Identification of Id2 as a globin regulatory protein by representational difference analysis of K562 cells induced to express gamma-globin with a fungal compound

Variation in Gamma-Globin Expression before and after Induction with Hydroxyurea Associated with BCL11A, KLF1 and TAL1

The molecular mechanisms governing γ-globin expression in a subset of fetal hemoglobin (α2γ2: HbF) expressing red blood cells (F-cells) and the mechanisms underlying the variability of response to hydroxyurea induced γ-globin expression in the treatment of sickle cell disease are not completely understood. Here we analyzed intra-person clonal populations of basophilic erythroblasts (baso-Es) derived from bone marrow common myeloid progenitors in serum free cultures and report the level of fetal hemoglobin production in F-cells negatively correlates with expression of BCL11A, KLF1 and TAL1. We then examined the effects of hydroxyurea on these three transcription factors and conclude that a successful induction of γ-globin includes a reduction in BCL11A, KLF1 and TAL1 expression. These data suggests that expression changes in this transcription factor network modulate γ-globin expression in F-cells during steady state erythropoiesis and after induction with hydroxyurea.

Cytokine-mediated increases in fetal hemoglobin are associated with globin gene histone modification and transcription factor reprogramming

Therapeutic regulation of globin genes is a primary goal of translational research aimed toward hemoglobinopathies. Signal transduction was used to identify chromatin modifications and transcription factor expression patterns that are associated with globin gene regulation. Histone modification and transcriptome profiling were performed using adult primary CD34(+) cells cultured with cytokine combinations that produced low versus high levels of gamma-globin mRNA and fetal hemoglobin (HbF). Embryonic, fetal, and adult globin transcript and protein expression patterns were determined for comparison. Chromatin immunoprecipitation assays revealed RNA polymerase II occupancy and histone tail modifications consistent with transcriptional activation only in the high-HbF culture condition. Transcriptome profiling studies demonstrated reproducible changes in expression of nuclear transcription factors associated with high HbF. Among the 13 genes that demonstrated differential transcript levels, 8 demonstrated nuclear protein expression levels that were significantly changed by cytokine signal transduction. Five of the 8 genes are recognized regulators of erythropoiesis or globin genes (MAFF, ID2, HHEX, SOX6, and EGR1). Thus, cytokine-mediated signal transduction in adult erythroid cells causes significant changes in the pattern of globin gene and protein expression that are associated with distinct histone modifications as well as nuclear reprogramming of erythroid transcription factors.

TLX1/HOX11 transcription factor inhibits differentiation and promotes a non-haemopoietic phenotype in murine bone marrow cells

The TLX/HOX11 subfamily of divergent homeobox genes are involved in various aspects of embryogenesis and, in the case of TLX1/HOX11 and TLX3/HOX11L2, feature prominently as oncogenes in human T-cell acute lymphoblastic leukaemia. TLX1 possesses immortalising activity in a wide variety of blood cell lineages, however, the effect of this oncogene on haemopoietic cell differentiation has not been fully investigated. We therefore constitutively expressed TLX1 in murine bone marrow or fetal liver cells using retroviral transfer followed by transplantation and/or in vitro culture. TLX1 was found to dramatically alter haemopoiesis, promoting the emergence of a non-haemopoietic CD45(-) CD31(+) cell population while markedly inhibiting erythroid and granulocytic cell differentiation. To identify genetic programs perturbed by TLX1, a comparison of transcript profiles from J2E erythroid cells with and without enforced TLX1 expression was undertaken. This revealed a pattern of gene expression indicative of enhanced proliferation coupled to differentiation arrest. Of the genes identified, two, KIT and VEGFC, were found to be potential TLX1 targets based on transcriptional assays. These results demonstrate that TLX1 can act broadly to impair haemopoiesis and divert differentiation to an alternative fate. This may account for its ability to promote the pre-leukaemic state via perturbation of specific gene expression programs.

