Isolation of brain fibroblast growth factor by heparin-Sepharose affinity chromatography: identity with pituitary fibroblast growth factor

Comparison of the ability of basic and acidic fibroblast growth factor to stimulate the proliferation of an established keratinocyte cell line: modulation of their biological effects by heparin, transforming growth factor beta (TGF beta), and epidermal growth factor (EGF)

The bioactivity of both bFGF and aFGF in the BALB/MK-1 cell line has been compared to that of EGF. Our results indicate that, for that cell type, aFGF was far more potent than bFGF in inducing cell proliferation. In the presence of heparin, aFGF was as potent as EGF. In addition, excess bFGF has an inhibitory effect on the proliferation of MK cells exposed to a saturating concentration of aFGF, therefore acting as a partial agonist of aFGF. Surprisingly, bFGF, although it had low biological activity, was capable of synergizing the effect of EGF. In its presence, cultures exposed to saturating concentration of EGF have a final cell density 3- to 4-fold higher than that of counterpart cultures exposed to EGF alone. TGF beta, which in previous studies has been shown to inhibit the growth of keratinocytes, also inhibited the growth of BALB/MK-1 cells in response to either bFGF or aFGF. These studies suggest a role for FGF in regulating BALB/MK proliferation. aFGF provides positive growth signals which can be negatively modulated by excess bFGF or TGF beta, while bFGF, although a poor mitogen, could act by potentiating the effect of subsaturating concentrations of EGF.

Basic fibroblast growth factor in ovulatory cycle and postmenopausal human endometrium

Biopsies of human endometrium were studied for the presence of basic fibroblast growth factor (bFGF). An immunoreactive Mr 18,000 bFGF-like molecule was detected at high levels both in ovulatory cycle and postmenopausal endometrium. This molecule was identified as bFGF on the basis of its molecular weight, its affinity for heparin, its capacity to induce plasminogen activator production and cell proliferation in endothelial GM 7373 cells, and its cross-reactivity with various anti-bFGF antibodies. The levels of endometrial bFGF do not change during the menstrual cycle but they increase significantly after menopause, as evaluated both by biological and immunological assays. Lower levels of an acidic FGF-like activity were also evident in ovulatory cycle endometrium but, at variance with bFGF, no significant increase of this activity was observed in postmenopausal endometrium. These data represent the first characterization of a polypeptide growth factor present in human endometrium.

Growth factors and growth factor receptors in the hippocampus. Role in plasticity and response to injury

Various growth factors are present in the hippocampal formation and appear responsible for the prominent plasticity of this brain area. Although hormone-like growth-promoting polypeptides are the best known, recent studies emphasize the importance in the growth response of molecules such as laminin proteoglycans, neurotransmitters and growth inhibitors. The progress and problems in the study of these substances are reviewed.

Disulfide bonds are neither required, present, nor compatible with full activity of human recombinant acidic fibroblast growth factor

Human acidic fibroblast growth factor (aFGF) is a potent broad-spectrum mitogen that contains three Cys residues within its monomeric structure. We have found that site-directed mutants in which any one of these Cys residues is converted to serine remain highly active, although variably dependent on heparin, so none of the three possible intramolecular disulfide bonds that can be formed are required for mitogenic activity. Furthermore, a dispensable disulfide bond that might stabilize the active conformation is not present since all three Cys residues are accessible to chemical modification in recombinant as well as brain-derived aFGFs. Finally, formation of a disulfide bond between the two Cys residues conserved among all seven known members of the FGF family results in a virtually inactive product that can subsequently be reactivated by reduction. Thus, despite the extracellular function of aFGF, its Cys residues do not form intramolecular disulfide bonds in the active conformation.

A potential new role for bFGF in host-parasite interactions

Basic fibroblast growth factor (bFGF) is a mitogenic polypeptide highly conserved between species, implicated in regenerative processes and present in all tissues examined. In the heart, bFGF is localized in association with nuclei, extracellular matrix and intercalated discs of cardiomyocytes. In this article is reported bFGF association with the intramuscular parasitic protozoan Sarcocystis in situ, in bovine hearts, detected by indirect immunofluorescence. Parasitic cysts appear connected directly to specialized host cell junctions: bFGF provides structural continuity between parasitic cyst wall and myocyte intercalated discs. Other proteins associated with intercalated discs such as desmin or desmoplakin are not detected in the cysts. Association with Sarcocystis suggests a new role for bFGF in the context of parasitic invasion and establishment.

Reactive astrogliosis after basic fibroblast growth factor (bFGF) injection in injured neonatal rat brain

Reactive gliosis was revealed by immunocytochemistry using antibodies against the glial fibrillary acidic protein (GFAP) after a stab or an electrolytic lesion administered to the cerebral cortex, corpus callosum, striatum, or hippocampus of a 6-day-old rat. The intensity of the gliosis was about the same in the various structures injured and did not change with the delay of 3, 7, or 20 days between the injury and the sacrifice of the animals. When basic fibroblast growth factor (bFGF) was injected in the lesion locus just after the lesion was performed, it resulted (as soon as 3 days after injury) in a strong astrogliosis that was enhanced after a delay of 7 days, the astrocytes in the lesion area exhibiting enlarged cell processes and intense GFAP-positive immunoreactivity. After a delay of 20 days, the astrocytes were not dispersed any more but packed in three or four layers along the borders of the lesion, thus reducing its extension. This suggests a possible role for bFGF in promoting scar formation following brain injury.

Appearance of basic fibroblast growth factor receptors upon differentiation of rat mammary epithelial to myoepithelial-like cells in culture

The binding of [125I]-epidermal growth factor (EGF) and [125I]-basic fibroblast growth factor (bFGF) to a number of single-cell cloned rat mammary cell lines was measured using a saturation assay. Similar numbers of high-affinity [125I]-EGF binding sites (KD 1.3 nM) were found in epithelial and myoepithelial-like cell lines. In contrast, high-affinity (KD 35-276 pM) [125I]-bFGF binding sites were present on fibroblastic and myoepithelial-like cell lines but were not detectable on epithelial cell lines. A series of cell lines representing stages in the differentiation pathway of epithelial cells to an elongated myoepithelial-like morphology showed a graded increase in the number of bFGF receptors. The sensitivity of a cell line to stimulation of DNA synthesis by bFGF correlated with the level of expression of bFGF receptors on the cellular surface. Complexes of cell surface receptors affinity-cross-linked to [125I]-bFGF were analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In each case two distinct complexes having apparent molecular weights of 180 kDa and 160 kDa were observed.

