Distribution of basic fibroblast growth factor binding sites in various tissue membrane preparations from adult guinea pig

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Fibroblast growth factor receptor (FGFR)-1 and -2 in the ovine corpus luteum throughout the estrous cycle

Fibroblast growth factors (FGFs) probably play an important role in development and maintenance of the vasculature of the corpus luteum (CL). The objective of the present study was to evaluate the distribution and levels of fibroblast growth factor receptors (FGFRs) in the ovine CL from the early, mid- and late stages of the estrous cycle. Presence of FGFR-1 and -2 receptors was evaluated in CL by using Western analysis, immunohistochemistry and topical autoradiography. Western analysis demonstrated that the levels of FGFR-1 and -2 were similar in the early and mid-cycle CL but increased (p < 0.05) in the late stage of the estrous cycle. Immunohistochemistry and topical autoradiography demonstrate that both parenchymal (steroidogenic) and nonparenchymal (e.g. endothelial, fibroblastic) cells express FGFR-1 and -2. FGFR-1 was localized to the luteal vasculature throughout the estrous cycle; in the parenchymal cells, it was present during mid-cycle but was barely detectable in the late stage. Conversely, FGFR-2 was present in the parenchymal cells at all stages of the estrous cycle but localized to the larger microvessels only at the late stage. These data demonstrate that FGF receptors are present in the parenchyma as well as the vasculature of the CL which suggests that FGF is involved in the regulation of luteal parenchymal and vascular function.

Repair of Chronic Tympanic Membrane Perforations with Fibroblast Growth Factor

A number of angiogenic growth factors have been shown to accelerate wound healing. Previous work has demonstrated that topical application of epidermal growth factor is effective in healing chronic tympanic membrane perforations in an animal model. Theoretically, fibroblast growth factor may result in a superior healed membrane through preferential stimulation of the fibroblasts within the middle layer of the tympanic membrane. To test this hypothesis, the effects of exogenously applied fibroblast growth factor on the chronically perforated tympanic membrane were evaluated. A buffered solution of fibroblast growth factor (25 μl of fibroblast growth factor, 0.2 mg/ml) was administered to a Gelfoam pledget placed over chronic tympanic membrane perforations in chinchillas. Control ears were treated with Gelfoam and the buffer solution only. Complete closure of the tympanic membrane perforation was observed in 81% (13 of 16) of the fibroblast growth factor-treated ears, but in only 41% (7 of 17) of the controls ( p = 0.05). Healing took place gradually, requiring an average of 4 weeks for the fibroblast growth factor-treated and 6.5 weeks for the control ears that healed. The relatively high healing rate for the control group does not imply that the pretreatment perforations were not chronic, rather there appears to be some efficacy to the control protocol of repeated applications of Gelfoam and buffer. A histologic analysis of the fibroblast growth factor-healed eardrums immediately after closure demonstrated hypertrophy of the squamous and fibrous layers of the tympanic membrane. Over time, the eardrum thinned to reach proportions similar to those of the normal tympanic membrane, including the presence of a substantial middle fibrous layer. A screening ototoxicity study revealed no structural damage to the organ of Corti after growth factor treatment. To assess the potential for systemic toxicity, blood and peripheral tissues were analyzed for radioactivity at time points during a 48-hour period after application of 25 μl of 125l-fibroblast growth factor to the perforated tympanic membrane. More than 78% of the radioactivity remained at the application site. Given the tiny original dosage, the small fraction absorbed systemically is minuscule and highly unlikely to induce adverse effects in light of published toxicity data. On the basis of these promising safety and efficacy data in the chinchilla model, clinical trials of fibroblast growth factor in repair of chronic tympanic membrane perforations in human beings are being initiated.

