Butyrate-induced erythroid differentiation of human K562 leukemia cells involves inhibition of ERK and activation of p38 MAP kinase pathways

RepID depletion enhances TWS119-induced erythropoiesis through chromatin reprogramming and transcription factor recruitment

BACKGROUND

Erythrocytes, derived from hematopoietic stem cells, are essential for oxygen transport, ensuring survival in all vertebrate animals. The process of erythropoiesis is associated with gene expression changes, but many key regulatory factors that govern erythroid differentiation remain to be fully understood.

OBJECTIVE

This study investigates the role of TWS119, a known GSK3β inhibitor, in inducing erythropoiesis in K562 erythroleukemia cells and explores the impact of Replication initiation determinant protein (RepID) depletion on the process.

METHODS

K562 cells were treated with TWS119 and erythropoiesis markers including various erythrocytic phenotypes were assessed. Chromatin-immunoprecipitation analysis was employed to examine the changes in chromatin structure and gene expression regulation. The impact of RepID depletion on TWS119-induced erythropoiesis was also evaluated by analyzing globin promoter euchromatinization and NRF2 binding.

RESULTS

TWS119 treatment led to erythrocytic phenotypes in K562 cells, such as red pellet formation, enucleation, and nucleus condensation, along with the upregulation of erythropoiesis markers. Furthermore, RepID depletion accelerated TWS119-mediated erythropoiesis. Chromatin-immunoprecipitation analysis revealed euchromatinization of the globin promoter and enhanced NRF2 binding in RepID-depleted cells, suggesting a mechanism of gene expression regulation during erythropoiesis.

CONCLUSION

This study demonstrates that TWS119 can induce erythropoiesis in K562 cells, and that RepID depletion enhances this process by modulating chromatin structure and facilitating transcription factor binding. These findings highlight a RepID-dependent mechanism in the regulation of gene expression during erythropoiesis.

Bidirectional interplay between metabolism and epigenetics in hematopoietic stem cells and leukemia

During the last decades, remarkable progress has been made in further understanding the complex molecular regulatory networks that maintain hematopoietic stem cell (HSC) function. Cellular and organismal metabolisms have been shown to directly instruct epigenetic alterations, and thereby dictate stem cell fate, in the bone marrow. Epigenetic regulatory enzymes are dependent on the availability of metabolites to facilitate DNA- and histone-modifying reactions. The metabolic and epigenetic features of HSCs and their downstream progenitors can be significantly altered by environmental perturbations, dietary habits, and hematological diseases. Therefore, understanding metabolic and epigenetic mechanisms that regulate healthy HSCs can contribute to the discovery of novel metabolic therapeutic targets that specifically eliminate leukemia stem cells while sparing healthy HSCs. Here, we provide an in-depth review of the metabolic and epigenetic interplay regulating hematopoietic stem cell fate. We discuss the influence of metabolic stress stimuli, as well as alterations occurring during leukemic development. Additionally, we highlight recent therapeutic advancements toward eradicating acute myeloid leukemia cells by intervening in metabolic and epigenetic pathways.

Extirpating the cancer stem cell hydra: Differentiation therapy and Hyperthermia therapy for targeting the cancer stem cell hierarchy

Ever since the discovery of cancer stem cells (CSCs), they have progressively attracted more attention as a therapeutic target. Like the mythical hydra, this subpopulation of cells seems to contribute to cancer immortality, spawning more cells each time that some components of the cancer cell hierarchy are destroyed. Traditional modalities focusing on cancer treatment have emphasized apoptosis as a route to eliminate the tumor burden. A major problem is that cancer cells are often in varying degrees of dedifferentiation contributing to what is known as the CSCs hierarchy and cells which are known to be resistant to conventional therapy. Differentiation therapy is an experimental therapeutic modality aimed at the conversion of malignant phenotype to a more benign one. Hyperthermia therapy (HT) is a modality exploiting the changes induced in cells by the application of heat produced to aid in cancer therapy. While differentiation therapy has been successfully employed in the treatment of acute myeloid leukemia, it has not been hugely successful for other cancer types. Mounting evidence suggests that hyperthermia therapy may greatly augment the effects of differentiation therapy while simultaneously overcoming many of the hard-to-treat facets of recurrent tumors. This review summarizes the progress made so far in integrating hyperthermia therapy with existing modules of differentiation therapy. The focus is on studies related to the successful application of both hyperthermia and differentiation therapy when used alone or in conjunction for hard-to-treat cancer cell niche with emphasis on combined approaches to target the CSCs hierarchy.

Loss of the mitochondrial protein Abcb10 results in altered arginine metabolism in MEL and K562 cells and nutrient stress signaling through ATF4

Abcb10 is a mitochondrial membrane protein involved in hemoglobinization of red cells. Abcb10 topology and ATPase domain localization suggest it exports a substrate, likely biliverdin, out of mitochondria that is necessary for hemoglobinization. In this study, we generated Abcb10 deletion cell lines in both mouse murine erythroleukemia and human erythroid precursor human myelogenous leukemia (K562) cells to better understand the consequences of Abcb10 loss. Loss of Abcb10 resulted in an inability to hemoglobinize upon differentiation in both K562 and mouse murine erythroleukemia cells with reduced heme and intermediate porphyrins and decreased levels of aminolevulinic acid synthase 2 activity. Metabolomic and transcriptional analyses revealed that Abcb10 loss gave rise to decreased cellular arginine levels, increased transcripts for cationic and neutral amino acid transporters with reduced levels of the citrulline to arginine converting enzymes argininosuccinate synthetase and argininosuccinate lyase. The reduced arginine levels in Abcb10-null cells gave rise to decreased proliferative capacity. Arginine supplementation improved both Abcb10-null proliferation and hemoglobinization upon differentiation. Abcb10-null cells showed increased phosphorylation of eukaryotic translation initiation factor 2 subunit alpha, increased expression of nutrient sensing transcription factor ATF4 and downstream targets DNA damage inducible transcript 3 (Chop), ChaC glutathione specific gamma-glutamylcyclotransferase 1 (Chac1), and arginyl-tRNA synthetase 1 (Rars). These results suggest that when the Abcb10 substrate is trapped in the mitochondria, the nutrient sensing machinery is turned on remodeling transcription to block protein synthesis necessary for proliferation and hemoglobin biosynthesis in erythroid models.

Replication of Dengue Virus in K562-Megakaryocytes Induces Suppression in the Accumulation of Reactive Oxygen Species

Dengue virus can infect human megakaryocytes leading to decreased platelet biogenesis. In this article, we report a study of Dengue replication in human K562 cells undergoing PMA-induced differentiation into megakaryocytes. PMA-induced differentiation in these cells recapitulates steps of megakaryopoiesis including gene activation, expression of CD41/61 and CD61 platelet surface markers and accumulation of intracellular reactive oxygen species (ROS). Our results show differentiating megakaryocyte cells to support higher viral replication without any apparent increase in virus entry. Further, Dengue replication suppresses the accumulation of ROS in differentiating cells, probably by only augmenting the activity of the transcription factor NFE2L2 without influencing the expression of the coding gene. Interestingly pharmacological modulation of NFE2L2 activity showed a simultaneous but opposite effect on intracellular ROS and virus replication suggesting the former to have an inhibitory effect on the later. Also cells that differentiated while supporting intracellular virus replication showed reduced level of surface markers compared to uninfected differentiated cells.

