Sumoylation of p45/NF-E2: nuclear positioning and transcriptional activation of the mammalian beta-like globin gene locus

SUMO and Transcriptional Regulation: The Lessons of Large-Scale Proteomic, Modifomic and Genomic Studies

One major role of the eukaryotic peptidic post-translational modifier SUMO in the cell is transcriptional control. This occurs via modification of virtually all classes of transcriptional actors, which include transcription factors, transcriptional coregulators, diverse chromatin components, as well as Pol I-, Pol II- and Pol III transcriptional machineries and their regulators. For many years, the role of SUMOylation has essentially been studied on individual proteins, or small groups of proteins, principally dealing with Pol II-mediated transcription. This provided only a fragmentary view of how SUMOylation controls transcription. The recent advent of large-scale proteomic, modifomic and genomic studies has however considerably refined our perception of the part played by SUMO in gene expression control. We review here these developments and the new concepts they are at the origin of, together with the limitations of our knowledge. How they illuminate the SUMO-dependent transcriptional mechanisms that have been characterized thus far and how they impact our view of SUMO-dependent chromatin organization are also considered.

miR-122-mediated translational repression of PEG10 and its suppression in human hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC), a primary liver malignancy, is the most common cancer in males and fourth common cancer in females in Taiwan. HCC patients usually have a poor prognosis due to late diagnosis. It has been classified as a complex disease because of the heterogeneous phenotypic and genetic traits of the patients and a wide range of risk factors. Micro (mi)RNAs regulate oncogenes and tumor suppressor genes that are known to be dysregulated in HCC. Several studies have found an association between downregulation of miR-122, a liver-specific miRNA, and upregulation of paternally expressed gene 10 (PEG10) in HCC; however, the correlation between low miR-122 and high PEG10 levels still remains to be defined and require more investigations to evaluate their performance as an effective prognostic biomarker for HCC.

Methods

An in silico approach was used to isolate PEG10, a potential miR-122 target implicated in HCC development. miR-122S binding sites in the PEG10 promoter were evaluated with a reporter assay. The regulation of PEG10 by miR-122S overexpression was examined by quantitative RT-PCR, western blotting, and immunohistochemistry in miR-122 knockout mice and liver tissue from HCC patients. The relationship between PEG10 expression and clinicopathologic features of HCC patients was also evaluated.

Results

miR-122 downregulated the expression of PEG10 protein through binding to 3′-untranslated region (UTR) of the PEG10 transcript. In miR-122 knockout mice and HCC patients, the deficiency of miR-122 was associated with HCC progression. The expression of PEG10 was increased in 57.3 % of HCC as compared to paired non-cancerous tissue samples. However, significant upregulation was detected in 56.5 % of patients and was correlated with Okuda stage (P = 0.05) and histological grade (P = 0.001).

Conclusions

miR-122 suppresses PEG10 expression via direct binding to the 3′-UTR of the PEG10 transcript. Therefore, while PEG10 could not be an ideal diagnostic biomarker for HCC but its upregulation in HCC tissue still has predictive value for HCC prognosis.

Regulation and function of the NFE2 transcription factor in hematopoietic and non-hematopoietic cells

The NFE2 transcription factor was identified over 25 years ago. The NFE2 protein forms heterodimers with small MAF proteins, and the resulting complex binds to regulatory elements in a large number of target genes. In contrast to other CNC transcription family members including NFE2L1 (NRF1), NFE2L2 (NRF2) and NFE2L3 (NRF3), which are widely expressed, earlier studies had suggested that the major sites of NFE2 expression are hematopoietic cells. Based on cell culture studies it was proposed that this protein acts as a critical regulator of globin gene expression. However, the knockout mouse model displayed only mild erythroid abnormalities, while the major phenotype was a defect in megakaryocyte biogenesis. Indeed, absence of NFE2 led to severely impaired platelet production. A series of recent data, also summarized here, shed new light on the various functional roles of NFE2 and the regulation of its activity. NFE2 is part of a complex regulatory network, including transcription factors such as GATA1 and RUNX1, controlling megakaryocytic and/or erythroid cell function. Surprisingly, it was recently found that NFE2 also has a role in non-hematopoietic tissues, such as the trophoblast, in which it is also expressed, as well as the bone, opening the door to new research areas for this transcription factor. Additional data showed that NFE2 function is controlled by a series of posttranslational modifications. Important strides have been made with respect to the clinical significance of NFE2, linking this transcription factor to hematological disorders such as polycythemias.

