[Phorbol 12-myristate 13-acetate inhibits apoptosis in erythroleukemia K562 cells induced by some nucleosides]

We studied the ability of phorbol 12-myristate 13-acetat to prevent erythroid differentiation and apoptosis in erythroleukemic K562 cells induced by cytidine, thymidine, and guanosine. The exposure of cancer cells to combinations of phorbol 12-myrsitate 13-acetate (100 nM) nucleosides for two days led to a loss of hemoglobin production (marker of erythroid differentiation) in cells and increased expression of monocyte-macrophage lineage associated surface antigen CD14. The treatment of K562 cells with nucleosides only was accompanied by the activation of caspase-3 and caspase-9, rather than caspase-6, increased fluorescence of ethidium bromide and DAPI upon binding to DNA, and apoptosis. Intracellular activation of caspase-6, inhibition of caspase-9, a markedly decreased activity of caspase-3 and of fluorescence of DNA-binding dyes, and inhibition of apoptosis were observed when the cells were treated with phorbol 12-myeristet 13-acetate combined with nucleosides.

The C-terminal peptide of thrombospondin-4 stimulates erythroid cell proliferation

Erythropoietin (EPO) stimulates the production of small erythroid cell stimulating factors (molecular weight <5 kDa) in cultures of bone marrow endothelial cells. We identified a fragment of thrombospondin-4 (TSP-4) as an EPO-stimulated protein in endothelial cell lysates. Pre-incubation of the low molecular weight fractions from supernatants of EPO-treated umbilical cord endothelial cells (HUVEC) with antibodies against the C-terminal residues of TSP-1,2 and TSP-4 decreased the erythroid cell stimulating activity. The C-terminal TSP-1 section corresponding to a molecular weight lower than 6 kDa has the integrin-associated protein binding motif VVM. The corresponding TSP-4 fragment, lacking the three residue sequence VVM, has a distinctive acidic peptide comprising the last 21 amino acids (C21) with the characteristics of an amphipathic helix. C21 stimulated thymidine incorporation into bovine erythroid cells, increased cell numbers in cultures of cord blood CD36+ erythroid precursors and skin fibroblasts, and decreased HUVEC proliferation. SC21, a homologous peptide of identical amino acid composition but with interchanged residues, was non-amphipathic and had no erythroid cell stimulating activity.

Transferrin receptor 2 protein is not expressed in normal erythroid cells

Human TFR2 (transferrin receptor 2) is a membrane-bound protein homologous with TFR1. High levels of TFR2 mRNA were found mainly in the liver and, to a lesser extent, in erythroid precursors. However, although the presence of the TFR2 protein in hepatic cells has been confirmed in several studies, evidence is lacking about the presence of the TFR2 protein in normal erythroid cells. Using two anti-TFR2 monoclonal antibodies, G/14C2 and G/14E8, we have provided evidence that TFR2 protein is not expressed in normal erythroid cells at any stage of differentiation, from undifferentiated CD34+ cells to mature orthochromatic erythroblasts. In contrast, erythroleukaemic cells (K562 cells) exhibited a high level of expression of TFR2 at both the mRNA and the protein level. We can therefore conclude that an elevated expression of TFR2 protein is observed in leukaemic cells, but not in normal erythroblasts. The implications of this observation for the understanding of the phenotypic features of haemochromatosis due to mutation of the TFR2 gene are discussed.

BMP4 and Madh5 regulate the erythroid response to acute anemia

Acute anemia initiates a systemic response that results in the rapid mobilization and differentiation of erythroid progenitors in the adult spleen. The flexed-tail (f) mutant mice exhibit normal steady-state erythropoiesis but are unable to rapidly respond to acute erythropoietic stress. Here, we show that f/f mutant mice have a mutation in Madh5. Our analysis shows that BMP4/Madh5-dependent signaling, regulated by hypoxia, initiates the differentiation and expansion of erythroid progenitors in the spleen. These findings suggest a new model where stress erythroid progenitors, resident in the spleen, are poised to respond to changes in the microenvironment induced by acute anemia.