Basic FGF treatment of endothelial cells down-regulates the 85-KDa TGF beta receptor subtype and decreases the growth inhibitory response to TGF-beta 1

Transforming growth factor-beta 1 (TGF beta 1) and basic fibroblast growth factor (bFGF) are known to be potent inhibitors and stimulators, respectively, of endothelial cell growth in vitro. In the present study we examined the effect of bFGF on endothelial cell growth inhibitory activity of TGF beta 1 and on the binding of (125I)-TGF beta 1 to these cells. The concentration of TGF beta 1 required for half-maximal inhibition of endothelial cell growth was increased in a dose-dependent manner by bFGF (a 20-100 fold increase at 1 ng/ml of bFGF). A 24 h-pretreatment of cells with bFGF resulted in abolition of the TGF beta 1 inhibitory effect on DNA synthesis. Moreover, the binding of (125I)-TGF beta 1 to the endothelial cell surface was decreased in a concentration-dependent and time-dependent manner after a preincubation of these cells with bFGF. Analysis of the binding parameters showed that bFGF decreased by two-fold the number of TGF beta receptors (to approximately 6000 receptors per cell). Cross-linking experiments with disuccinimidyl suberate demonstrated the presence of two TGF beta receptor subtypes, a predominant 85 kDa form and a minor 65 kDa form. Basic FGF decreased selectively the labeling of the 85 kDa TGF beta receptor subtype. These findings suggest that the growth stimulator bFGF can attenuate the cell's response to the growth inhibitor TGF beta 1.

Isolation and characterization of a newly identified endothelial cell mitogen produced by AtT-20 cells

An endothelial cell growth factor with unique specificity for vascular endothelial cells has been purified from the conditioned medium of the AtT-20 pituitary cell line. This growth factor, which has been characterized as a homodimer composed of two subunits with mol. wts of 23 kd is a potent mitogen for vascular endothelial cells in vitro with activity detectable at 50 pg/ml and saturation at 1 ng/ml. It was also angiogenic in vivo. In contrast with other endothelial mitogens of the fibroblast growth factor family, it has a unique target cell specificity. It did not stimulate the growth of other cell types of the vascular system such as vascular smooth muscle cells or that of mesoderm and neuroectoderm derived cells. Microsequencing revealed an amino-terminal sequence with no homology to any known protein. The release of this novel endothelial cell growth factor by pituitary derived cells and its unique target cell specificity suggest that it could play an important role in the angiogenic process.

Monoclonal antibodies against heparin-binding growth factor II/basic fibroblast growth factor that block its biological activity: invalidity of the antibodies for tumor angiogenesis

Two monoclonal antibodies (mAbs) against bovine heparin-binding growth factor II (HBGF-II)/basic fibroblast growth factor (bFGF) were obtained from mouse hybridoma cell lines. They were highly specific for bFGF from bovine, human, and mouse sources and did not cross-react with bovine heparin-binding growth factor I (HBGF-I)/acidic fibroblast growth factor (aFGF). The immunoglobulin class and subclass of these mAbs were IgG1, K. The apparent dissociation constant (Kd) for bFGF of these mAbs ranged from 10(-9) to 10(-10) M. One mAb (bFM-2) also cross-reacted with heat-inactivated bFGF, while the other mAb (bFM-1) did not, suggesting that bFM-1 recognized the conformation of the bFGF molecule necessary for its biological activity. These mAbs inhibited growth of cultured bovine capillary endothelial cells in both the presence and absence of exogenous bFGF, indicating the autocrine action of this growth factor in in vitro growth of these cells. On the other hand, injection of these hybridoma cell lines s.c. into the backs of athymic mice resulted in development of highly vascularized solid tumors and a sustained high level of anti-bFGF activity in the blood of the tumor-bearing mice. These findings suggest that bFGF is not essential as an autocrine or paracrine growth factor for angiogenesis in vivo. These mAbs should be useful in further studies on the physiological role and the conformation-function relationship of bFGF because they block its biological activity.

Differential effects of heparin, fibronectin, and laminin on the phosphorylation of basic fibroblast growth factor by protein kinase C and the catalytic subunit of protein kinase A

Basic fibroblast growth factor (FGF) is synthesized as a phosphoprotein by both bovine capillary endothelial and human hepatoma cells in culture. Because basic FGF is characterized by its high affinity for heparin and its association in vivo with the extracellular matrix, we examined the possibility that the phosphorylation of this growth factor by purified protein kinase C (PK-C) and the catalytic subunit of cAMP-dependent protein kinase-A (PK-A) can be modulated by components of the extracellular matrix. Heparin and other glycosaminoglycans (GAGs) inhibit the ability of PK-C to phosphorylate basic FGF. In contrast, heparin can directly increase the phosphorylation of basic FGF by PK-A. While fibronectin, laminin, and collagen IV have no effect on the ability of PK-C to phosphorylate basic FGF, they all can inhibit the effects of PK-A. Thus, there is a differential effect of extracellular matrix-derived proteins and GAGs on the phosphorylation of basic FGF. The enhanced phosphorylation of basic FGF that is mediated by heparin is associated with a change in the kinetics of the reaction and the identity of the amino acid targeted by this enzyme. The amino acids that are targeted by PK-C and PK-A have been identified by phosphopeptide analyses as Ser64 and Thr112, respectively. In the presence of heparin, basic FGF is no longer phosphorylated by PK-A at the usual PK-A consensus site (Thr112), but instead is phosphorylated at the canonical PK-C site (Ser64). Accordingly, heparin inhibits the phosphorylation of basic FGF by PK-C presumably by masking the PK-C dependent consensus sequence surrounding Ser64. Thus, when basic FGF is no longer phosphorylated by PK-A in the receptor binding domain (Thr112), it loses the increased receptor binding ability that characterizes PK-A phosphorylated basic FGF. The results presented here demonstrate three novel features of basic FGF. First, they identify a functional effect of the binding of heparin to basic FGF. Second, they establish that the binding of heparin to basic FGF can induce structural changes that alter the substrate specificity of protein kinases. Third, and perhaps most important, the results demonstrate the existence of a novel interaction between basic FGF, fibronectin, and laminin. Although the physiological significance of this phosphorylation is not known, these results clearly suggest that the biological activities of basic FGF are regulated by a complex array of biochemical interactions with the proteins, proteoglycans, and glycosaminoglycans present in the extracellular milieu and the cytoplasm.

