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The reexpression of the fetal γ-globin gene in adult erythrocytes is of therapeutic interest due to its ameliorating effects in β-hemoglobinopathies. We recently showed that Methyl CpG Binding Domain Protein2 (MBD2) contributes to the silencing of the chicken embryonic ρ-globin and human fetal γ-globin genes. We further biochemically characterized an erythroid MeCP1 complex that is recruited by MBD2 to mediate the silencing of these genes. These observations suggest that the disruption of the MeCP1 complex could augment the expression of the fetal/embryonic globin genes. In the studies presented in chapter 2, we have pursued a structural and biophysical analysis of the interaction between two of the six components of the MeCP1 complex: MBD2 and p66α. These studies show that the coiled coil regions from MBD2 and p66α form a highly stable heterodimeric complex. Further, overexpressing the p66α coiled coil domain in adult erythroid cells can augment the expression of the chicken ρ-globin and human γ-globin genes, by disrupting the assembly of a functional MeCP1 complex. This indicates that the exogenously expressed p66α coiled coil peptide competes with the endogenous p66α for the interaction with the coiled coil domain of MBD2. These studies show that the coiled coil interaction between MBD2 and p66α could serve as a potential targets for the therapeutic induction of fetal hemoglobin. The laboratory showed that knockout of MBD2 in transgenic mice carrying the human β-globin gene cluster, results in an elevated expression of γ-globin in adult erythrocytes. However, MBD2 does not directly bind to the γ-globin gene to mediate its silencing. In the work presented in chapter 3, we have tested the hypothesis that MBD2 may suppress γ-globin gene transcription in adult erythrocytes indirectly, by binding to and repressing transcription of intermediary gene/s which may be involved in γ-globin gene regulation. Employing microarray technology, we have identified Gab1 and ZBTB32 as candidate genes that may be involved in the MBD2 mediated silencing of γ-globin.

Krüppel-like factors KLF1 and KLF2 are closely related transcription factors with three zinc finger domains in their carboxy-termini. KLF1 (erythroid Krüppel-like factor, or EKLF) plays essential roles in embryonic and adult erythropoiesis. KLF2 is a positive regulator of the mouse and human embryonic β- globin genes. KLF1 and KLF2 have overlapping roles in embryonic erythropoiesis, as demonstrated using single and double knockout (KO) mouse models. Ablation of the KLF1 or KLF2 gene causes embryonic lethality, and double KO embryos are more anemic and die sooner than either single KO. We have shown that KLF1 and KLF2 positively regulate the human ϵ- (embryonic) and γ-globin (fetal) genes during embryonic erythropoiesis. Chromatin immunoprecipitation assays (ChIP) show that KLF1 and KLF2 bind to the promoters of the human ϵ- and γ-globin genes, the mouse embryonic Ey- and βh1-globin genes, and also to the β-globin locus control region (LCR) in mouse embryonic erythroid cells. ChIP assays show that KLF1 but not KLF2 ablation results in abnormal histone modifications in the β-globin locus in mouse embryonic erythroid cells. H3K9Ac and H3K4me3, which correlate with open chromatin and active transcription, are both reduced in KLF1-/- primitive erythroid cells. Human CD34+ hematopoietic stem cells obtained from umbilical cord blood were in vitro differentiated along the erythroid lineage. ChIP assays indicate that both KLF1 and KLF2 bind to the promoter of γ-globin gene in this fetal erythroid model. KLF1 knockdown in these cells affects mainly adult β- globin gene expression. However, the decrease in β- globin gene expression in KLF1 knockdown also affects the ratio of γ- to β- globin in these cells. H3K9Ac and H3K4me3 were decreased only at the β- globin gene which coincides with lower recruitment of RNA polymerase II and its active form, RNA polymerase II phospho-serine 2. In conclusion, we showed using mouse primitive erythroid cells and cord blood definitive cells that KLF1 and KLF2 coordinate the regulation of the mouse and human β- globin genes by direct binding to the promoters and LCR in the β- globin locus. In conclusion, cord blood hematopoietic cells could serve as a complimentary system in addition to the transgenic mouse models to study the regulation of γ- globin gene expression.

