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.     

1H NMR structural characterization of a nonmitogenic, vasodilatory, ischemia-protector and neuromodulatory acidic fibroblast growth factor

A shortened genetically engineered form of acidic fibroblast growth factor (aFGF), that includes amino acids 28-154 of the full-length sequence (154 residues) plus Met in substitution of Leu27, does not induce cell division even though it is recognized by the cell membrane receptor, triggers the early mitogenic events, and retains the neuromodulatory, vasoactive, and cardio- and neuroprotective properties of the native full-length molecule. Taken together, these properties make this truncated aFGF a promising compound in the treatment of a wide assortment of neurological and cardiovascular pathologies where aFGF mitogenic activity is dispensable. Differences in biological activities between the shortened aFGF and the wild-type form have been attributed to lack of stability, and to the specific amino acid sequence missing at the N-terminus. Here we show that this shortened aFGF form has a three-dimensional structure even more stable than the wild-type protein at the mitogenic assay conditions; that this structure is similar to that of the wild type except at site 1 of interaction with the cell membrane receptor; that its lack of mitogenic activity cannot be attributed to the specific missing sequence; and that the vasodilatory activity of aFGF seems impaired by alterations of the three-dimensional structure of site 2 of interaction with the cell membrane receptor.     

Stabilization by heparin of acidic fibroblast growth factor mitogenicity for human endothelial cells in vitro

The effects of heparin and other glycosaminoglycans (GAGs) on the mitogenicity and stability of acidic fibroblast growth factor (aFGF) were studied. The mitogenic activity of aFGF was assayed utilizing cultured adult human endothelial cells (AHECs) isolated from iliac arteries and veins as target cells. In most experiments, aFGF purified from bovine brain was employed; in some experiments recombinant bovine aFGF was used and qualitatively similar results were obtained. In the presence of heparin, bovine aFGF at doses between 0.5 and 1.0 ng/ml (30-60 pM) elicited half the maximum AHEC growth over a 4-day period depending on the cell line tested; in the absence of heparin, significant growth was not observed at aFGF concentrations less than 10-20 ng/ml. This effect of heparin was dose-dependent over the range 0.1-10 micrograms/ml (half-maximum dose, 2 micrograms/ml). The mitogenic activity of bovine aFGF for AHECs decreased by 50% after preincubation in culture medium without cells at 37 degrees C for 2 1/2 to 3 hours. In contrast, the mitogenic activity of bovine aFGF preincubated in the presence of heparin-containing culture medium without cells was dramatically stabilized (half-life 24-29 hours). These effects also were observed in serum-free medium. Several GAGs structurally related to heparin such as chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate, and hyaluronic acid neither potentiated nor stabilized aFGF mitogenic activity. However, heparan sulfate from bovine lung was found to be nearly as active as heparin in both these effects. These data suggest that the binding and stabilization of mitogens by extracellular and tissue-associated heparan sulfates might play important roles in the regulation of AHEC growth.     

Isolation of heparin-binding growth factors from bovine, porcine and canine hearts

Fresh bovine, porcine and canine hearts were homogenized and mitogens for mesoderm-derived cells were purified in three different steps. Extraction by two different ammonium sulfate precipitations was followed by cation-exchange chromatography and by heparin-Sepharose affinity chromatography. A heparin-Sepharose fraction from heart (eluted at 1.1 M NaCl) increased mitotic activity in serum-deprived cultures of porcine aortic endothelial and smooth muscle cells, and in human fibroblasts. This mitogenic activity is potentiated by heparin and inhibited by gamma-interferon. The heart mitogenic fraction showed one double peak on HPLC at A215 and one polypeptide band on SDS/PAGE. These peaks and bands were identical to those obtained from bovine brain. The heart acidic fibroblast growth factor (aFGF) showed a positive signal in Western blots using antibodies raised against brain aFGF. Gas-phase amino acid sequencing established that the mitogens were identical to aFGF and the N-terminally truncated aFGF. Extraction in the presence of a protease inhibitor (pepstatin A) produced a higher-molecular mass form of aFGF with a blocked amino terminus. Another mitogen, eluted at 1.6 M NaCl from heparin-Sepharose, reacted with polyclonal antiserum against human recombinant basic fibroblast growth factor (bFGF) and showed a 66% (12 from 18 amino acids determined by gas-phase sequencing) similarity with bFGF. This polypeptide increased the mitotic activity of the same cell lines but was more potent than aFGF.     