A rapid spectrophotometric method to identify inhibitors of human erythropoiesis

Erythropoiesis is a complex physiological process by which erythroid progenitors proliferate and differentiate into nonnucleated red blood cells. Several methods can be used to monitor in vitro the differentiation of erythroid precursors, and hence the toxic effects of drugs, chemicals, or pollutants. One of the most commonly available assay of erythropoiesis is the microscopic observation of differentiated cells after benzidine staining, which forms a blue complex with hemoglobin. However, this method is laborious and does not provide accurate results since it heavily relies on the reader's interpretation. Moreover, benzidine is a carcinogen and a highly reactive molecule which forces the reader to microscopically count differentiated and non-differentiated cells within a short time frame (5 min). Here we have developed a simple, inexpensive, in-vitro spectrophotometric assay to measure erythroid differentiation using K562 cell line as a model. Materials needed included 96-well round-bottomed microplates and a microplate reader. Remarkably, carcinogenic benzidine was replaced by its isomeric tetramethyl derivative, the 3,3', 5,5'- tetramethylbenzidine (TMB), which presents several advantages: it is cheap, not mutagenic and a ready-to-use chromogenic substrate. A small volume (50 μl) of TMB added to the samples forms a blue complex in 15 min, and the reaction can be easily stopped and stabilized by the addition of H₂SO₄. The yellow precipitate is then solubilized, and the absorbance is measured at 450 nm. In addition, the suitability of the assay to determine the effects of compounds on erythroid differentiation was further tested with known inhibitors (artemisinin derivatives) of K562 differentiation. Overall, the reported methodology permits to measure in an accurate and reproducible manner the K562 differentiation and can be used for medium throughput screenings (MTS) of compounds or environmental toxics with potential erythro-toxicity and ability to inhibit erythroid differentiation.

MS4A3-HSP27 target pathway reveals potential for haematopoietic disorder treatment in alimentary toxic aleukia

Alimentary toxic aleukia (ATA) is correlated with consuming grains contaminated by Fusarium species, particularly T-2 toxin, which causes serious hurt to human and animal health, chiefly in disorders of the haematopoietic system. However, the mechanism of haematopoietic dysfunction induced by T-2 toxin and the possible target pathway for the treatment of T-2 toxin-induced haematopoietic disorder of ATA remains unclear. In this study, genomes and proteomics were used for the first time to investigate the key differential genes and proteins that inhibit erythroid differentiation of K562 cells caused by T-2 toxin, and it was found that heat shock protein 27 (HSP27) and membrane-spanning 4-domains, subfamily A, member 3 (MS4A3) may play an important role in erythroid differentiation. Meanwhile, MS4A3 interference can inhibit the occurrence of erythroid differentiation of K562 cells and promote the phosphorylation of HSP27. Moreover, the binding of HSP27 to MS4A3 in natural state can activate the phosphorylation site of HSP27 (Ser-83), while T-2 toxin can abolish the activation of phosphorylation site by inhibiting the expression of MS4A3. These findings for the first time demonstrated that the MS4A3-HSP27 pathway may function an efficient therapeutic target pathway for treating T-2 toxin elicited haematopoietic disorders of ATA.

Cilostazol-mediated reversion of γ-globin silencing is associated with a high level of HbF production: A potential therapeutic candidate for β-globin disorders

Reversal of fetal hemoglobin (HbF) silencing is an attractive therapeutic intervention for β-thalassemia and sickle cell anemia. The current study proposes the therapeutic of repurposing of cilostazol, an FDA-approved antithrombotic agent, as a promising HbF inducer. Preliminary, we report that cilostazol induced erythroid differentiation and hemoglobinization of human erythroleukemia K562 cells. The erythroid differentiation was accompanied by increased expression of γ-globin mRNA transcripts and HbF production. Cilostazol induced erythroid differentiation and HbF production, without significantly affecting proliferation and viability of hemoglobin producing cells at maximum erythroid inducing concentration. Moreover, we investigated the effect of cilostazol on human β- and γ-globin transgenes in in vivo β-YAC transgenic mice, harboring human β-locus along with β-LCR. A good in vitro correlation was found with substantial up-regulation in fetal globin mRNA; whereas, the β-globin gene expression was not significantly changed. F-cells, analysis in the peripheral blood of cilostazol-treated mice, revealed a significant increase in the F-cells population as compared with sham control groups. Together, these findings support the potential of cilostazol as an HbF inducer, which can be evaluated further to develop a new HbF inducer.

Methylation of dual-specificity phosphatase 4 controls cell differentiation

Mitogen-activated protein kinases (MAPKs) are inactivated by dual-specificity phosphatases (DUSPs), the activities of which are tightly regulated during cell differentiation. Using knockdown screening and single-cell transcriptional analysis, we demonstrate that DUSP4 is the phosphatase that specifically inactivates p38 kinase to promote megakaryocyte (Mk) differentiation. Mechanistically, PRMT1-mediated methylation of DUSP4 triggers its ubiquitinylation by an E3 ligase HUWE1. Interestingly, the mechanistic axis of the DUSP4 degradation and p38 activation is also associated with a transcriptional signature of immune activation in Mk cells. In the context of thrombocytopenia observed in myelodysplastic syndrome (MDS), we demonstrate that high levels of p38 MAPK and PRMT1 are associated with low platelet counts and adverse prognosis, while pharmacological inhibition of p38 MAPK or PRMT1 stimulates megakaryopoiesis. These findings provide mechanistic insights into the role of the PRMT1-DUSP4-p38 axis on Mk differentiation and present a strategy for treatment of thrombocytopenia associated with MDS.

Cabozantinib promotes erythroid differentiation in K562 erythroleukemia cells through global changes in gene expression and JNK activation

Cabozantinib is a potent tyrosine kinase inhibitor with multiple targets including MET, VEGFR2, RET, KIT, and FLT3. Cabozantinib is widely used for the treatment of medullary thyroid cancer and renal cell carcinoma. We recently suggested cabozantinib as a potential therapeutic alternative for acute myeloid leukemia (AML) patients with FLT3-internal tandem duplication (FLT3-ITD). Here, we report that cabozantinib can promote differentiation in erythroid leukemia cells. We found that K562 erythroid leukemia cells treated with 1 μM cabozantinib for 72 h underwent erythroid lineage differentiation. Transcriptomic analysis revealed that various pathways associated with heme biosynthesis, hemoglobin production, and GATA1 targets were upregulated, whereas cell survival pathways were downregulated. Further examination revealed that cabozantinib-induced erythroid differentiation is at least in part regulated by JNK activation and phosphorylation. Levels of phosphorylated BCR-ABL, AKT, STAT5, ERK, and p38 also decreased following cabozantinib treatment. Therefore, we indicate that cabozantinib has dual functions. First, it induces K562 cell differentiation toward the erythroid lineage by upregulating heme biosynthesis, globin synthesis, and erythroid-associated reactions. Second, cabozantinib inhibits K562 cell proliferation by inhibiting the phosphorylation of BCR-ABL and the downstream MAPK, PI3K-AKT, and JAK-STAT signaling pathways.

Control of fetal globin expression in man: new opportunities to challenge past discoveries

Decades-old findings supporting origin of F cells in adult life from adult-type progenitors and the in vitro and in vivo enhancement of fetal globin under stress conditions have been juxtaposed against recent mechanistic underpinnings. An updated molecular interrogation did not debunk prior conclusions on the origin of F cells. Although fetal globin reactivation by widely diverse approaches in vitro and in response to anemic stresses in vivo is a work in progress, accumulating evidence converges toward an integrated stress response pathway. The newly uncovered developmental regulators of globin gene switching not only have provided answers to the long-awaited quest of transregulation of switching, they are also reaching a clinical threshold. Although the effect of fetal globin silencers has been robustly validated in adult cells, the response of cells at earlier developmental stages has been unclear and inadequately studied.

