A beta-globin gene, inactive in the K562 leukemic cell, functions normally in a heterologous expression system

Development of a novel PTD-mediated IVT-mRNA delivery platform for potential protein replacement therapy of metabolic/genetic disorders

The potential clinical applications of the powerful in vitro-transcribed (IVT)-mRNAs, to restore defective protein functions, strongly depend on their successful intracellular delivery and transient translation through the development of safe and efficient delivery platforms. In this study, an innovative (international patent-pending) methodology was developed, combining the IVT-mRNAs with the protein transduction domain (PTD) technology, as an efficient delivery platform. Based on the PTD technology, which enables the intracellular delivery of various cargoes intracellularly, successful conjugation of a PTD to the IVT-mRNAs was achieved and evaluated by band-shift assay and NMR spectroscopy. In addition, the PTD-IVT-mRNAs were applied and evaluated in two protein-disease models, including the mitochondrial disorder fatal infantile cardioencephalomyopathy and cytochrome c oxidase (COX) deficiency (attributed to SCO2 gene mutations) and β-thalassemia. The PTD-IVT-mRNA of SCO2 was successfully transduced and translated to the corresponding Sco2 protein inside the primary fibroblasts of a SCO2/COX-deficient patient, whereas the PTD-IVT-mRNA of β-globin was transduced and translated in bone marrow cells, derived from three β-thalassemic patients. The transducibility and the structural stability of the PDT-IVT-mRNAs, in both cases, were confirmed at the RNA and protein levels. We propose that our novel delivery platform could be clinically applicable as a protein therapy for metabolic/genetic disorders.

Inhibition of γ/β Globin Gene Switching in CD 34+ Derived Erythroid Cells by BCL11A RNA Silencing

The induction of fetal haemoglobin (Hb F), due to the sustained clinical effects, is one of the most promising methods for the treatment of β hemoglobinopathies, such as thalassemia major and sickle cell disease (SCD). Inhibition of γ-globin gene silencing, possibly is a suitable strategy to induce HbF expression in these patients. In this study, the possibility of increasing HbF in the CD34+ derived erythroid cells was investigated by BCL11A inhibition using specific small-interfering RNAs (siRNAs). Human peripheral blood-derived hematopoietic stem cells were isolated and differentiated to erythroid cells. Erythroid maturation was investigated using cell morphology parameters and flow cytometry analysis of CD235a expression On day 20, siRNA complementary to BCL11A was transfected to differentiating cells via electroporation. BCL11A expression was evaluated through real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) and enzyme linked immunosorbant assay (ELISA). β actin was used as the reference gene to confirm the relative expression level of BCL11A gene mRNA. 48 hours after transfection, BCL11A siRNA significantly reduced BCL11A mRNA levels and consequently led to 2.0 fold decrease in corresponding protein. On the 28th day, haemoglobin electrophoresis results showed that Hb F levels in transfected erythroid cells increased 3.3-fold when compared with non transfected cells. In this study we showed that BCL11A inhibition in erythroid cells could increase fetal hemoglobin, and this strategy can be the basis for designing a γ globin expressing cellular system to increase Hb F in patients with thalassemia and SCD.

Hypermethylated LTR retrotransposon exhibits enhancer activity

LTR retrotransposons are repetitive DNA elements comprising ∼10% of the human genome. They are silenced by hypermethylation of cytosines in CpG dinucleotides and are considered parasitic DNA serving no useful function for the host genome. However, hypermethylated LTRs contain enhancer and promoter sequences and can promote tissue-specific transcription of cis-linked genes. To resolve the apparent paradox of hypermethylated LTRs possessing transcriptional activities, we studied the ERV-9 LTR retrotransposon located at the 5' border of the transcriptionally active β-globin gene locus in human erythroid progenitor and erythroleukemia K562 cells. We found that the ERV-9 LTR, containing 65 CpGs in 1.7 kb DNA, was hypermethylated (with > 90% methylated CpGs). Hypermethylated LTR possessed transcriptional enhancer activity, since in vivo deletion of the LTR by CRISPR-cas9 suppressed transcription of the globin genes by > 50%. ChIP-qPCR and ChIP-seq studies showed that the hypermethylated LTR enhancer spanning recurrent CCAATCG and GATA motifs associated respectively with key transcription factors (TFs) NF-Y and GATA-1 and -2 at reduced levels, compared with the unmethylated LTR in transfected LTR-reporter gene plasmids. Electrophoretic mobility shift assays with methylated LTR enhancer probe showed that the methylated probe bound both NF-Y and GATA-1 and -2 with lower affinities than the unmethylated enhancer probe. Thus, hypermethylation drastically reduced, but did not totally abolish, the binding affinities of the enhancer motifs to the key TFs to assemble the LTR-pol II transcription complex that activated transcription of cis-linked genes at reduced efficiency.

