The role of fibroblast growth factors in vascular development

Fibroblast growth factors (FGFs) are considered angiogenic factors, yet the exact relationship between FGF and vascular development in normal and pathological tissue has long remained elusive. However, recent results from gene inactivation and transgenic studies in mice and in culture systems have demonstrated the role of FGFs in vessel assembly and sprouting. FGFs also promote blood-vessel branching and induce lymphangiogenesis. Novel players in FGF-mediated angiogenesis have been identified, such as p38 mitogen-activated protein kinase. Tumour angiogenesis is regulated by FGFs directly or indirectly via secondary angiogenesis factors, such as vascular endothelial growth factor. The newly established angiogenic role of FGFs makes FGF or molecules targeting FGF and its receptor promising candidates for the development of novel therapeutics.     

Auto and transactivation of FGF expression: Potential mechanism for regulation of myogenic differentiation

Summary Fibroblast growth factors (FGFs) are potent inhibitors of myogenic differentiation. The recent observation that the endogenous expression of acidic and basic FGF by myogenic cells decreases coordinately with differentiation suggests a regulatory role for these growth factors in myogenesis. Inasmuch as other proteins known to influence myogenesis (e.g., MyoD1 and myogenin) activate their own expression as well as the expression of other members of their family, we hypothesized that the FGFs might be capable of similar autoregulation. We examined the effect of exogenously supplied FGF on the abundance of the mRNAs encoding acidic and basic FGF in Sol 8 myoblasts, and demonstrate that either acidic or basic FGF stimulate, through paracrine mechanisms, the accumulation of the mRNAs encoding both of these FGFs. Thus FGFs can auto- and transregulate their own expression in a manner analogous to that observed for the myogenic determination proteins. In addition, similar to that previously observed for MyoD1, both acidic and basic FGF suppress myogenin expression in myoblasts. These results suggest two mechanisms whereby endogenously produced FGFs participate in the maintenance of the undifferentiated state of myogenic cells. These data provide support for paracrine, and suggest potential autocrine, roles for FGFs in the regulation of myogenic differentiation.     

Semirational design of a potent, artificial agonist of fibroblast growth factor receptors

Fibroblast growth factors (FGFs) are being investigated in human clinical trials as treatments for angina, claudication, and stroke. We designed a molecule structurally unrelated to all FGFs, which potently mimicked basic FGF activity, by combining domains that (1) bind FGF receptors (2) bind heparin, and (3) mediate dimerization. A 26-residue peptide identified by phage display specifically bound FGF receptor (FGFR) 1c extracellular domain but had no homology with FGFs. When fused with the c-jun leucine zipper domain, which binds heparin and forms homodimers, the polypeptide specifically reproduced the mitogenic and morphogenic activities of basic FGF with similar potency (EC50 = 240 pM). The polypeptide required interaction with heparin for activity, demonstrating the importance of heparin for FGFR activation even with designed ligands structurally unrelated to FGF. Our results demonstrate the feasibility of engineering potent artificial agonists for the receptor tyrosine kinases, and have important implications for the design of nonpeptidic ligands for FGF receptors. Furthermore, artificial FGFR agonists may be useful alternatives to FGF in the treatment of ischemic vascular disease.     

Fibroblast growth factor/fibroblast growth factor receptor system in angiogenesis

Fibroblast growth factors (FGFs) are a family of heparin-binding growth factors. FGFs exert their pro-angiogenic activity by interacting with various endothelial cell surface receptors, including tyrosine kinase receptors, heparan-sulfate proteoglycans, and integrins. Their activity is modulated by a variety of free and extracellular matrix-associated molecules. Also, the cross-talk among FGFs, vascular endothelial growth factors (VEGFs), and inflammatory cytokines/chemokines may play a role in the modulation of blood vessel growth in different pathological conditions, including cancer. Indeed, several experimental evidences point to a role for FGFs in tumor growth and angiogenesis. This review will focus on the relevance of the FGF/FGF receptor system in adult angiogenesis and its contribution to tumor vascularization.     

