Secondary Granule Protein Gene Expression Research Articles

C/EBPε Knockout (KO) EML and PBiIM Cell Lines Replicate the In Vivo Phenotype of the C/EBPε KO Mouse.

The appearance of the secondary granule proteins (SGP) lactoferrin (LF), transcobalamin I (TCI), neutrophil collagenase (NC) and neutrophil gelatinase (NG) marks the commitment to terminal neutrophil differentiation. C/EBPε plays a critical role in the coordinate upregulation of SGP genes. Disruption of the C/EBPε gene in mice leads to morphologic and functional defects in neutrophil maturation with a defective transition from the promyelocyte to the myelocyte stage. The neutrophils have bilobed nuclei, abnormal respiratory burst activity, and impaired chemotaxis and bactericidal activity. They lack specific granules and fail to express mRNAs encoding for secondary and tertiary granule content proteins. Phenotypic and functional defects of the C/EBPε −/− mice closely parallel those in patients with secondary granule deficiency. We have made 2 cell lines from the bone marrow of C/EBPε −/− mice and corresponding wildtype (WT) littermates. We first generated EML-like cell lines from WT and KO mice by transducing bone marrow with a retroviral vector expressing the dominant negative RARα and selecting for immortalized cells. We then induced the KO and WT EML cell lines with cytokines and ATRA to the neutrophil stage, and demonstrated that the KO cell morphology, functional responses (oxidative burst) and RNA expression patterns mimic the morphologic and functional abnormalities of the knockout mice. Transduction with a C/EBPε-expressing retrovirus corrects the phenotype of the KO cells, restoring normal morphology, oxidative burst, and secondary granule protein gene expression. Since C/EBPε is an RAR-responsive gene and because the dominant negative RARα also interferes with normal neutrophil maturation, we used an alternate approach to generate pBabePuro immortalized cell lines (PBiMs) by random insertional mutagenesis. We transduced WT and KO bone marrow cells with viral supernatent harboring the pBabepuro vector and selected for puromycin-resistant cells. Immortalized cells grew out 1–2 months after transduction and were maintained either in stem cell factor (SCF) alone or in SCF+IL-3 (interleukin 3). WT PBiMs are inducible with G-CSF to morphologically mature granulocytes or with GM-CSF to mature macrophages. KO PBiMs fail to mature to morphologically normal neutrophils, and form macrophage-like cells or die. By RNA analysis, both the EML and PBiM KO cells induced to differentiate toward neutrophils fail to express C/EBPε and lactoferrin, demonstrate absent oxidative burst, and fail to up-regulate Gr-1 upon induction as assayed by flow cytometry. Transduction of KO cells with a C/EBPε-containing retrovirus again restored respiratory burst activity. We have thus generated two independent C/EBPε −/− cell lines, each immortalized by a different mechanism, that should provide an important tool with which to study the transcriptional targets of C/EBPε in terminal myeloid differentiation. Since mutations in the C/EBPε gene have been reported in two patients with the rare clinical disorder specific granule deficiency, these lines will also serve as a convenient in vitro model for studying that disease.

Cytokine signals through STAT3 promote expression of granulocyte secondary granule proteins in 32D cells

In a previous study, we showed that activation of a transfected human erythropoietin receptor (EPOR) in the murine myeloid cell line 32D resulted in the development of morphologic features of granulocytic differentiation and expression of the neutrophil primary granule protein myeloperoxidase. We now studied if EPOR signaling could also mediate secondary granule protein gene expression and investigated the signal transduction requirements for induction of secondary granule gene expression in 32D cells. Wild-type and variant 32D cells expressing normal or chimeric EPORs or receptors for granulocyte colony-stimulating factor (G-CSFRs) were stimulated with EPO or G-CSF and the expression of granulocyte-specific genes was analyzed by Northern blot analysis. To determine the signaling mechanisms required for secondary granule protein gene induction, the activation of STAT pathways following growth factor stimulation was studied by Western blot analysis. We found that EPO treatment of 32D cells engineered to express EPOR did not result in induction of the secondary granule protein genes encoding lactoferrin and 24p3 lipocalin, the mouse homolog of human N-Gal, or the myeloid transcription factor C/EBPepsilon. Replacement of the intracellular domain of EPOR with the intracellular domain of G-CSFR in a chimeric receptor was associated with EPO-mediated induction of lactoferrin, 24p3 lipocalin, and C/EBPepsilon genes. We found that STAT3 phosphorylation was mediated by the intracellular domain of G-CSFR, but not EPOR. Replacement of one or two of the STAT5 binding sites in the intracytoplasmic domain of the EPOR with STAT3 binding sites resulted in EPO-mediated STAT3 activation and a marked increase in the expression of the 24p3 lipocalin gene. Knockdown of STAT3 protein levels with siRNA caused significant decrease in 24p3 lipocalin gene induction. These results indicate that EPOR signaling cannot substitute for G-CSFR signaling to stimulate secondary granule protein gene expression in 32D cells. In addition, STAT3 is a critical mediator of 24p3 lipocalin gene expression in these cells.

