The making of an erythroid cell. Molecular control of hematopoiesis

Effects of p38 MAP kinase inhibitors on the differentiation and maturation of erythroid progenitors

In rodents, p38 MAP kinase inhibitors (p38is) induce bone marrow hypocellularity and reduce reticulocyte and erythrocyte counts. To identify target cell populations affected, a differentiating primary liquid erythroid culture system using sca-1(+)cells from mouse bone marrow was developed and challenged with p38is SB-203580, SB-226882, and SB-267030. Drug-related alterations in genes involved at different stages of erythropoiesis, cell-surface antigen expression (CSAE), burst-forming unit erythroid (BFU-E) colony formation, and cellular morphology (CM), growth (CG), and viability were evaluated. CSAE, CM, and decreases in BFU-E formation indicated delayed maturation, while CG and viability were unaffected. Terminal differentiation was delayed until day 14 versus day 7 in controls. CSAE demonstrated higher percentages of sca-1(+)cells after day 2 and reduced percentages of ter119(+) cells after day 7 in all treated cultures. Real-time reverse transcriptase polymerase chain reaction revealed a transient delay in expression of genes involved at early, intermediate, and late stages of erythropoiesis, followed by rebound expression at later time points. Results demonstrate p38is do not irreversibly inhibit erythrogenesis but induce a potency-dependent, transient delay in erythropoietic activity. The delay in activity is suggestive of effects on sca-1(+)bone marrow cells caused by alterations in expression of genes related to erythroid commitment and differentiation resulting in delayed maturation.

Initial function analysis of a novel erythroid differentiation related gene EDRF1

Erythroid differentiation depends on the establishment of specific patterns of gene expression. Hypersensitive site 2 (HS2, serving as a major enhancer of globin genes)-binding proteins may be involved in its natural open chromosomal environment formation. Previously we prepared monoclonal antibodies against HS2-binding nuclear proteins of terminal differentiated erythroid cells. By utilizing the monoclonal antibodies, we screened lambda-gt11 human fetal liver cDNA expression library and obtained one cDNA clone, which was named erythroid differentiation related gene (EDRF1, Genbank accession number AF040247), encompassing an entire open reading frame. We investigated the expression pattern of EDRF1 by RT-PCR technique. And a clue to the function of EDRF1 has been found from confirmation of high levels of EDRF1 mRNA in differentiated K562 and human fetal liver tissue. To illuminate the function of EDRF1 in K562 cells, sense and antisense EDRF1 constructs were prepared and transfected into K562 cells. alpha-globin mRNA was down-regulated and EpoR (erythropoietin receptor) mRNA expression was increased in antisense transfected cells. Cells transfected with sense construct grew more slowly than control cells suggested by [(3)H] thimidine incorporation experiments. Suppression of K562 proliferation was accompanied by increased spontaneous hemoglobin synthesis demonstrated by spectrometry. K562 cells transfected with sense construct exhibited reduced clongenicity compared with control cells in methycellulose culture. These data provided the evidence that EDRF1 can influence globin expression and hemoglobin synthesis in K562 cells and modulated self-renewal in K562 cells.

Maxadilan, the vasodilator/immunomodulator from Lutzomyia longipalpis sand fly saliva, stimulates haematopoiesis in mice

Protozoal parasites of the genus Leishmania are transmitted to their vertebrate host within the saliva of the sand fly during a blood meal. The saliva of the sand fly Lutzomyia longipalpis contains maxadilan, a potent vasodilator and immunomodulator. Maxadilan has been shown to enhance the virulence of L. major in all strains of laboratory mice when injected along with the organism. Increased haematopoiesis has been associated with enhanced susceptibility to Leishmania organisms. Here, we show that maxadilan alone stimulates bone marrow haematopoiesis through its ability to stimulate interleukin-6 production by bone marrow stromal cells. Moreover, these effects of maxadilan are mediated through the interaction of maxadilan with the pituitary adenylate cyclase activating polypeptide receptor. These data suggest that increasing haematopoiesis may be yet another way that maxadilan enhances susceptibility of mice to Leishmania infection.

