC/VU specification. EGL-43 also regulates basement membrane breakdown during AC invasion through a FOS-1-responsive regulatory element that drives EGL-43 expression in the AC and VU cells at the later stage. Thus, egl-43 integrates temporally distinct upstream regulatory events and helps program cell fate specification and cell invasion.

Conservation and expression of a novel alternatively spliced Evi1 exon

The Evi1 transcriptional repressor protein is expressed in a developmentally regulated manner, is essential for normal development, participates in regulating cell proliferation and differentiation of cells of haemopoietic and neuronal origin and contributes to the progression of leukaemia. In this report we describe a new murine Evi1 gene transcript (Delta105) that contains two alternatively spliced regions encoding a 9 amino acid insertion (Rp+9) within the repressor domain (Rp) and a 105 amino acid C-terminal truncation. Abundant levels of the 105 amino acid truncated protein are observed in murine leukaemia cells. The combined primary sequence alterations do not affect the DNA binding, transcriptional repressor or CtBP2 protein binding properties of Evi1 but they do reduce its transforming and cell proliferation stimulating activities. Reduced transforming activity is most likely due to the C-terminal truncation as the activity of Evi1 containing either Rp or Rp+9 is indistinguishable. Both isoforms exist in all murine tissues and cell lines examined. However, only the Rp+9 alternative splice variant is also found in humans and other vertebrates. Murine and human forms of Evi1 with Rp or Rp+9 exist. The additional 9 amino acids are encoded by a conserved 27 nucleotide exon, the overall structural organisation of the gene being preserved in the two species. The function of the Rp+9 and Delta105 splice variants is unknown although the conservation of Rp+9 throughout evolution in vertebrate species suggests it is essential to the broad spectrum of biological activities attributed to this developmentally essential protein.

Fluorescence in situ hybridization studies using BAC clones of the EVI1 locus in hematological malignancies with 3q rearrangements

Chromosomal rearrangements involving 3q26 are a recurrent aberration in malignant myeloid disorders. Several of these rearrangements involve the EVI1 oncogene or its surrounding sequences and are associated with a poor prognosis. Fluorescence in situ hybridization (FISH) studies using bacterial artificial chromosome (BAC) clones were conducted to determine whether the EVI1 locus was rearranged in nine patients with hematological malignancies carrying 3q abnormalities. A dual-color probe was constructed with nine BACs; centromeric clones covering 1 Mb and including the EVI1 gene were labeled with a red fluorescent dye and telomeric clones covering 1 Mb were labeled with a green fluorescent dye. Two patients showed normal copies of the EVI1 locus, four patients showed one EVI1 locus rearranged (in all of them the breakpoint on 3q26 was telomeric to EVI1), one patient showed one copy of the EVI1 locus translocated to another chromosome, one patient showed one copy of the EVI1 locus rearranged and the other copy translocated, and one patient showed one extra copy of the EVI1 locus. In four cases, FISH studies using the EVI1 clones detected different 3q abnormalities not previously found by conventional cytogenetics. FISH analysis with BAC clones was a useful tool for identifying the chromosome breakpoints affecting the EVI1 locus in patients with 3q26 rearrangements.

The control of histone lysine methylation in epigenetic regulation

Histone lysine methylation plays a fundamental role in chromatin organization and function. This epigenetic mark is involved in many biological processes such as heterochromatin formation, chromosome X inactivation, genomic imprinting and transcriptional regulation. Here, we review recent advances in how histone lysine methylation participates in these biological events, and the enzymes that control histone lysine methylation and demethylation.