Growth Factor Independence 1 (Gfi-1) Plays a Role in Mediating Specific Granule Deficiency (SGD) in a Patient Lacking an Abnormality in the C/EBPε Gene.

Neutrophil specific granule deficiency (SGD) is a rare congenital disorder marked by recurrent bacterial infections of the skin and respiratory system. Neutrophils from SGD patients lack secondary and tertiary granules and their content proteins and exhibit defects in chemotaxis and bactericidal activity. A mouse model deficient for the transcription factor CCAAT/enhancer binding protein epsilon (C/EBPε) manifests a similar phenotype as SGD patients and prompted examination of the human C/EBPε gene for mutation in this disease. Mutations in the C/EBPε gene have been identified by others in two patients with SGD, resulting in loss of gene expression. However, other patients with a similar disease phenotype have a normal C/EBPε coding sequence, suggesting that other genetic abnormalities in myelopoiesis can lead to SGD. Studies in our laboratory on one such patient lacking a C/EBPε mutation demonstrated an elevated level of the C/EBPε protein in the patient's peripheral blood neutrophils as compared to the level in normal control neutrophils. Microarray analysis of this patient's bone marrow compared with that of a normal control revealed, among other genes, elevated levels of the transcription factors C/EBPε and PU.1. As a consequence, several PU.1 target genes showed increased expression in the SGD patient bone marrow. This observation was confirmed by both real time PCR and western blot analysis. PU.1 is a hematopoietic-specific transcription factor belonging to the Ets family of DNA binding proteins and plays a critical role in B-cell, macrophage and late stage neutrophil development. Sequence analysis of the PU.1 gene from our SGD patient however, did not reveal any mutation in the coding region of the gene. Western blot analysis of nuclear extracts prepared from peripheral blood neutrophils from this patient did however reveal significantly decreased levels of the transcription factor Gfi-1 (Growth factor independent-1), although no mutation has been found thus far in the coding region of the Gfi-1 gene from the SGD patient. Gfi-1 belongs to a family of zinc finger containing transcriptional repressor oncoproteins. Mice lacking Gfi-1 were found not only to be neutropenic, but also demonstrated defects in neutrophil differentiation, including loss of neutrophil secondary and tertiary granule proteins, reminiscent of SGD. More recently, heterozygous germline mutations of Gfi-1 were shown to cause severe congenital neutropenia (SCN) in humans. It has been suggested that Gfi1 represses neutrophil elastase (Ela2), germline mutations within which are a major contributor to hereditary neutropenias. Our data suggest that decreased levels of Gfi1 in our SGD patient result in increased levels of PU.1 and C/EBPε; an effect consistent with observations first made in the neutrophils of Gfi-1-null mice. The increased PU.1 levels might then act to sequester C/EBPε protein via direct protein-protein interaction. This in turn could explain the loss of secondary granule protein gene expression in the SGD patient by inducing functional C/EBPε deficiency.

Isolation and Characterization of the cDNA for Mouse Neutrophil Collagenase: Demonstration of Shared Negative Regulatory Pathways for Neutrophil Secondary Granule Protein Gene Expression

