EVI1 and GATA2 misexpression induced by inv(3)(q21q26) contribute to megakaryocyte-lineage skewing and leukemogenesis

Abstract

Chromosomal rearrangements between 3q21 and 3q26 elicit high-risk acute myeloid leukemia (AML), which is often associated with elevated platelet and megakaryocyte (Mk) numbers. The 3q rearrangements reposition a GATA2 enhancer near the EVI1 (or MECOM) locus, which results in both EVI1 overexpression and GATA2 haploinsufficiency. However, the mechanisms explaining how the misexpression of these 2 genes individually contribute to leukemogenesis are unknown. To clarify the characteristics of differentiation defects caused by EVI1 and GATA2 misexpression and to identify the cellular origin of leukemic cells, we generated a system to monitor both inv(3) allele-driven EVI1 and Gata2 expression in 3q-rearranged AML model mice. A cell population in which both EVI1 and Gata2 were highly induced appeared in the bone marrows before the onset of frank leukemia. This population had acquired serial colony-forming potential. Because hematopoietic stem/progenitor cells (HSPCs) and Mks were enriched in this peculiar population, we analyzed the independent EVI1 and GATA2 contributions to HSPC and Mk. We found that inv(3)-driven EVI1 promotes accumulation of Mk-biased and myeloid-biased progenitors, Mks, and platelets, and that Gata2 heterozygous deletion enhanced Mk-lineage skewing of EVI1-expressing progenitors. Notably, inv(3)-directed EVI1 expression and Gata2 haploinsufficient expression cooperatively provoke a leukemia characterized by abundant Mks and platelets. These hematological features of the mouse model phenocopy those observed in human 3q AML. On the basis of these results, we conclude that inv(3)-driven EVI1 expression in HSPCs and Mks collaborates with Gata2 haploinsufficiency to provoke Mk-lineage skewing and leukemogenesis with excessive platelets, thus mimicking an important feature of human AML.

EVI1 dysregulation: impact on biology and therapy of myeloid malignancies

“…Although not a mutation, almost all MDS, AML, and CML with inv(3)/t(3;3) have GATA2 haploinsufficiency due to the re-location of the GATA2 distal hematopoietic enhancer 53 , 54 . This was shown to contribute to EVI1-driven leukemia transformation 21 . Of note, despite loss of expression from one allele of GATA2, 15% of inv(3)/t(3;3) can carry additional mutations in GATA2 on the non-rearranged allele 52 , 77 .…”

“…In the megakaryocyte lineage, EVI1 is expressed in early precursor cells 20 . In a transgenic mouse model recapitulating human inv 3 (q21q26) AML that overexpresses EVI1 and also has GATA2 haploinsufficiency, EVI1 and GATA2 dysregulation together skewed hematopoiesis toward the megakaryocyte lineage more so than EVI1 overexpression alone 21 . This suggests that EVI1 may work in concert with other factors to promote the megakaryocyte lineage 21 .…”

“…In a transgenic mouse model recapitulating human inv 3 (q21q26) AML that overexpresses EVI1 and also has GATA2 haploinsufficiency, EVI1 and GATA2 dysregulation together skewed hematopoiesis toward the megakaryocyte lineage more so than EVI1 overexpression alone 21 . This suggests that EVI1 may work in concert with other factors to promote the megakaryocyte lineage 21 . In general, for most myeloid lineages, EVI1 functions to promote a stem or early progenitor transcriptional program 11 , 14 .…”

“…In general, for most myeloid lineages, EVI1 functions to promote a stem or early progenitor transcriptional program 11 , 14 . Forced EVI1 expression maintains the stem-like program while simultaneously suppressing myeloid transcription factors involved in myeloid differentiation 16 , 18 , 19 , 21 . Notably, endogenous EVI1 is generally downregulated under normal differentiation 14 , 15 .…”

Identification of therapeutic targets of the hijacked super-enhancer complex in EVI1-rearranged leukemia

“…In AML, 3q26.2 rearrangements targeting the MECOM locus typically abrogate expression of both the long MDS1-EVI1 isoform and, coincidentally, expression of other key myeloid regulators, such as GATA2 or MYC , while transcription of EVI1 becomes excessively increased. 15 – 18 Similar to EVI1 overexpression caused by inv(3)/t(3;3) in AML, also other PRDM family members are found upregulated in leukemias as for example PRDM16 ( MEL1 ) in t(1;3)/ MEL1 rearranged AML. 19 The underlying mechanism of forced EVI1 or MEL1 transcription and co-silencing of GATA2 in 3q-rearranged AML is the repositioning of a GATA2 distal hematopoietic enhancer ( G2DHE ) into the vicinity of these EVI1 homologues.…”