Evi-1 is a transcriptional target of mixed-lineage leukemia oncoproteins in hematopoietic stem cells

Abstract

Ecotropic viral integration site-1 (Evi-1) is a nuclear transcription factor that plays an essential role in the regulation of hematopoietic stem cells. Aberrant expression of Evi-1 has been reported in up to 10% of patients with acute myeloid leukemia and is a diagnostic marker that predicts a poor outcome. Although chromosomal rearrangement involving the Evi-1 gene is one of the major causes of Evi-1 activation, overexpression of Evi-1 is detected in a subgroup of acute myeloid leukemia patients without any chromosomal abnormalities, which indicates the presence of other mechanisms for Evi-1 activation. In this study, we found that Evi-1 is frequently up-regulated in bone marrow cells transformed by the mixed-lineage leukemia ( IntroductionThe ecotropic viral integration site-1 (Evi-1) is a nuclear transcription factor that plays an essential role in the proliferation and maintenance of hematopoietic stem cells (HSCs). 1-3 There are 2 major alternative forms generated from the Evi-1 gene, Evi-1a and Mds1-Evi-1 (also called Evi-1c). Mds1-Evi-1 is a fusion variant of Evi-1 generated through intergenic splicing with Mds1, 4 a gene located approximately 140 and 500 kb upstream of Evi-1 in the human and mouse genome, respectively. In contrast to Evi-1a, Mds1-Evi-1 possesses the PRDI-BF1-RIZ1 homologous (PR) domain in the N-terminus, which regulates oligomerization of the Evi-1 proteins. 5 Both Evi-1a and Mds1-Evi-1 are normally coexpressed in several developing and adult tissues, 6 and differences in the normal function between these proteins remain to be elucidated. Like all other PR domain proteins, Evi-1 contains several zinc finger motifs. They are grouped into N-terminal 7 and C-terminal 3 clusters, which are called the first and second zinc finger domain, respectively. 7,8 Between these 2 zinc finger domains lie the C-terminal binding protein (CtBP) domain and the repression domain. The first zinc finger, the repression, and the CtBP-binding domains exhibit a growth-promoting effect by blocking transforming growth factor-␤ signaling. 9 The first zinc finger domain also exhibits an antiapoptotic effect by repressing c-Jun N-terminal kinase signaling. 10 The second zinc finger domain stimulates proliferation by increasing activator protein-1 activity. 11 Thus, Evi-1 possesses diverse functions as an oncoprotein.Aberrant expression of EVI-1 frequently has been found in myeloid leukemia and in several solid tumors and is associated with poor prognosis of patients with leukemia. 12-15 Rearrangements of chromosome 3q26, which contains the EVI-1 gene, lead to overexpression of EVI-1 and are implicated in the development or progression of high-risk acute myeloid leukemia (AML). 16 Importantly, EVI-1 is also highly expressed in a subgroup of AML patients without 3q26 rearrangements, 12 which indicates the presence of other mechanisms of EVI-1 activation. Recently, several clinical studies revealed a positive correlation between EVI-1 (both EVI-1a and MDS1-EVI-1) overexpression and rearrangements of the mixed-lineage ...

EVI1 is critical for the pathogenesis of a subset of MLL-AF9–rearranged AMLs

“…25 Although others reported binding of MLL-ENL to the Evi1 promoter, we were not able to show direct interaction between MLL-AF9 and Evi1, possibly because of the lack of suitable ChIP-grade Abs. However, we observed clear differences between Evi1 pos and Evi1 neg MLL-AF9-transformed cells (both human or mouse) with regard to enrichments of H3K79/H3K4 versus H3K27 on the EVI1 promoter.…”

“…These results are corroborated by recent reports showing that MLL-ENL up-regulates Evi1 expression in a mouse leukemia model, in which leukemic transformation was dependent on Evi1. 24,25 We noted that although MLL-AF9 is readily able to transform normal mouse BM cells, only a fraction of colonies were Evi1 pos (supplementary figure S5B). Similar to Arai et al, we found that in these retroviral models of MLL-fusion gene leukemia, Evi1 overexpression was predominantly associated with the stem cell-enriched LSK raction of normal BM compared with the more differentiated myeloid progenitors CMP, GMP, and MEP.…”

“…Similar to Arai et al, we found that in these retroviral models of MLL-fusion gene leukemia, Evi1 overexpression was predominantly associated with the stem cell-enriched LSK raction of normal BM compared with the more differentiated myeloid progenitors CMP, GMP, and MEP. 25 Notably, several studies have shown that MLL-fusion geneinduced leukomogenesis is more efficient in LSKs compared with the more mature myeloid progenitors GMPs. 23,37 Because Evi1 expression is normally high in these LSK cells, our results suggest that coexpression of Evi1 is at least partly responsible for the observed transformation of LSKs.…”

“…We show that EVI1 expression is uncoupled from normal myeloid differentiation and is regulated by MLL-AF9, only in EVI1 pos -transformed cells, in agreement with data reported by Arai and colleagues. 25 The critical contribution of Evi1 in these model systems was shown by applying lentiviral knockdown strategies. Evi1 knockdown resulted in reduced survival in vitro and in vivo of MLL-AF9-transformed cells.…”

Genetically engineered mouse models of human B-cell precursor leukemias

“…81 Something similar had been shown before for Evi1 (ref. 82) and also, importantly in the case of MLL fusion genes, for Hox genes like Hoxa9 (ref. 83).…”