AbstractA characteristic of normal neutrophil maturation is the induction of secondary granule protein (SGP) mRNA expression. Several leukemic human cell lines mimic normal morphologic neutrophil differentiation but fail to express SGPs, such as lactoferrin (LF) and neutrophil gelatinase (NG). In contrast, two murine cell lines (32D C13 and MPRO) are able to differentiate into neutrophils and induce expression of LF and NG. Therefore, to study the normal regulation and function of these genes, the corresponding murine homologs must be isolated. Using cDNA representational difference analysis (RDA) to compare a committed myeloid progenitor cell line (EPRO) with the multipotent stem cell line from which it was derived (EML), we isolated a fragment bearing homology to human neutrophil collagenase (hNC). Here, we describe the cloning and characterization of a full-length (∼2 kb) clone that exhibits nearly 65% nucleotide and 73% amino acid identity to hNC. Ribonuclease protection analysis (RPA) of the tissues and cell lines shows that mouse NC (mNC) is expressed only in cell lines exhibiting neutrophilic characteristics, further confirming its identity as the mouse homolog of hNC. Furthermore, we have demonstrated a shared negative regulatory pathway for this and other SGP genes. We have previously shown that CCAAT displacement protein (CDP/cut) binds to a specific region of the LF promoter, and overexpression of CDP blocks G-CSF–induced upregulation of LF gene expression in 32D C13 cells. We show here that in these cells, upregulation of both NC and NG is also blocked. CDP is thus the first identified transcription factor that is a candidate for mediating the shared regulation of neutrophil SGP protein genes.

Isolation and Characterization of the cDNA for Mouse Neutrophil Collagenase: Demonstration of Shared Negative Regulatory Pathways for Neutrophil Secondary Granule Protein Gene Expression

A characteristic of normal neutrophil maturation is the induction of secondary granule protein (SGP) mRNA expression. Several leukemic human cell lines mimic normal morphologic neutrophil differentiation but fail to express SGPs, such as lactoferrin (LF) and neutrophil gelatinase (NG). In contrast, two murine cell lines (32D C13 and MPRO) are able to differentiate into neutrophils and induce expression of LF and NG. Therefore, to study the normal regulation and function of these genes, the corresponding murine homologs must be isolated. Using cDNA representational difference analysis (RDA) to compare a committed myeloid progenitor cell line (EPRO) with the multipotent stem cell line from which it was derived (EML), we isolated a fragment bearing homology to human neutrophil collagenase (hNC). Here, we describe the cloning and characterization of a full-length (∼2 kb) clone that exhibits nearly 65% nucleotide and 73% amino acid identity to hNC. Ribonuclease protection analysis (RPA) of the tissues and cell lines shows that mouse NC (mNC) is expressed only in cell lines exhibiting neutrophilic characteristics, further confirming its identity as the mouse homolog of hNC. Furthermore, we have demonstrated a shared negative regulatory pathway for this and other SGP genes. We have previously shown that CCAAT displacement protein (CDP/cut) binds to a specific region of the LF promoter, and overexpression of CDP blocks G-CSF–induced upregulation of LF gene expression in 32D C13 cells. We show here that in these cells, upregulation of both NC and NG is also blocked. CDP is thus the first identified transcription factor that is a candidate for mediating the shared regulation of neutrophil SGP protein genes.

Coordinate regulation of neutrophil secondary granule protein gene expression.

Evidence from study of both normal and leukemic cells suggests that a crucial step in neutrophil maturation occurs in the transition from the promyelocyte to the myelocyte stage. The transition from the promyelocyte to the myelocyte in normal marrow cells is accompanied both by the loss of proliferative capacity associated with terminal maturation [1], and by the loss of the capacity for alternative maturation [2]. Normal promyelocytes respond to stimuli of both granulocyte and monocyte differentiation, but myelocytes are restricted to terminal granulocyte maturation [2]. In this regard, it is striking that acute myeloid leukemias invariably involve proliferation of cells arrested in development at or before the promyelocyte stage. Consequently, an understanding of the transition from the promyelocyte to the myelocyte stage should provide crucial insights into both the control mechanisms governing normal hematopoietic cell differentiation and the ways in which disruption of the control mechanisms can contribute to leukemic transformation.KeywordsHL60 CellMature NeutrophilSecondary GranuleNeutrophil DifferentiationNeutrophil MaturationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

NB4 cells show bilineage potential and an aberrant pattern of neutrophil secondary granule protein gene expression

