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

Long Non-Coding RNA H19 Leads to Upregulation of γ-Globin Gene Expression during Erythroid Differentiation

Long noncoding RNAs (lncRNAs) are important because they are involved in a variety of life activities and have many downstream targets. Moreover, there is also increasing evidence that some lncRNAs play important roles in the expression and regulation of γ-globin genes. In our previous study, we analyzed genetic material from nucleated red blood cells (NRBCs) extracted from premature and full-term umbilical cord blood samples. Through RNA sequencing (RNA-Seq) analysis, lncRNA H19 emerged as a differentially expressed transcript between the two blood types. While this discovery provided insight into H19, previous studies had not investigated its effect on the γ-globin gene. Therefore, the focus of our study was to explore the impact of H19 on the γ-globin gene. In this study, we discovered that overexpressing H19 led to a decrease in HBG mRNA levels during erythroid differentiation in K562 cells. Conversely, in CD34+ hematopoietic stem cells and human umbilical cord blood-derived erythroid progenitor (HUDEP-2) cells, HBG expression increased. Additionally, we observed that H19 was primarily located in the nucleus of K562 cells, while in HUDEP-2 cells, H19 was present predominantly in the cytoplasm. These findings suggest a significant upregulation of HBG due to H19 overexpression. Notably, cytoplasmic localization in HUDEP-2 cells hints at its potential role as a competing endogenous RNA (ceRNA), regulating γ-globin expression by targeting microRNA/mRNA interactions.

Inhibiting AKT signaling pathway with cilostazol and meloxicam synergism for suppressing K562 cells in vitro

Despite advances in cancer treatment, chronic myeloid leukemia (CML) is still one of the leading causes of death in the world. Due to the role of inflammation in cancer promotion and progression, thus use of anti-inflammatory agents may suppress cancer cell growth. In this study, we used two anti-inflammatory drugs, cilostazol and meloxicam, for the treatment of CML. Cell viability was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and the synergism occurrence was calculated by compusyn software. Annexin V/PI test and Hoechst staining were used to determine the apoptosis rate. To determine the pathway of apoptosis induction, the expression of BCL2 Associated X (Bax) and B-cell lymphoma-2 (Bcl-2) apoptotic genes and caspases activity were evaluated. The cell cycle was analyzed by propidium iodide (PI) staining and flow cytometry. Western blot analysis and immunofluorescence were performed to estimate alterations in Ak strain transforming-1 (AKT-1), phosphprylated AKT-1 (p-AKT-1), adenosine mono-phosphate-kinase (AMPK), and phosphorylated AMPK (p-AMPK) proteins and BCR/ABL and c-Myc distribution, respectively. Results showed that cilostazol, meloxicam, and their combination drug reduced cell viability (p < 0.05). Compared with control, expression of Bax and Bcl-2 decreased in treated cells, respectively (p < 0.05). The caspase-9 activity increased in treated cells compared to control cells (p < 0.001). The applied drugs decreased the protein level of p-AKT-1 while increasing the p-AMPK protein level (p < 0.05). BCR/ABL and c-Myc Protein distribution significantly decreased in treated cells. In conclusion, the combination drug had more cytotoxic effects than cilostazol and meloxicam alone and induced apoptosis by inhibiting AKT-1 activation and c-Myc reduction. Therefore using combination drugs effectively can treat cancers of CML origin.

Sickle cell disease: progress towards combination drug therapy

Dr. John Herrick described the first clinical case of sickle cell anaemia (SCA) in the United States in 1910. Subsequently, four decades later, Ingram and colleagues characterized the A to T substitution in DNA producing the GAG to GTG codon and replacement of glutamic acid with valine in the sixth position of the β^S -globin chain. The establishment of Comprehensive Sickle Cell Centers in the United States in the 1970s was an important milestone in the development of treatment strategies and describing the natural history of sickle cell disease (SCD) comprised of genotypes including homozygous haemoglobin SS (HbSS), HbSβ⁰ thalassaemia, HbSC and HbSβ⁺ thalassaemia, among others. Early drug studies demonstrating effective treatments of HbSS and HbSβ⁰ thalassaemia, stimulated clinical trials to develop disease-specific therapies to induce fetal haemoglobin due to its ability to block HbS polymerization. Subsequently, hydroxycarbamide proved efficacious in adults with SCA and was Food and Drug Administration (FDA)-approved in 1998. After two decades of hydroxycarbamide use for SCD, there continues to be limited clinical acceptance of this chemotherapy drug, providing the impetus for investigators and pharmaceutical companies to develop non-chemotherapy agents. Investigative efforts to determine the role of events downstream of deoxy-HbS polymerization, such as endothelial cell activation, cellular adhesion, chronic inflammation, intravascular haemolysis and nitric oxide scavenging, have expanded drug targets which reverse the pathophysiology of SCD. After two decades of slow progress in the field, since 2018 three new drugs were FDA-approved for SCA, but research efforts to develop treatments continue. Currently over 30 treatment intervention trials are in progress to investigate a wide range of agents acting by complementary mechanisms, providing the rationale for ushering in the age of effective and safe combination drug therapy for SCD. Parallel efforts to develop curative therapies using haematopoietic stem cell transplant and gene therapy provide individuals with SCD multiple treatment options. We will discuss progress made towards drug development and potential combination drug therapy for SCD with the standard of care hydroxycarbamide.