Calcitriol Increases Burst-Forming Unit-Erythroid Proliferation in Chronic Renal Failure

BACKGROUND

Calcitriol (C) improves anemia in chronic renal failure. This effect may be related to the suppression of iPTH release, or to a direct effect on erythropoiesis.

METHODS

Thirty-three patients with chronic renal failure were enrolled; among them, 24 were on chronic hemodialysis and 9 on conservative management. None had other chronic or hematological disease, aluminum levels were below 20 microg/l and DFO testing was negative. The iPTH range was 250-480 pg/l. None were treated with C or r-HuEpo. In vitro study: Samples were drawn for a basal erythroid precursor (burst forming unit-erythroid BFU-E) study: Mononuclear cells were incubated for 14 days with r-HuEpo 3U/ml (A), r-HuEpo 3U/l + C 30 pg (B), r-HuEpo 3U/ml + C 300 pg (C), or r-HuEpo 30 U/ml + C 300 pg (D). In vivo study: After the basal evaluation, 10 patients on chronic dialysis were treated with C (Calcijex-Abbott) 1 microg three times a week, and 4 patients served as controls. BFU-E studies were performed after 1, 2 and 4 months.

RESULTS

In vitro, culture B showed increased BFU-E proliferation vs. A (41 +/- 23 vs. 27 +/- 15, p < 0.02); in cultures C and D, proliferation was 61 +/- 31 and 78 +/- 42, respectively, p < 0.01 vs. A. There was no difference among patients with predialysis renal failure and those on dialysis. BFU-E proliferation was inversely related to basal Hb (p < 0.04) and CRP levels (p < 0.05). During the in vivo study, all cultures showed a progressive increase in proliferation without a plateau level (basal, after 1, 2 and 4 months, respectively) In A: 17 +/- 8, 22 +/- 13, 30.9 +/- 14.9, 41.4 +/- 20; in B: 27.3 +/- 15, 35.6 +/- 20, 45.5 +/- 21, 57 +/- 26; in C: 48.2 +/- 20.6, 63.7 +/- 32, 75.7 +/- 37, 83 +/- 40; in D: 72 +/- 24, 91 +/- 42, 106 +/- 42, 110 +/- 42.3 (all p < 0.001). Hb and Hct showed a significant increase (p < 0.03) in the treatment group. The decrease in iPTH was not related to BFU-E proliferation.

CONCLUSIONS

In chronic uremia, C has a direct effect on erythroid precursors proliferation, as demonstrated both in vitro and in vivo, with a synergistic effect with r-HuEpo. C may be a useful adjuvant therapy to r-HuEpo treatment.

An erythroid differentiation-specific splicing switch in protein 4.1R mediated by the interaction of SF2/ASF with an exonic splicing enhancer

Protein 4.1R is a vital component of the red blood cell membrane cytoskeleton. Promotion of cytoskeletal junctional complex stability requires an erythroid differentiation stage-specific splicing switch promoting inclusion of exon 16 within the spectrin/actin binding domain. We showed earlier that an intricate combination of positive and negative RNA elements controls exon 16 splicing. In this report, we further identified 3 putative exonic splicing enhancers within exon 16 and investigated the function of the sequence CAGACAT in the regulation of exon 16 splicing. Mutation of these sequences leads to increased exclusion of exon 16 in both in vivo and in vitro splicing assays, indicating that CAGACAT is a functional exonic splicing enhancer. UV cross-linking further detects an approximately 33-kDa protein that specifically binds to the CAGACAT-containing transcript. An anti-SF2/ASF antibody specifically immunoprecipitates the approximately 33-kDa protein. Furthermore, SF2/ASF stimulates exon 16 inclusion in both in vitro complementation assays and minigene-transfected mouse erythroleukemia cells (MELCs). Finally, SF2/ASF expression is up-regulated and correlates with exon 16 inclusion in differentiated MELCs. These results suggest that increased splicing factor 2/alternative splicing factor (SF2/ASF) expression in differentiated mouse erythroleukemia mediates a differentiation stage-specific exon 16 splicing switch through its interaction with the exonic splicing enhancer.