Bovine brain endothelial cells express tight junctions and monoamine oxidase activity in long-term culture

The passage of substances across the blood-brain barrier is regulated by cerebral capillaries which possess certain distinctly different morphological and enzymatic properties compared to capillaries of other organs. Investigations of the functional characteristics of brain capillaries have been facilitated by the use of cultured brain endothelial cells, but in most studies a number of characteristics of the in vivo system are lost. To provide an in vitro system for studies of brain capillary functions, we developed a method of isolating and producing a large number of bovine brain capillary endothelial cells. These cells, absolutely free of pericyte contamination, are subcultured, at the split ratio of 1:20 (20-fold increase of the cultured surface), with no apparent changes in cell morphology up to the fiftieth generation (10 passages). Retention of endothelial-specific characteristics (factor VIII-related antigen, angiotensin-converting enzyme, and nonthrombogenic surface) is shown for brain capillary-derived endothelial cells up to passage 10, even after frozen storage at passage 3. Furthermore, we showed that bovine brain capillary endothelial cells retain, up to the fiftieth generation, some of the characteristics of the blood-brain barrier: occurrence of tight junctions, paucity of pinocytotic vesicles, and monoamine oxidase activity.

Tumor vascular permeability factor stimulates endothelial cell growth and angiogenesis

Vascular permeability factor (VPF) is an Mr 40-kD protein that has been purified from the conditioned medium of guinea pig line 10 tumor cells grown in vitro, and increases fluid permeability from blood vessels when injected intradermally. Addition of VPF to cultures of vascular endothelial cells in vitro unexpectedly stimulated cellular proliferation. VPF promoted the growth of new blood vessels when administered into healing rabbit bone grafts or rat corneas. The identity of the growth factor activity with VPF was established in four ways: (a) the molecular weight of the activity in preparative SDS-PAGE was the same as VPF (Mr approximately 40 kD); (b) multiple isoforms (pI greater than or equal to 8) for both VPF and the growth-promoting activity were observed; (c) a single, unique NH2-terminal amino acid sequence was obtained; (d) both growth factor and permeability-enhancing activities were immunoadsorbed using antipeptide IgG that recognized the amino terminus of VPF. Furthermore, 125I-VPF was shown to bind specifically and with high affinity to endothelial cells in vitro and could be chemically cross-linked to a high-molecular weight cell surface receptor, thus demonstrating a mechanism whereby VPF can interact directly with endothelial cells. Unlike other endothelial cell growth factors, VPF did not stimulate [3H]thymidine incorporation or promote growth of other cell types including mouse 3T3 fibroblasts or bovine smooth muscle cells. VPF, therefore, appears to be unique in its ability to specifically promote increased vascular permeability, endothelial cell growth, and angio-genesis.

Transforming growth factor beta-1 positively modulates the bioactivity of fibroblast growth factor on corneal endothelial cells

Transforming growth factor beta-1 (TGF beta-1), known as an inhibitor of vascular endothelial cell proliferation in vitro, stimulates bovine corneal endothelial cells (BCE) proliferation. It also positively modulates the response of BCE cells to fibroblast growth factor (FGF) and epidermal growth factor (EGF). This effect is concentration dependent within a physiological range of TGF beta-1, but it is blocked if cells are cultured on extracellular-matrix-coated dishes instead of plastic. TGF beta-1 does not modify the number or the affinity of bFGF receptors on BCE cell surface but increases the bFGF content of these cells. This suggests that TGF beta-1 might act through regulation of bFGF synthesis in BCE cells.

Basic fibroblast growth factor in atria and ventricles of the vertebrate heart

Extracts from atrial and ventricular heart tissue of several species (chicken, rat, sheep, and cow) are strongly mitogenic for chicken skeletal myoblasts, with the highest apparent concentration of biological activity in the atrial extracts. Using several approaches (biological activity assay and biochemical and immunological analyses), we have established that (a) all cardiac extracts contain an 18,000-D peptide which is identified as basic fibroblast growth factor (bFGF) since it elutes from heparin-Sepharose columns at salt concentrations greater than 1.4 M and is recognized by bFGF-specific affinity-purified antibodies; (b) bFGF is more abundant in the atrial extracts in all species so examined; (c) avian cardiac tissue extracts contain the highest concentration of immunoreactive bFGF; and (d) avian ventricles contain a higher relative molecular mass (23,000-D) bFGF-like peptide which is absent from atrial extracts. Examination of frozen bovine cardiac tissue sections by indirect immunofluorescence using anti-bFGF antibodies shows bFGF-like reactivity associated with nuclei and intercalated discs of muscle fibers. There is substantial accumulation of bFGF around atrial but not ventricular myofibers, resulting most likely from more extensive endomysium in the atria. Blood vessels and single, nonmuscle, connective tissue cells react strongly with the anti-bFGF antibodies. Higher bFGF content and pericellular distribution in atrial muscles suggest a correlation with increased regenerative potential in this tissue. Distribution within the myofibers is intriguing, raising the possibility for an intimate and continuous involvement of bFGF-like components with normal myocardial function.

