The loss of regulation of cell proliferation is a key event in leukemic transformation, and the oncogene tribbles (Trib)2 is emerging as a pivotal target of transcription factors in acute leukemias. Deregulation of the transcription factor E2F1, normally repressed by CCAAT enhancer-binding protein α (C/EBPα)-p42, occurs in acute myeloid leukemia (AML), resulting in the perturbation of cell cycle and apoptosis, emphasizing its importance in the molecular pathogenesis of AML. Here we show that E2F family members directly regulate Trib2 in leukemic cells and identify a feedback regulatory loop for E2F1, C/EBPα, and Trib2 in AML cell proliferation and survival. Further analyses revealed that E2F1-mediated Trib2 expression was repressed by C/EBPα-p42, and in normal granulocyte/macrophage progenitor cells, we detect C/EBPα bound to the Trib2 promoter. Pharmacological inhibition of the cell cycle or Trib2 knockdown resulted in a block in AML cell proliferation. Our work proposes a novel paradigm whereby E2F1 plays a key role in the regulation of Trib2 expression important for AML cell proliferation control. Importantly, we identify the contribution of dysregulated C/EBPα and E2F1 to elevated Trib2 expression and leukemic cell survival, which likely contributes to the initiation and maintenance of AML and may have significant implications for normal and malignant hematopoiesis.

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TRIB2, a serine/threonine pseudokinase identified as an oncogene, is expressed at high levels in the T-cell compartment of hematopoiesis. The proliferation of developing thymocytes is tightly controlled to prevent leukemic transformation of T cells. Here we examine Trib2 loss in murine hematopoiesis under steady state and proliferative stress conditions, including genotoxic and oncogenic stress. Trib2−/− developing thymocytes show increased proliferation, and Trib2−/− mice have significantly higher thymic cellularity at steady state. During stress hematopoiesis, Trib2−/− developing thymocytes undergo accelerated proliferation and demonstrate hypersensitivity to 5-fluorouracil (5-FU)-induced cell death. Despite the increased cell death post 5-FU-induced proliferative stress, Trib2−/− mice exhibit accelerated thymopoietic recovery post treatment due to increased cell division kinetics of developing thymocytes. The increased proliferation in Trib2−/− thymocytes was exacerbated under oncogenic stress. In an experimental murine T-cell acute lymphoblastic leukemia (T-ALL) model, Trib2−/− mice had reduced latency in vivo, which associated with impaired MAP kinase (MAPK) activation. High and low expression levels of Trib2 correlate with immature and mature subtypes of human T-ALL, respectively, and associate with MAPK. Thus, TRIB2 emerges as a novel regulator of thymocyte cellular proliferation, important for the thymopoietic response to genotoxic and oncogenic stress, and possessing tumor suppressor function.

Acute myeloid leukaemia (AML) affects children and adults of all ages. AML remains one of the major causes of death in children with cancer and for children with AML relapse is the most common cause of death. Here, by modelling AML in vivo we demonstrate that AML is discriminated by the age of the cell of origin. Young cells give rise to myeloid, lymphoid or mixed phenotype acute leukaemia, whereas adult cells give rise exclusively to AML, with a shorter latency. Unlike adult, young AML cells do not remodel the bone marrow stroma. Transcriptional analysis distinguishes young AML by the upregulation of immune pathways. Analysis of human paediatric AML samples recapitulates a paediatric immune cell interaction gene signature, highlighting two genes, RGS10 and FAM26F as prognostically significant. This work advances our understanding of paediatric AML biology, and provides murine models that offer the potential for developing paediatric specific therapeutic strategies.

C/EBPα (p42 and p30 isoforms) is commonly dysregulated in cancer via the action of oncogenes, and specifically in acute myeloid leukaemia (AML) by mutation. Elevated TRIB2 leads to the degradation of C/EBPα p42, leaving p30 intact in AML. Whether this relationship is a cooperative event in AML transformation is not known and the molecular mechanism involved remains elusive.Using mouse genetics our data reveal that in the complete absence of C/EBPα TRIB2 was unable to induce AML. Only in the presence of C/EBPα p42 and p30 were TRIB2 and p30 able to cooperate to decrease the latency of disease. We demonstrate the molecular mechanism involved in degradation of C/EBPα p42 requires site-specific direct interaction between TRIB2 and C/EBPα p42 for the K48-specific ubiquitin-dependent proteasomal degradation of C/EBPα p42. This interaction and ubiquitination is dependent on a critical C-terminal lysine residue on C/EBPα. We show effective targeting of this pathway pharmacologically using proteasome inhibitors in TRIB2 positive AML cells. Together, our data show that excess p30 cooperated with TRIB2 only in the presence of p42 to accelerate AML and the direct interaction and degradation of C/EBPα p42 is required for TRIB2-mediated AML.

