Requirement of GATA-1 and p45 NF-E2 expression in butyric acid-induced erythroid differentiation

Acyclovir induces fetal hemoglobin via downregulation of γ-globin repressors, BCL11A and SOX6 trans-acting factors

Pharmacological reactivation of developmentally silenced fetal hemoglobin (HbF) is an attractive approach to ameliorate the clinical manifestations of β-thalassemia and sickle cell anemia. Hydroxyurea, the only HbF inducer, has obtained regulatory approval. However, hydroxyurea non-responders and associated myelosuppression making its widespread use undesirable. A high level of HbF with safe and effective agents remains an elusive therapeutic goal for this global health burden. This study demonstrated the effect of acyclovir on γ-globin expression and erythropoiesis, associated with increased HbF production. In vitro, human erythroleukemia cells and human CD34⁺ erythroid progenitors, and in vivo β-YAC transgenic mice were used as experimental models. We found that acyclovir significantly induces expression of the γ-globin gene and HbF synthesis in CD34⁺ erythroid progenitors, without affecting terminal erythroid differentiation and erythroid cell proliferation. In contrast to other HbF inducers, no associated cytotoxicity with acyclovir was observed. Further, we reported the effect of acyclovir on γ-globin gene transcriptional regulators including BCL11A, FOP1, KLF1 SOX6, and GATA-1. Significant downregulation of the γ-globin repressors BCL11A and SOX6 was observed at both mRNA and protein levels. Whereas, GATA-1, a master erythroid transcription factor, was upregulated in acyclovir treated human CD34⁺ erythroid culture. Similarly, the HbF inducing effect of acyclovir in β-YAC transgenic mice revealed a good in vitro correlation, with a substantial increase in fetal globin mRNA, and F cells population. These findings collectively suggest acyclovir as an effective HbF inducer and pave the way to evaluate its clinical efficacy in treating β-globin disorders.

Resveratrol ameliorates TNFα-mediated suppression of erythropoiesis in human CD34(+) cells via modulation of NF-κB signalling

Overexpression of pro-inflammatory cytokines, including tumour necrosis factor alpha (TNFα), has been implicated in the pathogenesis of anaemia of inflammation. TNFα suppresses erythroid colony formation via both direct and indirect effects on haematopoietic progenitors, often involving activation of nuclear factor (NF)-κB signalling resulting in downregulation of transcription factors critical for erythropoiesis. There is a dearth of effective and safe therapies for many patients with inflammatory anaemia. Resveratrol is a flavanol found in red wine grapes that possesses potent anti-inflammatory properties, but studies of its impact on human erythropoiesis have proven contradictory. We investigated whether resveratrol ameliorates TNFα-mediated suppression of erythropoiesis in human CD34(+) haematopoietic progenitors. We found that resveratrol partially reverses the erythroid suppressive effects of TNFα, leading to significant recovery in burst forming unit-erythroid colony formation in human CD34(+) cells. CD34(+) cells pre-incubated with resveratrol for 72 h in the presence of TNFα inhibited NF-κB activation via decreased NF-κB nuclear localization without altering total NF-κB protein levels and independent of IκB degradation. Resveratrol also significantly restored the baseline expression of erythroid transcription factors NFE2 and the GATA1/GATA2 ratio in CD34(+) cells treated with TNFα. In conclusion, resveratrol may inhibit TNFα-mediated NF-κB activation and promote erythropoiesis in primary human CD34(+) cells.

Fetal hemoglobin reactivation and cell engineering in the treatment of sickle cell anemia

The natural history of severe hemoglobinopathies like sickle cell disease (SCD) is rather variable, depending on the circumstances, but the main influence on such variability is the level of fetal hemoglobin (HbF) in the patient's red cells. It is well known that a significant HbF level is associated with a milder course of disease and fewer complications. Therefore, attempts have been made to reactivate using various means the HbF production, which is normally switched off perinatally. A pharmacological approach has been attempted since the 1980s, ranging from drugs like 5-azacytidine and its derivative, decitabine, to a series of compounds like hydroxyurea and a number of histone deacetylase inhibitors like butyrate, which seem to act as epigenetic modifiers. Many other disparate agents have been tried with mixed results, but hydroxyurea remains the most effective compound so far available. Combinations of different compounds have also been tried with some success. Established treatments like bone marrow or cord blood transplantation are so far the only real cure for a limited number of patients with severe hemoglobinopathies. Improved chemotherapy regimens of milder toxicity than those employed in the past have made it possible recently to obtain a stable, mixed donor-recipient chimerism, with reversal of the SCD phenotype. However, great effort is directed to cell engineering, searching for an effective gene vector by which a desired gene can be transferred into new classes of vectors for autologous hemopoietic stem cells. Recent studies are also aiming at targeted insertion of the therapeutic gene into hemopoietic cells, which can also be "induced" human stem cells, obtained from somatic dedifferentiated cells. Attention in this area must be paid to the possibility of undesired effects, like the emergence of potentially oncogenic cell populations. Finally, an update is presented on improved HbF determination methods, because common international standards are becoming mandatory.

