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Results for “RUNX1 Translocation Partner 1 Protein”

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At least 19 recordsLinked to original sources
PubMed1998

ETO, fusion partner in t(8;21) acute myeloid leukemia, represses transcription by interaction with the human N-CoR/mSin3/HDAC1 complex.

The t(8;21) translocation between two genes known as AML1 and ETO is seen in approximately 12-15% of all acute myeloid leukemia (AML) and is the second-most-frequently observed nonrandom genetic alteration associated with AML. AML1 up-regulates a number of target genes critical to normal hematopoiesis, whereas the AML1/ETO fusion interferes with this trans-activation. We discovered that the fusion partner ETO binds to the human homolog of the murine nuclear receptor corepressor (N-CoR). The interaction is mediated by two unusual zinc finger motifs present at the carboxyl terminus of ETO. Human N-CoR (HuN-CoR), which we cloned and sequenced in its entirety, encodes a 2,440-amino acid polypeptide and has a central domain that binds ETO. N-CoR, mammalian Sin3 (mSin3A and B), and histone deacetylase 1 (HDAC1) form a complex that alters chromatin structure and mediates transcriptional repression by nuclear receptors and by a number of oncoregulatory proteins. We found that ETO, through its interaction with the N-CoR/mSin3/HDAC1 complex, is also a potent repressor of transcription. This observation provides a mechanism for how the AML1/ETO fusion may inhibit expression of AML1-responsive target genes and disturb normal hematopoiesis.

Acute Disease↗
PubMed1998

Aberrant recruitment of the nuclear receptor corepressor-histone deacetylase complex by the acute myeloid leukemia fusion partner ETO.

Nuclear receptor corepressor (CoR)-histone deacetylase (HDAC) complex recruitment is indispensable for the biological activities of the retinoic acid receptor fusion proteins of acute promyelocytic leukemias. We report here that ETO (eight-twenty-one or MTG8), which is fused to the acute myelogenous leukemia 1 (AML1) transcription factor in t(8;21) AML, interacts via its zinc finger region with a conserved domain of the corepressors N-CoR and SMRT and recruits HDAC in vivo. The fusion protein AML1-ETO retains the ability of ETO to form stable complexes with N-CoR/SMRT and HDAC. Deletion of the ETO C terminus abolishes CoR binding and HDAC recruitment and severely impairs the ability of AML1-ETO to inhibit differentiation of hematopoietic precursors. These data indicate that formation of a stable complex with CoR-HDAC is crucial to the activation of the leukemogenic potential of AML1 by ETO and suggest that aberrant recruitment of corepressor complexes is a general mechanism of leukemogenesis.

Cell Differentiation↗
PubMed1998

ETO, a target of t(8;21) in acute leukemia, interacts with the N-CoR and mSin3 corepressors.

t(8;21) is one of the most frequent translocations associated with acute myeloid leukemia. It produces a chimeric protein, acute myeloid leukemia-1 (AML-1)-eight-twenty-one (ETO), that contains the amino-terminal DNA binding domain of the AML-1 transcriptional regulator fused to nearly all of ETO. Here we demonstrate that ETO interacts with the nuclear receptor corepressor N-CoR, the mSin3 corepressors, and histone deacetylases. Endogenous ETO also cosediments on sucrose gradients with mSin3A, N-CoR, and histone deacetylases, suggesting that it is a component of one or more corepressor complexes. Deletion mutagenesis indicates that ETO interacts with mSin3A independently of its association with N-CoR. Single amino acid mutations that impair the ability of ETO to interact with the central portion of N-CoR affect the ability of the t(8;21) fusion protein to repress transcription. Finally, AML-1/ETO associates with histone deacetylase activity and a histone deacetylase inhibitor impairs the ability of the fusion protein to repress transcription. Thus, t(8;21) fuses a component of a corepressor complex to AML-1 to repress transcription.

Cell Line↗
PubMed2002

[Determination of ETO interaction domain within nuclear receptor co-repressor].

