Interleukin-3 and erythropoietin cooperate in the regulation of the expression of erythroid-specific transcription factors during erythroid differentiation

Prevention of Transcriptional γ-globin Gene Silencing by Inducing The Hereditary Persistence of Fetal Hemoglobin Point Mutation Using Chimeraplast-Mediated Gene Targeting

Objective

Hemoglobin F (HbF) augmentation is considered a clinically beneficial phenomenon in β-hemoglobinopathies. Prevention of γ-globin gene silencing, inspired by the hereditary persistence of fetal hemoglobin, may be a suitable strategy to upregulate HbF expression in these patients. Therefore, our objective was to assess the potential feasibility of induced -117 G→A substitution in HBG promoter in prevention of transcriptional silencing of the γ-globin.

Materials and Methods

In this experimental study, human peripheral blood-derived hematopoietic stem cells (HSCs) and the K562 cell line were differentiated to erythroid cells. Erythroid maturation was examined using cell morphology parameters and flow cytometry analysis of CD235a expression. A synthesised chimeraplast was transfected to differentiating cells. The efficiency of chimeraplast delivery into target cells was assessed by flow cytometry. Restriction-fragment length polymorphism and DNA sequencing verified oligonucleotide-directed mutagenesis. Gene conversion frequency and globin genes expression was quantified through Allele specific-quantitaive polymerase chain reaction (AS-qPCR) and quantitative-PCR respectively.

Results

Increase in CD235a-expressing cells along with observations made for different stages of erythroid maturation confirmed erythroid differentiation in HSCs and K562 cells. γ to β-globin gene switching was estimated to be on days 18-21 of HSC differentiation. Flow cytometry analysis showed that more than 70% of erythroid progenitor cells (EPCs) were transfected with the chimeraplast. The highest gene conversion efficiency was 7.2 and 11.1% in EPCs and K562 cells respectively. The induced mutation led to a 1.97-fold decrease in β/γ-globin gene expression in transfected EPCs at the experimental end point (day 28) whereas, due to the absence of β-globin gene expression following K562 differentiation, this rate was not evaluable.

Conclusion

Our results suggest the effectiveness of chimeraplasty in induction of the mutation of interest in both EPCs and K562 cells. We also demonstrate that the single nucleotide promoter variant was able to significantly inhibit γ-globin gene silencing during erythroid differentiation.

Combined Id1 and Id3 Deletion Leads to Severe Erythropoietic Disturbances

The Inhibitor of DNA Binding (Id) proteins play a crucial role in regulating hematopoiesis and are known to interact with E proteins and the bHLH family of transcription factors. Current efforts seek to elucidate the individual roles of Id members in regulating hematopoietic development and specification. However, the nature of their functional redundancies remains elusive since ablation of multiple Id genes is embryonically lethal. We developed a model to test this compensation in the adult. We report that global Id3 ablation with Tie2Cre-mediated conditional ablation of Id1 in both hematopoietic and endothelial cells (Id cDKO) extends viability to 1 year but leads to multi-lineage hematopoietic defects including the emergence of anemia associated with defective erythroid development, a novel phenotype unreported in prior single Id knockout studies. We observe decreased cell counts in the bone marrow and splenomegaly to dimensions beyond what is seen in single Id knockout models. Transcriptional dysregulation of hematopoietic regulators observed in bone marrow cells is also magnified in the spleen. E47 protein levels were elevated in Id cDKO bone marrow cell isolates, but decreased in the erythroid lineage. Chromatin immunoprecipitation (ChIP) studies reveal increased occupancy of E47 and GATA1 at the promoter regions of β-globin and E2A. Bone marrow transplantation studies highlight the importance of intrinsic Id signals in maintaining hematopoietic homeostasis while revealing a strong extrinsic influence in the development of anemia. Together, these findings demonstrate that loss of Id compensation leads to dysregulation of the hematopoietic transcriptional network and multiple defects in erythropoietic development in adult mice.

Transcriptional regulation of lineage commitment--a stochastic model of cell fate decisions

Molecular mechanisms employed by individual multipotent cells at the point of lineage commitment remain largely uncharacterized. Current paradigms span from instructive to noise-driven mechanisms. Of considerable interest is also whether commitment involves a limited set of genes or the entire transcriptional program, and to what extent gene expression configures multiple trajectories into commitment. Importantly, the transient nature of the commitment transition confounds the experimental capture of committing cells. We develop a computational framework that simulates stochastic commitment events, and affords mechanistic exploration of the fate transition. We use a combined modeling approach guided by gene expression classifier methods that infers a time-series of stochastic commitment events from experimental growth characteristics and gene expression profiling of individual hematopoietic cells captured immediately before and after commitment. We define putative regulators of commitment and probabilistic rules of transition through machine learning methods, and employ clustering and correlation analyses to interrogate gene regulatory interactions in multipotent cells. Against this background, we develop a Monte Carlo time-series stochastic model of transcription where the parameters governing promoter status, mRNA production and mRNA decay in multipotent cells are fitted to experimental static gene expression distributions. Monte Carlo time is converted to physical time using cell culture kinetic data. Probability of commitment in time is a function of gene expression as defined by a logistic regression model obtained from experimental single-cell expression data. Our approach should be applicable to similar differentiating systems where single cell data is available. Within our system, we identify robust model solutions for the multipotent population within physiologically reasonable values and explore model predictions with regard to molecular scenarios of entry into commitment. The model suggests distinct dependencies of different commitment-associated genes on mRNA dynamics and promoter activity, which globally influence the probability of lineage commitment.

Interaction between the glucocorticoid and erythropoietin receptors in human erythroid cells

OBJECTIVE

The aim of this study was to identify whether the rapid membrane-associated pathway of the glucocorticoid receptor (GR) is active in erythroid cells and plays any role in determining the reversible inhibition on erythroid maturation exerted by GR.

MATERIALS AND METHODS

First we determined the biological effects (inhibition of apoptosis and induction of beta-globin expression) induced in primary erythroblasts by erythropoietin (EPO) and the GR agonist dexamethasone (DXM), alone and in combination. Next, by biochemical analysis, we determined the association between GR and EPO receptor in proerythroblasts generated in vitro from 10 normal adult donors. These studies also analyzed the levels of signal transducers and activators of transcription-5 (STAT-5) phosphorylation induced when the cells were stimulated with DXM alone or in combination with EPO.

RESULTS

DXM antagonized the beta-globin messenger RNA increases, but not the inhibition of apoptosis induced by EPO in primary cells. DXM also antagonized the ability of EPO to induce STAT-5 phosphorylation in these cells. In fact, EPO and DXM alone, but not in combination, induced phosphorylation and nuclear translocation of STAT-5. The inhibition likely occurred through an interaction between the two receptors because GR became associated with the EPO receptor and STAT-5 in cells stimulated with EPO and DXM.

CONCLUSION

These data suggest that glucocorticoids inhibit erythroid maturation not only through a transcriptional mechanism, but also through a rapid membrane-associated pathway that interferes with EPO receptor signaling.