Recovery of mitogenic activity of a growth factor mutant with a nuclear translocation sequence

Mutants of basic fibroblast growth factor identify different cellular response programs

Mutations, expected to affect the intracellular routing, i.e. additional nuclear localization sequences (NLS; the natural 23 kDa isoform and a 17D27R mutant) and/or a deletion of amino acids 26-29 (23 delta 26-29 and 17 delta 26-29), were introduced in basic fibroblast growth factor (bFGF). The mutants were assayed for their mitotic activity and their capacity to induce a tissue-specific response in human umbilical vein endothelial cells [HUVECs; induction of urokinase plasminogen activator receptor (u-PAR)], or in rat lens epithelial cells (fibre cell differentiation). In HUVECs, the 17D27R mutant had wild type activity, the 23 kDa and the delta 26-29 proteins were impaired in the induction of both mitosis and u-PAR. The delta 26-29 proteins, but not the 23 kDa protein or 17D27R mutant, were also impaired in receptor binding in that they bound only to a subset of receptors. The concentration of 17 kDa bFGF required for half maximal u-PAR response was 30 fold higher than for the half maximal 3H-thymidine incorporation. Addition of an NLS to bFGF strongly inhibited the induction of fibre cell differentiation, though it had little effect on the stimulation of DNA synthesis. The 17 delta 26-29 kDa mutant had wild type differentiation activity but was a poor mitogen for lens epithelial cells.

Protection of rat myocardium by mitogenic and non-mitogenic fibroblast growth factor during post-ischemic reperfusion

The effects of acidic fibroblast growth factor (FGF-1) and basic fibroblast growth factor (FGF-2) and a non mitogenic form of FGF1 on myocardial ischemia and reperfusion were assessed. Rats underwent 10 minutes of coronary artery occlusion followed by 24 hours of reperfusion. Creatinine kinase content of the affected myocardium showed that both fibroblast growth factors 1 and 2 effectively protected against ischemia reperfusion injury (p < 0.01), and that the vasoactive but nonmitogenic form of the FGF1 was equally protective (p < 0.01 versus control + vehicle). The results were confirmed by light and electron-microscopy histological studies. Histological evaluations after treatment with the non-mitogenic fibroblast growth factor 1 showed that it did not generate the severe hyperplasia and connective tissue disorganization observed with the native mitogenic proteins. The possibility of using a non-mitogenic form of fibroblast growth factor for cardio-protection circumvents many of the potentially undesirable effects that may derive from systemically introducing broad spectrum acting fibroblast growth factors in vivo. This myocardial protection observed 24 hours after the treatment with fibroblast growth factors, and the efficacy of the non-mitogenic form of the protein, also suggest that the protective effect of fibroblast growth factors may be due to the increased blood flow rather than to angiogenesis.

Application of an optimised reverse transcriptase-polymerase chain reaction method to determine the cDNA nucleotide sequence of porcine basic fibroblast growth factor

In the present investigation, oligonucleotide primers of high hybridisation stringency have been used in combination with optimised reverse transcriptase-polymerase chain reaction (RT-PCR) methods for the determination of the cDNA sequence corresponding to porcine FGF-2 mRNA present in brain and uterine tissue. Application of these optimised methods have overcome previous limitations associated with the low abundance of the porcine FGF-2 mRNA, and allowed as little as 100 micrograms of tissue to be employed to generate the complete cDNA nucleotide sequences as well as to provide specific template fragments selected for their suitability in subsequent ligation and mutagenesis studies with conventional expression vectors. Comparisons of the cDNA nucleotide and the deduced amino-acid sequence of porcine FGF-2 and the known FGF-2s from other species have indicated nucleotide sequence homologies of 95.5% with the bovine, 94.7% with the human and 88.7% with the rat FGF-2 cDNA whilst amino-acid sequence homologies of 100% with the bovine, 98.7% with the human and 96.8% with the rat FGF-2, respectively, were found. Based on these investigations, application of analogous strategies and methods with low abundance mRNAs related to other members of this family of growth factors, as well as very low abundance mRNAs of other protein growth factor, in the pig should now be readily realised.

Bafilomycin A1 induces apoptosis in PC12 cells independently of intracellular pH

PC12 cells growth-arrested with bafilomycin A1 died showing apoptotic chromatin condensation in the nuclei. The bafilomycin A1-induced chromatin condensation was preceded by neurite outgrowth (NOG), required higher concentrations of bafilomycin A1 than NOG, and was suppressed by cycloheximide and aurintricarboxylic acid. NH4Cl (10 mM), another acidotropic pH perturbing agent, neither induced apoptotic chromatin condensation by itself nor suppressed that induced by bafilomycin A1, suggesting that bafilomycin A1-induced apoptosis occurs independently of intracellular pH in PC12 cells.

The human diploid fibroblast senescence pathway is independent of interleukin-1 alpha mRNA levels and tyrosine phosphorylation of FGFR-1 substrates

In vitro cellular senescence of human umbilical vein endothelial cells (HUVEC) may involve the intracellular activity of the signal peptide-less cytokine interleukin (IL)-1 alpha. To determine whether senescence of other human diploid cells involves the function of IL-1 alpha, we examined the steady-state expression of IL-1 alpha mRNA in IMR-90 fibroblasts. The IL-1 alpha transcript was not elevated in senescent IMR-90 cells. With the exception of the plasminogen activator inhibitor (PAI)-1 transcript, other IL-1 alpha-response gene mRNAs were not induced in senescent IMR-90, although the mRNA for each gene was induced by exogenous IL-1 alpha. The mRNA expression of cell cycle-specific genes demonstrated that Fos and ornithine decarboxylase (ODC) were induced in young and senescent cells in response to both serum and fibroblast growth factor (FGF)-1. Histone (H)3 mRNA was induced by serum in young cells, but not in senescent cells, and FGF-1 failed to induce H3 mRNA in either young or senescent cells. Further, while young IMR-90 populations were able to respond to serum as an initiator of DNA synthesis and cell growth, they did not exhibit a response to exogenous FGF-1. FGF receptor (R)-1 substrates were not tyrosine phosphorylated in either young or senescent IMR-90 cells. These data demonstrate that IL-1 alpha and FGF-1 may have different functions in HUVEC and IMR-90 fibroblast populations including distinct pathways for the regulation of cellular growth and senescence.

Molecular modeling and deletion mutagenesis implicate the nuclear translocation sequence in structural integrity of fibroblast growth factor-1

The sequence NYKKPKL in the NH2 terminus of fibroblast growth factor (FGF)-1 has been proposed to affect the long term activities of FGF-1 through its function as a nuclear translocation signal or its role in stabilization of the structure required to sustain binding and activation of the transmembrane receptor kinase. A dynamic molecular model of FGF-1 docked into a duplex of the FGF receptor ectodomain and a hexadecameric heparin chain suggests that the NYKKPKL sequence does not directly interact with heparin or the receptor, but rather the lysine-leucine residues within the sequence indirectly stabilize a major receptor-binding domain. Concurrent with a marked increase in dependence on exogenous heparin for optimal activity, sequential deletion of residues in the NYKKPKL sequence in FGF-1 resulted in a progressive loss of thermal stability, resistance to protease, mitogenic activity, and affinity for the transmembrane receptor. The largest change resulted from deletion of the entire sequence through the lysine-leucine residues. In the presence of sufficiently high concentrations of heparin, the deletion mutants exhibited mitogenic activity equal to wild-type FGF-1. The results confirm that a primary role of the NYKKPKL sequence domain is to maintain the structural integrity of FGF-1 required for optimal binding to and activation of the heparan sulfate-transmembrane receptor complex.