Genetic screens reveal CCDC115 as a modulator of erythroid iron and heme trafficking

Transferrin-bound iron (TBI), the physiological circulating iron form, is acquired by cells through the transferrin receptor (TfR1) by endocytosis. In erythroid cells, most of the acquired iron is incorporated into heme in the mitochondria. Cellular trafficking of heme is indispensable for erythropoiesis and many other essential biological processes. Comprehensive elucidation of molecular pathways governing and regulating cellular iron acquisition and heme trafficking is required to better understand physiological and pathological processes affecting erythropoiesis. Here, we report the first genome-wide clustered regularly interspaced short palindromic repeats (CRISPR) screens in human erythroid cells to identify determinants of iron and heme uptake, as well as heme-mediated erythroid differentiation. We identified several candidate modulators of TBI acquisition including TfR1, indicating that our approach effectively revealed players mechanistically relevant to the process. Interestingly, components of the endocytic pathway were also revealed as potential determinants of transferrin acquisition. We deciphered a role for the vacuolar-type H+ - ATPase (V- ATPase) assembly factor coiled-coil domain containing 115 (CCDC115) in TBI uptake and validated this role in CCDC115 deficient K562 cells. Our screen in hemin-treated cells revealed perturbations leading to cellular adaptation to heme, including those corresponding to trafficking mechanisms and transcription factors potentiating erythroid differentiation. Pathway analysis indicated that endocytosis and vesicle acidification are key processes for heme trafficking in erythroid precursors. Furthermore, we provided evidence that CCDC115, which we identified as required for TBI uptake, is also involved in cellular heme distribution. This work demonstrates a previously unappreciated common intersection in trafficking of transferrin iron and heme in the endocytic pathway of erythroid cells.

Dendritic Cell-Restricted Progenitors Contribute to Obesity-Associated Airway Inflammation via Adam17-p38 MAPK-Dependent Pathway

Proliferation of dendritic cell (DC)—restricted progenitor cells in bone marrow compartment is tightly regulated at steady state and responds to multiple tissue-specific triggers during disturbed homeostasis such as obesity. DCs in the lung stem from a rapidly dividing DC-restricted progenitor cells and are effective at generating adaptive immune responses in allergic airway inflammation. Precisely, how DC-restricted progenitor expansion and differentiation are influenced by airway inflammation to maintain constant supply of myeloid DCs is poorly understood. Here we show that a high fat diet (HFD) induces oxidative stress and accelerates the expansion of DC- restricted progenitor cells in bone marrow and correlates with persistent induction of p38 mitogen activated protein kinase (MAPK), which is blocked with a selective p38α/β MAPK inhibitor. Mice fed a HFD and sensitized to inhaled allergen house dust mite (HDM) led to alterations of DC- restricted progenitor cells that were characterized by increased expansion and seeding of lung DCs in airway inflammation. Mechanistically, we establish that the expansion induced by HFD dysregulates the expression of a disintegrin and metallopeptidase domain 17 (Adam17) and is required for p38 MAPK activation in DC-restricted progenitors. These results demonstrates that obesity produces persistent changes in DC precursors and that elevation of Adam17 expression is tightly coupled to p38 MAPK and is a key driver of proliferation. Altogether, these data provide phenotypic and mechanistic insight into dendritic cell supply chain in obesity-associated airway inflammation.

Proteomic Studies for the Investigation of γ-Globin Induction by Decitabine in Human Primary Erythroid Progenitor Cultures

Reactivation of γ-globin is considered a promising approach for the treatment of β-thalassemia and sickle cell disease. Therapeutic induction of γ-globin expression, however, is fraught with lack of suitable therapeutic targets. The aim of this study was to investigate the effects that treatment with decitabine has on the proteome of human primary erythroid cells from healthy and thalassemic volunteers, as a means of identifying new potential pharmacological targets. Decitabine is a known γ-globin inducer, which is not, however, safe enough for clinical use. A proteomic approach utilizing isobaric tags for relative and absolute quantitation (iTRAQ) analysis, in combination with high-pH reverse phase peptide fractionation followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), was employed to investigate the effects of decitabine treatment. Bioinformatics analysis making use of the Database for Annotation, Visualization and Integrated Discovery (DAVID) was employed for functional annotation of the 192 differentially expressed proteins identified. The data are available via ProteomeXchange with identifier PXD006889. The proteins fall into various biological pathways, such as the NF-κB signaling pathway, and into many functional categories including regulation of cell proliferation, transcription factor and DNA binding, protein stabilization, chromatin modification and organization, and oxidative stress proteins.

Sideroflexin 4 affects Fe-S cluster biogenesis, iron metabolism, mitochondrial respiration and heme biosynthetic enzymes

Sideroflexin4 (SFXN4) is a member of a family of nuclear-encoded mitochondrial proteins. Rare germline mutations in SFXN4 lead to phenotypic characteristics of mitochondrial disease including impaired mitochondrial respiration and hematopoetic abnormalities. We sought to explore the function of this protein. We show that knockout of SFXN4 has profound effects on Fe-S cluster formation. This in turn diminishes mitochondrial respiratory chain complexes and mitochondrial respiration and causes a shift to glycolytic metabolism. SFXN4 knockdown reduces the stability and activity of cellular Fe-S proteins, affects iron metabolism by influencing the cytosolic aconitase-IRP1 switch, redistributes iron from the cytosol to mitochondria, and impacts heme synthesis by reducing levels of ferrochelatase and inhibiting translation of ALAS2. We conclude that SFXN4 is essential for normal functioning of mitochondria, is necessary for Fe-S cluster biogenesis and iron homeostasis, and plays a critical role in mitochondrial respiration and synthesis of heme.

Conjugate prodrug AN-233 induces fetal hemoglobin expression in sickle erythroid progenitors and β-YAC transgenic mice

Pharmacologic induction of fetal hemoglobin (HbF) is an effective strategy for treating sickle cell disease (SCD) by ameliorating disease severity. Hydroxyurea is the only FDA-approved agent that induces HbF, but significant non-responders and requirement for frequent monitoring of blood counts for drug toxicity limit clinical usefulness. Therefore, we investigated a novel prodrug conjugate of butyric acid (BA) and δ-aminolevulinate (ALA) as a potential HbF inducing agent, using erythroid precursors and a preclinical β-YAC mouse model. We observed significantly increased γ-globin gene transcription and HbF expression mediated by AN-233 in K562 cells. Moreover, AN-233 stimulated mild heme biosynthesis and inhibited expression of heme-regulated eIF2α kinase involved in silencing γ-globin expression. Studies using primary erythroid precursors generated from sickle peripheral blood mononuclear cells verified the ability of AN-233 to induce HbF, increase histone H3 and H4 acetylation levels at the γ-globin promoter and reduce erythroid precursor sickling by 50%. Subsequent drug treatment of β-YAC transgenic mice confirmed HbF induction in vivo by AN-233 through an increase in the percentage of HbF positive red blood cells and HbF levels measured by flow cytometry. These data support the potential development of AN-233 for the treatment of SCD.

Thiourea derivatives induce fetal hemoglobin production in-vitro: A new class of potential therapeutic agents for β-thalassemia

Fetal hemoglobin (HbF) induction is a cost-effective therapeutic approach for the treatment of β-hemoglobinopathies like β-thalassemia and sickle cell anemia. The present study discusses the potential of thiourea derivatives as new class of compounds that induce the fetal hemoglobin production. HbF inducing effect of thiourea derivatives was studied using experimental cell system, the human erythroleukemic K562 cell line. Erythroid induction of K562 cells was studied by the benzidine/H₂O₂ reaction, total hemoglobin production was estimated by plasma hemoglobin assay kit, and γ-globin gene expression by RT-qPCR, whereas fetal hemoglobin production was estimated by flow cytometry and immunofluorescence microscopy. The results indicated that newly synthesized thiourea derivative are potent inducers of erythroid differentiation of K562 cells with an increased γ-globin gene expression and fetal hemoglobin production. Moreover, these compounds showed no cytotoxic effect and inhibition on K562 cells at HbF inducing concentrations. It is important to note that hydroxyurea is a cytotoxic chemotherapeutic agent and have deleterious side effects, reflecting the need to identify new safe and effective HbF induces. These results signify thiourea derivatives as promising HbF inducers, with the potential to be studied against hematological disorders, including β-thalassemia and sickle cell anemia.