Hemin induces mitophagy in a leukemic erythroblast cell line

BACKGROUND INFORMATION

In eukaryotic cells, autophagy is considered a lysosomal catabolic process which participates in the degradation of intracellular components in a vacuolar structure termed autolysosome. This pathway plays a significant role in the erythropoiesis process, contributing to the clearance of some organelles (such as mitochondria) that are not necessary in the mature red blood cells. Nevertheless, the role of autophagy in erythrocyte maturation has not been fully established.

RESULTS

Here, we have demonstrated that hemin (a physiological erythroid maturation stimulator) is able to induce the expression of critical autophagic genes (i.e., Map1a1b (LC3), Beclin-1 gen, Atg5) in an erythroleukemia cell type. We have also shown that hemin increased the size of autophagic vacuoles which were labelled with LC3 and the degradative lysosomal marker dye quenched-bovine serum albumin. In addition, we have determined by Western blot a rise in the lipidated form of the autophagic protein LC3 (i.e., LC3-II) upon hemin treatment. Moreover, we provide evidence that hemin induces mitochondrial membrane depolarisation and that mitochondria sequestration by autophagy requires the active form of the NIX protein.

CONCLUSIONS

We have found that the physiological erythroid maturation stimulator hemin is able to induce mitophagy in K562 cells, and that the autophagy adaptor NIX is necessary for mitophagy progression. K562 cells have been used as a relevant model to determine the possible therapeutic role of new differentiating compounds.

SIGNIFICANCE

It has been proposed that autophagy induction is a feasible new therapeutic key in fighting cancer. Our results suggest that hemin is favoring erythroid maturation by inducing an autophagic response in K562 cells, being a possible therapeutic candidate that may help in the chronic myelogenous leukemia (CML) treatment.

PLCβ1a and PLCβ1b selective regulation and cyclin D3 modulation reduced by kinamycin F during k562 cell differentiation

Here we report that both PLCβ1a and PLCβ1b are relevant regulators of erythropoiesis in that kinamycin F, a potent inducer of γ-globin production in K562 cells, caused a selectively reduction of both PLCβ1 isozymes even though the results point out that the effect of the drug is mainly directed toward the expression of the PLCβ1a isoform. We have identified a different role for the two isozymes as regulators of K562 differentiation process induced by kinamycin F. The overexpression of PLCβ1b induced an increase in γ-globin expression even in the absence of kinamycin F. Moreover during K562 differentiation, cyclin D3 level is regulated by PLCβ1 signaling pathway. Namely the amplification of the expression of the PLCβ1a, but not of PLCβ1b, is able to maintain high levels of expression of cyclin D3 even after treatment with kinamycin F. This could be due to their different distribution in the cell compartments since the amount of PLCβ1b is mainly present in the nucleus in respect to PLCβ1a. Our data indicate that the amplification of PLCβ1a expression, following treatment with kinamycin F, confers a real advantage to K562 cells viability and protects cells themselves from apoptosis.

Nuclease-mediated gene editing by homologous recombination of the human globin locus

Tal-effector nucleases (TALENs) are engineered proteins that can stimulate precise genome editing through specific DNA double-strand breaks. Sickle cell disease and β-thalassemia are common genetic disorders caused by mutations in β-globin, and we engineered a pair of highly active TALENs that induce modification of 54% of human β-globin alleles near the site of the sickle mutation. These TALENS stimulate targeted integration of therapeutic, full-length beta-globin cDNA to the endogenous β-globin locus in 19% of cells prior to selection as quantified by single molecule real-time sequencing. We also developed highly active TALENs to human γ-globin, a pharmacologic target in sickle cell disease therapy. Using the β-globin and γ-globin TALENs, we generated cell lines that express GFP under the control of the endogenous β-globin promoter and tdTomato under the control of the endogenous γ-globin promoter. With these fluorescent reporter cell lines, we screened a library of small molecule compounds for their differential effect on the transcriptional activity of the endogenous β- and γ-globin genes and identified several that preferentially upregulate γ-globin expression.

