Regulation of the myeloperoxidase enhancer binding proteins Pu1, C-EBP alpha, -beta, and -delta during granulocyte-lineage specification

CCAAT/enhancer binding protein alpha is a regulatory switch sufficient for induction of granulocytic development from bipotential myeloid progenitors

The transcription factor CCAAT/enhancer binding protein alpha (C/EBPalpha) regulates a number of myeloid cell-specific genes. To delineate the role of C/EBPalpha in human granulopoiesis, we studied its expression and function in human primary cells and bipotential (granulocytic/monocytic) myeloid cell lines. We show that the expression of C/EBPalpha initiates with the commitment of multipotential precursors to the myeloid lineage, is specifically upregulated during granulocytic differentiation, and is rapidly downregulated during the alternative monocytic pathway. Conditional expression of C/EBPalpha alone in stably transfected bipotential cells triggers neutrophilic differentiation, concomitant with upregulation of the granulocyte-specific granulocyte colony-stimulating factor receptor and secondary granule protein genes. Moreover, induced expression of C/EBPalpha in bipotential precursors blocks their monocytic differentiation program. These results indicate that C/EBPalpha serves as a myeloid differentiation switch acting on bipotential precursors and directing them to mature to granulocytes.

Use of RDA analysis of knockout mice to identify myeloid genes regulated in vivo by PU.1 and C/EBPalpha

PU.1 and C/EBPalpha are transcription factors essential for normal myeloid development. Loss-of-function mutation of PU.1 leads to an absolute block in monocyte/macrophage development and abnormal granulocytic development while that of C/EBPalpha causes a selective block in neutrophilic differentiation. In order to understand these phenotypes, we studied the role of PU.1 and C/EBPalpha in the regulation of myeloid target genes in vivo . Northern blot analysis revealed that mRNAs encoding receptors for M-CSF, G-CSF and GM-CSF, were expressed at low levels in PU.1(-/-) fetal liver compared with wild type. To identify additional myeloid genes regulated by PU.1 and C/EBPalpha, we performed representational difference analysis (RDA), a PCR-based subtractive hybridization using fetal livers from wild type and PU.1 or C/EBPalpha knockout mice. By introducing a new modification of RDA, that of tissue-specific gene suppression, we could selectively identify a set of differentially expressed genes specific to myeloid cells. Differentially expressed genes included both primary and secondary granule protein genes. In addition, eight novel genes were identified that were upregulated in expression during myeloid differentiation. These methods provide a general strategy for elucidating the genes affected in murine knockout models.

Differential constitutive activation between STAT-related proteins and MAP kinase in primary acute myelogenous leukaemia

Many cytokines and growth factors stimulate multiple signal transduction pathways essential for proliferation in human acute leukaemia cells, including a mitogen-activated protein (MAP) kinase pathway and a Janus kinase (JAK)-STAT (signal transducers and activators of transcription) pathway. We have previously shown constitutive activation of MAP kinase in approximately 50% of acute myelogenous leukaemia (AML) samples. Recently, STAT proteins have been reported to be constitutively activated in 10-20% of AML cases. STAT3 and STAT5 are the main STAT proteins activated in haemopoietic progenitors in response to cytokines such as IL-3, GM-CSF, erythropoietin and thrombopoietin. Although the possibility of STAT1 protein as a substrate for MAP kinase at a serine residue has been suggested, the cross-talk between STATs and MAP kinase pathways in vivo, especially in leukaemia cells, remains unknown. We examined the phosphorylation of STAT 3 and STAT 5 at the tyrosine residues in AML samples in which MAP kinase activity had already been found. 40/50 primary AML cases (80%) exhibited constitutive tyrosine phosphorylation of STAT5. Electrophoretic mobility shift assay showed DNA binding activity of STAT5 correlated with tyrosine phosphorylation of STAT5. Similarly, with respect to STAT3, 17/23 cases examined (74%) showed constitutive tyrosine phosphorylation of STAT3. In addition, we examined the tyrosyl-phosphorylation of STAT5 isoforms, STAT5A and STAT5B, in 20 AML cases, and found selective STAT5B phosphorylation in the absence of STAT5A phosphorylation in three cases. Furthermore, in certain AML cases, constitutive activation of MAP kinase and STAT proteins occurred independently. No significant correlation of MAP kinase activation was observed with either tyrosine phosphorylation of STAT3/STAT5 or positive DNA binding of STAT proteins. These results suggest that constitutive activation of STAT proteins occurs commonly and that the causes of constitutive activation of these two major cascades are heterogeneous in AML.