A non-apoptotic function of caspase-3 in pharmacologically-induced differentiation of K562 cells

BACKGROUND AND PURPOSE

Several anticancer drugs with diverse chemical structures can induce differentiation of cancer cells. This study was undertaken to explore the potential contribution of caspase-3 to pharmacologically-induced differentiation of K562 cells.

EXPERIMENTAL APPROACH

We assessed differentiation by measuring the expression of glycophorin A and haemoglobin synthesis in K562 cells treated with low concentrations of doxorubicin, hydroxyurea, cytosine arabinoside, cisplatin and haemin. Caspase-3 activation, mitochondrial membrane potential dissipation and viability were assessed by FACS. GATA-1-binding activity was evaluated by EMSA.

KEY RESULTS

Treatment of K562 cells with low concentrations of the tested drugs activated caspase-3 but did not trigger detectable apoptosis. Instead, elevated levels of haemoglobin-positive and glycophorin A/caspase-3-double-positive cells were observed, suggesting involvement of caspase-3 in drug-induced differentiation. Inhibition of caspase-3 activity significantly reduced the ability of K562 cells to execute the differentiation programme. Mitochondrial membrane potential dissipation was observed, indicating involvement of the mitochondrial pathway. Binding activity of GATA-1, transcription factor responsible for differentiation and cell survival, was not diminished by increased caspase-3 activity during drug-stimulated differentiation.

CONCLUSIONS AND IMPLICATIONS

Our results could explain how anticancer drugs, with diverse structures and modes of action, can stimulate erythroid differentiation in leukaemic cells with appropriate genetic backgrounds. Our findings imply that some similarities exist between pharmacologically-induced differentiation of erythroleukaemic cells and normal erythropoiesis, both involving caspase-3 activation at high levels of anti-apoptotic protein Bcl-X(L) and chaperone protein Hsp70 (heat shock protein 70). Therefore, the functions of caspase-3, unrelated to cell death, can be extended to pharmacologically-induced differentiation of some cancer cells.

p73 plays a role in erythroid differentiation through GATA1 induction

The TP73 gene gives rise to transactivation domain-p73 isoforms (TAp73) as well as DeltaNp73 variants with a truncated N terminus. Although TAp73alpha and -beta proteins are capable of inducing cell cycle arrest, apoptosis, and differentiation, DeltaNp73 acts in many cell types as a dominant-negative repressor of p53 and TAp73. It has been proposed that p73 is involved in myeloid differentiation, and its altered expression is involved in leukemic degeneration. However, there is little evidence as to which p73 variants (TA or DeltaN) are expressed during differentiation and whether specific p73 isoforms have the capacity to induce, or hinder, this differentiation in leukemia cells. In this study we identify GATA1 as a direct transcriptional target of TAp73alpha. Furthermore, TAp73alpha induces GATA1 activity, and it is required for erythroid differentiation. Additionally, we describe a functional cooperation between TAp73 and DeltaNp73 in the context of erythroid differentiation in human myeloid cells, K562 and UT-7. Moreover, the impaired expression of GATA1 and other erythroid genes in the liver of p73KO embryos, together with the moderated anemia observed in p73KO young mice, suggests a physiological role for TP73 in erythropoiesis.

