Purification of a skeletal growth factor from human bone

A skeletal growth factor was isolated and purified from demineralized human bone matrix. A dose of 6 micrograms/mL of the purified factor significantly increased the proliferation rate of embryonic chick bone cells in serum-free culture (292% of controls, p less than 0.0001) but had no effect on embryonic chick skin cells plated at the same initial density. The factor is sensitive to inactivation by trypsin and urea, but not by collagenase, 20% butanol, or 1% mercaptoethanol. It is also resistant to inactivation by heat (stable for 15 min at 75 degrees C) and extremes of pH (stable for 30 min at 4 degrees C from pH 2.5 to 10.0). Purification of the active factor by selective heat and acid precipitations, molecular sieve column chromatography, and preparative polyacrylamide gel electrophoresis provided a material that was homogeneous by the criteria of high-pressure liquid chromatography, polyacrylamide gel electrophoresis, and isoelectric focusing. The apparent molecular weight is 83 000. The purified factor increases bone cell proliferation at doses comparable to other mitogens: 0.3 microgram/mL (3.6 nM) significantly increases DNA synthesis to 231% of controls (p less than 0.001). The purified factor was also active on cultured embryonic chick bones, enhancing the growth rate of tibiae and femurs, as measured by increased dry weight (185% of controls, p less than 0.025) and [3H]proline incorporation (164% of control, p less than 0.001), respectively.     

Chemical and biological characterization of low-molecular-weight human skeletal growth factor

Skeletal growth factor (SGF) activity was extracted from human bone matrix by demineralization and purified under dissociative conditions using hydroxyapatite, HPLC gel-filtration and HPLC reverse-phase chromatography. Human SGF thus purified was characterized chemically and biologically. Purified human SGF stimulated chick embryo bone cell proliferation at picomolar concentrations (half maximum at 2-3 ng/ml) and had little or no activity on other cell types tested (mouse 3T3 and normal rat kidney fibroblasts, embryonic chick intestinal and human placental cells). Human SGF did not displace 125I-labeled epidermal growth factor binding to normal rat kidney cells and did not stimulate normal rat kidney cell colony formation in soft agar. Human SGF activity was sensitive to trypsin, chymotrypsin, papain, dithiothreitol and performic acid but was resistant to heat (upto 70 degrees C), pH (3-10), cyanogen bromide, alkaline phosphatase and neuraminidase and did not bind jack bean concanavalin A or kidney bean lectin. From our chemical and biological studies it appears that human SGF is different from other known polypeptide growth factors: epidermal growth factor, fibroblast growth factor, insulin, insulin-like growth factor-I, platelet-derived growth factor and transforming growth factor.     

A novel gene derived from developing spinal cords, SCDGF, is a unique member of the PDGF/VEGF family

We isolated a novel gene designated spinal cord-derived growth factor (SCDGF). Its expression was increased in chick spinal cords with embryonic development and decreased after hatching. The amino acid sequences of chick and human SCDGFs revealed a putative signal sequence followed by a CUB domain and a region homologous to the members of the platelet-derived growth factor/vascular endothelial growth factor family. Furthermore, human SCDGF secreted from the cells showed a mitogenic activity for 10T1/2 cells in vitro. These results led us to speculate that SCDGF plays an important role in the development of the spinal cord.     

Angiogenesis is stimulated by a tumor-derived endothelial cell growth factor

A growth factor mitogenic for BALB/C 3T3 cells and capillary endothelial cells was isolated from a rat chondrosarcoma and purified to homogeneity. Purification was accomplished by a combination of BioRex 70 cation exchange chromatography and heparin affinity chromatography. The pure chondrosarcoma-derived growth factor (ChDGF) had a molecular weight of about 18,000. The angiogenesis activity of pure ChDGF was tested by measuring its ability to vascularize the chorioallantoic membrane (CAM) and yolk sac membrane of the developing chick. The ability of ChDGF to induce the growth of limbal vessels in the rat cornea was also measured. To quantitate the angiogenesis response, a unit system based on the growth factor activity of ChDGF for 3T3 cells was adopted. ChDGF was found to have a specific activity of about 5 units/ng when applied to 3T3 cells. About 300-600 units of ChDGF in the two types of developing chick membrane and 30-5 units of ChDGF in the rat cornea were found to stimulate noninflammatory angiogenesis.     

