Structural analysis of the functional gene and pseudogene encoding the murine granulocyte colony-stimulating-factor receptor

Goldfish (Carassius auratus L.) as a model system to study the growth factors, receptors and transcription factors that govern myelopoiesis in fish

The process of myeloid cell development (myelopoiesis) in fish has mainly been studied in three cyprinid species: zebrafish (Danio rerio), ginbuna carp (Carassius auratus langsdorfii) and goldfish (C. auratus, L.). Our studies on goldfish myelopoiesis have utilized in vitro generated primary kidney macrophage (PKM) cultures and isolated primary kidney neutrophils (PKNs) cultured overnight to study the process of macrophage (monopoiesis) and neutrophil (granulopoiesis) development and the key growth factors, receptors, and transcription factors that govern this process in vitro. The PKM culture system is unique in that all three subpopulations of macrophage development, namely progenitor cells, monocytes, and mature macrophages, are simultaneously present in culture unlike mammalian systems, allowing for the elucidation of the complex mixture of cytokines that regulate progressive and selective macrophage development from progenitor cells to fully functional mature macrophages in vitro. Furthermore, we have been able to extend our investigations to include the development of erythrocytes (erythropoiesis) and thrombocytes (thrombopoiesis) through studies focusing on the progenitor cell population isolated from the goldfish kidney. Herein, we review the in vitro goldfish model systems focusing on the characteristics of cell sub-populations, growth factors and their receptors, and transcription factors that regulate goldfish myelopoiesis.

C/EBPγ deregulation results in differentiation arrest in acute myeloid leukemia

C/EBPs are a family of transcription factors that regulate growth control and differentiation of various tissues. We found that C/EBPγ is highly upregulated in a subset of acute myeloid leukemia (AML) samples characterized by C/EBPα hypermethylation/silencing. Similarly, C/EBPγ was upregulated in murine hematopoietic stem/progenitor cells lacking C/EBPα, as C/EBPα mediates C/EBPγ suppression. Studies in myeloid cells demonstrated that CEBPG overexpression blocked neutrophilic differentiation. Further, downregulation of Cebpg in murine Cebpa-deficient stem/progenitor cells or in human CEBPA-silenced AML samples restored granulocytic differentiation. In addition, treatment of these leukemias with demethylating agents restored the C/EBPα-C/EBPγ balance and upregulated the expression of myeloid differentiation markers. Our results indicate that C/EBPγ mediates the myeloid differentiation arrest induced by C/EBPα deficiency and that targeting the C/EBPα-C/EBPγ axis rescues neutrophilic differentiation in this unique subset of AMLs.

Essential role of C/EBPalpha in G-CSF-induced transcriptional activation and chromatin modification of myeloid-specific genes

Granulocyte colony-stimulating factor (G-CSF) regulates the proliferation and differentiation of neutrophilic progenitor cells. Here, we investigated the roles of CCAAT/enhancer-binding protein (C/EBP)alpha in the G-CSF-induced transcriptional activation and chromatin modification of the CCR2 and myeloperoxidase (MPO) genes in IL-3-dependent myeloid FDN1.1 cells. Chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift assays revealed that G-CSF activates C/EBPalpha to bind target promoters. ChIP mapping experiments across the CCR2 and MPO genes showed that G-CSF induces histone H3 modifications: the acetylation of Lys9, trimethylation of Lys4 and trimethylation of Lys9. The distribution profile of the trimethylated Lys9 was distinct from that of the two other modifications. All the G-CSF-induced C/EBPalpha recruitment, transcriptional activation and histone modifications were reversed by re-stimulation with IL-3, and were abolished by short hairpin RNA (shRNA)-mediated knockdown of C/EBPalpha. These results indicate that C/EBPalpha is activated by G-CSF to bind target promoters, and plays critical roles in the transcriptional activation and dynamic chromatin modification of target genes during neutrophil differentiation.

Exon-intron organization of the human gp130 gene

The exon-intron organization and sequences of the exon-intron boundaries of the human gp130 transmembrane receptor gene have been determined using genomic DNAs as samples. The gp130 gene comprises 17 exons and 16 introns. The positions of the exon-intron boundaries show good correlation to the functional/homology regions of gp130. Exons 3-17 code for the gp130 protein, and each subdomain of the receptor is encoded by a set of exons. The coding potential of exons and the intron phasing of the human gp130 gene conform to the patterns observed previously for other cytokine receptor genes. This supports the notions that the gp130 gene evolved from the same ancestral gene that gave rise to other members of the cytokine receptor family.