Mithramycin encapsulated in polymeric micelles by microfluidic technology as novel therapeutic protocol for beta-thalassemia

This report shows that the DNA-binding drug, mithramycin, can be efficiently encapsulated in polymeric micelles (PM-MTH), based on Pluronic^® block copolymers, by a new microfluidic approach. The effect of different production parameters has been investigated for their effect on PM-MTH characteristics. The compared analysis of PM-MTH produced by microfluidic and conventional bulk mixing procedures revealed that microfluidics provides a useful platform for the production of PM-MTH with improved controllability, reproducibility, smaller size, and polydispersity. Finally, an investigation of the effects of PM-MTH, produced by microfluidic and conventional bulk mixing procedures, on the erythroid differentiation of both human erythroleukemia and human erythroid precursor cells is reported. It is demonstrated that PM-MTH exhibited a slightly lower toxicity and more pronounced differentiative activity when compared to the free drug. In addition, PM-MTH were able to upregulate preferentially γ-globin messenger ribonucleic acid production and to increase fetal hemoglobin (HbF) accumulation, the percentage of HbF-containing cells, and their HbF content without stimulating α-globin gene expression, which is responsible for the clinical symptoms of β-thalassemia. These results represent an important first step toward a potential clinical application, since an increase in HbF could alleviate the symptoms underlying β-thalassemia and sickle cell anemia. In conclusion, this report suggests that PM-MTH produced by microfluidic approach warrants further evaluation as a potential therapeutic protocol for β-thalassemia.

CSF-1 signals directly to renal tubular epithelial cells to mediate repair in mice

Tubular damage following ischemic renal injury is often reversible, and tubular epithelial cell (TEC) proliferation is a hallmark of tubular repair. Macrophages have been implicated in tissue repair, and CSF-1, the principal macrophage growth factor, is expressed by TECs. We therefore tested the hypothesis that CSF-1 is central to tubular repair using an acute renal injury and repair model, ischemia/reperfusion (I/R). Mice injected with CSF-1 following I/R exhibited hastened healing, as evidenced by decreased tubular pathology, reduced fibrosis, and improved renal function. Notably, CSF-1 treatment increased TEC proliferation and reduced TEC apoptosis. Moreover, administration of a CSF-1 receptor-specific (CSF-1R-specific) antibody after I/R increased tubular pathology and fibrosis, suppressed TEC proliferation, and heightened TEC apoptosis. To determine the contribution of macrophages to CSF-1-dependent renal repair, we assessed the effect of CSF-1 on I/R in mice in which CD11b+ cells were genetically ablated and determined that macrophages only partially accounted for CSF-1-dependent tubular repair. We found that TECs expressed the CSF-1R and that this receptor was upregulated and coexpressed with CSF-1 in TECs following renal injury in mice and humans. Furthermore, signaling via the CSF-1R stimulated proliferation and reduced apoptosis in human and mouse TECs. Taken together, these data suggest that CSF-1 mediates renal repair by both a macrophage-dependent mechanism and direct autocrine/paracrine action on TECs.

Preapoptotic chromatin changes induced by ultraviolet B irradiation in human erythroleukemia K562 cells

Exponentially growing human erythroleukemia K562 cells were permeabilized and the dose dependent decrease of DNA synthesis rate was measured after ultraviolet (UV B, 290 nm) irradiation. Cells were able to overcome 2 and 5 J/m2 UV doses, partial recovery was observed at 15 J/m2, while at high (25 J/m2) UV dose replicative DNA synthesis remained suppressed. K562 cells were subjected to synchronization prior to and after UV irradiation (24 J/m2) and 18 fractions were collected by centrifugal elutriation. Cell cycle analysis by flow cytometry did not show early apoptotic cells after UV irradiation. The gradual increase in DNA content typical for non-irradiated cells was contrasted by an early S phase block between 2.2 and 2.4 C-values after UV irradiation. Cell cycle dependent chromatin changes after ultraviolet irradiation were seen as a fine fibrillary network covering the mainly fibrous chromatin structures and incompletely folded primitive chromosomes. Based on observations after UV irradiation and on earlier results with cadmium treatment and gamma irradiation, we confirm that typical chromatin changes characteristic to genotoxic agents can be recognized and classified.

