The int-2 gene product acts as a growth factor and substitutes for basic fibroblast growth factor in promoting the differentiation of a normal mouse mammary epithelial cell line.

We have investigated the effect of basic fibroblast growth factor (bFGF) and the related int-2 gene on the growth, transformation, and differentiation of HC11 mouse mammary epithelial cells. We show that in HC11 cells infected with int-2 retroviral expression vectors, the int-2 protein can function as a bFGF-like growth factor in stimulating: (a) HC11 cell proliferation in monolayer, (b) anchorage-independent growth in soft agar, and (c) soft agar growth of the bFGF-responsive SW13 tumor cell line. These effects are observed irrespective of whether the int-2 protein is expressed in its wild-type form or is linked to a signal peptide. A candidate bFGF receptor, which is the product of the flg gene and which may recognize the int-2 protein, is expressed at high levels in HC11 cells. Following epidermal growth factor or bFGF priming and subsequent treatment with lactogenic hormones, all of the int-2 infected and the parental HC11 cells synthesize similar levels of beta-casein. However, the autocrine expression of int-2 in HC11 cells abrogates their requirement for either exogenous epidermal growth factor or bFGF priming. These data suggest that, in HC11 cells, the growth factor activity of the int-2 gene is indistinguishable from that of bFGF and does not interfere with the mammary cell differentiation program associated with lactogenesis.     

The gefitinib-sensitizing mutant epidermal growth factor receptor enables transformation of a mouse fibroblast cell line

A specific inhibitor of the Epidermal Growth Factor Receptor (EGFR), Gefitinib, displays significant antitumor effects against non-small cell lung cancers (NSCLC) that express EGFR with mutations in their tyrosine kinase domain. Although previous reports have already demonstrated that oncogenic transformation can be induced by some mutant EGFR forms, the precise differences between mutant and wild-type EGFR in terms of mechanisms of transformation have not been fully elucidated. We show here that a murine fibroblast cell line, NR6 becomes transformed by an expression level of the mutant EGFR form lacking E746-A750 that is far less than that needed with transfected wild-type EGFR. However, the mutant EGFR was unable to transform NR6 in a ligand-independent manner, as was seen with the wild-type EGFR. The consequent biological features after transformation, including DNA synthesis or cell cycle progression and biochemical characteristics such as MAPK activation mediated by the mutant EGFR are comparable and equivalent to those mediated by wild-type EGFR. These data suggest that the mutant EGFR possesses greater ligand-dependent transformation when compared with wild-type EGFR, although the exact mechanisms to account for this characteristic remain to be defined.     

Increased expression of basic fibroblast growth factor in hyperoxic-injured mouse lung

Basic fibroblast growth factor (bFGF) is a mitogenic polypeptide for a wide variety of cell types and has been immunolocalized in the rodent and human lung. We investigated the mRNA and protein expression of bFGF in hyperoxic-injured adult mouse lungs using northern blot analysis and immunohistochemistry. Mece (6–8weeks) were continuously exposed to 80% osygen up to 4 days. Levels of bFGF mRNA were increased from room air control on days 3 and 4 of hyperoxia. mRNA levels of acidic fibroblast growth factor (aFGF), fibronectin, and transin/stromelysin were also examined in this injury model. Similar to bFGF, the fibronectin and transin/stromelysin mRNA levels were increased after 3 days of hyperoxia. In contrast, the aFGF mRNA levels were gradually reduced on each day of hyperoxia. A rabbit polyclonal anti-bFGF antibody was used to determine the distribution and levels of expression in the hyperoxic-injured lungs. The room air control and day 1 hyperoxic-exposed lungs exhibited staining for bFGF in the basement membranes of the blood vessels, airways, and alveoli. Patchy but intense alveolar staining was prominent on day 4 of hyperoxia. The bFGF immunoreactivity of blood vessels and airways unaffected by the hyperoxia exposure. These results suggest that bFGF may play a role in the alveolar response to hyperoxic-induced injury by virtye of the altered mRNA levels and protein distribution in this injury model.     

The basic fibroblast growth factor-saporin mitotoxin acts through the basic fibroblast growth factor receptor.

