Hematopoietic growth factor receptors.
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Amino Acid Sequence↗
Biomedical subjects
G Krystal
Publications and source records attributed to G Krystal.
A specific in vitro bioassay for measuring erythropoietin levels in human serum and plasma.
The accurate measurement of biologically active erythropoietin (Ep) in human serum and plasma using present in vivo and in vitro bioassays is difficult because of the presence of both inhibitors and non-Ep stimulators of erythropoiesis. We have developed a simple procedure to quantitatively purify Ep from serum and plasma for subsequent testing in the phenylhydrazine-treated mouse spleen cell assay. The method involves absorption of Ep to an immobilized high-affinity anti-Ep monoclonal antibody and acid elution of the antibody-bound material. After neutralization, the eluted EP is then tested directly in the in vitro bioassay without interference by other serum proteins. By using magnetic beads as a solid support for the antibody, washing and elution steps can be performed rapidly and efficiently. Recoveries of Ep after this procedure show very little sample-to-sample variation and are consistently between 45% and 55%, which is close to the maximum binding expected for the anti-Ep antibody. Coupled with the 7.4-fold concentration that this procedure affords, there is an overall increase in sensitivity of three- to fourfold, which makes this assay suitable for accurately measuring Ep levels in patients with below-average titers. Results with this magnetic bead assay indicate that accurate and reproducible estimates for Ep levels in the serum and plasma from healthy donors as well as from patients with hematologic disorders can be obtained. Titers of biologically active Ep in the sera from a group of patients with either leukemia or lymphoma were found to be elevated, and the values correlated well with titers of immunoreactive Ep measured in the Ep radioimmunoassay. Because of its specificity and high sensitivity, the magnetic bead assay is a valuable alternative to immunoassays for the measurement of elevated, normal, and even subnormal Ep levels in human serum and plasma.
Antibodies, Monoclonal↗
Detection and isolation of the erythropoietin receptor using biotinylated erythropoietin.
Procedures have been developed to label human erythropoietin (Ep) with biotin to detect and isolate the Ep-receptor. The labeling method used the abundant carbohydrate groups on Ep and resulted in biologically active biotin-Ep (b-Ep) containing 8 to 10 biotins per Ep molecule. Specific binding of b-Ep to cells from spleens of mice made anemic by phenylhydrazine injections was demonstrated using 125I-labeled streptavidin. B-Ep, together with fluorescently tagged streptavidin, was found to specifically detect Ep-receptor-bearing cells by flow cytometry. This was demonstrated in several ways. First, approximately 90% of nucleated spleen cells from phenylhydrazine-treated mice were clearly fluorescent after staining with b-Ep and streptavidin-phycoerythrin, whereas only background fluorescence was detected using spleen cells from untreated mice. In addition, Ep-receptors were detected on 5% to 10% of normal mouse bone marrow cells, and these cells could be identified as erythroid in nature by separating the cells into subpopulations based on light-scatter properties. Third, Ep-receptor expression was found to correlate positively with expression of transferrin receptors, confirming the erythroid nature of these cells. B-Ep was also used to isolate Ep-receptors from monkey COS cells transfected with the murine Ep-receptor cDNA. In these experiments a cell-surface-bound protein of approximately 65 Kd and an intracellular protein of approximately 60 Kd were isolated from these cells. The procedures described in this report for detecting Ep-receptor expressing cells and for isolating the Ep-receptor should be valuable for purifying erythroid cells from heterogeneous cell populations, for elucidating the structure of the Ep-receptor, and for studying the biological activities of Ep at the cellular and molecular level.
Animals↗
Binding competition of toxic shock syndrome toxin 1 and other staphylococcal exoproteins for receptors on human peripheral blood mononuclear cells.
Binding of toxic shock toxin 1 (TSST-1) and staphylococcal enterotoxin A (SEA) to human peripheral blood mononuclear cells (PBMC) was investigated by using 125I-labeled ligands. Scatchard analyses revealed similar numbers of receptors (approximately 5,000 to 8,000) and similar dissociation constants (Kd, approximately 20 to 25 nM) per PBMC. SEA but not enterotoxin B, C1, C2, C3, D, or E significantly inhibited binding of 125I-TSST-1 to PBMC. Cross-competition of TSST-1 and SEA in binding assays suggests that they may bind to overlapping or separate epitopes on the same receptor.