Fibroblast growth factor-2 binds to the regulatory beta subunit of CK2 and directly stimulates CK2 activity toward nucleolin

The presence of fibroblast growth factor-2 (FGF-2) in the nucleus has now been reported both in vitro and in vivo, but its nuclear functions are unknown. Here, we show that FGF-2 added to nuclear extract binds to protein kinase CK2 and nucleolin, a CK2 natural substrate. Added to baculovirus-infected cell extracts overexpressing CK2 or its isolated subunits, FGF-2 binds to the enzyme through its regulatory beta subunit. Using purified proteins, FGF-2 is shown to directly interact with CK2 and to stimulate CK2 activity toward nucleolin. Furthermore, a mitogenic-deficient FGF-2 mutant protein has an impaired ability to interact with CK2 and to stimulate CK2 activity using nucleolin as substrate. We propose that in growing cells, one function of nuclear FGF-2 is to modulate CK2 activity through binding to its regulatory beta subunit.

Fibroblast growth factor (FGF) homologous factors: new members of the FGF family implicated in nervous system development

Four new members of the fibroblast growth factor (FGF) family, referred to as fibroblast growth factor homologous factors (FHFs), have been identified by a combination of random cDNA sequencing, data base searches, and degenerate PCR. Pairwise comparisons between the four FHFs show between 58% and 71% amino acid sequence identity, but each FHF shows less than 30% identity when compared with other FGFs. Like FGF-1 (acidic FGF) and FGF-2 (basic FGF), the FHFs lack a classical signal sequence and contain clusters of basic residues that can act as nuclear localization signals. In transiently transfected 293 cells FHF-1 accumulates in the nucleus and is not secreted. Each FHF is expressed in the developing and adult nervous systems, suggesting a role for this branch of the FGF family in nervous system development and function.

Cloning of multiple chicken FGF1 mRNAs and their differential expression during development of whole embryo and of the lens

Five different 5' untranslated regions (5' UTRs) of FGF1 mRNAs were cloned in chicken. The structure of these transcripts suggests that, as in mammals, distinct 5' untranslated exons are spliced to the first coding exon via alternative splicing and alternative promoter usage. In an attempt to correlate the expression of specific transcripts to distinct biological activities, the distribution of these transcripts in different tissues and during the development of both the whole embryo and the lens was studied. In tissues, we have shown a differential, but not exclusive, expression of these transcripts. In the whole embryo, the expression of one transcript correlates with later developmental processes. In the lens, only two transcripts were detected that are both differently expressed and distributed. These results suggest that the biological properties of FGF1 depend on the expression of specific FGF1 mRNAs. Because these transcripts only differ in their 5' UTRs, they could be involved in distinct translational controls.

Immunolocalization of FGF-1 and receptors in human renal allograft vasculopathy associated with chronic rejection

Despite recognition of chronic vasculo-occlusive disease in solid organ transplantation, the exact pathophysiologic events resulting in neointima formation remain to be elucidated. Since acidic fibroblast growth factor (FGF-1) is an established modulator of vascular cell function, we examined the expression of this growth factor and its high affinity receptors in both relevant renal transplant controls (n = 5) and tissue from patients (n = 19) who underwent nephrectomy following graft loss secondary to chronic rejection. In situ hybridization and immunohistochemical studies demonstrated minimal vascular expression and distribution of FGF-1 and FGF high affinity receptors in the normal human kidney. In contrast, vascular lesions in kidney allografts experiencing chronic rejection demonstrated the exaggerated appearance of FGF-1 ligand and receptors. Immunoreactive FGF-1 readily was detected in medial smooth muscle cells and focal areas of intimal hyperplasia, particularly in association with the presence of inflammatory infiltrate. Enhanced staining for FGF-1 mRNA primarily was associated with the appearance of resident inflammatory cells. Medial smooth muscle cells of hyperplastic vascular structures demonstrated the greatest immunoappearance of FGF receptors-however, diffuse immunostaining also was observed in areas of intimal hyperplasia. The enhanced appearance of both FGF-1 and FGF receptors in the vascular wall suggests that this polypeptide mitogen may serve as an important mediator of growth responses associated with neointima development and angiogenesis during chronic rejection of human renal allografts.

FGF-1-dependent proliferative and migratory responses are impaired in senescent human umbilical vein endothelial cells and correlate with the inability to signal tyrosine phosphorylation of fibroblast growth factor receptor-1 substrates

Senescent cells do not proliferate in response to exogenous growth factors, yet the number and affinity of growth factor receptors on the cell surface appear to be similar to presenescent cell populations. To determine whether a defect in receptor signaling exists, we analyzed human umbilical vein endothelial cells (HUVEC) since HUVEC growth is absolutely dependent upon the presence of FGF. We report that in both presenescent and senescent HUVEC populations, FGF-1 induces the expression of cell cycle-specific genes, suggesting that functional FGF receptor (FGFR) may exist on the surface of these cells. However, the tyrosine phosphorylation of FGFR-1 substrates, Src and cortactin, is impaired in senescent HUVEC, and only the presenescent cell populations exhibit a FGF-1-dependent Src tyrosine kinase activity. Moreover, we demonstrate that senescent HUVEC are unable to migrate in response to FGF-1, and these data correlate with an altered organization of focal adhesion sites. These data suggest that the induction of gene expression is insufficient to promote a proliferative or migratory phenotype in senescent HUVEC and that the attenuation of the FGFR-1 signal transduction pathway may be involved in the inability of senescent HUVEC to proliferate and/or migrate.

Nuclear accumulation of fibroblast growth factor receptors is regulated by multiple signals in adrenal medullary cells

In an effort to determine the localization of fibroblast growth factor (FGF) receptors (FGFR) that could mediate the intracellular action of FGF-2, we discovered the presence of high-affinity. FGF-2 binding sites in the nuclei of bovine adrenal medullary cells (BAMC). Western blot analysis demonstrated the presence of 103-, 118-, and 145-kDa forms of FGFR1 in nuclei isolated from BAMC. 125I-FGF-2 cross-linking to nuclear extracts followed by FGFR1 immunoprecipitation showed that FGFR1 can account for the nuclear FGF-2 binding sites. Nuclear FGFR1 has kinase activity and undergoes autophosphorylation. Immunocytochemistry with the use of confocal and electron microscopes demonstrated the presence of FGFR1 within the nuclear interior. Nuclear subfractionation followed by Western blot or immunoelectron microscopic analysis showed that the nuclear FGFR1 is contained in the nuclear matrix and the nucleoplasm. Agents that induce translocation of endogenous FGF-2 to the nucleus (forskolin, carbachol, or angiotensin II) increased the intranuclear accumulation of FGFR1. This accumulation was accompanied by an overall increase in FGF-2-inducible tyrosine kinase activity. Our findings suggest a novel mode for growth factor action whereby growth factor receptors translocate to the nucleus in parallel with their ligand and act as direct mediators of nuclear responses to cell stimulation.

Immunolocalization of FGF-1 and receptors in glomerular lesions associated with chronic human renal allograft rejection

Glomerular lesions are considered one of the more detrimental pathologic changes associated with chronic rejection of renal allografts. To elucidate potential pathophysiologic mechanisms associated with transplant glomerulopathy, we examined the expression of acidic fibroblast growth factor (FGF-1) and its high-affinity receptors (FGFR) in both relevant renal transplant controls (n=5) and tissue from patients (n=19) who underwent nephrectomy following graft loss secondary to chronic rejection. In situ immunohistochemical analyses demonstrated minimal staining and distribution of FGFR and FGF-1, which was localized to the mesangial matrix in glomeruli from normal human kidneys. In situ hybridization failed to detect the presence of FGF-1 mRNA in control tissue. In contrast, each stage of the developing glomerular lesion associated with chronic rejection demonstrated the exaggerated appearance of FGF-1 protein in visceral and parietal epithelial cells. Intense staining for FGF-1 protein did not correlate with the increased appearance of FGF-1 mRNA, which was restricted to circulating inflammatory cells. Glomeruli in kidneys with findings of chronic rejection also exhibited increased immunodetection of both FGFR and PCNA in mesangial and epithelial cells. Immunogold labeling of chronically rejected visceral epithelial cells revealed both cytoplasmic and nuclear/localization of FGF-1, thereby establishing mitogenic potential of the growth factor. The enhanced appearance of both biologically active FGF-1 and FGFR suggests that this polypeptide may serve as an important mediator of growth responses associated with glomerular lesion development during chronic rejection.