Regulation of human fetal hemoglobin: new players, new complexities

The human globin genes are among the most extensively characterized in the human genome, yet the details of the molecular events regulating normal human hemoglobin switching and the potential reactivation of fetal hemoglobin in adult hematopoietic cells remain elusive. Recent discoveries demonstrate physical interactions between the beta locus control region and the downstream structural gamma- and beta-globin genes, and with transcription factors and chromatin remodeling complexes. These interactions all play roles in globin gene expression and globin switching at the human beta-globin locus. If the molecular events in hemoglobin switching were better understood and fetal hemoglobin could be more fully reactivated in adult cells, the insights obtained might lead to new approaches to the therapy of sickle cell disease and beta thalassemia by identifying specific new targets for molecular therapies.

Regulation of cyclin expression and cell cycle progression in breast epithelial cells by the helix–loop–helix protein Id1

The helix-loop-helix protein Id1 has been implicated in regulating mammary epithelial cell proliferation and differentiation but the underlying molecular mechanisms are not well characterized. Under low serum conditions, ectopic expression of Id1, but not Id2, allowed continued proliferation of immortalized mammary epithelial cells and breast cancer cells. Conversely, downregulation of Id1 impaired proliferation. The effects of short interfering RNA (siRNA)-mediated downregulation of Id1 were the same as those following downregulation of c-Myc: decreased expression of cyclins D1 and E, reduced phosphorylation of pRb at Ser780 (a site targeted by cyclin D1-Cdk4) and reduced cyclin E-Cdk2 activity. Decreased cyclin D1 expression was an early response to Id1 antisense oligonucleotide treatment. Inhibition of c-Myc function by siRNA, antisense oligonucleotides or a dominant repressor resulted in downregulation of Id1, while ectopic expression of c-Myc resulted in rapid induction of Id1, suggesting that Id1 may be downstream of c-Myc. These data indicate that in mammary epithelial cells, Id1 has cell cycle regulatory functions that are similar to those of c-Myc, and suggest that cyclin D1 may be involved in Id1 regulation of cell cycle progression.

Negative regulation of gamma-globin gene expression by cyclic AMP-dependent pathway in erythroid cells

OBJECTIVE

Fetal hemoglobin inducers such as hemin, butyrate, and hydroxyurea stimulate gamma-globin gene expression by activating the cyclic GMP (cGMP)-dependent pathway. Although cGMP activates the cyclic AMP (cAMP)-dependent pathway by suppressing cGMP-inhibited phosphodiesterase 3 (PDE3), the effects of the cAMP-dependent pathway on gamma-globin gene expression are unknown.

MATERIALS AND METHODS

The cAMP-dependent pathway was activated in K562 cells using the adenylate cyclase activator forskolin. Expression of gamma-globin mRNA was examined by primer extension, and transcriptional activity of the gamma-globin gene promoter was determined by reporter gene assays.

RESULTS

PDE3 was expressed in K562 cells at a high level. The cAMP-dependent pathway was found to be activated in K562 cells in which the cGMP-dependent pathway was activated by hemin. Activation of the cAMP-dependent pathway by forskolin inhibited hemin-induced expression of gamma-globin mRNA and decreased transcriptional activity of the gamma-globin gene promoter. The levels of phosphorylation of mitogen-activated protein kinases (MAPKs) were not affected by the cAMP-dependent pathway.

CONCLUSIONS

These results suggested that the cAMP-dependent pathway, which is independent of MAPK pathways, plays a negative role in gamma-globin gene expression in K562 cells. cAMP and cGMP may have differential roles in the regulation of gamma-globin gene expression in erythroid cells.

Identification and characterization of mechanistically distinct inducers of γ-globin transcription

Inhibition of HbS polymerization is a major target for therapeutic approaches in sickle cell anemia. Toward this goal, initial efforts at pharmacological elevation of fetal hemoglobin (HbF) has shown therapeutic efficacy. In order to identify well-tolerated, novel agents that induce HbF in patients, we developed a high-throughput screening approach based on induction of gamma-globin gene expression in erythroid cells. We measured gamma-globin transcription in K562 cells transfected with either gamma promoter elements fused with the locus control region hypersensitivity site 2 and luciferase reporter gene (HS2 gamma) or a beta-yeast artificial chromosome in which the luciferase reporter gene was recombined into the gamma-globin coding sequences (gamma YAC). Corresponding pharmacological increases in HbF protein were confirmed in both K562 cells and in human primary erythroid progenitor cells. Approximately 186,000 defined chemicals and fungal extracts were evaluated for their ability to increase gamma gene transcription in either HS2 gamma or gamma YAC models. Eleven distinct classes of compounds were identified, the majority of which were active within 24-48 hr. The short chain hydroxamate-containing class generally exhibited delayed maximal activity, which continued to increase transcription up to 120 hr. The cyclic tetrapeptide OSI-2040 and the hydroxamates were shown to have histone deacetylase inhibitory activity. In primary hematopoietic progenitor cell cultures, OSI-2040 increased HbF by 4.5-fold at a concentration of only 40 nM, comparable to the effects of hydroxyurea at 100 microM. This screening methodology successfully identifies active compounds for further mechanistic and preclinical evaluation as potential therapeutic agents for sickle cell anemia.