Transcriptional regulation of erythropoiesis. Fine tuning of combinatorial multi-domain elements

Haematopoiesis, the differentiation of haematopoietic stem cells and progenitors into various lineages, involves complex interactions of transcription factors that modulate the expression of downstream genes and mediate proliferation and differentiation signals. Commitment of pluripotent haematopoietic stem cells to the erythroid lineage induces erythropoiesis, the production of red blood cells. This process involves a concerted progression through an erythroid burst forming unit (BFU-E), an erythroid colony forming unit (CFU-E), proerythroblast and an erythroblast. The terminally differentiated erythrocytes, in mammals, lose their nucleus yet function several more months. A well-coordinated cohort of transcription factors regulates the formation, survival, proliferation and differentiation of multipotent progenitor into the erythroid lineage. Here, we discuss broad-spectrum factors essential for self-renewal and/or differentiation of multipotent cells as well as specific factors required for proper erythroid development. These factors may operate solely or as part of transcriptional complexes, and exert activation or repression. Sequence comparisons reveal evolutionarily conserved modular composition for these factors; X-ray crystallography demonstrates that they include multidomain elements (e.g. HLH or zinc finger motifs), consistent with their complex interactions with other proteins. Finally, transfections and genomic studies show that the timing of each factor's expression during the hematopoietic process, the cell lineages affected and the existing combination of other factors determine the erythroid cell fate.

Characterization and localization of expression of an erythropoietin-induced gene, ERIC-1/TACC3, identified in erythroid precursor cells

Gene expression profiles during erythropoietin (Epo)-induced differentiation of erythroid progenitor cells derived from the Friend virus anaemia (FVA) and phenylhydrazine (PHZ) murine models have been examined using differential display polymerase chain reaction (PCR). Ten cDNA fragments upregulated by Epo were isolated. The ribonuclease protection assay confirmed differential expression between Epo-stimulated and Epo-deprived cells for one of these, provisionally named ERIC-1. Sequencing of the full-length cDNA predicted a protein of 558 amino acids, 17 amino acids longer than mTACC3, the third member of a novel family of proteins that contain a coiled-coil domain. The human homologue, cloned using rapid amplification of cDNA ends (RACE)-PCR, encodes a larger protein of 838 amino acids that is identical to hTACC3. In addition to erythroid precursor cells, ERIC-1/TACC3 is expressed at high levels in the testes, at moderate levels in the thymus and peripheral leucocytes, and at lower levels in the spleen and intestinal tissue. Immunohistochemical analysis using an antibody to a GST fusion product of the C-terminus of hERIC-1/TACC3 revealed that it is localized to Sertoli cells in the human testes. Confocal microscopy demonstrated hERIC-1/TACC3 protein concentrated in the perinuclear vesicles of dermal microvascular endothelial cells. Although ERIC-1/TACC3 is expressed in a wide range of tissues, its upregulation by Epo in erythroid progenitors implies that it has a role in terminal erythropoiesis.

Erythroblasts from friend virus infected- and phenylhydrazine-treated mice accurately model erythroid differentiation

The dynamics of gene expression during terminal erythroid differentiation have been examined in three murine models; the erythroleukaemia cell line HCD-57 and splenic erythroblasts isolated from mice treated with either the anaemia-inducing strain of Friend virus (FVA cells) or the haemolytic agent phenylhydrazine (PHZ cells). In response to erythropoietin (EPO) and haemin, HCD-57 cells proliferated and synthesized haemoglobin, but failed to complete terminal differentiation as indicated by lack of change in both gene expression and morphological appearance. In contrast, EPO-induced terminal differentiation in FVA and PHZ cells in vitro was accompanied by increases in haemoglobin positivity, morphological maturation and a shared pattern of gene expression. EPO receptor (EPO-R) mRNA levels peaked before globin gene expression which was maximal at 24 h. Peak GATA-1 and EKLF mRNA levels also preceded the globin gene peak, but the highest NF-E2 levels coincided with maximal globin levels, suggesting a role for NF-E2 in the maintenance, rather than the initiation of globin gene expression. Peak expression of delta-aminolaevulinic acid synthase (ALAS) coincided with peak globin expression. FVA and PHZ cells represent more effective models than the HCD-57 cell line for the investigation of erythroid gene expression during EPO-regulated terminal erythropoiesis.