Fibroblast growth factors

Fibroblast growth factors (FGFs) make up a large family of polypeptide growth factors that are found in organisms ranging from nematodes to humans. In vertebrates, the 22 members of the FGF family range in molecular mass from 17 to 34 kDa and share 13-71% amino acid identity. Between vertebrate species, FGFs are highly conserved in both gene structure and amino-acid sequence. FGFs have a high affinity for heparan sulfate proteoglycans and require heparan sulfate to activate one of four cell-surface FGF receptors. During embryonic development, FGFs have diverse roles in regulating cell proliferation, migration and differentiation. In the adult organism, FGFs are homeostatic factors and function in tissue repair and response to injury. When inappropriately expressed, some FGFs can contribute to the pathogenesis of cancer. A subset of the FGF family, expressed in adult tissue, is important for neuronal signal transduction in the central and peripheral nervous systems.     

Normal patterning of the coronary capillary plexus is dependent on the correct transmural gradient of FGF expression in the myocardium

The formation of the coronary vessel system is vital for heart development, an essential step of which is the establishment of a capillary plexus that displays a density gradient across the myocardial wall, being higher on the epicardial than the endocardial side. This gradient in capillary plexus formation develops concurrently with transmural gradients of myocardium-derived growth factors, including FGFs. To test the role of the FGF expression gradient in patterning the nascent capillary plexus, an ectopic FGF-over-expressing site was created in the ventricular myocardial wall in the quail embryo via retroviral infection from E2-2.5, thus abolishing the transmural gradient of FGFs. In FGF virus-infected regions of the ventricular myocardium, the capillary density across the transmural axis shifted away from that in control hearts at E7. This FGF-induced change in vessel patterning was more profound at E12, with the middle zone becoming the most vascularized. An up-regulation of FGFR-1 and VEGFR-2 in epicardial and subepicardial cells adjacent to FGF virus-infected myocardium was also detected, indicating a paracrine effect on induction of vascular signaling components in coronary precursors. These results suggest that correct transmural patterning of coronary vessels requires the correct transmural expression of FGF and, therefore, FGF may act as a template for coronary vessel patterning.     

Fibroblast growth factors: from molecular evolution to roles in development, metabolism and disease

Fibroblast growth factors (FGFs) are a family of structurally related polypeptides that are essential for embryonic development and that function postnatally as homoeostatic factors, in the response to injury, in the regulation of electrical excitability of cells and as hormones that regulate metabolism. In humans, FGF signalling is involved in developmental, neoplastic, metabolic and neurological diseases. Fgfs have been identified in metazoans but not in unicellular organisms. In vertebrates, FGFs can be classified as having intracrine, paracrine and endocrine functions. Paracrine and endocrine FGFs act via cell-surface FGF receptors (FGFRs); while, intracrine FGFs act independent of FGFRs. The evolutionary history of the Fgf family indicates that an intracrine Fgf is the likely ancestor of the Fgf family. During metazoan evolution, the Fgf family expanded in two phases, after the separation of protostomes and deuterostomes and in the evolution of early vertebrates. These expansions enabled FGFs to acquire diverse actions and functions.     

Liver specification and early morphogenesis

The classically defined induction of the liver from the endoderm, elicited by the cardiac mesoderm, has recently been discovered to involve signaling by fibroblast growth factors (FGFs). Multiple FGFs induce hepatic gene expression independent of an effect on growth. A subset of these FGFs cooperates with other factors to promote morphogenesis of the newly specified hepatocytes. Subsequent to the formation of the liver bud, distinct mesenchymal signals and hepatic response pathways stimulate further growth and differentiation of the hepatic parenchymal cells and prevent apoptosis. The initial stages of hepatogenesis are therefore beginning to be understood, and serve as a paradigm for the development of other tissues from the endoderm.     

Functions of fibroblast growth factors in vertebrate development

Fibroblast growth factors (FGFs) are a class of secreted polypeptide ligands which mediate diverse cellular responses during embryonic, fetal, and postnatal vertebrate development. The purposes of this review are to provide a condensed overview of FGFs and their receptors, to catalog and categorize the functions of FGFs in vertebrate development, to present recent discoveries relating to the interplay of FGFs with other secreted ligands in the control of tissue growth and patterning, and to discuss several potential directions for future research in the field.     