Identification of Taxreb107 as a lactogenic hormone responsive gene in mammary epithelial cells

Mammary gland development and differentiation is regulated by a number of growth factors and hormones. Milk protein gene expression represents a hallmark of functional mammary epithelial differentiation and is coordinated by the lactogenic hormone prolactin and glucocorticoids. To date, few 'early-response' genes transcriptionally activated by lactogenic hormones have been described. We have used representational difference analysis (RDA) to search for lactogenic-responsive genes in SCp2 mouse mammary epithelial cells. One of the cDNAs identified encoded the DNA-binding protein Taxreb107, originally identified as a HTLV-I Tax responsive element binding protein. Increased Taxreb107 expression was confirmed following prolactin and dexamethasone-induced differentiation of SCp2 and HC11 mammary epithelial cells. Taxreb107 RNA levels were developmentally regulated in the mouse mammary gland, where levels increased substantially during mid- and late pregnancy and persisted during lactation. Overexpression of an antisense Taxreb107 cDNA construct or antisense oligonucleotide in HC11 mammary epithelial cells attenuated milk protein gene expression following prolactin and dexamethasone treatment. These findings indicate a role for Taxreb107 as a lactogenic hormone-responsive gene during differentiation of the mammary gland.

HbF reactivation in sibling BFU-E colonies: synergistic interaction of kit ligand with low-dose dexamethasone

Mechanisms underlying fetal hemoglobin (HbF) reactivation in stress erythropoiesis have not been fully elucidated. We suggested that a key role is played by kit ligand (KL). Because glucocorticoids (GCs) mediate stress erythropoiesis, we explored their capacity to potentiate the stimulatory effect of KL on HbF reactivation, as evaluated in unilineage erythropoietic culture of purified adult progenitors (erythroid burst-forming units [BFU-Es]). The GC derivative dexamethasone (Dex) was tested in minibulk cultures at graded dosages within the therapeutical range (10(-6) to 10(-9) M). Dex did not exert significant effects alone, but synergistically it potentiated the action of KL in a dose-dependent fashion. Specifically, Dex induced delayed erythroid maturation coupled with a 2-log increased number of generated erythroblasts and enhanced HbF synthesis up to 85% F cells and 55% gamma-globin content at terminal maturation (ie, in more than 80%-90% mature erythroblasts). Equivalent results were obtained in unicellular erythroid cultures of sibling BFU-Es treated with KL alone or combined with graded amounts of Dex. These results indicate that the stimulatory effect of KL + Dex is related to the modulation of gamma-globin expression rather than to recruitment of BFU-Es with elevated HbF synthetic potential. At the molecular level, Id2 expression is totally suppressed in control erythroid culture but is sustained in KL + Dex culture. Hypothetically, Id2 may mediate the expansion of early erythroid cells, which correlates with HbF reactivation. These studies indicate that GCs play an important role in HbF reactivation. Because Dex acts at dosages used in immunologic disease therapy, KL + Dex administration may be considered to develop preclinical models for beta-hemoglobinopathy treatment.