MK: a pluripotential embryonic stem-cell-derived neuroregulatory factor.

MK is a gene encoding a secreted heparin-binding polypeptide originally isolated by differential screening for genes induced by retinoic acid (RA) in HM-1 embryonal carcinoma cells. Here we report that MK is expressed at high levels in both embryonal carcinoma and pluripotential embryonic stem cells and their differentiated derivatives. MK expression in these cell types is unaffected by the presence or absence of RA. Recombinant MK protein (rMK) was produced by transient expression in COS cells and purified by heparin affinity chromatography. rMK is a weak mitogen for 10T1/2 fibroblast cells but inactive as a mitogen for Swiss 3T3 fibroblasts. rMK is a potent mitogen for neurectodermal precursor cell types generated by treatment of 1009 EC cells with RA but has no mitogenic or neurotrophic effects on more mature 1009-derived neuronal cell types. rMK is active as an in vitro neurotrophic factor for E12 chick sympathetic neurons and its activity is markedly potentiated by binding the factor to tissue-culture plastic in the presence of heparin. Stable 10T1/2 cells lines have been established which express MK. These cells do not exhibit any overt evidence of cell transformation but extracellular matrix preparations derived from these cells are a potent source of MK biological activity. It is concluded that MK is a multifunctional neuroregulatory molecule whose biological activity depends upon association with components of the extracellular matrix.     

Neurite outgrowth induced by an endothelial cell mitogen isolated from retina

Retina-derived growth factor (RDGF) is a polypeptide growth factor purified from salt extracts of bovine retinas on the basis of its mitogenic activity for capillary endothelial cells (EC) and BALB/c 3T3 cells. RDGF is angiogenic in vivo. We show here that RDGF induces neurite extension by PC12 cells and that this neurite outgrowth is dramatically potentiated by heparin. Neurite formation elicited by RDGF in the presence of heparin cannot be distinguished from that elicited by nerve growth factor (NGF) either by the time course of neurite formation or by the morphology of the neurites at the level of the light microscope. Neurite outgrowth induced by either purified RDGF or by a crude retinal extract is not blocked by antibodies to NGF. Furthermore, neurite outgrowth induced by NGF is not potentiated by heparin and NGF is not mitogenic for capillary EC. Thus, RDGF has profound regulatory effects on cell types of very different embryonic origins. These results indicate that the physiological role for this growth factor may be far more complex than previously suspected and suggest that the formation of neural connections and the process of vascularization may unexpectedly share common regulatory elements.     

Endothelial cell growth factors in embryonic and adult chick brain are related to human acidic fibroblast growth factor.

We have investigated the nature of endothelial cell growth factors in 14-day embryonic and adult chick brain extracts. Mitogenic activity was isolated by a combination of cation-exchange, heparin-Sepharose affinity, and reverse-phase HPLC. Two major mitogenic fractions eluted from heparin-Sepharose at 0.8-1.3 M and 1.5-2 M. Biologically active proteins eluting at 0.8-1.3 M NaCl, after purification to homogeneity from embryonic and adult brain, were found to possess the same amino-terminal sequence as human acidic fibroblast growth factor (aFGF). The notion that the isolated mitogens represent chick aFGF is further supported by the findings that their affinity for heparin and their retention behavior in highly resolutive HPLC are indistinguishable from those of genuine aFGF. Mitogenic activities eluting at 1.5-2 M NaCl were also present in embryonic and adult brain, but in quantities insufficient for preliminary characterization. The high specific mitogenic activity for endothelial cells, high affinity for heparin and cross-reactivity with antibodies against bovine basic FGF (bFGF) suggest a relationship of those materials with basic FGF. Our data also suggest that the sequence of aFGF is highly conserved among vertebrates. While angiogenesis occurs predominantly in the embryonic brain, the absence of notable differences in the contents of the potent angiogenic factors aFGF and bFGF in embryonic versus adult chick brain is interesting.     