Isolation and characterization of a vascular endothelial cell mitogen produced by pituitary-derived folliculo stellate cells

A growth factor with specificity for vascular endothelial cells has been identified in conditioned medium of pituitary-derived folliculo stellate cells. This factor, named folliculo stellate-derived growth factor (FSdGF), was purified to homogeneity by a combination of heparin-Sepharose affinity chromatography, Bio-Gel P-60 exclusion chromatography, Mono S ion-exchange chromatography, and hydrophobic chromatography on a C4 reverse-phase HPLC column. FSdGF was characterized as a homodimer composed of two subunits with a molecular mass of 23 kDa. FSdGF was a potent mitogen for vascular endothelial cells with activity detectable at 25 pg/ml and saturation at 500 pg/ml. It did not stimulate the proliferation of other cell types such as bovine vascular smooth muscle cells, corneal endothelial cells, adrenal cortex cells, granulosa cells, BALB/MK cells, or BHK-21 cells. Microsequencing revealed an N-terminal sequence having no significant homology to any known protein. The release of FSdGF by pituitary cells and its target cell specificity raise the possibility that FSdGF may play a role in angiogenesis.

Cloning of the gene coding for human class 1 heparin-binding growth factor and its expression in fetal tissues

We have identified four overlapping genomic DNA clones coding for human class 1 heparin-binding growth factor (HBGF-1), also known as acidic fibroblast growth factor, by screening genomic DNA libraries with an HBGF-1 cDNA probe. The exon-intron structure of the HBGF-1 gene was determined by Southern hybridization and nucleotide sequence analysis. The complete amino acid sequence of human HBGF-1 was deduced from the nucleotide sequence of these genomic DNA clones. The predicted amino acid sequence is identical to the published amino acid sequence determined by protein sequencing. Southern blot analysis of human DNA suggested that there is a single-copy gene coding for HBGF-1. A 4.5-kilobase mRNA and two minor species (3.4 and 2.0 kilobases) homologous to the HBGF-1 gene were detected in cellular RNA isolated from human adult brain and kidney. The HBGF-1 mRNAs from brain and kidney had slightly different sizes. The mechanism for the synthesis of different sizes of mRNA was not determined. We also detected HBGF-1 transcript from glioblastoma cells, fetal brain, and kidney but not from placenta or fetal liver. Since HBGF-1 is an angiogenic factor, these data suggest that it may play a role in embryonic angiogenesis during fetal development.

Mesoderm induction and blood island formation by angiogenic growth factors and embryonic inducing factors

Factors which induce mesoderm, including endothelium lined cavities and primitive blood cells in omnipotent amphibian ectoderm, have been isolated from different sources. Recently it was shown that angiogenic factors, which belong to the protein families of the heparin binding growth factors (acidic and basic fibroblast growth factor) and the transforming growth factors (TGF-beta 1 and -beta 2), also induce mesodermal tissues in amphibian ectoderm. In triturus ectoderm, capillary like endothelial networks are induced preferentially by the transforming growth factors. The relationship between growth factors and inducing factors is discussed.

v-src genes stimulate neurite outgrowth in pheochromocytoma (PC12) variants unresponsive to neurotrophic factors

The NGF-nonresponsive rat pheochromocytoma PC12 variant nnr5, isolated by Green et al. (J Cell Biol 102:830-843, 1986), responds poorly or not at all to fibroblast growth factor. Transformation of PC-12nnr5 cells with v-src-expressing retroviruses results in vigorous neurite outgrowth, similar to that seen in the parent cell line. Thus though the PC12nnr5 cell line has a greatly impaired ability to respond to neurotrophic factors it still may extend neurites. This data is consistent with a model in which PC12nnr5 cells are unable to propagate intracellular second messengers, and this defect may be related to the expression of c-src gene products.

Neovascularization of surface demineralized dentin

Uneventful healing of the wound site created by periodontal reconstructive surgery is crucial for the long term survival of the dentition. Wound healing has been shown to be initiated and mediated by matrix components and polypeptide growth factors. Neovascularization (or angiogenesis) is one of the most important events in the healing process of a wound site. Any increase in the degree and/or rate of neovascularization could result in more rapid or complete healing. Previously, we have shown that basic fibroblast growth factor (bFGF) selectively enhances periodontal ligament cell migration and proliferation. In addition, we have shown that FGF stimulates human umbilical vein endothelial cell migration and proliferation. In this study we examined whether human umbilical vein endothelial cells could be influenced to form capillary-like structures in a type I collagen stroma and on dentin surfaces in response to fibroblast growth factor (FGF). We observed tubule-like structures formed from a monolayer of endothelial cells within a type I collagen sponge in response to a gradient of FGF. Furthermore, we observed tubule-like structures formed from self-association of individual endothelial cells on partially demineralized dentin surfaces in response to FGF. Proliferation of human endothelial cells on dentin was dose dependent and maximally stimulated at a concentration of 10 ng/ml FGF. These data indicate that FGF can induce endothelial cell migration, proliferation and tubule formation on dentin.

Expression and control of vascular endothelial cells: proliferation and differentiation by fibroblast growth factors

Evidence from in vitro studies supports the concept that growth factors could be involved in the development and function of the vascular tree. Among the growth factors known to influence vascular endothelial cells' proliferation and differentiation, in vitro, are the fibroblast growth factors. These consist of two closely, structurally, related polypeptides that differ by their isoelectric point and have been called basic and acidic fibroblast growth factor. These growth factors, in particular basic fibroblast growth factor, which is expressed and synthesized by vascular endothelial cells, could influence the development, remodeling, and function of the vascular tree through regulating mechanisms involving paracrine and autocrine control of cell proliferation and differentiation.