The genes of the human β-globin locus are located on chromosome 11 in the order of their expression during development: 5' ε, γ, β 3'. During development, silencing of the 5' gene occurs with activation of the immediate 3' gene. This process occurs twice and is termed hemoglobin switching. The exact mechanism(s) of this process have not been fully described. Herein, we describe a role for DNA methylation and methyl binding domain protein 2 in the transcriptional regulation of the human embryonic and fetal beta type globin genes. Adult mice containing the entire human β-globin locus as a yeast artificial chromosome (βYAC) express very low levels of the fetal γ-globin gene. However, treatment of adult βYAC transgenic mice with the DNA methyltransferase inhibitor, 5-azacytidine, induces a >10-fold increase γ-globin mRNA levels. In addition, βYAC transgenic mice null for methyl binding domain protein 2 (MBD2) express a similar level of γ-globin mRNA. DNA methylation and MBD2 appear to induce γ-globin expression via the same pathway(s), as treatment of MBD2 null βYAC transgenic mice do not show an additive boost in γ-globin expression. MBD2 does not bind to the γ-globin promoter region in vivo indicating MBD2 mediated transcriptional silencing does not occur by recruitment of transcriptional repression complexes to the γ-globin gene promoter. Additionally, these transgenic mice contain only the 5' portion of the β-globin locus through the ε-globin, and do not express the ε-globin genes as adults. However, treatment with 5-azacytidine or loss of MBD2 induces expression of the ε-globin gene in adult transgenic mice. A similar induction of ε-globin is seen in βYAC transgenic mice under the same conditions. The level of expression of the ε-globin gene is much lower than the γ-globin gene, indicating the powerful effect of the cis elements mediating transcriptional repression of the ε-globin gene. These studies indicate DNA methylation and MBD2 contribute to the transcriptional repression of the human embryonic and fetal β-type globin genes. Additionally, MBD2 has been identified as a potential target for the therapeutic induction of fetal hemoglobin for the treatment of hemoglobinopathies.

Hemoglobinopathies are some of the most common monogenic disorders in the world, affecting millions of people and representing a growing burden on health systems worldwide. Although the pathophysiology of sickle cell anemia and beta-thalassemia, two of the most common hemoglobinopathies, have been the focus of much research over the last century, patients affected by these diseases still lack a widely applicable and easily available cure. Sickle cell anemia and beta-thalassemia are caused by defects in the structure and production of the beta-globin chains that, along with the alpha-globin chains make up the heterotetrameric hemoglobin molecule. Studies geared towards re-expression of the silenced fetal gamma-globin gene in adult erythroid cells as a therapeutic strategy to alleviate the symptoms of beta-globin deficiencies have met with some success for the treatment of sickle cell anemia but not for beta-thalassemia. A better understanding of normal gamma-globin gene regulation will undoubtedly advance the development of more effective therapeutic strategies. Because many of the potential targets that may be modulated to achieve gamma-globin re-expression also have functions in erythroid cells other than regulating the gamma-globin gene, it is imperative to understand their role in all aspects of erythropoiesis before they are used for therapy. The current study focuses on the role of two Krüppel-like transcription factors, KLF1 and KLF2, which have known roles in the processes of primitive and definitive erythropoiesis as well as globin gene regulation. The regulation of primitive erythropoiesis by KLF1 and