The role of the signaling pathway FGF/FGFR in pancreatic cancer

Fibroblast growth factors (FGFs) are signaling molecules with a wide range of actions that are involved in various processes in the body. Specifically for pancreas, FGFs are important for both organogenesis and carcinogenesis. They belong to the factors involved in the interaction between cancer and stromal cells representing a key component in the development of pancreatic cancer. Pathological changes in the FGF/FGFR signaling pathway is a complex process, which depends on type/isoforms of FGF receptors (FGFR) regulating the remodeling effect and subsequent activation of pancreatic cancer cells by FGF. FGFs and their receptors FGFR are considered as potential specific markers and putative targets for treatment of pancreatic cancer.     

Crystal structure of fibroblast growth factor 9 reveals regions implicated in dimerization and autoinhibition

Fibroblast growth factors (FGFs) constitute a large family of heparin-binding growth factors with diverse biological activities. FGF9 was originally described as glia-activating factor and is expressed in the nervous system as a potent mitogen for glia cells. Unlike most FGFs, FGF9 forms dimers in solution with a K(d) of 680 nm. To elucidate the molecular mechanism of FGF9 dimerization, the crystal structure of FGF9 was determined at 2.2 A resolution. FGF9 adopts a beta-trefoil fold similar to other FGFs. However, unlike other FGFs, the N- and C-terminal regions outside the beta-trefoil core in FGF9 are ordered and involved in the formation of a 2-fold crystallographic dimer. A significant surface area (>2000 A(2)) is buried in the dimer interface that occludes a major receptor binding site of FGF9. Thus, we propose an autoinhibitory mechanism for FGF9 that is dependent on sequences outside of the beta-trefoil core. Moreover, a model is presented providing a molecular basis for the preferential affinity of FGF9 toward FGFR3.     

Expression and processing of biologically active fibroblast growth factors in the yeast Saccharomyces cerevisiae

Chemically synthesized genes for bovine and human fibroblast growth factors (FGFs) were expressed in heterologous microorganisms. Although the intracellular expression or secretion of acidic and basic FGFs in Escherichia coli or Saccharomyces cerevisiae yielded recombinant growth factors with high biological activity, the resulting proteins had structural microheterogeneity due to modified amino termini. Expression of amino-terminal extended forms of human acidic and basic FGFs in S. cerevisiae gave rise to soluble, but cell-associated polypeptides, with potent biological activity. These yeast-derived proteins were processed in vivo by removal of initiation codon-derived methionine residues and by amino-terminal acetylation. Both of these processes have been observed in mammalian tissues. The yeast systems described here, therefore, provide a good model system for the expression of FGFs as intracellular proteins, but more importantly they give high levels of authentically processed human FGFs with many potential medical applications. Since the recombinant proteins have all the biological activities of their native counterparts, their possible applications in wound healing, tissue grafting, nerve regeneration, and treatment of ischemia are discussed.     

Hormone-like fibroblast growth factors and metabolic regulation

The family of fibroblast growth factors (FGFs) consisting now of 22 members is generally considered to control a wide range of biological functions such as development, differentiation and survival. However, research during the past decade provided substantial evidence that a so called “hormone-like” subgroup of FGFs, comprised of FGF19, FGF21 and FGF23, is involved in the regulation of diverse metabolic pathways to control glucose, lipid, bile acid, phosphate and vitamin D metabolism. The unique properties of these FGFs include predominant production of the factors in selective tissues, their abundance in the blood due to the lack of extracellular heparin-mediated sequestration, and highly specific tissue-targeted action via engagement of their respective co-receptors. The important metabolic context of FGF19, FGF21, and FGF23 actions has revealed important novel roles for FGFs and provided significant means to explore an opportunity for therapeutic targeting of these factors and their corresponding pathways.     

Fibroblast growth factors

Fibroblast growth factors (FGFs) are heparin-binding protein mitogens that induce division of most cultured cells derived from embryonic mesoderm and neuroectoderm. Terminally differentiated neurons also respond in vitro by eliciting outgrowth of neurites. In vivo, FGFs have been shown to induce DNA synthesis, cell migration, blood vessel growth, and dermal wound closure. The protein and nucleic acid sequences for two different FGFs, denoted acidic and basic FGF, have been determined and recognized to be homologous. Additional genes recently have been identified that extend this protein family.     

