Cloning and nucleotide sequence of the murine interleukin-3 gene

IL-3 in the development and function of basophils

The β common chain (βc) cytokine family includes granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3) and IL-5, all of which use βc as key signaling receptor subunit. GM-CSF, IL-3 and IL-5 have specific roles as hematopoietic growth factors. IL-3 binds with high affinity to the IL-3 receptor α (IL-3Rα/CD123) and then associates with the βc subunit. IL-3 is mainly synthesized by different subsets of T cells, but is also produced by several other immune [basophils, dendritic cells (DCs), mast cells, etc.] and non-immune cells (microglia and astrocytes). The IL-3Rα is also expressed by immune (basophils, eosinophils, mast cells, DCs, monocytes, and megacaryocytes) and non-immune cells (endothelial cells and neuronal cells). IL-3 is the most important growth and activating factor for human and mouse basophils, primary effector cells of allergic disorders. IL-3-activated basophils and mast cells are also involved in different chronic inflammatory disorders, infections, and several types of cancer. IL-3 induces the release of cytokines (i.e., IL-4, IL-13, CXCL8) from human basophils and preincubation of basophils with IL-3 potentiates the release of proinflammatory mediators and cytokines from IgE- and C5a-activated basophils. IL-3 synergistically potentiates IL-33-induced mediator release from human basophils. IL-3 plays a pathogenic role in several hematologic cancers and may contribute to autoimmune and cardiac disorders. Several IL-3Rα/CD123 targeting molecules have shown some efficacy in the treatment of hematologic malignancies.

JAK/STAT, Raf/MEK/ERK, PI3K/Akt and BCR-ABL in cell cycle progression and leukemogenesis

The roles of the JAK/STAT, Raf/MEK/ERK and PI3K/Akt signal transduction pathways and the BCR-ABL oncoprotein in leukemogenesis and their importance in the regulation of cell cycle progression and apoptosis are discussed in this review. These pathways have evolved regulatory proteins, which serve to limit their proliferative and antiapoptotic effects. Small molecular weight cell membrane-permeable drugs that target these pathways have been developed for leukemia therapy. One such example is imatinib mesylate, which targets the BCR-ABL kinase as well as a few structurally related kinases. This drug has proven to be effective in the treatment of CML patients. However, leukemic cells have evolved mechanisms to become resistant to this drug. A means to combat drug resistance is to target other prominent signaling components involved in the pathway or to inhibit BCR-ABL by other mechanisms. Treatment of imatinib-resistant leukemia cells with drugs that target Ras (farnysyl transferase inhibitors) or with the protein destabilizer geldanamycin has proven to be a means to inhibit the growth of resistant cells. This review will tie together three important signal transduction pathways involved in the regulation of hematopoietic cell growth and indicate how their expression is dysregulated by the BCR-ABL oncoprotein.

Molecular cloning, expression, purification, and characterization of soluble full-length, human interleukin-3 with a baculovirus-insect cell expression system

We report gene cloning, plasmid construction, baculovirus expression, purification, and biological activity testing of the human hematopoietic cytokine interleukin-3. cDNA was constructed from extracted total RNA of Jurkat cells. Both signal and structural fragment of interleukin-3 were cloned from this cDNA library, modified by adding a hexahistidine-tag at the C-terminus, and introduced into the pBacPAK9 transfer vector to generate recombinant baculoviruses. For protein expression High Five cells were infected either in spinner flasks or 2.5-L bioreactors in batch culture yielding levels of 1.5-3 mg L(-1) interleukin-3 in the cell culture supernatant. Interleukin-3 was purified by a single step chromatography using cobalt metal affinity resins, which yielded a highly stable and soluble protein. N-terminal amino acid sequencing of the purified interleukin-3 showed correct cleavage of the signal peptide during protein processing. The two N-glycosylation sites were found to be occupied by 100 and 35%, respectively, with an N-glycan pattern of paucimannosidic structures, which are typical for recombinant glycoproteins produced by High Five lepidopteran cells. The specific biological activity of purified interleukin-3 was several times higher when compared with different lots of commercially available material from Escherichia coli. The results indicate that the strategy we used in this experiment is a straightforward and convenient way for recombinant protein preparation and can be adapted to produce other recombinant cytokines.