NB4 is an acute promyelocytic leukemia cell line that has been shown to be inducible to terminal neutrophil maturation with all-trans retinoic acid (ATRA). HL60 cells are differentially inducible with 12-O- tetradecanoylphorbol-13-acetate (TPA) or dimethyl sulfoxide (DMSO) to monocytes or granulocytes, respectively. HL60 cells induced with DMSO undergo defective neutrophil maturation, manifested by a coordinate failure of secondary granule protein gene expression. We observed a similar defect in granulocytic maturation in ATRA-induced NB4 cells. In addition, because normal promyelocytes are known to have bilineage potential, we have investigated differentiation along monocytoid lines induced with TPA. We observed a striking phenotypic change along monocytoid/macrophage lines with TPA induction. Flow cytometry showed a TPA-induced increase in HLA-DR expression, and Northern blot analysis showed induction of expression of CD18, c-fos, and human neutrophil gelatinase (HNG). HNG is unique among the neutrophil secondary granule protein genes in that it is expressed in both the neutrophil and monocyte lineages. This again parallels our findings in TPA-induced HL60 cells, which retain the ability to express HNG. These findings confirm bilineage potential in NB4 cells. They also support the hypothesis of coordinate neutrophil secondary granule protein gene expression and a defect in this control as part of the leukemic phenotype.

NB4 Cells Show Bilineage Potential and an Aberrant Pattern of Neutrophil Secondary Granule Protein Gene Expression

NB4 is an acute promyelocytic leukemia cell line that has been shown to be inducible to terminal neutrophil maturation with all-trans retinoic acid (ATRA). HL60 cells are differentially inducible with 12-O-tetradecanoylphorbol-13-acetate (TPA) or dimethyl sulfoxide (DMSO) to monocytes or granulocytes, respectively. HL60 cells induced with DMSO undergo defective neutrophil maturation, manifested by a coordinate failure of secondary granule protein gene expression. We observed a similar defect in granulocytic maturation in ATRA-induced NB4 cells. In addition, because normal promyelocytes are known to have bilineage potential, we have investigated differentiation along monocytoid lines induced with TPA. We observed a striking phenotypic change along monocytoid/macrophage lines with TPA induction. Flow cytometry showed a TPA-induced increase in HLA-DR expression, and Northern blot analysis showed induction of expression of CD18, c-fos, and human neutrophil gelatinase (HNG). HNG is unique among the neutrophil secondary granule protein genes in that it is expressed in both the neutrophil and monocyte lineages. This again parallels our findings in TPA-induced HL60 cells, which retain the ability to express HNG. These findings confirm bilineage potential in NB4 cells. They also support the hypothesis of coordinate neutrophil secondary granule protein gene expression and a defect in this control as part of the leukemic phenotype.

Cloning and expression of the cDNA encoding mouse neutrophil gelatinase: demonstration of coordinate secondary granule protein gene expression during terminal neutrophil maturation

The 92-kD form of human type IV collagenase (gelatinase) is a member of the matrix metalloproteinase family. It is restricted in its expression to the granulocytic lineage of white blood cells. Within neutrophils it resides in secondary granules, which are markers of terminal myeloid differentiation. We have isolated and sequenced the cDNA encoding the murine counterpart to the human 92-kD metalloproteinase from a macrophage cDNA library. The human and murine genes are highly homologous and exist in an identical form in neutrophils and monocyte- macrophages in both species. Two polyadenylation signals are present in the murine 3′ untranslated sequence, accounting for equal expression of two messenger RNAs. We have shown that expression of gelatinase mRNA is controlled in a coordinate fashion together with lactoferrin, also a component of neutrophil secondary granules, and that this control occurs at the level of transcription. This is the first definitive demonstration of coordinate transcriptional regulation of secondary granule protein gene expression, a feature of normal myelopoiesis that is deranged in leukemogenesis.

Cloning and Expression of the cDNA Encoding Mouse Neutrophil Gelatinase: Demonstration of Coordinate Secondary Granule Protein Gene Expression During Terminal Neutrophil Maturation

The 92-kD form of human type IV collagenase (gelatinase) is a member of the matrix metalloproteinase family. It is restricted in its expression to the granulocytic lineage of white blood cells. Within neutrophils it resides in secondary granules, which are markers of terminal myeloid differentiation. We have isolated and sequenced the cDNA encoding the murine counterpart to the human 92-kD metalloproteinase from a macrophage cDNA library. The human and murine genes are highly homologous and exist in an identical form in neutrophils and monocyte-macrophages in both species. Two polyadenylation signals are present in the murine 3' untranslated sequence, accounting for equal expression of two messenger RNAs. We have shown that expression of gelatinase mRNA is controlled in a coordinate fashion together with lactoferrin, also a component of neutrophil secondary granules, and that this control occurs at the level of transcription. This is the first definitive demonstration of coordinate transcriptional regulation of secondary granule protein gene expression, a feature of normal myelopoiesis that is deranged in leukemogenesis.