EVI1 is consistently expressed as principal transcript in common and rare recurrent 3q26 rearrangements

In contrast to the well-documented involvement of EVI1 in various 3q26 aberrations, the transcriptional status of EVI1 in rare recurrent or sporadic 3q26 chromosomal defects has remained largely unexplored. Moreover, in a recent report, the association between 3q26 alterations in myeloid proliferations and ectopic EVI1 expression was questioned. Therefore, we performed a detailed physical mapping of 3q26 breakpoints using a 1.3-Mb tiling path BAC contig covering the EVI1 locus and a carefully designed quantification of both EVI1 and MDS/EVI1 transcripts in 30 hematological malignancies displaying 3q26 aberrations. Cases included well-known rare, recurring chromosomal aberrations such as t(3;17)(q26;q22), t(2;3)(p21-22;q26), and t(3;6)(q26;q25), as well as 10 new sporadic cases. Extensive 3q26 breakpoint mapping allowed unequivocal and sensitive FISH detection of EVI1 rearrangements on both metaphases and interphase nuclei. Real-time quantitative PCR analyses indicated that typically both MDS1/EVI1 and EVI1, but not MDS1, were expressed in these malignancies, with EVI1 the primary transcript. In conclusion, we have demonstrated EVI1 involvement in numerous novel sporadic and recurrent 3q26 rearrangements. Our results underscore the feasibility of FISH as an adjunct to PCR for the identification of EVI1 deranged leukemias and identified EVI1 as the principal transcript expressed in these malignancies.

Normal and transforming functions of RUNX1: a perspective

Converging studies from many investigators indicate that RUNX1 has a critical role in the correct maintenance of essential cellular functions during embryonic development and after birth. The discovery that this gene is also frequently mutated in human leukemia has increased the interest in the role that RUNX1 plays in both normal and transforming pathways. Here, we provide an overview of the many roles of RUNX1 in hematopoietic self-renewal and differentiation and summarize the information that is currently available on the many mechanisms of RUNX1 deregulation in human leukemia.

Evi1 is specifically expressed in the distal tubule and duct of the Xenopus pronephros and plays a role in its formation

The ecotropic viral integration site 1 (Evi1) and related MEL1 (MDS1/Evi1-like gene 1) genes are zinc finger oncogenic transcription factors involved in myeloid leukaemia. Here, we show that in Xenopus, Evi1 and MEL1 have partially overlapping restricted embryonic expression profiles. Within the pronephros, Evi1 and MEL1 are sequentially expressed within the distal tubule and duct compartments, Evi1 transcription being detected prior to any sign of pronephric morphogenesis. In the pronephros of zebrafish embryos, Evi1 expression is restricted to the posterior portion of the duct, the anterior portion having characteristics of proximal tubules. In the Xenopus pronephros, Evi1 expression is upregulated by retinoid signaling and repressed by overexpression of xWT1 and by Notch signaling. Overexpression of Evi1 from late neurula stage specifically inhibits the expression of proximal tubule and glomus pronephric markers. We show that the first zinc finger and CtBP interaction domains are required for this activity. Overexpression of a hormone-inducible Evi1-VP16 antimorphic fusion with activation at neurula stage disrupts distal tubule and duct formation and expands the expression of glomus markers. Although overexpression of this construct also causes in many embryos a reduction of proximal tubule markers, embryos with expanded and ectopic staining have been also observed. Together, these data indicate that Evi1 plays a role in the proximo-distal patterning of the pronephros and suggest that it may do so by functioning as a CtBP dependent repressor.

Evi1 is a survival factor which conveys resistance to both TGFbeta- and taxol-mediated cell death via PI3K/AKT