Induction of colony-stimulating factor expression following Staphylococcus or Salmonella interaction with mouse or human osteoblasts

Staphylococcus aureus and Salmonella spp. are common causes of bone diseases; however, the immune response during such infections is not well understood. Colony-stimulating factors (CSF) have a profound influence on osteoclastogenesis, as well as the development of immune responses following infection. Therefore, we questioned whether interaction of osteoblasts with two very different bacterial pathogens could affect CSF expression by these cells. Cultured mouse and human osteoblasts were exposed to various numbers of S. aureus or Salmonella dublin bacteria, and a comprehensive analysis of granulocyte-macrophage (GM)-CSF, granulocyte (G)-CSF, macrophage (M)-CSF, and interleukin-3 (IL-3) mRNA expression and cytokine secretion was performed. Expression of M-CSF and IL-3 mRNAs by mouse osteoblasts was constitutive and did not increase significantly following bacterial exposure. In contrast, GM-CSF and G-CSF mRNA expression by mouse osteoblasts was dramatically upregulated following interaction with either viable S. aureus or Salmonella. This increased mRNA expression also translated into high levels of GM-CSF and G-CSF secretion by mouse and human osteoblasts following bacterial exposure. Viable S. aureus and Salmonella induced maximal levels of CSF mRNA expression and cytokine secretion compared to UV-killed bacteria. Furthermore, GM-CSF and G-CSF mRNA expression could be induced in unexposed osteoblasts separated by a permeable Transwell membrane from bacterially exposed osteoblasts. M-CSF secretion was increased in cultures of exposed human osteoblasts but not in exposed mouse osteoblast cultures. Together, these studies are the first to define CSF expression and suggest that, following bacterial exposure, osteoblasts may influence osteoclastogenesis, as well as the development of an immune response, via the production of these cytokines.

Calcium-dependent and oncogenic IL-3 mRNA stabilization can be distinguished pharmacologically and by sequence requirements in the 3'UTR

In interleukin-3 (IL-3)-dependent PB-3c mast cells, the normally short-lived IL-3 mRNA is stabilized upon calcium-ionophore treatment or following v-H-ras induced oncogenesis. We compared the underlying stabilization mechanisms by analysing the response to the post-transcriptionally acting drugs cyclosporin A (CsA), FK506 and SB202190. Stable IL-3 transcripts in the PB-3c-derived tumour cell line V2D1 decayed in response to CsA and FK506, but not in response to SB202190. Transcripts stabilized by elevating intracellular calcium levels in PB-3c cells were destabilized in response to all three drugs. In PB-3c cells, six AUUUA pentamers within the AU-rich element were sufficient to confer responsiveness to calcium-ionophore and CsA treatment. In V2D1 tumour cells, sensitivity to CsA required additional nucleotides flanking these pentamers. Our data suggest that IL-3 mRNA stabilization by either calcium-dependent or oncogenic pathways involves different intracellular mechanisms.

Role of the transmembrane sequence of spleen focus-forming virus gp55 in erythroleukemogenesis

The membrane glycoprotein encoded by the env gene of either the polycythemia- or anemia-inducing spleen focus-forming virus (SFFVp or SFFVa, respectively) is responsible for the induction of erythroleukemia in mice. It has been shown that the SFFVp glycoprotein, gp55, interacts with the erythropoietin receptor (EPO-R) and promotes EPO-independent proliferation of an EPO-R-expressing hematopoietic cell line, Ba/F3 (Li et al., Nature 343:762, 1990). We show here that when residues within the transmembrane (TM) sequence of an SFFVp gp55 are altered based on the sequences of the anemia-inducing gp55s by a methionine-to-isoleucine (M-I) substitution, a di-leucine deletion (dLL), or both, the resulting mutants display an attenuated phenotype that resembles an SFFVa: they induce milder erythroproliferative disease without polycythemia in vivo and are unable to promote EPO-independent cell proliferation in vitro. The dLL mutation directly interferes with EPO-R binding by decreasing the affinity of gp55 for the receptor. On the other hand, the M-I mutation hampers the full mitogenic activation of EPO-R while having no effect on receptor binding and asserts a dominant negative effect over the wild-type SFFVp gp55. Two other sequence changes within the TM sequence did not affect the biological activities of the SFFVp gp55. These results indicate that the TM sequence of the SFFV env glycoprotein plays a prominent role in SFFV-induced erythroleukemogenesis through its influence on the mitogenic activation of EPO-R.

c-jun N-terminal kinase is involved in AUUUA-mediated interleukin-3 mRNA turnover in mast cells