KLF2 is studied using the mouse as a model system because it is not possible to study primitive erythropoiesis in humans. Previous studies have shown that KLF1 and KLF2 are essential for and have overlapping roles in primitive erythropoiesis. Simultaneous ablation of KLF1 and KLF2 results in a severely anemic embryonic phenotype that is not evident in KLF1 or KLF2 single knockout embryos. In this study, we show that this anemia is caused by a paucity of blood cells, and exacerbated by diminished beta-like globin gene expression. The anemia phenotype is dose-dependent, and interestingly, can be ameliorated by a single copy of the KLF2, but not the KLF1 gene. The roles of KLF1 and KLF2 in maintaining both normal peripheral blood cell numbers and globin mRNA amounts are erythroid cell-specific. It was discovered that KLF2 has an essential function in erythroid precursor maintenance. KLF1 can partially compensate for KLF2 in this role, but is uniquely crucial for erythroid precursor proliferation, through its regulation of G1- to S-phase cell cycle transition. A more drastic impairment of primitive erythroid colony formation from embryonic progenitor cells occurs with simultaneous deficiency of KLF1 and KLF2, than with loss of a single factor. The regulation of human beta-like globin gene expression is studied using a recently developed in vitro system for the production of erythroid cells from umbilical cord blood hematopoietic precursor cells, representing a more “fetal” model of globin gene expression. Previous studies have shown that KLF1 binds to the promoters of the gamma- and beta-globin genes, while KLF2 binds to the promoter of the gamma-globin gene in cord blood-derived erythroid cells. Studies using transgenic mice carrying the entire human beta-globin locus had indicated that KLF1 and KLF2 positively regulate gamma-globin expression in mouse embryonic erythroid cells. We demonstrate in this study that KLF1 appears to have dual roles in the regulation of gamma-globin expression in human cord blood-derived definitive erythroid cells. Partial depletion of KLF1 causes elevated gamma-globin expression, while nearly complete depletion of KLF1 results in a down-regulation of gamma-globin expression. Of particular interest was the observation that KLF2 positively regulates gamma-globin expression in cord blood-derived erythroid cells. Surprisingly, KLF2 also positively regulates beta-globin expression in these cells. If regulation of gamma-globin by KLF2 proves to be a direct effect, KLF2 will join a very small group of factors known to directly activate gamma-globin expression.

Chan Kai Man. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 109-119). / Abstracts in English and Chinese. / Title --- p.i / Thesis committee --- p.ii / Statement --- p.iii / Acknowledgement --- p.iv / Abbreviations --- p.v / Abstract (English) --- p.vii / Abstract (Chinese) --- p.ix / Table of contents --- p.xi / List of Figures --- p.xvi / Chapter Chapter 1: --- General Introduction --- p.1 / Chapter 1.1 --- Human Hemoglobin --- p.1 / Chapter 1.2 --- Hemoglobinopathies --- p.4 / Chapter 1.3 --- Hereditary Persistence of Fetal Hemoglobin (HPFH) and β - Thalassemias --- p.6 / Chapter 1.4 --- Globin Genes Switching --- p.7 / Chapter 1.5 --- Pharmaceutical Agents for γ-Globin Gene Reactivation --- p.9 / Chapter 1.6 --- Discovery of LC978: A Novel Fetal Hemoglobin Inducing Agent --- p.10 / Chapter 1.7 --- Aim of Study --- p.11 / Chapter Chapter 2: --- Specific Induction of Gamma Globin Gene Transcription in K562 Leukemia Cell Line by Lead Compound LC978 --- p.12 / Chapter 2.1 --- K562 Cell Line as a Model for Gamma Globin Gene Induction Studies --- p.12 / Chapter 2.2 --- LC978-Induced Fetal Hemoglobin Expression in K562 Cell Line --- p.12 / Chapter 2.3 --- Materials --- p.14 / Chapter 2.3.1 --- "Chemicals, Kits and