The effects of interleukin 7 (IL-7) on human bone marrow in vitro.

Interleukin 7 (IL-7) stimulates the proliferation of pre-B cells from long-term murine lymphoid cultures and normal bone marrow. In addition, IL-7 stimulates the proliferation of murine T cells, including fetal and adult thymocytes as well as peripheral T cells. Flow cytometry and cell enumeration analyses were carried out on light-density human bone marrow cells incubated in the presence or absence of IL-7. The data showed no evidence for a proliferative effect of IL-7 on B-lineage cells expressing CD24 or on myeloid cells expressing CD15; however, IL-7 did stimulate the growth of T cells expressing CD3. After 16 days of stimulation the number of CD3+ cells in marrow cultures increased 350% in the presence of IL-7. In contrast, cultures incubated in the absence of IL-7 showed a 50% decrease in the number of T cells, with a preponderance of myeloid lineage cells. Flow cytometry indicated that cells from IL-7-stimulated cultures were mature T cells because they also expressed cell surface antigens for either CD4 or CD8. These studies show that in contrast to the murine system, IL-7 does not appear to stimulate the growth of human pre-B cells from adult human bone marrow. This is consistent with other experiments that suggest that human pro-B cells and not human pre-B cells respond to IL-7. It appears that IL-7 preferentially promotes the growth of T cells from human marrow.

Interleukin 4 alone or in combination with interleukin 1 stimulates 3T3 fibroblasts to produce colony-stimulating factors.

Colony-stimulating activity (CSA) can be produced by fibroblasts when stimulated by interleukin 1 (IL-1). We show that like IL-1, interleukin 4 (IL-4) can stimulate 3T3 fibroblasts to produce CSA. Biological and molecular analyses show that a significant portion of the CSA is colony-stimulating factor 1 (CSF-1) and granulocyte colony-stimulating factor (G-CSF). CSF-1 production in cells stimulated with a combination of both IL-1 and IL-4 was greater than that observed when cells were stimulated with either cytokine alone. However, the data show a synergistic induction of the expression of high levels of G-CSF mRNA and protein in cells incubated in the presence of both IL-1 and IL-4. The concentration of G-CSF in supernatants from cells stimulated with both IL-1 and IL-4 was at least tenfold higher than that measured in supernatants harvested from cells stimulated with either IL-1 or IL-4 alone. Previous investigations have shown that IL-4 had direct effects on hematopoietic progenitor cell growth. The studies described herein indicate that IL-4 is also involved in the regulation of hematopoiesis in an indirect manner, that is, by playing a role in the regulation of hematopoietic growth factor production.

Interleukin 1 plus interleukin 3 plus colony-stimulating factor 1 are essential for clonal proliferation of primitive myeloid bone marrow cells.

The clonal growth in nutrient agar at low cell densities of high-proliferative potential colony-forming cells (HPP-CFC) of bone marrow obtained from mice treated 2 days earlier with 5-fluorouracil (FU) (FU2dBM) has been shown to require a combination of three growth factors, interleukin 1 (IL-1), interleukin 3 (IL-3), and macrophage colony-stimulating factor (CSF-1). These HPP-CFC have been enriched 140-fold from FU2dBM by fluorescence-activated cell sorting of 7/4-, B220-, and L3T4-negative cells. The mean of the plating efficiencies of these enriched populations was 4.4% and no growth was observed when the factors were used singly. Similarly, enrichments of 16-fold were obtained from FU2dBM using immunomagnetic Dynabeads with anti-7/4 plus anti-B220 (meaning plating efficiency 0.5%). The further additions of human granulocyte CSF or mouse granulocyte-macrophage CSF or both to IL-1 plus IL-3 plus CSF-1 did not increase HPP-CFC colony formation, but both augmented the small colony formation with IL-1 plus IL-3, IL-3 plus CSF-1, or IL-1 plus CSF-1.

Bovine GM-CSF: molecular cloning and biological activity of the recombinant protein.