Fibroblast Growth Factors Stimulate Protein Tyrosine Phosphorylation and Mitogen-Activated Protein Kinase Activity in Primary Cultures of Hippocampal Neurons

Abstract: Fibroblast growth factors (FGFs) are not only mitogens, but they also promote the differentiation of various cell types. For instance, basic FGF (bFGF) provides a critical trophic support for hippocampal neurons in culture. To elicit their biological effects, FGFs interact with high-affinity receptors that are transmembrane proteins with a cytoplasmic portion containing a tyrosine kinase activity. The tyrosine phosphorylation pattern was examined in primary cultures of hippocampal neurons derived from rat embryos. In these cultures grown for 3 days in the absence of serum, the addition of bFGF causes a rapid increase of tyrosine phosphorylation for various proteins with an optimal level after 5 min of bFGF exposure. Concomitantly, bFGF activates mitogen-activated protein kinase (MAP kinase) activity measured with a selective MAP kinase peptide. The activity increased rapidly after the addition of bFGF and remained elevated even when cultures were treated for 1 h with bFGF. Both acidic and basic FGF were able to enhance protein tyrosine phosphorylation and MAP kinase activity, whereas nerve growth factor and epidermal growth factor did not elicit any of these responses. These data indicate that some of the transduction signals (i.e., tyrosine phosphorylation and activation of MAP kinase) that have been described for the proliferative effect of FGFs are also involved when FGFs act as trophic factors for postmitotic neurons in culture.     

Stabilization of fibroblast growth factors by a non-cytotoxic zwitterionic detergent, 3-[(3-cholamidopropyl) dimethylammonio]-1-propane sulfonate (chaps)

Summary The potential usefulness of a zwitterionic detergent, 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS), in the stabilization of acidic and basic fibroblast growth factors (FGFs) was examined. Among several detergents, CHAPS was found to be not only non-cytotoxic but also most useful in handing the diluted preparations of FGFs. The advantages are as follows: 1) at lower concentrations than 0.01% CHAPS did not affect growth factor activity of calf serum (CS) and the growth rate of BLAB/c 3T3 cells. The primary culture of rat prostate epithelium and colony formation of NRK-49F cells were hardly influenced by CHAPS lower than 0.003%; 2) the loss of FGFs that usually occurs due to their adherence to the surface of storage containers was effectively prevented by inclusion of 0.1% CHAPS; 3) the recovery of FGFs after storage or dialysis was significantly enhanced by inclusion of 0.1% CHAPS; 4) CHAPS at lower concentrations than 0.1% does not interfere with amino acid analysis, except that Thr may be misled only when the ratio of protein/CHAPS is low; 5) amino acid sequence analysis was hardly disturbed by CHAPS up to 0.5%. These results indicate that CHAPS is useful as a stabilizing agent for various kinds of polypeptides capable of showing biological activity at a low concentration. Editor's statement Polypeptide growth factors and hormones, especially heparin-binding growth factors (FGF), are notoriously troublesome to handle in purified form at extremely low concentrations. This report demonstrates an interesting solution to this problem.     

Fibroblast growth factors: key players in epithelial morphogenesis, repair and cytoprotection

Fibroblast growth factors (FGFs) regulate early development and organogenesis. In particular, a subfamily of FGFs is essential for the formation and differentiation of epithelial tissues and organs. Recent studies revealed a crucial role for these FGFs in repair of the skin, intestine and liver. In addition, the cytoprotective potential of FGFs suggests their use for the protection of epithelial cells under conditions of stress in vivo. Indeed, the first successful clinical trials using FGFs for the treatment of radiation- and chemotherapy-induced mucosal epithelial damage have been announced.     