Whereas signalling pathways involved in transcriptional control have been studied extensively, the pathways regulating mRNA turnover remain poorly understood. We are interested in the role of mRNA stability in cell activation and oncogenesis using PB-3c mast cells as a model system. In these cells the short-lived interleukin-3 (IL-3) mRNA is stabilized by ionomycin treatment and following oncogenesis. To identify the signalling pathways involved in these mechanisms, we analysed the effect of different kinase inhibitors. SB202190 and wortmannin were shown to antagonize ionomycin-induced IL-3 mRNA stabilization in PB-3c cells in the presence of actinomycin D, and this effect coincided with their ability to inhibit c-jun N-terminal kinase (JNK) activation by ionomycin. Moreover, transfection of activated MEKK1 amplified ionomycin-induced IL-3 mRNA expression at the post-transcriptional level, and a dominant-negative mutant of JNK counteracted mRNA stabilization by ionomycin. Taken together, these data indicate that JNK is involved in the regulation of IL-3 mRNA turnover in mast cells. In addition, transfection experiments revealed that the cis-acting AU-rich element in the 3' untranslated region of IL-3 mRNA is necessary and sufficient to confer JNK-dependent mRNA stabilization in response to cell activation.

Cloning, biological characterization and high-level expression of rat interleukin-3 using recombinant adenovirus: description of a new splicing variant

In the present study, we describe the cloning and sequence analysis of rat IL-3. Two different mRNA isoforms were isolated after transfection of COS cells with the cytokine genomic sequences. One of the isoforms has been predicted before by Cohen et al. (1986), and the other one is identical except that it encodes a protein with an insertion of three amino acids at position 56. As names for the two isoforms, we propose IL-3alpha for the predicted and IL-3beta for the novel molecule. IL-3beta mRNA was detected as the predominant isoform in rat lymphocytes in vivo. High levels of the cytokine were obtained after infection of human cells (A549) with a recombinant adenovirus harboring rIL-3beta cDNA (IG.Ad.CMV.IL-3beta). The biological properties of the IL-3beta protein were tested in a FDC-P1 proliferation assay and in a hematopoietic progenitor colony forming assay. To assess in-vivo bioactivity, lysed 293 cells containing IG.Ad.CMV.rIL-3beta virus were injected subcutaneously into F344 rats. Stimulation of hematopoiesis and leucocytosis were observed during the treatment. After subcutaneous injections of the lysed adeno-producer cells in mice, the only effect observed was a cellular infiltration at the site of injection, confirming the poor cross-reactivity between the two species. The biological properties in vitro and in vivo demonstrate that the cDNA sequences of IL-3beta presented here encode active rat IL-3 protein.

Rapamycin destabilizes interleukin-3 mRNA in autocrine tumor cells by a mechanism requiring an intact 3' untranslated region

We analyzed the effect of rapamycin on autocrine mast cell tumor lines with abnormally stable interleukin-3 (IL-3) transcripts due to a defect in mRNA degradation. Rapamycin inhibited IL-3 mRNA expression specifically, while transcripts of IL-4 and IL-6 were not affected. As indicated by the use of the transcriptional inhibitor actinomycin D or by reporter constructs, inhibition was posttranscriptional and resulted from destabilization of the mRNA. Transcripts from transgenes lacking the AU-rich 3' untranslated region were refractory to drug-induced degradation, suggesting that these 3' sequences contain the target of the rapamycin effect. Rapamycin did not promote IL-3 mRNA degradation in cells of a tumor variant lacking expression of FKBP12, the binding protein of rapamycin. Experiments with wortmannin indicated that rapamycin does not act via p70S6 kinase. FK-506, another ligand of FKBP12 affecting the phosphatase calcineurin, did not antagonize but shared the effect of rapamycin. Our data fit a model whereby both FKBP12 and calcineurin target an unknown regulator of IL-3 mRNA turnover.

Alteration of major cytokines produced by mitogen-activated peritoneal macrophages and splenocytes in T-2 toxin-treated male CD-1 mice

Fusarium T-2 toxin has immunotoxic properties that may be related to the modulation of cytokine expression by cells of the immune system. Male CD-1 mice were used to study the effect of in vivo exposure to T-2 toxin on the alteration of interleukin (IL)-1α, tumor necrosis factor α (TNF), and IL-6 in lipopolysaccharide-stimulated peritoneal macrophages, and IL-2, IL-3, and interferon γ (IFNγ) in concanavalin A (Con A)-stimulated splenocytes. Mice were orally dosed with 0, 0.1, 0.5, and 2.5 mg T-2 toxin/kg body weight for 2 weeks on alternate days. Northern blot analysis of IL-1α, TNF, and IL-6 mRNA from activated peritoneal macrophages showed no significant differences between control and treated groups. Measurements of secreted protein by immunoassay demonstrated suppression of these cytokines in all treated groups, suggesting that T-2 toxin affects the translational or post-translational regulation of these cytokines from peritoneal macrophages. Levels of IL-2, IL-3, and IFNγ mRNA from Con A-activated splenocytes were higher in all treated groups. The increases were significant for IL-2 and IFNγ in the groups receiving low (0.1 mg/kg) and high (2.5 mg/kg) doses of T-2 toxin, and for IL-3 in the group receiving a medium (0.5 mg/kg) dose of this toxin (P ≤ 0.05). Results indicated that T-2 toxin given orally at low or medium doses induces transcription or increases mRNA stability of IL-2, IFNγ, and IL-3. Protein levels of all three cytokines were also increased, indicating that T-2 toxin also increases translational/post-translational efficiency of IFNγ, IL-2, and IL-3. Possible mechanisms in the immunosuppressive effects of T-2 toxin may involve endotoxemia resulting after the toxin administration, alteration of the stability of mRNA, or previously described effects of T-2 toxin on protein synthesis.