Reagents" --- p.14 / Chapter 2.3.2 --- Buffers and Solutions --- p.15 / Chapter 2.3.3 --- Cell Line --- p.16 / Chapter 2.3.4 --- Instruments and Equipments --- p.16 / Chapter 2.3.5 --- Enzymes --- p.16 / Chapter 2.3.6 --- Nucleic Acids --- p.17 / Chapter 2.3.7 --- Oligo Primers --- p.17 / Chapter 2.4 --- Methods --- p.17 / Chapter 2.4.1 --- In vitro Bioassay for Total Hemoglobin Production --- p.17 / Chapter (a) --- Preparation of Treatment Cell Culture Plates --- p.17 / Chapter (b) --- Treatment of K562 Cells by LC978 --- p.18 / Chapter (c) --- Signal Development --- p.18 / Chapter 2.4.2 --- Detection of Fetal Hemoglobin Production by HbF Sandwich ELISA --- p.18 / Chapter (a) --- Treatment of K562 Cells by LC978 --- p.18 / Chapter (b) --- Preparation of Capture Antibody-Coated and BSA-Blocked ELISA Plate --- p.19 / Chapter (c) --- Preparation of K562 Cell Lysates --- p.19 / Chapter (d) --- Antigen Capture and Signal Development --- p.19 / Chapter 2.4.3 --- Detection of Gamma Globin mRNA Level by Real-time RT-PCR --- p.20 / Chapter (a) --- Treatment of K562 Cells by LC978 --- p.20 / Chapter (b) --- Preparation of K562 Cell Lysate in Guanidium Thiocyanate (GT) Solution --- p.20 / Chapter (c) --- Isolation of Total RNA from LC978-treated K562 Cells --- p.21 / Chapter (d) --- cDNA Synthesis from mRNA by Reverse Transcriptase (RT) --- p.22 / Chapter (e) --- Real-Time Quantitative Polymerase Chain Reaction (PCR) --- p.23 / Chapter 2.5 --- Results --- p.24 / Chapter (a) --- In vitro Bioassay for Total Hemoglobin Production --- p.24 / Chapter (b) --- Fetal Hemoglobin Sandwich ELISA --- p.24 / Chapter (c) --- LC978-Induced Gamma Globin mRNA Accumulation --- p.25 / Chapter 2.6 --- Discussion --- p.31 / Chapter Chapter 3: --- Construction of Promoter-Reporter Plasmid Constructs --- p.33 / Chapter 3.1 --- The Human Gamma Globin Gene Promoter --- p.33 / Chapter 3.2 --- SEAP as a Reporter Gene for Promoter Deletion Study --- p.34 / Chapter 3.3 --- Materials --- p.35 / Chapter 3.3.1 --- "Chemicals, Kits and Reagents" --- p.35 / Chapter 3.3.2 --- Buffers and Solutions --- p.35 / Chapter 3.3.3 --- Bacterial Strain --- p.36 / Chapter 3.3.4 --- Cell Line --- p.36 / Chapter 3.3.5 --- Enzymes --- p.37 / Chapter 3.3.6 --- Nucleic Acids --- p.37 / Chapter 3.3.7 --- Oligo Primers --- p.37 / Chapter 3.4 --- Methods --- p.38 / Chapter 3.4.1 --- Molecular Cloning of A-Gamma Globin Gene Promoter and 3' Enhancer into pBlueScript II SK (-) --- p.38 / Chapter (a) --- Design and Synthesis of Oligo Primers --- p.38 / Chapter (b) --- Isolation of Genomic DNA from K562 Cells --- p.39 / Chapter (c) --- PCR Amplification of Gamma Globin Gene Promoter and 3' Enhancer --- p.40 / Chapter (d) --- Ligation of PCR Fragments into EcoR V-cut pBlueScript II SK (-) --- p.41 / Chapter (e) --- Preparation of E coli DH5a Competent Cells --- p.43 / Chapter (f) --- Heat-Shock Transformation of E. coli DH5a Competent Cells --- p.44 / Chapter (g) --- PCR Screening and Plasmid Purification of Putative pBlu2SKM-γAP and pBlu2SKM-γAE --- p.44 / Chapter (h) --- Isolation of Putative pBlu2SKM-γAP and pBlu2SKM-γAE Plasmid DNA --- p.45 / Chapter (j) --- Nucleotide Sequencing of Putative pBlu2SKM-yAP and pBlu2SKM-γAE --- p.47 / Chapter (j) --- Graphical Summary of Section 3.6.1 Sub-cloning Procedures --- p.49 / Chapter 3.4.2 --- Molecular Cloning of A-Gamma Globin Gene Promoter and 3' Enhancer into pSEAP2-Enhancer --- p.51 / Chapter (a) --- Sub-cloning of Promoter Fragment into pSEAP2-Enhancer --- p.51 / Chapter (b) --- Sub-cloning of 3' Enhancer Fragment into p 1224γAP-SEAP2 --- p.52 / Chapter (c) --- Graphical Summary of Section 3.6.2 Sub-cloning Procedures --- p.54 / Chapter 3.4.3 --- Construction of p 1224γAP-SEAP2-γAE Promoter Deletions Constructs --- p.56 / Chapter (a) --- Restriction Digestion at 5' End of A-Gamma Promoter Deletions --- p.56 / Chapter (b) --- Restriction Digestion at 3' Ends of A-Gamma Promoter Deletions --- p.56 / Chapter (c) --- Blunting 5'-overhangs and Self-Ligation of Linearized Plasmid Constructs --- p.57 / Chapter (d) --- Graphical Summary of Section 3.6.3 5，Deletions Procedures --- p.58 / Chapter 3.5 --- Results --- p.59 / Chapter (a) --- Nucleotide Sequence Confirmed by Cycle Sequencing --- p.60 / Chapter (b) --- "Resulting Plasmid Constructs p 1224γAP-SEAP2-yAE, p754yAP-SEAP2-yAE and p205yAP-SEAP2-γAE" --- p.64 / Chapter 3.6 --- Discussion --- p.67 / Chapter Chapter 4: --- Mapping of LC978-Responsive Elements on Human A-Gamma Globin Gene Promoter --- p.69 / Chapter 4.1 --- Introduction --- p.69 / Chapter 4.2 --- pSV-β-Galactosidase as a Transfection Normalization Standard --- p.69 / Chapter 4.3 --- pSV-β-Galactosidase as a Transfection Normalization Standard --- p.70 / Chapter 4.4 --- Materials --- p.72 / Chapter 4.4.1 --- "Chemicals, Kits and Reagents" --- p.72 / Chapter 4.4.2 --- Buffers and Solutions --- p.73 / Chapter 4.4.3 --- Cell Line --- p.74 / Chapter 4.4.4 --- Nucleic Acids --- p.74 / Chapter 4.4.5 --- Instruments and Equipments --- p.74 / Chapter 4.5 --- Methods --- p.74 / Chapter 4.5.1 --- Determination of Optimal Dose of Transfection Reagent for --- p.74 / Chapter (a) --- Sterilization of Plasmid DNA for Transfection --- p.74 / Chapter (b) --- Transient Transfection of K562 Cells by pEGFP-N 1 --- p.75 / Chapter (c) --- Examination of EGFP Expression Level --- p.76 / Chapter 4.5.2 --- β-Galactosidase as Normalization Standard for K562 Transfections --- p.76 / Chapter (a) --- Transient Transfection of K562 Cells by pSV-β-Gal --- p.76 / Chapter (b) --- Determination of β-Galactosidase Expression Level --- p.76 / Chapter 4.5.3 --- Mapping of LC978-Responsive Elements on Human Gamma Globin Gene Promoter --- p.77 / Chapter (a) --- Co-Transfection of K562 Cells by p1224/754/205γAP-SEAP2 -γAE and pSV-β-Gal --- p.77 / Chapter (b) --- Treatment of Co-Transfected K562 Cells by LC978 --- p.77 / Chapter (c) --- Determination of β-Galactosidase Expression Level --- p.78 / Chapter (d) --- Determination of Secreted Alkaline Phosphatase (SEAP) Expression Level --- p.78 / Chapter (e) --- Determination of Fetal Hemoglobin Expression Level --- p.79 / Chapter 4.5.4 --- Mapping of Hydroxyurea-Responsive Elements on Human Gammm Globin Gene Promoter --- p.80 / Chapter (a) --- Determination of Optimal Biological Dose (OBD) of Hydroxyurea --- p.80 / Chapter (b) --- Co-Transfection of K562 Cells and Subsequent Treatment by Hydroxyurea --- p.80 / Chapter (c) --- "Assay for β-Galactosidase (β-Gal), Secreted Alkaline Phosphatase (SEAP) and Fetal Hemoglobin (HbF) Expression Level" --- p.81 / Chapter 4.5.5 --- Sodium Butyrate-Induced SEAP Expression --- p.81 / Chapter (a) --- Determination of Optimal Biological Dose (OB(d) of Sodium Butyrate --- p.81 / Chapter (b) --- Co-Transfection of K562 Cells and Treatment by Sodium Butyrate --- p.82 / Chapter (c) --- "Assay for p-Galactosidase (β-Gal), Secreted Alkaline Phosphatase (SEAP) and Fetal Hemoglobin (HbF) Expression Level" --- p.83 / Chapter 4.5.6 --- Data Analysis --- p.83 / Chapter (a) --- "Data Processing, Normalization and Graphing" --- p.83 / Chapter (b) --- Statistical Analysis --- p.83 / Chapter 4.6 --- Results --- p.84 / Chapter 4.6.1 --- Optimal Dose of Transfection Reagent for K562 --- p.84 / Chapter 4.6.2 --- β-Galactosidase as Normalization Standard for K562 Transfections --- p.84 / Chapter 4.6.3 --- LC978 Induction on Co-Transfected K562 Cells --- p.84 / Chapter 4.6.4 --- Hydroxyurea Induction on Co-Transfected K562 Cells --- p.85 / Chapter 4.6.5 --- Sodium Butyrate Induction on Co-Transfected K562 Cells --- p.86 / Chapter 4.7 --- Discussion --- p.98 / Chapter 4.7.1 --- Theme Question to be Answered --- p.98 / Chapter 4.7.2 --- Optimal Dose of DMRIE-C Transfection