Noninsulin-dependent diabetes mellitus occurs in mice ectopically expressing the human Axl tyrosine kinase receptor

The axl tyrosine kinase receptor is aberrantly expressed on myeloid cells of many individuals afflicted with chronic myelogenous leukemia (CML) and other myeloid leukemias. Although previous studies demonstrated this kinase to have oncogenic potential, it is not known whether axl actively participates in the onset and/or progression of CML. We addressed this question by generating transgenic mice possessing constitutive ectopic expression of human axl throughout cells of the myeloid hematopoietic lineage through the use of the granulocyte colony-stimulating factor (GCSF) receptor promoter. The transgenics did not exhibit hematopoietic malignancies, but did exhibit phenotypic characteristics associated with noninsulin-dependent diabetes mellitus (NIDDM) including hyperglycemia and hyperinsulinemia, severe insulin resistance, progressive obesity, hepatic lipidosis, and pancreatic islet dysplasia. The obese-diabetes phenotype was similar to that observed in the agouti and melanocortin-4(-/-) mutants, however the axl transgenics were not hyperphagic. Axl transgenic animals expressed elevated serum tumor necrosis factor (TNF)-alpha levels that were further enhanced upon in vitro lipopolysaccharide (LPS) stimulation of peripheral blood. Administration of the axl ligand, gas6, to peripheral transgenic blood samples eliminated excessive TNF-alpha production in response to LPS stimulation. As a means to better understand axl-gas6 biology, transgenic animals were produced which systemically expressed the gas6-binding axl proteolytic cleavage product. A more severe NIDDM phenotype occurred in these mice. The observed phenotypes may be related to the axl receptor or proteolytic cleavage product competing with related axl family receptors for binding of the gas6 ligand. We conclude that axl expression in myeloid cells in itself does not lead to the onset or progression of leukemia and suggest that ectopic axl expression affects endogenous modulation of TNF-alpha production indirectly resulting in the NIDDM phenotype.

Mouse prolactin receptor gene: genomic organization reveals alternative promoter usage and generation of isoforms via alternative 3'-exon splicing

In rodents, the prolactin receptor is expressed as multiple isoforms with identical extracellular and membrane-proximal region sequences but with different 3' sequences, encoding different cytoplasmic regions, and different 5' untranslated region (UTR) sequences. These divergent sequences could be the result of multiple prolactin receptor genes or of a single gene which displays alternative promoter usage and 3'-exon splicing. To investigate the molecular basis for these observations, we have cloned and determined the organization of the mouse prolactin receptor gene. Genomic DNA cloning allowed the arrangement of promoters 1A, 1B, and 1C to be determined. 5'-RACE-PCR from mouse liver identified two novel 5' prolactin receptor sequences, indicating that the gene has at least five different promoters, four of which are active in liver. The remaining nonvariable 5' UTR is encoded by a separate exon (exon 2), while a further 11 coding exons follow, the last 4 of which are alternatively spliced to produce the four isoforms of the receptor. Functional units were found to be exon specific. Thus, the multiple prolactin receptor isoforms are the product of a single gene of >120 kb which displays multiple promoter usage and 3'-exon splicing.

Expression Profile of Active Genes in Granulocytes

A number of genes active in granulocytes have been intensively studied as to the function of their products and their expression controls. However, the intensities and relative order of these gene activities have not been studied. This report describes an expression profile of 748 different species of active genes in human peripheral granulocytes obtained by analyzing a 3′-directed cDNA library that faithfully represents the mRNA population in the source cells. A significant fraction (20.3% of the total) of the expressed genes in granulocytes consisted of nuclear proteins such as DNA binding proteins, of secretory proteins such as cytokines, and of membrane proteins such as major histocompatibility complex (MHC) proteins and receptors. By comparing this expression profile with 11 profiles similarly obtained with unrelated human cells/tissues, we discovered 10 novel genes that are likely to act specifically in granulocytes. Comparison of this expression profile with that obtained with granulocytoids widely used as a granulocyte model by inducing a cultured promyelocytic leukemia cell line HL60 showed similarities and dissimilarities of gene expressions.

© 1998 by The American Society of Hematology.