Bacterial Toxins↗
Immunochemical analysis of monoclonal antibodies to human erythropoietin.
We recently reported the development of three monoclonal antibodies (MoAbs) to biologically active human erythropoietin (Ep). In the present study, we investigated the epitope specificity of these three antibodies, as well as their reactivity with Eps derived from species other than man. All three antibodies reacted with the Ep polypeptide itself, rather than with its carbohydrate moieties. Moreover, all three antibodies recognized separate nonoverlapping epitopes. Further studies with reduced/alkylated Ep and with sodium dodecyl sulfate-denatured Ep suggested that two of the MoAbs, anti-Ep-2 and anti-Ep-16, were specific for conformational, nonlinear determinants on the Ep molecule, whereas the third MoAb, anti-Ep-26, appeared to recognize a linear epitope. However, anti-Ep-26 did not react with synthetic peptides representing the 26 amino-, the 99-129 mid-region, or the 10 carboxy-terminal residues of Ep, nor with trypsin-, chymotrypsin-, or V8 protease-digested fragments of Ep. When tested with Ep from different species, the neutralizing capabilities of the three MoAbs were clearly different. Comparing their effectiveness against baboon, ovine and murine Ep, antibody 2 was most effective at neutralizing baboon Ep, antibody 16 was most effective against murine Ep, and antibody 26 showed little reactivity with any of these nonhuman Eps. Because these various Eps readily stimulate across species barriers, it is likely that the receptor binding domain on Ep has remained relatively conserved during evolution. Our results therefore suggest that the neutralizing capacity of our three anti-Ep MoAbs is caused not by binding directly to the Ep receptor binding domain on Ep, but by binding to distant regions, causing conformational changes in Ep, or by binding to regions close to the binding site, steric hindrance.
Animals↗
The mechanism of action of murine interleukin-3: current status.
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Animals↗
Characterization of the interleukin 3 receptor.
A variety of homobifunctional crosslinking agents have been used to gain insight into the nature of the murine interleukin 3 (mIL-3) receptor. When [125I]mIL-3 was cross-linked to receptor sites on the surfaces of intact B6SUtA1 cells with disuccinimidyl suberate (DSS), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) revealed the existence of two radiolabeled species with molecular weights of 140 (p140) and 70 (p70) kd (after subtraction of [125I]mIL-3). The relative intensities of the two bands did not change when the [125I]mIL-3 concentration was varied, confirming Scatchard results which suggested only one affinity class. However, when [125I]mIL-3 was crosslinked to intact cells and then incubated at 37 degrees C, the intensity of p140 decreased relative to p70, suggesting a conversion of p140 to p70. This conversion could be inhibited by sodium azide, methylamine, and bacitracin and could also be prevented by first boiling for 1 min in 2% SDS and 5% 2-mercaptoethanol. The putative protease that carried out this apparent conversion appeared to be associated both with plasma membranes prepared from these cells and also with solubilized receptors. Moreover, when p140, crosslinked with both dithiobis succinimidylpropionate and glutaraldehyde, was purified and reelectrophoresed under reducing conditions, p70 could be generated. N-glycanase digestion of p140 and p70 revealed a similar level of N-linked carbohydrate, which upon closer study appeared to consist of two chains, a 3-kd and an 8-kd moiety. Consistent with this data, we propose that the receptor is a 140-kd glycoprotein that is cleaved to a 70-kd surface protein upon mIL-3 binding and chemical crosslinking.
Animals↗
Interleukin-3 stimulates the tyrosine phosphorylation of the 140-kilodalton interleukin-3 receptor.