Epigenetic analysis of the human alpha- and beta-globin gene clusters

K562 erythroleukemia cells have been widely used as a model for the study of globin gene regulation. A number of agents have been shown to activate or suppress globin gene expression in these cells. However, the molecular effects of these agents on the epigenetic configuration of the alpha- and gamma-globin genes that encode HbF are not known. In this report, we investigated the relationship between globin expression and histone acetylation of the human alpha- and beta-globin clusters in the fetal erythroid environment of K562 cells. Our studies suggest that acetylation of histone H3 may be important in regulating developmental stage-specific expression of the different beta-like globin genes while acetylation of both histones H3 and H4 may be important for the regulation of tissue-specific expression of these genes. In contrast, acetylation of both histones H3 and H4 at the alpha-like globin promoters appears to be important for both developmental stage- and tissue-specific expression. Interestingly, butyrate-induced activation of alpha-globin gene expression in K562 cells is associated with significant increase in histone acetylation levels while TPA-induced inhibition is associated with decreased histone acetylation at its promoters. In contrast, changes in histone acetylation and DNA methylation do not appear to be important in the regulation of gamma-globin gene expression by the same agents. These data suggest that the butyrate-mediated induction of the fetal gamma-globin genes in K562 cells is not a direct result of its histone deacetylase inhibitor activity of butyrate on the chromatin of the gamma-globin promoters, while the induction of the alpha-globin genes could be a result of a direct effect of butyrate on chromatin at its promoters. This is another example of the important differences in the molecular mechanisms of regulation of the genes of the alpha- and beta-like globin clusters.

Systematic RNAi studies on the role of Sp/KLF factors in globin gene expression and erythroid differentiation

Sp/KLF family of factors regulates gene expression by binding to the CACCC/GC/GT boxes in the DNA through their highly conserved three zinc finger domains. To investigate the role of this family of factors in erythroid differentiation and globin gene expression, we first measured the expression levels of selected Sp/KLF factors in primary cells of fetal and adult stages of erythroid development. This quantitative analysis revealed that their expression levels vary significantly in cells of either stages of the erythroid development. Significant difference in their expression levels was observed between fetal and adult erythroid cells for some Sp/KLF factors. Functional studies using RNA interference revealed that the silencing of Sp1 and KLF8 resulted in elevated level of gamma globin expression in K562 cells. In addition, K562 cells become visibly red after Sp1 knockdown. Benzidine staining revealed significant hemoglobinization of these cells, indicating erythroid differentiation. Moreover, the expression of PU.1, ETS1 and Notch1 is significantly down-regulated in the cells that underwent erythroid differentiation following Sp1 knockdown. Overexpression of PU.1 or ETS1 efficiently blocked the erythroid differentiation caused by Sp1 knockdown in K562 cells. The expression of c-Kit, however, was significantly up-regulated. These data indicate that Sp1 may play an important role in erythroid differentiation.

Transcriptional and post-transcriptional regulation of glutathione S-transferase P1 expression during butyric acid-induced differentiation of K562 cells

Over-expression of glutathione S-transferase P1 is related to chemotherapeutic drug resistance as well as to differentiation of human erythroleukemia cells. In opposition to previously described differentiating inducers which enhance the GST-resistance phenotype, time- and concentration-dependent activation of both erythroid and megakaryocytic differentiation pathways by butyric acid progressively diminished GSTP1 mRNA expression. GSTP1 mRNA expression decreased by 25% (p<0.01) and 64% (p<0.01) in 1mM and 2mM butyric acid-differentiated K562 cells, respectively. These results were associated to both a reduction of GATA-1 binding activity to the GSTP1 promoter and to a posttranscriptional destabilization of GSTP1 mRNA in a concentration dependent manner. Indeed, GSTP1 mRNA half-life decreased from 43.8 to 36.2 h and 12.6 h in 1mM- and 2mM-treated cells, respectively.

Induction of fetal hemoglobin in the treatment of sickle cell disease

Reactivation of fetal hemoglobin (HbF) expression is an important therapeutic option in patients with hemoglobin disorders. In sickle cell disease (SCD), an increase in HbF inhibits the polymerization of sickle hemoglobin and the resulting pathophysiology. Hydroxyurea, an inducer of HbF, has already been approved for the treatment of patients with moderate and/or severe SCD. Recent clinical trials with other pharmacological inducers of HbF, such as butyrate and decitabine, have shown considerable promise. In this chapter, we highlight the important clinical trials with pharmacological inducers of HbF, discuss their mechanisms of action and speculate about the future of this therapeutic approach in the treatment of patients with SCD.