We have confirmed the hypothesis that a mitotoxin resulting from the conjugation of basic fibroblast growth factor and saporin exerts its cytotoxic effect through specific interaction with the basic fibroblast growth factor (FGF) receptor. Accordingly, the mitotoxin stimulates tyrosine phosphorylation of the 90 kD substrate that characterizes the initial cellular response to basic FGF. Cross-linking experiments show that radio-labeled basic fibroblast growth factor-saporin (FGF-SAP) binds to the receptor. Suramin, an inhibitor of growth factor receptor binding, inhibits the cytotoxicity of basic FGF-SAP. In a study of 4 different cell types, there is a decrease in the ED50 of the mitotoxin as the receptor number per cell increases. We have verified the cytotoxicity of the mitotoxin in 3 different assay systems. As expected, it is effective in the inhibition of protein synthesis and DNA synthesis, as well as of cell count. Binding of basic FGF-SAP which will result in cytotoxicity occurs very rapidly; 5 minutes of incubation of 10 nM basic FGF-SAP with cells results in 80% inhibition of cell count. The in vitro data indicate that the basic FGF-SAP is a receptor specific and potent suicide antagonist of basic FGF. Its potential as an anti-FGF for therapeutic and research uses in vivo is discussed.     

Ontogeny of basic fibroblast growth factor binding sites in mouse ocular tissues

Basic fibroblast growth factor (bFGF) binding to ocular tissues has been studied by autoradiographical and biochemical approaches directly performed on sections during mouse embryonic and postnatal development. Frozen sections of embryos (9 to 18 days), newborns, and adults (1 day to 6 months) were incubated with iodinated bFGF. One specific FGF binding site (KD = 2.5 nM) is colocalized with heparan sulfate proteoglycans of the basement membranes and is heparitinase sensitive. It first appears at Day 9 around the neural tube, the optic vesicles, and below the head ectoderm and by Day 14 of embryonic development is found in all basement membranes of the eye. At Day 16, very intensely labeled patches appear, corresponding to mast cells which have been characterized by metachromatic staining of their heparin-rich granulations with toluidine blue. In addition to the latter binding, we have also observed a general diffuse distribution of silver grains on all tissues and preferentially in the ecto- and neuroectodermic tissues. From Days 17-18, there is heterogeneous labeling inside the retina, localized in the pigmented epithelium and in three different layers colocalized with the inner and outer plexiform layers and with the inner segments of the photoreceptors. This binding is heparitinase resistant but N-glycanase sensitive and may represent a second specific binding site corresponding to cellular FGF receptors (KD = 280 pM). Both types of binding patterns observed suggest a significant role for bFGF in eye development and physiology.     

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.     

Oncogene N-ras mediates selective inhibition of c-fos induction by nerve growth factor and basic fibroblast growth factor in a PC12 cell line.

A cell line was generated from U7 cells (a subline of PC12 rat pheochromocytoma cells) that contains a stably integrated transforming mouse N-ras (Lys-61) gene under the control of the long terminal repeat from mouse mammary tumor virus. Such cells, designated UR61, undergo neuronal differentiation upon exposure to nanomolar concentrations of dexamethasone, as a consequence of expression of the activated N-ras gene (I. Guerrero, A. Pellicer, and D.E. Burstein, Biochem, Biophys. Res. Commun. 150:1185-1192, 1988). Exposure of UR61 cells to either nerve growth factor (NGF) or basic fibroblast growth factor (bFGF) results in a marked induction of c-fos RNA, with kinetics paralleling those of NGF- or bFGF-induced expression of c-fos RNA in PC12 cells. Dexamethasone-induced expression of activated N-ras p21 results in blocking of c-fos RNA induction by NGF or bFGF in a time-dependent manner. Activated N-ras p21-mediated inhibition of c-fos RNA induction in UR61 cells is selective for NGF and bFGF and is not due to selective degradation of c-fos RNA. Normal and transforming N-ras can trans activate the chloramphenicol acetyltransferase gene linked to mouse c-fos regulatory sequences when transient expression assays are performed. Our observations suggest that N-ras p21 selectively interacts with pathways involved in induction of c-fos expression which initiate at the receptors for NGF and bFGF.     

The discovery of basic fibroblast growth factor/fibroblast growth factor-2 and its role in haematological malignancies

Basic fibroblast growth factor/fibroblast growth factor-2 is one of the best characterized of the pro-angiogenic cytokines. This review describes its history, as well as its role in tumor angiogenesis associated with haematological malignancies, as traced by the main contributions to the international medical literature.     

Regulation of basic fibroblast growth factor binding and activity by cell density and heparan sulfate