Overexpression and purification of full-length acidic fibroblast growth factor inE.coli

Summary A full-length aFGF cDNA was cloned and inserted into a T7 expression vector for heterologous expression inE. coli. For high level production of aFGF, an optimal condition for overexpression (incubation at 42 °C for 2 hours) and a simple purification procedure employingin vitro refolding and an affinity chromatography was established. The production yield was 40–50 μg/mg of inclusion body preparation and purified aFGF showed mitogenic activity.     

Conversion of cysteine to serine residues alters the activity, stability, and heparin dependence of acidic fibroblast growth factor.

Acidic fibroblast growth factor (aFGF) is a broad spectrum mitogen that is stabilized by complexation with heparin and heparan proteoglycans. The monomeric human protein contains 3 reduced cysteine residues of unknown function, the first 2 of which are conserved among all seven known fibroblast growth factors. The influence of these free sulfhydryl groups on the level, stability, and heparin dependence of the mitogenic activity at physiological temperature and pH is characterized using a complete set of site-directed mutants in which either any 1, 2, or all 3 of the cysteine residues are converted to serines. Mutants of aFGF in which either any 2 or all 3 cysteine residues are substituted by serines are more active, have longer activity half-lives, and are less heparin dependent than wild-type aFGF. In contrast, wild-type aFGF and the three mutants that each retain 2 cysteine residues inactivate more rapidly in the absence of heparin by a nonproteolytic mechanism but are markedly stabilized by heparin. This cysteine-mediated destabilization of aFGF not only diminishes its activity in the absence of heparin in tissue culture but also could functionally restrict its activity in vivo to the vicinity of mast cell-derived heparins and heparan proteoglycans associated with cell surfaces and basement membranes.     

Extracellular matrix heparan sulfate proteoglycans modulate the mitogenic capacity of acidic fibroblast growth factor

Confluent cultures of human endothelial cells deposit into extracellular matrix (ECM) distinct heparan sulfate proteoglycans (HSPG) which modulate acidic fibroblast growth factor's (aFGF) ability to stimulate human endothelial cell mitogenic capacity. Extracellular matrix 35S-HSPG were isolated from cultures metabolically labelled with Na235SO4 by DEAE-Sepharose, Sepharose CL-4B, and aFGF-Affi-Gel 15 column chromatography and identified by resistance to chondroitinase ABC and sensitivity to nitrous acid. Fifty to sixty percent of the 35S-HSPG deposited into ECM do not bind aFGF. The bound 35S-HSGP (40-50% of the total counts applied) eluted from the aFGF-Affi-Gel column after the addition of buffer containing 2 M NaCl. aFGF-binding and aFGF-nonbinding 35S-HSPG were individually pooled and further purified by Sepharose CL-4B column chromatography. 35S-HSPG which bind aFGF, designated HSPGP, were 100-fold superior to heparin in augmenting the mitogenic efficacy of aFGF in sparse proliferating cultures. In contrast, however, 35S-HSPG, which did not bind aFGF, designated HSPG1, inhibited aFGF-stimulated proliferation in both sparse and subconfluent endothelial cell cultures. The majority of the biological activity of both aFGF-potentiating HSPGP and aFGF-inhibitory HSPG1 was contained in the glycosaminoglycan chains released by alkaline borohydride treatment of intact HSPGP or HSPG1, respectively. 3H-Core protein derived from HSPGP or HSPG1 contained only minor biological activity. The ability of heparitinase or heparinase (Flavobacterium heparinum) to abolish biological activity differed, depending upon the HSPG tested, also suggested that these are two distinct HSPGs.     

改构型酸性成纤维细胞生长因子对细胞增殖活性的影响

目的:研究aFGF和MaFGF对正常的肾小管上皮细胞及胃癌细胞增殖的影响。方法:用不同浓度的aFGF和MaFGF分别作用于肾小管上皮细胞及胃癌细胞,48h后采用WST-8法测定aFGF和MaFGF对两种细胞的促增殖活性。结果:在各浓度下,MaFGF组对肾小管上皮细胞和胃癌细胞的促增殖作用都显著低于aFGF组。结论:MaFGF对肾小管上皮细胞及胃癌细胞的促分裂活性较aFGF明显下降。     

Investigation of the ability of several naturally occurring and synthetic polyanions to bind to and potentiate the biological activity of acidic fibroblast growth factor

