Dual requirement for the ETS transcription factors Fli-1 and Erg in hematopoietic stem cells and the megakaryocyte lineage

Abstract

Fli-1 and Erg are closely related members of the Ets family of transcription factors. Both genes are translocated in human cancers, including Ewing's sarcoma, leukemia, and in the case of Erg, more than half of all prostate cancers. Although evidence from mice and humans suggests that Fli-1 is required for megakaryopoiesis, and that Erg is required for normal adult hematopoietic stem cell (HSC) regulation, their precise physiological roles remain to be defined. To elucidate the relationship between Fli-1 and Erg in hematopoiesis, we conducted an analysis of mice carrying mutations in both genes. Our results demonstrate that there is a profound genetic interaction between Fli-1 and Erg. Double heterozygotes displayed phenotypes more dramatic than single heterozygotes: severe thrombocytopenia, with a significant deficit in megakaryocyte numbers and evidence of megakaryocyte dysmorphogenesis, and loss of HSCs accompanied by a reduction in the number of committed hematopoietic progenitor cells. These results illustrate an indispensable requirement for both Fli-1 and Erg in normal HSC and megakaryocyte homeostasis, and suggest these transcription factors may coregulate common target genes.T he E-twenty-six specific (Ets) proteins are a family of more than 20 helix-loop-helix domain transcription factors that have been implicated in a myriad of cellular processes (1). Fli-1 and Erg are Ets proteins that share greater homology to each other than to other Ets family members. Fli-1 is mutated in a number of cancers, including Ewing's sarcoma and erythroleukemia (2, 3). Genetic manipulation in mice (4, 5) and mutations in humans (4, 6) have revealed multiple roles for Fli-1 in hematopoiesis including the production of megakaryocytes and platelets. Fli-1 is also implicated in the regulation of important stem cell genes, suggesting a role within the hematopoietic stem cell compartment (7,8). Erg is also a proto-oncogene, translocated in Ewing sarcoma, leukemia, and prostate cancer (9-11). We recently reported a mouse model of Erg dysfunction, Erg Mld2 , in which an N-ethyl-N-nitrosourea (ENU)-induced point mutation causes profound loss of Erg function. These mice revealed an indispensable requirement for Erg in definitive hematopoiesis with Erg Mld2/Mld2 embryos dying at midgestation. Analyses of Erg ϩ/Mld2 adult mice revealed that Erg is required for normal adult HSC homeostasis. HSCs are reduced in number in Erg ϩ/Mld2 mice and unable to compete effectively with Erg ϩ/ϩ cells to reconstitute irradiated transplant recipients (12).In translocations driving Ewing's sarcoma, Fli-1 and Erg appear to be interchangeable; either Fli-1 or Erg can fuse with the gene encoding an RNA binding protein, EWS, and give rise to clinically indistinguishable disease (13). Moreover, in vitro data suggests that Fli-1 and Erg may heterodimerize to regulate sets of overlapping target genes (14, 15), raising the prospect that these proteins may, in part, be redundant. To explore the relationship between Fli-1 and Erg in a physiological setting, w...

A previously unrecognized promoter of LMO2 forms part of a transcriptional regulatory circuit mediating LMO2 expression in a subset of T-acute lymphoblastic leukaemia patients

“…We therefore investigated potential interactions between LMO2 and FLI1 in human T-ALL. ERG was included in this analysis as it has been shown that FLI1 and ERG, which is closely related to FLI1, may coregulate common target genes in haematopoietic stem cells and megakaryocytes (Kruse et al, 2009) and high ERG expression has recently been shown to predict adverse outcome in T-ALL (Baldus et al, 2006(Baldus et al, , 2007Bohne et al, 2009). ChIP using antibodies to ERG and FLI1 in Molt4 (LMO2-expressing non-translocated human T-ALL cell line) was therefore performed.…”

Expression of ERG, an Ets family transcription factor, identifies ERG-rearranged Ewing sarcoma

“…ERG has a critical function in normal hematopoiesis. 16,17 It is also constitutively expressed in normal endothelial cells and regulates angiogenesis and endothelial apoptosis. [18][19][20] Several studies have shown anti-ERG antibody useful for prostate carcinoma, metastatic and primary, and prostatic intraepithelial neoplasias.…”

Interplay of transcription factors and microRNAs during embryonic hematopoiesis

“…It was previously demonstrated that SCL and EKLF promoted erythropoiesis, whereas ETS family members, such as ERG and FLI1, enhanced megakaryopoietic differentiation by inhibiting erythrocyte formation (Kruse et al, 2009;Starck et al, 2010). We found that both SCL and EKLF increased the expression of miR-144/451, whereas FLI1 downregulated miR-144/451, in turn miR-144/451 might target FLI1 to inhibit its expression in erythrocytes, thus forming a negative feedback circuitry to fine-tune the formation of red blood cells.…”

“…Data were represented as mean±SE of replicates from at least three independent experiments. *, P<0.05; **, P<0.01; ***, P<0.001. ropoiesis mainly upregulated miR-144/451 and miR-142, whereas FLI1 and ERG, the key factors in megakaryocyte formation (Kruse et al, 2009), significantly increased the expression of miR-142 and miR-146b ( Figure 4A-D), implicating distinct roles of their target miRNAs during primitive hematopoiesis.…”