The lymphokine granulocyte-macrophage colony-stimulating factor (GM-CSF) mediates the growth and differentiation of granulocytes and macrophages from bone marrow progenitors, and regulates biological functions expressed by mature cells of these lineages. In order to isolate a bovine GM-CSF cDNA, a cDNA library, generated from the BT2 bovine T cell line, was screened with a human GM-CSF cDNA probe. A cDNA clone was isolated with an insert of 783 bp, that would encode a protein of 143 amino acids, with a predicted mol. wt of 16,160. Bovine GM-CSF exhibits a high degree of sequence homology with mouse and human GM-CSF at both the nucleotide and amino acid levels. Comparison of GM-CSF amino acid sequences from the three species indicates that the bovine GM-CSF precursor contains a putative 17 amino acid signal sequence, cleavage of which would yield a 14,250 mol. wt protein. The cDNA was inserted into a mammalian expression vector and transfected into COS-7 monkey kidney cells. Biologically active bovine GM-CSF was secreted as judged by a bovine bone marrow proliferation assay. Bovine GM-CSF was weakly active in both human and mouse bone marrow proliferation assays. In contrast, human GM-CSF was weakly active on bovine but not murine mouse bone marrow cells and mouse GM-CSF was only active on murine bone marrow cells.

Human macrophage-colony stimulating factor: alternative RNA and protein processing from a single gene.

Macrophage-colony stimulating factor (M-CSF, CSF-1) has been reported to be required for the proliferation and differentiation of macrophages from hematopoietic progenitor cells. Recently, two human M-CSF cDNA clones were isolated encoding proteins of 256 and 554 amino acids. We report here the isolation of a third M-CSF cDNA that encodes a protein of 438 amino acids. The coding regions for the three cDNA clones share a common amino-terminus of 149 amino acids and a common carboxyl-terminus of 75 amino acids including a membrane spanning region. In addition, we isolated a genomic clone of human M-CSF. When each of the cDNA clones or the genomic clone were transfected into COS-7 monkey kidney cells, biologically active M-CSF was expressed as judged by the ability of transfected cell supernatants to stimulate proliferation and colony formation of murine bone marrow cells, as well as formation of monocytic colonies from human bone marrow cells. Surprisingly, proliferation of human bone marrow cells was not induced by recombinant human M-CSF. Analysis of the M-CSF proteins released by COS-7 cells revealed that monomer subunit proteins of 44 or 28 kDa were produced. In addition, we found that the membrane spanning region, present in all three forms of M-CSF cDNA, was not required for the synthesis of a biologically active protein. However, when the membrane spanning region was present in the three M-CSF cDNAs, cell surface associated forms of M-CSF could be readily detected.

Interleukin 1 regulates hematopoietic activity, a role previously ascribed to hemopoietin 1.

A murine in vitro assay was developed to measure potentiation of a proliferative response to suboptimal concentrations of the hematopoietic regulatory molecule granulocyte/macrophage colony-stimulating factor by an immature bone marrow population. The assay, designated the 5-fluorouracil bone marrow proliferation assay, was used to characterize potentiating activity in serum-free culture supernatants of the human tumor cell line HBT 5637. Molecular and biochemical analyses indicated that the HBT 5637-derived potentiating activity could be attributed to interleukin 1 alpha. Serologic analysis using a monoclonal antibody against purified recombinant interleukin 1 alpha proved conclusively that the potentiating activity in HBT 5637 serum-free supernatants is due to interleukin 1 alpha. From these data, the activity of interleukin 1 alpha seems to be the same synergistic activity formerly ascribed to hemopoietin 1.

Expression and purification of native human granulocyte-macrophage colony-stimulating factor from an Escherichia coli secretion vector.

The human granulocyte-macrophage colony stimulating factor (GM-CSF) was expressed and purified from a high-level Escherichia coli secretion vector. A cDNA fragment encoding mature GM-CSF was fused with the aid of a synthetic oligonucleotide to the E. coli outer membrane signal peptide (ompA) of the secretion expression vector pIN-III-ompA3. The primary construction, designated pLB5001, is under transcriptional control of the tandem lipoprotein promoter (lppP) lactose promoter-operator (lacPO), and is regulated by the lactose repressor. Upon induction, a polypeptide of MW = 14,600 was produced which had GM-CSF activity in a human bone marrow colony assay. The linker sequence between the ompA signal peptide and the amino terminus of the mature GM-CSF was removed by oligonucleotide-directed site-specific mutagenesis to produce GM-CSF with an authentic amino terminus. The resulting construct, designated pLB5001-4, expressed authentic GM-CSF with a specific activity similar to that observed for the pLB5001 specified GM-CSF. Both versions of GM-CSF were associated with the membrane fraction after osmotic shock, and were purified to homogeneity by DEAE-Sephacel chromatography, followed by reversed-phase HPLC. Amino acid sequencing from the amino terminus of the purified GM-CSF established that the ompA signal peptide was cleaved at its normal processing site in both cases.

