High erythroferrone expression in CD71+ erythroid progenitors predicts superior survival in myelodysplastic syndromes.

Ineffective erythropoiesis and iron overload are common in myelodysplastic syndromes (MDS). Erythroferrone (ERFE) and growth/differentiation factor 15 (GDF15) are two regulators of iron homeostasis produced by erythroid progenitors. Elevated systemic levels of ERFE and GDF15 in MDS are associated with dysregulated iron metabolism and iron overload, which is especially pronounced in MDS with SF3B1 gene mutations. However, the role of ERFE and GDF15 in MDS pathogenesis and their influence on disease progression are largely unknown. Here, we analyzed the expression of ERFE and GDF15 in CD71+ erythroid progenitors of n = 111 MDS patients and assessed their effects on patient survival. The expression of ERFE and GDF15 in MDS was highly aberrant. Unexpectedly, ERFE expression in erythroprogenitors was highly relevant for MDS prognosis and independent of International Prognostic Scoring System (IPSS) stratification. Although ERFE expression was increased in patients with SF3B1 mutations, it predicted overall survival (OS) in both the SF3B1wt and SF3B1mut subgroups. Of note, ERFE overexpression predicted superior OS in the IPSS low/Int-1 subgroup and in patients with normal karyotype. Similar observations were made for GDF15, albeit not reaching statistical significance. In summary, our results revealed a strong association between ERFE expression and MDS outcome, suggesting a possible involvement of ERFE in molecular MDS pathogenesis.

Determination of complex subclonal structures of hematological malignancies by multiplexed genotyping of blood progenitor colonies.

Current next-generation sequencing (NGS) technologies allow unprecedented insights into the mutational profiles of tumors. Recent studies in myeloproliferative neoplasms have further demonstrated that, not only the mutational profile, but also the order in which these mutations are acquired is relevant for our understanding of the disease. Our ability to assign mutation order from NGS data alone is, however, limited. Here, we present a strategy of highly multiplexed genotyping of burst forming unit-erythroid colonies based on NGS results to assess subclonal tumor structure. This allowed for the generation of complex clonal hierarchies and determination of order of mutation acquisition far more accurately than was possible from NGS data alone.

Parvovirus B19 integration into human CD36+ erythroid progenitor cells.

The pathogenic autonomous human parvovirus B19 (B19V) productively infects erythroid progenitor cells (EPCs). Functional similarities between B19V nonstructural protein (NS1), a DNA binding endonuclease, and the Rep proteins of Adeno-Associated Virus (AAV) led us to hypothesize that NS1 may facilitate targeted nicking of the human genome and B19 vDNA integration. We adapted an integration capture sequencing protocol (IC-Seq) to screen B19V infected human CD36+ EPCs for viral integrants, and discovered 40,000 unique B19V integration events distributed throughout the human genome. Computational analysis of integration patterns revealed strong correlations with gene intronic regions, H3K9me3 sites, and the identification of 41 base pair consensus sequence with an octanucleotide core motif. The octanucleotide core has homology to a single region of B19V, adjacent to the P6 promoter TATA box. We present the first direct evidence that B19V infection of erythroid progenitor cells disrupts the human genome and facilitates viral DNA integration.

Interlaboratory trial of the rat Pig-a mutation assay using an erythroid marker HIS49 antibody.