The ability of several animal, plant, and bacterial derived polyanions (PAs) as well as synthetic PAs to compete with heparin for the binding of acidic fibroblast growth factor (aFGF) was correlated with their ability to potentiate the mitogenic and neurotrophic actions of this factor. Dextran sulphate, K-carrageenan, pentosan sulphate, polyanethole sulfonate, heparin, and fucoidin competed for the heparin binding site on aFGF at relatively low concentrations (≤50 μg/ml). λ-carrageenan, ι-carrageenan, and polyvinyl sulphate exhibited lower affinity for aFGF, whereas hyaluronic acid, dermatan sulphate, chondroitin-6-sulphate, chondroitin-4-sulphate, and uncharged dextran displayed very low or no demonstrable affinity. Potentiation of the mitogenic action of aFGF for Balb/c 3T3 fibroblasts tended to be in general agreement with the aFGF binding affinity of the PAs. However, polyanethole sulfonate, the carrageenans, polyvinyl sulphate, fucoidin, and pentosan sulphate exerted a mitogenic action on the 3T3 cells that was independent of, and in addition to, the ability of these GAGs to potentiate the action of aFGF. The ability to potentiate the neurotrophic action of aFGF for E8 chick ciliary neurons was a general property of those PA with low or no activity in the mitogen assay. Thus hyaluronic acid, dermatan sulphate, chondroitin-4-sulphate, chondroitin-6-sulphate, and even uncharged dextran all potentiated aFGF induced neuronal survival. The differential effects of these PA in potentiating the biological activities of aFGF are discussed in relation to their ability to compete for the heparin-binding site of aFGF. © 1993 Wiley-Liss, Inc.     

Growth of normal human keratinocytes and fibroblasts in serum-free medium is stimulated by acidic and basic fibroblast growth factor

Keratinocytes and fibroblasts isolated from human neonatal foreskin can be plated and grown through multiple rounds of division in vitro under defined serum-free conditions. We utilized these growth conditions to examine the mitogenic potential of acidic and basic fibroblast growth factor (aFGF and bFGF) on these cells. Our results demonstrate that both aFGF and bFGF can stimulate the proliferation of keratinocytes and fibroblasts. aFGF is a more potent mitogen than bFGF for keratinocytes. In contrast, bFGF appears to be more potent than aFGF in stimulating the growth of fibroblast cultures. Heparin sulfate (10 micrograms/ml) dramatically inhibited the ability of bFGF to stimulate the proliferation of keratinocytes. In comparison, heparin slightly inhibited the stimulatory effect of aFGF and had no effect on epidermal growth factor (EGF) stimulation in keratinocyte cultures. In fibroblast cultures the addition of heparin enhanced the mitogenic effect of aFGF, had a minimal stimulatory effect on the mitogenic activity of bFGF, and had no effect on EGF-stimulated growth. Our results demonstrate that the proliferation in vitro of two normal cell types found in the skin can be influenced by aFGF and bFGF and demonstrate cell-type specific differences in the responsiveness of fibroblasts and keratinocytes to these growth factors and heparin.     

Heparin-derived oligosaccharides: affinity for acidic fibroblast growth factor and effect on its growth-promoting activity for human endothelial cells

The minimal structural requirements for the interaction of heparin with acidic fibroblast growth factor (aFGF) were investigated. Oligosaccharides (tetra- to decasaccharides) obtained by nitrous acid depolymerisation of standard heparin were separated by affinity chromatography on Sepharose-immobilised aFGF. The shortest fragment retained by the affinity column at 0.2 M NaCl and eluted at 1 M NaCl was a "regular" hexasaccharide, a trimer of the most abundant disaccharide sequence in heparin. More complex octa- and decasaccharides were also retained by the column. The oligosaccharides eluted by 1 M NaCl from the affinity column ("high-affinity" oligosaccharides) and those washed from the column at 0.2 M NaCl ("low-affinity" oligosaccharides) were compared for their capacity to protect aFGF from proteolysis and to potentiate its mitogenic activity. At a low ionic strength, all oligosaccharides tested, except the "regular" disaccharide, protected aFGF against trypsin and collagenase digestion. At higher ionic strength (greater than 0.2 M NaCl), only high-affinity oligosaccharides showed a protective effect. The high-affinity oligosaccharides (hexa- to decasaccharides) potentiated the mitogenic activity of aFGF, as measured by [3H]thymidine incorporation into DNA of human fibroblasts. The effect of the oligosaccharides on human endothelial cell proliferation was more complex: inhibition of proliferation was observed in the presence of serum and low concentrations of aFGF (1-5 ng/ml) and potentiation in the presence of higher concentrations of aFGF. The potentiating effect increased as a function of molecular size of the heparin fragments and, for a given size, as a function of the anionic charge of the oligosaccharide. Our results suggest that inhibition of cell proliferation by heparin may result from interference with an autocrine basic FGF-like activity.     