Isolation and partial characterization of mitogenic factors from cementum.

Cementum is the mineralized structure through which soft connective tissues are attached to the teeth. It is a unique calcified tissue characterized by a low metabolic turnover, lack of blood supply, and presence of very few cells. However, it contains substances that influence the biological activities of fibroblasts of adjacent soft tissues. We have partially characterized cementum proteins that have mitogenic activity toward fibroblasts. Cementum was harvested from bovine teeth, and mitogenic factors were extracted in 0.5 M CH3COOH. Heparin-Sepharose chromatography separated the mitogenic activity into a major and a minor fraction eluted by 0.5 and 2.0 M NaCl, respectively. The distribution of cementum mitogens in heparin-Sepharose fractions was different from that of alveolar bone and other bones. The cementum mitogenic factor eluting with 2.0 M NaCl from a heparin-Sepharose column was shown to be basic fibroblast growth factor (bFGF) on the basis of inhibition by anti-bFGF antibody and Western blots. The 0.5 M NaCl fraction was purified by HPLC with use of a combination of a DEAE-3W column followed by TSK-250 and C18 columns. NaDodSO4-polyacrylamide gel electrophoresis revealed that the purified fraction contained two protein bands with Mr 22,000 and 19,000, and mitogenic activity was associated with the Mr 22,000 species. The activity of this mitogen, designated as CGF, was potentiated by small quantities of plasma-derived serum or epidermal growth factor. It was heat resistant, but was destroyed by reduction. Assays of CGF preparations revealed that they contained no detectable platelet-derived growth factor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Low molecular weight mitogenic factor produced by BRL-3A cultured rat liver cells

A new mitogenic factor has been isolated from medium conditioned by BRL-3A rat liver cells. The factor has been partially purified by a two step procedure involving ion exchange chromatography on Dowex 50 followed by gel filtration chromatography on Sephadex G-75 in 1 M acetic acid. The factor is eluted from the Sephadex G-75 column in the low molecular weight region, behin three peaks of multiplication stimulating activity. The factor is inactivated by treatment with trypsin and dithiothreitol, suggesting that it is a peptide that contains a disulfide linkage. Unlike multiplication stimulating activity, the new factor only weakly stimulates DNA synthesis in quiescent chick fibroblasts, whereas it strongly stimulates DNA synthesis in quiescent NIL8 hamster cells, $\text{BALB}\text{c}$ 3T3 cells, and IMR-90 human fibroblasts.     

Characterization and partial purification of a neurotrophic factor for cerebrocortical neurons from chicken cerebral extract

The survival of cerebrocortical neurons from 6 to 8-day-old chick embryos was investigated in a serum-free hormone-supplemented medium. The addition of cerebral extract promoted the survival of cortical neurons in a dose-dependent manner, but induced almost no neurite outgrowth. The trophic activity was higher in the adult cerebrum than in the embryonic cerebrum. The tropic factor was partially purified from adult chicken cerebrum, and the molecular weight of the factor was estimated to be about 60 kDa. The activity for survival factor was fairly resistant to heat or trypsin treatment. When the partially purified sample was, however, treated with trypsin (1 mg/ml) for 20 h and applied to a TSK G2000 SW gel filtration column, the activity moved from 60 to 70 kDa untreated active fractions to fractions with about 10 kDa. These physicochemical properties of the survival factor suggest a new class of macromolecular trophic factors in the brain.     

Cell-cell adhesion in the embryonic chick: Partial purification of liver adhesion molecules from liver membranes

Polyspecific xenoantisera specific for embryonic chick liver cells have been used to develop an assay for the detection of embryonic chick liver adhesion molecules (LAM). The neutralization of the antiaggregation immune sera and subsequent semiquantitative assessment of the remaining activity is the basis for this assay. Embryonic chick liver membrane proteins have been solubilized using a number of detergents and the LAM activity has been partially purified using sucrose-gradient sedimentation, isoelectric focusing, gel filtration, affinity chromatography, and preparative polyacrylamide gel electrophoresis procedures. The isolated LAM appears to be an intrinsic, trypsin-resistant, membrane glycoprotein of approximately 65,000 daltons. The 65K preparation of LAM is an effective immunogen in generating an aggregation blocking xenoantiserum specific for embryonic chick liver cells. Purification of LAM to homogeneity has been hampered by an apparent lability by self-association or loss by adsorption of the more purified LAM antigen(s).     