The peripheral blood Pig-a assay has shown promise as a tool for evaluating in vivo mutagenicity. In this study five laboratories participated in a collaborative trial that evaluated the transferability and reproducibility of a rat Pig-a assay that uses a HIS49 antibody reacts with an antigen found on erythrocytes and erythroid progenitors. In preliminary work, flow cytometry methods were established that enabled all laboratories to detect CD59-negative erythrocyte frequencies (Pig-a mutant frequencies) of <10×10(-6) in control rats. Four of the laboratories (the in-life labs) then treated male rats with a single oral dose of N-nitroso-N-ethylurea, 7,12-dimethylbenz[a]anthracene (DMBA), or 4-nitroquinoline-1-oxide (4NQO). Blood samples were collected up to 4 weeks after the treatments and analyzed by flow cytometry for the frequency of CD59-negative cells among total red blood cells (RBCs; RBC Pig-a assay). RBC Pig-a assays were conducted in the four in-life laboratories, plus a fifth laboratory that received blood samples from the other laboratories. In addition, three of the five laboratories performed a Pig-a assay on reticulocytes (RETs; PIGRET assay), using blood from the rats treated with DMBA and 4NQO. The four in-life laboratories detected consistent, time- and dose-related increases in RBC Pig-a mutant frequency (MF) for all three test articles. Furthermore, comparable results were obtained in the fifth laboratory that received blood samples from other laboratories. The three laboratories conducting the PIGRET assay also detected consistent, time- and dose-related increases in Pig-a MF, with the RET MFs increasing more rapidly with time than RBC MFs. These results indicate that rat Pig-a assays using a HIS49 antibody were transferable between laboratories and that data generated by the assays were reproducible. The findings also suggest that the PIGRET assay may detect the in vivo mutagenicity of test compounds earlier than the RBC Pig-a assay.

Aging increases nuclear chromatin entropy of erythroid precursor cells in mice spleen hematopoietic tissue.

Despite recent advances in hematopoietic tissue research, effects of aging on hematopoietic erythroid precursor (EP) cells are unclear. In this article we present results suggesting that chromatin textural entropy of EP cells in mouse spleen increases with age, while chromatin homogeneity decreases. The experiment was conducted on a total of 32 male Swiss white mice. Spleen tissue was acquired from four age groups: 10 days, 1 month, 4 months, and 7 months old mice. A total of 640 randomly selected, nonoverlapping EP cell nuclei (20 per animal) were analyzed using the gray level co-occurrence matrix method. There was statistically highly significant difference between the age groups, both in chromatin entropy (ANOVA, F = 12.99, p < 0.0001) and in homogeneity (ANOVA, F = 7.05, p < 0.001). When the individual groups were compared (ANOVA post hoc test), statistical difference was detected in all group pairs, except between the animals 4 months and 7 months old, either in chromatin entropy or homogeneity. The detected increase of chromatin disorder in mouse juvenile period/early adulthood suggests that cell intrinsic factors such as epigenetic dysregulation and DNA damage accumulation may have an important role in EP cell aging.

Suppression of erythroid development in vitro by Plasmodium vivax.

BACKGROUND: Severe anaemia due to dyserythropoiesis has been documented in patients infected with Plasmodium vivax, however the mechanism responsible for anaemia in vivax malaria is poorly understood. In order to better understand the role of P. vivax infection in anaemia the inhibition of erythropoiesis using haematopoietic stem cells was investigated. METHODS: Haematopoietic stem cells/CD34+ cells, isolated from normal human cord blood were used to generate growing erythroid cells. Exposure of CD34+ cells and growing erythroid cells to P. vivax parasites either from intact or lysed infected erythrocytes (IE) was examined for the effect on inhibition of cell development compared with untreated controls. RESULTS: Both lysed and intact infected erythrocytes significantly inhibited erythroid growth. The reduction of erythroid growth did not differ significantly between exposure to intact and lysed IE and the mean growth relative to unexposed controls was 59.4 ± 5.2 for lysed IE and 57 ± 8.5% for intact IE. Interestingly, CD34+ cells/erythroid progenitor cells were susceptible to the inhibitory effect of P. vivax on cell expansion. Exposure to P. vivax also inhibited erythroid development, as determined by the reduced expression of glycophorin A (28.1%) and CD 71 (43.9%). Moreover, vivax parasites perturbed the division of erythroid cells, as measured by the Cytokinesis Block Proliferation Index, which was reduced to 1.35 ± 0.05 (P-value<0.01) from a value of 2.08 ± 0.07 in controls. Neither TNF-a nor IFN-g was detected in the culture medium of erythroid cells treated with P. vivax, indicating that impaired erythropoiesis was independent of these cytokines. CONCLUSIONS: This study shows for the first time that P. vivax parasites inhibit erythroid development leading to ineffective erythropoiesis and highlights the potential of P. vivax to cause severe anaemia.