The nuclear trafficking of extracellular fibroblast growth factor (FGF)-1 correlates with the perinuclear association of the FGF receptor-1alpha isoforms but not the FGF receptor-1beta isoforms

The alternatively spliced fibroblast growth factor receptor (FGFR)-1 isoforms, FGFR-1alpha and FGFR-1beta, are characterized by the presence of either three or two Ig-like loops in the extracellular domain and are differentially expressed during embryonic development and tumor progression. We have previously shown that in cells irreversibly committed to DNA synthesis by FGF-1, approximately 15% of cell surface FGFR-1 traffics to a perinuclear locale as a structurally intact and functional tyrosine kinase (Prudovsky, I., Savion, N., Zhan, X., Friesel, R., Xu, J., Hou, J., McKeehan, W. L., and Maciag, T. (1994) J. Biol. Chem. 269, 31720-31724). In order to define the structural requirement for association of FGFR-1 with the nucleus, the expression and trafficking of FGFR-1 in FGFR-1alpha and FGFR-1beta L6 myoblast transfectants was studied. Although FGFR-1alpha was expressed as p145 and p125 forms, FGFR-1beta was expressed as p120 and p100 forms in the L6 myoblast transfectants. Tunicamycin and N-glyconase experiments suggest that these forms of FGFR-1alpha and FGFR-1beta are the result of differential glycosylation. However, only the p145 form of FGFR-1alpha and the p120 form of FGFR-1beta were able to bind FGF-1 and activate tyrosine phosphorylation. Pulse-chase analysis of FGFR-1 biosynthesis suggests that the p125 and p100 proteins are the precursor forms of p145 FGFR-1alpha and p120 FGFR-1beta, respectively. Because ligand-chase analysis demonstrated that FGFR-1beta L6 myoblast transfectants exhibited a reduced efficiency of nuclear translocation of exogenous FGF-1 when compared with FGFR-1alpha transfectants, the intracellular trafficking of the FGFR-1alpha and FGFR-1beta isoforms was studied using an in vitro kinase assay to amplify immunoprecipitated FGFR-1. Indeed, the appearance of the FGFR-1alpha but not FGFR-1beta isoform in the nuclear fraction of L6 myoblast transfectants suggests that the distal Ig-like loop in FGFR-1alpha mediates the differential nuclear association of FGFR-1alpha as a structurally intact and functional tyrosine kinase. Further, the FGFR-1beta L6 myoblast transfectants but not the FGFR-1alpha myoblast transfectants exhibited a pronounced morphologic change in response to exogenous FGF-1. Because this phenotype change involves the induction of a rounded cellular shape, it is possible that the FGFR-1alpha and FGFR-1beta may ultimately exhibit differential trafficking to adhesion sites.

Serum-starvation induces the extracellular appearance of FGF-1

Autocrine/paracrine stimulation of cell growth by members of the fibroblast growth factor (FGF) family of polypeptides is dependent upon extracellular interactions with specific high affinity receptors at the cell surface. Acidic FGF (FGF-1) lacks a classical signal sequence for secretion, suggesting that intrinsic levels of this mitogen may not stimulate cell growth and utilizes a non-classical pathway to gain access to the extracellular compartment. To evaluate the biological potential of intracellular FGF-1 more rigorously, human cDNA sequences for the growth factor were introduced into primary murine embryonic fibroblasts using retrovirally mediated gene transfer. Heparin affinity, Western analysis, mitogenic assays, in situ immunohistochemical techniques, induction of tyrosine phosphorylation and antibody inhibition studies were used to demonstrate functionality of the FGF-1 transgene in this experimental model. Under normal culture conditions, cells constitutively expressing intracellular FGF-1 exhibited a slight growth advantage. In contrast, when maintained in reduced serum, these cells adopted a transformed phenotype and demonstrated an enhanced growth potential, induction of FGF-specific phosphotyrosyl proteins and the nuclear association of the growth factor. Analysis of the conditioned media from these stressed cells indicated that serum starvation induces the secretion of FGF-1 as latent high molecular mass complexes requiring reducing agents to activate its full biological potential.

Late signals are required for the stimulation of DNA synthesis in rat mammary fibroblasts by growth factors

Maximal stimulation of DNA synthesis in quiescent rat mammary (Rama) 27 fibroblasts is elicited by epidermal growth factor (EGF) or basic fibroblast growth factor (bFGF) 18 h after the initial addition of the growth factors-the 'lag' period. At maximally-stimulating concentrations, EGF and bFGF are interchangeable 9 h after their initial addition. When the initial concentration of growth factor is below that required to elicit a maximal response, it is possible to increase the level of DNA synthesis by increasing the concentration of growth factor 9 h after its initial addition. When the initial concentration of growth factor is high, substitution by a lower concentration of growth factor after 9 h allows a greater proportion of cells to synthesize DNA than would be expected from a continuous low dose of growth factor. Similar results are obtained when both the growth factor and its concentration are changed 9 h after the initial addition of growth factor. However, when EGF at a low concentration is substituted for a high concentration of EGF or bFGF the resulting increase in the levels of DNA synthesis is greater when EGF rather than bFGF is added for a second time. The half-life of the growth-stimulatory signals delivered by EGF and by bFGF 9 h after their initial addition is 1-2 h. These results suggest that to stimulate DNA synthesis: (i) EGF or bFGF must deliver a signal(s) continuously; (ii) the initial signals produced by EGF and bFGF are equivalent; (iii) the signals produced between 9-18 h by EGF may be different to those produced by bFGF.

Nuclear localization of functional FGF receptor 1 in human astrocytes suggests a novel mechanism for growth factor action

Fractionation of human astrocytes revealed the presence of 103, 118, and 145 kDa forms of FGF receptor 1 (FGFR1) in isolated nuclei. Only trace amounts of FGFR1 proteins were detected in the cell membrane or cytoplasmic fractions. Nuclear FGFR1 is found in the nucleoplasm and nuclear matrix but not in chromatin. Immuno-confocal microscopy further demonstrates the intranuclear presence of FGFR1 and its colocalization with FGF-2. Nuclear FGFR1 binds to FGF-2 and has tyrosine kinase activity. Translocation of functional growth factor receptors into the cell nucleus offers a novel mechanism for growth factor action.

Identification of a 79-kDa heparin-binding fibroblast growth factor (FGF) receptor in rat hepatocytes and its correlation with the different growth responses to FGF-1 between hepatocyte subpopulations

We reported previously that the potency of heparin-binding fibroblast growth factor-1 (FGF-1) as a mitogen for rat hepatocytes in primary culture is as high as that of epidermal growth factor (EGF) and hepatocyte growth factor. To gain insight into the pathophysiological significance of FGF-1 in hepatocyte growth, we analyzed the cooperative mitogenicity of FGF-1 and EGF. Results from a nuclear labeling assay using [3H]thymidine suggest that most hepatocytes in primary culture consist of two cell populations that differ in response to FGF-1; one is an FGF-1-responsive cell population, and the other is an EGF-responsive (but not FGF-1-responsive) cell population. On the other hand, autoradiographic analysis of 125I-FGF-1 binding demonstrated that high affinity FGF receptors were homogeneously distributed on the surface of all hepatocytes. Cross-linking 125I-FGF-1 to the nonstimulated hepatocyte surface indicated that the high affinity FGF receptors comprise two FGF receptors that differ in molecular mass (128 and 79 kDa). Furthermore, the 79-kDa receptor was preferentially down-regulated when the hepatocytes were stimulated with EGF or hepatocyte growth factor. These data suggest that the abundant expression of the 79-kDa FGF receptor on some populations of hepatocytes is involved in their lack of response to FGF-1. The 128- and 79-kDa FGF receptors were assigned as FGFR2 using an antibody specific to the ectodomain of FGFR2, whereas the 79-kDa receptor was not reactive to the antibody against the carboxyl terminus of FGFR2. This 79-kDa FGF receptor was not tyrosine-phosphorylated in response to FGF-1 stimulation, while the 128-kDa FGF receptor was recognized by anti-phosphotyrosine antibody under the same conditions. Also, the heterodimer of 79- and 128-kDa FGF receptors was less tyrosine-phosphorylated than the homodimer of 128-kDa FGF receptors. These data suggest that the 79-kDa FGF receptor inhibits the function of the 128-kDa FGF receptor through their heterodimerization. Thus, we surmise that the difference in response to FGF-1 between the cell populations of normal rat hepatocytes was caused by the different levels of the 79-kDa FGF receptor in each cell population.

