Fibroblast growth factor receptor deficiency in dystrophic retinal pigmented epithelium

The retinal pigmented epithelium (RPE) is known to be site of the primary lesion in inherited retinal dystrophy in the Royal College of Surgeons (RCS) rat, a model for retinitis pigmentosa. Although the only functional defect so far detected in these cells is their failure to efficiently phagocytose shed photoreceptor outer segment debris, the actual cause of photoreceptor cell death is still unknown. Recently the possibility of “trophic factors” important in photoreceptor survival produced by normal RPE but not by dystrophic RPE has been suggested. Hence we decided to investigate the presence and abundance of two candidate diffusible factors, the acidic and basic fibroblast growth factors (aFGF and bFGF, respectively), as well as their high affinity cell surface receptors (FGF-R). mRNA was isolated from primary cultures of purified normal and dystrophic RPE and analyzed by PCR amplification using specific oligonucleotide primers for aFGF and bFGF: the size and abundance of amplified fragments was similar for both cell types. Also, aFGF protein, detected by immunocytochemistry using specific antisera, appeared to be present in approximately equal amounts and distributed in a similar pattern. However, scatchard analysis of radio-labelled bFGF binding to primary cultures of normal and dystrophic rat RPE revealed that dystrophic RPE possess only 29% the number of surface receptors compared to congenic normal cells. Furthermore, the level of expression of FGF-R2 mRNA, but not that of FGF-R1, was significantly different. Other parameters measured (receptor affinity, profile of ligand internalization and degradation, receptor molecular weight and mitogenic activity) did not show any significant differences between normal and dystrophic RPE. The precise role of FGF-R deficiency in the etiology of the disease hence remains to be determined, but it indicates the importance of trophic factors in the normal functioning of the retina. © 1993 Wiley-Liss, Inc.     

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.     

Modulation of growth of human carcinoma SW-13 cells by heparin and growth factors

This study reports on the effects of heparin, basic and acidic fibroblast growth factors (bFGF and aFGF, respectively), and transforming growth factor type-e (TGFe) on the growth of a human adrenocortical carcinoma cell line, SW-13. Heparin has previously been shown to inhibit growth in several cell types, including smooth muscle cells, certain fibroblasts, and epithelial cells, and to modulate the effects of fibroblast growth factors. Whereas bFGF and aFGF bind tightly to heparin and elute from a heparin-Sepharose column with 2 M NaCl and 1.6 M NaCl, respectively, TGFe binds to heparin with lower affinity and can be eluted from heparin-Sepharose column with 0.5 M NaCl. TGFe is a polypeptide unrelated to FGF, is present in neoplastic and nonneoplastic tissues, and stimulates the growth of certain epithelial cells and fibroblasts in soft agar and monolayer. Since the growth of SW-13 cells is stimulated by TGFe and by bFGF, we hypothesized that heparin would inhibit the growth of SW-13 cells by binding to these growth factors and that the effects of heparin could be overcome with the addition of either growth factor. Our experiments confirmed that heparin inhibits the growth of SW-13 cells. A dose-dependent growth inhibition was observed in both monolayer and soft agar. The inhibition in monolayer was partially reversed upon heparin withdrawal. The effects of heparin in both monolayer and soft agar were at least partially overcome by TGFe and by basic or acidic FGF. Overall protein synthesis does not appear to be affected by heparin as measured by [35S]methionine uptake. In contrast, epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) were unable to overcome heparin-induced inhibition both in monolayer and in soft agar. Heparin also inhibited [3H]thymidine incorporation in AKR-2B and partially inhibited AKR-2B cell stimulation by TGFe; however, it further potentiated the already potent stimulation by bFGF. We propose that heparin, TGFe, bFGF, and aFGF modulate the growth of SW-13 cells and possibly of other epithelial cells in complex ways and that heparin-like substances present in the extracellular matrix play an important role in the control of epithelial growth.     

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.     

Fibroblast growth factor phosphorylation and receptors in rod outer segments.