Visualization of several binding sites for basic fibroblast growth factor (FGF-2) on fibroblasts by photoaffinity labeling: evidence for intracellular complexes

The internalization of basic fibroblast growth factor (FGF-2) was studied in Chinese hamster lung fibroblasts (CCL39). Recombinant FGF-2 was derivatized with a photoactivable agent, N-hydroxysuccinimidyl-4-azidobenzoate (HSAB), iodinated, and used to visualize intracellular FGF-2-affinity-labeled molecules after internalization at 37 degrees C. Iodinated HSAB-FGF-2 maintained the properties of natural FGF-2 such as affinity for heparin, binding to Bek and Fig receptors, interaction with high- and low-affinity binding sites, and reinitiating of DNA synthesis in CCL39 cells. Affinity-labeling experiments at 4 degrees C with 125I-HSAB-FGF-2 led to the detection of several FGF-cell surface complexes with apparent molecular mass of 80, 100, 125, 150, 170-180, 220, 260, and about 320 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), whereas two specific bands at 80 and 130-160 kDa were obtained using the homobifunctional cross-linking reagent, disuccinimidyl suberate. When the cells, preincubated with 125I-HSAB-FGF-2 at 4 degrees C and then washed, were shifted to 37 degrees C, irradiation of the internalized labeled FGF-2 led to detection of a similar but fainted profile with one major specific band at 80 kDa. Heparitinase II treatment of the cells reduced binding of 125I-HSAB-FGF-2 to its cell surface sites by 80% and internalization by 55%, indicating the involvement of heparan sulfate proteoglycans in these processes. Among the heparitinase-sensitive bands was the 80-kDa complex.

A rapid, high capacity assay for basic fibroblast growth factor binding

A rapid, high capacity assay for the binding of basic fibroblast growth factor has been developed. Rat lung tissue was selected as the optimum source of membranes and 2M sodium chloride used to remove endogenous growth factor. The assay has been adapted to the Millipore Multi-Screen system so that it can be run in 96-well format with a volume of 300 microliters. The assay has been validated through the demonstration of inhibition by standard inhibitors such as suramin and protamine sulfate. The assay has proven useful for the screening of random compounds as well as the more detailed examination of suspected inhibitors. By running compounds in the presence and absence of a mid-range concentration of unlabeled bFGF, an estimate of the proportion of the inhibition due to high affinity binding can be obtained. Suramin and protamine sulfate show no selectivity and inhibit high affinity binding and overall binding with similar potencies. Another inhibitor, dimercaptothiadiazole, is more potent against high affinity binding.

Interaction of fibroblast growth factor with turkey embryonic myoblasts and myogenic satellite cells

1. The interaction of fibroblast growth factor (FGF) with receptors on clonal-derived turkey embryonic and posthatch muscle cells was compared using saturation isotherms. 2. At least two binding sites, including a high affinity receptor and sites of low affinity, which are likely heparin sulfate proteoglycans, were observed on both embryonic myoblasts (EM) and myogenic satellite cells (SC). 3. The FGF binding affinities (Kds) were similar between SC and EM. Receptor Kds were also similar between SC derived from turkeys both selected and unselected for rapid, growth and skeletal muscle accretion rates.

Biphasic effect of basic fibroblast growth factor on 125I-human chorionic gonadotropin binding to cultured immature Leydig cells

The present studies examined the effects of basic fibroblast growth factor (bFGF or FGF-2) on 125I-human chorionic gonadotropin (hCG) binding to cultured immature rat Leydig cells. We found that low concentrations of bFGF (0.1-1.0 ng/ml) inhibited 125I-hCG binding to cultured immature Leydig cells in a dose- and time-dependent manner; however, this inhibition was reversed partially at higher bFGF concentrations (10-200 ng/ml). The decline in 125I-hCG binding by bFGF was due to a reduction in the number of binding sites per cell and not to a change in receptor affinity for the ligand. The inclusion of 10 micrograms/ml heparin (a concentration that is reported to block bFGF binding to heparan sulfate proteoglycans) with increasing bFGF concentrations had no effect on the inhibition of 125I-hCG binding by low bFGF concentrations, but completely blocked the secondary increase in binding by higher bFGF concentrations. In addition, neither varying heparin concentrations (0.1-25 micrograms/ml) nor insulin or insulin-like growth factor-I had any effect on the inhibition of 125I-hCG binding by 1 ng/ml bFGF. These studies suggest that receptor-mediated actions of bFGF (inhibition of hCG binding by low bFGF concentrations) on cultured immature Leydig cells are unaffected by heparin; however, the secondary increase in 125I-hCG binding observed with higher bFGF concentrations (mediated by bFGF binding to heparan sulfate proteoglycans) is blocked by heparin.