Induction of macrophage tumoricidal activity by granulocyte-macrophage colony-stimulating factor.

Monocytes are a subpopulation of peripheral blood leukocytes, which when appropriately activated by the regulatory hormones of the immune system, are capable of becoming macrophages--potent effector cells for immune response to tumors and parasites. A complementary DNA for the T lymphocyte-derived lymphokine, granulocyte-macrophage colony-stimulating factor (GM-CSF), has been cloned, and recombinant GM-CSF protein has been expressed in yeast and purified to homogeneity. This purified human recombinant GM-CSF stimulated peripheral blood monocytes in vitro to become cytotoxic for the malignant melanoma cell line A375. Another T cell-derived lymphokine, gamma-interferon (IFN-gamma), also stimulated peripheral blood monocytes to become tumoricidal against this malignant cell line. When IFN-gamma activates monocytes to become tumoricidal, additional stimulation by exogenously added lipopolysaccharide is required. No such exogenous signals were required for the activation of monocytes by GM-CSF.

Cloning, sequence, and expression of a human granulocyte/macrophage colony-stimulating factor.

Human granulocyte/macrophage colony-stimulating factor (GM-CSF) is a glycoprotein that is essential for the in vitro proliferation and differentiation of precursor cells into mature granulocytes and macrophages. In this report we have used a mouse GM-CSF cDNA clone to isolate human GM-CSF clones from libraries made from HUT-102 messenger RNA and mitogen-stimulated T-lymphocyte messenger RNA. The human cDNA clones contained a single open-reading frame encoding a protein of 144 amino acids with a predicted molecular mass of 16,293 daltons and showed 69% nucleotide homology and 54% amino acid homology to mouse GM-CSF. One of these cDNA clones was shown to direct the synthesis of biologically active GM-CSF using a yeast expression system. The gene for human GM-CSF appears to exist as a single-copy gene.

The regulation of mononuclear phagocyte entry into S phase by the colony stimulating factor CSF-1.

CSF-1 is a hemopoietic growth factor that specifically regulates the survival, proliferation, and differentiation of mononuclear phagocytic cells. Populations of adherent bone marrow-derived macrophages (BMM) devoid of CSF-1 producing cells were used to study regulation by CSF-1 of macrophage entry into S phase. More than 95% of BMM possess the CSF-1 receptor. It was shown that 93-98% of BMM are cycling (S phase 8-9 hr, doubling time 24-28 hr) when cultured in the presence of CSF-1. BMM incubated with 15% FCS in the absence of CSF-1 or in the presence of CSF-1 concentrations inducing survival without proliferation enter a quiescent state. This state is characterized by a reduction in the synthesis of DNA (98%), total protein (35%), ribosomal protein (76%), and histone (96%) compared with the synthetic rate of these components in exponentially growing cells. Addition of CSF-1 to BMM rendered quiescent by removal of CSF-1 stimulated entry into S phase with a lag period of approximately 12 h. This lag period is reduced to 8 hr in BMM made quiescent at concentrations of CSF-1 inducing survival without proliferation, an effect which may be related to the expected higher protein content of these cells (Tushinski and Stanley, J. Cell. Physiol., 116:67-75). Neutralization of CSF-1 by antibody at different times during the lag period indicates that CSF-1 is required for almost the entire lag period for the entry of any cells into S phase. In BMM rendered quiescent by removal of both serum and CSF-1, purified CSF-1 without serum stimulated entry of cells into S phase, whereas serum alone was ineffective. The results are consistent with a primary regulatory role of CSF-1 in mononuclear phagocyte proliferation, survival, and function.

The regulation of macrophage protein turnover by a colony stimulating factor (CSF-1).