Cloning and analysis of the thrombopoietin-induced megakaryocyte-specific glycoprotein VI promoter and its regulation by GATA-1, Fli-1, and Sp1

The exposure of collagen fibers at sites of vascular injury results in the adherence of platelets and their subsequent activation. The platelet collagen receptor glycoprotein (GP)(1) VI plays a crucial role in platelet activation and thrombus formation and decreased levels or defective GPVI may lead to excessive bleeding. In addition, elevated levels of collagen receptors may predispose individuals to coronary heart disease or strokes. GPVI expression is restricted to platelets and their precursor cell, the megakaryocyte. In this study we investigate the regulation of GPVI expression and show that thrombopoietin induces its expression in the megakaryocytic cell line UT-7/TPO. A 5'-region flanking the transcription start point of the GPVI gene was cloned (-694 to +29) and we report that this putative GPVI promoter bestows megakaryocye-specific expression. Deletion analyses and site-directed mutagenesis identified Sp1(227), GATA(177), and Ets(48) sites as essential for GPVI expression. We show that transcription factors GATA-1, Fli-1, and Sp1 can bind to and activate this promoter. Finally, GPVI mRNA was detected only in megakaryocytic cell lines expressing both Fli-1 and GATA-1, and we show that overexpression of Fli-1 in a stable cell line (which expresses endogenous GATA-1 and Sp1) results in expression of the endogenous GPVI gene.

Development of sensitive fluorescent assays for embryonic and fetal hemoglobin inducers using the human beta -globin locus in erythropoietic cells

Reactivation of fetal hemoglobin genes has been proposed as a potential therapeutic procedure in patients with beta-thalassemia, sickle cell disease, or other beta-hemoglobinopathies. In vitro model systems based on small plasmid globin gene constructs have previously been used in human and mouse erythroleukemic cell lines to study the molecular mechanisms regulating the expression of the fetal human globin genes and their reactivation by a variety of pharmacologic agents. These studies have led to great insights in globin gene regulation and the identification of a number of potential inducers of fetal hemoglobin. In this study we describe the development of enhanced green fluorescence protein (EGFP) reporter systems based on bacterial artificial chromosomes (EBACs) to monitor the activity of the epsilon-, (G)gamma-, (A)gamma-, delta-, and beta-globin genes in the beta-globin locus. Additionally, we demonstrate that transfection of erythroleukemia cells with our EBACs is greatly enhanced by expression of EBNA1, which also facilitates episomal maintenance of our constructs in human cells. Our studies in human cells have shown physiologically relevant differences in the expression of each of the globin genes and also demonstrate that hemin is a potent inducer of EGFP expression from EGFP-modified epsilon-, (G)gamma-, and (A)gamma-globin constructs. In contrast, the EGFP-modified delta- and beta-globin constructs consistently produced much lower levels of EGFP expression on hemin induction, mirroring the in vivo ontogeny. The EGFP-modified beta-globin eukaryotic BAC (EBAC) vector system can thus be used in erythroleukemia cells to evaluate induction of the epsilon- and gamma-globin genes from the intact human beta-globin locus.

High-level erythroid lineage-directed gene expression using globin gene regulatory elements after lentiviral vector-mediated gene transfer into primitive human and murine hematopoietic cells

Lentiviral vectors efficiently transduce primitive human hematopoietic cells and are capable of transferring complex genomes. Vectors were designed with hypersensitive sites containing regulatory elements from the beta-globin locus control region linked to the beta-globin gene promoter to drive expression of the enhanced green fluorescent protein marker to facilitate analysis of the pattern of gene expression in various hematopoietic lineages. Such vectors gave higher level, induced expression in mouse erythroleukemia cells than a previously described vector that utilized an enhancer from the alpha locus and the ankyrin-1 promoter [Moreau-Gaudry, F., Xia, P., Jiang, G., Perelman, N.P., Bauer, G., Ellis, J., Surinya, K.H., Mavilio, F., Shen, C.K., and Malik, P. (2001). Blood 98, 2664-2672]. The addition of gamma-globin intron sequences further augmented vector expression. Expression was also effectively targeted to the erythroid lineage in cultured human cells from peripheral blood and in mouse red blood cells in vivo, although lower levels of expression were also observed in other lineages. Thus, these newly described vectors provide a means to achieve high-level gene expression, predominantly in erythroid cells, an outcome that may have potential therapeutic application.