Purification of a heparin binding FGF receptor (HB-FGFR) from adult bovine brain membranes

A new form of high affinity fibroblast growth factor receptor has been purified from adult bovine brain membranes. Purification was performed by chromatography on DEAE-Trisacryl and wheat germ agglutinin-agarose followed by FGF-2 affinity chromatography. Affinity labeling of purified fractions with 125I-FGF-2 showed after cross-linking a 170-kDa complex, suggesting the existence of a 150-kDa FGF receptor. No cross-reactivity with anti-FGF receptor 1 (FGFR-1 or flg) or with anti-receptor 2 (FGFR-2 or bek) antibodies could be detected with this partially purified receptor. Heparitinase treatment of the partially purified FGF receptor abolished the formation of the ligand receptor complex. The complex was restored in the presence of heparin in a dose dependent fashion, supporting the idea that heparin-like molecules are needed for proper binding. Further purification of the receptor was achieved by heparin-Sepharose affinity chromatography and yielded a purification of over 320,000-fold. The purified receptor fraction was radiolabeled and loaded on RPLC C4 column. Eluted fractions were analysed by SDS-PAGE. A major 150-kDa band was detected. These data show for the first time a new form of FGF receptor isolated from bovine brain membranes. This purified receptor displays affinity for heparin and was therefore named heparin binding FGF receptor (HB-FGFR). It remains unclear whether the receptor is a proteo-heparin sulfate or whether heparans are strongly associated and therefore are copurified. Large scale preparations are in progress for core protein structure studies.

Purification of an active receptor for acidic and basic fibroblast growth factor from bovine retina

Acidic and basic fibroblast growth factors (FGFs) influence cell division and differentiation in retina cells. Their effects are thought to be mainly mediated through stimulation of a specific membrane receptor and subsequent generation of an intracellular signal pathway. In this study, we purified a FGF receptor of 130 kDa from bovine neural retina using wheat germ agglutinin affinity chromatography followed by FGF-affinity chromatography. The isolated receptor showed ligand binding activity with dissociation constants of 0.8 nM and 2 nM for aFGF and bFGF, respectively. Furthermore, binding of aFGF and bFGF to purified receptor resulted in self-phosphorylation, demonstrating that the isolated receptor had an unaltered intrinsic kinase activity.

Basic fibroblast growth factor induces proliferation of a rat pancreatic cancer cell line. Inhibition by somatostatin

AR4-2J, a rat pancreatic acinar-tumor cell line, was used to investigate long-term effects of basic fibroblast growth factor (bFGF) and somatostatin on pancreatic cancer cells. We observed that bFGF stimulated cell proliferation when cells were cultured in serum-free medium. The effect was dose-dependent with half-maximal and maximal effects at 25 pM and I nM bFGF, respectively. The somatostatin analog SMS 201-995 (SMS) decreased the growth-promoting effect of bFGF. The maximal effect was observed at I nM SMS and the half-maximal effect at 20 pM SMS. Characterization of bFGF receptor-binding properties with [125I]bFGF revealed that AR4-2J cells exhibited 2 classes of bFGF binding site with respective KD values of 47 pM and 3 nM and binding capacities of 14 fmol and 0.9 pmol/10(6) cells. High-affinity receptors correlated with bFGF stimulation of AR4-2J cell growth, suggesting that the effects of bFGF are receptor-mediated.

High and low affinity membrane binding sites for fibroblast growth factors in the developing chick brain

Acidic and basic fibroblast growth factors (aFGF and bFGF), two mitogenic, neurotrophic and angiogenic molecules, are present in the embryonic chick brain but their function remains unclear. In order to approach the biological activity of FGFs during brain development, we have looked for their receptors and studied their regulation through chick brain development. Competitive binding studies realized on brain membranes indicated the presence of two classes of FGF binding sites: high affinity binding sites (dissociation constant, Kd = 100 pM) and low affinity binding sites (Kd = 20 nM). Cross-competition experiments show that these two classes of binding sites both interact with aFGF and bFGF. The number of sites in these two classes of binding sites changes during embryogenesis. On the one hand, the membrane capacity of high affinity sites decreases from E7 (1 +/- 0.2 pmol/mg of protein) to E15 (0.5 +/- 0.2 pmol/mg of protein); on the other hand, the membrane capacity of low affinity sites increases from E15 (25 +/- 4 pmol/mg of protein) to P1 (75 +/- 20 pmol/mg of protein). Cross-linking experiments revealed the presence of two putative receptor forms of molecular masses of about 130 and 95 kDa. These results suggest that the biological activity of aFGF and bFGF during brain embryogenesis could be regulated by the expression of high and low affinity binding sites for these growth factors.