Cell signaling pathways involved in drug-mediated fetal hemoglobin induction: Strategies to treat sickle cell disease

The developmental regulation of globin gene expression has shaped research efforts to establish therapeutic modalities for individuals affected with sickle cell disease and β-thalassemia. Fetal hemoglobin has been shown to block sickle hemoglobin S polymerization to improve symptoms of sickle cell disease; moreover, fetal hemoglobin functions to replace inadequate hemoglobin A synthesis in β-thalassemia thus serving as an effective therapeutic target. In the perinatal period, fetal hemoglobin is synthesized at high levels followed by a decline to adult levels by one year of age. It is known that naturally occurring mutations in the γ-globin gene promoters and distant cis-acting transcription factors produce persistent fetal hemoglobin synthesis after birth to ameliorate clinical symptoms. Major repressor proteins that silence γ-globin during development have been targeted for gene therapy in β-hemoglobinopathies patients. In parallel effort, several classes of pharmacological agents that induce fetal hemoglobin expression through molecular and cell signaling mechanisms have been identified. Herein, we reviewed the progress made in the discovery of signaling molecules targeted by pharmacologic agents that enhance γ-globin expression and have the potential for future drug development to treat the β-hemoglobinopathies.

A systematic review of known mechanisms of hydroxyurea-induced fetal hemoglobin for treatment of sickle cell disease

AIM

To report on molecular mechanisms of fetal hemoglobin (HbF) induction by hydroxyurea (HU) for the treatment of sickle cell disease.

STUDY DESIGN

Systematic review.

RESULTS

Studies have provided consistent associations between genomic variations in HbF-promoting loci and variable HbF level in response to HU. Numerous signal transduction pathways have been implicated, through the identification of key genomic variants in BCL11A, HBS1L-MYB, SAR1 or XmnI polymorphism that predispose the response to the treatment, and signal transduction pathways that modulate γ-globin expression (cAMP/cGMP; Giα/c-Jun N-terminal kinase/Jun; methylation and miRNA). Three main molecular pathways have been reported: i) Epigenetic modifications, transcriptional events and signaling pathways involved in HU-mediated response, ii) Signaling pathways involving HU-mediated response and iii) Post-transcriptional pathways (regulation by miRNAs).

CONCLUSIONS

The complete picture of HU-mediated mechanisms of HbF production in Sickle Cell Disease remains elusive. Research on post-transcriptional mechanisms could lead to therapeutic targets that may minimize alterations to the cellular transcriptome.

Molecular mechanisms underlying synergistic adhesion of sickle red blood cells by hypoxia and low nitric oxide bioavailability

The molecular mechanisms by which nitric oxide (NO) bioavailability modulates the clinical expression of sickle cell disease (SCD) remain elusive. We investigated the effect of hypoxia and NO bioavailability on sickle red blood cell (sRBC) adhesion using mice deficient for endothelial NO synthase (eNOS) because their NO metabolite levels are similar to those of SCD mice but without hypoxemia. Whereas sRBC adhesion to endothelial cells in eNOS-deficient mice was synergistically upregulated at the onset of hypoxia, leukocyte adhesion was unaffected. Restoring NO metabolite levels to physiological levels markedly reduced sRBC adhesion to levels seen under normoxia. These results indicate that sRBC adherence to endothelial cells increases in response to hypoxia prior to leukocyte adherence, and that low NO bioavailability synergistically upregulates sRBC adhesion under hypoxia. Although multiple adhesion molecules mediate sRBC adhesion, we found a central role for P-selectin in sRBC adhesion. Hypoxia and low NO bioavailability upregulated P-selectin expression in endothelial cells in an additive manner through p38 kinase pathways. These results demonstrate novel cellular and signaling mechanisms that regulate sRBC adhesion under hypoxia and low NO bioavailability. Importantly, these findings point us toward new molecular targets to inhibit cell adhesion in SCD.

Genomic variation in the MAP3K5 gene is associated with β-thalassemia disease severity and hydroxyurea treatment efficacy

AIM

In this study we explored the association between genetic variations in MAP3K5 and PDE7B genes, residing on chromosome 6q23, and disease severity in β-hemoglobinopathy patients, as well as the association between these variants with response to hydroxyurea (HU) treatment. Furthermore, we examined MAP3K5 expression in the context of high fetal hemoglobin (HbF) and upon HU treatment in erythroid progenitor cells from healthy and KLF1 haploinsufficient individuals.