Interleukin-3 mRNA stabilization by a trans-acting mechanism in autocrine tumors lacking interleukin-3 gene rearrangements

Tumors obtained from v-Ha-ras-transformed PB-3c cells are characterized by autocrine interleukin-3 (IL3) expression, which occurs either without (class I tumors) or with enhanced transcription (class II tumors). To address possible post-transcriptional mechanisms of IL3 expression, IL3 mRNA stability was examined in both tumor classes. Increased stability of IL3 mRNA was detected in class I tumor lines (t1/2 > 3 h), whereas rapid decay of IL3 transcripts (t1/2 < 0.5 h) was found in class II tumor lines. In both tumor classes, the c-myc and interleukin-6 transcripts were short-lived. Transcripts of a constitutively expressed IL3 reporter gene were stable in class I tumor cells but unstable in class II tumor cells, suggesting that IL3 mRNA stabilization involved a trans-acting mechanism. Rapid decay of IL3 reporter transcripts was observed in untransformed PB-3c as well as in v-Ha-ras expressing precursor cells linking transcript stabilization to the tumor stage. Reporter transcript stabilization in class I tumor cells correlated with increased IL3 production. Deletion of the AU-rich element from the IL3 reporter gene further augmented IL3 mRNA levels as well as IL3 production, suggesting that the stabilizing mechanism in class I tumor cells is not equivalent to AU-rich element deletion.

Production of interleukin-3 by murine central nervous system neurons

We examined expression and production of interleukin-3 (IL-3) mRNA and IL-3 protein in mouse primary cultured neurons and glia by the reverse transcription and polymerase chain reaction and a bioassay using an IL-3-dependent cell line. IL-3 mRNA was demonstrated mainly in hippocampal neurons but not in glia, while a small but definite production of bioactive IL-3 was detected in septal and hippocampal neuronal cultures. Thus, endogenous IL-3 might be produced by certain neurons in situ.

Cyclosporin A inhibits growth of autocrine tumour cell lines by destabilizing interleukin-3 mRNA

In T cells, cyclosporin A (CsA) exerts its immunosuppressive effect by preventing transcriptional induction of the expression of interleukin(IL)-2. This is achieved by a mechanism that involves binding of a CsA-cyclophilin complex to calcineurin, which in turn inhibits the phosphatase-controlled translocation of transcription factor NFAT to the nucleus. We have previously identified IL-3 as an autocrine oncogenic regulator in tumour cell lines generated by introducing the v-H-ras oncogene into IL-3-dependent mast cells. Here we report that CsA specifically blocks autocrine tumour cell growth. The mechanism involves down-regulation of IL-3 expression by destabilization of the messenger RNA and requires ongoing transcription. Transcripts from exogenous IL-3 genes lacking the (A+U)-rich element (ARE) in the 3' untranslated terminal repeat could not be destabilized, suggesting that at least part of this sequence, which is known to mediate decay of short-lived mRNA, participates in a CsA-sensitive regulatory mechanism.

Suppressible and nonsuppressible autocrine mast cell tumors are distinguished by insertion of an endogenous retroviral element (IAP) into the interleukin 3 gene

After v-H-ras expression, the interleukin 3 (IL-3)-dependent PB-3c mast cells progress in vivo to two different classes of IL-3 autocrine tumors. Class I tumors show a germline configuration of the IL-3 gene and represent more than 90% of tumors analyzed so far. Somatic cell fusion of class I tumor lines with the nontumorigenic parental PB-3c resulted in loss of oncogenic IL-3 expression by a posttranscriptional mechanism with concomitant tumor suppression. Class II tumors arise rarely and contain an insertion in one IL-3 allele. This alteration was linked to enhanced IL-3 gene transcription. For one tumor, the insertion was shown to be an endogenous retroviral element (intracisternal A-particle). Cell hybrids of class II tumors with PB-3c remained IL-3 independent, expressed IL-3, and formed tumors rapidly. These results suggest that the v-H-ras oncogene synergizes with a recessive and a dominant lesion in class I and II tumors, respectively, both of which lead to the autocrine production of IL-3.