Interactions of FGFs with target cells

Growth factors play a key role in cellular communication, a necessary step for the development of pluricellular organisms. The fibroblast growth factors (FGF) are among these polypeptides and have seven known members: FGF 1 to FGF 7 which are also known as acidic FGF, basic FGF, translation products of oncogenes hst, int 2, FGF 5, FGF 6 and FGF 7 or keratinocyte growth factor (KGF) respectively [1]. The best known and the most abundant in normal adult tissues are acidic and basic FGFs, or FGF 1 and 2 respectively, which have been subjected to extensive studies both in vitro and in vivo. These two factors have almost ubiquitous distribution and a wide spectrum of biological activity including action on cellular proliferation and differentiation, as well as neurotrophic and angiogenic properties [1]. These different activities are induced by triggering specific receptors present at the surface of the target cell. Following this interaction, the FGF-receptor complexes are internalized and activate intracellular pathways. An important effort of investigations has been produced to characterize these receptors and intracellular pathways. It is the purpose of this review to present this work which will focus on FGFs 1 and 2. The existence of two classes of interactions has been reported as early as 1987 [52, 53, 54] suggesting the presence of high and low affinity receptors for FGFs.

Enhanced MYCN oncogene expression in human neuroblastoma cells is associated with altered FGF receptor expression and cellular growth response to basic FGF

We have examined the effect of human basic fibroblast growth factor (bFGF) on the proliferation of human neuroblastoma cells with normal and enhanced MYCN oncogene expression. bFGF stimulated the proliferation of the neuroblastoma cells with enhanced, but not normal, MYCN expression. Both cell species express FGFR-1, but not FGFR-2, receptors and both harbor FGF receptor species of Mr 145.000, but they differ in their pattern of lower and higher-molecular weight FGF receptor species. Our results demonstrate that enhanced MYCN expression confers to neuroblastoma cells the ability to respond to bFGF, possibly by inducing functional FGF receptors. This mechanism may contribute to the advanced malignant phenotype of human neuroblastomas with enhanced MYCN expression.

Biotinylated basic fibroblast growth factor is biologically active

Basic fibroblast growth factor (bFGF) was modified by biotinylation via amino group substitution, using biotin-N-hydroxysuccinimide ester at molar reaction ratios of 20, 200, and 2000 per bFGF molecule (respectively named bio-bFGF.20, bio-bFGF.200, and bio-bFGF.2000). The biotinylated bFGF derivatives, bio-bFGF.20 and bio-bFGF.200, conserved the same affinity for heparin as native bFGF, in contrast to bio-FGF.2000 which lost this property. Bio-bFGF.20 and bio-bFGF.200 were as effective as native bFGF in their capacity to compete with 125I-bFGF for binding to bFGF receptor on bovine brain membranes. The biological activity of these bFGF derivatives was tested on CCL39 cells; bio-bFGF.20 and bio-bFGF.200 were as able as native bFGF to promote growth of CCL39.

Acidic fibroblast growth factor is present in regenerating limb blastemas of axolotls and binds specifically to blastema tissues