MATERIALS & METHODS

For this purpose, we genotyped β-thalassemia intermedia and major patients and healthy controls, as well as a cohort of compound heterozygous sickle cell disease/β-thalassemia patients receiving HU as HbF augmentation treatment. Furthermore, we examined MAP3K5 expression in the context of high HbF and upon HU treatment in erythroid progenitor cells from healthy and KLF1 haploinsufficient individuals.

RESULTS

A short tandem repeat in the MAP3K5 promoter and two intronic MAP3K5 gene variants, as well as a PDE7B variant, are associated with low HbF levels and a severe disease phenotype. Moreover, MAP3K5 mRNA expression levels are altered in the context of high HbF and are affected by the presence of HU. Lastly, the abovementioned MAP3K5 variants are associated with HU treatment efficacy.

CONCLUSION

Our data suggest that these MAP3K5 variants are indicative of β-thalassemia disease severity and response to HU treatment.

cAMP response element-binding protein 1 is required for hydroxyurea-mediated induction of γ-globin expression in K562 cells

1. Hydroxyurea (HU) is a drug used for the treatment of haemoglobinopathies. Hydroxyurea functions by upregulating γ-globin transcription and fetal haemoglobin (HbF) production in erythroid cells. The K562 erythroleukaemia cell line is widely used as a model system in which to study the mechanism of γ-globin induction by HU. However, the transcription factors required for the upregulation of γ-globin expression by HU in K562 cells have not been identified. Similarities between the HU and sodium butyrate (SB) pathways suggest cAMP response element-binding protein (CREB) 1 as a potential candidate. Thus, the aim of the present study was to investigate the possible role of CREB1 in the HU pathway. 2. Experiments were performed using transient and stable RNA interference (RNAi) to show that CREB1 is necessary for HU-mediated induction of γ-globin expression and haemoglobin production in K562 cells. 3. Furthermore, western blot analyses demonstrated that CREB1 becomes phosphorylated in a dose-dependent manner after HU (100-400 µmol/L) treatment of K562 cells for 72 h. 4. We also investigated role of a Gγ promoter CREB1 response element (G-CRE) in this pathway. Quantitative amplification refractory mutation system-polymerase chain reaction experiments were performed to demonstrate that HU induces the expression of both Gγ and Aγ in this cell line. In addition, electrophoretic mobility shift assays were used to show that levels of CREB1 complexes binding to the G-CRE site are increased following HU treatment and are decreased in CREB1-knockdown cells. 5. The results suggest that CREB1 is necessary for γ-globin induction by HU in K562 cells, a role that may be mediated, in part, through the G-CRE element.

The proinflammatory cytokine GM-CSF downregulates fetal hemoglobin expression by attenuating the cAMP-dependent pathway in sickle cell disease

Although reduction in leukocyte counts following hydroxyurea therapy in sickle cell disease (SCD) predicts fetal hemoglobin (HbF) response, the underlying mechanism remains unknown. We previously reported that leukocyte counts are regulated by granulocyte-macrophage colony-stimulating factor (GM-CSF) in SCD patients. Here we examined the roles of GM-CSF in the regulation of HbF expression in SCD. Upon the analysis of retrospective data in 372 patients, HbF levels were inversely correlated with leukocyte counts and GM-CSF levels in SCD patients without hydroxyurea therapy, while HbF increments after hydroxyurea therapy correlated with a reduction in leukocyte counts, suggesting a negative effect of GM-CSF on HbF expression. Consistently, in vitro studies using primary erythroblasts showed that the addition of GM-CSF to erythroid cells decreased HbF expression. We next examined the intracellular signaling pathway through which GM-CSF reduced HbF expression. Treatment of erythroid cells with GM-CSF resulted in the reduction of intracellular cAMP levels and abrogated phosphorylation of cAMP response-element-binding-protein, suggesting attenuation of the cAMP-dependent pathway, while the phosphorylation levels of mitogen-activated protein kinases were not affected. This is compatible with our studies showing a role for the cAMP-dependent pathway in HbF expression. Together, these results demonstrate that GM-CSF plays a role in regulating both leukocyte count and HbF expression in SCD. Reduction in GM-CSF levels upon hydroxyurea therapy may be critical for efficient HbF induction. The results showing the involvement of GM-CSF in HbF expression may suggest possible mechanisms for hydroxyurea resistance in SCD.