Murine interleukin-3 (mIL-3) stimulates the rapid and transient tyrosine phosphorylation of a number of proteins in mIL-3-dependent B6SUtA1 cells. Two of these proteins, p68 and p140, are maximally phosphorylated at tyrosine residues within 2 min of addition of mIL-3. Because 125I-mIL-3 can be cross-linked to both 70- and 140-kDa proteins on intact B6SUtA1 cells, we investigated whether the tyrosine phosphorylated p68 and p140 were these two mIL-3 receptor proteins. Addition of antiphosphotyrosine antibodies (alpha PTyr Abs) to cell lysates from B6SUtA1 cells, to which 125I-mIL-3 had been disuccinimidyl suberate-cross-linked, resulted in the immunoprecipitation of 125I-mIL-3 complexed to both 70- and 140-kDa proteins. To determine if the observed immunoprecipitation pattern was due to the direct interaction of alpha-PTyr Abs with these two mIL-3 receptor proteins or with tyrosine-phosphorylated proteins that were associated with the receptor proteins, cell lysates were treated with 2% sodium dodecyl sulfate, 5% 2-mercaptoethanol, and boiled for 1 min. After removal of sodium dodecyl sulfate and 2-mercaptoethanol, alpha PTyr Abs immunoprecipitated 125I-mIL-3 cross-linked to only the 140-kDa protein. To confirm this finding, 32P-labeled B6SUtA1 cells were treated with biotinylated or fluoresceinated mIL-3. Addition of immobilized streptavidin or antifluorescein antibodies, respectively, to cell lysates from these cells resulted in the enrichment of only a 140-kDa tyrosine phosphorylated protein. Taken together, these results strongly suggest that only the 140-kDa receptor protein is tyrosine phosphorylated upon mIL-3 binding.
Animals↗
An enzyme-linked immunosorbent assay for erythropoietin using monoclonal antibodies, tetrameric immune complexes, and substrate amplification.
We recently reported the development of several monoclonal antibodies (MoAbs) to native human erythropoietin (Ep). In the present study we have used the two antibodies with highest affinity to develop a two-sided or sandwich enzyme-linked immunosorbent assay (ELISA) to measure Ep in human serum. In this assay Ep is incubated in microtiter wells precoated with the first (IgE) anti-Ep antibody. Assay wells are then incubated with the second (IgG1) anti-Ep antibody, which is labeled noncovalently with the enzyme alkaline phosphatase (AP) by means of bispecific tetrameric antibody complexes consisting of IgG1 anti-Ep cross-linked to IgG1 anti-AP using rat MoAbs specific for mouse IgG1. Application of this noncovalent labeling procedure, in combination with substrate amplification, results in a detection sensitivity of 0.5 to 1.0 mU/sample (5 to 10 mU/mL), which makes this assay suitable for measuring normal serum Ep levels. The validity of this ELISA for quantitating Ep in biological fluids was demonstrated by the parallelism obtained between pure recombinant Ep dose-response curves and those obtained with plasma and serum from healthy donors and patients with various hematologic disorders. Normal plasma Ep levels detected with this ELISA ranged from 9 to 101 mU/mL with a mean of 32 +/- 23 (SD) mU/mL. Ep levels in sera from patients with polycythemia vera were in the low to normal range, whereas Ep levels in sera from patients with secondary polycythemia and patients with aplastic anemia were moderately to strongly elevated. These results demonstrate that the Ep-ELISA is a sensitive, reliable, and nonradioactive immunologic method for quantitating Ep levels and should prove useful in a variety of clinical and laboratory settings.
Alkaline Phosphatase↗
Application of a silver-binding assay to the determination of protein in cerebrospinal fluid.
We evaluated a silver-binding assay for use in measuring total protein in cerebrospinal fluid. The advantage of this procedure over other methods is that, because of its sensitivity, it requires only a 0.5-microL sample. The procedure, which takes approximately 40 min to complete, involves dilution of 0.5-microL samples to 1 mL with distilled water containing sodium dodecyl sulfate, followed by addition of glutaraldehyde and an ammoniacal silver solution. After color development for 30 min, the reaction is terminated with sodium thiosulfate and the absorbance is measured at 420 nm. This assay displayed within-run and day-to-day precision (CV) of 3.1% to 13% over the range of 210 to 1370 mg/L. It showed substantially less protein-to-protein variation than the Coomassie Blue dye-binding procedure when tested with albumin, globulin, and transferrin. It also yielded an accurate estimation of hemoglobin. Moreover, preliminary studies suggested that it was capable of quantifying immunoglobulin light chains and glycoproteins. In a study of 54 human cerebrospinal fluid samples, results of the silver-binding assay corresponded more closely with those obtained with a rate biuret assay (intraclass correlation coefficient = 0.91) than did either the dye-binding or classical Lowry methods.
Albumins↗
Interleukin-3, GM-CSF, and TPA induce distinct phosphorylation events in an interleukin 3-dependent multipotential cell line.