Inhibitory effect of tellimagrandin I on chemically induced differentiation of human leukemia K562 cells

Tellimagrandin I is a hydrolysable tannin compound widely present in plants. In this study, the effect of tellimagrandin I on chemically induced erythroid and megakaryocytic differentiation was investigated using K562 cells as differentiation model. It was found that tellimagrandin I not only inhibited the hemoglobin synthesis in butyric acid (BA)- and hemin-induced K562 cells with IC50 of 3 and 40microM, respectively, but also inhibited other erythroid differentiation marker including acetylcholinesterase (AChE) and glycophorin A (GPA) in BA-induced K562 cells. Tellimagrandin I also inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced expression of CD61 protein, a megakaryocytic marker. RT-PCR analysis showed that tellimagrandin I decreased the expression of erythroid genes (gamma-globin and porphobilinogen deaminase (PBGD)) and related transcription factors (GATA-1 and NF-E2) in BA-induced K562 cells, whereas tellimagrandin I induced the overexpresison of GATA-2 transcription factor that played negative regulation on erythroid differentiation. These results indicated that tellimagrandin I had inhibitory effects on erythroid and megakaryocytic differentiation, which suggested that tannins like tellimagrandin I might influence the anti-tumor efficiency of some drugs and the hematopoiesis processes.

Butyric acid increases invasiveness of HL-60 leukemia cells: role of reactive oxygen species

Butyric acid (BA) induces differentiation of human leukemia, including HL-60 cells. By using a fluorescent probe, we showed that reactive oxygen species (ROS) were generated in BA-treated cells. BA-induced differentiation was accompanied with an increased secretion of pro-matrix metalloproteinase (MMP)-9. Both phenomena were inhibited by antioxidants. Tissue inhibitors of MMP (TIMP)-1 and -2 secretion were increased by BA, but differently affected by antioxidants. By contrast, BA did not affect MMP-9 mRNA, and decreased TIMP-1 and TIMP-2 mRNA levels. In addition, migratory and invasive properties of HL-60 cells were enhanced by BA, but differently affected by antioxidants. Altogether, these results indicate that ROS are messengers of BA-induced differentiation and increased invasiveness.

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.

Oxidative stress involvement in chemically induced differentiation of K562 cells

The erythroid differentiation of K562 cells could be achieved by exposure to several pharmacologic agents, including hemin, butyric acid (BA), and anthracycline antitumor drugs such as aclarubicin (ACLA) and doxorubicin (DOX). When used at subtoxic concentrations, these drugs induce the overexpression of erythroid genes, leading to hemoglobinization of cells. Because anthracyclines are known to generate oxidative damage, we intended to demonstrate the involvement of an oxidative stress in the chemically induced differentiation process. The addition of antioxidants to anthracycline- and BA-induced cells decreased their growth and dramatically reduced the percentage of differentiated cells at day 3. Northern blot analysis showed that antioxidants also decrease the expression of erythroid genes and related transcription factors in induced cells. Moreover, analyses of oxidative stress markers showed that treatment with BA, ACLA, and DOX lead to a decrease in reduced glutathione and antioxidant enzymes (glutathione peroxidase [GPx], glutathione reductase [GRase], CuZn superoxide dismutase [SOD], and catalase [CAT]). In addition, DOX increased thiobarbituric acid reactants (TBARs), and MnSOD activity was decreased by BA and DOX. Finally, the production of reactive oxygen species (ROS) by differentiating agents was demonstrated using the dihydroethidium probe in a microspectrofluorometric assay. Altogether, these results strongly suggest the involvement of an oxidative stress generated by BA or anthracyclines as the first step in the irreversible differentiation process. Additionally, these results underline the differences between BA, ACLA, and DOX molecular mechanisms.

Inhibitory effect of nitric oxide on chemically induced differentiation of human leukemic K562 cells

The effect of nitric oxide (NO) was investigated in the human K562 cell line during chemically induced erythroid differentiation. Butyric acid (BA) and the anthracycline antitumour drugs aclarubicin (ACLA) and doxorubicin (DOX) were used as differentiating agents. In all cases, cell hemoglobinization was dose dependently inhibited by NO donors such as sodium nitroprusside (SNP). A 50% inhibition of cell differentiation was obtained with 25 microM SNP, which generated less than 2 microM nitrite in 3-day culture media. Increasing SNP concentrations led to higher nitrite accumulation (up to 12 microM with 1 mM SNP) and total inhibition of cell hemoglobinization, but did not have a significant effect on cell proliferation. As shown by Northern blotting, high concentrations of SNP (1 mM) reduced the expression of gamma-globin and porphobilinogen deaminase, but did not change GATA-1 and NF-E2 mRNA levels in ACLA- and BA-treated cells. In contrast, hemin-induced erythroid differentiation was not affected by the presence of NO donors. Altogether, these results show that NO is able to inhibit cell differentiation induced by some (ACLA, DOX, BA), but not all (hemin), agents. The inhibitory effect of NO seems to take place downstream of the regulation of erythroid gene expression.