Heme-dependent up-regulation of the α-globin gene expression by transcriptional repressor Bach1 in erythroid cells

The transcriptional factor Bach1 forms a heterodimer with small Maf family, and functions as a repressor of the Maf recognition element (MARE) in vivo. To investigate the involvement of Bach1 in the heme-dependent regulation of the expression of the alpha-globin gene, human erythroleukemia K562 cells were cultured with succinylacetone (SA), a heme biosynthetic inhibitor, and the level of alpha-globin mRNA was examined. A decrease of alpha-globin mRNA was observed in SA-treated cells, which was restored by the addition of hemin. The heme-dependent expression of alpha-globin occurred at the transcriptional level since the expression of human alpha-globin gene promoter-reporter gene containing hypersensitive site-40 (HS-40) was decreased when K562 cells were cultured with SA. Hemin treatment restored the decrease of the promoter activity by SA. The regulation of the HS-40 activity by heme was dependent on the NF-E2/AP-1 (NA) site, which is similar to MARE. The NA site-binding activity of Bach1 in K562 increased upon SA-treatment, and the increase was diminished by the addition of hemin. The transient expression of Bach1 and mutated Bach1 lacking CP motifs suppressed the HS-40 activity, and cancellation of the repressor activity by hemin was observed when wild-type Bach1 was expressed. The expression of NF-E2 strengthened the restoration of the Bach1-effect by hemin. Interestingly, nuclear localization of Bach1 increased when cells were treated with SA, while hemin induced the nuclear export of Bach1. These results indicated that heme plays an important role in the induction of alpha-globin gene expression through disrupting the interaction of Bach1 and the NA site in HS-40 enhancer in erythroid cells.

Evolutionary conservation of KLF transcription factors and functional conservation of human γ-globin gene regulation in chicken☆

The Krüppel-like factors (KLFs) are a family of Cys2His2 zinc-finger DNA binding proteins with homology to Drosophila Krüppel. KLFs can bind to CACCC elements, which are important in controlling developmental programs. The CACCC promoter element is critical for the developmental regulation of the human gamma-globin gene. In the present study, chicken homologues of the human KLF2, 3, 4, 5, 9, 11, 12, 13, and 15 genes were identified. Phylogenetic analysis confirms that these genes are more closely related to their human homologues than they are to other chicken KLFs. This work also represents the first systematic study of the expression patterns of KLFs during erythroid development. In addition, transient transfections of human globin constructs into 5-day (primitive) chicken red blood cells show that human gamma-globin expression is regulated via its CACCC promoter element. This indicates that a CACCC-binding factor(s) important for gamma-globin expression functions in 5-day chicken red cells.

GATA-1 and NF-Y cooperate to mediate erythroid-specific transcription of Gfi-1B gene

Expression of Gfi (growth factor-independence)-1B, a Gfi-1-related transcriptional repressor, is restricted to erythroid lineage cells and is essential for erythropoiesis. We have determined the transcription start site of the human Gfi-1B gene and located its first non-coding exon approximately 7.82 kb upstream of the first coding exon. The genomic sequence preceding this first non-coding exon has been identified to be its erythroid-specific promoter region in K562 cells. Using gel-shift and chromatin immunoprecipitation (ChIP) assays, we have demonstrated that NF-Y and GATA-1 directly participate in transcriptional activation of the Gfi-1B gene in K562 cells. Ectopic expression of GATA-1 markedly stimulates the activity of the Gfi-1B promoter in a non-erythroid cell line U937. Interestingly, our results have indicated that this GATA-1-mediated trans-activation is dependent on NF-Y binding to the CCAAT site. Here we conclude that functional cooperation between GATA-1 and NF-Y contributes to erythroid-specific transcriptional activation of Gfi-1B promoter.