Isolation of diallyl trisulfide inducible differentially expressed genes in human gastric cancer cells by modified cDNA representational difference analysis

Extensive epidemiologic studies indicated protective effects of consumption of garlic on reducing human gastric cancer (HGC) incidence. Diallyl trisulfide (DATS), a critical organic allyl sulfur component of garlic, was reported to have chemopreventive effects in inhibiting tumor process. We used DATS to treat HGC cell line BGC823 cells, and showed that DATS induces G1/S arrest and apoptosis in BGC823 cells demonstrated by a flow cytometric analysis. To further isolate DATS inducible differentially expressed genes in BGC823 cells, we combined a highly specific subtractive hybridization of cDNA representational difference analysis (cDNA RDA) with a sensitive bidirectional radioactive detection of mRNA differential display (mRNA DD) to develop a subtractive hybridization differential display (SHDD) method. This modified method adopted a first round of bidirectional subtractive hybridization between two sample cDNAs and a second round of bidirectional subtractive hybridization between the two resultant first-round difference products. Bidirectional subtractive hybridizations magnified the differences between the two sample cDNAs and favored isolating mRNA species with very small expression differences. We employed the SHDD method to detect DATS inducible differentially expressed genes in BGC823 cells. A total of 14 cDNA fragments (11 upregulated and 3 downregulated by DATS treatment) were isolated and confirmed by reverse Northern blot analysis. Our data show that SHDD is a powerful technique for identifying differentially expressed mRNA species between two sample cDNAs and provide useful cellular and molecular information for understanding the effects of garlic against human gastric cancer.

Chromatin structure and control of beta-like globin gene switching

The human beta-globin locus is a complex genetic system widely used for analysis of eukaryotic gene expression. The locus consists of five functional beta-like globin genes, epsilon, (G)gamma, (A)gamma, delta, and beta, arrayed on the chromosome in the order that they are expressed during ontogeny. Globin gene expression is regulated, in part, by the locus control region, which physically consists of five DNaseI-hypersensitive sites located 6-22 Kb upstream of the epsilon -globin gene. During ontogeny two switches occur in beta-globin gene expression that reflect the changing oxygen requirements of the fetus. The first switch from embryonic epsilon - to fetal gamma-globin occurs at six weeks of gestation. The second switch from gamma- to adult delta- and beta-globin occurs shortly after birth. Throughout the locus, cis-acting elements exist that are dynamically bound by trans-acting proteins, including transcription factors, co-activators, repressors, and chromatin modifiers. Discovery of novel erythroid-specific transcription factors and a role for chromatin structure in gene expression have enhanced our understanding of the mechanism of globin gene switching. However, the hierarchy of events regulating gene expression during development, from extracellular signaling to transcriptional activation or repression, is complex. In this review we attempt to unify the current knowledge regarding the interplay of cis-acting elements, transcription factors, and chromatin modifiers into a comprehensive overview of globin gene switching.

Modulation of fetal hemoglobin in sickle cell anemia

A partial understanding of the pathophysiology of sickle cell disease has suggested one means of treatment-increasing the distribution and concentration of fetal hemoglobin in sickle erythrocytes. Although this can be accomplished clinically with drugs like hydroxyurea, a complete understanding of the molecular and cellular basis of fetal hemoglobin regulation may suggest new and better ways of attaining this goal.

Advances in experimental treatment of beta-thalassaemia

Beta-thalassaemia is highly prevalent and world wide in its distribution. The gene to modify the clinical course of patients with transfusion-dependent thalassaemia (thalassaemia major), the gamma-globin gene, is already present in these patients but silenced in the course of development. During erythropoiesis, progenitors are believed to go through a phase where the milieu favours gamma-globin production. One pharmacological strategy to increase gamma-globin production is directed at recruiting such early progenitors through the use of cytotoxic agents (+/- erythropoietin) that presumably deplete more mature progenitors. Another promising strategy is to use chromatin-modifying agents that prevent the silencing of the gamma-globin gene that occurs during development. These agents, the methyl-transferase inhibitors and histone deacetylase inhibitors, either alone or in combination, may be able to produce the robust increase in gamma-globin and hence fetal haemoglobin and total haemoglobin, needed to successfully treat thalassaemia major. Studies of these agents, which are already available for clinical trials, should be encouraged.