OBJECTIVE: To determine the ETO-interaction domain of nuclear receptor co-repressor (N-CoR) for abolishing the biological function of AML1-ETO. METHODS: Ten different regions of N-CoR (N-CoRYs) were generated by means of polymerase chain reaction (PCR), and cloned into yeast expression plasmid pGADGL to construct pGADGL/N-CoRYs. The yeast two-hybrid technique and X-gal staining were used to determine the binding between the 10 different regions of N-CoR and ETO. RESULTS: It was shown that the co-existence of 988-1,126 and 1,551-1,803 amino acid residues of N-CoRY was the ETO-interaction domains required for the binding with ETO. CONCLUSION: Two domains of N-CoR that interact with two zinc fingers of ETO, and keep stable binding between the two proteins were identified.

Binding Sites↗
PubMed2004

The nuclear receptor co-repressor (N-CoR) utilizes repression domains I and III for interaction and co-repression with ETO.

The acute human leukemias are associated with the presence of chimeric gene products that arise from spontaneous chromosomal translocations. The t(8;21) translocation gene product led to the discovery of the Eight Twenty-One (ETO) gene. When fused to RUNX1, ETO is thought to mediate the formation of a repressive complex at RUNX1-dependent genes. ETO has also been found to act as a co-repressor of the promyelocytic zinc finger and Bcl-6 oncoproteins, suggesting that it may play a common role as a transcriptional co-repressor leading to human disease. An analysis of ETO-mediated repression revealed that one of the key binding partners of ETO is the nuclear receptor co-repressor (N-CoR). It is shown that two highly conserved domains of ETO interact with repression domains I and III of N-CoR. One of the ETO domains displays significant homology to Drosophila TAF(II)110, whereas the other is a predicted zinc binding motif that engages a conserved PPLXP motif in repression domain III of N-CoR. Together, these domains of ETO cooperate in repression with N-CoR and the binding sites in N-CoR overlap with those for other repressive factors. Thus, ETO has the potential to participate in a number of repressive complexes, which can be distinguished by their binding partners and target genes.

Amino Acid Motifs↗
PubMed2001

ETO, a target of t(8;21) in acute leukemia, makes distinct contacts with multiple histone deacetylases and binds mSin3A through its oligomerization domain.

t(8;21) and t(16;21) create two fusion proteins, AML-1-ETO and AML-1-MTG16, respectively, which fuse the AML-1 DNA binding domain to putative transcriptional corepressors, ETO and MTG16. Here, we show that distinct domains of ETO contact the mSin3A and N-CoR corepressors and define two binding sites within ETO for each of these corepressors. In addition, of eight histone deacetylases (HDACs) tested, only the class I HDACs HDAC-1, HDAC-2, and HDAC-3 bind ETO. However, these HDACs bind ETO through different domains. We also show that the murine homologue of MTG16, ETO-2, is also a transcriptional corepressor that works through a similar but distinct mechanism. Like ETO, ETO-2 interacts with N-CoR, but ETO-2 fails to bind mSin3A. Furthermore, ETO-2 binds HDAC-1, HDAC-2, and HDAC-3 but also interacts with HDAC-6 and HDAC-8. In addition, we show that expression of AML-1-ETO causes disruption of the cell cycle in the G(1) phase. Disruption of the cell cycle required the ability of AML-1-ETO to repress transcription because a mutant of AML-1-ETO, Delta469, which removes the majority of the corepressor binding sites, had no phenotype. Moreover, treatment of AML-1-ETO-expressing cells with trichostatin A, an HDAC inhibitor, restored cell cycle control. Thus, AML-1-ETO makes distinct contacts with multiple HDACs and an HDAC inhibitor biologically inactivates this fusion protein.

Amino Acid Sequence↗
PubMed2005

Transcriptional repression of the Neurofibromatosis-1 tumor suppressor by the t(8;21) fusion protein.