The growth of regenerating limbs of amphibians depends upon proliferation of the blastema cells that accumulate beneath the epidermal cap. The epidermal cap is known to be mitogenic for the blastema cells. We have extracted a mitogenic activity from both the mesenchymal and epidermal (epidermal cap) components of cone stage blastemas which is retained on heparin-Sepharose and elutes with 1.15 M NaCl. This fraction stimulates neurite outgrowth of PC12 cells and [3H]thymidine incorporation into CCL 39 cells and is potentiated by heparin. The 2 M fraction was inactive. The heparin-Sepharose-purified growth factor cross-reacts with bovine acidic FGF polyclonal antibodies and shows a Mr of 16,000 on Western blots. Blastema membranes contain specific high affinity binding sites (Kd = 25 pM; capacity = 30 fmole/mg protein) and low affinity binding sites (Kd = 18 nM; capacity = 30 pmole/mg protein) for aFGF as revealed by Scatchard analysis. 125I-aFGF which is bound specifically by both the epidermal cap and mesenchyme of blastema frozen sections is displaced by an excess of unlabeled factor and inhibited by heparin. Heparinase treatment and 2 M NaCl washing which decreased the binding was fourfold more efficient for epidermal cap than for mesenchyme suggesting the presence of high affinity receptors in the latter tissue. The presence of aFGF (or a closely related molecule) in blastemas is consistent with our earlier results that showed stimulation of proliferation of cultured blastema cells by acidic or basic FGF or heparin alone. These results suggest the possibility that aFGF is stored in the epidermal cap during limb regeneration and that it stimulates the proliferation of the underlaying mesenchyme.

Effects of fibroblasts and basic fibroblast growth factor on facilitation of dermal wound healing by type I collagen matrices

Healing of large open dermal wounds is associated with decreased values of the tensile strength even up to 6 months post-wounding. Results of previous studies have shown that healing is facilitated in the presence of a type I collagen sponge by promoting deposition of newly synthesized large-diameter collagen fibers parallel to the fibers of the sponge. In this study healing is evaluated in dermal wounds treated with a collagen sponge seeded with fibroblasts or coated with basic fibroblast growth factor (bFGF). Experimental results indicate that the presence of a collagen sponge results in increased wound tensile strength and increased collagen fiber diameters in the upper dermis 15 days post-wounding in an excisional guinea pig dermal wound model. In comparison, dermal wounds treated with collagen sponges seeded with fibroblasts or coated with bFGF showed increased tensile strengths 15 days postimplantation and increased degree of reepithelialization. These results indicate that fibroblast seeding and bFGF coating in conjunction with a type I collagen sponge matrix facilitate early dermal and epidermal wound healing.

High affinity receptors to acidic and basic fibroblast growth factor (FGF) are detected mainly in adult brain membrane preparations but not in liver, kidney, intestine, lung or stomach

We have previously shown that only adult brain contained a detectable amount of high affinity receptors for basic Fibroblast growth factor (bFGF) whereas adult liver, kidney, lung, intestine or stomach showed only low affinity binding sites. We now have studied and compared the distribution of the receptors for acidic Fibroblast growth factor (aFGF) with that of bFGF receptors in the same tissues. Membrane binding of 125I-aFGF was time dependent, reversible and displaced by an excess of unlabeled aFGF. Scatchard analyses of binding data obtained with all tissue membrane preparations revealed the presence of at least one class of low affinity/high capacity interaction sites characterized by apparent Kd values ranging from 3.9 to 6.9 x 10(-8) M. Interestingly and as for bFGF, high affinity receptors for aFGF could be detected only in adult brain membranes. Cross-linking and Scatchard analyses indicate that this family of interaction was characterized by four molecular species of 175, 125, 95 and 70 kDa and by an apparent Kd value of 1.8 x 10(-10) M. Moreover, cross-competition binding assay revealed that these brain high affinity receptors were common for both acidic and basic FGF. These results suggest that these growth factors may share identical functions mediated by the same receptors highly expressed in the brain. Using a cDNA probe for the Bek form of FGF receptors, we were able to show that all the tissues studied expressed this mRNA (4.5 kb transcript) but probably not in sufficient amounts to account for the number of high affinity receptors that we detected only in the brain.