The role of cell density in modulating basic fibroblast growth factor binding and activity was investigated. A primary corneal stromal fibroblast cell culture system was used, since these cells do not constitutively express heparan sulfate proteoglycans in vivo except after injury. A 3-5-fold reduction in bFGF binding per cell was observed as cell density increased from 1000 to 35,000 cells/cm2. The cell density-dependent change in bFGF binding was not the result of altered FGFR expression as determined by equilibrium binding experiments and by immunoblot analysis. However, bFGF-cell surface receptor binding affinities were measured to be 10-20-fold higher at low cell densities than at intermediate and high cell density. bFGF-induced cell proliferation was also cell density-dependent, with maximal stimulation of proliferation 190-280% greater at intermediate densities (15,000 cells/cm2) than at other cell densities. This effect was specific to bFGF as serum, epidermal growth factor, and transforming growth factor-beta did not exhibit the same density-dependent profile. Further, heparan sulfate proteoglycans and, specifically, syndecan-4 were implicated as the modulator of bFGF binding and activity. Pretreatment of cell cultures with heparinase resulted in reduced bFGF binding to the cells and abrogated bFGF induced proliferation. These data suggest a mechanism by which cell density regulates heparan sulfate proteoglycan expression and modulates the cellular response to bFGF. Modulation of heparan sulfate proteoglycan expression might be an important aspect of the regulation of stromal cell migration and proliferation during wound healing.     

The int-2 gene product acts as an epithelial growth factor in transgenic mice.

The induction of mammary tumors by mouse mammary tumor virus (MMTV) is thought to occur through proviral activation of one or more cellular genes. One of these, int-2, encodes a 27 kd protein which exhibits striking homology to the basic fibroblast growth factor family. To assess directly the role of the int-2 protein in cell proliferation, we have established transgenic mice which carry the int-2 gene driven by the MMTV promoter/enhancer. Expression of the int-2 gene in female transgenic mice results in pronounced mammary gland hyperplasia. Interestingly, expression of the MMTV-int-2 transgene in the prostate gland of male carriers results in a benign, but dramatic, epithelial hyperplasia similar to benign prostatic hypertrophy (BPH), a common but poorly understood disorder in human populations. Together, these results indicate that the int-2 product can act as a potent growth factor in these epithelial tissues.     

Immunohistochemical localization of basic fibroblast growth factor within the mouse uterus.

Uterine samples were either rapidly frozen in liquid nitrogen or placed in Bouin's fixative. A commercial primary polyclonal antibody made in rabbits against human recombinant basic fibroblast growth factor (bFGF) was used. Western blot analysis indicated that the antibody was specific for bFGF and did not react with acidic FGF. The primary antibody was followed by either goat anti-rabbit immunoglobulin G (IgG) conjugated to the fluorescent phycobiliprotein tracer phycoerythrin or biotinylated goat anti-rabbit IgG and a biotin-avidin-peroxidase complex. Specificity controls using adjacent sections were carried out by (i) substituting normal rabbit sera for the primary antisera, (ii) omitting the primary antisera or (iii) extracting sections with NaCl (2 mol l-1) prior to the immunochemical procedures. No binding of the antibody was observed with any of the specificity control sections. The connective tissue stroma and the basal lamina associated with uterine glandular and surface epithelial layers were positive for bFGF. Localization was not observed within surface or glandular epithelial cells. The basal lamina and endothelial cells associated with blood vessels within the uterus and the smooth muscle cells of the myometrium were positive for bFGF. There were no differences in uterine localization patterns or intensity during the oestrous cycle or after ovariectomy and steroid hormone supplementation. These studies demonstrate the specific localization of bFGF within the mouse uterus.     

Alpha 2-macroglobulin is a binding protein for basic fibroblast growth factor

After incubation with human serum or plasma, 125I-basic fibroblast growth factor (bFGF) (molecular mass 18.5 kDa) exhibits molecular mass forms greater than 200 kDa as determined by nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by autoradiography. These high molecular mass forms of bFGF are immunoprecipitable with antiserum raised against alpha 2-macroglobulin (alpha 2M). Purified alpha 2M and 125I-bFGF form a covalent complex in a specific, saturable manner. Excess unlabeled bFGF competes with 125I-bFGF for complex formation. Complex formation is complete after 4 h and is inhibited by pretreating alpha 2M with dithiothreitol, iodoacetamide, iodoacetic acid, and N-ethylmaleimide. The complex is resistant to acidic conditions and denaturants such as urea. Heparin, which binds bFGF, has no effect on complex formation. Methylamine, which blocks protease binding to alpha 2M, increases the amount of 125I-bFGF that can be bound 2-fold. Plasmin and trypsin treatment of alpha 2M has no effect on 125I-bFGF binding. The ability of growth factors to compete for binding is specific, as aFGF and TGF-beta compete for binding to alpha 2M, whereas platelet-derived growth factor does not. 125I-bFGF.alpha 2M complexes do not bind to low affinity bFGF binding sites and bind poorly to high affinity bFGF binding sites on BHK-21 cells. In addition, 125I-bFGF bound to alpha 2M has decreased ability to stimulate plasminogen activator production in bovine capillary epithelial cells.     