Acidic and basic fibroblast growth factors (aFGF and bFGF) have been isolated and purified from rod outer segments (ROS). aFGF is tightly bound to ROS membranes and can be specifically released by ATP. We show that this mechanism is dependent on the phosphorylation of aFGF itself. Phorbol 12-myristate 13-acetate (PMA) enhances this phenomenon independently of rhodopsin phosphorylation. This demonstrates that aFGF release from ROS membranes is dependent on its phosphorylation by endogenous kinase C. In addition specific binding sites for exogenous FGFs have been identified on ROS and disc membranes. A single high affinity site with a Kd of 40 pM was present in intact ROS while an additional low affinity site with a Kd of 300-600 pM was present in leaky ROS or in disc membranes. Light or ATP modified neither these Kd nor the apparent number of sites. The presence of specific receptors for FGFs and the kinase C dependent release of endogenous membrane bound aFGF suggest an autocrine mechanism which may be involved in photoreceptor cell biology.     

Heparin modulation of the neurotropic effects of acidic and basic fibroblast growth factors and nerve growth factor on PC12 cells

Nerve growth factor (NGF) and acidic or basic fibroblast growth factor (aFGF and bFGF, respectively) induce neurite outgrowth from the rat pheochromocytoma cell line, PC12. The neurites induced by these three factors are stable for up to a month in cell culture in the continued presence of any of the above growth factors. bFGF (ED50 = 30 pg/ml) is 800 fold more potent in stimulating neurite outgrowth than aFGF (ED50 = 25 ng/ml) and 260 fold more potent than NGF (ED50 = 8 ng/ml). While the neurotropic activities of aFGF and NGF are potentiated by heparin, that of bFGF is both partially inhibited or stimulated, depending upon the concentration of bFGF. Radioreceptor binding experiments show that aFGF and bFGF bind to a common binding site on the PC12 cell surface. Affinity labeling studies demonstrate a single receptor with an apparent molecular weight of 145,000 daltons, which corresponds to the high molecular weight receptor identified in BHK-21 cells. NGF does not appear to compete with aFGF or bFGF for binding to the receptor. Heparin blocked the binding of bFGF to the receptor but had only a small inhibitory effect on the binding of aFGF to the receptor. Thus, it appears that heparin inhibition of the neurotropic effects of bFGF occurs, at least in part, by impairing the interaction of bFGF with the receptor, while having little effect on that of aFGF. The stimulatory effects of heparin on the neurotropic activity of aFGF, bFGF, and NGF may occur through a site not associated with the respective cellular receptor for the growth factors.     

Basic fibroblast growth factor expression in human omental microvascular endothelial cells and the effect of phorbol ester.

The human omentum contains a potent, not yet identified angiogenic activity. The omentum is very vascularized. Therefore, we investigated whether human omental microvascular endothelial cells (HOME cells) express the angiogenic peptide basic fibroblast growth factor (bFGF). Cytosol prepared from HOME cells stimulated DNA synthesis in bovine epithelial lens cells (BEL cells). The mitogenic activity could be neutralized by an anti-bFGF antibody. Basic FGF-like material from the HOME cell cytosol was bound onto a heparin-Sepharose column at 0.6 M and was eluted at 3 M NaCl. The 3 M NaCl eluted material reacted with the specific anti-bFGF antibody in an ELISA and stimulated DNA synthesis. It did not react with a specific anti-acidic fibroblast growth factor (aFGF) antibody. Western blotting experiments using the same bFGF antibody showed the presence of a major band of 17 Kd and a doublet of 20-22 Kd. Northern blotting of non-stimulated HOME cells using a specific 1.4 kb bFGF probe showed the presence of 5 molecular species of 6.6, 3.7, 2.2, 2.0, and 1.0 kb. No aFGF mRNA was detected with a specific previously characterized 4.04 kb probe. 12-O-tetradecanoylphorbol 13-acetate (TPA) did not influence significantly the expression of bFGF at the protein and mRNA level in HOME cells. Thus, protein kinase C activation by TPA did not appear to modulate significantly the expression of bFGF for that cell type. Contrastingly, human umbilical vein endothelial cells (HUVE cells), which expressed no bFGF and aFGF mRNA at a basal level, were induced to express bFGF but not aFGF mRNA when stimulated by TPA. These results suggest that the described angiogenic activity could be the bFGF-like mitogen contained in HOME cells and that these cells are different from endothelial cells derived from large vessels (HUVE cells) regarding the expression of bFGF.     