Smooth muscle cell growth factors

While the roles of the platelet-derived growth factors (PDGFs) in vascular smooth muscle cells (SMCs) continue to be elucidated, these cells, especially in their activated 'synthetic' state, have also been found to express, and proliferate in response to, many of the other families of polypeptide growth factors, such as the fibroblast growth factors. Other stimulators of DNA synthesis, and particularly of SMC hypertrophy, include the vasoconstrictor hormones such as angiotensin II, as well as physical forces, especially stretch or tension. For many of these ligands, multiple receptors have been identified and their means of signal transduction are being characterized rapidly. Regulatory regions of these genes are being identified as are transcription factors. Complex post-transcriptional regulation has also been shown by the findings that some growth factors are phosphorylated, or translocated to the nucleus or the extracellular matrix. Inhibitors have also been identified. These include some prostaglandins, calcium antagonists, agonists that activate guanylate and adenylate cyclases, inhibitors of angiotensin-converting enzyme, interferon gamma, and heparin. Future studies are likely to show that tyrosine phosphatases and recessive oncogenes also regulate growth. The existence of so many autocrine/paracrine mitogens--together with some experimental data--suggests some redundancy in the system as well as some additive effects. Redundancy may limit the efficacy of antibodies to a single growth factor to block cell proliferation. Their evolutionary conservation implies some unique roles for each growth factor but these have not been apparent from in vitro studies to date. Further insights are apt to come from the increasing recognition that growth factors have other effects--on cell attachment, migration, survival, production of extracellular matrix, thrombosis, vaso-constriction, regulation of cytokine synthesis, and inhibition of growth. Many of these effects may prove to be context-dependent, as with the case of growth inhibition by transforming growth factor-beta. Studies in monolayer cultures may not obtain the same results as studies using cocultures of endothelial and smooth muscle cells, or 3-dimensional matrix cultures, organ cultures, or in the intact animal. In vivo descriptive studies of growth factors expressed in vascular embryogenesis, hypertension, atherosclerosis, acute balloon injury and thrombosis are being supplemented by interventions such as infusions with growth factors, antibodies, and toxin conjugates. These studies, and studies using transgenic mice and homologous recombination, should yield information as to mechanisms and may also suggest new therapies.

Evidence of high and low affinity binding sites for basic fibroblast growth factor in mouse placenta

The placenta has been shown to contain bFGF, but the presence of specific binding sites for this growth factor in this tissue remained to be established. In order to study the role of bFGF in the placenta growth, we looked for specific binding sites on mouse placental cell membranes at days 12, 14, 16, and 18 of pregnancy. At day 12, Scatchard analyses indicated that two classes of specific interaction sites for bFGF were detected. One class of high affinity binding sites was characterized by an apparent Kd of 10 pM and a binding capacity of 10 fmoles per mg of membrane protein. A second class of low affinity binding sites was detected with an apparent Kd of 60 nM and a binding capacity of 26 pmoles per mg of membrane protein. At days 14, 16 or 18, Scatchard analyses only showed low affinity binding sites with an apparent Kd of 24 nM and a binding capacity of 230 pmoles per mg of membrane protein. The characterization of these binding sites was performed by cross linking experiments that revealed two forms of specific complexes. This result suggested that the high affinity binding sites correspond to putative receptors with relative molecular masses equal to 65,000 and 85,000. The dramatic decrease of the high affinity receptor number after the 12th day of pregnancy, which is synchronous with the 9-fold increase of the low affinity binding site number, suggests that the biological activity of bFGF could be regulated by a balance between both the numbers of high and low affinity binding sites on placenta cell membranes. Thus, as it was shown for other growth factors, bFGF could only be involved at specific pregnancy stages.

Detection of the basic fibroblast growth factor low affinity binding site in cardiac sarcolemmal vesicles

Bovine cardiac sarcolemmal (SL) vesicles contain basic fibroblast growth factor (bFGF)-binding proteins. Binding to native SL vesicles was specific and saturable with a Kd of 6.9 nM and a Bmax of 15.2 pmoles bFGF/mg vesicle protein. Using radioiodinated bFGF as a probe, autoradiography of SL proteins subjected to SDS-PAGE and electroblotting onto nitrocellulose revealed a set of 3-4 bands, of an apparent molecular weight of 100-150 kDa. bFGF binding to these bands was reduced by pretreatment of SL vesicles with heparinase. Binding was abolished by treatment of blot strips with heparinase or high salt concentrations (greater than 0.6 NaCl) but not endoglycosidase F. bFGF-binding activity remained associated with the membrane fraction following an alkaline wash, which removed peripheral membrane proteins. These data suggest that the cardiac SL contains an integral proteoglycan(s) which may be a low affinity binding/storage site of endogenous bFGF.