Basic fibroblast growth factor for stimulation of bone formation in osteoinductive or conductive implants

Basic Fibroblast Growth Factor (bFGF) is one of the endogenous factors found in bone matrix. bFGF is a mitogen for many cell types, including osteoblasts and chondrocytes. It can stimulate angiogenesis and osteoblast gene expression. The purpose of this study was to investigate whether exogenous bFGF can stimulate the formation of bone in bone grafts and in a bone graft substitute. In a model using demineralized bone matrix implants for bone induction, a dose of 15 ng bFGF per implant increased the number of chondrocytes and the amount of bone, whereas 1900 ng greatly inhibited cartilage and bone formation. These results are consistent with previous studies with this model, showing that a lower dose of bFGF increased bone calcium content and a higher dose reduced it. Thus, exogenous bFGF can stimulate proliferation during early phases of bone induction. A new device, the bone conduction chamber, was developed for the application of bFGF to bone conductive materials. This model made it possible to demonstrate a difference between the conductive properties of bone grafts and porous hydroxyapatite. bFGF increased bone ingrowth into bone graft inside the chamber and showed a biphasic dose-response curve, so that 8-200 ng per implant (0.4-10 ng/mm3) increased bone ingrowth, but higher or lower doses had no effect. The same doses had the same effects in porous hydroxyapatite. In both bone grafts and porous hydroxyapatite, the highest dose still caused an increase in ingrowth of fibrous tissue. The effect on bone ingrowth was first detected after 6 weeks, regardless if administration of bFGF started at implantation or 2 weeks later, using an implanted minipump. Hyaluronate gel was effective as a slow-release carrier for bFGF. In conclusion, bFGF stimulates bone formation in bone implants, depending on dose and method for administration.

Role of the nuclear localization sequence in fibroblast growth factor-1-stimulated mitogenic pathways

Fibroblast growth factor-1 (FGF-1) is a potent mitogen for mesoderm- and neuroectoderm-derived cell types in vitro. However, a mutant FGF-1 with deletion in its nuclear localization sequence (NLS, residues 21-27) is not mitogenic in vitro. We demonstrated that synthetic peptides containing this NLS were able to stimulate DNA synthesis in a FGF receptor-independent manner after they were delivered into living NIH 3T3 cells by a cell-permeable peptide import technique. The stimulation of maximal DNA synthesis by these peptides required the presence of peptides during the entire G1 phase of the cell cycle. The mitogenic effect was specific for the NLS of FGF-1 because a peptide with double point mutations at lysine residues was inactive in stimulating DNA synthesis. Our results suggest that the NLS plays an important role in the mitogenic pathway initiated by exogenous FGF-1 by its direct involvement in the nuclear transport and signaling of internalized FGF-1.

The neurotrophic activity of fibroblast growth factor 1 (FGF1) depends on endogenous FGF1 expression and is independent of the mitogen-activated protein kinase cascade pathway

The expression of fibroblast growth factor (FGF) 1, a potent neurotrophic factor, increases during differentiation and remains high in adult neuronal tissues. To examine the importance of this expression on the neuronal phenotype, we have used PC12 cells, a model to study FGF-induced neuronal differentiation. After demonstrating that FGF1 and FGF2 are synthesized by PC12 cells, we investigated if FGF1 expression could be a key element in differentiation. Using the cell signaling pathway to determine the effects of FGF1 alone, FGF1 plus heparin, or a mutated FGF1, we showed an activation to the same extent of mitogen-activated protein (MAP) kinase kinase and MAP kinase (extracellular regulated kinase 1). However, only FGF1 plus heparin could promote PC12 cell differentiation. Thus, the MAP kinase pathway is insufficient to promote differentiation. Analysis of the PC12 cells after the addition of FGF1 plus heparin or FGF2 demonstrated a significant increase in the level of FGF1 expression with the same time course as the appearance of the neuritic extensions. Transfection experiments were performed to enhance constitutivly or after dexamethasone induction the level of FGF1 expression. The degree of differentiation achieved by the cells correlated directly with the amount of FGF1 expressed. The MAP kinase pathway did not appear to be involved. Interestingly, a 5-fold increase in FGF1 in constitutive transfected cells extended dramatically their survival in serum-free medium, suggesting that the rise of FGF1 synthesis during neuronal differentiation is probably linked to their ability to survive in the adult. All of these data demonstrate that, in contrast to the MAP kinase cascade. FGF1 expression is sufficient to induce in PC12 cells both differentiation and survival. It also shows that auto- and trans-activation of FGF1 expression is involved in the differentiation process stimulated by exogenous FGFs through a new pathway which remains to be characterized.

Stimulation of proliferation of a human osteosarcoma cell line by exogenous acidic fibroblast growth factor requires both activation of receptor tyrosine kinase and growth factor internalization

U2OS Dr1 cells, originating from a human osteosarcoma, are resistant to the intracellular action of diphtheria toxin but contain toxin receptors on their surfaces. These cells do not have detectable amounts of fibroblast growth factor receptors. When these cells were transfected with fibroblast growth factor receptor 4, the addition of acidic fibroblast growth factor to the medium induced tyrosine phosphorylation, DNA synthesis, and cell proliferation. A considerable fraction of the cell-associated growth factor was found in the nuclear fraction. When the growth factor was fused to the diphtheria toxin A fragment, it was still bound to the growth factor receptor and induced tyrosine phosphorylation but did not induce DNA synthesis or cell proliferation, nor was any fusion protein recovered in the nuclear fraction. On the other hand, when the fusion protein was associated with the diphtheria toxin B fragment to allow translocation to the cytosol by the toxin pathway, the fusion protein was targeted to the nucleus and stimulated both DNA synthesis and cell proliferation. In untransfected cells containing toxin receptors but not fibroblast growth factor receptors, the fusion protein was translocated to the cytosol and targeted to the nucleus, but in this case, it stimulated only DNA synthesis. These data indicate that the following two signals are required to stimulate cell proliferation in transfected U2OS Dr1 cells: the tyrosine kinase signal from the activated fibroblast growth factor receptor and translocation of the growth factor into the cell.

Translocation of cytosol of exogenous, CAAX-tagged acidic fibroblast growth factor

Acidic fibroblast growth factor (aFGF) added externally to cells has been proposed to enter the nucleus and stimulate DNA synthesis, but it has remained controversial whether or not exogenous aFGF has the capability of crossing cellular membranes. To test this, a novel principle to study translocation of proteins to the cytosol was developed by fusing a C-terminal farnesylation signal, a CAAX tag (C = Cys, A = an aliphatic amino acid, and X = any amino acid), onto aFGF. Farnesylation is only known to occur in the cytosol and possibly in the nucleus. When incubated with NIH3T3 cells overnight, about one-third of the cell-associated, CAAX-tagged growth factor was farnesylated, indicating that efficient translocation had taken place. Binding to specific FGF receptors was required for translocation to occur. Part of the farnesylated growth factor was found in the nuclear fraction. The data indicate that CAAX-tagged aFGF added externally to cells is able to cross cellular membranes and enter the cytosol and the nucleus.

Actions of acidic fibroblast growth factor fragments on food intake in rats

Acidic fibroblast growth factor (aFGF) has suppressive effects on food intake. In the present study, the effect of aFGF fragments on food intake were investigated in rats. Infusion of a carboxyl-terminal fragment of aFGF, aFGF-(114-140), did not affect food intake, whereas an amino-terminal fragment of aFGF, aFGF-(1-15), was significantly inhibitory. Other amino-terminal fragments, aFGF-(1-20), aFGF-(1-29) and aFGF-(9-29), did not affect food intake. However, [Ala16]aFGF-(1-29) and [Ser16]aFGF-(1-29) in which the cysteine residue at position 16 was replaced with alanine and serine, respectively, had significant suppressive effects on food intake. Infusion of a functional antagonist for FGF receptor, anti-FGFR-1 antibody, into the lateral hypothalamus (LHA) significantly increased food intake. The results suggest that: the amino-terminal portion of aFGF is active in food intake suppression; the replacement of cysteine residue by alanine or serine is important in some amino-terminal aFGF fragments; and the LHA is involved in feeding suppression actions by aFGF and some fragments.