Accumulation of gamma-globin mRNA and induction of irreversible erythroid differentiation after treatment of CML cell line K562 with new doxorubicin derivatives

Human chronic myelogenous leukemia (CML) cell line K562 can be chemically induced to differentiate and express embryonic and fetal globin genes. In this study, the effects of doxorubicin (DOX), an inducer of K562 cell erythroid differentiation, with those of epidoxorubicin (EDOX) as well as newly synthesized derivatives of both drugs (DOXM, DOXH, and EDOXM) on cell growth and differentiation were compared. Our results revealed that DOX, EDOX and their derivatives caused irreversible differentiation of K562 cells into more mature hemoglobin-containing cells. This phenomenon was linked to time-dependent inhibition of cell proliferation. Considering the impact of the structure of newly synthesized anthracyclines on their cellular activity, our data clearly indicated that among tested anthracyclines DOXM, a morpholine derivative of DOX exerted the highest antiproliferative and differentiating activity. An increase of gamma-globin mRNA level caused both by high transcription rate and by mRNA stabilization, as well as an enhancement of expression but not activity of erythroid transcription factor GATA-1 were observed. Therefore, a high level of hemoglobin-containing cells in the presence of DOXM resulted from transcriptional and post-transcriptional events on gamma-globin gene regulation. The same morpholine modification introduced to EDOX did not cause, however, similar effects on cellular level. Characterization of new powerful inducers of erythroid differentiation may contribute to the development of novel compounds for pharmacological approach by differentiation therapy to leukemia or to beta-globin disorder, beta-thalassemia.

delta-Globin gene structure and expression in the K562 cell line

The delta-globin gene produces the delta chain of Hb A2 which represents less than 3% of the hemoglobin (Hb) in normal individuals. The delta-globin gene is also expressed in the human erythroleukemia cell line K562. The expression of the delta-globin gene in this cell line is unexpected since K562 shows an embryonic-fetal globin gene expression pattern with no expression of the adult beta-globin gene. delta-Globin gene activation has been proposed as a potential therapeutic tool for the cure of delta-thalassemia (thal). In order to shed some light on the delta-globin gene activation in K562 the present study has: (1) determined the complete nucleotide sequence of the delta- and beta-globin genes; (2) assessed, by reverse transcription-polymerase chain reaction (RT-PCR), the relative delta- and beta-globin mRNA level; and (3) analyzed the exact level of the endogenous expression delta-globin gene by S1 mapping. No sequence variations were identified in the (delta- and beta-globin genes when compared to the normal sequences. delta-Globin mRNA represent more than 95% of the total delta + beta-mRNA content. The level of expression of the delta-globin gene is 12.3% (+/- 1.2) compared to the endogenous alpha-globin gene. These results indicate that the high expression of the delta-globin gene in K562 is most likely due to the transacting environment. Therefore, the presence and/or absence of specific transacting factors are able to specifically activate the human delta-globin gene. The level of expression of the delta-globin gene in this cell line suggests that it could be of relevance to identify the transacting factor(s) responsible for this selective activation in order to better understand the molecular mechanisms undergoing gene activation.

Mechanisms involved in the induced differentiation of leukemia cells

Despite the remarkable progress achieved in the treatment of leukemias over the last several years, many problems (multidrug resistance [MDR], cellular heterogeneity, heterogeneous molecular abnormalities, karyotypic instability, and lack of selective action of antineoplastic agents) still remain. The recent progress in tumor molecular biology has revealed that leukemias are likely to arise from disruption of differentiation of early hematopoietic progenitors that fail to give birth to cell lineage restricted phenotypes. Evidence supporting such mechanisms has been derived from studying bone marrow leukemiogenesis and analyzing differentiation of leukemic cell lines in culture that serve as models of erythroleukemic (murine erythroleukemia [MEL] and human leukemia [K562] cells) and myeloid (human promyelocytic leukemia [HL-60] cells) cell maturation. This paper reviews the current concepts of differentiation, the chemical/pharmacological inducing agents developed thus far, and the mechanisms involved in initiation of leukemic cell differentiation. Emphasis was given on commitment and the cell lineage transcriptional factors as key regulators of terminal differentiation as well as on membrane-mediated events and signaling pathways involved in hematopoietic cell differentiation. The developmental program of MEL cells was presented in considerable depth. It is quite remarkable that the erythrocytic maturation of these cells is orchestrated into specific subprograms and gene expression patterns, suggesting that leukemic cell differentiation represents a highly coordinated set of events that lead to irreversible growth arrest and expression of cell lineage restricted phenotypes. In MEL and other leukemic cells, differentiation appears to be accompanied by differentiation-dependent apoptosis (DDA), an event that can be exploited chemotherapeutically. The mechanisms by which the chemical inducers promote differentiation of leukemic cells have been discussed.