ZNF232: structure and expression analysis of a novel human C(2)H(2) zinc finger gene, member of the SCAN/LeR domain subfamily

We have identified a novel zinc finger gene, ZNF232, mapped to human chromosome 17p12. The coding region of the gene is organized in three exons corresponding to a 417 amino acid long polypeptide containing a SCAN/LeR domain and five C(2)H(2)-type zinc fingers. ZNF232 is possibly a nuclear protein, as suggested by expression analysis of GFP/ZNF232 chimeric constructs. ZNF232 transcripts were detected in a wide collection of adult human tissues. The gene is possibly subjected to tissue-specific post-transcriptional regulation by means of alternative splicing.

Gene Expression Profiling during Erythroid Differentiation of K562 Cells

We studied the temporal changes in gene expression in K562 cells at intervals from 2 to 48 h following induction using differential display polymerase chain reaction and gene expression arrays. More than 110 cDNA fragments representing 86 unique mRNAs were either up- or downregulated during erythroid differentiation. Sixty-one of the differentially expressed cDNA fragments had more than 95% homology to known GenBank sequences; 21 represented cDNA sequences with only dbEST or high-throughput gene-screening database matches. Four fragments had no database matches. Using gene expression arrays, 73 differentially expressed genes were observed. Unique expressed sequence tags (ESTs) were used to "clone" two novel genes from available databases and their tissue expression was examined. Erythroid maturation in induced K562 cells is associated with differential expression of many genes. Some differentially expressed clones were transcription factors and 25 expressed fragments with open reading frames were found whose function remains unknown.

ID helix-loop-helix proteins in cell growth, differentiation and tumorigenesis

The ubiquitously expressed family of ID helix-loop-helix (HLH) proteins function as dominant negative regulators of basic HLH (bHLH) transcriptional regulators that drive cell lineage commitment and differentiation in metazoa. Recent data from cell line and in vivo studies have implicated the functions of ID proteins in other cellular processes besides negative regulation of cell differentiation. ID proteins play key roles in the regulation of lineage commitment, cell fate decisions and in the timing of differentiation during neurogenesis, lymphopoiesis and neovascularisation (angiogenesis). They are essential for embryogenesis and for cell cycle progression, and they function as positive regulators of cell proliferation. ID proteins also possess pro-apoptotic properties in a variety of cell types and function as cooperating or dominant oncoproteins in immortalisation of rodent and human cells and in tumour induction in Id-transgenic mice. In several human tumour types, the expression of ID proteins is deregulated, and loss- and gain-of-function studies implicate ID functions in the regulation of tumour growth, vascularisation, invasiveness and metastasis. More recent biochemical studies have also revealed an emerging ‘molecular promiscuity’ of mammalian ID proteins: they directly interact with and modulate the activities of several other families of transcriptional regulator, besides bHLH proteins.

Induction of human fetal globin gene expression by a novel erythroid factor, NF-E4

The stage selector protein (SSP) is a heteromeric complex involved in preferential expression of the human gamma-globin genes in fetal-erythroid cells. We have previously identified the ubiquitous transcription factor CP2 as a component of this complex. Using the protein dimerization domain of CP2 in a yeast two-hybrid screen, we have cloned a novel gene, NF-E4, encoding the tissue-restricted component of the SSP. NF-E4 and CP2 coimmunoprecipitate from extract derived from a fetal-erythroid cell line, and antiserum to NF-E4 ablates binding of the SSP to the gamma promoter. NF-E4 is expressed in fetal liver, cord blood, and bone marrow and in the K562 and HEL cell lines, which constitutively express the fetal globin genes. Enforced expression of NF-E4 in K562 cells and primary erythroid progenitors induces endogenous fetal globin gene expression, suggesting a possible strategy for therapeutic intervention in the hemoglobinopathies.

GTP-mediated differentiation of the human K562 cell line: transient overexpression of GATA-1 and stabilization of the gamma-globin mRNA

Induction of specific gene expression may provide an alternative or a support to conventional cytotoxic chemotherapy of cancer, as well as to therapy for sickle cell diseases. In this respect, pharmacological induction of expression of the endogenous gamma-globin gene is a realistic approach to therapy of beta-globin disorders. Erythroid differentiation and inhibition of proliferation of the human CML K562 cell line was induced by guanosine 5'-triphosphate (GTP). The hemoglobin production in cells was correlated to an increase in alpha- and gamma-globin mRNA expression. At the transcriptional level, we showed that both the expression of the major erythroid transcription factor GATA-1 (protein and mRNA) and its binding capacity to the gamma-globin gene promoter was transiently increased. Moreover, GTP moderately stimulated the gamma-globin gene promoter after 48 h of treatment. At the post-transcriptional level, GTP treatment led to a drastic increase of the gamma-globin mRNA half-life. This stabilizing effect of GTP was mediated via the 3'-untranslated region (3'-UTR) of the gamma-globin mRNA. In conclusion, mechanism of GTP-mediated differentiation of K562 cells is linked to an early activation of gamma-globin gene transcription followed by a stabilization of its mRNA.