Identification of an alternate delta-globin mRNA in adult human erythroid cells

Here we describe the identification and characterization of an alternate delta-globin mRNA (Alt-d) discovered during high-throughput sequencing of mRNA from adult human erythroid cells. Alt-d mRNA shares the same coding region, splicing pattern, downstream untranslated region, and site of polyadenylation with the previously defined delta-globin (Delta) mRNA. Alt-d mRNA encodes an additional 145 nt in the upstream untranslated region, suggesting an alternative site of transcriptional initiation and transcription through the previously defined promoter, which contains several protein-binding motifs and a TATA box. Northern blot and PCR analyses demonstrated a restricted expression of Alt-d in fetal liver, bone marrow, and adult reticulocytes. Quantitative PCR demonstrated an Alt-d expression pattern similar to that of the Delta transcripts. In addition to intergenic RNA species and the dominant delta-globin transcripts, these data suggest that a third form of RNA is produced from low-level transcription through the delta-globin gene promoter.

Extended beta-globin locus control region elements promote consistent therapeutic expression of a gamma-globin lentiviral vector in murine beta-thalassemia

Since increased fetal hemoglobin diminishes the severity of beta-thalassemia and sickle cell anemia, a strategy using autologous, stem cell-targeted gene transfer of a gamma-globin gene may be therapeutically useful. We previously found that a gamma-globin lentiviral vector utilizing the beta-globin promoter and elements from the beta-globin locus control region (LCR) totaling 1.7 kb could correct murine beta-thalassemia. However, therapeutic consistency was compromised by chromosomal position effects on vector expression. In contrast, we show here that the majority of animals that received transplants of beta-thalassemic stem cells transduced with a new vector containing 3.2 kb of LCR sequences expressed high levels of fetal hemoglobin (17%-33%), with an average vector copy number of 1.3. This led to a mean 26 g/L (2.6 g/dL) increase in hemoglobin concentration and enhanced amelioration of other hematologic parameters. Analysis of clonal erythroid cells of secondary spleen colonies from mice that underwent transplantation demonstrated an increased resistance of the larger LCR vector to stable and variegating position effects. This trend was also observed for vector insertion sites located inside genes, where vector expression was often compromised, in contrast to intergenic sites, where higher levels of expression were observed. These data emphasize the importance of overcoming detrimental position effects for consistent therapeutic globin vector expression.

Ex vivo and in vivo biological effects of a truncated form of the receptor tyrosine kinase stk when activated by interaction with the friend spleen focus-forming virus envelope glycoprotein or by point mutation

The erythroleukemia-inducing Friend spleen focus-forming virus (SFFV) encodes a unique envelope protein, gp55, which interacts with the erythropoietin (Epo) receptor complex, causing proliferation and differentiation of erythroid cells in the absence of Epo. Susceptibility to SFFV-induced erythroleukemia is conferred by the Fv-2 gene, which encodes a short form of the receptor tyrosine kinase Stk/Ron (sf-Stk) only in susceptible strains of mice. We recently demonstrated that sf-Stk becomes activated by forming a strong interaction with SFFV gp55. To examine the biological consequences of activated sf-Stk on erythroid cell growth, we prepared retroviral vectors which express sf-Stk, either in conjunction with gp55 or alone in a constitutively activated mutant form, and tested them for their ability to induce Epo-independent erythroid colonies ex vivo and disease in mice. Our data indicate that both gp55-activated sf-Stk and the constitutively activated mutant of sf-Stk induce erythroid cells from Fv-2-susceptible and Fv-2-resistant (sf-Stk null) mice to form Epo-independent colonies. Mutational analysis of sf-Stk indicated that a functional kinase domain and 8 of its 12 tyrosine residues are required for the induction of Epo-independent colonies. Further studies demonstrated that coexpression of SFFV gp55 with sf-Stk significantly extends the half-life of the kinase. When injected into Fv-2-resistant mice, neither the gp55-activated sf-Stk nor the constitutively activated mutant caused erythroleukemia. Surprisingly, both Fv-2-susceptible and -resistant mice injected with the gp55-sf-Stk vector developed clinical signs not previously associated with SFFV-induced disease. We conclude that sf-Stk, activated by either point mutation or interaction with SFFV gp55, is sufficient to induce Epo-independent erythroid colonies from both Fv-2-susceptible and -resistant mice but is unable to cause erythroleukemia in Fv-2-resistant mice.