Factors in the rat submaxillary gland that stimulate growth of cultured glioma cells: identification and partial characterization

The effect of rat submaxillary extract on the growth of rat C6 glioma cells in serum-free culture has been examined. Extracts (10-15 microgram/ml) of submaxillary glands from both male and female rats markedly enhanced the growth of serum-deprived C6 cells and, in combination with insulin, transferrin, and NIH-LH (a source of fibroblast growth factor), were able to stimulate C6 cell growth to an extent comparable to that achieved with an optimal amount of fetal calf serum. The mitogenic activity of rat submaxillary extracts was found to be heat-labile, acid-stable, and partially inactivated by protease and 2-mercaptoethanol. Under our assay conditions, biologically active preparations of purified mouse submaxillary gland epidermal growth factor (EGF) or nerve growth factor (NGF) were not mitogenic for C6 cells, nor was the mitogenic activity of rat submaxillary extracts inhibited by antiserum to these mouse submaxillary gland growth factors. These results suggest that the active component(s) of rat submaxillary extracts is unrelated to either EGF or NGF. The growth-enhancing effect also appears unrelated to esteropeptidase activity present in these extracts since the mitogenic activity was unaffected by several protease inhibitors. Moreover, two purified mouse submaxillary gland arginylesteropeptidases, EGF-binding protein and gamma-subunit of 7 S NGF, were unable to elicit a comparable growth response even when added to cell culture medium at unreasonably high concentrations. The C6 cell mitogenic activity of crude submaxillary extracts could be separated into two biologically similar components by either gel filtration on Sephadex G-100, preparative isoelectric focusing in a pH gradient of 3-10, or adsorption to DEAE-cellulose followed by elution with a sodium chloride gradient. One of the active components was acidic in nature and had an apparent molecular weight of 40,000, while the other was near neutral in charge and possessed a molecular weight of approximately 20,000. The relationship between these two C6 cell mitogenic components and the rat submaxillary gland component responsible for stimulating Balb/c-3T3 cell growth in serum-free, factor supplemented medium (McClure et al., 1979, J. Cell Biol. 83:96a) is also discussed.     

Molecular characterization of recombinant human acidic fibroblast growth factor produced in E. coli: comparative studies with human basic fibroblast growth factor.

Synthetic cDNA coding for human acidic fibroblast growth factor (haFGF) was expressed in E. coli under the control of the T7 promoter. The haFGF produced was purified extensively using heparin-Sepharose and phenyl-Sepharose columns. The mitogenic activity of haFGF on 3T3 and endothelial cells was significantly potentiated in the presence of heparin (10-50 micrograms/ml), while angiogenic activity was observed on chick embryo chorioallantoic membrane without exogenously added heparin. This significant potentiation of mitogenic activity was observed specifically with haFGF, not human basic fibroblast growth factor (hbFGF). Circular dichroism spectra of haFGF was not affected by the presence of heparin. The affinity of haFGF for heparin was examined using heparin affinity HPLC and was precisely confirmed to be relatively lower than that of hbFGF. These results implied that haFGF was potentiated by heparin and that this potentiation did not involve a significant change in the conformation of the haFGF molecule. The affinity of haFGF for copper was also confirmed to be higher than that of hbFGF using a copper affinity HPLC column. In addition, under acidic conditions, haFGF appeared more stable than hbFGF and was further stabilized in the presence of heparin.     

Cloning, expression during development, and evidence for release of a trophic factor for ciliary ganglion neurons.

Ciliary ganglion (CG) neurons undergo a period of cell death during development that may be regulated by the limited availability of trophic factor produced by their target tissues. We have previously reported the purification of a ciliary neurotrophic factor from adult chick sciatic nerve that we called growth promoting activity (GPA). Here we demonstrate that GPA can be purified and cloned from embryonic day 15 (E15) chick eyes, which contain all the target tissues of the CG. Our studies show the following: GPA mRNA is induced in embryonic chick eyes during the period of CG neuron cell death; GPA mRNA is expressed specifically in the layer of the eye that contains the targets of the CG and in primary cultures of smooth muscle cells isolated from the choroid layer of the eye; and biologically active GPA is released from cells transfected with a GPA cDNA.     