Co-localisation of autoimmune antibodies specific for double stranded DNA with procorticotrophin-releasing hormone within the nucleus of stably transfected CHO-K1 cells

Human autoantibodies and corticotrophin-releasing hormone (CRH)-specific antibodies have been used in a double-labelling immunofluorescence technique to demonstrate that immunoreactive CRH structures are co-localised with immunostaining produced by double stranded DNA-specific human autoantibodies within the nucleus of cultured ovarian cells of Chinese hamsters (CHO-K1). This co-localisation was confirmed using confocal microscopy. A metabolic labelling technique was used to investigate the role of the cytoskeleton in mediating nuclear translocation of proCRH within stably transfected CHO-K1 cells and showed that microtubule and actin disrupting agents had no effect upon the nuclear translocation of proCRH. These results, therefore, suggest that nuclear translocation of proCRH is not affected by drugs which disrupt the cytoskeleton and, consequently, modify the diameter of the nuclear pores.

Insulin-induced egr-1 expression in Chinese hamster ovary cells is insulin receptor and insulin receptor substrate-1 phosphorylation-independent. Evidence of an alternative signal transduction pathway

Insulin's effects primarily are initiated by insulin binding to its plasma membrane receptor and the sequential tyrosine phosphorylation of the insulin receptor and intracellular substrates, such as insulin receptor substrate-1 (IRS-1). However, studies suggest some insulin effects, including those at the nucleus, may not be regulated by this pathway. The present study compared the levels of insulin binding, insulin receptor and IRS-1 tyrosine phosphorylation, and phosphatidylinositol 3'-kinase activity to immediate early gene c-fos and egr-1 mRNA expression in Chinese hamster ovary (CHO) cells expressing only neomycin-resistant plasmid (CHONEO), overexpressing wild type human insulin receptor (CHOHIRc) or ATP binding site-mutated insulin receptors (CHOA1018K). Insulin binding in CHONEO cells was markedly lower than that in other cell types. 10 nM insulin significantly increased tyrosine phosphorylation of insulin receptor and IRS-1 in CHOHIRc cells. Phosphorylation of insulin receptor and IRS-1 in CHONEO and CHOA1018K cells was not detected in the presence or absence of insulin. Similarly, insulin increased phosphatidylinositol 3-kinase activity only in CHOHIRc cells. As determined by Northern blot, nuclear run-on analysis, and in situ hybridization, insulin induced c-fos mRNA expression, through transcription, in CHOHIRc cells but not in CHONEO and CHOA1018K cells, consistent with previous reports. In contrast, all three cell types showed a similar insulin dose-dependent increase of egr-1 mRNA expression through transcription. These data indicated that insulin-induced egr-1 mRNA expression did not correlate with the levels of insulin binding to insulin receptor or phosphorylation of insulin receptor and IRS-1. These results suggest that different mechanisms are involved in induction of c-fos and egr-1 mRNA expression by insulin, the former by the more classic insulin receptor tyrosine kinase pathway and the latter by a yet to be determined alternative signal transduction pathway.

Analysis of putative heparin-binding domains of fibroblast growth factor-1. Using site-directed mutagenesis and peptide analogues

The contribution of individual basic amino acids within three putative "consensus sequences" for heparin binding of fibroblast growth factor-1 have been examined by site-directed mutagenesis. The results indicate that a significant reduction in the apparent affinity of fibroblast growth factor-1 for heparin is only observed when basic residues in one of the three regions are mutated. Mutation in the other regions are without affect on heparin binding. The heparin binding properties of synthetic peptides based on the three "consensus sequences" paralleled the mutagenesis results. That is, synthetic peptides corresponding to regions of the protein that were affected by mutagenesis with respect to heparin binding exhibited a relatively high affinity for immobilized heparin, whereas those corresponding to regions of similar charge density that were unaffected by mutagenesis did not. In addition, amino acid substitution of a nonbasic residue in the heparin-binding peptide could abolish its heparin binding capacity. The heparin-binding peptide could antagonize the mitogenic activity of FGF-1, probably because of the heparin dependence of this activity. Together these data demonstrate that the heparin binding properties of fibroblast growth factor-1 are dictated by structural features more complex than clusters of basic amino acids. The results of these and other studies indicate that consensus motifs for heparin-binding require further definition. More importantly, the results provide a basis for the design of peptide-based inhibitors of FGF-1.

Inhibition by 5'-methylthioadenosine of cell growth and tyrosine kinase activity stimulated by fibroblast growth factor receptor in human gliomas

Stimulation of three human glioma cell lines with basic fibroblast growth factor (bFGF) led to the enhancement of cell growth and the rapid tyrosine phosphorylation of cellular proteins, including major substrates of 90 kD. A methyltransferase inhibitor, 5'-methylthioadenosine (MTA), inhibited dose dependently the bFGF-stimulated cell growth and protein tyrosine phosphorylation in glioma cells by blocking both receptor autophosphorylation and substrate phosphorylation, as shown by immunoblotting with antiphosphotyrosine antibodies and cross-linking bFGF to receptors. The antiproliferative activity of MTA correlated quantitatively with its potency as an inhibitor of bFGF-stimulated protein tyrosine kinase activity. The methyltransferase inhibitor MTA had no effect on either epidermal growth factor- or platelet-derived growth factor-stimulated protein tyrosine phosphorylation in glioma cells, but inhibited specifically bFGF-stimulated protein tyrosine kinase activity. The concentration of MTA required for inhibition of protein methylation correlated well with the concentration required for inhibition of bFGF-stimulated cell growth and protein tyrosine phosphorylation. Because MTA had no effect on numbers and dissociation constants of high- and low-affinity bFGF receptors, the inhibition of bFGF-stimulated bFGF receptor tyrosine kinase activity is not likely to be the result of a reduction in bFGF receptor and bFGF binding capacity. In fact, MTA delayed and reduced the internalization and nuclear translocation of bFGF, and the internalized bFGF was submitted to a limited proteolysis that converted it to lower molecular peptides whose presence remained for at least 22 hours. The effect of MTA on bFGF-stimulated tyrosine phosphorylation was immediate and readily reversible.

Farnesylation of CaaX-tagged diphtheria toxin A-fragment as a measure of transfer to the cytosol

Diphtheria toxin binds to receptor-positive cells through its B-fragment, the toxin is then endocytosed, and the low pH in endosomes triggers the translocation of the enzymatically active A-fragment to the cytosol. A synchronous release of A-fragments into the cytosol can be induced by exposing cells with surface-bound toxin to low pH. We have used this protein translocation system to develop a novel method to study whether or not a protein is exposed to the cytosol. Protein farnesylation is a cytosolic modification signaled by a C-terminal CaaX motif, and to visualize the translocation process, we added a farnesylation signal to the toxin A-fragment. The A-fragment with an added CaaX motif was farnesylated within 1 h after exposure of cells with surface-bound toxin to low pH, and also A-fragment translocated from endosomes was quantitatively farnesylated. The results indicate that all cell-mediated reduction of the toxin implicates translocation of the A-fragment to the cytosol. The farnesylation was inhibited by lovastatin, the alkylating agent NEM, and the peptidomimetic farnesylation inhibitor B581. Farnesylated A-fragment partitioned preferentially into the detergent phase upon extraction with Triton X-114. Our data suggest that farnesylation of a CaaX tag is generally applicable as a cytosolic marker, and this strategy for monitoring protein transfer to the cytosol may have considerable potential for studying the transport to the cytosol of proteins added externally to cells.