The mechanism of action of the hemopoietic growth factor, murine interleukin-3 (mIL-3), was investigated using an mIL-3-dependent multipotential hematopoietic cell line, B6SUtA1. Murine granulocyte-macrophage colony-stimulating factor (mGM-CSF) was as potent as mIL-3 in stimulating these cells. In addition, sodium orthovanadate, an inhibitor of phosphotyrosine phosphatase, and 12-O-tetradecanoyl-phorbol-13-acetate (TPA), a known activator of protein kinase C, also stimulated DNA synthesis in these cells, suggesting that protein phosphorylation might be involved in the mechanism of action of mIL-3 and mGM-CSF. To assess this possibility, intact B6SUtA1 cells exposed for brief periods to mIL-3, mGM-CSF, and TPA were analyzed for changes in phosphorylation patterns using metabolic 32P-labeling and antibodies to phosphotyrosine. Both mIL-3 and mGM-CSF induced the serine-specific phosphorylation of a 68-Kd cytosolic protein, whereas all three agents stimulated the serine-specific phosphorylation of a 68-Kd membrane protein. Furthermore, mIL-3 stimulated tyrosine phosphorylation of the 68-Kd membrane protein, as well as of 140-, 90-, 55, and 40-Kd proteins. The 90-Kd protein was also tyrosine phosphorylated in response to mGM-CSF. These phosphotyrosine containing proteins were not detected in TPA-treated cells. These results indicate that protein phosphorylations on tyrosine and serine residues occur in B6SUtA1 cells following short-term incubation with mIL-3 or mGM-CSF and that most of these phosphorylation events are mediated by kinases other than protein kinase C (PkC).
Amino Acids↗
Interleukin-3 down-regulates its own receptor.
To gain insight into the mechanisms involved in regulating murine interleukin-3 (mIL-3) receptor expression, we have examined the effects of mIL-3 and murine granulocyte-macrophage colony-stimulating factor (mGM-CSF) on mIL-3 receptor internalization and re-expression and studied the relationship between mIL-3 cell surface receptor density and growth factor sensitivity. As a source of cells for our studies, we used a B6SUtA clone, B6SUtA1, which grows equally well in mIL-3 or mGM-CSF when supplemented with 20% fetal calf serum (FCS) in RPMI 1640. Intracellular processing studies carried out in the presence and absence of methylamine suggested that mIL-3 is cleaved at two specific sites before its complete digestion within lysosomes. However, unlike its ligand, cycloheximide studies indicated that internalized mIL-3 receptors are recycled to the cell surface. When B6SUtA1 cells were continuously passaged in mIL-3, cell populations allowed to exhaust the mIL-3 in the medium (high density cells) expressed more than ten times (ie, approximately 100,000/cell) the mIL-3 receptor number of those growing exponentially at low cell concentrations (low density cells). Since the high density cells were no larger than the low density cells, the marked increase in mIL-3 receptor number per cell reflects a true up-regulation of receptor expression. A kinetic analysis of this up-regulation revealed that it begins within one hour of mIL-3 exhaustion. Moreover, proliferation assays with these two cell populations, using 3H-thymidine incorporation, suggested that the high density cells were 30-fold more responsive to mIL-3. However, when B6SUtA1 cells were passaged in mGM-CSF, there was no difference in mIL-3 receptor number between high density and low density cells (ie, approximately 100,000/cell). Identical studies carried out with another mIL-3 dependent cell line, 32D C3, demonstrated that this phenomenon was not unique to B6SUtA1 cells.
Animals↗
A simple three-step purification procedure for interleukin 3 involving absorption to fixed cells.
We have found that treatment of B6SUtA1 cells with 0.01% glutaraldehyde transformed them into mechanically resistant spheres, thereby making it possible to use these high interleukin 3 (IL-3) receptor-bearing cells as a solid phase reagent suitable for the large scale purification of murine IL-3 (mIL-3). Using this technique, mIL-3 was purified from serum-free pokeweed mitogen-stimulated spleen cell-conditioned medium (PWM-SCCM) approximately 16,000-fold using absorption to B6SUtA1 cells, Sephadex G75 superfine chromatography, and reverse phase high performance liquid chromatography on a C18 column. The overall yield was 16%. The final product consisted of two proteins with molecular weights of 19.5 and 16.5 kd. Both species possessed mIL-3-like activity. N-glycanase treatment of the purified preparation converted all of the 19.5-kd material into the lower molecular weight species, suggesting that the two species represented different glycosylated states of mIL-3 produced by activated T cells. This was confirmed by competition studies that showed that excess pure Escherichia coli-derived recombinant mIL-3, but not granulocyte-macrophage colony-stimulating factor (GM-CSF), could prevent the binding of both species of the PWM-SCCM-derived material to B6SUtA1 cells.