TRPM7-mediated spontaneous Ca2+ entry regulates the proliferation and differentiation of human leukemia cell line K562

Continuous Ca2+ influx is essential to maintain intracellular Ca2+ homeostasis and its dysregulation leads to a variety of cellular dysfunctions. In this study, we explored the functional roles of spontaneous Ca2+ influx for the proliferation and differentiation of a human erythromyeloid leukemia cell line K562. mRNA/protein expressions were assessed by the real-time RT-PCR, western blotting, and immunocytochemical staining. Intracellular Ca2+ concentration ([Ca2+ ]i ) and ionic currents were measured by fluorescent imaging and patch clamping techniques, respectively. Cell counting/viability and colorimetric assays were applied to assess proliferation rate and hemoglobin synthesis, respectively. Elimination of extracellular Ca2+ decreased basal [Ca2+ ]i in proliferating K562 cells. Cation channel blockers such as SK&F96365, 2-APB, Gd3+ , and FTY720 dose dependently decreased basal [Ca2+ ]i . A spontaneously active inward current (Ispont ) contributive to basal [Ca2+ ]i was identified by the nystatin-perforated whole-cell recording. Ispont permeated Ca2+ comparably to Na+ , and was greatly eliminated by siRNA targeting TRPM7, a melastatin member of the transient receptor potential (TRP) superfamily. Consistent with these findings, TRPM7 immune reactivity was detected by western blotting, and immunofluorescence representing TRPM7 was found localized to the K562 cell membrane. Strikingly, all these procedures, that is, Ca2+ removal, TRPM7 blockers and siRNA-mediated TRPM7 knockdown significantly retarded the growth and suppressed hemin-induced γ-globin and hemoglobin syntheses in K562 cells, respectively, both of which appeared associated with the inhibition of ERK activation. These results collectively suggest that spontaneous Ca2+ influx through constitutively active TRPM7 channels may critically regulate both proliferative and erythroid differentiation potentials of K562 cells.

Generation of erythroid cells from polyploid giant cancer cells: re-thinking about tumor blood supply

INTRODUCTION

During development and tumor progression, cells need a sufficient blood supply to maintain development and rapid growth. It is reported that there are three patterns of blood supply for tumor growth: endothelium-dependent vessels, mosaic vessels, and vasculogenic mimicry (VM). VM was first reported in highly aggressive uveal melanomas, with tumor cells mimicking the presence and function of endothelial cells forming the walls of VM vessels. The walls of mosaic vessels are randomly lined with both endothelial cells and tumor cells. We previously proposed a three-stage process, beginning with VM, progressing to mosaic vessels, and eventually leading to endothelium-dependent vessels. However, many phenomena unique to VM channel formation remain to be elucidated, such as the origin of erythrocytes before VM vessels connect with endothelium-dependent vessels.

RESULTS

In adults, erythroid cells are generally believed to be generated from hematopoietic stem cells in the bone marrow. In contrast, embryonic tissue obtains oxygen through formation of blood islands, which are largely composed of embryonic hemoglobin with a higher affinity with oxygen, in the absence of mature erythrocytes. Recent data from our laboratory suggest that embryonic blood-forming mechanisms also exist in cancer tissue, particularly when these tissues are under environmental stress such as hypoxia. We review the evidence from induced pluripotent stem cells in vitro and in vivo to support this previously underappreciated cell functionality in normal and cancer cells, including the ability to generate erythroid cells. We will also summarize the current understanding of tumor angiogenesis, VM, and our recent work on polyploid giant cancer cells, with emphasis on their ability to generate erythroid cells and their association with tumor growth under hypoxia.

CONCLUSION

An alternative embryonic pathway to obtain oxygen in cancer cells exists, particularly when they are under hypoxic conditions.

Hepatic inflammation caused by dysregulated bile acid synthesis is reversible by butyrate supplementation

Dysregulated bile acid (BA) synthesis or reduced farnesoid X receptor (FXR) levels are found in patients having metabolic diseases, autoimmune hepatitis, and liver cirrhosis or cancer. The objective of this study was to establish the relationship between butyrate and dysregulated BA synthesis-induced hepatitis as well as the effect of butyrate in reversing the liver pathology. Wild-type (WT) and FXR knockout (KO) male mice were placed on a control (CD) or western diet (WD) for 15 months. In the presence or absence of butyrate supplementation, feces obtained from 15-month-old WD-fed FXR KO mice, which had severe hepatitis and liver tumors, were transplanted to 7-month-old WD-fed FXR KO for 3 months. Hepatic phenotypes, microbiota profile, and BA composition were analyzed. Butyrate-generating bacteria and colonic butyrate concentration were reduced due to FXR inactivation and further reduced by WD intake. In addition, WD-fed FXR KO male mice had the highest concentration of hepatic β-muricholic acid (β-MCA) and bacteria-generated deoxycholic acid (DCA) accompanied by serious hepatitis. Moreover, dysregulated BA and reduced SCFA signaling co-existed in both human liver cancers and WD-fed FXR KO mice. Microbiota transplantation using butyrate-deficient feces derived from 15-month-old WD-fed FXR KO mice increased hepatic lymphocyte numbers as well as hepatic β-MCA and DCA concentrations. Furthermore, butyrate supplementation reduced hepatic β-MCA as well as DCA and eliminated hepatic lymphocyte infiltration. In conclusion, reduced butyrate contributes to the development of hepatitis in the FXR KO mouse model. In addition, butyrate reverses dysregulated BA synthesis and its associated hepatitis. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Induction of GD3/α1-adrenergic receptor/transglutaminase 2-mediated erythroid differentiation in chronic myelogenous leukemic K562 cells

The disialic acid-containing glycosphingolipid GD3 recruited membrane transglutaminase 2 (TG2) as a signaling molecule for erythroid differentiation in human chronic myelogenous leukemia (CML) K562 cells. The α1-adrenergic receptor (α1-AR)/TG2-mediated signaling pathway regulated GD3 functions, including gene expression and production, to differentiate CML K562 cells into erythroid lineage cells. Epinephrine, an AR agonist, increased membrane recruitment as well as GTP-photoaffinity of TG2, inducing GD3 synthase gene expression. Epinephrine activated PI3K/Akt signaling and GTPase downstream of TG2 activated Akt. The coupling of TG2 and GD3 production was specifically suppressed by prazosin (α1-AR antagonist), but not by propranolol (β-AR antagonist) or rauwolscine (α2-AR antagonist), indicating α1-AR specificity. Small interfering RNA (siRNA) experiment results indicated that the α1-AR/TG2-mediated signaling pathway activated PKCs α and δ to induce GD3 synthase gene expression. Transcription factors CREB, AP-1, and NF-κB regulated GD3 synthase gene expression during α1-AR-induced differentiation in CML K562 cells. In addition, GD3 synthase gene expression was upregulated in TG2-transfected cells via α1-AR with expression of erythroid lineage markers and benzidine-positive staining. α1-AR/TG2 signaling pathway-directed GD3 production is a crucial step in erythroid differentiation of K562 cells and GD3 interacts with α1-AR/TG2, inducing GD3/α1-AR/TG2-mediated erythroid differentiation. These results suggest that GD3, which acts as a membrane mediator of erythroid differentiation in CML cells, provides a therapeutic avenue for leukemia treatment.