Sustained Swimming Increases Erythrocyte MCT1 During Erythropoiesis and Ability to Regulate pH Homeostasis in Rat

We investigated the effect of sustained swimming exercise on the increase in monocarboxylate transporter 1 (MCT1) concentration and its ability to regulate pH homeostasis in rat erythrocytes. Male Sprague-Dawley rats aged 9 weeks were divided into sedentary and swimming groups for both 1- and 3-week experiments. The exercise group swam for 30 - 60 min/day, 5 days/week. Before and 1 and 3 weeks after initiation of the exercise, blood was collected for lactate concentration measurement during pre-exercise rest and post-exercise recovery periods. On the last day of each experiment, venous blood and erythroid cells in bone marrow were collected to assay the capacity for erythropoiesis and MCT1 concentration. In the swimming group at 0 weeks (p < 0.05), 1 week (p < 0.01) and 3 weeks (p < 0.001), the blood lactate concentration post-exercise was significantly higher than at rest. The ratio of young erythrocytes to total erythrocytes was significantly higher in the 3-week swimming group than in the sedentary group (p < 0.05). The MCT1 concentration in erythrocytes was higher in the 3-week swimming group than in the sedentary group (18 %, p < 0.05), which was found in young erythrocytes (22 %, p < 0.05) when total erythrocytes were separated into young and old fractions. The MCT1 concentration in erythroid cells was higher in both the 1-week and 3-week swimming groups than in either of the sedentary groups (27 and 28 %, respectively, p < 0.05). The pH recovery of erythrocyte suspensions at 10, 15 and 20 seconds after addition of lactate to the suspension medium was significantly faster in the 3-week swimming group than in the sedentary group (p < 0.001). These findings suggest that erythrocyte MCT1 is increased during erythropoiesis in bone marrow and that the increase of the transporter facilitates, at least partly, lactate/proton co-transport due to sustained swimming exercise in rats.

Neurokinin-B transcription in erythroid cells: direct activation by the hematopoietic transcription factor GATA-1

The GATA family of transcription factors establishes genetic networks that control developmental processes including hematopoiesis, vasculogenesis, and cardiogenesis. We found that GATA-1 strongly activates transcription of the Tac-2 gene, which encodes proneurokinin-B, a precursor of neurokinin-B (NK-B). Neurokinins function through G protein-coupled transmembrane receptors to mediate diverse physiological responses including pain perception and the control of vascular tone. Whereas an elevated level of NK-B was implicated in pregnancy-associated pre-eclampsia (Page, N. M., Woods, R. J., Gardiner, S. M., Lomthaisong, K., Gladwell, R. T., Butlin, D. J., Manyonda, I. T., and Lowry, P. J. (2000) Nature 405, 797-800), the regulation of NK-B synthesis and function are poorly understood. Tac-2 was expressed in normal murine erythroid cells and was induced upon ex vivo erythropoiesis. An estrogen receptor fusion to GATA-1 (ER-GATA-1) and endogenous GATA-1 both occupied a region of Tac-2 intron-7, which contains two conserved GATA motifs. Genetic complementation analysis in GATA-1-null G1E cells revealed that endogenous GATA-2 occupied the same region of intron-7, and expression of ER-GATA-1 displaced GATA-2 and activated Tac-2 transcription. Erythroid cells did not express neurokinin receptors, whereas aortic and yolk sac endothelial cells differentially expressed neurokinin receptor subtypes. Since NK-B induced cAMP accumulation in yolk sac endothelial cells, these results suggest a new mode of vascular regulation in which GATA-1 controls NK-B synthesis in erythroid cells.