In hematopoietic cells the transforming potential of the ecotropic viral integration site 1 (Evi1) oncogene is thought to be dependent upon the ability to inhibit TGFbeta signaling. Although Evi1 has recently been implicated in certain epithelial cancers, the effects of Evi1 on transformation and TGFbeta signaling in epithelial cells are not completely understood. Herein, we have determined the effects of Evi1 on TGFbeta signaling in intestinal epithelial cells. Stable expression of Evi1 in non-transformed intestinal epithelial cells inhibited induction of some Smad3-dependent TGFbeta target genes, such as PAI1. However, TGFbeta-mediated induction of cellular adhesion signaling components such as integrin1 and paxillin was not inhibited by Evi1; nor did Evi1 inhibit TGFbeta-mediated epithelial to mesenchymal transition. Likewise, Evi1 did not inhibit TGFbeta-mediated downregulation of cyclin D1 or block TGFbeta-mediated growth inhibition. However, Evi1 did inhibit TGFbeta-mediated apoptosis by a process that involves phosphoinositide-3-kinase (PI3K) and its downstream effector AKT. The ability of Evi1 to suppress apoptosis is not restricted to TGFbeta-mediated cell death, since Evi1 also protects intestinal epithelial cells from taxol-mediated apoptosis. Evi1 is overexpressed in some human colon cancer cell lines, and overexpression is associated with amplification of the Evi1 gene. Knockdown of Evi1 by siRNA inhibited AKT phosphorylation in HT-29 human colon cancer cells and increased their sensitivity to taxol-mediated apoptosis. These data indicate that Evi1 functions as a survival gene in intestinal epithelial cells and colon cancer cells, activating PI3K/AKT and conveying resistance to both physiological and therapeutic apoptotic stimuli.

Sox4 cooperates with Evi1 in AKXD-23 myeloid tumors via transactivation of proviral LTR

Myeloid leukemias in AKXD23 mice contain proviral insertions at Evi1, resulting in transcriptional activation. Although Evi1 is clearly involved in leukemia, gene transfer studies in mice with Evi1 fail to cause leukemia, arguing that cooperating events are necessary. We reanalyzed AKXD-23 tumors for cooperating proviral insertion and found that each tumor had a proviral insertion in Sox4, which encodes an HMG-box transcription factor. RNA analysis revealed these insertions cause increased Sox4 expression. Overexpression of Sox4 in 32Dcl3 cells markedly inhibited cytokine-induced granulocyte maturation, as documented by morphologic and mRNA analysis. Sox4-expressing cells had higher levels of transcripts associated with proliferation, including Evi1. Conversely, in leukemic cells that express Sox4 and bear provirally activated Evi1, suppression of Sox4 with short hairpin RNAs resulted in down-regulation of both Sox4 and Evi1. By cotransfection studies, Sox4 is able to transactivate the AKV long terminal repeat, which likely explains how Sox4 transcriptionally up-regulates provirally activated Evi1; however, Sox4 does not appear to regulate the native Evi1 promoter. We propose that Sox4 proviral activation is selected for in the setting of prior proviral activation of Evi1, because it transactivates the relatively weak LTR of AKV leading to higher Evi1 expression and consequent block to differentiation.

Retroviral insertional mutagenesis: past, present and future

Retroviral insertion mutagenesis screens in mice are powerful tools for efficient identification of oncogenic mutations in an in vivo setting. Many oncogenes identified in these screens have also been shown to play a causal role in the development of human cancers. Sequencing and annotation of the mouse genome, along with recent improvements in insertion site cloning has greatly facilitated identification of oncogenic events in retrovirus-induced tumours. In this review, we discuss the features of retroviral insertion mutagenesis screens, covering the mechanisms by which retroviral insertions mutate cellular genes, the practical aspects of insertion site cloning, the identification and analysis of common insertion sites, and finally we address the potential for use of somatic insertional mutagens in the study of nonhaematopoietic and nonmammary tumour types.

Evi-1 expression in Xenopus

The Evi-1 gene was first identified as a site for viral integration in murine myeloid leukemia. Evi-1 is a zinc finger transcription factor that has been implicated in the development of myeloid neoplasia. In humans, disruption of the Evi-1 locus, by chromosomal rearrangements, is associated with myeloid leukemia and myelodyplastic syndromes. Here, we report the cloning and developmental pattern of expression of Xenopus Evi-1. xEvi-1 is expressed during oogenesis and during embryonic development. In situ hydridization reveals that xEvi-1 has a dynamic expression profile during early embryonic development. Expression of Evi-1 is detected by in situ hybridization in the pronephric tissue, the brain and in neural crest derivatives of the head and neck.