The Role of Transcription Factor PU.I in the Activity of the Intronic Enhancer of the Eosinophil-Derived Neurotoxin (RNS2) Gene

Eosinophil-derived neurotoxin (EDN) found in the granules of human eosinophils is a cationic ribonuclease toxin. Expression of the EDN gene (RNS2) in eosinophils is dependent on proximal promoter sequences in combination with an enhancer located in the first intron. We further define here the active region of the intron using transfections in differentiated eosinophilic HL60 cells. We show that a region containing a tandem PU.I binding site is important for intronic enhancer activity. This region binds multiple forms of transcription factor PU.I as judged by gel-shift analysis and DNA affinity precipitation. Importantly, introducing point mutations in the PU.I site drastically reduces the intronic enhancer activity, showing the importance of PU.I for expression of EDN in cells of the eosinophilic lineage.

The Role of Transcription Factor PU.I in the Activity of the Intronic Enhancer of the Eosinophil-Derived Neurotoxin (RNS2) Gene

Eosinophil-derived neurotoxin (EDN) found in the granules of human eosinophils is a cationic ribonuclease toxin. Expression of the EDN gene (RNS2) in eosinophils is dependent on proximal promoter sequences in combination with an enhancer located in the first intron. We further define here the active region of the intron using transfections in differentiated eosinophilic HL60 cells. We show that a region containing a tandem PU.I binding site is important for intronic enhancer activity. This region binds multiple forms of transcription factor PU.I as judged by gel-shift analysis and DNA affinity precipitation. Importantly, introducing point mutations in the PU.I site drastically reduces the intronic enhancer activity, showing the importance of PU.I for expression of EDN in cells of the eosinophilic lineage.

Hematopoietic transcription factor GATA-2 activates transcription from HIV-1 long terminal repeat

OBJECTIVES

To study the role of the hematopoietic transcription factor GATA-2 in long terminal repeat (LTR)-directed transcriptional activation of HIV-1 in hematopoietic progenitor cells, and to investigate possible GATA-2 binding sites in HIV-1 LTR.

DESIGN AND METHODS

Wild-type HIV-1 LTR, or mutants, ligated to a luciferase reporter gene with or without a GATA-2 expression vector, were transfected into COS cells, and standardized luciferase activity was examined. The binding activity of GATA-2 to these sites was examined by electrophoretic mobility shift assay. These wild-type or mutant reporter genes were also transfected into the murine hematopoietic progenitor cells, BAF3, in which GATA-2 was the predominantly expressed transcription factor of the GATA family, to assay LTR-directed transcription in intact hematopoietic machinery. Using a Tat expression plasmid for cotransfection, the influence of Tat protein on GATA-2-induced transactivation was determined.

RESULTS

In COS cells, LTR-dependent transactivation was highly enhanced by the coexpression of GATA-2. Experiments with mutant LTR suggested the presence of multiple GATA-2 binding sites, of which the major sites were identified. Cotransfection of Tat with GATA-2 indicated that GATA-2 and Tat synergistically enhanced the transcriptional activity. Transfection experiments in BAF3 cells showed that the disruption of these GATA sites diminished LTR-driven activity to 40% of the wild-type.

CONCLUSIONS

GATA-2 may be a key host cell regulator of HIV-1 expression in hematopoietic stem cells. Manipulating this transactivation may represent a valuable approach to controlling virus production in infected hematopoietic progenitors. To elucidate the possible interaction between GATA-2 and Tat protein in vivo might give new insights to the mechanism of impaired hematopoiesis in AIDS patients.

Mice Transgenic for the Human CGM6 Gene Express Its Product, the Granulocyte Marker CD66b, Exclusively in Granulocytes

The nonspecific cross-reacting antigen-95 (NCA-95/CD66b), is a member of the human carcinoembryonic antigen (CEA) family encoded by the CGM6 gene that is exclusively expressed in neutrophils and eosinophils. No murine counterpart is known to exist. We have analyzed a cosmid containing the complete CGM6 gene. The coding sequence is contained within six exons spanning a 16.5 kb region. The main transcriptional start site was mapped to a tight cluster between nucleotides -95 and -101 relative to the translational start site. As with other members of the CEA gene family, no typical TATA or CAAT-box sequences were found in the CGM6 gene. Transgenic mice were established with the cosmid insert. CD66b expression is first seen in the fetal liver on day 12.5 of mouse embryonic development, and it first appears in the bone marrow at day 17.5. Northern blot analysis showed that CD66b transcripts are confined to the bone marrow of adult mice, whereas immunohistochemistry also showed CD66b-positive granulocytes in the spleen, thymus, and lungs. FACScan analyses of bone marrow and spleen cells showed CD66b expression to be exclusive to granulocytes. Thus, all the elements necessary for regulating granulocyte-specific expression are present within this cosmid clone. These mice could provide a model for transplantation and for inflammation studies using CD66b as a granulocyte-specific marker.