The role of trans-acting factors and DNA-bending in the silencing of human beta-globin gene expression

The molecular mechanisms which govern the develop-mental specificity of human beta-globin gene transcription have been studied in K562 cells, a human eyrthroleukemia line that expresses minimal beta-globin. Protein-binding analysis reveals that the 5' region contains three elements bound by trans-acting factors, beta-protein 1 (BP1) and beta-protein 2 (BP2). In vitro mutagenesis of each individual element in a beta-globin vector containing chloramphenicol acetyl-transferase (pCAT) followed by transient transfection into K562 cells increased levels of CAT activity 5. 5-fold higher than wild-type (wt) betaCAT, consistent with their silencing role. Mutagenesis of all three elements, however, resulted in activity significantly lower than wt betaCAT. BP1 and BP2 motifs have overlapping binding sites for high mobility group proteins (HMG1+2), DNA-bending factors, shown here to extrinsically bend the beta-globin promoter. Theoretically, mutations in all beta-protein binding sites could affect the binding of HMG1+2 sufficiently to impede DNA-protein and/or protein-protein interactions needed to facilitate constitutive gene expression. Placing two turns of DNA between BP1 and BP2 motifs also increased expression 3-fold, indicative of spatial constraints required for optimal silencing. However, insertion of the HMG1+2 DNA-bending motif (also equivalent to two turns) facilitates beta-silencing by re-establishment of BP1-BP2 proximity. Thus a combination of general DNA-bending and specific transcriptional factors appear to be involved in beta-globin silencing in the embryonic/fetal erythroid stage.

Binding of HMG-I(Y) elicits structural changes in a silencer of the human beta-globin gene

Proteins involved in repression of the human beta-globin gene may be useful in the treatment of sickle cell anemia, in conjunction with therapy to reactivate fetal globin genes. If there is a reciprocal elevation of gamma-globin expression upon repression, this approach could be useful in additional hemoglobinopathies. We previously showed that repression of the beta-globin gene appears to be mediated through two DNA sequences, silencers I and II, and identified a protein termed BP1 which binds to both silencer sequences. In this study, we cloned two cDNAs encoding proteins which bind to an oligonucleotide in silencer I containing a BP1 binding site. These cDNAs correspond to HMG-I and HMG-Y, isoforms regarded as architectural proteins. We demonstrate that binding of HMG-I(Y) to this oligonucleotide causes bending/flexure of the DNA. HMG-I(Y) also binds to a second oligonucleotide containing a BP1 binding site located in a negative control region upstream of the delta-globin gene, suggesting a role for HMG-I(Y) in repression of adult globin genes. Expression studies revealed that HMG-I(Y) is ubiquitously expressed in human tissues that do not express beta-globin, being present in 48 of 50 tissues and six hematopoietic cell lines examined. Furthermore, HMG-I(Y) expression is down-regulated during differentiation of primary erythroid cells. We present a model in which HMG-I(Y) alters DNA conformation to allow binding of repressor proteins, and in which the relative amount of HMG-I(Y) helps to determine the repressive state of the beta-globin gene.