Tight regulation of a timed nuclear import wave of EKLF by PKCθ and FOE during Pro-E to Baso-E transition

Erythropoiesis is a highly regulated process during which BFU-E are differentiated into RBCs through CFU-E, Pro-E, PolyCh-E, OrthoCh-E, and reticulocyte stages. Uniquely, most erythroid-specific genes are activated during the Pro-E to Baso-E transition. We show that a wave of nuclear import of the erythroid-specific transcription factor EKLF occurs during the Pro-E to Baso-E transition. We further demonstrate that this wave results from a series of finely tuned events, including timed activation of PKCθ, phosphorylation of EKLF at S68 by P-PKCθ(S676), and sumoylation of EKLF at K74. The latter EKLF modifications modulate its interactions with a cytoplasmic ankyrin-repeat-protein FOE and importinβ1, respectively. The role of FOE in the control of EKLF nuclear import is further supported by analysis of the subcellular distribution patterns of EKLF in FOE-knockout mice. This study reveals the regulatory mechanisms of the nuclear import of EKLF, which may also be utilized in the nuclear import of other factors.

SUMOylation regulates the transcriptional repression activity of FOG-2 and its association with GATA-4

Friend of GATA 2 (FOG-2), a co-factor of several GATA transcription factors (GATA-4, -5 and 6), is a critical regulator of coronary vessel formation and heart morphogenesis. Here we demonstrate that FOG-2 is SUMOylated and that this modification modulates its transcriptional activity. FOG-2 SUMOylation occurs at four lysine residues (K312, 471, 915, 955). Three of these residues are part of the characteristic SUMO consensus site (ψKXE), while K955 is found in the less frequent TKXE motif. Absence of SUMOylation did not affect FOG-2′s nuclear localization. However, mutation of the FOG-2 SUMOylation sites, or de-SUMOylation, with SENP-1 or SENP-8 resulted in stronger transcriptional repression activity in both heterologous cells and cardiomyocytes. Conversely, increased FOG-2 SUMOylation by overexpression of SUMO-1 or expression of a SUMO-1-FOG-2 fusion protein rendered FOG-2 incapable of repressing GATA-4-mediated activation of the B-type natriuretic peptide (BNP) promoter. Moreover, we demonstrate both increased interaction between a FOG-2 SUMO mutant and GATA-4 and enhanced SUMOylation of wild-type FOG-2 by co-expression of GATA-4. These data suggest a new dynamics in which GATA-4 may alter the activity of FOG-2 by influencing its SUMOylation status.

Phosphorylation-dependent SUMOylation of the transcription factor NF-E2

Nuclear factor erythroid-derived 2 (NF-E2), a heterodimer composed of p45 and p18, is a transcriptional activator in hematopoietic progenitors. The transcriptional activity of NF-E2 is not only upregulated by SUMOylation but also stimulated by the cAMP-dependent protein kinase A (PKA). However, the relationship between SUMOylation and phosphorylation in the activation of NF-E2 is unclear. In the present studies, we have demonstrated that PKA enhances NF-E2 SUMOylation in an in vitro system using purified proteins, suggesting a possible mechanism for PKA-dependent activation of the NF-E2 transcription factor through SUMOylation.

Chromatin modification by SUMO-1 stimulates the promoters of translation machinery genes

SUMOylation of transcription factors and chromatin proteins is in many cases a negative mark that recruits factors that repress gene expression. In this study, we determined the occupancy of Small Ubiquitin-like MOdifier (SUMO)-1 on chromatin in HeLa cells by use of chromatin affinity purification coupled with next-generation sequencing. We found SUMO-1 localization on chromatin was dynamic throughout the cell cycle. Surprisingly, we observed that from G1 through late S phase, but not during mitosis, SUMO-1 marks the chromatin just upstream of the transcription start site on many of the most active housekeeping genes, including genes encoding translation factors and ribosomal subunit proteins. Moreover, we found that SUMO-1 distribution on promoters was correlated with H3K4me3, another general chromatin activation mark. Depletion of SUMO-1 resulted in downregulation of the genes that were marked by SUMO-1 at their promoters during interphase, supporting the concept that the marking of promoters by SUMO-1 is associated with transcriptional activation of genes involved in ribosome biosynthesis and in the protein translation process.