Basic fibroblast growth factor enhances the capacity of bone marrow cells to form bone-like nodules in vitro

The role of basic fibroblast growth factor (bFGF) in the proliferation and differentiation of rat bone marrow cells in culture was studied. bFGF stimulated [3H]thymidine incorporation into these cells by 4-fold at a concentration of 0.3 ng/ml and half-maximal effect was observed at a concentration of 15 pg/ml. In addition to its mitogenic effect, bFGF stimulated alkaline phosphatase activity by 3.6-fold. Continuous treatment with bFGF (for 21 days) resulted in a 6.3-fold increase in the culture dish surface area covered by bone-like mineralized tissue. Maximal bone-like tissue formation was observed in the presence of 3 ng/ml bFGF with half-maximal effect at a concentration of 0.3 ng/ml. These results indicate the possible role of bFGF in the proliferation of osteogenic rat bone marrow cells and their differentiation into cells of osteoblast-like phenotype.

Role of extracellular matrix in the action of basic fibroblast growth factor: matrix as a source of growth factor for long-term stimulation of plasminogen activator production and DNA synthesis

When bovine capillary endothelial (BCE) cells were treated with 10 ng/ml of basic fibroblast growth factor (bFGF) for 10 or 30 minutes at 37 degrees C, washed extensively with phosphate-buffered saline (PBS) and incubated in bFGF-free medium, plasminogen activator (PA) production was stimulated to the same extent as in cells exposed continuously to bFGF. Three methods of removing bFGF from heparin-like binding sites in the extracellular matrix, but not from bFGF receptors, abolished this long-term effect of a brief exposure to bFGF. First, BCE cells exposed to bFGF for 30 minutes were washed with 2M NaCl and incubated in bFGF-free medium. Second, BCE cells were incubated with bFGF for 10 minutes in the presence of heparin, and cells were washed with PBS and incubated in bFGF-free medium. Third, BCE cell cultures were treated with heparinase and exposed to bFGF. Each of these treatments abolished the long-term (24-48 hours) stimulation of PA production normally observed after brief exposure to bFGF. In each of these experiments, incubation of cells in bFGF-containing medium after the treatments resulted in normal stimulation of PA production, demonstrating that the treatments did not harm the cells. Stimulation of DNA synthesis was observed when cells were exposed to bFGF for 2 hours at 4 degrees C, incubated in bFGF-free medium for 24 hours at 37 degrees C, and assayed for 3H-thymidine incorporation. However, no stimulation was observed if the 2 hours incubation at 4 degrees C was carried out in the presence of heparin. Thus, long-term stimulation of PA activity and DNA synthesis after a brief exposure to bFGF seems to be a consequence of bFGF binding to the extracellular matrix. The extracellular matrix may act as a physiologic buffer, binding bFGF when concentrations are high and releasing it later for interaction with its receptor. This interaction with matrix may be required for the in vivo action of bFGF.

Rapid chromatographic isolation and immunoblot characterization of immunoreactive fibroblast growth factor-related polypeptides from various tissues

Procedures to rapidly isolate fibroblast growth factor (FGF)-like activity from a number of tissue sources (lung, plasma, brain, ovary, corpus luteum, pituitary, chondrosarcoma) of bovine, porcine or rat origin are described. In addition, immunoblotting experiments using well characterized and specific rabbit polyclonal anti-fibroblast growth factor beta (anti-FGF-beta) sera have been performed. Besides documenting the first report of the isolation of FGF-beta from bovine lung and plasma, these studies provide evidence for the existence of higher-molecular-mass proteins with FGF-beta-like immunoreactivity. For example, in addition to new truncated forms of the acidic and basic FGF (FGF-alpha and FGF-beta), respectively, other higher-molecular-mass immunoreactive proteins were detected in bovine, pig and rat brain, and in rat chondrosarcoma. The tissue distribution of these immunoreactive proteins and their competitive inhibition characteristics mitigate against the possibility that the polyclonal antisera are cross-reacting non-specifically with common cellular proteins. Rather, the data suggest that the immunoblotting technique is either detecting other proteins structurally related to FGF-beta or alternatively FGF-beta is strongly bound to specific carrier proteins (e.g. heparan sulphate proteoglycan fragments) associated with their transport and recognition at the cellular level.

Cloning of the gene coding for human class 1 heparin-binding growth factor and its expression in fetal tissues

We have identified four overlapping genomic DNA clones coding for human class 1 heparin-binding growth factor (HBGF-1), also known as acidic fibroblast growth factor, by screening genomic DNA libraries with an HBGF-1 cDNA probe. The exon-intron structure of the HBGF-1 gene was determined by Southern hybridization and nucleotide sequence analysis. The complete amino acid sequence of human HBGF-1 was deduced from the nucleotide sequence of these genomic DNA clones. The predicted amino acid sequence is identical to the published amino acid sequence determined by protein sequencing. Southern blot analysis of human DNA suggested that there is a single-copy gene coding for HBGF-1. A 4.5-kilobase mRNA and two minor species (3.4 and 2.0 kilobases) homologous to the HBGF-1 gene were detected in cellular RNA isolated from human adult brain and kidney. The HBGF-1 mRNAs from brain and kidney had slightly different sizes. The mechanism for the synthesis of different sizes of mRNA was not determined. We also detected HBGF-1 transcript from glioblastoma cells, fetal brain, and kidney but not from placenta or fetal liver. Since HBGF-1 is an angiogenic factor, these data suggest that it may play a role in embryonic angiogenesis during fetal development.

Growth stimulation of human breast epithelial cells by basic fibroblast growth factor in serum-free medium

Growth-stimulating activities of basic and acidic fibroblast growth factors (FGFs) toward human breast epithelial cells were examined and compared with the mitogenic activity of bovine pituitary extract (BPE) by the use of a serum-free medium which contained epidermal growth factor, insulin, transferrin, hydrocortisone, ethanolamine, phosphoethanolamine, prolactin and prostaglandin. Addition of 1 ng/ml of basic FGF (bFGF) to the serum-free medium significantly enhanced the growth potential of epithelial cells derived from human breast carcinoma, and the number of cells grown for 7 days with bFGF was more than 1 1/2 times higher than that in the serum-free medium containing BPE instead of prolactin and prostaglandin. Growth responsiveness toward bFGF of epithelial cells derived from histologically non-malignant breast tissues was lower than that of carcinoma-derived cells, and the growth-stimulating activity of bFGF was lower than that of BPE, which could significantly enhance the growth potential of the cells. Contrary to bFGF, acidic FGF at 1 ng/ml had no significant effect on the growth potential of breast epithelial cells which had grown out from either carcinoma or non-malignant tissues. The present results suggest that bFGF is a putative growth-stimulating factor for human breast epithelial cells, especially for carcinoma-derived cells, and can substitute at least in part for BPE in serum-free monolayer culture of the cells.