Von Recklinghausen's disease is a relatively common familial genetic disorder characterized by inactivating mutations of the Neurofibromatosis-1 (NF1) gene that predisposes these patients to malignancies, including an increased risk for juvenile myelomonocytic leukemia. However, NF1 mutations are not common in acute myeloid leukemia (AML). Given that the RUNX1 transcription factor is the most common target for chromosomal translocations in acute leukemia, we asked if NF1 might be regulated by RUNX1. In reporter assays, RUNX1 activated the NF1 promoter and cooperated with C/EBPalpha and ETS2 to activate the NF1 promoter over 80-fold. Moreover, the t(8;21) fusion protein RUNX1-MTG8 (R/M), which represses RUNX1-regulated genes, actively repressed the NF1 promoter. R/M associated with the NF1 promoter in vivo and repressed endogenous NF1 gene expression. In addition, similar to loss of NF1, R/M expression enhanced the sensitivity of primary myeloid progenitor cells to granulocyte-macrophage colony-stimulating factor. Our results indicate that the NF1 tumor suppressor gene is a direct transcriptional target of RUNX1 and the t(8;21) fusion protein, suggesting that suppression of NF1 expression contributes to the molecular pathogenesis of AML.

Animals↗
PubMed2001

Multiple regions of ETO cooperate in transcriptional repression.

In acute myeloid leukemias (AMLs) with t(8;21), the transcription factor AML1 is juxtaposed to the zinc finger nuclear protein ETO (Eight-Twenty-One), resulting in transcriptional repression of AML1 target genes. ETO has been shown to interact with corepressors, such as N-CoR and mSin3A to form complexes containing histone deacetylases. To define regions of ETO required for maximal repressor activity, we analyzed amino-terminal deletions in a transcriptional repression assay. We found that ETO mutants lacking the first 236 amino acids were not affected in their repressor activity, whereas a further deletion of 85 amino acids drastically reduced repressor function and high molecular weight complex formation. This latter mutant can still homodimerize and bind to N-CoR but shows only weak binding to mSin3A. Furthermore, we could show that a "core repressor domain" comprising nervy homology region 2 and its amino- and carboxyl-terminal flanking sequences recruits mSin3A and induces transcriptional repression. These results suggest that mSin3A and N-CoR bind to ETO independently and that both binding sites cooperate to maximize ETO-mediated transcriptional repression. Thus, ETO has a modular structure, and the interaction between the individual elements is essential for the formation of a stable repressor complex and efficient transcriptional repression.

Amino Acids↗
PubMed2002

The transcriptional corepressor MTG16a contains a novel nucleolar targeting sequence deranged in t (16; 21)-positive myeloid malignancies.

The MTG (Myeloid Translocation Gene) proteins are a family of novel transcriptional corepressors. We report that MTG16a, a protein isoform encoded by the MTG16 gene deranged by the t (16; 21) in myeloid malignancies, is targeted to the nucleolus. The amino acid sequence necessary for nucleolar localization was mapped to the MTG16a N-terminal region. MTG16a, like MTG8, the nuclear corepressor deranged by the t (8; 21), is capable to interact with specific histone deacetylases (HDACs) suggesting that the protein may mediate silencing of nucleolar gene transcription. In addition, MTG16a is capable to form oligomers with other MTG proteins. As a consequence of the t (16; 21) the AML1 DNA-binding domain replaces the MTG16a N-terminal region. The AML1-MTG16 fusion protein is targeted to the nucleoplasm where it is capable to oligomerize with MTG16a and interact with HDAC1 and HDAC3. The deficiency of HDAC-containing complexes at nucleolar sites and the accumulation of HDAC-containing complexes at AML1-sites may be critical in the pathogenesis of t (16; 21) myeloid malignancies.

Amino Acid Sequence↗
PubMed2001

Oligomerization of ETO is obligatory for corepressor interaction.

