Biomedical subjects

B S Pace

Publications and source records attributed to B S Pace.

11 recordsLinked to original sources

PubMed2005

Erk pathway inhibitor U0126 induces gamma-globin expression in erythroid cells.

Fetal hemoglobin (HbF) induction is an effective approach to improve clinical symptoms in sickle cell disease. Understanding molecular mechanisms for gamma-gene re-activation will aid efforts to design lead compounds. A potential inhibitory role for the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) pathway in gamma-gene expression has been suggested recently. Therefore, we determined the ability of U0126, a selective inhibitor of MEK1/2 the upstream activators of ERK, to re-activate gamma-globin expression. K562 stable lines over-expressing constitutively active MEK1 were established. A significant increase in ERK phosphorylation was observed and gamma-gene expression was silenced concomitantly, however U0126 attenuated this effect. Studies in human erythroid progenitors confirmed the ability of U0126 to induce HbF. Cellular mechanisms for the inhibitory role of ERK signaling in drug-mediated HbF induction will be discussed.

Blotting, Western↗

PubMed2005

Fetal hemoglobin induction by the histone deacetylase inhibitor, scriptaid.

Many different classes of drugs induce fetal hemoglobin (HbF) including histone deacetylase (HDAC) inhibitors such as butyrate and trichostatin A. Although these agents induce gamma-globin expression in culture many are ineffective in vivo, therefore research efforts continue to identify clinically useful fetal globin inducers. We and others demonstrated a role for p38 mitogen activated protein kinase (MAPK) in gamma-globin promoter activation by HDAC inhibitors. In this study we determined the ability of scriptaid, a novel HDAC inhibitor, to induce gamma-globin expression via p38 MAPK signaling. Scriptaid induced gamma-globin in K562 cells and human erythroid progenitors. Furthermore the p38-selective inhibitor SB203580 completely reversed the ability of scriptaid to induce HbF. To test the potential efficacy of scriptaid in humans, in vivo studies were completed in beta-YAC transgenic mice where the gamma-gene is completely silenced. Scriptaid induced reticulocytosis and human gamma-globin mRNA synthesis. At a concentration of 1 mg/kg/day given by intraperitoneal injections twice weekly we observed a significant 1.8-fold increase in gamma-globin mRNA transcripts. The potential for scriptaid as a treatment option for sickle cell disease will be discussed.

Anemia, Sickle Cell↗

PubMed2004

Selective inhibition of beta-globin RNA transcripts by antisense RNA molecules.

Inhibition of beta-globin gene expression by antisense nucleic acids is a potentially powerful therapeutic strategy for sickle cell disease. To develop clinically relevant beta-globin antisense agents we created nine stable mouse erythroleukemia cell lines expressing unique anti-beta-globin RNA transcripts with different potentials for cross-hybridization with gamma-globin mRNA. We observed variable inhibition of beta-globin expression independent of the hybridization potential of the respective antisense beta-globin RNA transcript. Similarly, inhibition of gamma-globin expression by anti-beta transcripts varied widely in the nine stable cell lines. Three neighboring regions in the beta-globin gene with low RNA folding potentials conferred significantly stronger antisense effect toward beta-globin while sparing the homologous targets in gamma-globin. We have identified for the first time targets in the beta-globin gene for which the homologous regions in gamma-globin are relatively inaccessible to antisense attack. Our findings offer the prospect of using this approach to reduce the proportion of intracellular hemoglobin S. Gene therapy strategies which combine gamma-globin induction along with beta-globin inhibition using antisense vectors may yield more favorable anti-sickling effects longterm.

Animals↗

PubMed2001

Short-chain fatty acid derivatives stimulate cell proliferation and induce STAT-5 activation.

Current chemotherapeutic and butyrate therapeutics that induce fetal hemoglobin expression generally also suppress erythropoiesis, limiting the production of cells containing fetal hemoglobin (F cells). Recently, selected short-chain fatty acid derivatives (SCFADs) were identified that induce endogenous gamma-globin expression in K562 cells and human burst-forming units-erythroid and that increase proliferation of human erythroid progenitors and a multilineage interleukin-3-dependent hematopoietic cell line. In this report, gamma-globin inducibility by these SCFADs was further demonstrated in mice transgenic for the locus control region and the entire beta-globin gene locus in a yeast artificial chromosome and in 2 globin promoter-reporter assays. Conditioned media experiments strongly suggest that their proliferative activity is a direct effect of the test compounds. Investigation of potential mechanisms of action of these SCFADs demonstrates that these compounds induce prolonged expression of the growth-promoting genes c-myb and c-myc. Both butyrate and specific growth-stimulatory SCFADs induced prolonged signal transducer and activator of transcription (STAT)-5 phosphorylation and activation, and c-cis expression, persisting for more than 120 minutes, whereas with IL-3 alone phosphorylation disappeared within minutes. In contrast to butyrate treatment, the growth-stimulating SCFADs did not result in bulk histone H4 hyperacetylation or induction of p21(Waf/Cip), which mediates the suppression of cellular growth by butyrate. These findings suggest that the absence of bulk histone hyperacetylation and p21 induction, but prolonged induction of cis, myb, myc, and STAT-5 activation, contribute to the cellular proliferation induced by selected SCFADs.