Fibroblast growth factor in the extracellular matrix of dystrophic (mdx) mouse muscle

Polyclonal antibody F547 reacts with a bovine basic fibroblast growth factor (bFGF) and a human recombinant bFGF, but not with bovine acidic fibroblast growth factor. This antibody localized bFGF in the extracellular matrix of mouse skeletal muscle, primarily in the fiber endomysium, which includes the heparin-containing basal lamina. In mdx mouse muscle, which displays persistent regeneration, FGF levels in the extracellular matrix are higher than those in controls. Overabundance of matrix FGF in mdx muscles may be related to an increase in both satellite cell and regenerative activity in the dystrophic muscle and may help explain the benign phenotype of mdx animals compared with the genetically identical human Duchenne muscular dystrophy.

Monoclonal antibodies against human basic fibroblast growth factor

Recombinant human basic fibroblast growth factor (hbFGF) was used as an antigen to develop, by a somatic cell fusion technique, four monoclonal antibodies (MAbs), that recognize the complete and amino-terminal truncated form of hbFGF. Isotype identification showed that MAbs designated MAb12 and MAb98 were IgG1; and those designated MAb52 and MAb78 were IgG2b. All these MAbs bound the complete form of hbFGF produced in E.coli. Competition with synthetic polypeptides, a replication of 1-9 aa and of 141-146 aa of hbFGF, and truncated forms of hbFGF by 13 and 40 amino acid residues in its amino-terminal produced in E. coli by recombinant technique, revealed at least two epitopes recognized by the four IgG type MAbs. MAb12 and MAb78 recognized the epitope located within the first 9 amino acid residues at the amino terminal of the complete hbFGF. MAb52 and MAb98 recognized the one located between the amino acid residue no. 14 and 40. None of MAbs bound bovine acidic FGF (aFGF). Using MAb52 or MAb98 and MAb78, a two-site EIA has been developed. This EIA is sensitive enough to detect 0.5 ng/ml of hbFGF. Furthermore, MAb78 was used as a ligand for affinity chromatography to purify hbFGF mutein CS4, which binds weakly to a heparin affinity column.

Analysis of cell variants showing differential susceptibilities to radiation- or chemical-induced neoplastic transformation: differences in their responses to growth factors

The induction of DNA synthesis in quiescent, density-arrested Balb/c 3T3 cells is known to be controlled by the sequential action of at least two functionally distinct sets of growth factors, so-called "competence factors" and "progression factors." Here we examined this induction pathway in Balb/c 3T3 A31-I variants, which showed differential susceptibilities to radiation- and chemical-induced neoplastic transformation despite their similar susceptibilities to radiation- or chemical-induced cell killing and mutagenesis. DNA synthesis was acquired only with the exposure to progression factors in a highly susceptible cell variant (A31-1-13) whereas both competence factors and progression factors were required for a less susceptible cell variant (A31-I-1). The competent state constitutively produced by an autologous mechanism in the highly transformation-susceptible A31-I-13 cells suggests the existence of an endogenous promoter that acts for the expression of the transformed phenotype in an autocrine fashion when the cells have been initiated by radiation or chemical carcinogens. The growth factor requirements acting as a determining factor for susceptibilities to transformation are discussed.

Sulfated polysaccharides modulate effects of acidic and basic fibroblast growth factors on repair of injured confluent human vascular endothelium

Semi-automatic analysis of the repair process of a circular mechanical lesion of confluent human vascular endothelial cells in vitro was used to evaluate the contributions of cell migration and cell proliferation. Standard heparin added to culture medium that contained 30% human serum induced an inhibition of cell migration at the lesion margin during the first day after injury. Several sulfated polysaccharides were tested in the presence of 5% human serum. Standard heparin, low molecular weight heparin, or pentosan polysulfate markedly reduced the rate of lesion regeneration. Cell proliferation, measured by 3H-thymidine incorporation at the lesion margin, and cell migration were both decreased. In contrast, the combination of acidic fibroblast growth factor with a sulfated polysaccharide accelerated the repair process. Basic fibroblast growth factor combined with a sulfated polysaccharide gave a regeneration rate similar to that of the control; however, at 4 days after injury, the residual lesion was the same when basic fibroblast growth factor was used alone or when it was combined with sulfated polysaccharides. Acidic fibroblast growth factor totally reversed the effects of sulfated polysaccharides on the repair process by enhancing endothelial cell proliferation and allowing endothelial cell migration.

High molecular mass forms of basic fibroblast growth factor are initiated by alternative CUG codons

A 6.75-kilobase human hepatoma-derived basic fibroblast growth factor (bFGF) cDNA was cloned and sequenced. An amino-terminal sequence generated from a purified hepatoma bFGF was found to correspond to the nucleotide sequence and to begin 8 amino acids upstream from the putative methionine start codon thought to initiate a 154-amino acid bFGF translation product. This sequence suggests that a form of bFGF of at least 163 amino acids exists. The hepatoma cDNA was transcribed in vitro into RNA; in vitro translation of this RNA generated three forms of bFGF with molecular masses of 18, 21, and 22.5 kDa. By use of in vitro mutagenesis, it was found that the 22.5-kDa bFGF and possibly the 21-kDa form were initiated with CUG start codons. The 18-kDa bFGF was initiated with an AUG codon. By transfecting into COS cells human hepatoma bFGF cDNA and a construct from which the AUG initiator was eliminated, it was found that the higher molecular mass forms of bFGF were as biologically active as the 18-kDa form.