Hematopoietic stem cell gene therapy: dead or alive?

Despite some reports of toxicity in recent clinical trials, many scientists believe that the use of gene therapy in the treatment of congenital genetic defects and acquired disorders has too much potential to abandon. Hematopoietic stem cells (HSCs) have been primary targets for gene therapy owing to their capacity for differentiation and self-renewal, whereby multiple cell lineages can potentially be corrected for the lifetime of an individual. These efforts represent a long-term investment towards broadening physicians' treatment options for patients whose diseases, in particular certain immunodeficiencies, are fatal and where no other therapy is available. We review the recent progress and clinical triumphs as well as the reported toxicity related to insertional mutagenesis. We also discuss the current risk-to-benefit estimates and future strategies to reduce the risks and allow full realization of clinical potential. Scientists are continually revising protocols: going both from "bench to bedside" and, as strikingly demonstrated by HSC gene therapy, from "bedside to bench."

Characterization of the PR domain of RIZ1 histone methyltransferase

RIZ1 (PRDM2) and PRDI-BF1 (PRDM1) are involved in B cell differentiation and the development of B cell lymphomas. These proteins are expressed in two forms that differ by the presence or absence of a PR domain. The protein product that retains the PR domain is anti-tumorigenic while the product that lacks the PR domain is oncogenic and over-expressed in tumor cells. The conserved PR domain is homologous to the SET domain from a family of histone methyltransferases. RIZ1 is also a histone methyltransferase and methylates lysine 9 in histone H3. This activity has been mapped to the PR domain. In the present study, deuterium exchange mass spectrometry was used to define the structural boundaries of the RIZ1 PR domain and to map sites of missense mutations that occur in human cancers and reduce methyltransferase activity. Flexible segments were selectively deleted to produce protein products that crystallize for structural studies. Segments at the carboxyl terminus of the PR domain that are involved in methylation of H3 were shown to be flexible, similar to SET domains, suggesting that the PR and SET methyltransferases may belong to an emerging class of proteins that contain mobile functional regions.

GATA motifs regulate early hematopoietic lineage-specific expression of the Gata2 gene

Transcription factor GATA-2 is essential for definitive hematopoiesis, which developmentally emerges from the para-aortic splanchnopleura (P-Sp). The expression of a green fluorescent protein (GFP) reporter placed under the control of a 3.1-kbp Gata2 gene regulatory domain 5' to the distal first exon (IS) mirrored that of the endogenous Gata2 gene within the P-Sp and yolk sac (YS) blood islands of embryonic day (E) 9.5 murine embryos. The P-Sp- and YS-derived GFP(+) fraction of flow-sorted cells dissociated from E9.5 transgenic embryos contained far more CD34(+)/c-Kit(+) cells than the GFP(-) fraction did. When cultured in vitro, the P-Sp GFP(+) cells generated both immature hematopoietic and endothelial cell clusters. Detailed transgenic mouse reporter expression analyses demonstrate that five GATA motifs within the 3.1-kbp Gata2 early hematopoietic regulatory domain (G2-EHRD) were essential for GFP expression within the dorsal aortic wall, where hemangioblasts, the earliest precursors possessing both hematopoietic and vascular developmental potential, are thought to reside. These results thus show that the Gata2 gene IS promoter is regulated by a GATA factor(s) and selectively marks putative hematopoietic/endothelial precursor cells within the P-Sp.