Thrombopoietin receptor(Mpl) expression by megakaryocytes in myeloproliferative disorders

The thrombopoietin receptor (Mpl) is involved in the pathogenesis of chronic myeloproliferative disorders (CMPD). In this study, we determined Mpl expression by bone marrow cells and megakaryocytes in CMPD by applying laser microdissection, real-time RT-PCR, and immunohistochemistry. Mpl mRNA expression was significantly increased up to 9-fold in total bone marrow cells (p < 0.001) and up to 4-fold in megakaryocytes in chronic myeloproliferative disorders (n = 73) compared to normal controls (n = 26, p = 0.01). Immunohistochemistry revealed heterogeneous Mpl expression by megakaryocytes in CMPD with a stronger accentuation in idiopathic myelofibrosis (IMF) in comparison to polycythaemia vera (PV) and essential thrombocythemia (ET). In addition to megakaryocytes, the erythropoietic lineage was prominently labelled by Mpl antiserum, with considerably stronger staining in polycythaemia vera. We conclude that, in CMPD, megakaryocytes and erythroid cells exhibit increased Mpl expression levels which may contribute to the sustained proliferation of both cell lineages in CMPD.

Leukemia-related transcription factor TEL is negatively regulated through extracellular signal-regulated kinase-induced phosphorylation

TEL is an ETS family transcription factor that possesses multiple putative mitogen-activated protein kinase phosphorylation sites. We here describe the functional regulation of TEL via ERK pathways. Overexpressed TEL becomes phosphorylated in vivo by activated ERK. TEL is also directly phosphorylated in vitro by ERK. The inducible phosphorylation sites are Ser(213) and Ser(257). TEL binds to a common docking domain in ERK. In vivo ERK-dependent phosphorylation reduces trans-repressional and DNA-binding abilities of TEL for ETS-binding sites. A mutant carrying substituted glutamates on both Ser(213) and Ser(257) functionally mimics hyperphosphorylated TEL and also shows a dominant-negative effect on TEL-induced transcriptional suppression. Losing DNA-binding affinity through phosphorylation but heterodimerizing with unmodified TEL could be an underlying mechanism. Moreover, the glutamate mutant dominantly interferes with TEL-induced erythroid differentiation in MEL cells and growth suppression in NIH 3T3 cells. Finally, endogenous TEL is dephosphorylated in parallel with ERK inactivation in differentiating MEL cells and is phosphorylated through ERK activation in Ras-transformed NIH 3T3 cells. These data indicate that TEL is a constituent downstream of ERK in signal transduction systems and is physiologically regulated by ERK in molecular and biological features.

New Insights into the Regulation of Erythroid Cells

The regulation of erythroid cells is complex and occurs at multiple levels. Erythroid precursors, once committed to this lineage, develop in association with specific macrophages within erythroblastic islands. While erythropoietin (Epo) is the principal regulator of erythroid progenitors, other cytokines and nuclear hormones also play an important role in the maturation of these cells. Signalling from the Epo-receptor activates several pathways, including the JAK/STAT, ras/raf/MAP kinase and PI3 kinase/Akt cascades to promote cell survival, proliferation and differentiation. Transcription factors such as GATA-1, EKLF and NF-E2 are crucial for progression along the erythroid maturation pathway; these, and a myriad of other transcription factors, must be expressed at the correct developmental stage for normal red blood cells to be formed.

Haemoglobin biosynthesis site in rabbit embryo erythroid cells

Properly metabolized globin synthesis and iron uptake are indispensable for erythroid cell differentiation and maturation. Mitochondrial participation is crucial in the process of haeme synthesis for cytochromes and haemoglobin. We studied the final biosynthesis site of haemoglobin using an ultrastructural approach, with erythroid cells obtained from rabbit embryos, in order to compare these results with those of animals treated with saponine or phenylhydrazine. Our results are similar to those obtained in assays with adult mammals, birds, amphibians, reptiles and fish, after induction of haemolytic anaemia. Therefore, the treatment did not interfere with the process studied, confirming our previous findings. Immunoelectron microscopy showed no labelling of mitochondria or other cellular organelles supposedly involved in the final biosynthesis of haemoglobin molecules, suggesting instead that it occurs free in the cytoplasm immediately after the liberation of haeme from the mitochondria, by electrostatic attraction between haeme and globin chains.