The human FGF-5 oncogene encodes a novel protein related to fibroblast growth factors

We previously described the isolation of a human oncogene which had acquired transforming potential by a DNA rearrangement accompanying transfection of NIH 3T3 cells with human tumor DNA (X. Zhan, A. Culpepper, M. Reddy, J. Loveless, and M. Goldfarb, Oncogene 1:369-376, 1987). We now term this oncogene the FGF-5 gene, since it specifies the fifth documented protein related to fibroblast growth factors (FGFs. Two regions of the FGF-5 sequence, containing 122 of its 267 amino acid residues, were 40 to 50% homologous to the sequences of acidic and basic FGFs as well as to the sequences of the FGF-related oncoproteins int-2 and hst/KS3. The FGF-5 gene bears the three exon structures typical for members of this family. FGF-5 was found to be expressed in the neonatal brain and in 3 of the 13 human tumor cell lines examined. Several experiments strongly suggested that FGF-5 is a growth factor with properties common to those of acidic and basic FGFs. The rearrangement which activated the FGF-5 gene during DNA transfection had juxtaposed a retrovirus transcriptional enhancer just upstream from the native promoter of the gene.

Stimulation of cartilage-matrix proteoglycan synthesis by morphologically transformed chondrocytes grown in the presence of fibroblast growth factor and transforming growth factor-beta

The effects of transforming growth factor-beta (TGF-beta) on the synthesis of cartilage-matrix proteoglycan by cultured rabbit chondrocytes were examined. Rabbit chondrocytes were seeded at low density and exposed to a 1:1 mixture of Dulbecco's modified Eagle's medium and Ham's F-12 medium supplemented with 0.5% fetal bovine serum, 1% bovine serum albumin, 50 micrograms/ml ascorbic acid, and 2 x 10(-7) M hydrocortisone (Medium A). Various combinations of TGF-beta, insulin-like growth factor-I (IGF-I), and fibroblast growth factor (FGF) were also added to Medium A, and the chondrocytes were grown to confluency. Chondrocytes grown with TGF-beta or FGF alone became flat or fibroblastic, those grown with FGF and TGF-beta became very elongated and formed distinct foci, and those grown with FGF and IGF-I showed the spherical configuration characteristic of overtly differentiated chondrocytes. Nevertheless, the incorporation of 3H with glucosamine into the large, chondroitin sulfate proteoglycan synthesized by cultures with FGF and TGF-beta was similar to that in cells grown with FGF and IGF-I and five times that in cells cultured with FGF alone. The increases in incorporation of 3H reflected real increases in proteoglycan synthesis, because chemical analyses showed an increase in the accumulation of macromolecules containing uronic acid in cultures with FGF and TGF-beta or with FGF and IGF-I. However, FGF in combination with either TGF-beta or IGF-I had little effect on the incorporation of 3H into small proteoglycans or hyaluronic acid. These results indicate that chondrocytes morphologically transformed with TGF-beta and FGF fully express the differentiated proteoglycan phenotype rather than the transformed glycosaminoglycan phenotype.

Partial purification and characterization of a membrane-derived factor regulating neurotransmitter phenotypic expression

Cell membrane contact induces the de novo expression of choline O-acetyltransferase (CAT; acetyl-CoA: choline O-acetyltransferase, EC 2.3.1.6) activity in cultures of virtually pure neonatal rat dissociated sympathetic neurons. To identify molecular mechanisms underlying membrane-associated CAT induction, the responsible membrane component was characterized and partially purified. Substantial CAT-inducing activity was found in membranes from adult rat spinal cord and sensory and sympathetic ganglia. Whole brain membranes demonstrated significantly less activity. CAT induction in sympathetic neurons in response to spinal cord membranes was linear with respect to time, after an initial 6-hr lag. It was also linear with respect to concentrations of spinal cord protein from 2 to 100 micrograms per ml. CAT-inducing activity was extracted from spinal cord membranes by incubation with 100 mM NaCl and was purified approximately 5000-fold by DEAE ion-exchange and gel filtration chromatography. The active factor appears to be an extrinsic protein with an apparent molecular mass of 27 kDa. It is inactivated by trypsin and chymotrypsin but is moderately thermostable, retaining activity at 60 degrees C but not at 90 degrees C.

Characterization of polyclonal antibodies that distinguish acidic and basic fibroblast growth factors by using western immunoblotting and enzyme-linked immunosorbent assays

Rabbit polyclonal antibodies were raised against ovalbumin conjugates of purified bovine brain acidic fibroblast growth factor (aFGF) and a synthetic peptide containing the N alpha-terminal 1-24 amino acid sequence of bovine basic fibroblast growth factor (bFGF). These antibodies were used to specifically detect 1-ng quantities of aFGF and bFGF by using enzyme-linked immunosorbent assay (ELISA) and Western immunoblot procedures. Antibodies raised against aFGF recognized bovine brain aFGF and bovine recombinant aFGF but very poorly recognized recombinant bFGF or purified porcine or bovine pituitary bFGF with ELISA and Western immunoblot procedures. Antibodies raised against bFGF (1-24) recognized purified bovine, porcine, and recombinant human bFGF but only very poorly recognized aFGF with ELISA and Western immunoblot procedures. In vitro addition of anti-bFGF antibodies was able to partially neutralize bFGF-stimulated 3H-thymidine incorporation by COMMA-D mouse mammary epithelial cells while having no effect on aFGF or epidermal growth factor (EGF) stimulation. In vitro addition of anti-aFGF antibodies had no effect on bFGF- or EGF-stimulated 3H-thymidine incorporation, but surprisingly, had a potentiating effect on aFGF stimulation. Antibodies against aFGF immobilized on protein A-Sepharose were able to specifically and completely remove mitogenic activity from solutions containing aFGF but had no effect on removal of mitogenic activity from control solutions containing bFGF or EGF. Similarly, immobilized anti-bFGF antibodies completely removed mitogenic activity from solutions of bFGF, but not aFGF or EGF controls. These antibodies have been useful for the identification and characterization of growth factors from tissue and recombinant sources.