Identification and analysis of mouse erythroid progenitors using the CD71/TER119 flow-cytometric assay.

The study of erythropoiesis aims to understand how red cells are formed from earlier hematopoietic and erythroid progenitors. Specifically, the rate of red cell formation is regulated by the hormone erythropoietin (Epo), whose synthesis is triggered by tissue hypoxia. A threat to adequate tissue oxygenation results in a rapid increase in Epo, driving an increase in erythropoietic rate, a process known as the erythropoietic stress response. The resulting increase in the number of circulating red cells improves tissue oxygen delivery. An efficient erythropoietic stress response is therefore critical to the survival and recovery from physiological and pathological conditions such as high altitude, anemia, hemorrhage, chemotherapy or stem cell transplantation. The mouse is a key model for the study of erythropoiesis and its stress response. Mouse definitive (adult-type) erythropoiesis takes place in the fetal liver between embryonic days 12.5 and 15.5, in the neonatal spleen, and in adult spleen and bone marrow. Classical methods of identifying erythroid progenitors in tissue rely on the ability of these cells to give rise to red cell colonies when plated in Epo-containing semi-solid media. Their erythroid precursor progeny are identified based on morphological criteria. Neither of these classical methods allow access to large numbers of differentiation-stage-specific erythroid cells for molecular study. Here we present a flow-cytometric method of identifying and studying differentiation-stage-specific erythroid progenitors and precursors, directly in the context of freshly isolated mouse tissue. The assay relies on the cell-surface markers CD71, Ter119, and on the flow-cytometric 'forward-scatter' parameter, which is a function of cell size. The CD71/Ter119 assay can be used to study erythroid progenitors during their response to erythropoietic stress in vivo, for example, in anemic mice or mice housed in low oxygen conditions. It may also be used to study erythroid progenitors directly in the tissues of genetically modified adult mice or embryos, in order to assess the specific role of the modified molecular pathway in erythropoiesis.

Precise quantification of haemoglobin in erythroid precursors and plasma.

INTRODUCTION: Haemoglobin (Hb) quantification in whole blood is possible by various spectrophotometric methods. However, determination of low-level Hb in erythroid precursors or haemolytic plasma is inaccurate because of contribution from light scatter and/or nonhaemoglobin components with overlapping absorbance. Therefore, this study developed a sole method allowing accurate spectrophotometric quantification of Hb at a low concentration range. METHODS: Advantage was taken of the unique absorption spectra of carbon monoxide-Hb complex (COHb) as compared to oxyHb. The visible absorption spectra of samples were recorded prior and following carbon monoxide exposure. A difference extinction coefficient at the maximal difference absorption was used to calculate Hb concentrations. RESULTS: Known amounts of Hb were added to mouse erythroleukaemia (MEL) cells lysate or plasma to yield known 'theoretical' concentrations. The concentrations were measured by the current and known methods. The current method was found much more accurate compared with previous methods specifically at low concentrations. CONCLUSION: The method is valid for accurate quantification of Hb at a wide concentration range (>0.1 µm/L) in erythroid precursors or plasma and is optional for other biological fluids.

Global gene expression analysis of human erythroid progenitors.