Involvement of Band3 in the efflux of sphingosine 1-phosphate from erythrocytes

Sphingosine 1-phosphate (S1P) is a bioactive lipid mediator that is thought to be involved in various diseases. Although the main source of S1P in the plasma is erythrocytes, how S1P is exported from erythrocytes has not been elucidated. When we differentiated K562 cells into erythroblast-like cells with sodium butyrate, we observed that the efflux of S1P was increased without increased expression of previously proposed S1P transporters, while the expression levels of Band3 were increased. Therefore, in this study, we investigated the involvement of Band 3, the most characteristic membranous transporter for erythrocytes, in S1P efflux, using 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonic acid, disodium salt (H2DIDS), which is an inhibitor of Band3. First, we treated human washed erythrocytes with H₂DIDS and found that H₂DIDS decreased the S1P levels in the supernatant, while it increased the cellular S1P contents. Next, when we injected H₂DIDS into mice, the plasma S1P level was significantly decreased. Finally, when we overexpressed or suppressed Band3 in K562 cells, S1P efflux was enhanced or decreased, respectively, while the overexpression of Band3 in HEK293 cells did not modulate S1P efflux. These results suggested the possible involvement of Band3 in the transport of S1P, a multi-functional bioactive phospholipid, from erythrocytes.

Notch1-promoted TRPA1 expression in erythroleukemic cells suppresses erythroid but enhances megakaryocyte differentiation

The Notch1 pathway plays important roles in modulating erythroid and megakaryocyte differentiation. To screen the Notch1-related genes that regulate differentiation fate of K562 and HEL cells, the expression of transient receptor potential ankyrin 1 (TRPA1) was induced by Notch1 receptor intracellular domain (N1IC), the activated form of Notch1 receptor. N1IC and v-ets erythroblastosis virus E26 oncogene homolog 1 (Ets-1) bound to TRPA1 promoter region to regulate transcription in K562 cells. Transactivation of TRPA1 promoter by N1IC depended on the methylation status of TRPA1 promoter. N1IC and Ets-1 suppressed the DNA methyltransferase 3B (DNMT3B) level in K562 cells. Inhibition of TRPA1 expression after Notch1 knockdown could be attenuated by nanaomycin A, an inhibitor of DNMT3B, in K562 and HEL cells. Functionally, hemin-induced erythroid differentiation could be suppressed by TRPA1, and the reduction of erythroid differentiation of both cells by N1IC and Ets-1 occurred via TRPA1. However, PMA-induced megakaryocyte differentiation could be enhanced by TRPA1, and the surface markers of megakaryocytes could be elevated by nanaomycin A. Megakaryocyte differentiation could be reduced by Notch1 or Ets-1 knockdown and relieved by TRPA1 overexpression. The results suggest that Notch1 and TRPA1 might be critical modulators that control the fate of erythroid and megakaryocyte differentiation.

Histone deacetylase inhibitors suppress ABO transcription in vitro, leading to reduced expression of the antigens

BACKGROUND

The ABO system is of fundamental importance in the fields of transfusion and transplantation and has apparent associations with certain diseases, including cardiovascular disorders. ABO expression is reduced in the late phase of erythroid differentiation in vitro, whereas histone deacetylase inhibitors (HDACIs) are known to promote cell differentiation. Therefore, whether or not HDACIs could reduce the amount of ABO transcripts and A or B antigens is an intriguing issue.

STUDY DESIGN AND METHODS

Quantitative polymerase chain reactions were carried out for the ABO transcripts in erythroid-lineage K562 and epithelial-lineage KATOIII cells after incubation with HDACIs, such as sodium butyrate, panobinostat, vorinostat, and sodium valproate. Flow cytometric analysis was conducted to evaluate the amounts of antigen in KATOIII cells treated with panobinostat. Quantitative chromatin immunoprecipitation (ChIP) assays and luciferase assays were performed on both cell types to examine the mechanisms of ABO suppression.

RESULTS

HDACIs reduced the ABO transcripts in both K562 and KATOIII cells, with panobinostat exerting the most significant effect. Flow cytometric analysis demonstrated a decrease in B-antigen expression on panobinostat-treated KATOIII cells. ChIP assays indicated that panobinostat altered the modification of histones in the transcriptional regulatory regions of ABO, and luciferase assays demonstrated reduced activity of these elements.

CONCLUSION

ABO transcription seems to be regulated by an epigenetic mechanism. Panobinostat appears to suppress ABO transcription, reducing the amount of antigens on the surface of cultured cells.

A Novel Role for Progesterone Receptor Membrane Component 1 (PGRMC1): A Partner and Regulator of Ferrochelatase

Heme is an iron-containing cofactor essential for multiple cellular processes and fundamental activities such as oxygen transport. To better understand the means by which heme synthesis is regulated during erythropoiesis, affinity purification coupled with mass spectrometry (MS) was performed to identify putative protein partners interacting with ferrochelatase (FECH), the terminal enzyme in the heme biosynthetic pathway. Both progesterone receptor membrane component 1 (PGRMC1) and progesterone receptor membrane component 2 (PGRMC2) were identified in these experiments. These interactions were validated by reciprocal affinity purification followed by MS analysis and immunoblotting. The interaction between PGRMC1 and FECH was confirmed in vitro and in HEK 293T cells, a non-erythroid cell line. When cells that are recognized models for erythroid differentiation were treated with a small molecule inhibitor of PGRMC1, AG-205, there was an observed decrease in the level of hemoglobinization relative to that of untreated cells. In vitro heme transfer experiments showed that purified PGRMC1 was able to donate heme to apo-cytochrome b5. In the presence of PGRMC1, in vitro measured FECH activity decreased in a dose-dependent manner. Interactions between FECH and PGRMC1 were strongest for the conformation of FECH associated with product release, suggesting that PGRMC1 may regulate FECH activity by controlling heme release. Overall, the data illustrate a role for PGRMC1 in regulating heme synthesis via interactions with FECH and suggest that PGRMC1 may be a heme chaperone or sensor.

The SHP2-ERK2 signaling pathway regulates branched I antigen formation by controlling the binding of CCAAT/enhancer binding protein α to the IGnTC promoter region during erythroid differentiation

BACKGROUND

Phosphorylation status of the transcription factor CCAAT/enhancer binding protein α (C/EBPα) has been demonstrated in a human hematopoietic cell model to regulate the formation of branched I antigen by affecting its binding affinity to the promoter region of the IGnTC gene during erythroid and granulocytic differentiation.

STUDY DESIGN AND METHODS

The K-562 cell line was induced to differentiate into red blood cells (RBCs) or granulocytes by sodium butyrate or retinoic acid, respectively, to study the involvement of three MAP kinase pathways in I antigen synthesis. The regulatory effects of the extracellular signal-regulated kinase (ERK)2-Src homology region 2 domain-containing phosphatase 2 (SHP2) pathway on phosphorylation status and binding affinities of C/EBPα as well as the subsequent activation of IGnTC and synthesis of surface I formation were studied in wild-type K-562 cells and in mutant cells that overexpress ERK2 and SHP2.

RESULTS

We found that SHP2-ERK2 signaling regulates the phosphorylation status of C/EBPα to alter its binding affinity onto the IGnTC promoter region, thereby activating the synthesis of cell surface I antigen formation during erythropoiesis.

CONCLUSION

SHP2-ERK2 signaling acts upstream of C/EBPα as a regulator of cell surface I antigen synthesis. Such regulation is specific for RBC but not for granulocyte differentiation.

Comparison of different methods for erythroid differentiation in the K562 cell line

OBJECTIVE

To compare methods for erythroid differentiation of K562 cells that will be promising in the treatment of beta-thalassemia by inducing γ-globin synthesis.