Distribution of acidic fibroblast growth factor mRNA-expressing neurons in the adult mouse central nervous system

The distribution of acidic fibroblast growth factor (aFGF) mRNA-expressing neurons was studied throughout the adult mouse central nervous system (CNS) with in situ hybridization histochemistry using a radiolabelled synthetic oligodeoxynucleotide probe complementary to the mRNA of human aFGF. We report here a widespread distribution of aFGF mRNA in several defined functional systems of the adult mouse brain, whereby the highest levels of aFGF mRNA were found in large somatomotor neurons in the nuclei of the oculomotor, trochlear, abducens, and hypoglossal nerves; in the motoneurons of the ventral spinal cord and the special visceromotor neurons in the motor nucleus of the trigeminal nerve; and in the facial and ambiguus nuclei. Labelled perikarya were also detected in all central structures of the auditory pathway including the level of the inferior colliculus, i.e., the lateral and medial superior nuclei; the trapezoid, cochlear, and lateral lemniscal nuclei; and parts of the anterior colliculus. Furthermore, many aFGF-positive cell bodies were found in the vestibular system and other structures projecting to the cerebellum, in the deep cerebellar nuclei, in somatosensory structures of the medulla (i.e., in the gracile, cuneate, and external cuneate nuclei), as well as in the spinal nucleus of the trigeminal nerve. The findings that aFGF mRNA is expressed in all components of several well-defined systems (i.e., in sensory structures) as well as in central neurons that process sensory information and, finally, in some efferent projections point towards a concept of aFGF expression primarily within certain neuronal circuitries.

Nucleolar association of fibroblast growth factor 3 via specific sequence motifs has inhibitory effects on cell growth

The dual subcellular fate of fibroblast growth factor 3 (FGF3) is determined by the competing effects of amino-terminal signals for nuclear localization and secretion (P. Kiefer, P. Acland, D. Pappin, G. Peters, and C. Dickson, EMBO J. 13:4126-4136, 1994). Mutation analysis has implicated additional basic domains in the carboxy-terminal region of the protein as necessary for nuclear uptake and the association of FGF3 with the nucleoli. Immunogold electron microscopy shows that FGF3 is predominantly within the dense fibrillar component of the nucleolus. A form of FGF3 that localizes exclusively in the nucleus and nucleolus was generated by removing signals for secretion, and expression of this nonsecreted FGF3 in a mammary epithelial cell line resulted in slowly growing colonies of enlarged cells. Thus, nuclear import and nucleolar association of FGF3 are determined by the concerted interaction of several distinct motifs, and the exclusive production of the nuclear isoform can inhibit DNA synthesis and cell proliferation.

Nucleolar localization of parathyroid hormone-related peptide enhances survival of chondrocytes under conditions that promote apoptotic cell death

Parathyroid hormone-related peptide (PTHrP) is a mediator of cellular growth and differentiation as well as a cause of malignancy-induced hypercalcemia. Most of the actions of PTHrP have been attributed to its interaction with a specific cell surface receptor that binds the N-terminal domain of the protein. Here we present evidence that PTHrP promotes some of its cellular effects by translocating to the nucleolus. Localization of transiently expressed PTHrP to the nucleolus was dependent on the presence of a highly basic region at the carboxyl terminus of the molecule that bears homology to nucleolar targeting sequences identified within human retroviral (human immunodeficiency virus type 1 and human T-cell leukemia virus type 1) regulatory proteins. Endogenous PTHrP also localized to the nucleolus in osseous cells in vitro and in vivo. Moreover, expression of PTHrP in chondrocytic cells (CFK2) delayed apoptosis induced by serum deprivation, and this effect depended on the presence of an intact nucleolar targeting signal. The present findings demonstrate a unique intracellular mode of PTHrP action and a novel mechanism by which this peptide growth factor may modulate programmed cell death.

Neurons express ciliary neurotrophic factor mRNA in the early postnatal and adult rat brain

The regional and subcellular localization in the central nervous system (CNS) of postnatal day 5, day 15, and adult rats of ciliary neurotrophic factor (CNTF) mRNA was examined by in situ hybridization with biotinylated riboprobes. Probe specificity was determined by Northern blot analysis of poly(A)+ RNA extracted from adult rat brain using digoxigenin labeled riboprobes and chemiluminescent detection. Both a 4 kb and a 1.2 kb transcript were detected in the cortex and brainstem. In situ hybridization revealed that CNTF mRNA was widely distributed in neurons and glia throughout the CNS at each of the developmental time points. The density of the neuronal hybridization signal was found to be greater in neuronal nuclei than in their cytoplasm. In the nucleus of most neurons, CNTF mRNA distribution was concentrated in a perinucleolar fashion. Alternate sections from the same animals, which were incubated with a specific polyclonal antibody against a CNTF peptide fragment, revealed that both neurons and glia in postnatal day 5, day 15, and adult rat brain were immunoreactive for CNTF.

The HIV-1 TAT protein induces the expression and extracellular appearance of acidic fibroblast growth factor

Mounting experimental evidence suggests that the TAT protein, released from human immunodeficiency virus-1 (HIV-1)-infected inflammatory cells, may genetically reprogram targeted cells within a localized environment to develop highly vascularized tumors of mesenchymal origin. The fibroblast growth factor (FGF) family of polypeptides has gained general acceptance as initiators of angiogenesis and functions as potent mitogens for mesoderm-derived cells. To evaluate a potential biological relationship between TAT and acidic FGF (FGF-1), primary murine embryonic fibroblasts either were transfected with the viral transactivator or were transduced (retrovirally mediated) with a secreted, chimeric form of the human polypeptide growth factor, human stomach tumor/Kaposi's sarcoma (hst/KS)FGF-1. Reverse transcriptase-polymerase chain reaction, Western blotting, in situ immunohistochemical, heparin affinity, DNA synthesis, and transient transfection techniques were used to confirm expression, localization, and functionality of the transgenes. Both transfected and transduced cells constitutively expressing either TAT or (hst/KS)FGF-1 adopted a transformed phenotype, maintained aggressive growth behavior, and demonstrated both induction of FGF-specific phosphotyrosyl proteins and nuclear association of FGF-1 and FGF-1 receptor. Increased levels of endogenous, murine FGF-1 mRNA (reverse transcriptase-polymerase chain reaction) and protein (immunoblot analysis) were apparent in both (hst/KS)FGF-1- and TAT-transformed cells. Medium conditioned by (hst/KS)FGF-1-transduced cells contained steady-state levels of biologically active FGF-1 which exhibited a representative molecular weight. Limited sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the conditioned medium from TAT-transformed cells demonstrated the appearance of FGF-1 as latent, high molecular weight complexes requiring reducing agents to activate full biological activity. Collectively, these results suggest that TAT induces the expression and secretion of FGF-1, which may be potentially relevant to the pathophysiological development of AIDS-Kaposi's sarcoma.

Inhibition of nuclear translocation of transcription factor NF-kappa B by a synthetic peptide containing a cell membrane-permeable motif and nuclear localization sequence

To control agonist-induced nuclear translocation of transcription factor kappa B (NF-kappa B) in intact cells, cell-permeable synthetic peptides were devised. Their import into intact cells was dependent on a hydrophobic region selected from the signal peptide sequences and was verified by their inaccessibility to extracellular proteases and by confocal laser scanning microscopy. When a cell-permeable peptide carried a functional cargo representing the nuclear localization sequence of NF-kappa B p50, it inhibited in a concentration-dependent manner nuclear translocation of NF-kappa B in cultured endothelial and monocytic cells stimulated with lipopolysaccharide or tumor necrosis factor-alpha. Synthetic peptide analogues with deleted hydrophobic cell membrane-permeable motif or with a mutated nuclear localization sequence were inactive. Cell membrane-permeable peptides were not cytotoxic within the concentration range used in these experiments. These results suggest that cell-permeable synthetic peptides carrying a functional cargo can be applied to control signal transduction-dependent subcellular traffic of transcription factors mediating the cellular responses to different agonists. Moreover, this approach can be used to study other intracellular processes involving proteins with functionally distinct domains.

