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Identification and characterization of Hoxa9 binding sites in hematopoietic cells

Yongsheng Huang, Kajal Sitwala, Joel Bronstein, Daniel Sanders, Monisha Dandekar, Cailin Collins, Gordon Robertson, James MacDonald, Timothee Cezard, Misha Bilenky, Nina Thiessen, Yongjun Zhao, Thomas Zeng, Martin Hirst, Alfred Hero, Steven Jones, Jay L. Hess

Abstract

The clustered homeobox proteins play crucial roles in development, hematopoiesis and leukemia yet the targets they regulate and their mechanisms of action are poorly understood. Here, we identified the binding sites for Hoxa9 and the Hox cofactor Meis1 on a genome-wide level and profiled their associated epigenetic modifications and transcriptional targets. Hoxa9 and the Hox cofactor Meis1 co-bind at hundreds of highly evolutionarily-conserved sites, most of which are distant from transcription start sites. These sites show high levels of histone H3K4 monomethylation and CBP/P300 binding characteristic of enhancers. Furthermore, a subset of these sites shows enhancer activity in transient transfection assays. Many Hoxa9 and Meis1 binding sites are also bound by PU.1 and other lineage-restricted transcription factors previously implicated in establishment of myeloid enhancers. Conditional Hoxa9 activation is associated with CBP/P300 recruitment, histone acetylation and transcriptional activation of a network of proto-oncogenes including Erg, Flt3, Lmo2, Myb and Sox4. Collectively this work suggests that Hoxa9 regulates transcription by interacting with enhancers of genes important for hematopoiesis and leukemia.

  • Submitted March 9, 2011.
  • Accepted October 26, 2011.