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.

Purification and characterization of a newly identified growth factor specific for epithelial cells

A growth factor specific for epithelial cells was identified in conditioned medium of a human embryonic lung fibroblast cell line. The factor, provisionally termed keratinocyte growth factor (KGF) because of its predominant activity on this cell type, was purified to homogeneity by a combination of ultrafiltration, heparin-Sepharose affinity chromatography, and hydrophobic chromatography on a C4 reversed-phase HPLC column. KGF was both acid and heat labile and consisted of a single polypeptide chain of approximately 28 kDa. Purified KGF was a potent mitogen for epithelial cells, capable of stimulating DNA synthesis in quiescent BALB/MK epidermal keratinocytes by greater than 500-fold with activity detectable at 0.1 nM and maximal at 1.0 nM. Lack of mitogenic activity on either fibroblasts or endothelial cells indicated that KGF possessed a target cell specificity distinct from any previously characterized growth factor. Microsequencing revealed an amino-terminal sequence containing no significant homology to any known protein. The release of this growth factor by human embryonic fibroblasts raises the possibility that KGF may play a role in mesenchymal stimulation of normal epithelial cell proliferation.

Localization of basic fibroblast growth factor to the developing capillaries of the bovine retina

The basic fibroblast growth factor (FGF) is a potent mitogen that has vascular endothelium as one of its principle target cells. Recent work has provided both the complete amino acid sequence of basic FGF and the nucleotide sequence of the genes for both human and bovine basic FGF. Although capillary endothelial cells have been shown to produce basic FGF in vitro and to deposit basic FGF in their extracellular matrix in vitro as well, no direct evidence yet exists for the distribution of basic FGF in vivo. Antipeptide antibodies were prepared against a 15-amino-acid sequence from the amino terminus of basic FGF in order to avoid cross-reactivity with acidic FGF, a protein with 55% overall homology to basic FGF. After affinity purification, these antisera were used to localize the basic fibroblast growth factor in the fetal and adult bovine retina. Immunoreactive material was found in capillaries of the inner nuclear layer, a capillary network undergoing development during the third trimester in the fetal bovine eye. Although the resolution of the technique does not permit a unique assignment of cellular localization, the presence of stain immediately adjacent to the lumen of capillaries suggests that capillary endothelial cells may produce the basic fibroblast growth factor in vivo during vascular development.

Cell biology of arterial proteoglycans

Although proteoglycans constitute a minor component of vascular tissue, these molecules have been shown to influence a number of arterial properties such as viscoelasticity, permeability, lipid metabolism, hemostasis, and thrombosis. A hallmark of early and late atherosclerosis is the accumulation of proteoglycans in the intimal lesions. Yet, it is not clear why this accumulation occurs. This article reviews the classes of proteoglycans synthesized by the two major cell types of the arterial wall--the endothelial and smooth muscle cell. Detailed consideration is then given to the modulation of proteoglycan metabolism and the role that proteoglycans play in a number of cellular events such as adhesion, migration, and proliferation--important processes in both the development and the pathogenesis of blood vessels. Last, the involvement of proteoglycans in two critical vascular wall processes--hemostasis and lipid metabolism--is reviewed, because these events pertain to atherogenesis. This review emphasizes the importance of proteoglycans in regulating several key events in normal and pathophysiological processes in the vascular tissue.

Neuronal aggregation and neurotransmitter regulation: partial purification and characterization of a membrane-derived factor

Cell membrane contact induces marked differential changes in neurotransmitter expression. In cultures of virtually pure dissociated sympathetic neurons, when such contact is provided by either high cell densities or addition of membranes derived from specific tissues, there is a marked increase in cell-specific content of substance P and de novo induction of choline acetyltransferase. To identify molecular mechanisms underlying regulation of transmitter expression by neuronal aggregation and membrane contact, we have begun to isolate and characterize a membrane-associated factor responsible for stimulation of choline acetyltransferase activity. The factor was found in substantial quantities in membranes from adult rat spinal cord as well as from sympathetic and sensory ganglia. Ionic mechanisms were employed to extract transmitter-inducing activity from spinal cord membranes in soluble form. The solubilized factor was then partially purified by ion exchange and gel filtration chromatography. It appears to be an extrinsic (non-integral) protein with an apparent molecular weight of 27. It is inactivated by trypsin and chymotrypsin, but is only moderately sensitive to heat inactivation, retaining activity at 60 degrees C but not at 90 degrees C. Neuronal perikaryal contact via aggregation represents a critical mechanism by which neurons themselves may influence phenotypic expression. Membrane localization of the factor provides a means by which cell contact may regulate transmitter expression.

Internalization and limited processing of basic fibroblast growth factor on Chinese hamster lung fibroblasts

Using either acidic (pH 2.5) or trypsic treatments, we demonstrated that 125I-labeled basic Fibroblast Growth Factor (125I-bFGF) was submitted to an internalization process on responsive Chinese hamster lung fibroblasts (CCL39) at 37 degrees C. Various experiments based on the measurement of cell-associated radioactivity, as well as on research of degradated products of 125I-bFGF in cellular supernatants, showed that most of the internalized radioactivity remained intracellularly located after up to 5 hr of incubation. Analyses of this radioactivity by NaDodSO4-PAGE revealed the presence of labeled peptides issued from the limited processing of the native 125I-bFGF form (17 kD) and whose molecular weights were estimated to be 9 and 6 kD. Kinetic experiments indicated that proteolysis of the 125I-bFGF began early on incubation (less than 30 min) and led to a prolonged preservation of the 9- and 6-kD peptides which were still detectable after 13 hr of incubation. Preincubation of the cells with different lysosomotropic agents completely inhibited the proteolysis, indicating that this event occurred probably in an intracellular acidic compartment. Two enzyme inhibitors, leupeptin and N-alpha-tosyl-L-lysine chloromethyl ketone (TLCK), were also shown to interfere with the formation of both 9- and 6-kD peptides, thus suggesting a way to control the appearance of these fragments, and hence to determine their potential intracellular role.