Expression Profile of Active Genes in Granulocytes

A number of genes active in granulocytes have been intensively studied as to the function of their products and their expression controls. However, the intensities and relative order of these gene activities have not been studied. This report describes an expression profile of 748 different species of active genes in human peripheral granulocytes obtained by analyzing a 3′-directed cDNA library that faithfully represents the mRNA population in the source cells. A significant fraction (20.3% of the total) of the expressed genes in granulocytes consisted of nuclear proteins such as DNA binding proteins, of secretory proteins such as cytokines, and of membrane proteins such as major histocompatibility complex (MHC) proteins and receptors. By comparing this expression profile with 11 profiles similarly obtained with unrelated human cells/tissues, we discovered 10 novel genes that are likely to act specifically in granulocytes. Comparison of this expression profile with that obtained with granulocytoids widely used as a granulocyte model by inducing a cultured promyelocytic leukemia cell line HL60 showed similarities and dissimilarities of gene expressions.

© 1998 by The American Society of Hematology.

Perturbed Granulopoiesis in Mice With a Targeted Mutation in the Granulocyte Colony-Stimulating Factor Receptor Gene Associated With Severe Chronic Neutropenia

Mutations in the granulocyte colony-stimulating factor (G-CSF) receptor gene are found in a number of patients with severe chronic neutropenia predisposed to acute myeloid leukemia. These mutations result in the absence of the C-terminal domain of the G-CSF-R, a region which has been implicated in differentiation signaling. We generated mice with an equivalent mutation (gcsfr-▵715) by homologous and Cre-mediated recombination in embryonic stem cells. Both wt/▵715 and▵715/▵715 mice have significantly reduced numbers of blood neutrophils compared with their wt/wt littermates. However, under continuous G-CSF administration mutant mice develop peripheral neutrophil counts that significantly exceed those of wild-type littermates. These findings indicate that depending on G-CSF levels in mice, the ▵715 mutation can contribute both to neutropenia and to neutrophilia.

Swapping between Fas and granulocyte colony-stimulating factor receptor

Fas belongs to the tumor necrosis factor/nerve growth factor receptor family. The Fas ligand binds to its receptor, Fas, and induces apoptosis in Fas-bearing cells. The granulocyte colony-stimulating factor receptor (G-CSFR) is a member of the hemopoietic growth factor receptor family. G-CSF induces its dimerization and regulates the proliferation and differentiation of neutrophilic granulocytes. We constructed hybrid receptors between Fas and G-CSFR and expressed them in the mouse T cell line WR19L or the mouse myeloid interleukin-3-dependent FDC-P1 cell line. The Fas ligand or an agonistic anti-Fas antibody stimulated proliferation of the FDC-P1 transformants expressing a chimera consisting of the Fas extracellular and G-CSFR cytoplasmic regions. On the other hand, G-CSF could not induce apoptosis in the transformants expressing the chimera consisting of the G-CSFR extracellular and Fas cytoplasmic regions, but these cells were killed by a polyclonal antibody against G-CSFR. These results indicated that receptors belonging to different receptor families can be functionally exchanged and confirm that a homodimer of G-CSFR can transduce the growth signal, whereas Fas must be oligomerized (probably trimerized) to transduce the apoptotic signal.

Overexpression of granulocyte colony-stimulating factor in vivo decreases the level of polyploidization of mouse bone marrow megakaryocytes

The in vivo effect of G-CSF on the maturation of mouse bone marrow megakaryocytes was studied by monitoring the DNA contents. Megakaryocytes were first identified by a specific 1C2 monoclonal antibody against mouse platelets and megakaryocytes and DNA contents of these cells were measured by propidium iodine. Megakaryocytes of mice transgenic for human G-CSF had a modal DNA class of 8N, showing a striking contrast to the previous reports that normal mouse megakaryocytes from most strains have 16N DNA content as a modal class. Daily 10 micrograms administration of G-CSF to mice for three to five days affected the DNA distribution pattern of bone marrow megakaryocytes, with a higher proportion of cells having 8N DNA contents. This G-CSF treatment, however, did not influence the peripheral blood platelet count or bone marrow megakaryocyte number. Administration of G-CSF along with thrombopoietin (TPO) reduced the proportion of megakaryocytes, with 32N DNA, the DNA class that was increased by TPO. Finally, the presence of mRNA for the mouse G-CSF receptor was demonstrated in two megakaryoblastic cell lines by reverse transcriptase polymerase chain reaction. These results indicated that G-CSF may have a suppressive effect on the maturation of mouse bone marrow megakaryocytes when monitored by the DNA polyploidy. Although further study is clearly necessary, the presence of mRNA for the G-CSF receptor in megakaryocytic lineage strongly suggests the direct action of G-CSF on this cell lineage.