Understanding the pattern of gene expression during erythropoiesis is crucial for a synthesis of erythroid developmental biology. Here, we isolated 4 distinct populations at successive erythropoietin-dependent stages of erythropoiesis, including the terminal, pyknotic stage. The transcriptome was determined using Affymetrix arrays. First, we demonstrated the importance of using defined cell populations to identify lineage and temporally specific patterns of gene expression. Cells sorted by surface expression profile not only express significantly fewer genes than unsorted cells but also demonstrate significantly greater differences in the expression levels of particular genes between stages than unsorted cells. Second, using standard software, we identified more than 1000 transcripts not previously observed to be differentially expressed during erythroid maturation, 13 of which are highly significantly terminally regulated, including RFXAP and SMARCA4. Third, using matched filtering, we identified 12 transcripts not previously reported to be continuously up-regulated in maturing human primary erythroblasts. Finally, using transcription factor binding site analysis, we identified potential transcription factors that may regulate gene expression during terminal erythropoiesis. Our stringent lists of differentially regulated and continuously expressed transcripts containing many genes with undiscovered functions in erythroblasts are a resource for future functional studies of erythropoiesis. Our Human Erythroid Maturation database is available at https://cellline.molbiol.ox.ac.uk/eryth/index.html. [corrected].

PRMT5-mediated methylation of histone H4R3 recruits DNMT3A, coupling histone and DNA methylation in gene silencing.

Mammalian gene silencing is established through methylation of histones and DNA, although the order in which these modifications occur remains contentious. Using the human beta-globin locus as a model, we demonstrate that symmetric methylation of histone H4 arginine 3 (H4R3me2s) by the protein arginine methyltransferase PRMT5 is required for subsequent DNA methylation. H4R3me2s serves as a direct binding target for the DNA methyltransferase DNMT3A, which interacts through the ADD domain containing the PHD motif. Loss of the H4R3me2s mark through short hairpin RNA-mediated knockdown of PRMT5 leads to reduced DNMT3A binding, loss of DNA methylation and gene activation. In primary erythroid progenitors from adult bone marrow, H4R3me2s marks the inactive methylated globin genes coincident with localization of PRMT5. Our findings define DNMT3A as both a reader and a writer of repressive epigenetic marks, thereby directly linking histone and DNA methylation in gene silencing.

Growth differentiation factor 15 production is necessary for normal erythroid differentiation and is increased in refractory anaemia with ring-sideroblasts.

The disturbed erythropoiesis in patients with refractory anaemia with ring-sideroblasts (RARS) is characterized by intramedullary apoptosis of erythroid precursors and increased iron accumulation in mitochondria. To gain insight into these pathophysiological mechanisms we compared the gene expression profile (GEP) of erythroid precursors from RARS patients to the GEP of normal erythroid precursors. Three hundred sixty four probe sets were up-, and 253 probe sets downregulated in RARS cells. Interestingly, Growth Differentiation factor 15 (GDF15), a cytokine from the TGFbeta family, was dramatically upregulated in all RARS patients. Measurement of GDF15 in the sera from twenty RARS patients confirmed this finding by showing significantly, 7.2-fold, increased protein levels (3254 +/- 1400 ng/ml vs. 451 +/- 87 ng/ml in normals). In vitro studies demonstrated erythroid-specific production of GDF15 and dependence on erythropoietin. Induction of apoptosis by arsenic trioxide, a drug which acts via reduction of the mitochondrial membrane potential, also stimulated GDF15 production. Downregulation of endogenous GDF15 production in erythoblasts by specific siRNA led to diminished erythroid differentiation. Taken together, our findings demonstrate a new role for GDF15 in normal erythropoiesis as well as in the ineffective erythropoiesis of RARS patients.

Spontaneous and Fas-induced apoptosis of low-grade MDS erythroid precursors involves the endoplasmic reticulum.