Anthracyclines as tumor cell differentiating agents: effects on the regulation of erythroid gene expression

Tumor cells, and particularly leukemic cells, can be considered as maturation-arrested cells which have escaped some normal control and continue to proliferate. This maturation arrest can be reversed by differentiation agents such as antitumor drugs currently used in conventional cytotoxic chemotherapy. In this respect, anthracyclines have been shown to trigger the differentiation of leukemic and solid tumor cells, but the molecular mechanisms by which such drugs lead to the differentiating phenotype are still poorly understood. Using human leukemic multipotent K562 cells, we have demonstrated that subtoxic concentrations of aclacinomycin (ACLA) and doxorubicin (DOX) preferentially stimulate the hemoglobinic pathway (globins and heme synthesis) and the expression of mRNAs of globins and of porphobilinogen deaminase (PBGD). However, our results indicate that both drugs exert this differentiating effect along distinct regulatory pathways. Indeed, only ACLA and not DOX induces the expression of erythropoietin receptor (EpoR) mRNAs and of membrane EpoR, as well as an overexpression of the erythroid transcription factors GATA-1 and NF-E2 known to play a central role in erythroid gene regulation. Similarly, using transfection assays, ACLA but not DOX activates the regulatory regions (promoters and enhancers) of GATA-1, EpoR, PBGD, epsilon- and gamma-globin genes. Finally, results of run-on assays indicate that ACLA induces an enhancement of the transcription rate of these erythroid genes whereas DOX preferentially increases stability of GATA-1, NF-E2 and PBGD mRNAs. In conclusion, ACLA mainly acts at the transcriptional level via specific activation of erythroid regulatory regions whereas DOX rather acts at the posttranscriptional level by increasing the half-lives of erythroid mRNAs.

Differential expression of alpha- and beta-globin genes in erythroleukemic cell lines

The IW32, NN10, and IW201 cell lines are erythroleukemic cell lines isolated from the spleens of mice infected with the Friend virus. IW32 and NN10 cells can be induced toward erythroid differentiation and hemoglobin synthesis by hemin or butyrate. Both cell lines contain some mature alpha- and beta-globin mRNA before induction, and addition of the inducers greatly increases the amount of globin message. Unlike IW32 and NN10 cells, IW201 cells are only partially inducible. Uninduced 201 cells contain a small amount of alpha-globin mRNA but no detectable beta-globin message. After induction, the cells contain markedly increased amounts of alpha-globin mRNA but still do not express the beta-globin gene. Southern blot analysis with 10 restriction enzymes shows that the restriction map of the beta-globin gene in IW201 cells is indistinguishable from that in IW32 and NN10 cells.

Differential expression of alpha- and beta-globin genes in erythroleukemic cell lines

The IW32, NN10, and IW201 cell lines are erythroleukemic cell lines isolated from the spleens of mice infected with the Friend virus. IW32 and NN10 cells can be induced toward erythroid differentiation and hemoglobin synthesis by hemin or butyrate. Both cell lines contain some mature alpha- and beta-globin mRNA before induction, and addition of the inducers greatly increases the amount of globin message. Unlike IW32 and NN10 cells, IW201 cells are only partially inducible. Uninduced 201 cells contain a small amount of alpha-globin mRNA but no detectable beta-globin message. After induction, the cells contain markedly increased amounts of alpha-globin mRNA but still do not express the beta-globin gene. Southern blot analysis with 10 restriction enzymes shows that the restriction map of the beta-globin gene in IW201 cells is indistinguishable from that in IW32 and NN10 cells.

Hemin increase production of beta-like globin RNA transcripts in human erythroleukemia K-562 cells

Previous studies have indicated that control and hemin-treated human erythroleukemia K-562 cells fail to produce adult-type beta-globin mRNA transcripts and to translate them into nascent beta-globin chains. Expression of the beta-globin DNA sequences in K-562 cells can occur, however, under certain conditions. To readdress this issue and to examine the possibility of whether these cells produce immature and untranslatable beta-globin RNA transcripts, we prepared total cytoplasmic RNA from control and inducer-treated cells and performed Northern blot hybridization analysis using 5' end-labeled fragments of the human beta-globin DNA rather than 3' end fragments as probes. Although hybridization of both cytoplasmic and nuclear K-562 RNA with a 32P-labeled 3' end fragment (1.6kb Bam H1 cut) coding for a large part of the first exon of beta-globin failed to detect beta-globin RNA transcripts, hybridization with a 5' end 32P-Labeled 2.0kb Bam H1 fragment (coding for the third exon and part of the second) revealed the presence of relatively small (less than 7S) RNA molecules both in nuclear and cytoplasmic fraction. S1 nuclease mapping of both cytoplasmic and nuclear RNA with the use of 5' end-labeled 2.0 kb Bam H1 fragment of human beta-globin DNA indicated protection of a small portion located 64 bp 5' upstream from the Bam H1 site of the second exon. The amount of protected portion was relatively higher in K-562 cells undergoing erythroid maturation.(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclease hypersensitivity in the beta-globin gene region of K562 cells