Reagent on K562 Cell Line --- p.98 / Chapter 4.7.3 --- pSV-β-gal as an Internal Normalization Control --- p.99 / Chapter 4.7.4 --- Responsive Element Mapping --- p.99 / Chapter (a) --- LC978-Induced Response --- p.100 / Chapter (b) --- Hydroxyurea-Induced Response --- p.100 / Chapter (c) --- Sodium Butyrate-Induced Response --- p.101 / Chapter 4.7.5 --- LCR-Dependent Gamma Globin Gene Reactivation --- p.101 / Chapter 4.7.6 --- Induction of Gamma Globin by Histone Deacetylase Inhibitor --- p.104 / Chapter 4.7.7 --- Basal SEAP Expression Levels of the Promoter-Reporter Constructs --- p.105 / Chapter 4.7.8 --- Summary --- p.105 / Chapter Chapter 5: --- General Discussion --- p.106 / References Cited --- p.109

Bibliography: 31 unnumbered leaves at end of vol / vii, 143 leaves, [50] leaves, [31] leaves of plates : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Genetics, 1984

Η αύξηση της έκφρασης του γονιδίου της γ-σφαιρίνης και κατ’ επέκταση και της εμβρυικής αιμοσφαιρίνης (HbF), μέσω ενεργοποίησης με φαρμακολογικούς παράγοντες ή μεταφοράς του γονιδίου της γ-σφαιρίνης, αποτελούν σημαντικές στρατηγικές για την θεραπεία της δρεπανοκυτταρικής και μεσογειακής αναιμίας. Καινοτομία αποτελεί η δημιουργία ενός ειδικού συνθετικού ενεργοποιητή της γ-σφαιρίνης, του Zif-VP64, με δομή δακτύλων ψευδαργύρου, ειδικά σχεδιασμένη για πρόσδεση σε αλληλουχία 18bp, περί την θέση -117HPFH του υποκινητή της γ-σφαιρίνης. Επιδίωξη της εργασίας αυτής ήταν η ανάπτυξη ενός μη ιϊκού, επισωματικού φορέα, που φέρει τον συνθετικό ενεργοποιητή του γονιδίου της γ-σφαιρίνης, ικανού να λειτουργεί με επάρκεια σε κύτταρα του αιμοποιητικού ιστού. Η φορέας αυτός, Zif-VP64-Ep1, περιλαμβάνει τον ενεργοποιητή της γ-σφαιρίνης και την μεταγραφική κασέτα CMV-eGFP-S/MAR, για την εξασφάλιση της επισωματικής του κατάστασης μέσω του στοιχείου S/MAR. Τα αποτελέσματά μας δείχνουν ότι ο φορέας Zif-VP64-Ep1: i. διαμολύνει επιτυχώς, K562 κύτταρα σε ποσοστό 45% παραμένοντας σε επισωματική κατάσταση και υποστηρίζοντας έκφραση του διαγονιδίου για τουλάχιστον 200 γενεές, προγονικά κύτταρα μυελού τον οστών ποντικού β-YAC BMCs σε ποσοστό 23% και CD34+ κύτταρα περιφερικού αίματος κινητοποιημένου υγιούς δότη σε ποσοστό 22,5%. ii. ο φορέας Zif-VP64-Ep1 υποστηρίζει σημαντική αύξηση των επιπέδων της γ-σφαιρίνης κατά 3.3±0.2 φορές σε Κ562 και 3.0±1 φορές σε CD34+ κύτταρα, και ενεργοποίηση του ανενεργού γονιδίου γ-σφαιρίνης σε κύτταρα β-YAC BMCs. Επιτυγχάνεται έτσι, για πρώτη φορά, επισωματική γονιδιακή μεταφορά του ενεργοποιητή Zif-VP64 και trans-ενεργοποίηση του γ-γονιδίου σε επίπεδο θεραπευτικής σημασίας. / The increase of HbF through activation of gamma-globin gene is a valid strategy for the treatment of hemoglobinopathies. Zif-VP64 is a selective, synthetic gamma-globin activator, containing a zinc-finger DNA protein that binds the gamma-globin promoter -117HPFH area and a transcription inducer that induces gamma globin gene in K562 cells, after viral transfer. We report the study of an episomal vector of this activator, which is based on a Scaffold/Matrix attachment region (S/MAR) that supports retention of episomes in the nucleus of the host cell. We constructed an episomal vector, Zif-VP64-Ep1, containing the activator Zif-VP64, the reporter gene cassette CMV-eGFP and the S/MAR element. Gene transfer into cells was done by electroporation or nucleofection. Expression of eGFP was documented by Florescent Microscopy and Flow Cytometry, while the fate of vector molecules in the cells was studied by Southern Blot and plasmid rescue experiments. Real time PCR, Western blotting and Intracellular Flow Cytometry were used to investigate gamma-globin mRNA, gamma-globin protein and HbF protein levels respectively. Binding specificity of the activator was determined by Chromatin Immunoprecipitation (ChIP). Gene transfer was done in K562 cells producing