Regulation of interleukin-2 gene enhancer activity by the T cell accessory molecule CD28

The mechanism by which cell surface molecules regulate T cell production of lymphokines is poorly understood. Production of interleukin-2 (IL-2) can be regulated by signal transduction pathways distinct from those induced by the T cell antigen receptor. Stimulation of CD28, a molecule expressed on most human T cells, induced the formation of a protein complex that bound to a site on the IL-2 gene distinct from previously described binding sites and increased IL-2 enhancer activity fivefold. The CD28-responsive complex bound to the IL-2 gene between -164 and -154 base pairs from the transcription start site. The sequence of this element is similar to regions conserved in the 5' flanking regions of several other lymphokine genes.

Retrotransposition of a mouse IAP sequence tagged with an indicator gene

We have marked a cloned mouse IAP sequence with a neomycin-containing indicator gene whose expression is conditioned by passage of the transposon through an RNA intermediate. Transposition of the marked IAP introduced into tumor cells could be detected by simple selection of the cells in G418, at a frequency of 10(-6) per cell per generation. Southern blot analysis and nucleotide sequencing after PCR amplification demonstrated "retrotransposition" of the marked element, with splicing out of an intron contained in the indicator gene, and retroviral-like reverse transcription and integration of the transposed IAPs, with 6 bp duplications of the identified target sites. Transposition was found to be mutagenic for the element, as might be expected if the identified marked and endogenous IAP transcripts were coencapsidated into IAP particles as dimers.

Systematic analysis of the ability of stromal cell lines derived from different murine adult tissues to support maintenance of hematopoietic stem cells in vitro

Hematopoietic stem cells interact with a complex microenvironment both in vivo and in vitro. In association with this microenvironment, murine stem cells are maintained in vitro for several months. Fibroblast-like stromal cells appear to be important components of the microenvironment, since several laboratories have demonstrated that cloned stromal cell lines support hematopoiesis in vitro. The importance of the tissue of origin of such cell lines remains unknown, since systematic generation of stromal cell lines from adult tissues has never been accomplished. In addition, the capacity of stromal cell lines to support reconstituting stem cell has not been examined. We have previously described an efficient and rapid method for the immortalization of primary bone marrow stromal cell lines (Williams et al., Mol. Cell. Biol. 8:3864-3871, 1988) which can be used to systematically derive cell lines from multiple tissues of the adult mouse. Here we report the immortalization of primary murine lung, kidney, skin, and bone marrow stromal cells using a recombinant retrovirus vector (U19-5) containing the simian virus large T antigen (SV40 LT) and the neophosphotransferase gene. The interaction of these stromal cells with factor-dependent cells Patterson-Mix (FDCP-Mix), colony forming units-spleen (CFU-S), and reconstituting hematopoietic stem cells was studied in order to analyze the ability of such lines to support multipotent stem cells in vitro. These studies revealed that stromal cell lines from these diverse tissues were morphologically and phenotypically similar and that they quantitatively bound CFU-S and FDCP-Mix cells equally well. However, only those cell lines derived from bone marrow-supported maintenance of day 12 CFU-S in vitro. One lung-derived stromal cell line, ULU-3, supported the survival of day 8 CFU-S, but not the more primitive CFU-S12. A bone marrow-derived stromal cell line, U2, supported the survival of long-term reconstituting stem cells for up to 3 weeks in vitro as assayed by reconstitution 1 year post-transplant. These studies suggest that adherence of HSC to stromal cells is necessary but not sufficient for maintenance of these stem cell populations and that bone marrow provides specific signals relating to hematopoietic stem cell survival and proliferation.

The IL-4 and IL-5 genes are closely linked and are part of a cytokine gene cluster on mouse chromosome 11

The murine IL-4 and IL-5 genes encode hemopoietic growth factors involved in the stimulation, proliferation, and differentiation of cells of the T lymphocyte, B lymphocyte, and granulocyte lineages. We have mapped the Il-4 and Il-5 loci representing the structural genes for IL-4 and IL-5, respectively, to mouse chromosome 11 using Chinese hamster x mouse and rat x mouse somatic cell hybrids. Physical linkage studies of the IL-4 and IL-5 genes by pulsed field gel electrophoresis have shown that they are closely linked, being 110-180 kb apart. Since the Il-5 locus maps to the interface of bands A5 and B1 in the same location as the genes for IL-3 and GM-CSF, this places these three cytokine genes, as well as the IL-4 gene, within a region of about 5000-10,000 kb. The present physical linkage studies indicate that the IL-4 and IL-5 genes are a minimum of 600 kb apart from the closely linked IL-3 and GM-CSF genes. The gene clustering, together with similarities in gene structure, regulation, and biological function, raises the possibility that the four genes may be part of a distantly related cytokine gene family.