Short-chain fatty acid-mediated effects on erythropoiesis in primary definitive erythroid cells

Short-chain fatty acids (SCFAs; butyrate and propionate) up-regulate embryonic/fetal globin gene expression through unclear mechanisms. In a murine model of definitive erythropoiesis, SCFAs increased embryonic beta-type globin gene expression in primary erythroid fetal liver cells (eFLCs) after 72 hours in culture, from 1.7% (+/- 1.2%) of total beta-globin gene expression at day 0 to 4.9% (+/- 2.2%) in propionate and 5.4% (+/- 3.4%) in butyrate; this effect was greater in butyrate plus insulin/erythropoietin (BIE), at 19.5% (+/- 8.3%) compared with 0.1% (+/- 0.1%) in ins/EPO alone (P < .05). Fetal gamma-globin gene expression was increased in human transgene-containing eFLCs, to 35.9% (+/- 7.0%) in BIE compared with 4.4% (+/- 4.2%) in ins/EPO only (P < .05). Embryonic globin gene expression was detectable in 11 of 15 single eFLCs treated with BIE, but in0 of 15 ins/EPO-only treated cells. Butyrate-treated [65.5% (+/- 9.9%)] and 77.5% (+/- 4.0%) propionate-treated eFLCs were highly differentiated in culture, compared with 21.5% (+/- 3.5%) in ins/EPO (P < .005). Importantly, signaling intermediaries, previously implicated in induced embryonic/fetal globin gene expression (STAT5, p42/44, and p38), were not differentially activated by SCFAs in eFLCs; but increased bulk histone (H3) acetylation was seen in SCFA-treated eFLCs. SCFAs induce embryonic globin gene expression in eFLCS, which are a useful short-term and physiologic primary cell model of embryonic/fetal globin gene induction during definitive erythropoiesis.

A cell stress signaling model of fetal hemoglobin induction: what doesn't kill red blood cells may make them stronger

A major goal of hemoglobinopathy research is to develop treatments that correct the underlying molecular defects responsible for sickle cell disease and beta-thalassemia. One approach to achieving this goal is the pharmacologic induction of fetal hemoglobin (HbF). This strategy is capable of inhibiting the polymerization of sickle hemoglobin and correcting the globin chain imbalance of beta-thalassemia. Despite this promise, none of the currently available HbF-inducing agents exhibit the combination of efficacy, safety, and convenience of use that would make them applicable to most patients. The recent success of targeted drug therapies for malignant diseases suggests that this approach could be effective for developing optimal HbF-inducing agents. A first step in applying this approach is the identification of specific molecular targets. However, while >70 HbF-inducing agents have been described, neither molecular mechanisms nor target molecules have been definitively verified for any of these compounds. To help focus investigation in this area, we have reviewed known HbF-inducing agents and their proposed mechanisms of action. We find that in many cases, current models inadequately explain key experimental results. By integrating features of the erythropoietic stress model of HbF induction with data from recent intracellular signaling experiments, we have developed a new model that has the potential to explain several findings that are inconsistent with previous models and to unify most HbF-inducing agents under a common mechanism: cell stress signaling. If correct, this or related models could lead to new opportunities for development of targeted therapies for the beta-hemoglobinopathies.

Inhibition of erythroblast growth and fetal hemoglobin production by ribofuranose-substituted adenosine derivatives

In vivo, inhibition of fetal hemoglobin (HbF) expression in humans around the time of birth causes the clinical manifestation of sickle cell and beta-thalassemia syndromes. Inhibition of HbF among cultured cells was recently described by the adenosine derivative molecule named SQ22536. Here, a primary cell culture model was utilized to further explore the inhibition of HbF by adenosine derivative molecules. SQ22536 demonstrated down-regulation of growth and HbF expression among erythroblasts cultured from fetal and adult human blood. The effects upon HbF were noted in a majority of cells, and quantitative PCR analysis demonstrated a transcriptional mechanism. Screening assays demonstrated that two additional molecules named 5'-deoxy adenosine and 2',3'-dideoxy adenosine had effects on HbF comparable to SQ22536. Other adenosine derivative molecules, adenosine receptor binding ligands, and cAMP-signaling regulators failed to inhibit HbF in matched cultures. These results suggest that structurally related ribofuranose-substituted adenosine analogues act through an unknown mechanism to inhibit HbF expression in fetal and adult human erythroblasts.

Immunoblotting conditions for human hemoglobin chains

Immunoblotting to analyze low-molecular-weight proteins like calmodulin and metallothioneins is challenging and requires modifications for reproducible detection. Human globin chains are 17-kDa proteins and are not detectable by conventional immunoblotting using nitrocellulose membranes. Here we describe an immunoblotting method using nitrocellulose membranes that allows quantitative analyses of globin chains. Although previous studies have demonstrated that the fixation of blotted membranes with glutaraldehyde improves immunodetection of low-molecular-weight proteins, we found that the detection sensitivity for human globins is increased markedly by fixation with paraformaldehyde, but not glutaraldehyde. This immunoblotting procedure facilitates studies of posttranscriptional mechanisms for globin gene expression.