Nearly 40% of cases of acute myelogenous leukemia (AML) of the M2 subtype are due to a chromosomal translocation that combines a sequence-specific DNA binding protein, AML1, with a potent transcriptional repressor, ETO. ETO interacts with nuclear receptor corepressors SMRT and N-CoR, which recruit histone deacetylase to the AML1-ETO oncoprotein. SMRT-N-CoR interaction requires each of two zinc fingers contained in C-terminal Nervy homology region 4 (NHR4) of ETO. However, here we show that polypeptides containing NHR4 are insufficient for interaction with SMRT. NHR2 is also required for SMRT interaction and repression by ETO, as well as for inhibition of hematopoietic differentiation by AML1-ETO. NHR2 mediates oligomerization of ETO as well as AML1-ETO. Fusion of NHR4 polypeptide to a heterologous dimerization domain allows strong interaction with SMRT in vitro. These data support a model in which NHR2 and NHR4 have complementary functions in repression by ETO. NHR2 functions as an oligomerization domain bringing together NHR4 polypeptides that together form the surface required for high-affinity interaction with corepressors. As nuclear receptors also interact with corepressors as dimers, oligomerization may be a common mechanism regulating corepressor interactions.

Binding Sites↗
PubMed2004

Translocation products in acute myeloid leukemia activate the Wnt signaling pathway in hematopoietic cells.

The acute myeloid leukemia (AML)-associated translocation products AML1-ETO, PML-retinoic acid receptor alpha (RARalpha), and PLZF-RARalpha encode aberrant transcription factors. Several lines of evidence suggest similar pathogenetic mechanisms for these fusion proteins. We used high-density oligonucleotide arrays to identify shared target genes in inducibly transfected U937 cells expressing AML1-ETO, PML-RARalpha, or PLZF-RARalpha. All three fusion proteins significantly repressed the expression of 38 genes and induced the expression of 14 genes. Several of the regulated genes were associated with Wnt signaling. One of these, plakoglobin (gamma-catenin), was induced on the mRNA and protein level by all three fusion proteins. In addition, primary AML blasts carrying one of the fusion proteins significantly overexpressed plakoglobin. The plakoglobin promoter was cloned and shown to be induced by AML1-ETO, with promoter activation depending on the corepressor and histone deacetylase binding domains. The induction of plakoglobin by AML fusion proteins led to downstream signaling and transactivation of TCF- and LEF-dependent promoters, including the c-myc promoter, which was found to be bound by plakoglobin in vivo after AML1-ETO expression. beta-Catenin protein levels and TCF and LEF target genes such as c-myc and cyclin D1 were found to be induced by the fusion proteins. On the functional level, a dominant negative TCF inhibited colony growth of AML1-ETO-positive Kasumi cells, whereas plakoglobin transfection into myeloid 32D cells enhanced proliferation and clonal growth. Injection of plakoglobin-expressing 32D cells into syngeneic mice accelerated the development of leukemia. Transduction of plakoglobin into primitive murine hematopoietic progenitor cells preserved the immature phenotype during colony growth, suggesting enhanced self-renewal. These data provide evidence that activation of Wnt signaling is a common feature of several balanced translocations in AML.

Animals↗
PubMed2005

Interplay of RUNX1/MTG8 and DNA methyltransferase 1 in acute myeloid leukemia.