SCL interacts with VEGF to suppress apoptosis at the onset of hematopoiesis

During development, hematopoiesis initiates in the yolk sac through a process that depends on VEGF/Flk1 signaling and on the function of the SCL/Tal1 transcription factor. Here we show that VEGF modifies the developmental potential of primitive erythroid progenitors and prolongs their life span. Furthermore, the survival of yolk sac erythrocytes in vivo depends on the dose of VEGF. Interestingly, in Vegflo/lo embryos carrying a hypomorph allele, Flk1-positive cells reach the yolk sac at E8.5,but are severely compromised in their ability to generate primitive erythroid precursors. These observations indicate that during embryonic development,different thresholds of VEGF are required for the migration and clonal expansion of hematopoietic precursors. The near absence of primitive erythroid precursors in Vegflo/lo embryos correlates with low levels of Scl in the yolk sac. Strikingly, gain-of-function of SCL partially complements the hematopoietic defect caused by the hypomorph Vegflo allele, and re-establishes the survival of erythroid cells and the expression of erythroid genes (Gata1 andβH1). This indicates that SCL functions downstream of VEGF to ensure an expansion of the hematopoietic compartment.

Heme Positively Regulates the Expression of β-Globin at the Locus Control Region via the Transcriptional Factor Bach1 in Erythroid Cells

The transcription factor Bach1 heterodimerizes with small Maf proteins to repress Maf recognition element (MARE)-dependent gene expression. The repressor activity of Bach1 is inhibited by the direct binding of heme. To investigate the involvement of Bach1 in the heme-dependent regulation of the expression of the beta-globin gene, mouse erythroleukemia (MEL) cells were cultured with succinylacetone (SA), a specific inhibitor of heme biosynthesis, and the level of beta-globin mRNA was examined. A marked decrease of beta-globin mRNA in SA-treated cells was observed, and this decrease was reversed by the addition of hemin. An iron chelator, desferrioxamine, also lowered the level of beta-globin mRNA. The heme-dependent expression of beta-globin is a transcriptional event since the expression of the human beta-globin gene promoter-reporter gene containing the microlocus control region (microLCR) was inhibited when human erythroleukemia K562 cells and MEL cells were cultured with SA. Hemin treatment restored the decrease in promoter activity caused by SA. The control of the microLCR-beta-globin promoter reporter gene by heme was dependent on DNase I-hypersensitive site 2 (HS2), which contains MARE. The MARE binding activity of Bach1 in K562 and MEL cells increased upon SA treatment, and the increase was diminished by the treatment with hemin. Transient expression of Bach1 suppressed the microLCR activity, and this repressor activity was cancelled by treatment with hemin. The expression of a mutated Bach1 lacking heme-binding sites led to a loss in the heme responsiveness of the microLCR. Furthermore, chromatin immunoprecipitation experiments revealed that Bach1 bound to the MARE of HS2 increased by the treatment of MEL cells with SA, and this was cancelled by hemin. We propose that heme positively regulates the beta-globin gene expression by blocking the interaction of Bach1 with the MARE in the LCR.

Human beta-globin locus control region HS5 contains CTCF- and developmental stage-dependent enhancer-blocking activity in erythroid cells

The human beta-globin locus contains five developmentally regulated beta-type globin genes. All five genes depend on the locus control region (LCR), located at the 5' end of the locus, for abundant globin gene transcription. The LCR is composed of five DNase I-hypersensitive sites (HSs), at least a subset of which appear to cooperate to form a holocomplex in activating genes within the locus. We previously tested the requirement for proper LCR polarity by inverting it in human beta-globin yeast artificial chromosome transgenic mice and observed reduced expression of all the beta-type globin genes regardless of developmental stage. This phenotype clearly demonstrated an orientation-dependent activity of the LCR, although the mechanistic basis for the observed activity was obscure. Here, we describe genetic evidence demonstrating that human HS5 includes enhancer-blocking (insulator) activity that is both CTCF and developmental stage dependent. Curiously, we also observed an attenuating activity in HS5 that was specific to the epsilon-globin gene at the primitive stage and was independent of the HS5 CTCF binding site. These observations demonstrate that the phenotype observed in the LCR-inverted locus was in part attributable to placing the HS5 insulator between the LCR HS enhancers (HS1 to HS4) and the promoter of the beta-globin gene.