Acidic fibroblast growth factor is present in nonneural tissue: isolation and chemical characterization from bovine kidney

Endothelial cell growth factor activity purified from bovine kidney by heparin-Sepharose affinity chromatography was previously identified as basic fibroblast growth factor [Baird, A., Esch, F., B?hlen, P., Ling, N., & Gospodarowicz, D. (1985) Regul. Pept. 12, 202-213]. We now show that a major mitogenic fraction, isolated from heparin-Sepharose-purified material by Mono-S cation-exchange chromatography and reverse-phase high-performance liquid chromatography, is related to acidic fibroblast growth factor (aFGF). Sequence analysis showed the amino-terminal sequence to be Tyr-Lys-Lys-Pro-Lys-Leu-Leu-Tyr-X-Ser-Asn-Gly-Gly-Tyr-Phe-Leu-Arg-Ile-Le u-Pro- Asp-Gly-Thr-Val-Asp-. The molecular mass of the protein, as determined by polyacrylamide gel electrophoresis, was 15.5 kDa. In combination, those data strongly suggest that this mitogen is amino terminally truncated acidic fibroblast growth factor. So far, aFGF has only been found in neural tissues, i.e., in the brain and retina. Our results strongly suggest that this mitogen also occurs in extraneural tissue.     

Strategy for fluorescent labeling of human acidic fibroblast growth factor without impairment of mitogenic activity: A bona fide tracer

Here we describe, for the first time, the design and characterization of a bona fide fluorescently labeled mutant of the human acidic fibroblast growth factor (aFGF). The aFGF–Cys2 mutant was recombinantly synthesized by substituting the second amino acid with a reactive cysteine whose sulfhydryl group’s side chain reactivity facilitated the covalent binding of a fluorescent probe as a thiolyte monobromobimane. Using a combination of biophysical and functional assays, we found that the fluorescently labeled mutant aFGF is characterized by essentially the same global folding, mitogenic activity, and association behavior with heparin, its physiological activator, as the unlabeled wild-type protein. We used this new tracer protein mutant to determine the association behavior of aFGF with heparin in the presence of high concentrations of albumin that mimicked more closely the plasma medium in which aFGF is naturally located and in which it has evolved to function. By exposing the aFGF–Cys2–heparin complex to increasing concentrations of albumin up to physiological plasma levels, we were able to demonstrate that macromolecular crowding does not affect the stoichiometry of the interaction. In summary, the dimeric aFGF–Cys2–heparin complex might represent a biologically relevant complex in physiological media.     

Thrombin inactivates acidic fibroblast growth factor but not basic fibroblast growth factor

Incubation of bovine brain derived acidic fibroblast growth factor (aFGF) with bovine or human thrombin, 0.5 NIH unit/mL, for 24 h at 37 degrees C results in cleavage of the mitogen, generating a 14-kilodalton fragment which has significantly reduced affinity for immobilized heparin as compared to aFGF, and is at least 50-fold less potent at stimulating mitogenesis. In addition, an 18 amino acid peptide, aFGF(123-140), is generated, identifying one of the thrombin cleavage sites as the Arg-122/Thr-123 bond. The peptide, aFGF(123-140), is neither mitogenic itself nor an inhibitor of the mitogenic activity of aFGF. The cleavage of aFGF by thrombin is inhibited by heparin (50 micrograms/mL) and is completely blocked by the irreversible thrombin inhibitors D-Phe-Pro-Arg chloromethyl ketone and hirudin. Incubation of aFGF with 50 units/mL thrombin at 37 degrees C results in rapid cleavage of the mitogen into several fragments. In contrast, incubation of bovine brain derived basic fibroblast growth factor with 1 unit/mL thrombin for 24 h, or 50 units/mL thrombin for 6 h, does not result in significant cleavage of mitogen. The results show that the C-terminal region of aFGF is of functional importance in both mitogenesis and heparin binding. Most importantly, a novel role for anionic heparin-binding growth factors and their fragments is indicated in physiologic and pathologic situations associated with thrombin generation.     

Effect of heparin on the binding affinity of acidic FGF for the cloned human FGF receptors, flg and bek.