Fetal hemoglobin in sickle cell anemia: Bayesian modeling of genetic associations

We genotyped single nucleotide polymorphisms (SNPs) in: (1) the beta-globin gene-like cluster, (2) quantitative trait loci (QTL) previously associated with fetal hemoglobin (HbF) concentration on chromosomes 6q, 8q, and Xp, and (3) candidate genes that could effect HbF levels, in sickle cell anemia subjects. HbF concentration was modeled as a continuous variable with values in a finite interval using a novel Bayesian approach. We first tested the associations of SNPs with HbF in a group of 1,518 adults and children (CSSCD study), and validated the results in a second independent group of 211 adults (MSH study). In subjects aged >or=24 years, 5 SNPs in TOX (8q12.1), 2 SNPs in the beta-globin gene-like cluster, 2 SNPs in the Xp QTL, and 1 SNP in chromosome 15q22 were associated with HbF in the CSSCD and also validated in the MSH. Four other SNPs in 15q22 were associated with HbF only in the larger CSSCD data. When patients aged <24 years in the CSSCD were examined, additional genes, including 4 with roles in nitric oxide metabolism, were associated with HbF level. These studies confirm prior analyses using traditional analytical approaches showing associations of SNPs in TOX, GPM6B, and the beta-globin gene-like cluster with HbF levels. We also identified an additional candidate regulatory region in chromosome 15q22 that is associated with HbF level. By stratifying patients by age, our results also suggest that different genes might modulate the rate of decline of HbF and the final level of HbF levels in sickle cell anemia.

Hematologic, biochemical, and cardiopulmonary effects of L-arginine supplementation or phosphodiesterase 5 inhibition in patients with sickle cell disease who are on hydroxyurea therapy

OBJECTIVES

Fetal hemoglobin (HbF) induction involves NO-cGMP signaling pathways. L-arginine, an NO precursor, and the phosphodiesterase (PDE) 5 inhibitor sildenafil, which potentiates cGMP, were studied in adults with sickle cell disease (SCD) who were stably on HU.

METHODS

Twenty four courses of L-arginine (0.1-0.2 g/kg divided TID) or sildenafil (25-100 mg TID), assigned based on gender due to concerns about sildenafil-related priapism, were successfully completed. Biochemical assays, pulmonary pressures, and cardiopulmonary exercise capacity are reported from patients in whom serial values are available. Hematologic responses are reported in 14 subjects with HbSS who had stable baseline HbF levels.

RESULTS

L-arginine increased plasma arginine and ornithine, but not citrulline, suggesting diversion by plasma arginase from NO, and citrulline, generation. Glutathione increased only in patients on L-arginine. Sildenafil increased plasma cGMP and citrulline, but not other amino acids. Pulmonary pressures and 6-min walk distances improved only in patients on sildenafil. In subjects with stable baseline HbF levels, HbF levels changed little from a normalized baseline on l-arginine, decreasing by 2.9 +/- 16.1%, n = 6; P = n.s., but increased on sildenafil, by 7.5 +/- 11.7%, n = 8, P < 0.05. Absolute reticulocyte counts initially decreased in patients on sildenafil.

CONCLUSIONS

L-arginine, at doses that increase plasma arginine levels, altered redox potential in red cells. The lack of clinically detectable efficacy of L-arginine may be due to increased arginine metabolism in SCD patients. In vivo augmentation of the cyclic nucleotide pathway by PDE inhibition may induce HbF slightly, but strikingly improves hemodynamic and functional status in SCD.

Hydroxyurea nitrosylates and activates soluble guanylyl cyclase in human erythroid cells

Hydroxyurea, a drug widely used for treating myeloproliferative diseases, has also been approved for the treatment of sickle cell disease by raising fetal hemoglobin (HbF). We have shown that nitric oxide (NO) and the soluble guanylyl cyclase (sGC) pathways are involved in hydroxyurea induction of HbF levels in erythroid progenitor cells (EPCs). We demonstrate now that during erythroid differentiation, endothelial NO synthase mRNA and protein levels decline steadily, as does the production of NO derivatives and cyclic adenosine monophosphate (cAMP) levels, but guanosine 3',5'-cyclic monophosphate (cGMP) levels are stable. Hydroxyurea increased intracellular cGMP levels and cAMP levels in EPCs. The NO donor, DEANONOate, induced much higher cGMP levels, but reduced cAMP levels. Hydroxyurea (1 mM) induced production of approximately 45 pM cGMP/minute/ng of purified sGC, similar to induction by 1 muM DEANONOate. We found that hydroxyurea and ProliNONOate produced iron-nitrosyl derivatives of sGC. Thus, we confirm that hydroxyurea can directly interact with the deoxy-heme of sGC, presumably by a free-radical nitroxide pathway, and activate cGMP production. These data add to an expanding appreciation of the role of hydroxyurea as an inducer of the NO/cGMP pathway in EPCs. These mechanisms may also be involved in the cytostatic effects of hydroxyurea, as well as the induction of HbF.