Basic and acidic fibroblast growth factors modulate the epidermal growth factor receptor by a protein kinase C-independent pathway

Human acidic and basic fibroblast growth factors (aFGF and bFGF) inhibit epidermal growth factor (EGF) receptor binding in mouse Swiss 3T3 cells. Scatchard analysis indicates that aFGF and bFGF cause a decrease in the high affinity EGF receptor population, similar to that observed for activators of protein kinase C such as phorbol esters, platelet-derived growth factor (PDGF) and bombesin. However, unlike phorbol esters, aFGF and bFGF inhibit EGF binding in protein kinase C-deficient cells. The time course and dose response of inhibition of EGF binding by both aFGF and bFGF are very similar, with an ID50 of approximately 0.10 ng/ml. In contrast to bombesin but like PDGF, neither aFGF nor bFGF act on the EGF receptor through a pertussis toxin-sensitive G protein. These results indicate that both acidic and basic FGF depress high affinity EGF binding in Swiss 3T3 cells with similar potency through a protein kinase C/Gi-independent pathway.     

Visual arrestin modulates gene expression in the retinal pigment epithelium: Implications for homeostasis in the retina

The retinal pigment epithelium (RPE) is essential for maintaining retinal homeostasis by removing and recycling photoreceptor outer segment (POS) in membranes. It also produces and secretes growth factors involved in retinal homeostasis. Arrestin 1 (ARR1) is specifically expressed in photoreceptors (PRs) and a vital molecule for keeping visual cycle between PRs and RPE. In the present study, we showed the expression of ARR1 was decreased by form-deprivation (FD) in retina of rat. The ARR1 was detected in the RPE of the controls but not in the RPE of FD, which indicates RPE phagocytes POS containing ARR1. Furthermore, we overexpressed ARR1 in cultured human RPE and revealed the ARR1 upregulates bFGF expression and downregulates TGF-β1, -β2 and bone morphogenetic protein-2 (BMP-2). The upregulation of bFGF by ARR1 directly works for PR survival and the downregulation of TGF-βs by ARR1 inhibits epithelial mesenchymal transition (EMT) of RPE, which is the underlying mechanism of keeping retinal homeostasis. Our results also indicate the regulation of ARR1 expression in RPE might become a novel therapeutic option for various ocular diseases.     

Cell fate decisions in a human retinal precursor cell line: basic fibroblast growth factor- and transforming growth factor-alpha-mediated differentiation

The purpose of this study was to determine if immortalized human retinal precursor cells could serve as a model to investigate cues that modulate cell fate and differentiation. We investigated the effects of a variety of growth factors broadly but specifically tested the effects of basic fibroblast growth factor (bFGF) and transforming growth factor (TGF)a in retinal cell differentiation and commitment. To determine the role of exogenously added growth factors in a human retinal precursor cell line (KGLDMSM), established from a first-trimester retina, cells were adapted to grow in a defined medium and exposed to a variety of trophic factors (epidermal growth factor [EGF], neuron growth factor [NGF], TGFalpha, TGFbeta, acidic FGF, and bFGF). Dose-response curves were developed to arrive at optimal concentrations. The neurotrophic potential of growth factors was determined by 3H-thymidine incorporation and bromodeoxyuridine (BrdU) labeling. The identity of the emerging neuronal phenotypes were determined by phase-contrast microscopy, immunolabeling for the neuron-specific antigens neurofilament protein (NF) and neuron-specific enolases (NSE), and photoreceptor-specific antigens (Rho1D4, 7G6) using immunocytochemistry and Western blot analysis. To identify some of the early response genes (c-fos, c-myc) expressed in response to growth factors, Northern blot analysis was performed. Almost all of the factors tested increased the total number of cells with a neuronal phenotype. Potency of growth factors to generate neurons was TGFalpha > bFGF > EGF > NGF. Both TGFalpha and bFGF, alone or in combination, increased the total number of neurons. Most of the neurons generated were photoreceptors, as depicted by the polarized phenotype, expression of photoreceptor-specific antigens, and processes resembling rudimentary outer segments. The increase in photoreceptor-like neurons is possibly attributable to an increase in numbers rather than greater survival. Additionally, the majority of the photoreceptors generated labeled with BrdU and for photoreceptor-specific antigens, suggesting that an inductive effect of bFGF and TGFalpha could occur in the cell cycle or shortly thereafter. Both bFGF and TGFalpha induced the expression of the early response gene c-fos while not altering the expression of c-actin or c-myc. The emergence of a photoreceptor phenotype was confirmed by both immunocytochemistry and Western blot analysis. The immortalized retinal precursor cell line could prove valuable in determining the role of exogenously added growth factors in retinal development and differentiation. Both bFGF and TGFalpha enhance the photoreceptor phenotype in medium-density cultures under conditions of defined medium. The same was confirmed by phase-contrast microscopy, immunocytochemistry, and Western blot analysis. Furthermore, cell fate determination in cultured precursor cells could occur during the late part of the cell cycle or shortly after completion of cell division. The effects of TGFalpha and bFGF seem to be slightly additive. The cell line will be extremely valuable in studying mechanisms of cell commitment and generation of retinal cell types, which could be tested for their potential for transplantation.     