Identification of binding sites of EVI1 in mammalian cells

The leukemia-associated protein EVI1 possesses seven zinc fingers within an N-terminal domain (amino acids 1-250) that binds to GACAAGATA. Single amino acid missense mutants of EVI1 were developed that failed to bind DNA either in vitro, as assessed by gel shift assay, or in vivo, as shown by transactivation studies. Specifically, mutation R205N lacks high affinity binding to the GACAAGATA motif. Putative EVI1 target genes were identified by using an EVI1-(1-250)-VP16 fusion protein that acts as a transcriptional activator with the binding specificity of EVI1. Sixteen genes induced in NIH 3T3 cells by wild type EVI1-VP16 but not by mutant forms were identified. Sequence analysis revealed evolutionarily conserved GACAAGATA-like motifs within 10 kb of their transcription start sites, and by chromatin immunoprecipitation in fibroblasts, we showed occupancy of many of these sites by EVI1-VP16. To assess whether native EVI1 binds to these sites in EVI1-transformed myeloid cells, we performed chromatin immunoprecipitation in 32Dcl3 and NFS58 cells, using anti-EVI1 antisera, and we showed that the majority of these sites is bound by wild type EVI1. These putative target genes include Gadd45g, Gata2, Zfpm2/Fog2, Skil (SnoN), Klf5 (BTEB2), Dcn, and Map3k14 (Nik). In this study we demonstrated for the first time that the N-terminal DNA binding domain of EVI1 has the capacity to bind to endogenous genes. We hypothesized that these genes play a critical role in EVI1-induced transformation.

Animal models of acute myelogenous leukaemia - development, application and future perspectives

From the early inception of the transplant models through to contemporary genetic and xenograft models, evolution of murine leukaemic model systems have been critical to our general comprehension and treatment of cancer, and, more specifically, disease states such as acute myelogenous leukaemia (AML). However, even with modern advances in therapeutics and molecular diagnostics, the majority of AML patients die from their disease. Thus, in the absence of definitive in vitro models which precisely recapitulate the in vivo setting of human AMLs and failure of significant numbers of new drugs late in clinical trials, it is essential that murine AML models are developed to exploit more specific, targeted therapeutics. While various model systems are described and discussed in the literature from initial transplant models such as BNML and spontaneous murine leukaemia virus models, to the more definitive genetic and clinically significant NOD/SCID xenograft models, there exists no single compendium which directly assesses, reviews or compares the relevance of these models. Thus, the function of this article is to provide clinicians and experimentalists a chronological, comprehensive appraisal of all AML model systems, critical discussion on the elucidation of their roles in our understanding of AML and consideration to their efficacy in the development of AML chemotherapeutics.

Oncogenic transcription factor Evi1 regulates hematopoietic stem cell proliferation through GATA-2 expression

The ecotropic viral integration site-1 (Evi1) is an oncogenic transcription factor in murine and human myeloid leukemia. We herein show that Evi1 is predominantly expressed in hematopoietic stem cells (HSCs) in embryos and adult bone marrows, suggesting a physiological role of Evi1 in HSCs. We therefore investigate the role and authentic target genes of Evi1 in hematopoiesis using Evi1-/- mice, which die at embryonic day 10.5. HSCs in Evi1-/- embryos are markedly decreased in numbers in vivo with defective self-renewing proliferation and repopulating capacity. Notably, expression rate of GATA-2 mRNA, which is essential for proliferation of definitive HSCs, is profoundly reduced in HSCs of Evi1-/- embryos. Restoration of the Evi1 or GATA-2 expression in Evi1-/- HSCs could prevent the failure of in vitro maintenance and proliferation of HSC through upregulation of GATA-2 expression. An analysis of the GATA-2 promoter region revealed that Evi1 directly binds to GATA-2 promoter as an enhancer. Our results reveal that GATA-2 is presumably one of critical targets for Evi1 and that transcription factors regulate the HSC pool hierarchically.