Mice Transgenic for the Human CGM6 Gene Express Its Product, the Granulocyte Marker CD66b, Exclusively in Granulocytes

The nonspecific cross-reacting antigen-95 (NCA-95/CD66b), is a member of the human carcinoembryonic antigen (CEA) family encoded by the CGM6 gene that is exclusively expressed in neutrophils and eosinophils. No murine counterpart is known to exist. We have analyzed a cosmid containing the complete CGM6 gene. The coding sequence is contained within six exons spanning a 16.5 kb region. The main transcriptional start site was mapped to a tight cluster between nucleotides -95 and -101 relative to the translational start site. As with other members of the CEA gene family, no typical TATA or CAAT-box sequences were found in the CGM6 gene. Transgenic mice were established with the cosmid insert. CD66b expression is first seen in the fetal liver on day 12.5 of mouse embryonic development, and it first appears in the bone marrow at day 17.5. Northern blot analysis showed that CD66b transcripts are confined to the bone marrow of adult mice, whereas immunohistochemistry also showed CD66b-positive granulocytes in the spleen, thymus, and lungs. FACScan analyses of bone marrow and spleen cells showed CD66b expression to be exclusive to granulocytes. Thus, all the elements necessary for regulating granulocyte-specific expression are present within this cosmid clone. These mice could provide a model for transplantation and for inflammation studies using CD66b as a granulocyte-specific marker.

The lineage commitment of haemopoietic progenitor cells

Multipotent haemopoietic progenitor cells appear to be 'primed' for commitment by co-expression of a multiplicity of genes characteristic of different lineages. Lineage commitment proceeds as the consolidation of a distinct pattern of gene expression out of this milieu.

Isolation of cDNA encoding guinea pig neutrophil cationic antibacterial polypeptide of 11 kDa (CAP11) and evaluation of CAP11 mRNA expression during neutrophil maturation

Neutrophils contain various antibacterial polypeptides and proteins in the granules that contribute to the killing of microorganisms. Recently, we have purified a cationic antibacterial polypeptide of 11 kDa (CAP11) from guinea pig neutrophil granules. CAP11 is a homodimer of G1LRKKFRKTRKRIQKLGRKIGKTGRKVWKAWREYGQIPYPCRI43 joined with one disulfide bond. In this study, to understand the regulation of CAP11 expression, we isolated and analyzed cDNA encoding CAP11. Furthermore, we investigated the expression of CAP11 mRNA during neutrophil maturation and localization of CAP11 among neutrophil granule subsets. Sequence analysis of CAP11 cDNA isolated from guinea pig bone marrow cells using rapid amplification of cDNA ends technique indicated that CAP11 is synthesized as a precursor comprising 178 amino acid residues, which is composed of a signal peptide (N-terminal 29 residues), a propeptide (106 residues), and a C-terminal mature peptide (43 residues). Interestingly, the predicted CAP11 precursor displayed the characteristic features of cathelicidins, a novel protein family of antibacterial polypeptides with a conserved cathelin-like pro-region and a variable C-terminal antibacterial domain. Northern blot and Western blot analyses using neutrophils, macrophages, eosinophils, mononuclear cells, and bone marrow cells revealed that only neutrophils and bone marrow cells expressed CAP11 mRNA and contained CAP11, suggesting that expression of CAP11 is neutrophil lineage-specific. Furthermore, Northern blot analysis using bone marrow cells separated according to their maturation stages showed that CAP11 mRNA was predominantly expressed in the cells at later stages of neutrophil maturation. Consistent with this, in situ hybridization using CAP11-specific cRNA probe demonstrated that CAP11 mRNA was primarily expressed at metamyelocyte stage. In addition, extracellular release assay revealed that CAP11 was readily released from neutrophils accompanied with gelatinase by low concentrations of N-formyl-Met-Leu-Phe without release of specific and azurophil granule components, and CAP11 was found to be exclusively present in the fraction containing gelatinase granules, prepared by Percoll density gradient centrifugation. Together these observations indicate that CAP11 is a member of cathelicidin family and its mRNA is preferentially expressed at the later stage of neutrophil maturation (i.e. metamyelocyte stage). Furthermore, CAP11 may be stored in the granule subset, possibly the gelatinase granule.