Regulation of rat proximal tubule epithelial cell growth by fibroblast growth factors, insulin-like growth factor-1 and transforming growth factor-beta, and analysis of fibroblast growth factors in rat kidney.

Growth factors may play an important role in regulating the growth of the proximal tubule epithelium. To determine which growth factors could be involved, we have investigated the mitogenicity of various purified factors in rat kidney proximal tubule epithelial (RPTE) cells cultured in defined medium. Fibroblast growth factors, aFGF (acidic FGF) and bFGF (basic FGF), stimulate DNA synthesis in a dose-dependent manner, with ED50 values of 4.5 and 3.2 ng/ml, respectively; their effects are not additive. With cholera toxin in the medium, both aFGF and bFGF can replace insulin or epidermal growth factor (EGF) to attain the maximum level of cell growth, but they cannot replace cholera toxin. Cholera toxin specifically potentiates the effects of FGFs on DNA synthesis. At high cell density, both insulin and insulin-like growth factor 1 (IGF-1) induce DNA synthesis more effectively than EGF, FGFs and cholera toxin. The high concentration (0.2-1.0 microgram/ml) of insulin required for cell growth can be replaced by a low concentration of IGF-1 (10-20 ng/ml), indicating that insulin probably acts through a low affinity interaction with the IGF-1 receptor. Transforming growth factor-beta 1 (TGF-beta 1) inhibits DNA synthesis induced by individual factors and combinations of factors in a concentration-dependent manner. Northern blot analysis shows that mRNA for TGF-beta 1, IGF-1, and aFGF, but not bFGF are present in rat kidney. Western blot analysis and bioassay data confirmed that the majority of FGF-like protein in rat kidney is aFGF. The data suggest that in addition to EGF, IGFs, and TGF-beta, FGFs may also be important kidney-derived regulators of proximal tubule epithelial cell growth in vivo and in vitro.     

Immunological study of acidic fibroblast growth factor (aFGF) distribution in the eye

During the last ten years, several groups, including the present authors, have detected growth factor activities in various ocular tissues, and the presence of a ubiquitous Eye-Derived Growth Factor (EDGF) has been described. More recently, isolation and characterization of this growth factor activity from the retina led to the identification of two molecules. These molecules were shown to be identical to other growth factors isolated from neuronal and non-neuronal tissues and are now designated as acidic and basic fibroblast growth factor (aFGF, bFGF). The biological function and the reason for the ubiquitous distribution of these factors remain unclear. Understanding may be improved by quantification of this distribution in various tissues during development. In the present study, specific polyclonal antibodies were raised against acidic FGF, aFGF was determined in various ocular tissues by enzyme immunoassay, and the localization of immunoreactive aFGF by immunohistological staining with fluorescent antibodies or with enzyme- or gold-labeled antibodies was studied. In almost all tissues tested aFGF was found; but the retina, cornea, and vitreous body contained the highest levels of aFGF per gram of tissue. In the retina, aFGF was associated primarily with the nerve fiber layer and the inner and outer segments of the photoreceptors, whereas corneal aFGF was detected in the cytoplasma of the basal layer of epithelial cells.     