Fibroblast (heparin-binding) growing factors in neuronal development and repair

Nearly thirty growth and trophic factors that have been purified from mammalian tissues in the last 15 yr have been found to share chemical identity. The results of their chemical purification and molecular cloning show that they are two distinct polypeptides (Mr 17,400 and 18,400), each of which gives rise to families of smaller size peptides. These peptides share a common affinity for heparin. In view of this property, a common nomenclature for the two principle peptide growth factors (heparin-binding growth factor classes 1 and 2; HBGF-1 and -2) has been proposed. However, the names acidic and basic Fibroblast Growth Factors (aFGF,bFGF), which were applied to them originally to describe their mitogenic activity, are more commonly in use and will therefore be adopted in this review. Brain tissue is one of the richest sources of FGFs. It has been used as a starting point for their chemical purification and to prepare genomic libraries for molecular cloning of the aFGF and bFGF genes. There is increasing evidence that these growth factors, expressed in neurons and glia throughout the mammalian nervous system, are implicated in neuronal cell proliferation, differentiation, and histogenesis. FGFs have a strong affinity not only for heparin, but also for the related heparan sulphate proteoglycans that are abundant in neural tissues. This fact provides a clue to the importance of tissue-associated proteoglycans in mediating the release, sequestration, and activation of FGFs and the modulation of their receptor binding and bioactivity. The relevance of FGFs to neural development and their mechanisms of action in neurons will be considered in light of the existing literature describing their biological properties and activity in mesodermal cell types. Evidence is reviewed showing that FGFs have in vivo biological activity, ameliorating the degeneration of central and peripheral neurons after axotomy. The presence and implications of high levels of FGFs in adult mammalian brain provides a direction for future research into neural regeneration. The bioactivity of FGFs in neural tissue may not depend on the regulation of their expression per se, but on the subregional modification of their interaction with proteoglycans.     

Effect of zinc on gene expression in osteoblastic MC3T3-E1 cells: enhancement of Runx2, OPG, and regucalcin mRNA expressions

Activation of fibroblast growth factor receptors (FGFRs) requires the formation of a ternary complex between fibroblast growth factors (FGFs), FGFRs, and heparan sulfate proteoglycans, which are all located on the cell surface and the basement membrane (BM)/extracellular matrix (ECM). Heparan sulfate proteoglycans appear to stabilize FGFs by inhibiting the rapid degradation of FGFs normally observed in solution. Because of the pivotal role of FGFs in proliferative and developmental pathways, a number of recent studies have attempted to engineer microenvironments to stabilize growth factors for use in applications in tissue culture and regenerative medicine. In this communication, we demonstrate that covalent linkage of FGF-2 to nanofibrillar surfaces (defined as covalently bound FGF-2) composed of a network of polyamide nanofibers resulted in the maintenance of the biological efficacy of FGF-2 when stored dry for at least 6 months at 25°C or 4°C. Moreover, covalently bound FGF-2 was more potent than FGF-2 in solution when measured in cellular assays of proliferation and viability using a variety of cell types. Covalently bound FGF-2 also strongly activated FGFR, extracellular signal-regulated kinase (ERK1/2), and c-fos. Hence cell-signaling molecules can be incorporated into a synthetic nanofibrillar surface, providing a novel means to enhance their stability and biological activity.     

Glycosaminoglycan affinity of the complete fibroblast growth factor family

BACKGROUND: Many fibroblast growth factor family proteins (FGFs) bind to the heparan sulfate/heparin (HP) subtypes of sulfated glycosaminoglycans (GAGs), and a few have recently been reported to also interact with chondroitin sulfate (CS), another sulfated GAG subtype. METHODS: To gain additional insight into this interaction, we prepared all currently known FGFs (i.e., FGF1-FGF23) and assessed their affinity for HP, CS-B, CS-D and CS-E. In addition, midkine, hepatocyte growth factor and pleiotrophin were studied as other known HP-binding proteins. RESULTS: We found that members of the FGF19 subfamily (i.e., FGF15, 19, 21 and 23) had little or no affinity for HP; all of the other secretable growth factors tested had strong affinities for HP, as was indicated by the finding that their elution from HP-Sepharose columns required 1.0-1.5 M NaCl. We also found that FGF3, 6, 8 and 22 had strong affinities for CS-E, while FGF5 had a moderate affinity for CS-D. The interactions between FGFs and GAGs thus appear to be more diverse than previously understood. GENERAL SIGNIFICANCE: This is noteworthy, as the differential interactions of these growth factors with GAGs may be key determinants of their specific biological activities.