Mechanisms of overexpression of the EVI1 gene (3q26) and its role in the leukemic transformation of patients with acute myeloid leukemia

Resumen

The EVI1 gene (3q26) codes for a transcription factor with important roles in development and leukemogenesis. Overexpression of EVI1 through either 3q26 rearrangements or other unknown mechanisms is associated with a particularly aggressive acute myeloid leukemia (AML). Evi1 acts in several pathways through the interaction with proteins with important functions in hematopoiesis; however, its role as a transcription factor is not well known, and only in mice some Evi1 target genes have been identified. We have characterized at molecular level 16 myeloid cell lines and 80 patients with 3q rearrangements, confirming that EVI1 overexpression is sometimes irrespective of 3q26 rearrangements, and demonstrating that the mechanism that leads to EVI1 aberrant expression involves epigenetic changes. Analysis of EVI1 alternative splicing variants showed that 43.5% patients have an aberrant splicing pattern of form Ä324, suggesting that this could have a functional role in EVI1-positive AML. Moreover, we identified a novel alternative splicing of MDS1EVI1. Our study in 476 patients confirms that EVI1 overexpression is an adverse prognostic factor in AML associated with -7 and MLL rearrangements; and identified EVI1-1C overexpression as a prognostic marker of poor prognosis in patients <60 years-old. Moreover, differential expression profiles after EVI1 knockdown allowed us to identify 125 genes involved in cell growth, differentiation and signal transduction that could be related to EVI1. Furthermore, we looked for potential EVI1 binding sites within the region 1,000bp upstream of the transcription start sites of all human genes. ChIP assay demonstrated that EVI1 binds to the proximal promoter regions of 18 of these genes, most of them involved in important differentiation and proliferation pathways. Importantly, EVI1 binds to the proximal region of its own promoter, acting as a silencer of its transcription. Although further functional studies are needed, these data provide a starting point for further studies aimed at uncovering the mechanism for EVI1-induced transformation leukemias.