Functional and Physical Interactions between AML1 Proteins and an ETS Protein, MEF: Implications for the Pathogenesis of t(8;21)-Positive Leukemias

Abstract

The AML1 and ETS families of transcription factors play critical roles in hematopoiesis; AML1, and its non-DNA-binding heterodimer partner CBFbeta, are essential for the development of definitive hematopoiesis in mice, whereas the absence of certain ETS proteins creates specific defects in lymphopoiesis or myelopoiesis. The promoter activities of numerous genes expressed in hematopoietic cells are regulated by AML1 proteins or ETS proteins. MEF (for myeloid ELF-1-like factor) is a recently cloned ETS family member that, like AML1B, can strongly transactivate several of these promoters, which led us to examine whether MEF functionally or physically interacts with AML1 proteins. In this study, we demonstrate direct interactions between MEF and AML1 proteins, including the AML1/ETO fusion protein, in t(8;21)-positive acute myeloid leukemia (AML) cells. Using mutational analysis, we identified a novel ETS-interacting subdomain (EID) in the C-terminal portion of the Runt homology domain (RHD) in AML1 proteins and determined that the N-terminal region of MEF was responsible for its interaction with AML1. MEF and AML1B synergistically transactivated an interleukin 3 promoter reporter gene construct, yet the activating activity of MEF was abolished when MEF was coexpressed with AML1/ETO. The repression by AML1/ETO was independent of DNA binding but depended on its ability to interact with MEF, suggesting that AML1/ETO can repress genes not normally regulated by AML1 via protein-protein interactions. Interference with MEF function by AML1/ETO may lead to dysregulation of genes important for myeloid differentiation, thereby contributing to the pathogenesis of t(8;21) AML.

Common themes in the pathogenesis of acute myeloid leukemia

“…The ALM1/CBPb complex cooperates with other lineage-restricted transcription factors such as c-Myb, C/EBPa, Ets family members PU.1 and MEF, HES-1, Pax5 and Smad, which bind adjacent sites on DNA Jakubowiak et al, 2000;Kim et al, 1999;Libermann et al, 1999;Mao et al, 1999;McLarren et al, 2000). In most cases this functional synergy requires direct physical interaction of the transcription factors.…”

Role of RUNX family members in transcriptional repression and gene silencing

“…However, when placed in the appropriate context, RUNX family members act as organizing factors at the promoters and enhancers of target genes where they associate with cofactors and other DNA-binding transcription factors that are required for gene regulation. These factors include C/EBPa (Zhang et al, 1996;Westendorf et al, 1998), ETS family members (Giese et al, 1995;Petrovick et al, 1998;Kim et al, 1999;Mao et al, 1999), SMADs (Hanai et al, 1999;Gu et al, 2000;Jakubowiak et al, 2000;Pardali et al, 2000;Zhang and Derynck, 2000) and histone acetyltransferases including p300/CBP (Kitabayashi et al, 1998;Pelletier et al, 2002).…”

ELF4 (E74-like factor 4 (ets domain transcription factor))

“…ELF4 contains, from N-term to C-term, transactivation domain (53-86), AML1 interacting domain , ETS domain (207-291), serine/threonine rich region (306-347) and proline rich region (477-517) (Miyazaki et al, 1996;Mao et al, 1999;Lacorazza and Nimer, 2003).…”

“…ELF4 binds to DNA sequences containing the consensus 5'-WGGA-3' and transactivates promoters of the hematopoietic growth factor genes CSF2, IL3, IL8, and of the bovine lysozyme gene (Miyazaki et al, 1996;Mao et al, 1999;Hedvat et al, 2004;Suico et al, 2004). ELF4 acts synergistically with RUNX1 to transactivate the IL3 promoter (Mao et al, 1999). It also transactivates the PRF1 promoter in natural killer (NK) cells (Lacorazza et al, 2002).…”

“…ELF4 has important molecular functions, including protein binding, transcription activator activity, sequence-specific DNA binding, transcription factor activity. ELF4 interacts with multiple proteins, including Cyclin A/CDK2 kinase complex, FBXO4, FBXO7, PML, RUNX1, SKP2 and UBB (Miyazaki et al, 1996;Mao et al, 1999;Miyazaki et al, 2001;Liu et al, 2006;Suico et al, 2006).…”