Spontaneous apoptosis of bone marrow erythroid precursors accounts for the anemia that characterizes most low-grade myelodysplastic syndromes (MDS). We have shown that death of these precursors involved the Fas-dependent activation of caspase-8. To explore the pathway leading from caspase-8 activation to apoptosis, we transduced MDS bone marrow CD34(+) cells with a lentivirus encoding wild-type (WT) or endoplasmic reticulum (ER)-targeted Bcl-2 protein before inducing their erythroid differentiation. Both WT-Bcl-2 and ER-targeted Bcl-2 prevented spontaneous and Fas-dependent apoptosis in MDS erythroid precursors. ER-targeted Bcl-2 inhibited mitochondrial membrane depolarization and cytochrome c release in MDS erythroid precursors undergoing apoptosis, indicating a role for the ER in the death pathway, upstream of the mitochondria. MDS erythroid precursors demonstrated elevated ER Ca(2+) stores and these stores remained unaffected by ER-targeted Bcl-2. The ER-associated protein Bcl-2-associated protein (BAP) 31 was cleaved by caspase-8 in MDS erythroid precursors undergoing apoptosis. The protective effect of ER-targeted Bcl-2 toward spontaneous and Fas-induced apoptosis correlated with inhibition of BAP31 cleavage. A protective effect of erythropoietin against Fas-induced BAP31 cleavage and apoptosis was observed. We propose that apoptosis of MDS erythroid precursors involves the ER, downstream of Fas and upstream of the mitochondria, through the cleavage of the ER-associated BAP31 protein.

Modulation of erythroid adhesion receptor expression by hydroxyurea in children with sickle cell disease.

BACKGROUND: We investigated adhesion receptor levels on red blood cells, reticulocytes and erythroid progenitors from children with sickle cell disease treated or not with hydroxyurea. DESIGN AND METHODS: Four groups of patients were investigated: (i) children receiving hydroxyurea for severe vaso-occlusive events (n=26); (ii) untreated children with a history of vaso-occlusive events (n=20); (iii) children with no history of vaso-occlusive events (n=28); and (iv) healthy African controls (n=27). Expression of adhesion receptors was analyzed by flow cytometry with specific mono-clonal antibodies. RESULTS: Reticulocytes and/or red blood cells from the children with sickle cell disease showed significantly higher expression of CD36, alpha 4beta 1, Lu/BCAM than those from controls, whatever the severity of the disease, as well as less marked increases in expression of ICAM-4, CD47 and CD147. Under hydroxyurea treatment, the expression of CD36, alpha 4beta 1 and ICAM-4 (to a lesser extent) was decreased, but surprisingly the expression of Lu/BCAM (and also CD47 and CD147 to a lesser extent) was significantly increased. Alterations of levels of adhesion receptors could be recapitulated in two-phase liquid cultures of erythroid progenitors from controls and untreated children with a history of vaso-occlusive disease, grown in the absence or presence of hydroxyurea. CONCLUSIONS: Our results suggest that hydroxyurea acts during erythroid development and modulates adhesion receptor expression and function differently, possibly by acting on gene expression and the signaling cascade leading to receptor activation.

Single-stranded DNA-binding proteins regulate the abundance of LIM domain and LIM domain-binding proteins.

The LIM domain-binding protein Ldb1 is an essential cofactor of LIM-homeodomain (LIM-HD) and LIM-only (LMO) proteins in development. The stoichiometry of Ldb1, LIM-HD, and LMO proteins is tightly controlled in the cell and is likely a critical determinant of their biological actions. Single-stranded DNA-binding proteins (SSBPs) were recently shown to interact with Ldb1 and are also important in developmental programs. We establish here that two mammalian SSBPs, SSBP2 and SSBP3, contribute to an erythroid DNA-binding complex that contains the transcription factors Tal1 and GATA-1, the LIM domain protein Lmo2, and Ldb1 and binds a bipartite E-box-GATA DNA sequence motif. In addition, SSBP2 was found to augment transcription of the Protein 4.2 (P4.2) gene, a direct target of the E-box-GATA-binding complex, in an Ldb1-dependent manner and to increase endogenous Ldb1 and Lmo2 protein levels, E-box-GATA DNA-binding activity, and P4.2 and beta-globin expression in erythroid progenitors. Finally, SSBP2 was demonstrated to inhibit Ldb1 and Lmo2 interaction with the E3 ubiquitin ligase RLIM, prevent RLIM-mediated Ldb1 ubiquitination, and protect Ldb1 and Lmo2 from proteasomal degradation. These results define a novel biochemical function for SSBPs in regulating the abundance of LIM domain and LIM domain-binding proteins.

Fetal hemoglobin induction by the histone deacetylase inhibitor, scriptaid.