RESULTS

Cells were treated separately with: RPMI 1640 medium without glutamine, RPMI 1640 medium without glutamine supplemented with 1 mM sodium butyrate, RPMI 1640 medium supplemented with 1 mM sodium butyrate, 25 µg cisplatin/ml, 0.1 µg cytosine arabinoside/ml. The highest differentiation (84 %) with minimum toxicity was obtained with cisplatin at 15 µg /ml. Real-time RT-PCR showed that expression of the γ-globin gene was significantly higher in the cells differentiated with cisplatin compared to undifferentiated cells (P < 0.001).

CONCLUSIONS

Cisplatin is useful in the experimental therapy of ß-globin gene defects and can be considered for examining the basic mechanism of γ-reactivation.

Butyrate regulates the expression of inflammatory and chemotactic cytokines in human acute leukemic cells during apoptosis

Butyrate is a histone deacetylase inhibitor implicated in many studies as a potential therapy for various forms of cancer. High concentrations of butyrate (>1.5mM) have been shown to activate apoptosis in several cancer cell lines including prostate, breast, and leukemia. Butyrate is also known to influence multiple signaling pathways that are mediators of cytokine production. The purpose of this study was to evaluate the impact of high concentrations of butyrate on the cancer microenvironment vis-à-vis apoptosis, cellular migration, and capacity to modulate cytokine expression in cancer cells. The results indicate that high concentrations of butyrate induced a 2-fold activation of caspase-3 and reduced cell viability by 60% in U937 leukemia cells. Within 24h, butyrate significantly decreased the levels of chemokines CCL2 and CCL5 in HL-60 and U937 cells, and decreased CCL5 in THP-1 leukemia cells. Differential effects were observed in treatments with valproic acid for CCL2 and CCL5 indicating butyrate-specificity. Many of the biological effects examined in this study are linked to activation of the AKT and MAPK signaling pathways; therefore, we investigated whether butyrate alters the levels of phosphorylated forms of these signaling proteins and how it correlated with the expression of chemokines. The results show that butyrate may partially regulate CCL5 production via p38 MAPK. The decrease in p-ERK1/2 and p-AKT levels correlated with the decrease in CCL2 production. These data suggest that while promoting apoptosis, butyrate has the potential to influence the cancer microenvironment by inducing differential expression of cytokines.

HDAC inhibitors cause site-specific chromatin remodeling at PU.1-bound enhancers in K562 cells

Background

Small molecule inhibitors of histone deacetylases (HDACi) hold promise as anticancer agents for particular malignancies. However, clinical use is often confounded by toxicity, perhaps due to indiscriminate hyperacetylation of cellular proteins. Therefore, elucidating the mechanisms by which HDACi trigger differentiation, cell cycle arrest, or apoptosis of cancer cells could inform development of more targeted therapies. We used the myelogenous leukemia line K562 as a model of HDACi-induced differentiation to investigate chromatin accessibility (DNase-seq) and expression (RNA-seq) changes associated with this process.

Results

We identified several thousand specific regulatory elements [~10 % of total DNase I-hypersensitive (DHS) sites] that become significantly more or less accessible with sodium butyrate or suberanilohydroxamic acid treatment. Most of the differential DHS sites display hallmarks of enhancers, including being enriched for non-promoter regions, associating with nearby gene expression changes, and increasing luciferase reporter expression in K562 cells. Differential DHS sites were enriched for key hematopoietic lineage transcription factor motifs, including SPI1 (PU.1), a known pioneer factor. We found PU.1 increases binding at opened DHS sites with HDACi treatment by ChIP-seq, but PU.1 knockdown by shRNA fails to block the chromatin accessibility and expression changes. A machine-learning approach indicates H3K27me3 initially marks PU.1-bound sites that open with HDACi treatment, suggesting these sites are epigenetically poised.

Conclusions

We find HDACi treatment of K562 cells results in site-specific chromatin remodeling at epigenetically poised regulatory elements. PU.1 shows evidence of a pioneer role in this process by marking poised enhancers but is not required for transcriptional activation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13072-016-0065-5) contains supplementary material, which is available to authorized users.

Voltage-Gated K+ Channel, Kv3.3 Is Involved in Hemin-Induced K562 Differentiation

Voltage-gated K⁺ (K_v) channels are well known to be involved in cell proliferation. However, even though cell proliferation is closely related to cell differentiation, the relationship between K_v channels and cell differentiation remains poorly investigated. This study demonstrates that K_v3.3 is involved in K562 cell erythroid differentiation. Down-regulation of K_v3.3 using siRNA-K_v3.3 increased hemin-induced K562 erythroid differentiation through decreased activation of signal molecules such as p38, cAMP response element-binding protein, and c-fos. Down-regulation of K_v3.3 also enhanced cell adhesion by increasing integrin β3 and this effect was amplified when the cells were cultured with fibronectin. The K_v channels, or at least K_v3.3, appear to be associated with cell differentiation; therefore, understanding the mechanisms of K_v channel regulation of cell differentiation would provide important information regarding vital cellular processes.

A novel miR-200b-3p/p38IP pair regulates monocyte/macrophage differentiation

Monocyte/macrophage differentiation represents a major branch of hematopoiesis and is a central event in the immune response, but the molecular mechanisms underlying are not fully delineated. Here we show that p38 mitogen-activated protein kinase (MAPK) interacting protein (p38IP) is downregulated during monocyte/macrophage differentiation in vitro. Overexpression of p38IP halted monocyte/macrophage differentiation, whereas forward knockdown of p38IP by RNA interference induced G1/S arrest and promoted monocyte differentiation into macrophages and the maturation of macrophages as well. Moreover, we found that miR-200b-3p was upregulated during monocyte/macrophage differentiation and mediated the downregulation of p38IP by binding to the 3′ untranslated terminal region of p38IP mRNA. Overexpression of a miR-200b-3p mimic resembled the effect of p38IP knockdown, whereas a miR-200b-3p inhibitor blocked monocyte/macrophage differentiation by enhancing p38IP expression. Further western blotting analysis revealed that p38IP downregulation enhanced the activity of p38 MAPK and the subsequent accumulation of cyclin-dependent kinase inhibitor p21, thus promoting G1/S arrest and monocyte/macrophage differentiation. Moreover, the decline of GCN5 acetyltransferase caused by p38IP downregulation was required but was not sufficient for monocyte/macrophage differentiation. This study demonstrated a new role for p38IP and a novel miR-200b-3p/p38IP pair in the regulation of monocyte/macrophage differentiation.

Functional characterization of the ectopically expressed olfactory receptor 2AT4 in human myelogenous leukemia

The olfactory receptor (OR) family was found to be expressed mainly in the nasal epithelium. In the last two decades members of the OR family were detected to be functional expressed in different parts of the human body such as in liver, prostate or intestine cancer cells. Here, we detected the expression of several ORs in the human chronic myelogenous leukemia (CML) cell line K562 and in white blood cells of clinically diagnosed acute myeloid leukemia (AML) patients by RT-PCR and next-generation sequencing. With calcium-imaging, we characterized in greater detail the cell biological role of one OR (OR2AT4) in leukemia. In both cell systems, the OR2AT4 agonist Sandalore-evoked strong Ca²⁺ influx via the adenylate cyclase-cAMP-mediated pathway. The OR2AT4 antagonist Phenirat prevented the Sandalore-induced intracellular Ca²⁺ increase. Western blot and flow cytometric experiments revealed that stimulation of OR2AT4 reduced the proliferation by decreasing p38-MAPK phosphorylation and induced apoptosis via phosphorylation of p44/42-MAPK. Furthermore, Sandalore increased the number of hemoglobin-containing cells in culture. We described for the first time an OR-mediated pathway in CML and AML that can regulate proliferation, apoptosis and differentiation after activation. This mechanism offers novel therapeutic options for the treatment of AML.