CSF-1 is a hemopoietic growth factor that specifically regulates the survival, proliferation, and differentiation of mononuclear phagocytic cells. A homogeneous population of mononuclear phagocytes, bone marrow derived macrophages (BMM), were used to study the regulation of protein turnover by CSF-1. Removal of CSF-1 (approximately 0.4 nM) from exponentially growing BMM cultured in 15% fetal calf serum containing medium decreases the rate of DNA synthesis by more than 100-fold. Addition of CSF-1 to these cells causes them to resume DNA synthesis within 12 h. More immediate effects of CSF-1 were observed on BMM protein metabolism. BMM cultured for 24 h in the absence of CSF-1 reduce their protein synthetic rate by 50-60%. The protein synthetic rate commences to decrease at 2-3 h after CSF-1 removal. Readdition of CSF-1 to BMM previously incubated in its absence causes a return to the protein synthetic rate of exponentially growing cells within 2 h. In the presence of CSF-1, BMM synthesize protein at a rate of approximately 8.7%/h and degrade it at a rate of approximately 0.9%/h. Removal of CSF-1 results in a decrease in the protein synthetic rate to approximately 3.4%/h and an increase in the rate of protein degradation to approximately 3.4%/h. The rate of protein synthesis by BMM increases linearly with CSF-1 concentration over the range of concentrations stimulating both survival and proliferation, while the rate of protein degradation decreases exponentially over the range of concentrations stimulating survival without proliferation. Therefore, it appears that the stimulation of the rate of protein synthesis and inhibition of the rate of protein degradation are two distinct effects of CSF-1, both part of the pleiotropic response to this growth factor. The inhibition of the rate of protein degradation by CSF-1 may be most significant for its survival inducing effect.

Ribosomal proteins are synthesized preferentially in cells commencing growth.

Mouse 3T3 cells, in stationary phase because of serum deprivation, have only half the ribosome content of growing cells. Furthermore, the proportion of protein synthesis devoted to ribosomal proteins is only half that in growing cells. On addition of serum the synthesis of each ribosomal protein increases threefold, demonstrating the coordination of the synthesis of the ribosomal proteins. Half that increase is due to a general increase in total protein synthesis; half is due to a differential increase in ribosomal protein synthesis. The latter is abolished by a concentration of actinomycin D which blocks only ribosomal RNA transcription. The results are discussed with reference to a general hypothesis of growth regulation proposed by Stanners et al. (1979).

Survival of mononuclear phagocytes depends on a lineage-specific growth factor that the differentiated cells selectively destroy.

CSF-1 is a hemopoietic growth factor that specifically causes the proliferation and differentiation of mononuclear phagocytic cells. Receptors for CSF-1 occur exclusively on cells of the mononuclear phagocytic series (precursor leads to monoblast leads to promonocyte leads to monocyte leads to macrophage). Studies of the actions of CSF-1 on freshly explanted macrophages have been complicated by contamination of the primary cell isolates with CSF-1-producing cells and by the heterogeneity of the proliferative responses of individual macrophages. A method is described for the production of a highly purified and homogeneous population of adherent bone marrow-derived macrophages (BMMs) that are devoid of CSF-1-producing cells. The method may also be used to obtain nonadherent precursors of the mononuclear phagocytic series. Studies of CSF-1 action and degradation in cultures of BMMs have revealed several new findings. First, CSF-1 is required for both the survival (without proliferation) and the proliferation of BMMs. Second, CSF-1 is degraded by BMMs in a concentration-dependent manner, over the range of concentrations that stimulates both cell survival and proliferation. Third, the rate of CSF-1 degradation is saturable (or approximately 7 X 10(4) molecules per cell per hour) at CSF-1 concentrations that cause maximum proliferation (or approximately 0.4 nM). Under these conditions, BMMs are greatly enlarged and contain numerous phase-lucent vacuoles. Thus macrophages specifically require CSF-1 for both survival and proliferation, yet selectively and rapidly degrade it. This apparent dichotomy may have important implications for the role of CSF-1 in macrophage homeostasis in vivo.

Pregrowth hormone messenger RNA: glucocorticoid induction and identification in rat pituitary cells.