Animals↗

PubMed2000

Mechanism for fetal hemoglobin induction by hydroxyurea in sickle cell erythroid progenitors.

Hydroxyurea (HU) is a widely used cytotoxic agent that is known to induce fetal hemoglobin (HbF) production and is presently used to ameliorate the severity of pain episodes in patients with sickle cell anemia (HbSS). Previously we have shown that HU inhibits growth of burst forming unit-erythroid (BFU-E) colonies in a dose-dependent manner, while fetal hemoglobin levels were increased. In the present report, we extended our analysis demonstrating the number of S phase cells is significantly higher for HbSS patients that respond to HU therapy. Studies were completed in vitro using erythroid progenitors derived from umbilical cord samples or peripheral blood from patients with HbS-hereditary persistence of fetal hemoglobin (HbS-HPFH) or HbSS disease. The effect of HU on (a) S phase erythroid progenitors, (b) BFU-E colony growth, (c) HbF levels in BFU-E colonies, and (d) total cellular RNA synthesis was analyzed in vitro for the three groups. The level of S phase erythroid progenitors was similar for all three groups and BFU-E colony growth was inhibited 92-94% for all samples in a dose-dependent manner. The HbF levels were increased in BFU-E colonies from HbSS patients (control, 4.0% +/- 1.15% vs. +HU, 22.67% +/- 2.03%) whereas HbF levels were decreased in BFU-E colonies derived from umbilical cord samples (control, 80% +/- 9.07% vs. +HU, 35.7% +/- 4.81%) or HbS-HPFH patients (control, 49.67% +/- 3.84% vs. +HU, 23.3% +/- 0.88%). Total RNA synthesis measured by 3H-uridine incorporation increased with increasing concentrations of HU; however, actinomycin D inhibited HU-induced RNA synthesis. These results suggest that HU can inhibit an active globin gene without preference and that newly synthesized RNA is under transcriptional control mechanisms.

Adolescent↗

PubMed2000

Butyrate-inducible elements in the human gamma-globin promoter.

OBJECTIVE: Several agents including hydroxyurea, erythropoietin and butyric acid have been shown to reactivate gamma gene expression during adult stage development by unknown molecular mechanisms. In addition to inhibiting the enzyme histone deacetylase, butyrate may modulate transcription factor binding to specific DNA sequences defined as butyrate response elements (BREs). The purpose of this study was to identify promoter sequences involved in gamma gene activation by butyrate using truncation mutants in stable cell lines. MATERIALS AND METHODS: A detailed analysis of Agamma gene activation in the presence of alpha-aminobutyric acid and sodium butyrate was completed in stable mouse erythroleukemia (MEL) cell pools established with seven Agamma promoter truncation mutants. Functional studies were performed in a transient assay system followed by gel mobility shift assays to define protein binding patterns and to demonstrate transcription factor interactions in the gamma promoter BRE. RESULTS: Agamma promoter analysis in stable MEL cell pools revealed BREs between nucleotide-141 and -201, and nucleotide-822 and -893 (gammaBRE). The gammaBRE required the minimal Agamma promoter (-201 to +36) to stimulate gene expression. We observed a 6.1-fold (p < 0.05) increase in CAT activity for the minimal Agamma promoter alone compared with an 11.5-fold (p < 0.05) increase when the gamma promoter was combined with the -822 to -893 fragment. Protein binding studies demonstrated altered protein-DNA interactions in the gammaBRE after butyrate induction. The pattern for binding observed suggest both negative- and positive-acting transcription factors may interact in this region. CONCLUSION: The data supports the -822 to -893 region as a DNA regulatory element that contributes to Agamma gene inducibility by butyrate.

Animals↗

PubMed2000

Beta globin gene inhibition by antisense RNA transcripts.

Sickle cell disease is caused by a mutation in the beta globin gene leading to hemoglobin S (Hb S) production. Several approaches have been explored to prevent Hb S polymerization in red blood cells and the symptoms associated with this disorder. To this end we tested a mammalian expression vector carrying a human beta globin antisense cDNA (pZeobetaAS) fragment in a mouse erythroleukemia cell line expressing the human gamma and beta globin genes. We observed a relative reduction in beta globin mRNA levels compared with gamma mRNA levels in the presence of pZeobetaAS. Moreover, analysis at the protein level showed an average 76% decrease in beta chains and a 517% increase in gamma chain biosynthesis. The inhibitory effect of the antisense vector on globin expression was maintained long term in culture. The expression vector pZeobetaAS was also transfected into primary erythroid progenitors to test its effects on globin genes undergoing normal developmental switching during differentiation. We observed a relative reduction of beta globin mRNA levels compared with gamma mRNA levels. These results support a novel role for antisense cDNA expression vectors as an alternative gene therapy strategy to inhibit betas gene expression in sickle cell disease. Gene Therapy (2000) 7, 438-444.

Anemia, Sickle Cell↗

PubMed1997

Globin gene silencing in primary erythroid cultures. An inhibitory role for interleukin-6.