Many different classes of drugs induce fetal hemoglobin (HbF) including histone deacetylase (HDAC) inhibitors such as butyrate and trichostatin A. Although these agents induce gamma-globin expression in culture many are ineffective in vivo, therefore research efforts continue to identify clinically useful fetal globin inducers. We and others demonstrated a role for p38 mitogen activated protein kinase (MAPK) in gamma-globin promoter activation by HDAC inhibitors. In this study we determined the ability of scriptaid, a novel HDAC inhibitor, to induce gamma-globin expression via p38 MAPK signaling. Scriptaid induced gamma-globin in K562 cells and human erythroid progenitors. Furthermore the p38-selective inhibitor SB203580 completely reversed the ability of scriptaid to induce HbF. To test the potential efficacy of scriptaid in humans, in vivo studies were completed in beta-YAC transgenic mice where the gamma-gene is completely silenced. Scriptaid induced reticulocytosis and human gamma-globin mRNA synthesis. At a concentration of 1 mg/kg/day given by intraperitoneal injections twice weekly we observed a significant 1.8-fold increase in gamma-globin mRNA transcripts. The potential for scriptaid as a treatment option for sickle cell disease will be discussed.

Microcytic anemia, erythropoietic protoporphyria, and neurodegeneration in mice with targeted deletion of iron-regulatory protein 2.

Iron-regulatory proteins (IRPs) 1 and 2 posttranscriptionally regulate expression of transferrin receptor (TfR), ferritin, and other iron metabolism proteins. Mice with targeted deletion of IRP2 overexpress ferritin and express abnormally low TfR levels in multiple tissues. Despite this misregulation, there are no apparent pathologic consequences in tissues such as the liver and kidney. However, in the central nervous system, evidence of abnormal iron metabolism in IRP2-/- mice precedes the development of adult-onset progressive neurodegeneration, characterized by widespread axonal degeneration and neuronal loss. Here, we report that ablation of IRP2 results in iron-limited erythropoiesis. TfR expression in erythroid precursors of IRP2-/- mice is reduced, and bone marrow iron stores are absent, even though transferrin saturation levels are normal. Marked overexpression of 5-aminolevulinic acid synthase 2 (Alas2) results from loss of IRP-dependent translational repression, and markedly increased levels of free protoporphyrin IX and zinc protoporphyrin are generated in IRP2-/- erythroid cells. IRP2-/- mice represent a new paradigm of genetic microcytic anemia. We postulate that IRP2 mutations or deletions may be a cause of refractory microcytic anemia and bone marrow iron depletion in patients with normal transferrin saturations, elevated serum ferritins, elevated red cell protoporphyrin IX levels, and adult-onset neurodegeneration.

Podocalyxin is a CD34-related marker of murine hematopoietic stem cells and embryonic erythroid cells.

Podocalyxin/podocalyxin-like protein 1 [PCLP1]/thrombomucin/MEP21 is a CD34-related sialomucin. We have performed a detailed analysis of its expression during murine development and assessed its utility as a marker of hematopoietic stem cells (HSCs) and their more differentiated progeny. We find that podocalyxin is highly expressed by the first primitive hematopoietic progenitors and nucleated red blood cells to form in the embryonic yolk sac. Likewise, podocalyxin is expressed by definitive multilineage hematopoietic progenitors and erythroid precursors in fetal liver. The level of podocalyxin expression gradually declines with further embryo maturation and reaches near-background levels at birth. This is followed by a postnatal burst of expression that correlates with the seeding of new hematopoietic progenitors to the spleen and bone marrow. Shortly thereafter, podocalyxin expression gradually declines, and by 4 weeks postpartum it is restricted to a rare population of Sca-1(+), c-kit(+), lineage marker(-) (Lin(-)) cells in the bone marrow. These rare podocalyxin-expressing cells are capable of serially reconstituting myeloid and lymphoid lineages in lethally irradiated recipients, suggesting they have HSC activity. In summary, we find that podocalyxin is a marker of embryonic HSCs and erythroid cells and of adult HSCs and that it may be a valuable marker for the purification of these cells for transplantation.