Distribution of fibroblast growth factors in cultured tumor cells and their transplants

Summary The distributions of acidic fibroblast growth factor (aFGF) and basic FGF (bFGF) in extracts of various cultured mammalian cells were determined from their elution profiles on heparin-affinity chromatography, and assay of activity as ability to stimulate DNA synthesis in BALB/c3T3 cells. Only aFGF was found in extracts of mouse melanoma B 16 cell and rat Morris hepatoma cell (MH₁C₁) lines. Other tumor cell lines established from solid tumors and some normal cells contained bFGF as a main component, but blood tumor cell lines contained no aFGF or bFGF. The FGFs in extracts of solid tumor tissues derived by transplantations of these cultured tumor cells and various normal tissues of mice were also examined. Tumors formed by all cell lines, regardless of whether they produced aFGF, bFGF, or neither, contained bFGF that was probably derived from host cells including capillary endothelial cells, in addition to the tumor-derived aFGF or bFGF, if produced. The content of bFGF, possibly derived from the host, in these tumor tissues was comparable to those of various mouse organs other than thymus, lung, spleen, and testis, which have higher bFGF contents. Tumor tissues derived from cultured cells producing bFGF had relatively higher bFGF contents. Like bFGF, aFGF was distributed almost ubiquitously in normal mouse tissues.     

FGF binding by extracellular matrix components of Wharton's jelly

Our earlier paper has reported that Wharton's jelly is a reservoir of several peptide growth factors, including acidic and basic fibroblast growth factors (aFGF and bFGF, respectively). Both can be extracted by buffered salts solutions in the form of high molecular mass complexes, probably with a component(s) of the extracellular matrix. Both aFGF and bFGF from such extracts hardly penetrate 10% polyacrylamide gels during electrophoresis. Pre-treatment of Wharton's jelly with hyaluronidase slightly increased the extractability of aFGF, but did not affect the extractability of bFGF. In contrast, the pre-treatment of tissue homogenate with bacterial collagenase (2000 U/ml, 37 degrees C, 18 h) increased the extractability of bFGF. The presence of beta-mercaptoethanol in the extracting solutions increased the extractability of both FGFs, but did not release FGFs in their free form, despite reducing the molecular mass of the FGF-containing complexes. We conclude that both aFGF and bFGF are bound through disulphide bonds to a protein component of Wharton's jelly. We propose that ground substance composed mainly of collagen fibrils and hyaluronate molecules, which surrounds the cells of Wharton's jelly, prevents the access of the extracting solution to aFGF and bFGF. Although hyaluronate and collagen do not bind aFGF or bFGF directly, they may constitute a barrier which prevents the dispersion of FGFs in Wharton's jelly. Thus, the high concentration of FGFs around the cells of Wharton's jelly may facilitate the interaction of these factors with membrane receptors, thereby resulting in stimulation of cell division and differentiation, as well as of the synthesis of extracellular matrix components.     

Effects of acidic and basic fibroblast growth factors (aFGF, bFGF) on glial precursor cell proliferation: age dependency and brain region specificity.

Acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF) are present in high levels in most areas of the embryonic rodent brain. To begin to understand the role of these growth factors in brain development, the effects of aFGF and bFGF on dissociated cell cultures prepared from embryonic and neonatal rat brain were studied. Addition of aFGF and heparin or bFGF alone to serum-free cultures of the dissociated Embryonic Day (E) 14.5 mesencephalon stimulates cell proliferation, as judged by [3H]thymidine autoradiography, leading to a maximal 75-fold increase in the total number of cells. This effect is dose-dependent with half-maximal increases at concentrations of about 5-6 ng/ml of aFGF or bFGF and is inhibited by the FGF antagonist HBGF-1U. The effect of aFGF on cell proliferation in cultures prepared from E14.5 mesencephalon is similar to that in cultures prepared from E14.5 cortex. However, in cultures prepared from E14.5 rhombencephalon or diencephalon, the proliferative effect of aFGF is much reduced. In all brain areas studied, the proliferative effect of aFGF declines with increasing age. Immunocytochemical analysis of E14.5 mesencephalic cultures demonstrated that the aFGF-induced increase in cell number is due to the proliferation of A2B5-immunoreactive (IR) glial precursor cells, but not of neuronal precursors, fibroblasts, or microglial cells. Moreover, differentiated glial fibrillary acidic protein-IR astrocytes and 2',3'-cyclic nucleotide 3'-phosphohydrolase-IR oligodendrocytes were not observed in cultures continuously treated with aFGF or bFGF, but were observed in high numbers after removal of the growth factors. These results suggest (1) that aFGF and bFGF are potent mitogens for glial precursor cells in all embryonic brain regions, (2) that the magnitude of the effects of aFGF depends on embryonic age and brain region, and (3) that both growth factors inhibit the differentiation of astrocyte or oligodendrocyte precursors. These observations made in vitro strongly support the hypothesis that FGF plays a critical role in gliogenesis and the timing of glial differentiation in the brain.     