Inducible COX-2-dependent apoptosis in human ovarian cancer cells

Resveratrol is a naturally occurring trihydroxyl-diphenylethylene compound that has been shown experimentally to have beneficial effects in the treatment of cancer and cardiovascular disease. Resveratrol induces programmed cell death (apoptosis) in these cells and activates important signal transducing proteins including extracellular signal-regulated kinases (ERKs) 1 and 2 in cancer cells. Resveratrol also causes nuclear accumulation of the enzyme cyclooxygenase (COX)-2 and of the oncogene suppressor protein, p53. We have studied the molecular basis of the anticancer actions of resveratrol using human ovarian carcinoma (OVCAR-3) cells. Our findings include the following: (i) nuclear accumulation of COX-2 in resveratrol-treated cells is blocked by the ERK1/2 inhibitor, PD98059; (ii) an inhibitor of COX-2 activity, NS398, prevents accumulation of ERK1/2, COX-2, activated p53 and small ubiquitin-like modifier (SUMO-1) in the nucleus; (iii) apoptosis, quantitated by nucleosome enzyme-linked immunosorbent assay and the nuclear abundance of the pro-apoptotic protein, BcL-xs, were inhibited by NS398. This finding implicates nuclear COX-2 in p53-mediated apoptosis induced by resveratrol. Sumoylation is important to stabilization of p53 and a COX-2-SUMO-1 interaction suggests sumoylation of COX-2 in resveratrol-treated cells and (iv) chromatin immunoprecipitation studies showed binding of induced nuclear COX-2 to the promoter region of PIG3 and Bax, pro-apoptotic gene targets of transcriptionally active p53. Nuclear accumulation of activated ERK1/2 and sumolyated COX-2 are essential to resveratrol-induced pSer-15-p53-mediated apoptosis in human ovarian cancer cells.

A monopartite sequence is essential for p45 NF-E2 nuclear translocation, transcriptional activity and platelet production

BACKGROUND

p45 NF-E2 is a bZIP transcription factor crucial for thrombopoiesis, as indicated by the fact that loss of p45 NF-E2 function results in dramatic embryonic lethal thrombopoietic defects and its overexpression boosts platelet release.

OBJECTIVES

In the present study, we set out to identify the sequences responsible for p45 NF-E2 nuclear import, evaluate its transport mechanism and ascertain its functional significance.

METHODS

A series of p45 NF-E2 deletion constructs fused to green fluorescent protein (GFP) was created and their cellular localization examined in mammalian cells, with the factor responsible for nuclear import identified using an in vitro transport assay. A p45 NF-E2 derivative mutated in the nuclear targeting sequence (NLS) was generated and its biological activity compared with wild type (wt) in luciferase assays, and proplatelet and platelet production measured in murine megakaryocytes transduced with a retroviral vector.

RESULTS

Here we show that residues 271-273 are essential for nuclear import of p45 NF-E2 in COS-7 and in primary bone marrow cells. The p45 NF-E2 NLS facilitates nuclear import specifically via importin (IMP) 7. Although within the DNA-binding domain of p45 NF-E2, the NLS is not essential for DNA-binding, but is crucial for transcriptional activation and biological activity; where, in contrast to wt, a mutant derivative with a mutated NLS failed to promote proplatelet and platelet production in murine megakaryocytes.

CONCLUSIONS

The NLS is critical for p45 NF-E2 function, with the present study being the first to demonstrate the importance of NLS-dependent nuclear import of p45 NF-E2 for platelet development.

