Abstract 85: RUNX1 and ELK1 directly regulate the transcription of EVI1 during megakaryocytic differentiation

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL High expression of EVI1 is a negative prognostic indicator of survival in patients with acute myeloid leukemia (AML). The EVI1 gene (3q26) codes for a transcription factor indispensable for the proliferation and self-renewal of HSCs during embryogenesis and in the adult, and is downregulated upon differentiation; however, the regulation of EVI1 in megakaryocytic differentiation should be different, as it is highly expressed in megakaryocytes and platelets, but not in other committed hematopoietic cells. Our aim was to identify transcription factors involved in the regulation of EVI1. Site-directed mutagenesis and ChIP assays identified RUNX1 and ELK1 as putative transcription factors of EVI1. Furthermore, knockdown of RUNX1 and ELK1 led to EVI1 downregulation, and their overexpression to upregulation of EVI1. Of note, in a series of patient samples with AML at diagnosis (n=46), we found a significant positive correlation between EVI1 and RUNX1, and EVI1 and ELK1 mRNA expression levels. RUNX1 has been reported as a key transcription factor in megakaryocytic development. To investigate whether RUNX1 could regulate EVI1 in this process, we treated K562 cells with TPA. After the treatment, we observed an increase in RUNX1, as previously described, and in ELK1 and EVI1. Knockdown of RUNX1 resulted in a marked decrease of the megakaryocytic markers ITGA2B and ITGB3, and of EVI1. Moreover, EVI1 knockdown led to the same effects by blocking the differentiation process, suggesting that the role of EVI1 in megakaryocytic differentiation would be through RUNX1. Interestingly, chromatin immunoprecipitation assay (ChIP) showed that RUNX1 regulates the transcription of EVI1 by acetylation of the histone H3 on its promoter region. In conclusion, we demonstrate that RUNX1 and ELK1, two proteins with essential functions in hematopoiesis, regulate EVI1 in AML. Moreover, our results suggest that these transcription factors could regulate EVI1 expression during megakaryocytic differentiation, and that RUNX1 would activate EVI1 expression through acetylation of the histone H3 on its promoter region. This study opens new directions to further understand the mechanisms of EVI1 overexpressing leukemias. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 85. doi:1538-7445.AM2012-85