Isolation, structure and expression of cDNA and genomic clones for murine eosinophil differentiation factor. Comparison with other eosinophilopoietic lymphokines and identity with interleukin-5

Eosinophil differentiation factor (EDF) is a recently described regulator affecting eosinophil growth and activation. cDNA clones for murine EDF were isolated by direct expression from libraries prepared from the T cell hybrid NIMP-TH1. The longest cDNA clone obtained was 1534 bp in length encoding a polypeptide of 133 amino acids. Two variant cDNAs suggesting alternative RNA processing events were detected. The EDF gene was cloned from a genomic lambda library and a region of 6727 bp encompassing the gene was sequenced. The gene contains three introns 829, 1875 and 79 bases in length and has numerous repetitive sequences. A common, possible regulatory element, including a conserved decamer, lies adjacent to the TATA boxes of the EDF and granulocyte-macrophage colony-stimulating factor (GM-CSF) genes and similar sequences are present in some other lymphokine genes. Recombinant EDF produced in monkey COS cells strongly stimulated the eosinophil lineage and also showed B-cell-growth factor II (BCGFII) activity whereas recombinant murine interleukin-3 and GM-CSF showed much broader activity towards the different myeloid lineages, were less active on eosinophils and had no BCGFII activity. The BCGFII activity of recombinant EDF together with a comparison of the BCGFII (interleukin-5) cDNA sequence with that of the EDF cDNA establishes that these two activities are the properties of a single polypeptide.

Nuclear proteins interacting with the promoter region of the human granulocyte/macrophage colony-stimulating factor gene

The gene for human granulocyte/macrophage colony-stimulating factor (GM-CSF) is expressed in a tissue-specific as well as an activation-dependent manner. The interaction of nuclear proteins with the promoter region of the GM-CSF gene that is likely to be responsible for this pattern of GM-CSF expression was investigated. We show that nuclear proteins interact with DNA fragments from the GM-CSF promoter in a cell-specific manner. A region spanning two cytokine-specific sequences, cytokine 1 (CK-1, 5' GAGATTCCAC 3') and cytokine 2 (CK-2, 5' TCAGGTA 3') bound two nuclear proteins [nuclear factor (NF)-GMa and NF-GMb] from GM-CSF-expressing cells in gel retardation assays. NF-GMb was inducible with phorbol 12-myristate 13-acetate and accompanied induction of GM-CSF message. NF-GMb was absent in cell lines not producing GM-CSF, some of which had other distinct binding proteins. NF-GMa and NF-GMb eluted from a heparin-Sepharose column at 0.3 and 0.6 M KCl, respectively. We hypothesize that the sequences CK-1 and CK-2 bind specific proteins and regulate GM-CSF transcription.

The production of myeloid blood cells and their regulation during health and disease

The regulation of myelopoiesis in vivo most likely entails a complex set of interactions between cell-derived biomolecules and their target cells: hematopoietic stem and progenitor cells and accessory cells. Stimulating and suppressing factors have been characterized through in vitro studies, and their mechanisms of action in vitro and in vivo have begun to be elucidated. Among those factors being studied are the hematopoietic colony-stimulating factors (CSF): interleukin-3 (multi-CSF), granulocyte-macrophage-CSF, granulocyte-CSF, and macrophage-CSF; other molecules include erythropoietin, B-cell-stimulating factor-1, interleukin-1, interleukin-2, prostaglandin E, leukotrienes, acidic ferritins, lactoferrin, transferrin, the interferons-gamma, -alpha, and -beta, and the tumor necrosis factors-alpha and -beta (lymphotoxin). These factors interact to modulate blood cell production in vitro and in vivo. The proposed review characterizes these biomolecules biochemically and functionally, including receptor-ligand interactions and the secondary messengers within the cell which mediate their functional activity. The production and action of the molecules are described under conditions of hematopoietic disorders, as well as under normal conditions. Studies in vitro are correlated with studies in vivo using animal models to give an overall view of what is known about these molecules and their relevance physiologically and pathologically.