Identification of a 15,000-molecular-weight form of immunoreactive transforming growth factor alpha in extracts of porcine pituitary

Two different mitogenic activities were identified from extracts of porcine pituitary by using COMMA-D mouse mammary epithelial cells in a serum-free 3H-thymidine incorporation assay. Porcine pituitaries were extracted in phosphate-buffered saline (pH 7.4) and 25-80% (NH4)2SO4 pellets were dialyzed and chromatographed by using DEAE-Sepharose chromatography (pH 8.0), resulting in two peaks (I and II) of mitogenic activity. Peak I represented a recovery of 73% of the units of mitogenic activity present in crude extract of pituitary while only 1.25% of the activity was recovered in peak II. Peak I was further purified by using CM-Sephadex and heparin-Sepharose chromatographies and yielded a mitogen that was able to elicit one-half-maximal stimulation of 3H-thymidine incorporation by COMMA-D cells at 48 pg/ml. As expected with pituitary as the tissue source, peak I was confirmed to be basic fibroblast growth factor (bFGF) by using specific antibodies in enzyme-linked immunosorbent assay and Western immunoblotting procedures. Peak II was further purified by using chromatofocusing (pH 7.3-5.0), reverse-phase, and cation-exchange HPLCs. The mitogenic activity eluted at pH 6.3 from chromatofocusing, migrated as a 13-kDa molecule on gel filtration HPLC, and did not bind to heparin-Sepharose under conditions which bound fibroblast growth factors. The material purified from peak II and rat synthetic transforming growth factor alpha (TGF alpha) competed in a parallel fashion with 125I-epidermal growth factor for receptor binding with A431 human epidermal carcinoma cells. In addition, the mitogen purified from peak II showed a single immunoreactive band migrating at 15 kDa when specific antiserum against TGF alpha was used in a Western immunoblotting procedure. The data suggest that in addition to the well-documented presence of bFGF, normal adult porcine pituitaries contain a 15-kDa form of immunoreactive TGF alpha that binds to EGF receptors and is mitogenic for mammary epithelial cells.     

Pituitary follicular cells secrete a novel heparin-binding growth factor specific for vascular endothelial cells

A growth factor for vascular endothelial cells was identified in the media conditioned by bovine pituitary follicular cells and purified to homogeneity by a combination of ammonium sulfate precipitation, heparin-sepharose affinity chromatography and two reversed phase HPLC steps. The growth factor was a cationic, heat stable and relatively acid stable protein and had a molecular weight, as assessed by silver-stained SDS-PAGE gel, of approximately 45,000 under non reducing conditions and approximately 23,000 under reducing conditions. The purified growth factor had a maximal mitogenic effect on adrenal cortex-derived capillary endothelial cells at the concentration of 1-1.2 ng/ml (22-26 pM). Further characterization of the bioactivity of the growth factor reveals that it exerts mitogenic effects also on vascular endothelial cells isolated from several districts but not on adrenal cortex cells, lens epithelial cells, corneal endothelial cells, keratynocytes or BHK-21 fibroblasts, indicating that its target cells specificity is unlike that of any previously characterized growth factor. Microsequencing reveals a unique N-terminal amino acid sequence. On the basis of its apparent target cell selectivity, we propose to name this factor vascular endothelial growth factor (VEGF).     

Sympathetic neuronal survival induced by retinal trophic factors.

