ETO, a Target of t(8;21) in Acute Leukemia, Interacts with the N-CoR and mSin3 Corepressors

Abstract

The gene for acute myeloid leukemia-1 (AML-1) is one of the most frequently translocated genes in human cancer. It is targeted by t(8;21) and t(3;21) in AML and by t(12;21) in acute lymphocytic leukemia (39). AML-1 is also indirectly targeted by inv(16), which disrupts core binding factor beta, an AML-1-interacting protein. AML-1 binds the enhancer core motif (TGT/cGGT) and regulates a variety of viral and cellular genes in concert with other factors (31). t(8;21) is one of the most frequent translocations found in AML, comprising 10 to 15% of cases with discernible translocations (39). The t(8;21) fusion protein AML-1/ETO acts as a repressor of transcription in transient-transfection assays (10,31,32,43). When expressed during development, the t(8;21) fusion protein yielded the same phenotype as AML-1 deficiency (37, 45).Although eight-twenty-one (ETO; also known as MTG8 [myeloid tumor gene 8] [8,34]) was identified at the breakpoint of t(8;21), little is known about the normal function of the protein. ETO is the human homologue of the Drosophila Nervy protein (9), and it shares four homologous domains with the Nervy protein. These include a region with extensive homology to a Drosophila coactivator, transcription-activating factor 110 (TAF110), a predicted hydrophobic heptad repeat (HHR), a small domain with no other homology, termed the Nervy domain (27), and the MYND (myeloid-Nervy-DEAF-1 [12]) domain. The MYND domain is present in numerous human, murine, Caenorhabditis elegans, and Drosophila proteins and contains two putative zinc finger (ZF) motifs (9,12,31). ETO is expressed in hematopoietic cells and in the brain, but another closely related family member is ubiquitously expressed (19). A third closely related factor, MTG16, is fused to AML-1 by t(16;21) (20).AML-1 is a site-specific DNA binding protein that can both activate and repress transcription (2, 28, 36). The t(8;21) fusion protein AML-1/ETO contains the N-terminal 177 amino acids of AML-1, including the DNA binding domain, fused to nearly all of ETO (7,8,34). The fusion protein inhibits AML-1-dependent transactivation (10, 32). AML-1/ETO also repressed both basal transcription and Ets-1-dependent activation of the multidrug resistance 1 promoter (27). Similarly, AML-1/ETO inhibited both AML-1 and C/EBP␣-dependent transactivation of the neutrophil protein 3 (NP-3) promoter (44). AML-1/ETO-mediated repression is dependent on both the DNA binding domain of AML-1 and ETO sequences (24). AML-1/ETO acts at substoichiometric levels and thus does not compete with AML-1 for DNA binding sites within promoters, nor does it act to "squelch" transcription (24). Thus, we hypothesized that ETO recruits a corepressor or normally functions as a corepressor to inhibit transcription (30,31,33).Several corepressor proteins have been recently described that associate with histone deacetylases (HDACs) to repress transcription (3,5,13,17,38,40,42). The nuclear hormone corepressor N-CoR was identified through interactions with the thyroid hormone receptor and associa...

The adenovirus E1A binding protein BS69 is a corepressor of transcription through recruitment of N-CoR

“…Sin3/HDAc complexes were found to associate with AML/ETO, however ETO can interact with Sin3A directly and independently of N-CoR, which may strengthen the interaction signi®cantly (Lutterbach et al, 1998b). BS69 repression appeared to be highly refractory to inhibition by the histone deacetylase inhibitor Trichostatin A at concentrations ranging from 40 nM to 1.2 mM (data not shown).…”

“…The C-terminus harbours a region with homology to the MYND domain, a two zinc ®nger motif ®rst identi®ed in DEAF-1 (Gross and McGinnis, 1996) and in MTG8/ETO (Lutterbach et al, 1998a). This domain was shown to be required for both repression of basal transcription by the AML/ETO fusion protein and binding of the transcriptional corepressors N-CoR and SMRT (Lutterbach et al, 1998b;Gelmetti et al, 1998;Wang et al, 1998). N-CoR and its close homologue SMRT were cloned as co-repressors of the thyroidhormone and retinoic acid receptors (Chen and Evans, 1995;Horlein et al, 1995).…”

RUNX1 associates with histone deacetylases and SUV39H1 to repress transcription

“…This may be due to the need to create the correct context, conformation or spacing for the associated histone-modifying enzymes to function. For example, ETO/MTG8 contains multiple contact sites for mSin3, nuclear hormone co-repressors and histone deacetylases (Lutterbach et al, 1998b;Amann et al, 2001;Hildebrand et al, 2001), but mutation of only one site can significantly impair RUNX1-ETOmediated repression (Lutterbach et al, 1998b;Amann et al, 2001). In fact, a completely inactive form of RUNX1-ETO retains the ability to bind to the nuclear hormone co-repressor N-CoR and histone deacetylase-1 (Lenny et al, 1995;Amann et al, 2001).…”

ELA2 is regulated by hematopoietic transcription factors, but not repressed by AML1-ETO

“…The resulting AML1-ETO fusion protein is expressed in E12% of AML of the M2 subtype (Look, 1997). AML1-ETO has been shown to interact with a number of proteins present in corepressor complexes, suggesting that AML1-ETO may act as a transcriptional repressor (Meyers et al, 1995;Gelmetti et al, 1998;Lutterbach et al, 1998;Wang et al, 1998;Westendorf et al, 1998;Amann et al, 2001;Hildebrand et al, 2001;Zhang et al, 2001;Linggi et al, 2002;Lausen et al, 2004). However, there have been very few studies that correlate a DNA binding event by AML1-ETO at a target gene's promoter with a direct consequence on transcription (see, e.g.…”