Research Article: AML1/ETO Oncoprotein Is Directed to AML1 Binding Regions and Co-Localizes with AML1 and HEB on Its Targets

Date Published: November 28, 2008

Publisher: Public Library of Science

Author(s): Alessandro Gardini, Matteo Cesaroni, Lucilla Luzi, Akiko J. Okumura, Joseph R. Biggs, Simone P. Minardi, Elisa Venturini, Dong-Er Zhang, Pier Giuseppe Pelicci, Myriam Alcalay, Vivian G. Cheung

Abstract: A reciprocal translocation involving chromosomes 8 and 21 generates the AML1/ETO oncogenic transcription factor that initiates acute myeloid leukemia by recruiting co-repressor complexes to DNA. AML1/ETO interferes with the function of its wild-type counterpart, AML1, by directly targeting AML1 binding sites. However, transcriptional regulation determined by AML1/ETO probably relies on a more complex network, since the fusion protein has been shown to interact with a number of other transcription factors, in particular E-proteins, and may therefore target other sites on DNA. Genome-wide chromatin immunoprecipitation and expression profiling were exploited to identify AML1/ETO-dependent transcriptional regulation. AML1/ETO was found to co-localize with AML1, demonstrating that the fusion protein follows the binding pattern of the wild-type protein but does not function primarily by displacing it. The DNA binding profile of the E-protein HEB was grossly rearranged upon expression of AML1/ETO, and the fusion protein was found to co-localize with both AML1 and HEB on many of its regulated targets. Furthermore, the level of HEB protein was increased in both primary cells and cell lines expressing AML1/ETO. Our results suggest a major role for the functional interaction of AML1/ETO with AML1 and HEB in transcriptional regulation determined by the fusion protein.

Partial Text: Chromosomal translocations generating fusion genes are the genetic hallmark of Acute Myeloid Leukemia (AML) [1]. Approximately 10–15% of AML cases carry the t(8;21) translocation, which involves the AML1 and ETO genes, and express the resulting AML1/ETO fusion protein. AML1 is a DNA-binding transcription factor required for hematopoiesis [2],[3] while ETO is a co-repressor molecule expressed in a variety of tissues [4]. In hematopoietic cells, the fusion protein determines a stage specific arrest of maturation and increases cell survival, thus predisposing to leukemia [5].

The analysis of transcription factor binding patterns using genome-wide approaches can serve not only to identify direct target genes, but also to discover interactions among transcription factors that could help in defining disease-linked regulatory networks. We investigated the genome-wide binding profile of AML1/ETO at human promoters and in a contiguous genomic region, and its correlation with AML1 and HEB, with the aim of understanding the determinants of its transcriptional regulatory function.