Differentiation of human erythroid cells in culture.

A culture procedure for growing erythroid progenitors in liquid medium is described. The procedure is divided into two phases. The first is an erythropoietin (EPO)--independent phase in which peripheral blood mononuclear cells are isolated and cultured in the presence of a combination of growth factors, but in the absence of EPO. During this phase, early erythroid-committed progenitors proliferate and differentiate into more mature progenitors. In the second phase, the latter cells, cultured in an EPO-supplemented medium, continue to proliferate and mature into hemoglobin-containing nucleated erythroid cells. The culture procedure yields populations that are large, relatively pure, and synchronized (in terms of differentiation), and which recapitulate in vivo erythropoiesis. Since the cells are grown in suspension, samples of cells can be withdrawn at any time, without disturbing the cultures, and assayed for various parameters, e.g., morphology, size, number, viability, apoptosis, cell cycle, surface antigens, or gene expression. Several procedures for analyzing the cultured cells with respect to their hemoglobin content during their differentiation are included.

Two different pathways link G-protein-coupled receptors with tyrosine kinases for the modulation of growth and survival in human hematopoietic progenitor cells.

The G-protein-coupled receptor agonists CXCL12 (SDF-1, a chemokine) and thrombin showed opposite effects on growth and survival of multipotent and erythroid human hematopoietic progenitor cells. CXCL12 promoted growth in multipotent cells by activating the RhoA-Rho kinase pathway. Its effect was largely blocked by Y-27632, a specific inhibitor of Rho kinase, and by clostridial toxin B, a specific inhibitor of Rho family proteins. Rho activation required a G(i)-mediated stimulation of tyrosine kinases, which was blocked by PP2 and tyrphostin AG 490, inhibitors of Src and Jak type kinases, respectively. By contrast, in erythroid cells, inhibitors of Src family and c-Abl tyrosine kinases (tyrphostin AG 82, PP2, imatinib) enhanced protein kinase C (PKC)-dependent cell growth and antagonized thrombin-promoted apoptosis by specifically stimulating PKCbeta activity. The PKC activating phorbol ester PMA (a growth factor in erythroid cells) induced the activation of Lyn and c-Abl tyrosine kinases, thus establishing a feedback inhibition of PKCbeta. Hence, developmental stage-specific crosstalk between PKC subtypes and tyrosine kinases appear to determine whether growth and survival of hematopoietic cells are promoted or inhibited by G-protein-coupled receptor agonists.

Analysis of remnant reticulocyte mRNA reveals new genes and antisense transcripts expressed in the human erythroid lineage.

BACKGROUND AND OBJECTIVES: We studied the gene expression profile of human purified reticulocytes to provide a transcriptional basis for the study of erythroid biology, differentiation and hematologic disorders. DESIGN AND METHODS: We screened highly purified blood reticulocytes from ten healthy adult volunteers. We chose a modified protocol of serial analysis of gene expression (SAGE), the serial analysis of downsized extracts (SADE). RESULTS: Data analysis revealed that 64% of gene signatures (tags) matched with known genes; mainly hemoglobin. In addition to the abundant globin mRNA, SAGE analysis identified previously described genes and new transcripts. In reticulocytes, which are poor in mRNA, we also identified 9% of EST and 27% of tags that did not match with any known genes. Mining our data, 70% of the unknown tags and 39% of tags identifying EST were found to be specific to the reticulocyte. We demonstrated the presence of a mRNA that matched with the reverse sequence of the hemoglobin b (HBB) transcript. INTERPRETATION AND CONCLUSIONS: This is the first description of an antisense transcript of the human HBB gene suggesting regulation by way of sense-antisense pairing. The well-characterized genes found in the SAGE library were genes specific to the blood cell lineage, housekeeping genes and, interestingly, genes not previously described in the reticulocyte. Furthermore the study provides markers of the erythroid lineage regulated during the differentiation process as observed in in vitro experiments.