Trib2 pseudokinase has oncogenic and tumour suppressive functions depending on the cellular context. We investigated the ability of Trib2 to transform different haemopoietic stem and progenitor cells (HSPCs). Our study identified the granulocyte-macrophage progenitor (GMP) subpopulation as a potent leukaemia initiating cell of Trib2-driven AML in vivo. Trib2 transformed GMPs generated a fully penetrant and short latency AML. AML cells expressing elevated Trib2 led to a chemoresistant phenotype following chemotherapy treatment. We show that Trib2 overexpression results in an increase in BCL2 expression, and high Trib2 expressing cells are highly sensitive to cell killing by BCL2 inhibition (ABT199). Combined treatment with chemotherapeutic agents and BCL2 inhibition resulted in synergistic killing of Trib2+ AML cells. Trib2 transformed GMP AML cells showed more chemoresistance compared with HSPC derived Trib2 AML cells associated with higher Bcl2 expression. There is significant correlation of high TRIB2 and BCL2 expression in patient derived human AML cells. These data demonstrate that the cell of origin influences the leukaemic profile and chemotherapeutic response of Trib2+ AML. Combined TRIB2 and BCL2 expression in AML cells may have clinical utility relevant for monitoring drug resistance and disease relapse.

The commitment of stem and progenitor cells toward specific hematopoietic lineages is tightly controlled by a number of transcription factors that regulate differentiation programs via the expression of lineage restricting genes. Nuclear factor one (NFI) transcription factors are important in regulating hematopoiesis and here we report an important physiological role of NFIX in B- and myeloid lineage commitment and differentiation. We demonstrate that NFIX acts as a regulator of lineage specification in the haematopoietic system and the expression of Nfix was transcriptionally downregulated as B cells commit and differentiate, whilst maintained in myeloid progenitor cells. Ectopic Nfix expression in vivo blocked early B cell development stage, coincident with the stage of its downregulation. Furthermore, loss of Nfix resulted in the perturbation of myeloid and lymphoid cell differentiation, and a skewing of gene expression involved in lineage fate determination. Nfix was able to promote myeloid differentiation of total bone marrow cells under B cell specific culture conditions but not when expressed in the hematopoietic stem cell (HSPC), consistent with its role in HSPC survival. The lineage choice determined by Nfix correlated with transcriptional changes in a number of genes, such as E2A, C/EBP, and Id genes. These data highlight a novel and critical role for NFIX transcription factor in hematopoiesis and in lineage specification.

Objective: To study patterns of phytosterol intakes in the Irish population from enriched sources. Design: An interview-assisted questionnaire, which recorded information on sociodemographics, product types, intake amounts and patterns of intake. Independent samples t tests, one-way ANOVA and cross-tabulations were used to establish significant relationships between groups of variables. The top tertile of phytosterol intakes was also calculated. Setting: Point-of-purchase of phytosterol-enriched products in Irish supermarkets. Subjects: Four hundred and sixty-eight consumers (186 men and 282 women) of phytosterol-enriched foods. Results: The mean phytosterol intake from enriched sources for the sample population was 2?45 g/d. Men had greater intakes than women (2?71 g/d v. 2?29 g/d, respectively). A total of 62 % of consumers were unaware of the importance of consuming fruit and vegetables while taking these products. The majority of respondents reported that they had high cholesterol (61 %) and 22 % of consumers also took cholesterol-lowering medication (statins). In total, 23 % had phytosterol intakes .3?0 g/d and the majority of consumers (58 %) had been consuming these products for .1 year. The mean intake for respondents with phytosterol intakes .3?0 g/d was 4?1 g/d and 74 % of this subgroup had been consuming these products for .1 year. Conclusion: In general, phytosterol intakes are within efficacious levels in the Irish population. However, there appears to be a subgroup that has been consuming these products at intakes greater than current recommendations for .1 year.