Sumoylation regulates interaction of FOG1 with C-terminal-binding protein (CTBP)

Erythropoietic and megakaryocytic programs are specified from multipotential progenitors by the transcription factor GATA1. FOG1, a GATA1-interaction partner, is critical for GATA1 function in several contexts by bringing multiple complexes into association with GATA1 to facilitate activation or repression of target genes. To further elucidate regulation of these associations by cellular and extracellular cues, we examined FOG1 for post-translational modifications. We found that FOG1 is SUMOylated and phosphorylated in erythroid cells in a differentiation-dependent manner. Removal of the SUMOylation sites in FOG1 does not impair nuclear localization, protein stability, or chromatin occupancy. However, SUMOylation of FOG1 modulates interactions with C-terminal binding protein family members, specifically promoting CTBP1 binding. Phosphorylation of FOG1 modulates SUMOylation and, therefore, indirectly regulates the CTBP interaction. Post-translational modification of FOG1 may contribute to control of co-occupancy by CTBP family members, the NuRD complex, and GATA1 at differentially regulated genes.

Developmental silencing of human zeta-globin gene expression is mediated by the transcriptional repressor RREB1

The mammalian embryonic zeta-globin genes, including that of humans, are expressed at the early embryonic stage and then switched off during erythroid development. This autonomous silencing of the zeta-globin gene transcription is probably regulated by the cooperative work of various protein-DNA and protein-protein complexes formed at the zeta-globin promoter and its upstream enhancer (HS-40). We present data here indicating that a protein-binding motif, ZF2, contributes to the repression of the HS-40-regulated human zeta-promoter activity in erythroid cell lines and in transgenic mice. Combined site-directed mutagenesis and EMSA suggest that repression of the human zeta-globin promoter is mediated through binding of the zinc finger factor RREB1 to ZF2. This model is further supported by the observation that human zeta-globin gene transcription is elevated in the human erythroid K562 cell line or the primary erythroid culture upon RNA interference (RNAi)(2) knockdown of RREB1 expression. These data together suggest that RREB1 is a putative repressor for the silencing of the mammalian zeta-globin genes during erythroid development. Because zeta-globin is a powerful inhibitor of HbS polymerization, our experiments have provided a foundation for therapeutic up-regulation of zeta-globin gene expression in patients with severe hemoglobinopathies.

JNK-mediated turnover and stabilization of the transcription factor p45/NF-E2 during differentiation of murine erythroleukemia cells

Regulation of the homeostatic concentrations of specific sets of transcription factors is essential for correct programming of cell proliferation and differentiation. We have characterized the signal transduction pathways regulating the catabolisis of p45/NF-E2, a bZIP factor activating the erythroid and megakaryocytic gene transcription. Through use of different approaches including nano-scale proteomics, we show that activated-JNK, or Phospho-JNK (P-JNK), physically interacts with p45/NF-E2 and phosphorylates its Ser157 residue. This reaction leads to the poly-ubiquitination of p45/NF-E2 at one or more of six Lys residues, one of which being also a sumoylation site, and its degradation through the proteasome pathway. Significantly, this regulatory pathway of p45/NF-E2 by P-JNK exists only in uninduced murine erythroleukemia (MEL) cells but not in differentiated MEL cells in which JNK is inactivated on DMSO induction. Based on the above data and analysis of the chromatin-binding kinetics of p45/NF-E2 and the erythroid gene repressor Bach1 during the early phase of MEL differentiation, we suggest a model for the regulation of erythroid maturation. In the model, the posttranslational modifications and turnover of p45/NF-E2, as mediated by P-JNK, contribute to the control of its homeostatic concentration and consequently, its regulatory functions in the progression of erythroid differentiation and erythroid gene expression.

Extracellular signal-regulated kinase mitogen-activated protein kinase signaling initiates a dynamic interplay between sumoylation and ubiquitination to regulate the activity of the transcriptional activator PEA3