Heparin potentiates the mitogenic activity of acidic fibroblast growth factor (aFGF) by 20-100 fold but mechanisms detailing this potentiation have not yet been fully elucidated. We report that heparin increases the binding affinity of aFGF for the two cloned and overexpressed human FGF receptors, flg and bek, by 2-3 fold. This increase in binding affinity, together with previous data demonstrating a 3-5 fold increase in the stability of aFGF, are likely to account for a significant portion of heparin's potentiation of aFGF activity observed in biological assay systems.     

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.     

Identification of ribosome-binding protein p34 as an intracellular protein that binds acidic fibroblast growth factor

With the aim of identifying new intracellular binding partners for acidic fibroblast growth factor (aFGF), proteins from U2OS human osteosarcoma cells were adsorbed to immobilized aFGF. One of the adsorbed proteins is a member of the leucine-rich repeat protein family termed ribosome-binding protein p34 (p34). This protein has previously been localized to endoplasmic reticulum membranes and is thought to span the membrane with the N terminus on the cytosolic side. Confocal microscopy of cells transfected with Myc-p34 confirmed the endoplasmic reticulum localization, and Northern blotting determined p34 mRNA to be present in a multitude of different tissues. Cross-linking experiments indicated that the protein is present in the cell as a dimer. In vitro translated p34 was found to interact with maltose-binding protein-aFGF through its cytosolic coiled-coil domain. The interaction between aFGF and p34 was further characterized by surface plasmon resonance, giving a K(D) of 1.4 +/- 0.3 microm. Even though p34 interacted with mitogenic aFGF, it bound poorly to the non-mitogenic aFGF(K132E) mutant, indicating a possible involvement of p34 in intracellular signaling by aFGF.     

TAT-aFGF融合蛋白在大肠杆菌中的表达及其生物活性测定

构建表达Tat与人酸性成纤维细胞生长因子（acidic fibroblast growth factor, aFGF）融合蛋白的重组质粒pET3c–Tat-aFGF14-154和pET3c-Tat-aFGF27-154,并转化大肠杆菌BL21（DE3）中。37℃,l mmol/L的IPTG诱导4 hrs后,获得分子量约为18 kDa的融合蛋白,表达量分别占菌体总蛋白的42%和24%。利用阳离子交换（CM-Sepharose FF）、肝素亲和层析（Heparin-Sepharose CL-6B）以及分子筛（Sephadex G-25）联用的方法可获得纯度大于95%的目的蛋白,得率分别为93和78 mg/L。Tat-aFGF14-154及其对照蛋白aFGF14-154对Balb/c 3T3细胞有明显促细胞增殖的作用,最佳作用浓度分别为1280 ng/ml和160 ng/ml。而Tat-aFGF27-154 及其对照蛋白aFGF27-154则几乎没有促细胞增殖活性。免疫荧光分析结果表明,Tat-aFGF14-154及Tat-aFGF27-154均能穿过PC12、Balbc/3T3、HaCaT和海马神经元细胞的细胞膜,并主要定位于细胞浆中。此外,四种重组蛋白均能降低Aβ25-35对大鼠海马神经元细胞的毒性,在剂量为1000 ng/ml时,Tat-aFGF14-154、Tat-aFGF27-154、aFGF14-154及aFGF27-154细胞存活率分别为90.66%、81.87%、85.71%和78.02%,而Aβ25-35模型组的存活率仅为56.87%。     

Characterization of acidic and basic fibroblast growth factors in brain, retina and vitreous chick embryo

We have purified acidic and basic fibroblast growth factors (c-aFGF, c-bFGF) from 11 day-old chick embryo brain, retina and vitreous by heparin-Sepharose chromatography and reverse phase HPLC. The analysis of their biological activity as well as their molecular weight indicates that they were analogous to basic or acidic human and bovine FGF. The ratio of c-aFGF to c-bFGF activity depended of the tissue. In brain c-aFGF represented 66% of the total mitogenic activity retained on the heparin-sepharose column and c-bFGF 34% while retina contained 16% of c-aFGF and 84% of c-bFGF; vitreous 78% of c-aFGF and 22% of c-bFGF. Like human aFGF, Heparin stimulated purified c-aFGF mitogenic activity in the absence of serum but inhibited the activity of the retina acid soluble extract, in the presence of foetal calf serum (FCS). Thus, chick embryo and adult human acidic and basic FGF respectively share the same biochemical properties. Since there are no blood vessels in chick retina or vitreous, their presence in these tissues suggests that angiogenesis is not the only role of these growth factors.