Expression of the gamma-globin gene is sustained by the cAMP-dependent pathway in beta-thalassaemia

The present study found that the cyclic adenosine monophosphate (cAMP)-dependent pathway efficiently induced gamma-globin expression in adult erythroblasts, and this pathway plays a role in gamma-globin gene (HBG) expression in beta-thalassaemia. Expression of HBG mRNA increased to about 46% of non-HBA mRNA in adult erythroblasts treated with forskolin, while a cyclic guanosine monophosphate (cGMP) analogue induced HBG mRNA to levels <20% of non-HBA mRNA. In patients with beta-thalassaemia intermedia, cAMP levels were elevated in both red blood cells and nucleated erythroblasts but no consistent elevation was found with cGMP levels. The transcription factor cAMP response element binding protein (CREB) was phosphorylated in nucleated erythroblasts and its phosphorylation levels correlated with HBG mRNA levels of the patients. Other signalling molecules, such as mitogen-activated protein kinases and signal transducers and activators of transcription proteins, were phosphorylated at variable levels and showed no correlations with the HBG mRNA levels. Plasma levels of cytokines, such as erythropoietin, stem cell factor and transforming growth factor-beta were increased in patients, and these cytokines induced both HBG mRNA expression and CREB phosphorylation. These results demonstrate that the cAMP-dependent pathway, the activity of which is augmented by multiple cytokines, plays a role in regulating HBG expression in beta-thalassaemia.

Mechanism for fetal hemoglobin induction by histone deacetylase inhibitors involves gamma-globin activation by CREB1 and ATF-2

The histone deacetylase inhibitors (HDA-CIs) butyrate and trichostatin A activate gamma-globin expression via a p38 mitogen-activating protein kinase (MAPK)-dependent mechanism. We hypothesized that down-stream effectors of p38 MAPK, namely activating transcription factor-2 (ATF-2) and cyclic AMP response element (CRE) binding protein (CREB), are intimately involved in fetal hemoglobin induction by these agents. In this study, we observed increased ATF-2 and CREB1 phosphorylation mediated by the HDACIs in K562 cells, in conjunction with histone H4 hyperacetylation. Moreover, enhanced DNA-protein interactions occurred in the CRE in the (G)gamma-globin promoter (G-CRE) in vitro after drug treatments; subsequent chromatin immunoprecipitation assay confirmed ATF-2 and CREB1 binding to the G-CRE in vivo. Enforced expression of ATF-2 and CREB produced (G)gamma-promoter trans-activation which was abolished by a 2-base pair mutation in the putative G-CRE. The data presented herein demonstrate that gamma-gene induction by butyrate and trichostatin A involves ATF-2 and CREB1 activation via p38 MAPK signaling.

Role of cyclic nucleotides in fetal hemoglobin induction in cultured CD34+ cells

OBJECTIVE

In vivo, several drugs have been shown to increase fetal hemoglobin (HbF), including 5-azacytidine (AZA), sodium butyrate (SB), and hydroxyurea (HU). Studies in K562 cells suggest that cyclic guanosine monophosphate (cGMP) is required for HbF induction; however, the role of cyclic nucleotides in HbF induction in primary erythroid cultures has not been established.

METHODS

CD34-selected peripheral blood monocytes cultured in a semi-solid serum-free system that mimics in vivo F-cell production are utilized to explore the role of cyclic adenosine monophosphate (cAMP) and cGMP in HbF induction in response to HU, AZA, and SB.

RESULTS

In serum-free CD34 cultures, HU, SB, and AZA all markedly stimulate FNRBC production up to 30-fold, associated with induction of gamma-globin mRNA and total HbF protein. Guanylate cyclase inhibition results in only minimal blunting of HbF induction by each agent. In contrast, adenylate cyclase inhibition markedly reduces HU, SB, and AZA-mediated FNRBC induction and gamma-globin mRNA induction. The adenylate cyclase activator forskolin modestly induces FNRBC production and augments the action of standard induction agents. HU, AZA, and SB, however, fail to significantly stimulate adenylate cyclase themselves.

CONCLUSIONS

In human CD34(+) cultures, cAMP production is required for full induction of HbF by HU, SB, and AZA, while perturbation of cGMP production has only minimal effects. These findings are in marked contrast to data in K562 cells where cGMP production is critical for HbF induction while cAMP stimulation blunts HbF response, and suggest that these agents may share a common induction pathway.