Many transcription factors are controlled through SUMO modification, and in the majority of cases this modification results in enhancements in their repressive properties. In some instances, SUMO modification and its associated repressive activities can be reversed by the action of intracellular signaling pathways, leading to enhanced transcriptional capacities of transcription factors. Here we have investigated sumoylation of the ETS domain transcription factor PEA3 and its interplay with the extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase signaling pathway. PEA3 is modified by SUMO in vitro and in vivo on multiple sites in its N-terminal region. Activation of the ERK MAP kinase pathway promotes sumoylation of PEA3. Importantly, sumoylation of PEA3 is required for maximal activation of target gene promoters, including MMP-1 and COX-2. Molecularly, sumoylation is selectively required for synergistic activation of target gene expression with the coactivator CBP. Moreover, sumoylation of PEA3 is required for ubiquitination of PEA3 and promotes its degradation, suggesting that SUMO-mediated recycling of PEA3 plays a role in PEA3-mediated promoter activation. Thus, in contrast to the majority of other transcription factors studied, sumoylation of PEA3 plays a positive role in PEA3-mediated transcriptional activation and the ERK MAP kinase pathway cooperates with rather than antagonizes this process.

SUMOylation regulates the transcriptional activity of JunB in T lymphocytes

The AP-1 family member JunB is a critical regulator of T cell function. JunB is a transcriptional activator of various cytokine genes, such as IL-2, IL-4, and IL-10; however, the post-translational modifications that regulate JunB activity in T cells are poorly characterized. We show here that JunB is conjugated with small ubiquitin-like modifier (SUMO) on lysine 237 in resting and activated primary T cells and T cell lines. Sumoylated JunB associated with the chromatin-containing insoluble fraction of cells, whereas nonsumoylated JunB was also in the soluble fraction. Blocking JunB sumoylation by mutation or use of a dominant-negative form of the SUMO-E2 Ubc-9 diminished its ability to transactivate IL-2 and IL-4 reporter genes. In contrast, nonsumoylable JunB mutants showed unimpaired activity with reporter genes controlled by either synthetic 12-O-tetradecanoylphorbol-13-acetate response elements or NF-AT/AP-1 and CD28RE sites derived from the IL-2 promoter. Ectopic expression of JunB in activated human primary CD4(+) T cells induced activation of the endogenous IL-2 promoter, whereas the nonsumoylable JunB mutant did not. Thus, our work demonstrates that sumoylation of JunB regulates its ability to induce cytokine gene transcription and likely plays a critical role in T cell activation.

Transcriptional control of erythropoiesis: emerging mechanisms and principles

Transcriptional networks orchestrate fundamental biological processes, including hematopoiesis, in which hematopoietic stem cells progressively differentiate into specific progenitors cells, which in turn give rise to the diverse blood cell types. Whereas transcription factors recruit coregulators to chromatin, leading to targeted chromatin modification and recruitment of the transcriptional machinery, many questions remain unanswered regarding the underlying molecular mechanisms. Furthermore, how diverse cell type-specific transcription factors function cooperatively or antagonistically in distinct cellular contexts is poorly understood, especially since genes in higher eukaryotes commonly encompass broad chromosomal regions (100 kb and more) and are littered with dispersed regulatory sequences. In this article, we describe an important set of transcription factors and coregulators that control erythropoiesis and highlight emerging transcriptional mechanisms and principles. It is not our intent to comprehensively survey all factors implicated in the transcriptional control of erythropoiesis, but rather to underscore specific mechanisms, which have potential to be broadly relevant to transcriptional control in diverse systems.

Sumoylation of EKLF promotes transcriptional repression and is involved in inhibition of megakaryopoiesis

Erythroid Krüppel-like factor (EKLF [KLF1]) is a transcriptional regulator that plays a critical role within a specific subset of hematopoietic cells, particularly in the erythroid lineage and its immediate precursor, the megakaryocyte-erythroid progenitor (MEP). We find that EKLF is posttranslationally modified by sumoylation at a single site near its amino terminus and that PIAS1 plays a critical role in this process. Mutation of this site has little effect on EKLF's ability to function as a transcriptional activator; however, it has a dramatic effect on its repressive abilities. The mechanism of repression likely involves a novel small ubiquitin-related modifier (SUMO)-dependent EKLF interaction with the Mi-2beta component of the NuRD repression complex. Mutated EKLF is attenuated in its ability to repress megakaryocyte differentiation, implicating EKLF sumoylation status in differentiative decisions emanating from the MEP. These studies demonstrate a novel mechanism by which transcription factor sumoylation can alter protein-protein interactions and bipotential lineage decisions.