Vascular endothelial growth factor and basic fibroblast growth factor in patients with squamous cell oesophageal cancer

It is suggested that vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) play an important role in tumor-induced angiogenesis. The purpose of this study was to estimate the correlation between VEGF and bFGF levels and tumor pathological status according to pTNM classification in patients with squamous cell oesophageal cancer. A group of 25 healthy controls and 32 consecutive patients with oesophageal cancer were included in this study. Serum VEGF and bFGF levels were determined by enzyme-linked immunosorbent assay (Quantikine R&D Systems). Serum VEGF and bFGF levels were significantly elevated in the patient groups (VEGF: 146.0 pg/ml, 79.0-386.3 pg/ml vs. 38.0 pg/ml, 6.5-135.1 pg/ml, p<0.005, and bFGF: 5.2 pg/ml, 1.2-10.6 pg/ml vs. 2.06 pg/ml, 0.07-4.0 pg/ml, p<0.02 Fisher test). The highest correlation between serum VEGF and bFGF levels were found in patients with advanced cancers, especially with: T4, N1, and M1 factors. The VEGF and bFGF levels were significantly higher in patients with pT4 (p<0.01). Patients with N1 lymph node invasion, compared with N0 factor, have higher levels of angiogenetic factors (p<0.04). Also in patients with advanced cancers with liver metastases the serum levels VEGF and bFGF were significantly higher (M1 vs. M0, VEGF p<0.001 and bFGF p<0.05). Consecutive monitoring of VEGF and bFGF serum levels may be a useful prognostic marker for patients with squamous cell oesophageal cancer.     

Syndecan-4 modulates basic fibroblast growth factor 2 signaling in vivo

Syndecan-4 is one of the principal heparan sulfate-carrying proteins on the cell surface. Unlike other members of syndecan family, syndecan-4 mediates phosphatidylinositol 4,5-bisphosphate 2 (PIP(2))-dependent PKC-alpha activation, and overexpression of syndecan-4 in vitro results in enhanced FGF2 signaling. The present study was designed to test the functional effect of increased syndecan-4 expression in endothelial cells in transgenic mice. Several transgenic mice lines expressing syndecan-4 cDNA under control of human endothelial nitric oxide (NO) synthase (eNOS) promoter were generated. Exogenous syndecan-4 was mainly expressed in the heart, brain, and lungs. In particular, the heart demonstrated the greatest increase in the ratio of transgenic-to-native syndecan-4 gene expression. Vessels from the eNOS-syndecan-4 mice demonstrated more pronounced vasodilation to FGF2 but not to VEGF-A(165), sodium nitroprusside, and A 23187 compared with wild-type mice. To elucidate the mechanism of this effect, we measured NO release from primary cardiac endothelial cells isolated from transgenic or wild-type adult mice. Cells from the eNOS-syndecan-4 transgenic mice had a significant increase in FGF2- and VEGF-A(165)-induced NO release compared with endothelial cells from the wild-type mice. However, the absolute magnitude of this increase was higher for FGF2 than VEGF-A(165). In conclusion, enhanced syndecan-4 expression in mouse cardiac endothelial cells results in preferential augmentation of FGF2 but not VEGF-A(165)-induced NO release.     

Immuno-electron-microscopic localization of basic fibroblast growth factor in the dystrophic mdx mouse masseter muscle

Summary The localization of basic fibroblast growth factor (bFGF)-like immunoreactivity in the masseter muscle of dystrophic mdx mice on postnatal day 28 was investigated by immunoblot analysis and electron microscopy. Crude homogenate of the masseter muscle, when subjected to immunoblotting with a bFGF antiserum, exhibited a main band with the same molecular weight (18 kDa) as bovine bFGF. By electron microscopy, bFGF immunoreactivity was detected in small regenerating myocytes; the smaller cells were the premature myocytes, the most intense staining was the immunoreactivity within the cytoplasm. Putative precursors of the muscle cells with a few myofilaments, which were most intensely labeled with anti-bFGF, contacted each other and possibly developed into multinucleated myocytes through cell fusion. Mature myocytes with densely packed myofilaments and peripherally located nuclei did not exhibit bFGF immunoreactivity; they formed myoneural junctions with motor nerve endings immunoreactive for bFGF. Early differentiating myocytes with intense bFGF-like immunoreactivity did not make contact with immunoreactive nerve terminals. Degenerating large myocytes with a limited number of distorted and/or disrupted myofilaments exhibited electron-dense deposits in the cristae of mitochondria; these deposits were not abolished by immunoadsorption control experiments. Thus, the cell-size-dependent decrease in bFGF immunoreactivity in regenerating but not in degenerating myocytes provides a morphological basis for an autoregulatory role of bFGF in muscle regeneration. This study suggests that neuronal bFGF is not involved in initial muscle regeneration in the dystrophic mdx mouse.