Modifier genes and sickle cell anemia

PURPOSE OF REVIEW

With the completion of the human genome project and HapMap, previously unknown genetic polymorphisms associated with disease have been observed. This review highlights genetic polymorphisms that have provided insight into the pathophysiology underlying the many phenotypes of sickle cell disease.

RECENT FINDINGS

The phenotypes of sickle cell disease are likely to be modulated by polymorphisms in genes that are involved in inflammation, cell-cell interaction, and nitric oxide biology. Case-control studies are beginning to define the relationships between single-nucleotide polymorphisms in candidate genes and the many subphenotypes of sickle cell anemia. A common theme emerging from these studies is that single-nucleotide polymorphisms in genes of the transforming growth factor-beta/bone morphogenetic protein and a few other genes such as Klotho are associated with several subphenotypes of sickle cell disease.

SUMMARY

Genomic medicine is merging with clinical practice as our understanding of the structure and variability of the human genome increases. Patients with diseases caused by identical mutations in a single gene - sickle cell anemia is a prime example - can have clinical courses very different from one another, and when environmental influences are removed the phenotypic heterogeneity of mendelian single-gene disorders is best explained by single-nucleotide polymorphisms in genes that modulate the disease phenotype. As this field expands, insights will be gained into complex epistatic factors that influence the clinical presentation of sickle cell disease, enabling physicians to better predict and manage the many complications of this disease.

cAMP differentially regulates gamma-globin gene expression in erythroleukemic cells and primary erythroblasts through c-Myb expression

Our previous studies demonstrated roles of cyclic nucleotides in gamma-globin gene expression. We recently found that, upon activation of the cAMP pathway, expression of the gamma-globin gene is inhibited in K562 cells but induced in adult erythroblasts. Here we show that c-Myb, a proto-oncogene product that plays a role in cell growth and differentiation, is involved in the cAMP-mediated differential regulation of gamma-globin gene expression in K562 cells and primary erythroblasts. Our studies found that c-Myb is expressed at a high level in K562 cells compared to primary erythroblasts, and that c-Myb expression is further increased following the treatment with forskolin, an adenylate cyclase activator. The induction of gamma-globin gene expression was also inhibited in K562 cells by raising the levels of c-Myb expression. Importantly, forskolin-induced erythroid differentiation in K562 cells, as determined by the expression of glycophorins and CD71, suggesting that high-level expression of c-Myb may not be sufficient to inhibit the differentiation of erythroid cells. In contrast, c-Myb was not expressed in adult erythroblasts treated with forskolin and primary erythroblasts may lack the c-Myb-mediated inhibitory mechanism for gamma-globin gene expression. Together, these results show that the cAMP pathway blocks gamma-globin gene expression in K562 cells by increasing c-Myb expression and c-Myb plays a role in defining the mode of response of the gamma-globin gene to fetal hemoglobin inducers in erythroid cells.

Cyclic nucleotide phosphodiesterases as targets for treatment of haematological malignancies

The cAMP signalling pathway has emerged as a key regulator of haematopoietic cell proliferation, differentiation and apoptosis. In parallel, general understanding of the biology of cyclic nucleotide PDEs (phosphodiesterases) has advanced considerably, revealing the remarkable complexity of this enzyme system that regulates the amplitude, kinetics and location of intracellular cAMP-mediated signalling. The development of therapeutic inhibitors of specific PDE gene families has resulted in a growing appreciation of the potential therapeutic application of PDE inhibitors to the treatment of immune-mediated illnesses and haematopoietic malignancies. This review summarizes the expression and function of PDEs in normal haematopoietic cells and the evidence that family-specific inhibitors will be therapeutically useful in myeloid and lymphoid malignancies.

The HIV-1 Tat protein enhances megakaryocytic commitment of K562 cells by facilitating CREB transcription factor coactivation by CBP