Core binding factor cannot synergistically activate the myeloperoxidase proximal enhancer in immature myeloid cells without c-Myb

The myeloperoxidase (MPO) gene is transcribed specifically in immature myeloid cells and is regulated in part by a 414-bp proximal enhancer. Mutation of a core binding factor (CBF)-binding site at -288 decreased enhancer activity 30-fold in 32D cl3 myeloid cells cultured in granulocyte colony-stimulating factor (G-CSF). A novel functional analysis, linking the CBF-binding site to an enhancer deletion series, located at -147 an evolutionarily conserved c-Myb-binding site which was required for optimal enhancer activity and synergy with CBF in 32D cells. These sites cooperated in isolation and independent of a precise spacing. Deletional analysis carried out in the absence of the c-Myb-binding site at -147 located at -301 a second c-Myb-binding site which also synergized with CBF to activate the enhancer. A GA-rich region at -162 contributed to cooperation with CBF when the adjacent c-Myb-binding site was intact. Mutation of both c-Myb-binding sites in the context of the entire enhancer greatly impaired activation by endogenous CBF in 32D cells. Similarly, activation by c-Myb was impaired in constructs lacking the CBF-binding site. CBF and c-Myb were required for induction of MPO proximal enhancer activity when 32D cells differentiated in response to G-CSF. A fusion protein containing the Gal4 DNA-binding domain and the AML-1B activation domain, amino acids 216 to 480, activated transcription alone and cooperatively with c-Myb in nonmyeloid CV-1 cells. Determining how CBF and c-Myb synergize in myeloid cells might contribute to our understanding of leukemogenesis by the AML1-ETO, AML1-MDS1, CBFbeta-SMMHC, and v-Myb oncoproteins.

CCAAT/enhancer binding protein epsilon is preferentially up-regulated during granulocytic differentiation and its functional versatility is determined by alternative use of promoters and differential splicing

CCAAT/enhancer binding protein (C/EBP) epsilon is a recently cloned member of the C/EBP family of transcription factors and is expressed exclusively in cells of hematopoietic origin. The human C/EBPepsilon gene is transcribed by two alternative promoters, Palpha and Pbeta. A combination of differential splicing and alternative use of promoters generates four mRNA isoforms, of 2.6 kb and 1.3-1.5 kb in size. These transcripts can encode three proteins of calculated molecular mass 32.2 kDa, 27.8 kDa, and 14.3 kDa. Accordingly, Western blots with antibodies specific for the DNA-binding domain, that is common to all forms, identify multiple proteins. C/EBPepsilon mRNA was greatly induced during in vitro granulocytic differentiation of human primary CD34(+) cells. Retinoic acid treatment of HL60 promyelocytic leukemia cells for 24 hr induced C/EBPepsilon mRNA levels by 4-fold, while prolonged treatment gradually reduced mRNA expression to pretreatment levels. Transient transfection experiments with expression vectors for two of the isoforms demonstrated that the 32.2-kDa protein is an activator of transcription of granulocyte colony-stimulating factor receptor promoter, while the 14.3-kDa protein is not. Thus, C/EBPepsilon is regulated in a complex fashion and may play a role in the regulation of genes involved in myeloid differentiation.

Multilineage gene expression precedes commitment in the hemopoietic system

We have tested the hypothesis that multipotential hemopoietic stem and progenitor cells prime several different lineage-affiliated programs of gene activity prior to unilineage commitment and differentiation. Using single cell RT-PCR we show that erythroid (beta-globin) and myeloid (myeloperoxidase) gene expression programs can be initiated by the same cell prior to exclusive commitment to the erythroid or granulocytic lineages. Furthermore, the multipotential state is characterized by the coexpression of several lineage-affiliated cytokine receptors. These data support a model of hemopoietic lineage specification in which unilineage commitment is prefaced by a "promiscuous" phase of multilineage locus activation.

Absence of granulocyte colony-stimulating factor signaling and neutrophil development in CCAAT enhancer binding protein alpha-deficient mice

Transcription factors are master regulatory switches of differentiation, including the development of specific hematopoietic lineages from stem cells. Here we show that mice with targeted disruption of the CCAAT enhancer binding protein alpha gene (C/EBP alpha) demonstrate a selective block in differentiation of neutrophils. Mature neutrophils and eosinophils are not observed in the blood or fetal liver of mutant animals, while other hematopoietic lineages, including monocytes, are not affected. Instead, most of the white cells in the peripheral blood of mutant mice had the appearance of myeloid blasts. We also observed a selective loss of expression of a critical gene target of CCAAT enhancer binding protein alpha, the granulocyte colony-stimulating factor receptor. As a result, multipotential myeloid progenitors from the mutant fetal liver are unable to respond to granulocyte colony-stimulating factor signaling, although they are capable of forming granulocyte-macrophage and macrophage colonies in methylcellulose in response to other growth factors. Finally, we demonstrate that the lack of granulocyte development results from a defect intrinsic to the hematopoietic system; transplanted fetal liver from mutant mice can reconstitute lymphoid but not neutrophilic cells in irradiated recipients. These studies suggest a model by which transcription factors can direct the differentiation of multipotential precursors through activation of expression of a specific growth factor receptor, allowing proliferation and differentiation in response to a specific extracellular signal. In addition, the c/ebp alpha -/- mice may be useful in understanding the mechanisms involved in acute myelogenous leukemia, in which a block in differentiation of myeloid precursors is a key feature of the disease.