Expansion of functionally defined mouse hematopoietic stem and progenitor cells by a short isoform of RUNX1/AML1.
ABSTRACT Self-renewal activity is essential for the maintenance and regeneration of the hematopoietic system. The search for molecules capable of promoting self-renewal and expanding hematopoietic stem cells (HSCs) has met with limited success. Here, we show that a short isoform (AML1a) of RUNX1/AML1 has such activities. Enforced AML1a expression expanded functionally defined HSCs, with an efficiency that was at least 20 times greater than that of the control in vivo and by 18-fold within 7 days ex vivo. The ex vivo-expanded HSCs could repopulate hosts after secondary transplantations. Moreover, AML1a expression resulted in vigorous and long-term (> 10(6)-fold at 4 weeks) ex vivo expansion of progenitor cell populations capable of differentiating into multilineages. Gene expression analysis revealed that AML1a expression was associated with up-regulation of genes, including Hoxa9, Meis1, Stat1, and Ski. shRNA-mediated silencing of these genes attenuated AML1a-mediated activities. Overall, these findings establish AML1a as an isoform-specific molecule that can influence several transcriptional regulators associated with HSCs, leading to enhanced self-renewal activity and hematopoietic stem/progenitor cell expansion ex vivo and in vivo. Therefore, the abilities of AML1a may have implications for HSC transplantation and transfusion medicine, given that the effects also can be obtained by cell-penetrating AML1a protein.
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ABSTRACT: Oncogenic transcription factors such as RUNX1/ETO, which is generated by the chromosomal translocation t(8;21), subvert normal blood cell development by impairing differentiation and driving malignant self-renewal. Here, we use digital footprinting and chromatin immunoprecipitation sequencing (ChIP-seq) to identify the core RUNX1/ETO-responsive transcriptional network of t(8;21) cells. We show that the transcriptional program underlying leukemic propagation is regulated by a dynamic equilibrium between RUNX1/ETO and RUNX1 complexes, which bind to identical DNA sites in a mutually exclusive fashion. Perturbation of this equilibrium in t(8;21) cells by RUNX1/ETO depletion leads to a global redistribution of transcription factor complexes within preexisting open chromatin, resulting in the formation of a transcriptional network that drives myeloid differentiation. Our work demonstrates on a genome-wide level that the extent of impaired myeloid differentiation in t(8;21) is controlled by the dynamic balance between RUNX1/ETO and RUNX1 activities through the repression of transcription factors that drive differentiation.Cell Reports 09/2014; DOI:10.1016/j.celrep.2014.08.024 · 7.21 Impact Factor
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ABSTRACT: RUNX1 is an important transcription factor for hematopoiesis. There are multiple alternatively spliced isoforms of RUNX1. The best known isoforms are RUNX1a from use of exon 7A and RUNX1b and c from use of exon 7B. RUNX1a has unique functions due to its lack of C-terminal regions common to RUNX1b and c. Here, we report that the ortholog of human RUNX1a was only found in primates. Furthermore, we characterized three Runx1 isoforms generated by exon 6 alternative splicing. Runx1bEx6- (Runx1b without exon 6) and a unique mouse Runx1bEx6e showed higher colony-forming activity than the full length Runx1b (Runx1bEx6+). They also facilitated the transactivation of Runx1bEx6+. To gain insight into in vivo functions, we analyzed a knock-in (KI) mouse model that lacks isoforms Runx1b/cEx6- and Runx1bEx6e. KI mice had significantly fewer lineage-Sca1+c-Kit+ cells, short-term hematopoietic stem cells and multipotent progenitors than controls. In vivo competitive repopulation assays demonstrated a 7-fold difference of functional hematopoietic stem cells (HSCs) between WT and KI mice. Together, our results show that Runx1 isoforms involving exon 6 support high self-renewal capacity in vitro, and their loss results in reduction of the HSC pool in vivo, which underscore the importance of fine tuning RNA splicing in hematopoiesis.Blood 04/2014; 123(24). DOI:10.1182/blood-2013-08-521252 · 9.78 Impact Factor
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ABSTRACT: Background: Maternal smoking in pregnancy is associated with adverse health outcomes in children, including cancers; underlying mechanisms may include epigenetic modifications. Using Illumina's 450K array, we previously identified differential DNA methylation related to maternal smoking during pregnancy at 26 CpG sites (CpGs) in 10 genes in newborn cord bloods from the Norwegian Mother and Child Cohort Study (MoBa). Whether these methylation signals in newborns reflect in utero exposure only or possibly epigenetic inheritance of smoking-related modifications is unclear. Methods: We therefore evaluated the impact of the timing of mother's smoking (before or during pregnancy using cotinine measured at 18 weeks gestation), the father's smoking before conception, and the grandmother's smoking during her pregnancy with the mother on methylation at these 26 CpGs in 1,042 MoBa newborns. We used robust linear regression, adjusting for covariates, applying Bonferroni correction. Results: The strongest and only statistically significant associations were observed for sustained smoking by the mother during pregnancy through at least gestational week 18 (p<1.6x10-5 for all 26 CpGs). We observed no statistically significant differential methylation due to smoking by the mother prior to pregnancy or that ceased by week 18, father's smoking before conception, or grandmother's smoking while pregnant with the mother. Conclusions: Differential methylation at these CpGs in newborns appears to reflect sustained in utero exposure rather than epigenetic inheritance. Impact: Smoking cessation in early pregnancy may negate effects on methylation. Analyses of maternal smoking during pregnancy and offspring health outcomes, including cancer, limited to ever smoking might miss true associations.Cancer Epidemiology Biomarkers & Prevention 04/2014; 23(6). DOI:10.1158/1055-9965.EPI-13-1256 · 4.56 Impact Factor