There are numerous similarities between the erythroid and megakaryocytic lineages which suggest that commitment to either lineage occurs relatively late in hematopoiesis. Commitment toward megakaryocyte development requires obligatory silencing of erythroid-specific genes. Therefore, we investigated the effects of interleukin-6, a known inducer of thrombocyte production, on globin gene expression during erythroid differentiation. Studies in K562 cells demonstrated inhibition of gamma globin gene mRNA production and chain biosynthesis in the presence of exogenous interleukin-6 which was abrogated by anti-interleukin-6 monoclonal antibody. Similar studies in primary erythroid progenitors showed inhibition of burst-forming unit-erythroid colony formation when interleukin-6 was added late in cultures with decreased gamma and beta globin gene mRNA production. Protein binding studies demonstrated an increase in activator protein-1 binding to its consensus sequence by 24 h of interleukin-6 treatment. Inhibition of activator protein-1 gene activity had no effect on gamma gene silencing by interleukin-6. A potential interleukin-6 response element was identified in the gamma globin gene. Interleukin-6 treatment led to a rapid increase in protein binding to the target DNA sequence. These results suggest that interleukin-6 may play an important role in globin gene silencing during megakaryocytic lineage commitment.

Butyrates↗

PubMed1997

Abrogation of IL-3 requirements and stimulation of hematopoietic cell proliferation in vitro and in vivo by carboxylic acids.

Short-chain fatty acids, such as butyrate and propionate, induce fetal globin gene expression and are under clinical investigation in the beta-hemoglobinopathies. Limitations of the short-chain fatty acids as therapeutics include their rapid metabolism and a tendency to induce cell growth arrest if administered for prolonged periods. In studies described here, the cellular effects of other inducers of fetal globin, phenoxyacetic acid and derivatives of short-chain fatty acids and cinnamic acids, were investigated in the human erythroid cell line K562, the IL-3 dependent multi-lineage cell line (32D), and in mice and primates. Several test compounds supported 32D cell proliferation despite a 50-fold depletion of IL-3, which resulted in growth arrest and apoptotic death in control cells. The degree of proliferation induced by certain test compounds was similar to the degree of proliferation induced by Erythropoietin and G-CSF in the cells. Eight of ten compounds induced gamma globin mRNA in K562 cells. A 2.5 to 6-fold increase in reticulocytosis was observed in vivo in mice treated with two prototype compounds. Pharmacokinetic studies of three prototype compounds demonstrated millimolar plasma concentrations after single oral doses for many hours in primates. These findings identify orally bioavailable compounds which induce gamma globin gene expression and hematopoietic cell proliferation through an activity which partially abrogates requirements for IL-3. Such compounds provide potential for oral therapeutics which stimulate proliferation of hematopoietic cells of multiple lineages, as well as inducing fetal globin.

Animals↗

PubMed1996

In vivo search for butyrate responsive sequences using transgenic mice carrying A gamma gene promoter mutants.

We describe an in vivo approach, in transgenic mice, aimed to identify promoter elements responsible for the induction of gamma globin expression by butyrate. Transgenic lines carrying human A gamma gene promoter truncations at position -141, -201, -382, and -730 A gamma were treated with alpha amino butyric acid (alpha ABA), and effects on gamma globin expression were analyzed at the messenger RNA level. No induction of gamma gene expression was observed in animals carrying promoters truncated at positions -141, -201, or -382 A gamma, suggesting either that butyrate response elements (BRE) are not located in the proximal gamma gene promoter or, if they were, they require the cooperation of upstream sequences for gamma gene induction. Two animals from one line carrying the -730 A gamma truncation responded to alpha ABA treatment with significant increases in gamma gene expression, indicating that a BRE is located between position -382 and -730 region of the A gamma gene promoter. Because the maximum induction by alpha ABA is observed in transgenic mice carrying a A gamma gene promoter extending to nucleotide -1350, it is likely that another butyrate responsive element is located between -730 and -1350 of the A gamma gene promoter. These results indicate that the transgenic mouse model can be used for identification of DNA regions that contain cis elements involved in gamma globin gene inducibility.

Aminobutyrates↗

PubMed1994

Transgenic mouse model of pharmacologic induction of fetal hemoglobin: studies using a new ribonucleotide reductase inhibitor, Didox.

Evaluation of pharmacologic agents that stimulate fetal hemoglobin production has been done mainly in baboons and macaques. We investigated whether results in transgenic mice can predict the stimulation of fetal hemoglobin in primates, by testing gamma globin induction in response to a new ribonucleotide reductase inhibitor, Didox. A transgenic mouse line carrying the human A gamma gene linked to a locus control region cassette was used. Treatment of transgenic mice with Didox resulted in induction of gamma gene expression as documented by an increase in F reticulocytes and F cells and an elevation of gamma/gamma + beta biosynthetic ratio. Similarly, administration of Didox to a baboon in the nonanemic and chronically anemic state resulted in induction of gamma gene expression as shown by increases in F reticulocytes, F cells, and Hb F. These results suggest that the muLCR-A gamma transgenic mice can be used to screen new pharmacologic compounds for gamma globin inducibility.

Anemia↗