Absorption↗
Autocrine production of pre-B-cell stimulating activity by a variety of transformed murine pre-B-cell lines.
Current evidence suggests that the proliferation and differentiation of normal pre-B-cells may be regulated by interactions with mesenchymally derived stromal cells. The nature of these cell-cell interactions has not yet been fully elucidated, but the involvement of pre-B-cell stimulating factors produced by various mesenchymal cell lines has recently been demonstrated in the murine system. In this model, transformed pre-B-cells differ from their normal counterparts in their acquisition of autonomous growth potential, as seen by an ability to be maintained in vitro in the absence of mesenchymal cell feeders. To test the hypothesis that autonomy might be associated with autocrine growth factor production, we tested the ability of a spontaneous pre-B-cell transformant (H9 cells) and two independently derived Abelson murine leukemia virus transformed pre-B-cell lines to produce pre-B-cell stimulating factors. All three lines released activities that stimulated the proliferation of themselves or H9 cells when cultured at low cell densities. One of the three transformed pre-B-cell lines could also substitute for mesenchymal feeders to stimulate normal pre-B-cells. Time course studies of an evolving Abelson murine leukemia virus transformant showed that the production of an autocrine pre-B-cell growth factor increased concomitantly with the acquisition of autonomous growth potential suggesting a relationship between these two phenotypic changes. Preliminary characterization of the growth factor responsiveness of H9 cells and the nature of the autostimulatory activity produced by this line suggested its nonidentity with any known hemopoietic growth factor. Activation of autocrine growth factor production appears to be a common event in the evolution of malignant pre-B-cells arising through different oncogenic mechanisms and may therefore be relevant to the pathogenesis of human acute lymphoid leukemia.
Abelson murine leukemia virus↗
Comparison of c-, N-, and L-myc transcriptional regulation.
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Amanitins↗
Regulation of the expression of the human preprogastrin-releasing peptide gene and post-translational processing of its gene product.
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Genes↗
Multiple mechanisms for transcriptional regulation of the myc gene family in small-cell lung cancer.
The molecular mechanisms reported to regulate the expression of myc family genes are multiple and complex and include gene amplification, transcriptional activation, transcriptional attenuation, and mRNA stability. We have investigated which of these mechanisms are responsible for the extreme variation in myc gene family mRNA levels observed in human small-cell lung cancer cell lines. In addition to gene amplification, a block to nascent mRNA chain elongation, causing attenuation of transcription, is an important regulatory mechanism controlling the steady-state levels of c-myc and L-myc mRNA. The loss of transcriptional attenuation is correlated with overexpression of these two genes in cell lines which do not show gene amplification. Expression of c-myc mRNA appears to be dependent on promoter activity and attenuator function. In contrast, regulation of expression of the N-myc gene does not involve transcriptional attenuation; steady-state mRNA levels are correlated with promoter activity as well as gene amplification. We conclude that transcriptional regulation of each member of the myc gene family is accomplished by a different assortment of complex mechanisms, including gene copy number, promoter activation, and transcriptional attenuation. Interference at multiple points in this complex regulatory process appears to be an important mechanism by which small-cell lung cancer and other human tumors evade growth control.
Carcinoma, Small Cell↗
Transcriptional activation and DNase I hypersensitive sites are associated with selective expression of the gastrin-releasing peptide gene.
The gastrin-releasing peptide (GRP) is a neuropeptide hormone and growth factor produced normally by neural and neuroendocrine cells, as well as by human small-cell lung cancer (SCLC) tumors and derived cell lines. This study compares the structure of the human prepro-GRP gene in four SCLC cell lines that express variable levels of steady-state GRP mRNA. The regulation of GRP gene expression appears to be at the level of primary transcription based on nuclear run on studies. In the two SCLC cell lines expressing GRP we find a single transcription start site for GRP mRNA, and near this site we find four DNase I hypersensitive sites. These hypersensitive sites are absent in the two cell lines that do not express GRP. The presence of DNase hypersensitive sites in the promoter region of the GRP gene is the structural feature that best correlates with transcriptional activation. These four DNase hypersensitive sites are candidates for cis acting regulatory regions, which may be important in determining the level of transcription of the human prepro GRP gene.
Base Sequence↗