The 33 kb transcript of the chicken ?-globin gene domain is part of the nuclear matrix

Giant nuclear transcripts, and in particular the RNAs of the globin gene domains which are much larger than their canonical pre-mRNAs, have been an enigma for many years. We show here that in avian erythroblastosis virus (AEV)-transformed chicken erythroleukaemic cells, where globin gene expression is abortive, the whole domain of alpha-globin genes is transcribed for about 33 kb in the globin direction and that this RNA is part of the nuclear matrix. Northern blot hybridisation with strand-specific riboprobes, recognising genes and intergenic sequences, and RT-PCR with downstream primers, show that the continuous full domain transcript (FDT) starts in the vicinity of a putative LCR and includes all the genes as well as known regulatory sites, the replication origin, and the DNA loop anchorage region in the upstream area. Absent in chicken fibroblasts, the globin FDT overlaps the major part of the ggPRX housekeeping gene that is transcribed in the opposite direction. RT-PCR and in situ hybridisation with genic and extra-genic globin probes demonstrated that the globin FDT is a component of the nuclear matrix. We suggest that the globin FDTs keep the domain in an active state, and the globin RNAs on the processing pathway are a component of the nuclear matrix. They may take part in the dynamic nuclear architecture when productively processed, or turn over slowly when globins are not synthesised.

[Involvement of apoptosis and proinflammatory cytokines in the pathogenesis of anemia in multiple myeloma]

Multiple myeloma is a neoplasmatic disease of the hematopoietic system which constitutes about 10% of all hematological proliferations. Anemia is a common symptom of myeloma, especially in patients with advanced disease, and its severity correlates with the clinical stage of myeloma. There are several factors involved in the pathogenesis of anemia in multiple myeloma: infiltration of the bone marrow with monoclonal plasma cells, inadequate secretion of erythropoietin, shortened erythrocyte survival time, dysregulated iron metabolism, impaired marrow function due to proinflammatory cytokine secretion, and interaction between erythroblasts and malignant plasma cells. Recent findings indicate an important function of apoptosis in regulating physiological erythropoiesis. In physiological conditions some erythroblasts undergo apoptosis, which is induced by proteins belonging to the TNF family, i.e. Fas(CD95), FasL(CD95L),and TRAIL (TNF-related apoptosis inducing-ligand) with its receptors--DR4 (Death Receptor 4), and DR5 (Death Receptor 5). Expression of Fas, DR4, and DR5 is detected on the cell membrane of erythroblasts in all stages, whereas FasL and TRAIL are present only in more mature erythroblasts. Interaction of mature erythroblast FasL+/TRAIL+ with immature erythroblast FasL-/TRAIL--results in apoptosis of the immature cell, which contributes to the down-regulation of physiological erythropoiesis. The expression of proteins involved in erythropoiesis regulation is controlled by erythropoietin (EPO), which decreases erythroblast susceptibility to FasL and TRAIL stimulation and prevents apoptosis. On the other hand interferon gamma (IFN-gamma) and tumor necrosis factor (TNF) increase Fas expression on erythroid cells and enhance their apoptosis. Malignant plasma cells show increased expression of FasL and TRAIL and decreased expression of Fas, which make them more resistant to apoptotic signals. FasL+/TRAIL+ plasmocytes are involved in anemia pathogenesis in multiple myeloma patients by inducing apoptosis of erythroid cells. Monoclonal plasmocytes also secrete numerous cytokines involved in plasma cell growth, bone marrow neovascularisation and anemia.