MiR-218 Inhibits Erythroid Differentiation and Alters Iron Metabolism by Targeting ALAS2 in K562 Cells

microRNAs (miRNAs) are involved in a variety of biological processes. The regulatory function and potential role of miRNAs targeting the mRNA of the 5'-aminolevulinate synthase 2 (ALAS2) in erythropoiesis were investigated in order to identify miRNAs which play a role in erythroid iron metabolism and differentiation. Firstly, the role of ALAS2 in erythroid differentiation and iron metabolism in human erythroid leukemia cells (K562) was confirmed by ALAS2 knockdown. Through a series of screening strategies and experimental validations, it was identified that hsa-miR-218 (miR-218) targets and represses the expression of ALAS2 by binding to the 3'-untranslated region (UTR). Overexpression of miR-218 repressed erythroid differentiation and altered iron metabolism in K562 cells similar to that seen in the ALAS2 knockdown in K562 cells. In addition to iron metabolism and erythroid differentiation, miR-218 was found to be responsible for a reduction in K562 cell growth. Taken together, our results show that miR-218 inhibits erythroid differentiation and alters iron metabolism by targeting ALAS2 in K562 cells.

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.

ERK2-Pyruvate Kinase Axis Permits Phorbol 12-Myristate 13-Acetate-induced Megakaryocyte Differentiation in K562 Cells

Metabolic changes that contribute to differentiation are not well understood. Overwhelming evidence shows the critical role of glycolytic enzyme pyruvate kinase (PK) in directing metabolism of proliferating cells. However, its role in metabolism of differentiating cells is unclear. Here we studied the role of PK in phorbol 12-myristate 13-acetate (PMA)-induced megakaryocytic differentiation in human leukemia K562 cells. We observed that PMA treatment decreased cancer-type anabolic metabolism but increased ATP production, along with up-regulated expression of two PK isoforms (PKM2 and PKR) in an ERK2-dependent manner. Interestingly, silencing of PK (PKM2 and PKR) inhibited PMA-induced megakaryocytic differentiation, as revealed by decreased expression of megakaryocytic differentiation marker CD61 and cell cycle behavior. Further, PMA-induced ATP production reduced greatly upon PK silencing, suggesting that PK is required for ATP synthesis. In addition to metabolic effects, PMA treatment also translocated PKM2, but not PKR, into nucleus. ERK1/2 knockdowns independently and together suggested the role of ERK2 in the up-regulation of both the isoforms of PK, proposing a role of ERK2-PK isoform axis in differentiation. Collectively, our findings unravel ERK2 guided PK-dependent metabolic changes during PMA induction, which are important in megakaryocytic differentiation.

Pharmacological Induction of Human Fetal Globin Gene in Hydroxyurea-Resistant Primary Adult Erythroid Cells

Pharmacological induction of the fetal γ globin gene and the consequent formation of HbF (α2/γ2) in adult erythroid cells are one feasible therapeutic strategy for sickle cell disease (SCD) and severe β-thalassemias. Hydroxyurea (HU) is the current drug of choice for SCD, but serious side effects limit its clinical use. Moreover, 30 to 50% of patients are irresponsive to HU treatment. We have used high-throughput screening to identify benzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one and its derivatives (compounds I to VI) as potent γ globin inducers. Of the compounds, I to V exert superior γ globin induction and have better therapeutic potential than HU, likely because of their activation of the p38 mitogen-activated protein kinase (MAPK) signaling pathway and modulation of expression levels and/or chromosome binding of γ globin gene regulators, including BCL11A, and chromatin structure over the γ globin promoter. Unlike sodium butyrate (NaB), the global levels of acetylated histones H3 and H4 are not changed by compound II treatment. Remarkably, compound II induces the γ globin gene in HU-resistant primary human adult erythroid cells, the p38 signaling pathway of which appears to be irresponsive to HU and NaB as well as compound II. This study provides a new framework for the development of new and superior compounds for treating SCD and severe β-thalassemias.

Natural Remedies for the Treatment of Beta-Thalassemia and Sickle Cell Anemia-Current Status and Perspectives in Fetal Hemoglobin Reactivation

For the treatment of β-thalassemia and sickle cell disease (SCD), pharmacological induction of fetal hemoglobin (HbF) production may be a promising approach. To date, numerous studies have been done on identifying the novel HbF-inducing agents and understanding the underlying mechanism for stimulating the HbF production. In this review, we have summarized the identified HbF-inducing agents by far. By examining the action mechanisms of the HbF-inducing agents, various studies have suggested that despite the ability of stimulating HbF production, the chemotherapeutic agents could not be practically applied for treating β-hemoglobinopathies, especially β-thalassemia, due to the their cytotoxicity and growth-inhibitory effect. Owing to this therapeutic obstacle, much effort has been put on identifying new HbF-inducing agents from the natural world with the combination of efficacy, safety, and ease of use. Therefore, this review aims to (i) reveal the novel screening platforms for identifying potential inducers with high efficiency and accuracy and to (ii) summarize the new identified natural remedies for stimulating HbF production. Hopefully, this review can provide a new insight into the current status and future perspectives in fetal hemoglobin reactivation for treating β-thalassaemia and SCD.

Erythroid differentiation is augmented in Reelin-deficient K562 cells and homozygous reeler mice

Reelin is an extracellular glycoprotein that is highly conserved in mammals. In addition to its expression in the nervous system, Reelin is present in erythroid cells but its function there is unknown. We report in this study that Reelin is up-regulated during erythroid differentiation of human erythroleukemic K562 cells and is expressed in the erythroid progenitors of murine bone marrow. Reelin deficiency promotes erythroid differentiation of K562 cells and augments erythroid production in murine bone marrow. In accordance with these findings, Reelin deficiency attenuates AKT phosphorylation of the Ter119(+)CD71(+) erythroid progenitors and alters the cell number and frequency of the progenitors at different erythroid differentiation stages. A regulatory role of Reelin in erythroid differentiation is thus defined.

Aclacinomycin A sensitizes K562 chronic myeloid leukemia cells to imatinib through p38MAPK-mediated erythroid differentiation

Expression of oncogenic Bcr-Abl inhibits cell differentiation of hematopoietic stem/progenitor cells in chronic myeloid leukemia (CML). Differentiation therapy is considered to be a new strategy for treating this type of leukemia. Aclacinomycin A (ACM) is an antitumor antibiotic. Previous studies have shown that ACM induced erythroid differentiation of CML cells. In this study, we investigate the effect of ACM on the sensitivity of human CML cell line K562 to Bcr-Abl specific inhibitor imatinib (STI571, Gleevec). We first determined the optimal concentration of ACM for erythroid differentiation but not growth inhibition and apoptosis in K562 cells. Then, pretreatment with this optimal concentration of ACM followed by a minimally toxic concentration of imatinib strongly induced growth inhibition and apoptosis compared to that with simultaneous co-treatment, indicating that ACM-induced erythroid differentiation sensitizes K562 cells to imatinib. Sequential treatment with ACM and imatinib induced Bcr-Abl down-regulation, cytochrome c release into the cytosol, and caspase-3 activation, as well as decreased Mcl-1 and Bcl-xL expressions, but did not affect Fas ligand/Fas death receptor and procaspase-8 expressions. ACM/imatinib sequential treatment-induced apoptosis was suppressed by a caspase-9 inhibitor and a caspase-3 inhibitor, indicating that the caspase cascade is involved in this apoptosis. Furthermore, we demonstrated that ACM induced erythroid differentiation through the p38 mitogen-activated protein kinase (MAPK) pathway. The inhibition of erythroid differentiation by p38MAPK inhibitor SB202190, p38MAPK dominant negative mutant or p38MAPK shRNA knockdown, reduced the ACM/imatinib sequential treatment-mediated growth inhibition and apoptosis. These results suggest that differentiated K562 cells induced by ACM-mediated p38MAPK pathway become more sensitive to imatinib and result in down-regulations of Bcr-Abl and anti-apoptotic proteins, growth inhibition and apoptosis. These results provided a potential management by which ACM might have a crucial impact on increasing sensitivity of CML cells to imatinib in the differentiation therapeutic approaches.