Bovine interleukin 2: regulatory mechanisms

A cDNA clone of the bovine interleukin-2 (IL-2) gene has been isolated and demonstrated to produce a functional bovine IL-2 protein when transfected into either CV-1 or COS-1 monkey cells. Homology comparisons of both the nucleotide and predicted amino acid sequences of bovine IL-2 with those of the human and mouse show extensive regions of sequence conservation between the species. The amino acid sequence of the mature bovine IL-2 protein shares about 60-63% homology with those of the human and mouse, but the 3' untranslated regions of the human and mouse gene share as much, if not greater, sequence homology with the 3' untranslated regions of the human and mouse genes. In particular, a tandemly repeated sequence (TATT), n, found in the 3' untranslated tail of the bovine IL-2 clone is also found in the 3' untranslated region of a large group of cytokine genes and other inducible genes of the lymphoid and immune response systems. This sequence may serve a specific regulatory function in the immune system.

Molecular cloning, nucleotide sequence, and expression of the gene encoding human eosinophil differentiation factor (interleukin 5)

The human eosinophil differentiation factor (EDF) gene was cloned from a genomic library in lambda phage EMBL3A by using a murine EDF cDNA clone as a probe. The DNA sequence of a 3.2-kilobase BamHI fragment spanning the gene was determined. The gene contains three introns. The predicted amino acid sequence of 134 amino acids is identical with that recently reported for human interleukin 5 but shows no significant homology with other known hemopoietic growth regulators. The amino acid sequence shows strong homology (approximately 70% identity) with that of murine EDF. Recombinant human EDF, expressed from the human EDF gene after transfection into monkey COS cells, stimulated the production of eosinophils and eosinophil colonies from normal human bone marrow but had no effect on the production of neutrophils or mononuclear cells (monocytes and lymphoid cells). The apparent specificity of human EDF for the eosinophil lineage in myeloid hemopoiesis contrasts with the properties of human interleukin 3 and granulocyte/macrophage and granulocyte colony-stimulating factors but is directly analogous to the biological properties of murine EDF. Human EDF therefore represents a distinct hemopoietic growth factor that could play a central role in the regulation of eosinophilia.

Intron-dependent evolution: preferred types of exons and introns

Exon insertions and exon duplications, two major mechanisms of exon shuffling, are shown to involve modules that have introns of the same phase class at both their 5'- and 3'-ends. At the sites of intronic recombinations exon insertions and duplications create new introns which belong to the same phase class as the recipient introns. As a consequence of repeated exon insertions and exon duplications introns of a single phase class predominate in the resulting genes, i.e. gene assembly by exon shuffling is reflected both by this nonrandom intron phase usage and by the correlation between the domain organization of the proteins and exon-intron organization of their genes. Genes that appeared before the eukaryote-prokaryote split do not show these diagnostic signs of exon shuffling. Since ancestral introns (e.g. self-splicing introns) did not favour intronic recombination, exon shuffling may not have been significant in the early part of protein evolution.

Comparative effects in vivo of recombinant murine interleukin 3, natural murine colony-stimulating factor-1, and recombinant murine granulocyte-macrophage colony-stimulating factor on myelopoiesis in mice

Purified murine colony-stimulating factors (CSF) recombinant interleukin 3 (IL-3), natural CSF-1, and recombinant granulocyte-macrophage (GM) CSF were assessed in vivo for their effects on BDF1 mouse bone marrow and spleen granulocyte-macrophage (CFU-GM), erythroid (BFU-E), and multipotential (CFU-GEMM) progenitor cells in untreated mice and in mice pretreated with purified iron-saturated human lactoferrin (LF). The CSF and LF preparations did not contain detectable endotoxin (less than 0.1 ng). Mice pretreated with LF were more sensitive to the effects of CSF. In mice pretreated with LF, 2,000 U IL-3 or 20,000 U CSF-1 significantly enhanced the cycling status and absolute numbers of all progenitors, whereas 20,000 U GM-CSF significantly increased the cycling status of CFU-GM and CFU-GEMM, but had no effect on cycling of BFU-E or on numbers of any of the progenitors. The effects of CSF in mice pretreated with LF were not mimicked by 0.1-100 ng E. coli lipopolysaccharide.

A sequence homology between the pX genes of HTLV-I/II and the murine IL-3 gene

Searching the protein sequence database for amino acid sequences homologous to the x-lor sequence in the pX region of human T-cell leukemia virus types I and II (HTLV-I/II), we found that there is a region of 38 amino acids where the murine interleukin 3 (IL-3) sequence has a 40% homology with the x-lor sequence. A statistical analysis shows that this homology is highly significant with a probability of 1.57 X 10(-10). The biological implication of this homology is discussed.