We have investigated whether the large (5- to 15-fold) stimulation of synthesis of growth hormone (somatotropin) observed upon exposure of a strain of rat pituitary (GH3) cells to dexamethasone (a synthetic glucocorticoid) arises from a stimulation of pregrowth hormone mRNA. A good agreement was observed between the stimulation of growth hormone synthesis and the stimulation of cytoplasmic levels of pregrowth hormone mRNA, assayed by translation in wheat germ extracts. Electrophoresis on formamide-acrylamide gels of oligo(dT)-treated membrane fraction RNA revealed a band that was induced by dexamethasone to about the same extent as was translatable pregrowth hormone mRNA. Elution of the band and translation in wheat germ extracts showed directly that it contained pregrowth hormone mRNA. These results suggest that the dexamethasone induction of growth hormone synthesis in GH3 cells arises from an accumulation of pregrowth hormone mRNA in the cytoplasm of the cells. The pregrowth hormone mRNA band observed by gel electrophoresis had an estimated molecular weight of 3.6 X 10(5), suggesting the existence in this molecule of an untranslated region at least 200 nucleotides in length.

Glucocorticoid induction of growth hormone synthesis in a strain of rat pituitary cells.

Conditions were determined for measuring growth hormone synthesis by a clonal strain of rat pituitary cells grown in suspension culture. Incubation of the cells with [3H]leucine in either continuous labeling or pulse-chase experiments showed that secretion of newly synthesized growth hormone commences only after a lag of about 15 min. The pulse-chase experiments also demonstrated that there is no detectable degradation by the cells of growth hormone. Thus growth hormone synthesis could be measured, in the absence of complications arising either from secretion or degradation of growth hormone, by incubating the cells with [3H]leucine for 10 min. Exposure of cells grown under the usual culture conditions to dexamethasone (a synthetic glucocorticoid) led to an average stimulation of specific growth hormone synthesis (growth hormone synthesis/total cytoplasmic protein synthesis) of only 2.6-fold. However, two other growth conditions were found in which dexamethasone routinely yielded a 5- to 15-fold stimulation of specific growth hormone synthesis. One of these conditions, involving substitution of 10% fetal calf serum for the normal serum supplement, was employed in subsequent experiments. A stimulation of specific growth hormone synthesis could be observed at 10(-9) M dexamethasone, and the maximum stimulation was observed at dexamethasone concentrations of about 10(-8) to 10(-7) M. There was a lag of about 6 h before a stimulation by dexamethasone of specific growth hormone synthesis was detected. Thereafter, the stimulation increased in a nearly linear fashion until maximum stimulation was reached at about 48 h.

Pregrowth hormone: product of the translation in vitro of messenger RNA coding for growth hormone.

Membrane fraction RNA isolated from rat pituitary tumor (GC) cells has been translated in a wheat germ extract. A product was synthesized which was immunologically related to growth hormone, but which migrated more slowly than growth hormone upon sodium dodecyl sulfate-acrylamide gel electrophoresis. The mobility of the cell-free product on gels of this type was unchanged by treatment with either KOH or RNase. The mobilities during paper electrophoresis of the methionine-containing tryptic peptides obtained from the cell-free product were identical to those obtained from growth hormone synthesized and secreted by the GC cells. Molecular weights for growth hormone and the cell-free product of 19,500 and 24,000, respectively, were determined by gel electrophoresis of these proteins together with marker proteins of known molecular weights. No protein with the properties of the cell-free product was detected after a 2 min incubation of the GC cells with [35S]methionine. However, treatment of the GC cells, with a protease inhibitor, L-1-tosylamide-2-phenyl-ethylchloromethyl ketone (TPCK), led to the appearance of a new polypeptide, immunologically related to growth hormone, and with a mobility on gels identical to that of the cell-free product. These results strongly imply that the cell-free product represents a growth hormone precursor (pregrowth hormone) which is rapidly converted to growth hormone in pituitary cells.

An adenylic acid-rich sequence in messenger RNA of HeLa cells and its possible relationship to reiterated sites in DNA.

Messenger RNA from HeLa cells contains, as part of the polynucleotide chain, RNase-resistant sequences that are labeled by adenosine but not by uridine. Heterogeneous nuclear RNA also contains adenylate-rich RNase-resistant regions, but in lower proportion than messenger RNA. Hybridization to DNA of (32)P-labeled messenger RNA reveals that some of the adenylate-rich region is included in the rapidly-hybridizing fraction.