A requirement for fibroblast growth factor in regulation of skeletal muscle growth and differentiation cannot be replaced by activation of platelet-derived growth factor signaling pathways

The distinct effects of cytokines on cellular growth and differentiation suggest that specific signaling pathways mediate these diverse biological activities. Fibroblast growth factors (FGFs) are well-established inhibitors of skeletal muscle differentiation and may operate via activation of specific signaling pathways distinct from recently identified mitogen signaling pathways. We examined whether platelet-derived growth factor (PDGF)-activated signaling pathways are sufficient to mediate FGF-dependent repression of myogenesis by introducing the PDGF beta receptor into a mouse skeletal muscle cell line. Addition of PDGF-BB to cells expressing the PDGF beta receptor activated the PDGF beta receptor tyrosine kinase, stimulated mitogen-activated protein (MAP) kinase, and increased the steady-state levels of junB and c-fos mRNAs. Despite the activation of these intracellular signaling molecules, PDGF beta receptor activation elicited no detectable effect on cell proliferation or differentiation. In contrast to PDGF-BB, addition of FGF-2 to myoblasts activated signaling pathways that resulted in DNA synthesis and repression of differentiation. Because of the low number of endogenous FGF receptors expressed, FGF-stimulated signaling events, including tyrosine phosphorylation and activation of MAP kinase, could be detected only in cells expressing higher levels of a transfected FGF receptor cDNA. As the PDGF beta receptor- and FGF receptor-stimulated signaling pathways yield different biological responses in these skeletal muscle cells, we hypothesize that FGF-mediated repression of skeletal muscle differentiation activates signaling pathways distinct from those activated by the PDGF beta receptor. Activation of PDGF beta receptor tyrosine kinase activity, stimulation of MAP kinase, and upregulation of immediate-early gene expression are not sufficient to repress skeletal muscle differentiation.

Identification of the domain within fibroblast growth factor-1 responsible for heparin-dependence

While the prototype members of the fibroblast growth factor (FGF) family, FGF-1 and FGF-2 are structurally related, the structural differences between these polypeptides predict that they will ultimately exhibit different biological roles. Indeed, a significant difference between these proteins is the dependence of FGF-1 on heparin for the generation of maximal mitogenic activity. In order to gain structural insight into the issue of FGF-1 heparin-dependence, a synthetic gene encoding FGF-2 was constructed with oligonucleotides in a four-cassette format similar to a synthetic gene previously constructed for FGF-1 (Forough et al. 1992, Biochem. Biophys. Acta 1090 293-298). This strategy permitted the molecular shuffling of corresponding cassette(s) between FGF-1 and FGF-2 to yield FGF-1:FGF-2 chimeras. Three amino acid changes (Lys86-->Glu, Tyr120-->His, and Thr121-->Ala) were introduced into the synthetic FGF-2 gene by the cassette format to generate convenient FGF-1 restriction sites, but these alterations did not significantly affect the mitogenic activity or the heparin-binding affinity of the recombinant FGF-2 protein when compared with native FGF-2. Among the various FGF-1:FGF-2 chimeric constructs, one designated FGF-C(1(1/2)1 1), which represents FGF-1 containing FGF-2 amino acid residues 65 to 81, displayed FGF-1-like heparin-binding affinity but it did not require the addition of exogenous heparin to manifest its mitogenic activity. These data suggest that the sequence within residues 65 and 81 from FGF-2 significantly contributes to the heparin-dependent character of FGF-1.

Antagonistic effects of different members of the fibroblast and platelet-derived growth factor families on adipose conversion and NADPH-dependent H2O2 generation in 3T3 L1-cells

3T3 L1-cells, which undergo adipose conversion in vitro, possess a stimulus-sensitive H2O2-generating system in their plasma membrane, and its properties are virtually identical with those of the insulin-sensitive human fat-cell oxidase [Krieger-Brauer and Kather (1992) J. Clin. Invest. 89, 1006-1013]. Insulin and insulin-like growth factor I were found to be active stimulators of NADPH-dependent H2O2 generation. Surprisingly, the acidic (a) and basic (b) isoforms of fibroblast growth factor (FGF) as well as the AA and BB homodimers of platelet-derived growth factor (PDGF) had antagonistic effects on NADPH-dependent H2O2 generation in plasma membranes which were parallelled by corresponding changes in H2O2 accumulation in intact cells. bFGF and PDGF BB (which inhibit NADPH-dependent H2O2 generation) prevented the adipose conversion of 3T3 L1-preadipocytes, and this effect could be reversed by exogenously supplied H2O2. Conversely, aFGF and PDGF AA, which stimulated H2O2 generation, accelerated adipocyte conversion in the presence of insulin and were adipogenic in themselves. Consistently, expression of the adipocyte phenotype induced by insulin, dexamethasone and isobutylmethylxanthine was enhanced in the presence of exogenous hypoxanthine/xanthine oxidase, whereas antioxidants, such as N-acetylcysteine or ascorbate, suppressed the process of differentiation. It is concluded that the H2O2 produced in response to hormones and cytokines may contribute to the development and maintenance of the differentiated state.

Differential modulation of cell phenotype by different molecular weight forms of basic fibroblast growth factor: possible intracellular signaling by the high molecular weight forms

To study possible functional differences of the 18-kD and high molecular weight forms of basic fibroblast growth factor (bFGF), we have examined the effect of endogenous production of different bFGF forms on the phenotype of NIH 3T3 cells. Cells transfected with cDNAs coding for either 18-kD bFGF (18-kD bFGF) or all four molecular forms (18, 22, 22.5, 24 kD; wild type [WT] bFGF) exhibit increased migration and decreased FGF receptor number compared to parental cells. However, migration and FGF receptor number of cells transfected with a cDNA coding only for high molecular weight bFGF (22, 22.5, and 24 kD; HMW bFGF) were similar to that of parental cells transfected with vector alone. Cells expressing HMW, 18 kD, or WT bFGF grew to high saturation densities in 10% serum. However, only cells expressing HMW or WT bFGF grew in low serum. Cell surface or metabolic labeling of the different cell types followed by immunoprecipitation with anti-bFGF antibody showed primarily cell surface-associated 18-kD bFGF. In addition, when cells expressing exclusively HMW bFGF were transfected with a cDNA coding for 18-kD bFGF, migration was increased, bFGF receptors were down-regulated, and 18-kD bFGF was found on the cell surface. Cells expressing 18-kD bFGF transfected with a cDNA encoding FGF receptor-2 lacking the COOH-terminal domain (dominant negative bFGF receptor) exhibited a flat morphology and decreases in migration and saturation density. Cells expressing HMW bFGF transfected with the dominant negative bFGF receptor continued to grow to a high saturation density, proliferated in low serum, and exhibited no morphological changes. These results indicate that increased cell migration and FGF receptor down-regulation are mediated by the extracellular interaction of 18-kD bFGF with its cell surface receptor. Growth in low serum may be stimulated by the intracellular action of HMW bFGF through mechanisms independent of the presence of a cell surface receptor. Thus, the different molecular forms of bFGF may act through distinct but convergent pathways.

Activation of a transfected FGFR-1 receptor in Madin-Darby epithelial cells results in a reversible loss of epithelial properties

Basic fibroblast growth factor (bFGF) is a potent mitogen for a wide variety of cell types derived from mesoderm and neuroectoderm. The activity of bFGF is mediated by several types of closely related receptors belonging to the tyrosine-kinase family of receptors. We have found that Madin-Darby epithelial cells (MDCK) do not seem to produce bFGF or bFGF receptors. High level expression of human bFGF cDNA in these cells did not produce any mitogenic or morphological effects. Expression of the mouse-derived cDNA encoding FGF receptor-1 (FGFR-1) in MDCK cells resulted in the acquisition of a fibroblast-like morphology when the transfected cells were cultured at low density in the presence of 0.6% fetal calf serum and 20 ng/ml bFGF. Acidic fibroblast growth factor (aFGF) also induced these morphological changes but not keratinocyte growth factor. The morphological effect was not accompanied by increased bFGF-induced cell proliferation and did not result in the loss of epithelial cell markers such as cytokeratins. However, the morphological transition was accompanied by changes in the intracellular distribution of actin. In spite of these changes the transfected cells formed monolayers even in the presence of bFGF. Coexpression of bFGF and FGFR-1 in the MDCK cells resulted in similar morphological effects that were not dependent upon exogenous bFGF. These morphological effects were mimicked by exposure of MDCK cells to either orthovanadate or phorbol ester. Parental and FGFR-1-expressing MDCK cells formed monolayers that displayed high electrical resistance. Incubation of monolayers of FGFR-1-transfected cells with bFGF resulted in the loss of trans-epithelial resistance. Monolayers of parental MDCK cells did not lose their trans-epithelial resistance in response to bFGF, although exposure to phorbol ester did result in the loss of their trans-epithelial resistance, indicating that the effects on the trans-epithelial resistance are mediated by protein kinase C activation. Interestingly, orthovanadate did not cause a loss of transepithelial resistance, suggesting that the loss of trans-epithelial resistance is separable from the morphological transition.