long term stable cell lines; murine beta-YAC cells, where the YAC contains the complete human, beta-globin gene locus; and human progenitor hemopoietic CD34+ cells from healthy, mobilized individuals, with transfection efficiencies of 65%, 25% and 23% respectively. In K562 cells, gamma-globin mRNA levels showed an increase of 250%, gamma-globin protein of 350% and HbF protein of 165%, as compared to the corresponding levels in the untransfected K562 cells, at least 200 generations post-transfection. Interestingly, vector Zif-VP64-Ep1 was able to mediate the activation of expression of the silent, human gamma-globin gene of the murine beta-YAC cells, at a level matching the (active) human beta-globin gene of the YAC, as well as the murine beta-globin gene, showing that it can efficiently activate the gamma-globin gene from within a heterochromatic region. Finally and most significantly, vector Zif-VP64-Ep1 was able to transfect the human, hemopoietic progenitor CD34+ cells and to mediate a 3.0±1 fold increase of gamma globin mRNA, compared to untrasnfected CD34+ cells, as estimated in cultures of 7-8 days after transfection. In conclusion, activation of human gamma-globin by episomal gene transfer of a synthetic activator, in three different hemopoietic cells, is documented, including the CD43+ cells, that are the target cells for gene therapy of the Hemoglobinopathies. This is the first time that an S/MAR based episomal vector is used for gene transactivation in a cell line and progenitor cells, aiming at specific gene therapy.

Sickle cell disease (SCD) is a monogenic disorder with multi-organ involvement(1). Patients with SCD suffer from recurrent vaso-occlusive crisis (VOC) resulting from sickling of red blood cells, which is induced by polymerization of deoxy-sickle hemoglobin (HbS)(1,2). Fetal hemoglobin (HbF) can ameliorate symptoms of SCD by inhibiting deoxy-HbS polymerization(3). Hydroxyurea (HU) is approved by FDA for the treatment of SCD(4). It induces HbF synthesis through multifactorial and still not well understood mechanisms(4-7). However, approximately 5-15% of patients show no significant clinical improvement(8). Additionally, numerous patient and physician-related factors limit its utilization(9). Therefore, it is important to identify additional HbF-inducing therapeutic agents, particularly those that act by mechanisms different from HU to allow potential combination therapy in the future. Previously, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) was shown to activate γ-globin gene transcription(10). Forced overexpression of PGC-1α in erythroid progenitors obtained from Lin- cells from SCD transgenic mice induces γ-globin expression(10), suggesting that PGC-1α represents a new molecular target for potential therapeutic intervention in treating SCD. In the present study, the effect of PGC-1α upregulation in primary human CD34+ derived erythroid cells was explored; an increase in γ-globin mRNA and the percent of F-cells was observed. Through literature search, ZLN005 and SR-18292 were identified as potential PGC-1α agonists(11,12). Both compounds increase the percentage of F-cells in primary human CD34+ derived erythroid cell culture. Combined treatment with HU led to a significantly higher increase in F-cell % than the increase observed under treatment with either HU, ZLN005 or SR-18292 alone. Results from those studies add to the understanding of PGC-1α and its effects on primary human erythroid cell differentiation, maturation, and HbF induction. Additionally, the results show proof of principle for combination therapy to treat SCD patients to ameliorate their disease severity by up-regulating HbF expression. Together, the knowledge gained through these studies is novel and will potentiate the development of a new class of compounds to induce HbF synthesis in adults.