Plastrum testudinis induces γ-globin gene expression through epigenetic histone modifications within the γ-globin gene promoter via activation of the p38 MAPK signaling pathway

The pharmacologically-induced expression of the γ-globin gene, to increase fetal hemoglobin (HbF) production, is a therapeutic strategy used for the treatment of β-thalassemia and sickle cell anemia (SCA). The aim of this study was to investigate the effects of Plastrum testudinis (PT) on differentiation, proliferation, γ-globin gene expression and HbF synthesis in human erythroid cells. For this purpose, we used the K562 human leukemia cell line and human erythroid progenitor cells from normal donors and patients with β-thalassemia cultured using the two-phase liquid culture system. The effects of PT on erythroid differentiation, proliferation, γ-globin gene expression and HbF synthesis, as well as the involvement of epigenetic histone modifications within the γ-globin gene promoter via activation of the p38 mitogen-activated protein kinase (MAPK) signaling pathway, were assessed by benzidine staining, trypan-blue dye exclusion, quantitative real-time RT-PCR (qRT-PCR), western blot analysis and chromatin immunoprecipitation (ChIP). PT promoted the erythroid differentiation of K562 cells, and increased γ-globin mRNA accumulation and HbF synthesis without inhibiting cell proliferation in K562 cells and human erythroid progenitors. PT exerted no effect on α- and β-globin gene expression. In human erythroid cells, PT activated the p38 MAPK signaling pathway, and enhanced the acetylation of histone H3 and H4, the phosphorylation of histone H3 within the Gγ- and Aγ-globin gene promoter regions, γ-globin mRNA accumulation and HbF synthesis. These effects were suppressed by pre-treatment with the p38 MAPK inhibitor, SB203580. Epigenetic histone modifications within γ-globin gene promoter regions, via activation of the p38 MAPK signaling pathway, are important for the induction of γ-globin gene expression in human erythroid cells by PT. PT may be a novel potential therapeutic agent for β-hemoglobinopathies, including β-thalassemia and SCA.

High-efficiency transduction of primary human hematopoietic stem cells and erythroid lineage-restricted expression by optimized AAV6 serotype vectors in vitro and in a murine xenograft model in vivo

We have observed that of the 10 AAV serotypes, AAV6 is the most efficient in transducing primary human hematopoietic stem cells (HSCs), and that the transduction efficiency can be further increased by specifically mutating single surface-exposed tyrosine (Y) residues on AAV6 capsids. In the present studies, we combined the two mutations to generate a tyrosine double-mutant (Y705+731F) AAV6 vector, with which >70% of CD34⁺ cells could be transduced. With the long-term objective of developing recombinant AAV vectors for the potential gene therapy of human hemoglobinopathies, we generated the wild-type (WT) and tyrosine-mutant AAV6 vectors containing the following erythroid cell-specific promoters: β-globin promoter (βp) with the upstream hyper-sensitive site 2 (HS2) enhancer from the β-globin locus control region (HS2-βbp), and the human parvovirus B19 promoter at map unit 6 (B19p6). Transgene expression from the B19p6 was significantly higher than that from the HS2-βp, and increased up to 30-fold and up to 20-fold, respectively, following erythropoietin (Epo)-induced differentiation of CD34⁺ cells in vitro. Transgene expression from the B19p6 or the HS2-βp was also evaluated in an immuno-deficient xenograft mouse model in vivo. Whereas low levels of expression were detected from the B19p6 in the WT AAV6 capsid, and that from the HS2-βp in the Y705+731F AAV6 capsid, transgene expression from the B19p6 promoter in the Y705+731F AAV6 capsid was significantly higher than that from the HS2-βp, and was detectable up to 12 weeks post-transplantation in primary recipients, and up to 6 additional weeks in secondary transplanted animals. These data demonstrate the feasibility of the use of the novel Y705+731F AAV6-B19p6 vectors for high-efficiency transduction of HSCs as well as expression of the b-globin gene in erythroid progenitor cells for the potential gene therapy of human hemoglobinopathies such as β-thalassemia and sickle cell disease.

Histone deacetylase inhibitors suppress mechanical stress-induced expression of RUNX-2 and ADAMTS-5 through the inhibition of the MAPK signaling pathway in cultured human chondrocytes

OBJECTIVE

To investigate the inhibitory effects and the regulatory mechanisms of histone deacetylase (HDAC) inhibitors on mechanical stress-induced gene expression of runt-related transcription factor (RUNX)-2 and adisintegrin and metalloproteinase with thrombospondin motif (ADAMTS)-5 in human chondrocytes.

METHODS

Human chondrocytes were seeded in stretch chambers at a concentration of 5 × 10(4)cells/chamber. Cells were pre-incubated with or without HDAC inhibitors (MS-275 or trichostatin A; TSA) for 12h, followed by uniaxial cyclic tensile strain (CTS) (0.5Hz, 10% elongation), which was applied for 30 min using the ST-140-10 system (STREX, Osaka, Japan). Total RNA was extracted and the expression of RUNX-2, ADAMTS-5, matrix metalloproteinase (MMP)-3, and MMP-13 at the mRNA and protein levels were examined by real-time polymerase chain reaction (PCR) and immunocytochemistry, respectively. The activation of diverse mitogen-activated protein kinase (MAPK) pathways with or without HDAC inhibitors during CTS was examined by western blotting.

RESULTS

HDAC inhibitors (TSA: 10 nM, MS-275: 100 nM) suppressed CTS-induced expression of RUNX-2, ADAMTS-5, and MMP-3 at both the mRNA and protein levels within 1h. CTS-induced activation of p38 MAPK (p38), extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) MAPKs was downregulated by both HDAC inhibitors.

CONCLUSION

The CTS-induced expression of RUNX-2 and ADAMTS-5 was suppressed by HDAC inhibitors via the inhibition of the MAPK pathway activation in human chondrocytes. The results of the current study suggested a novel therapeutic role for HDAC inhibitors against degenerative joint disease such as osteoarthritis.

A potential role of fetal hemoglobin in the development of multidrug resistance

Our previous data from a human leukemic cell line made resistant to the nucleoside analog (NA) 9-β-D-arabinofuranosylguanine (AraG) revealed a massive upregulation of fetal hemoglobin (HbF) genes and the ABCB1 gene coding for the multidrug resistance P-glycoprotein (P-gp). The expression of these genes is regulated through the same mechanisms, with activation of the p38-MAPK pathway and inhibition of methylation making transcription factors more accessible to activate these genes. We could show that AraG, as well as other NAs, and P-gp substrates could induce global DNA demethylation and induction of Hbγ and P-gp both at the mRNA and protein expression level. We speculate that the expression of HbF prior to drug exposure or in drug-resistant cell lines is a strategy of the cancer to gain more oxygen, and thereby survival benefits. We also believe that P-gp may be induced in order to excrete Hb degradation products from the cells that would otherwise be toxic. By using Hbγ siRNA and pharmacological inhibitors of HbF production we here present a possible relationship between HbF induction and multi-drug resistance in a human leukemia cell line model.