Neuronal survival in the vertebrate peripheral nervous system depends on neurotrophic factors available from target tissues. In an attempt to identify novel survival factors, we have studied the effect of secreted factors from retinal cells on the survival of chick sympathetic ganglion neurons. Embryonic day 10 sympathetic neurons undergo programmed cell death after 48 h without appropriate levels of nerve growth factor (NGF). Retina Conditioned Media (RCM) from explants of embryonic day 11 retinas maintained for 4 days in vitro supported 90% of E10 chick sympathetic neurons after 48 h. Conditioned medium from purified chick retinal Muller glial cells supported nearly 100% of E10 chick sympathetic neurons. Anti-NGF (1 microg/mL) blocked the survival effect of NGF, but did not block the trophic effect of RCM. Neither BDNF nor NT4 (0.1-50 ng/mL) supported E10 sympathetic neuron survival. Incubation of chimeric immunoglobulin-receptors TrkA, TrkB, or TrkC had no effect on RCM-induced sympathetic neuron survival. The survival effects were not blocked by anti-GDNF, anti-TGFbeta, and anti-CNTF and were not mimicked by FGFb (0.1-10 nM). LY294002 at 50 microM, but not PD098059 blocked sympathetic survival induced by RCM. Further, the combination of RCM and NGF did not result in an increase in neuronal survival compared with NGF alone (82% survival after 48 h). The secreted factor in RCM is retained in subfractions with a molecular weight above 100 kDa, binds to heparin, and is unaffected by dialysis, but is heat sensitive. Our results indicate the presence of a high-molecular weight retinal secreted factor that supports sympathetic neurons in culture.     

Purification of a new neurotrophic factor from mammalian brain.

We report the purification from pig brain of a factor supporting the survival of, and fibre outgrowth from, cultured embryonic chick sensory neurons. The purified factor migrates as one single band, mol. wt. 12 300, on gel electrophoresis in the presence of sodium dodecylsulphate (SDS) and is a basic molecule (pI greater than or equal to 10.1). Approximately 1 microgram factor was isolated from 1.5 kg brain. The final degree of purification was estimated to be 1.4 X 10(6)-fold, and the specific activity 0.4 ng/ml/unit, which is similar to that of nerve growth factor (NGF) using the same assay system. This factor is the first neurotrophic factor to be purified since NGF, from which it is clearly distinguished because it has different antigenic and functional properties.     

Partial purification and characterization of mammary stimulating factor, a protein which promotes proliferation of mammary epithelium.

This report describes the partial purification and characterization of mammary stimulating factor (MSF), a mitogenic peptide isolated from serum which initiates growth in mouse mammary epithelium. By using ion-exchange chromatography, gel filtration, and isoelectric focusing, MSF was purified 250-fold from porcine serum. It is a heat-stable protein of molecular weight 10,100--10,400 with an isoelectric point of 5.5--6.0. MSF initiates DNA synthesis in vitro in mammary epithelium to a greater extent than in mouse mammary tumor cells (CZF), 3T3 cells, or chick embryo cells. Comparison of the biological, physical, and immunological properties of MSF with other established growth-promoting peptides suggests that MSF is a unique serum factor.     

The antiproliferative effect of interferon and the mitogenic activity of growth factors are independent cell cycle events : Studies with vascular smooth muscle cells and endothelial cells

We studied the antagonistic effects of interferon (IFN) and growth factors in G0/G1-arrested normal bovine aortic smooth muscle cells (SMC) which were stimulated by serum, or purified platelet derived growth factor (PDGF), supplemented with plasma-derived serum (PDS). The growth response, measured as [3H]thymidine incorporation into DNA, was dependent on the concentration of the mitogen. Human IFN alpha, recombinant human IFN alpha 2, or a crude bovine-IFN preparation prepared from virus-infected bovine aortic endothelial cells, inhibited SMC growth induced by either serum or PDGF with PDS. The extent of IFN inhibition was inversely related to the concentration of the mitogenic stimulus. We also investigated whether IFN inhibited the early events in G1 phase, stimulated by the competence factor PDGF, or the progression of the cell into the S phase induced by PDS. The results indicated that IFN inhibited these two stages of the G1 phase independently. In addition, we investigated the antiproliferative effect of IFN on bovine aortic endothelial cells (BAEC), which do not respond to PDGF but to the mitogenic activity of fibroblast growth factor (FGF). IFN inhibited the mitogenic activity of FGF in a dose-dependent manner. The results indicate that the anti-proliferative activity of IFN and the mitogenic effects of different growth factors are independent.