Nucleotide sequence of the intracisternal A-particle genome inserted 5' to the interleukin-3 gene of the leukemia cell line WEHI-3B

The nucleotide sequence of the intracisternal A-particle genome IAP-IL3 is presented. This IAP element was found to have inserted upstream of the promoter of the interleukin-3 gene of the leukemia cell line WEHI-3B. IAP-IL3 is 5095 bp in length, with identical long terminal repeats (LTRs) of 337 bp. The LTRs show many of the conserved sequence elements identified in other retroviruses. Comparison with other available sequences of IAP genomes indicates that IAP-IL3 is a deleted type I element. It carries a deletion covering the 3' end of the putative IAP gag gene and extending into the 5' end of the putative IAP pol gene. IAP-IL3 has extensive sequence homology with an IgE-binding factor cDNA and evidence is presented indicating that it was derived from a member of the mouse IAP sequence family. Comparison between the pol region of IAP-IL3 and other retroviruses suggests that IAP-IL3 is most closely related to type B and type D retroviruses.

Cloning and expression of the rat interleukin-3 gene

Genomic clones carrying the rat interleukin-3 (IL-3) gene have been isolated and the nucleotide sequence of the gene determined. Alignment of this sequence with that of the mouse IL-3 gene has allowed the structure of the rat IL-3 gene to be deduced. The intron-exon boundaries are conserved and extensive nucleotide homology (approx 90%) is present in the 5' flanking region and the portion of the gene coding for the signal peptide. Several proposed regulatory sequences are conserved and an analogous element to the tandem repeat in intron 2 of the mouse gene is also present. The predicted amino acid sequence for mature rat IL-3 shows surprisingly low homology (54%) with its murine counterpart, although all four cysteine residues are conserved. The rat IL-3 gene was expressed in monkey COS-1 cells and colony assays established that rat IL-3 is a multi-lineage haemopoietic growth regulator. There was little cross-reactivity of the respective IL-3 species on mouse and rat bone marrow cells suggesting that rat IL-3, in concert with its receptor, has evolved significantly away from the mouse IL-3/receptor system.

Molecular cloning of a functional bovine interleukin 2 cDNA

A cDNA clone of the bovine interleukin 2 (IL-2) gene has been isolated and demonstrated to be functional in the production of secreted bovine IL-2 protein when transfected into monkey cells. The bovine IL-2 clone is 791 base pairs in length and contains an open reading frame of 474 base pairs coding for a bovine IL-2 precursor polypeptide of 158 amino acids with an estimated molecular weight of 17,884. The putative hydrophobic leader or signal sequence of the precursor protein is 23 amino acid residues long, suggesting that, after removal by processing, the mature secreted bovine IL-2 protein contains 135 amino acids and has a molecular weight of 15,464. Comparisons of both the nucleotide sequence and the predicted amino acid sequence of bovine IL-2 with those of the human and mouse IL-2 show extensive regions of sequence conservation between the species, interspersed with other regions of less similarity. The 3' untranslated region of the bovine IL-2 gene shares as much, if not greater, sequence homology with the 3' untranslated regions of the human and mouse genes as do the transcribed coding regions of these genes, suggesting an involvement of this region in regulation. In particular, a tandemly repeated sequence, (TATT)n, found in the 3' untranslated tail of the bovine IL-2 clone is also found in the 3' untranslated region of the other known interleukin and interferon genes, as well as in similar regions of many other inducible genes of the lymphoid and immune response systems, suggesting a cell or tissue-specific regulatory function for these evolutionarily conserved sequences.

Constitutive synthesis of interleukin-3 by leukaemia cell line WEHI-3B is due to retroviral insertion near the gene

Interleukin-3 (multi-CSF) is a multilineage haematopoietic growth regulator that initiates the proliferation and differentiation of multipotential stem cells. Complementary DNA clones encoding interleukin-3 (IL-3) have recently been isolated and the structure of the IL-3 gene determined. IL-3 is produced by T lymphocytes or T lymphomas only after stimulation with antigens, mitogens or chemical activators such as phorbol esters. The myelomonocytic leukaemia line WEHI-3B also produces IL-3 but its production is constitutive and the WEHI-3B cells do not appear to produce significant levels of any of the other lymphokines normally secreted by T lymphocytes after stimulation. It has been proposed that the genetic change leading to the constitutive expression of IL-3 may have been a key event in the development of this leukaemia. We report here that the constitutive synthesis of IL-3 by the WEHI-3B cell line is due to the insertion of an endogenous retrovirus-like element close to the 5' end of the gene. The insertion, an intracisternal A particle (IAP) genome, is positioned with its 5' long terminal repeat (LTR) close to the promoter region of the IL-3 gene, resulting in constitutive synthesis of IL-3.