The human immunodeficiency virus type 1 (HIV-1) Tat protein regulates transcription factor functions and alters cellular gene expression. Because hematopoietic progenitor cell (HPC) differentiation requires activation of lineage-specific transcription factors, Tat may affect hematopoiesis in HIV-1-infected micro-environments. We have monitored the molecular effects of Tat on megakaryocytic differentiation in the HPC line, K562. Flow cytometry analysis of CD61 indicated that phorbol myristate acetate (PMA) (16 nM) stimulated megakaryocytic commitment of K562 cells was increased (3- to 4-fold) following exposure to Tat (1-100 ng/ml). Activation of the megakaryocytic transcription factor cAMP regulatory element binding protein (CREB) and its coactivation by the CREB binding protein (CBP) was subsequently monitored. CREB phosphorylation and DNA binding were measured by Western immunodetection and electrophoretic mobility shift assays (EMSA), respectively. Within 2 hrs after stimulation, Tat increased both CREB phosphorylation and DNA binding by 7- to 10-fold. Transient cotransfection with CREB reporter and CBP expression plasmids demonstrated that Tat treatment increases (3- to 4-fold) both PMA-stimulated and CBP-mediated transcription via the cAMP regulatory element. Histone acetyl transferase (HAT) activity was increased (8- to 10-fold) in Tat-stimulated cells, which suggested increased chromosomal accessibility of transcription factors. Two-hybrid cotransfection assays using reporter plasmid containing the GAL4 DNA-binding domain and expression plasmid coding for the GAL4-CBP fusion protein, showed that Tat increases (2-fold) CBP-mediated coactivation of CREB. Both reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis showed that Tat treatment increases CBP gene expression (7- to 9-fold) and protein levels (5- to 7-fold) within 6-12 hrs after stimulation. Our findings indicated that Tat treatment increases both CREB function and CREB coactivation by CBP, which may facilitate megakaryocytic commitment of K562 cells. Induction of this molecular signaling by HIV-1 Tat protein may have relevance in understanding the HIV-induced hematologic manifestations and possibly in regulation of viral infectivity parameters in progenitor cell reservoirs.

Protein kinase A-dependent phosphorylation of Lutheran/basal cell adhesion molecule glycoprotein regulates cell adhesion to laminin alpha5

Lutheran (Lu) blood group and basal cell adhesion molecule (B-CAM) antigens reside on two glycoprotein (gp) isoforms Lu and Lu(v13) that belong to the Ig superfamily and differ only by the size of their cytoplasmic tail. Lu/B-CAM gps have been recognized as laminin alpha5 receptors on red blood cells and epithelial cells in multiple tissues. It has been shown that sickle red cells exhibit enhanced adhesion to laminin alpha5 when intracellular cAMP is up-regulated by physiological stimuli such as epinephrine and that this signaling pathway is protein kinase A- and Lu/B-CAM-dependent. In this study, we analyzed the relationship between the phosphorylation status of Lu/B-CAM gps and their adhesion function to laminin alpha5. We showed that Lu isoform was phosphorylated in sickle red cells as well as in erythroleukemic K562 and epithelial Madin-Darby canine kidney cells and that this phosphorylation is enhanced by different stimuli of the PKA pathway. Lu gp is phosphorylated by glycogen synthase kinase 3 beta, casein kinase II, and PKA at serines 596, 598, and 621, respectively. Alanine substitutions of serines 596 and 598 abolished phosphorylation by glycogen synthase kinase 3 beta and casein kinase II, respectively, but had no effect on adhesion of K562 cells to laminin under flow conditions. Conversely, mutation of serine 621 prevented phosphorylation by PKA and dramatically reduced cell adhesion. Furthermore, stimulation of K562 cells by epinephrine increased Lu gp phosphorylation by PKA and enhanced adhesion to laminin. It is postulated that modulation of the phosphorylation state of Lu gp might be a critical factor for the sickle red cells adhesiveness to laminin alpha5 in sickle cell disease.

Predicting clinical severity in sickle cell anaemia

The ability to predict the phenotype of an individual with sickle cell anaemia would allow a reliable prognosis and could guide therapeutic decision making. Some risk factors for individual disease complications are known but are insufficiently precise to use for prognostic purposes; predicting the global disease severity is not yet possible. Genetic association studies, which attempt to link gene polymorphisms with selected disease subphenotypes, may eventually provide useful methods of foretelling the likelihood of certain complications and allow better individualized treatment.

Induction of fetal haemoglobin expression in erythroid cells – A model based on iron availability signalling

The K562 cell line has erythroid origin and is used for the study of fetal haemoglobin (HbF) production after treatment with several drugs, such as hydroxyurea, cisplatin and cytosine arabinoside (Ara C). It represents an important tool for the study of cancer differentiation therapy and treatment of thalassaemia and sickle cell disease. Although subject to intense research, the mechanisms involved in the induction of HbF are not fully established, and the regulation of several genes and signalling pathways has been proposed. Using the methodology of differential display, we investigated the changes in gene expression in K562 cells treated with doxorubicin and aclarubicin, which induce HbF expression and cell cycle arrest. Several genes were shown to present differential expression patterns, many of them related to the iron signalling pathway. Particular attention was given to Ndrg1, expressed as early as 24 h after treatment, which can be regulated by iron and is involved with blocking of the cell cycle. A review of the literature shows that, similar to doxorubicin and aclarubicin, most of the drugs used to induce HbF present some kind of effect on the iron signalling pathway, activating in the cells the machinery necessary for the incorporation of extracellular iron. Considering these results, as well as the fact that in erythroid cells the synthesis of haemoglobin is of vital importance, we propose that the production of fetal haemoglobin in erythroid cells is highly dependent on the iron signalling pathway.