We have investigated chromatin structure in the beta-globin gene region of the K562 human erythroleukemic cell line by using S1 and DNase I nuclease sensitivity assays. Despite the lack of beta-globin gene expression in these cells, we find nuclease-hypersensitive sites to these enzymes in its 5' and 3' flanking regions in K562 chromatin. This result is in contrast to previous reports in which no hypersensitive sites were found in the immediate vicinity of this gene. In the 3' region, one major hypersensitive site at 0.9 kpb 3' and three minor hypersensitive sites at 0.7 kbp, 0.5 kbp 3' and 0.2 kbp 5' of the polyadenylation site were observed; these sites are very similar to those found in fetal liver and adult bone marrow cells in which the beta-globin gene is expressed. We find hypersensitive sites to both enzymes in the 5' region of the beta-globin gene: a major site 0.8 kbp 5' to the cap site, and two minor sites 1.2 and 1.5 kbp 5' to the cap site. The -0.8 kbp site is also present in plasmids containing the beta-globin gene. Our results suggest that the lack of beta-globin gene expression may be related to the lack of hypersensitivity sites in the immediate (150 bp) 5' flanking region of the beta-globin gene, as occurs in other active globin genes.

Regulation of fetal globin gene expression in human erythroleukemia (K562) cells

We have analyzed the transcription and induction of fusion globin genes comprised of portions of either gamma and beta globin sequences or gamma and neomycin resistance gene sequences. The analysis of gamma promoter beta and gamma-neo fusion genes indicates that 5' gamma flanking sequences are sufficient for tissue specific expression but not induction in K562 cells. A beta gene containing only the substitution of gamma IVS 2 for beta IVS 2 is expressed and induced when transcripts are analyzed with a 3' probe in contrast to the lack of expression seen with an intact beta gene. Thus, fusion globin genes containing gamma IVS 2 are both expressed and induced indicating that this region may be involved in the response to hemin stimulation, however, the mechanism is unclear. A gamma-neo fusion gene containing the gamma 5' region is expressed but not induced. When an EcoRI-Bg1 II fragment containing the beta 3' enhancer is ligated downstream of the gamma-neo gene this gene is now inducible. Multiple genetic elements are involved in the regulated expression of gamma genes in fetal erythroid cells. These experiments begin to localize these sequences to specific regions within the gamma globin gene.

Evidence for a locus activation region: the formation of developmentally stable hypersensitive sites in globin-expressing hybrids

We have analyzed the chromatin structure of the human beta-globin locus in somatic cell hybrids resulting from the fusion of human non-erythroid cells and mouse erythroleukemia (MEL) cells. In these hybrids, the human adult beta-globin gene, but neither the embryonic nor fetal globin genes, is activated transcriptionally. In addition, the DNase I-resistant beta-like globin locus characteristic of the parental non-erythroid human cells (1,2) is reorganized over an approximately 80 kb region, including the formation of the developmentally stable hypersensitive sites 50 kb 5' and 20 kg 3' of the activated adult beta-globin gene (2,3). These results are consistent with the hypothesis that events occurring at the 5' and/or 3' developmentally stable hypersensitive sites are important, if not necessary, for the activation of the beta-globin locus.

Regulation of adult and embryonic genes in human leukemia cells

In this article, we have reviewed studies showing that altered expression of regulatory genes results in activation of embryonic genes in human leukemia cells. These data have led to important new insights as to how mutations in regulatory genes can lead to disease states in man.