Dysplastic definitive hematopoiesis in AML1/EVI1 knock-in embryos

The AML1/EVI1 chimeric gene is created by the t(3;21)(q26;q22) chromosomal translocation seen in patients with leukemic transformation of myelodysplastic syndrome or blastic crisis of chronic myelogenous leukemia. We knocked-in the AML1/EVI1 chimeric gene into mouse Aml1 genomic locus to explore its effect in developmental hematopoiesis in vivo. AML1/EVI1/+ embryo showed defective hematopoiesis in the fetal liver and died around embryonic day 13.5 (E13.5) as a result of hemorrhage in the central nervous system. The peripheral blood had yolk-sac-derived nucleated erythroblasts but lacked erythrocytes of the definitive origin. Although E12.5 fetal liver contained progenitors for macrophage only, E13.5 fetal liver contained multilineage progenitors capable of differentiating into dysplastic myelocyte and megakaryocyte. No erythroid progenitor was detected in E12.5 or E13.5 fetal liver. Hematopoietic progenitors from E13.5 AML1/EVI1/+ fetal liver were highly capable of self-renewal compared with those from wild-type liver. Maintained expression of PU.1 gene and decreased expression of LMO2 and SCL genes may explain the aberrant hematopoiesis in AML1/EVI1/+ fetal liver.

EVI1 Abrogates Interferon-α Response by Selectively Blocking PML Induction

EVI1 is an oncogene frequently associated with chronic and acute myeloid leukemia. In hematopoietic cells, EVI1 impairs several pathways including proliferation, differentiation, and apoptosis. Interferon-alpha (IFN-alpha) is a powerful cytokine that controls the immune response and limits the expansion of several tissues including bone marrow. These properties contribute to the effectiveness of IFN-alpha in the treatment of many neoplastic disorders especially chronic myeloid leukemia. We report here that in murine hematopoietic progenitors the expression of EVI1 completely abrogates the antiproliferative and apoptotic effects of IFN-alpha. EVI1 does not repress the JAK/STAT signaling pathway or the activation of many IFN-responsive genes. On the contrary, EVI1 prolongs the phosphorylation of STAT1 and the activation of an IFN-dependent reporter gene. However, EVI1 specifically represses the IFN-dependent induction of the tumor suppressor PML and blocks the apoptotic pathways activated by PML. We show that the position of the ISRE, which is located within the first exon of PML, is critical to block PML induction by IFN-alpha. The relocation of the ISRE to a position upstream of the transcription start site is sufficient to re-establish the response to IFN in the presence of EVI1. Our data suggest that stabilized STAT1 phosphorylation and prolonged binding of the STAT1 complex to the first exon could impair PML transcription and inhibit the activation of PML-dependent apoptotic pathways resulting in loss of IFN response. These results point to a novel mechanism utilized by an oncogene to escape normal cell response to growth-controlling cytokines.

Targeted therapies in myelodysplastic syndromes: ASH 2003 review

The myelodysplastic syndromes (MDS) continue to pose conceptual and practical conundrums because of their heterogeneity and therapeutic challenges. They are not restricted to the presence of clonal cells that are prone to excessive proliferation and premature apoptosis. In MDS the bone marrow microenvironment also is abnormal and exhibits an excess of proinflammatory cytokines, especially tumor necrosis factor (TNF), neoangiogenesis, and poorly defined immune defects. Thalidomide, a drug with anti-TNF, antiangiogenic, and immunomodulatory activities, and other agents with anti-TNF effects, such as pentoxifylline, etanercept, and infliximab, have produced hematologic improvement in 20% to 40% of patients. These agents may provide effective therapy for a subset of lower-risk MDS patients, even if the drugs target the bone marrow microenvironment predominantly. However, in higher-risk MDS patients, especially those with more than 10% blasts, it is important to eliminate abnormal cell clones; drugs used for this purpose have included arsenic trioxide, topotecan, the farnesyl transferase inhibitor tipifarnib, and demethylating agents, such as 5-azacytidine and decitabine. To increase the therapeutic index, a combination strategy may be preferable for higher-risk MDS patients, in whom the seed (clone) and the soil (bone marrow microenvironment) must be targeted simultaneously. The challenge is to recognize the subset that is likely to respond to a given drug so that patients can be preselected for therapy.