Hemoglobin switching in unicellular erythroid culture of sibling erythroid burst-forming units: kit ligand induces a dose-dependent fetal hemoglobin reactivation potentiated by sodium butyrate

Mechanisms underlying fetal hemoglobin (HbF) reactivation in adult life have not been elucidated; particularly, the role of growth factors (GFs) is controversial. Interestingly, histone deacetylase (HD) inhibitors (sodium butyrate, NaB, trichostatin A, TSA) reactivate HbF. We developed a novel model system to investigate HbF reactivation: (1) single hematopoietic progenitor cells (HPCs) were seeded in serum-free unilineage erythroid culture; (2) the 4 daughter cells (erythroid burst-forming units, [BFU-Es]), endowed with equivalent proliferation/differentiation and HbF synthesis potential, were seeded in 4 unicellular erythroid cultures differentially treated with graded dosages of GFs and/or HD inhibitors; and (3) HbF levels were evaluated in terminal erythroblasts by assay of F cells and γ-globin content (control levels, 2.4% and 1.8%, respectively, were close to physiologic values). HbF was moderately enhanced by interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor treatment (up to 5%-8% γ-globin content), while sharply reactivated in a dose-dependent fashion by c-kit ligand (KL) and NaB (20%-23%). The stimulatory effects of KL on HbF production and erythroid cell proliferation were strictly correlated. A striking increase of HbF was induced by combined addition of KL and NaB or TSA (40%-43%). This positive interaction is seemingly mediated via different mechanisms: NaB and TSA may modify the chromatin structure of the β-globin gene cluster; KL may activate the γ-globin promoter via up-modulation of tal-1 and possibly FLKF transcription factors. These studies indicate that KL plays a key role in HbF reactivation in adult life. Furthermore, combined KL and NaB administration may be considered for sickle cell anemia and β-thalassemia therapy.

Hemoglobin switching in unicellular erythroid culture of sibling erythroid burst-forming units: kit ligand induces a dose-dependent fetal hemoglobin reactivation potentiated by sodium butyrate

Mechanisms underlying fetal hemoglobin (HbF) reactivation in adult life have not been elucidated; particularly, the role of growth factors (GFs) is controversial. Interestingly, histone deacetylase (HD) inhibitors (sodium butyrate, NaB, trichostatin A, TSA) reactivate HbF. We developed a novel model system to investigate HbF reactivation: (1) single hematopoietic progenitor cells (HPCs) were seeded in serum-free unilineage erythroid culture; (2) the 4 daughter cells (erythroid burst-forming units, [BFU-Es]), endowed with equivalent proliferation/differentiation and HbF synthesis potential, were seeded in 4 unicellular erythroid cultures differentially treated with graded dosages of GFs and/or HD inhibitors; and (3) HbF levels were evaluated in terminal erythroblasts by assay of F cells and γ-globin content (control levels, 2.4% and 1.8%, respectively, were close to physiologic values). HbF was moderately enhanced by interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor treatment (up to 5%-8% γ-globin content), while sharply reactivated in a dose-dependent fashion by c-kit ligand (KL) and NaB (20%-23%). The stimulatory effects of KL on HbF production and erythroid cell proliferation were strictly correlated. A striking increase of HbF was induced by combined addition of KL and NaB or TSA (40%-43%). This positive interaction is seemingly mediated via different mechanisms: NaB and TSA may modify the chromatin structure of the β-globin gene cluster; KL may activate the γ-globin promoter via up-modulation of tal-1 and possibly FLKF transcription factors. These studies indicate that KL plays a key role in HbF reactivation in adult life. Furthermore, combined KL and NaB administration may be considered for sickle cell anemia and β-thalassemia therapy.