The translocation t(8;21)(q22;q22) in acute myeloid leukemia (AML) results in the expression of the fusion protein RUNX1/MTG8, which in turn recruits histone deacetylases (HDAC) to silence RUNX1 target genes [e.g., interleukin-3 (IL-3)]. We previously reported that expression of the RUNX1/MTG8 target gene IL-3 is synergistically restored by the combination of inhibitors of HDACs (i.e., depsipeptide) and DNA methyltransferases (DNMT; i.e., decitabine) in RUNX1/MTG8-positive Kasumi-1 cells. Thus, we hypothesized that DNMT1 is also part of the transcriptional repressor complex recruited by RUNX1/MTG8. By a chromatin immunoprecipitation assay, we identified a RUNX1/MTG8-DNMT1 complex on the IL-3 promoter in Kasumi-1 cells and in primary RUNX1/MTG8-positive AML blasts. The physical association of RUNX1/MTG8 with DNMT1 was shown by coimmunoprecipitation experiments. Furthermore, RUNX1/MTG8 and DNMT1 were concurrently released from the IL-3 promoter by exposure to depsipeptide or stabilized on the promoter by decitabine treatment. Finally, we proved that RUNX1/MTG8 and DNMT1 were functionally interrelated by showing an enhanced repression of IL-3 after coexpression in 293T cells. These results suggest a novel mechanism for gene silencing mediated by RUNX1/MTG8 and support the combination of HDAC and DNMT inhibitors as a novel therapeutic approach for t(8;21) AML.

Acute Disease↗
PubMed2001

Prevalence of molecular mechanisms of resistance to azole antifungal agents in Candida albicans strains displaying high-level fluconazole resistance isolated from human immunodeficiency virus-infected patients.

Molecular mechanisms of azole resistance in Candida albicans, including alterations in the target enzyme and increased efflux of drug, have been described, but the epidemiology of the resistance mechanisms has not been established. We have investigated the molecular mechanisms of resistance to azoles in C. albicans strains displaying high-level fluconazole resistance (MICs, > or =64 microg/ml) isolated from human immunodeficiency virus (HIV)-infected patients with oropharyngeal candidiasis. The levels of expression of genes encoding lanosterol 14alpha-demethylase (ERG11) and efflux transporters (MDR1 and CDR) implicated in azole resistance were monitored in matched sets of susceptible and resistant isolates. In addition, ERG11 genes were amplified by PCR, and their nucleotide sequences were determined in order to detect point mutations with a possible effect in the affinity for azoles. The analysis confirmed the multifactorial nature of azole resistance and the prevalence of these mechanisms of resistance in C. albicans clinical isolates exhibiting frank fluconazole resistance, with a predominance of overexpression of genes encoding efflux pumps, detected in 85% of all resistant isolates, being found. Alterations in the target enzyme, including functional amino acid substitutions and overexpression of the gene that encodes the enzyme, were detected in 65 and 35% of the isolates, respectively. Overall, multiple mechanisms of resistance were combined in 75% of the isolates displaying high-level fluconazole resistance. These results may help in the development of new strategies to overcome the problem of resistance as well as new treatments for this condition.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

Regulation of c-fos gene transcription and myeloid cell differentiation by acute myeloid leukemia 1 and acute myeloid leukemia-MTG8, a chimeric leukemogenic derivative of acute myeloid leukemia 1.

Both acute myeloid leukemia 1 and c-Fos are regulatory factors of hematopoietic cell differentiation. We identified that the c-fos promoter contains an acute myeloid leukemia 1 binding site at nucleotide positions -6-+14. c-fos promoter activity was induced by transient overexpression of acute myeloid leukemia 1 in Jurkat T-cells, but not by that of the short form of acute myeloid leukemia 1-MTG8, a chimeric acute myeloid leukemia 1 protein. In 32Dcl3 myeloid cells, stable overexpression of acute myeloid leukemia 1-MTG8 blocked the c-fos gene transcription and cell differentiation, but that of acute myeloid leukemia did not. These data suggest that acute myeloid leukemia 1 and acute myeloid leukemia 1-MTG8 reciprocally regulate the myeloid cell differentiation, possibly by the way of regulating c-fos gene transcription.

Cell Differentiation↗
PubMed1999

ETO-2, a new member of the ETO-family of nuclear proteins.