Activation of the human beta-globin promoter in K562 cells by DNA sequences 5' to the fetal gamma- or embryonic zeta-globin genes

Regulatory sequences of the human fetal gamma-globin gene were studied by constructing composite gamma/beta globin promoters and comparing their function to that of intact beta promoters in human K562 cells. The beta-globin gene with either 1,600 or 127 basepairs of beta promoter sequence was not expressed after stable introduction into K562 cells, consistent with the known inactivity of the beta-globin gene in these cells. In contrast, a gamma/beta promoter composed of a gamma fragment spanning positions -408 to -137 joined to the 127-bp beta promoter was able to drive the beta-globin gene. The gene appeared to be inducible with hemin. A zeta-globin 5' flanking fragment also activated the beta promoter. The function of a series of composite gamma/beta promoters was then assessed by their ability to drive directly the neomycin resistance gene, again in stably transformed cells. The -408 to -137 gamma fragment activated the beta promoter in an orientation-specific manner in this assay. Deletion analysis showed that regulatory sequences were present between positions -259 and -137 of the fetal gamma-globin gene flanking region.

v-abl activates embryonic globin gene expression in mouse erythroleukemia cells

The Philadelphia chromosome translocation, which is present in 90-95% of chronic myelogenous leukemia patients, involves translocation of the c-abl protooncogene to chromosome 22 and is accompanied by activation of embryonic globin gene expression in the K562 chronic myelogenous leukemia cell line. To test directly if the protein products of the translocated c-abl protooncogene can activate embryonic globin gene expression, we transfected the v-abl oncogene (which shares the property of autophosphorylation with the translocated c-abl protooncogene) into mouse erythroleukemia cells. v-abl-transfected mouse erythroleukemia cells, which contained multiple copies of the v-abl transgenome, exhibited activation of mouse embryonic globin gene expression. These results suggest that the translocated c-abl protooncogene of the Philadelphia chromosome translocation is central to the pathogenesis of chronic myelogenous leukemia and that it may result in the activation of embryonic globin genes in some chronic myelogenous leukemia cell lines.

Trans acting regulation of beta globin gene expression in erythroleukemia (K562) cells

K562 cells are induced by hemin to produce gamma and epsilon globin but not beta globin, although the beta globin gene is intact, and when isolated is expressed in a transient expression assay (1, 2). We have previously shown that an epsilon globin gene transferred into K562 cells is expressed and inducible (3). In this paper, we report the stable transfer of a sickle or betaS globin gene into K562 cells. Thirty-six different transformed lines were tested; 24 of 36 lines contained an intact betaS globin gene. However, using S1 nuclease, Dot blot, and Northern blotting analyses, none of these lines showed beta globin mRNA expression. These results indicate that trans acting factors are responsible for the lack of expression of the beta globin gene in K562 cells.

Differential expression of human globin genes introduced in K562 cells

We have constructed a series of hybrid globin genes between the 5' half of the human epsilon-, gamma- and beta-globin genes, and the 3' half of the rabbit beta-globin gene. These hybrid genes were introduced into the cell line K562. Analysis of the hybrid mRNA populations show that only the hybrid epsilon- and gamma-globin genes are expressed in these cells in concordance with the endogenous K562 globin gene expression. It is therefore likely that these cells contain transcriptional factors which allow the specific expression of introduced epsilon- and gamma-, but not beta-globin genes, irrespective of their chromosomal localization.

Adult and fetal human globin genes are expressed following chromosomal transfer into MEL cells

Somatic cell hybridization of mouse erythroleukemia (MEL) cells and HEL cells, a human erythroleukemia line that produces fetal (gamma) but fails to express adult (beta) globin, was used to test whether the expression of the two human globin genes is regulated cis or trans. An experimental approach using anti-human globin monoclonal antibodies for detection, efficient cloning, and monitoring of hybrids of interest was employed. Further characterization of hybrids used isoelectric focusing for detection of human globins and S1 nuclease mapping. In contrast to the parental HEL line, all chromosome 11-retaining HEL-MEL hybrids expressed human beta-globin, suggesting that the HEL beta-globin genes (i) are transcriptionally competent, (ii) become activated in response to a positive trans-acting element within the MEL environment, and (iii) fail to express into the HEL environment because of either the absence of a positive trans-acting element or the presence of a trans-acting inhibitor of beta-globin gene expression. In addition to beta-globin, the primary HEL-MEL hybrids co-expressed gamma-globin; however, gamma-globin expression segregated by subcloning so that secondary and tertiary clones either expressed only beta-globin or co-expressed gamma- and beta-globin. The results of subcloning can be explained by assuming that gamma-globin gene expression is controlled by a HEL cell-derived transacting element encoded by a gene not syntenic to chromosome 11 or by postulating that the HEL gamma-globin genes become randomly modified during the continuous proliferation of hybrids.