Subcellular transport of EKLF and switch-on of murine adult beta maj globin gene transcription

Erythroid Krüppel-like factor (EKLF) is an essential transcription factor for mammalian beta-like globin gene switching, and it specifically activates transcription of the adult beta globin gene through binding of its zinc fingers to the promoter. It has been a puzzle that in the mouse, despite its expression throughout the erythroid development, EKLF activates the adult beta(maj) globin promoter only in erythroid cells beyond the stage of embryonic day 10.5 (E10.5) but not before. We show here that expression of the mouse beta(maj) globin gene in the aorta-gonad-mesonephros region of E10.5 embryos and in the E14.5 fetal liver is accompanied by predominantly nuclear localization of EKLF. In contrast, EKLF is mainly cytoplasmic in the erythroid cells of E9.5 blood islands in which beta(maj) is silenced. Remarkably, in a cultured mouse adult erythroleukemic (MEL) cell line, the activation of the beta(maj) globin gene by dimethyl sulfoxide (DMSO) or hexamethylene-bis-acetamide (HMBA) induction is also paralleled by a shift of the subcellular location of EKLF from the cytoplasm to the nucleus. Blockage of the nuclear import of EKLF in DMSO-induced MEL cells with a nuclear export inhibitor repressed the transcription of the beta(maj) globin gene. Transient transfection experiments further indicated that the full-sequence context of EKLF was required for the regulation of its subcellular locations in MEL cells during DMSO induction. Finally, in both the E14.5 fetal liver cells and induced MEL cells, the beta-like globin locus is colocalized the PML oncogene domain nuclear body, and concentrated with EKLF, RNA polymerase II, and the splicing factor SC35. These data together provide the first evidence that developmental stage- and differentiation state-specific regulation of the nuclear transport of EKLF might be one of the steps necessary for the switch-on of the mammalian adult beta globin gene transcription.

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

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

Globin genes transcriptional switching, chromatin structure and linked lessons to epigenetics in cancer: a comparative overview

At the present time research situates differential regulation of gene expression in an increasingly complex scenario based on interplay between genetic and epigenetic information networks, which need to be highly coordinated. Here we describe in a comparative way relevant concepts and models derived from studies on the chicken alpha- and beta-globin group of genes. We discuss models for globin switching and mechanisms for coordinated transcriptional activation. A comparative overview of globin genes chromatin structure, based on their genomic domain organization and epigenetic components is presented. We argue that the results of those studies and their integrative interpretation may contribute to our understanding of epigenetic abnormalities, from beta-thalassemias to human cancer. Finally we discuss the interdependency of genetic-epigenetic components and the need of their mutual consideration in order to visualize the regulation of gene expression in a more natural context and consequently better understand cell differentiation, development and cancer.

Chromatin-binding in vivo of the erythroid kruppel-like factor, EKLF, in the murine globin loci

EKLF is an erythroid-specific, zinc finger-containing transcription factor essential for the activation of the mammalian beta globin gene in erythroid cells of definitive lineage. We have prepared a polyclonal anti-mouse EKLF antibody suitable for Western blotting and immunoprecipitation (IP) qualities, and used it to define the expression patterns of the EKLF protein during mouse erythroid development. We have also used this antibody for the chromatin-immunoprecipitation (ChIP) assay. EKLF was found to bind in vivo at both the mouse beta-major-globin promoter and the HS2 site of beta-LCR in the mouse erythroleukemia cells (MEL) in a DMSO-inducible manner. The DMSO-induced bindings of EKLF as well as three other proteins, namely, RNA polymerase II, acetylated histone H3, and methylated histone H3, were not abolished but significantly lowered in CB3, a MEL-derived cell line with null-expression of p45/NF-E2, an erythroid-enriched factor needed for activation of the mammalian globin loci. Interestingly, binding of EKLF in vivo was also detected in the mouse alpha-like globin locus, at the adult alpha globin promoter and its far upstream regulatory element alpha-MRE (HS26). This study provides direct evidence for EKLF-binding in vivo at the major regulatory elements of the mouse beta-like globin gene clusters the data also have interesting implications with respect to the role of EKLF-chromatin interaction in mammalian globin gene regulation.