The t(8;21) is associated with 12-15% of acute myelogenous leukemias of the M2 subtype. The translocation results in the fusion of two genes, AML1 (CBFA2) on chromosome 21 and ETO (MTG8) on chromosome 8. AML1 encodes a DNA binding factor; the ETO protein product is less well characterized, but is thought to be a transcription factor. Here we describe the isolation and characterization of ETO-2, a murine cDNA that encodes a new member of the ETO family of proteins. ETO-2 is 75% identical to murine ETO and shares very high sequence identities over four regions of the protein with ETO (domain I-III and zinc-finger). Northern analysis identifies ETO-2 transcripts in many of the murine tissues analysed and in the developing mouse embryo. ETO-2 is also expressed in myeloid and erythroid cell lines. We confirmed the nuclear localization of ETO-2 and demonstrated that domain III and the zinc-finger region are not required for nuclear localization. We further showed that a region within ETO, containing domain II, mediates dimerization among family members. This region is conserved in the oncoprotein AML-1/ETO. The recent identification of another ETO-like protein, myeloid translocation gene-related protein 1, together with the data presented here, demonstrates that at least three ETO proteins exist with the potential to form dimers in the cell nucleus.

Amino Acid Sequence↗
PubMed1998

The partner gene of AML1 in t(16;21) myeloid malignancies is a novel member of the MTG8(ETO) family.

The t(16;21)(q24;q22) translocation is a rare but recurrent chromosomal abnormality associated with therapy-related myeloid malignancies and a variant of the t(8;21) translocation in which the AML1 gene on chromosome 21 is rearranged. Here we report the molecular definition of this chromosomal aberration in four patients. We cloned cDNAs from the leukemic cells of a patient carrying t(16;21) by the reverse transcription polymerase chain reaction using an AML1-specific primer. The structural analysis of the cDNAs showed that AML1 was fused to a novel gene named MTG16 (Myeloid Translocation Gene on chromosome 16) which shows high homology to MTG8 (ETO/CDR) and MTGR1. Northern blot analysis using MTG16 probes mainly detected 4.5 kb and 4.2 kb RNAs, along with several other minor RNAs in various human tissues. As in t(8;21), the t(16;21) breakpoints occurred between the exons 5 and 6 of AML1, and between the exons 1 and 2 or the exons 3 and 4 of MTG16. The two genes are fused in-frame, resulting in the characteristic chimeric transcripts of this translocation. Although the reciprocal chimeric product, MTG16-AML1, was also detected in one of the t(16;21) patients, its protein product was predicted to be truncated. Thus, the AML1-MTG16 gene fusion in t(16;21) leukemia results in the production of a protein that is very similar to the AML1-MTG8 chimeric protein.

Amino Acid Sequence↗
PubMed2005

Role for Runx1 in the proliferation and neuronal differentiation of selected progenitor cells in the mammalian nervous system.

Neurogenesis requires factors that regulate the decision of dividing progenitors to leave the cell cycle and activate the neuronal differentiation program. It is shown here that the murine runt-related gene Runx1 is expressed in proliferating cells on the basal side of the olfactory epithelium. These include both Mash1+ olfactory receptor neuron (ORN) progenitors and NeuroD+ ORN precursors. Disruption of Runx1 function in vivo does not cause a change in Mash1 expression but leads to a decrease in the number of NeuroD+ neuronal precursors and an increase in differentiated ORNs. These effects result in premature and ectopic ORN differentiation. It is shown further that exogenous Runx1 expression in cultured olfactory neural progenitors causes an expansion of the mitotic cell population. In agreement with these findings, exogenous Runx1 expression also promotes cortical neural progenitor cell proliferation without inhibiting neuronal differentiation. These effects are phenocopied by a chimeric protein containing ETO, the eight twenty one transcriptional repressor, fused to the Runx1 DNA-binding domain, which suggests the involvement of transcription repression mechanisms. Consistent with this possibility, Runx1 represses transcription driven by the promoter of the cell cycle inhibitor p21Cip 1 in cortical progenitors. Together, these findings suggest a previously unrecognized role for Runx1 in coordinating the proliferation and neuronal differentiation of selected populations of neural progenitors.

Amino Acid Substitution↗