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.     

Alternative splicing in fibroblast growth factor receptor 2 is associated with induced epithelial-mesenchymal transition in rat bladder carcinoma cells.

We described previously that acidic fibroblast growth factor (aFGF), but not basic fibroblast growth factor (bFGF), can induce the rat carcinoma cell line NBT-II to undergo a rapid and reversible transition from epithelial to mesenchymal phenotype (EMT). We now find that NBT-II EMT is stimulated by keratinocyte growth factor (KGF) in cells grown at low density. Accordingly, a high-affinity receptor showing 98% homology to mouse FGF receptor 2b/KGF receptor was cloned and sequenced from NBT-II cells. Northern analysis indicated that mRNA for FGF receptor 2b/KGF receptor was drastically down-regulated within 1 wk in aFGF-induced mesenchymal NBT-II cells. This decrease coincided with an up-regulation of FGF receptor 2c/Bek, a KGF-insensitive, alternatively spliced form of FGF receptor 2b/KGF receptor. Functional studies confirmed that KGF could not maintain EMT induction on mesenchymal NBT-II cells. FGF receptor 1 and FGF receptor 2c/Bek could also support EMT induction when transfected into NBT-II cells in response to aFGF or bFGF. Such transfected cells could bind bFGF as well as aFGF. Therefore, EMT can be induced through different FGF receptors, but EMT may also regulate FGF receptor expression itself.     

Localisation of acidic and basic fibroblast growth factors during mouse palate development and their effects on mouse palate mesenchyme cells in vitro

Summary The distribution of acidic and basic fibroblast growth factors (aFGF, bFGF) was mapped during mouse embryonic palate development. Generally, they localised most intensely in the basement membrane and epithelia rather than the mesenchyme. Localisation was predominantly restricted to the palatal nasal, and medial edge epithelia. Staining was particularly intense in the medial edge epithelia at the time of mid-line epithelial seam formation. Intense staining persisted in the epithelia of the degenerating seam and later in the oral and nasal epithelial triangles. Mouse embryonic palate mesenchyme (MEPM) cells cultured in vitro on a variety of substrata (on plastic, on the surface of a collagen gel and within a collagen gel) responded to treatment with aFGF or bFGF. These responses were modulated by the culture substratum. The FGFs stimulated MEPM cell proliferation on plastic and on collagen, but inhibited cell growth in collagen. The FGFs had little effect on protein production when cells were cultured on plastic, but caused a large reduction in on-collagen and incollagen cultures. This reduction was greater in collagenous than non-collagenous proteins. Generally, treatment with FGFs stimulated the production of glycosaminoglycans (GAGs), particularly hyaluronan (HA) and dermatan sulphate (DS). In addition, the size class of HA was shifted to a higher molecular weight form. These data indicate that aFGF and bFGF may play a role in modulating mesenchymal cell matrix biosynthesis, so facilitating palatal epithelial seam degeneration. Correspondence to: M.W.J. Ferguson     

Autocrine activation of EGF receptor promotes oscillation of glutamate-induced calcium increase in astrocytes cultured in rat cerebral cortex

We previously reported that astrocytes cultured for more than 2 days in a defined medium containing epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) showed calcium oscillation in response to glutamate, whereas the response pattern was transient in the absence of the exogenous growth factors. In the present study, we found that astrocytes showed glutamate-induced calcium oscillation, even in growth factor-free medium, if the cells had been cultured for more than 5 days. The calcium oscillation promoted by the prolonged culture period was suppressed by an inhibitor of EGF receptor tyrosine kinase, but not by a neutralizing antibody to bFGF, indicating that the accumulation of an autocrine factor that activates the EGF receptor leads to calcium oscillation. Astrocytes in our culture system expressed EGF, transforming growth factor alpha (TGFalpha), bFGF and acidic fibroblast growth factor (aFGF). Exogenous aFGF, which induced astrocyte immediate early gene expression to the same extent as EGF or bFGF, did not affect calcium oscillation. Exogenous EGF and bFGF promoted astrocyte hypertrophic morphology and proliferation, as well as calcium oscillation. In contrast, these properties did not accompany calcium oscillation induced by the prolonged culture period. These results suggest that astrocytes possess the ability to promote their own calcium oscillation, which is independent of hypertrophic changes to reactive astrocytes.