Le facteur de transcription BP1 humain est exprimé dans les cellules érythroïdes pendant le développement fœtal mais son niveau d’expression est réduit au stade adulte. Les études antérieures in vitro ont montré que BP1 est un répresseur du gène adulte de β-globine mais sa fonction dans la régulation des gènes ε et γ n’a pas été abordée à ce jour. Dans notre étude, nos analyses de BP1 humain ont été menées in vivo au stade embryonnaire en utilisant une lignée de souris transgénique surexprimant BP1 dans les cellules érythroïdes définitives murines. Au niveau protéique, BP1 humain est exprimé aux âges E12.5 et E13.5 dans les cellules érythroïdes fœtales des embryons transgéniques. Toutefois, les niveaux de BP1 humain ne perturbent pas l’érythropoïèse définitive fœtale: les embryons transgéniques ne sont pas anémiques et ne meurent pas in utero. La surexpression de BP1 humain altère tout de même le niveau endogène des facteurs de transcription Ikaros et SOX6 impliqués dans la régulation des gènes de β-globine durant l’érythropoïèse définitive fœtale murine. Chez les embryons doubles transgéniques exprimant BP1 et les gènes humains de β-globine à E12.5, l’expression du gène adulte β est réduite alors que celle des gènes ε et γ est non réprimée. Les mesures d’expression des gènes humains de β-globine effectuées en absence d’Ikaros à E12.5 précisent le rôle de BP1 humain dans l’activation du gène embryonnaire ε. Dans les cellules érythroïdes fœtales murines dépourvues d’Ikaros à E12.5, BP1 humain augmente grandement l’expression des facteurs de transcription EKLF et BCL11A et semble déréprimer l’expression de SOX6, ce qui conduit à une répression des gènes fœtaux et une activation du gène adulte β au jour embryonnaire murin suivant. Puisque BP1 atténue l’altération de l’expression des gènes fœtaux et adultes causée par l’absence d’Ikaros, nous proposons que BP1 et Ikaros soient liés dans les mécanismes de transcription des gènes humains de β-globine. / The transcription factor BP1 is expressed in erythroid cells during fetal development but is downregulated at adult stage. In vitro previous studies revealed that BP1 acts as a repressor of adult β-globin gene expression but its function in ε and γ globin gene regulation has not been investigated so far. In our studies, BP1 functions analyses were proceeded in vivo at embryonic stage by using a transgenic mouse line overexpressing human BP1 in murine definitive erythroid cells. At protein level, human BP1 is expressed in E12.5 and E13.5 fetal erythroid cells of transgenic embryos. However, levels of human BP1 do not impair murine fetal definitive erythropoiesis : transgenic embryos are not anemic and survive during gestation. Overexpression of human BP1 impairs, nonetheless, endogenous level of the transcription factors Ikaros and SOX6 involved in β-globin gene regulation during murine fetal definitive erythropoiesis. In double transgenic mice expressing BP1 and human β-globin genes at embryonic day E12.5, β gene expression is reduced whereas ε- and γ-globin genes are not repressed. Measurements of β-globin gene expression in absence of Ikaros pinpoint the role of human BP1 in embryonic ε-globin gene activation. In E12.5 Ik-/- murine fetal erythroid cells, human BP1 highly increases EKLF and BCL11A transcription level and seems to derepress SOX6 expression which lead to γ silencing and β activation at E13.5. Since BP1 attenuates globin gene alterations caused by absence of Ikaros, we propose that BP1 and Ikaros are linked in transcriptional mechanisms of human β-globin genes.