The release of fibroblast growth factor-1 from NIH 3T3 cells in response to temperature involves the function of cysteine residues

Fibroblast growth factor (FGF)-1 is released from NIH 3T3 cells in response to heat shock as a biologically inactive protein that is unable to bind heparin and requires activation by (NH4)2SO4 to generate a biologically active extracellular heparin-binding growth factor (Jackson, A., Friedman, S., Zhan, X., Engleka, K. A., Forough, R., and Maciag, T. (1992) Proc. Natl. Acad. Sci. USA 89, 10691-10695). To further study the mechanism of FGF-1 release in response to heat shock (42 degrees C), we examined the kinetics of FGF-1 release from FGF-1-transfected NIH 3T3 cells and observed that the cells require at least 1 h of exposure to heat shock conditions for the release of FGF-1. Interestingly, agents that interfere with the function of the endoplasmic reticulum-Golgi apparatus, exocytosis, and the multidrug resistance pathway (brefelden A, methylamine, and verapamil, respectively) do not inhibit the release of FGF-1 in response to temperature; rather, they exaggerate the release of FGF-1. Because immunoblot analysis of FGF-1 in the conditioned medium of heat-shocked NIH 3T3 cells revealed the presence of a minor band with an apparent molecular weight of a FGF-1 homodimer and because we have previously shown that FGF-1, but not FGF-2, is able to form a homodimer in response to chemical oxidation by CuCl2 (Engleka, K. A., and Maciag, T. (1992) J. Biol. Chem. 267, 11307-11315), we examined whether reducing agents would substitute for (NH4)2SO4 and activate extracellular FGF-1. Indeed, dithiothreitol and reduced glutathione are able to individually generate a FGF-1 monomer as a heparin-binding protein from the conditioned medium of heat-shocked NIH 3T3 cell transfectants. To confirm that cysteine residues are involved in the release of FGF-1 in response to temperature, we used mutagenesis to prepare a human FGF-1 Cys-free mutant in which Cys30, Cys97, and Cys131 were converted to serine. Analysis of the release of the FGF-1 Cys-free mutant in NIH 3T3 cells transfected with the FGF-1 Cys-free mutant demonstrated that the FGF-1 Cys-free mutant is not released into the conditioned medium in response to temperature. Interestingly, exposure of the NIH 3T3 cell FGF-1 Cys-free transfectants to brefelden A followed by heat shock also demonstrated the absence of the extracellular FGF-1 Cys-free mutant.(ABSTRACT TRUNCATED AT 400 WORDS)

An amino-terminal fragment peptide of acidic fibroblast growth factor modulates synaptic transmission in rat hippocampal slices

Effects of acidic fibroblast growth factor (aFGF) fragments such as aminoterminal aFGF (1-15) and carboxyl-terminal aFGF (114-140) on synaptic transmission were investigated in rat hippocampal slices. Stimulation was applied to Schaffer collateral/commissural afferents, and evoked population spikes were recorded in the CA1 pyramidal cell layer. Continuous perfusion of slices with aFGF (1-15) slightly decreased the basal amplitude of population spikes and significantly increased the paired-pulse facilitation. When brief tetanic stimulation (7 pulses at 100 Hz) was applied 30 min after the perfusion of aFGF (1-15), aFGF (1-15)-treated slices enhanced the magnitude of short-term potentiation after the tetanus and facilitated a generation of long-term potentiation. These effects of aFGF (1-15) were dose-dependent. Perfusion of slices with aFGF (114-140) had no effect on the basal spike amplitude, paired-pulse facilitation, and short-term potentiation. Both aFGF (1-15) and aFGF (114-140) had no effect on the DNA synthesis-stimulating activity in BALB/c 3T3-L1 cells. The results suggest that aFGF (1-15), which is not involved in mitogenic activity, is implicated in a modulatory mechanism of synaptic plasticity.

Nuclear accumulation of exogenous basic fibroblast growth factor in endothelial, fibroblast, and myoblast cell lines results in diverse biological responses

During studies comparing 125I-bFGF internalization between endothelial cells and other cell types, we found, unexpectedly, internalization and nuclear translocation of exogenously added 125I-bFGF in two cell lines: Chinese hamster ovary cells (CHO) and rat L6 myoblasts. These cell lines were previously reported to be devoid of FGF receptors. Furthermore, CHO cells showed a weak mitogenic response to added bFGF, while L6 cells were mitogenically unresponsive. By comparison, coronary venular endothelial cells (CVEC), BALB/c 3T3 fibroblasts, and BHK-21 cells, demonstrated internalization and nuclear translocation of added 125I-bFGF, and mitogenic responsiveness to the growth factor. Insulin alone stimulated DNA synthesis in all cell types, yet augmented bFGF-dependent DNA synthesis only in CVEC, 3T3, and BHK. All five cell types expressed FGF receptors as assessed by covalent crosslinking with 125I-bFGF and immunoblotting with anti-FGF receptor antibodies. Differing rates of cytoplasmic and nuclear accumulation of 125I-bFGF and partial inhibition of internalization by pretreatment of CVEC with chlorate support a recent model that bFGF can internalize by two mechanisms. Insulin did not significantly affect 125I-bFGF internalization or metabolism in any cell type. bFGF treatment resulted in weak inhibition of RNA synthesis in L6 cells. bFGF appears firmly bound to the nuclear matrix as little nuclear-bound 125I-bFGF in CVEC is released by DNAse I or RNAse A digestion, while washes with 0.5 M NaCl result in partial release. Nuclear bFGF may thus be involved in regulation of nuclear events (e.g., gene transcription and/or DNA replication).

The heparin-binding domain of heparin-binding EGF-like growth factor can target Pseudomonas exotoxin to kill cells exclusively through heparan sulfate proteoglycans

Heparin-binding EGF-like growth factor (HB-EGF) is a smooth muscle cell mitogen composed of both EGF receptor and heparin-binding domains. To better understand the function of its domains, intact HB-EGF or its heparin-binding (HB) domain (amino acids 1-45) were fused to a mutant Pseudomonas exotoxin with an inactivated cell-binding domain. The resulting chimeric toxins, HB-EGF-PE* and HB-PE*, were tested on tumor cells, proliferating smooth muscle cells and a mutant Chinese hamster ovary cell line deficient in heparan sulfate proteoglycans (HSPGs). Two targets were found for HB-EGF-PE*. Cells were killed mainly through EGF receptors, but the HB domain was responsible for killing via HSPGs. HB-PE* did not bind to the EGF receptor and thus was cytotoxic by interacting exclusively with HSPGs. We conclude that the HB domain of HB-EGF is able to mediate internalization through HSPGs, without requiring the EGF receptor.

Effects of fibroblast growth factors and related peptides on food intake by rats

The effects of acidic fibroblast growth factor (aFGF), basic FGF (bFGF), and related peptides, such as aFGF fragments, on food and water intake were investigated. Infusion of aFGF and bFGF into the third cerebral ventricle significantly suppressed food intake. The potency of aFGF was 1.5 that of bFGF in food intake inhibition. Both FGFs also suppressed water intake. Infusion of a carboxyl-terminal fragment of aFGF, aFGF-(114-140), did not affect food intake, whereas an amino-terminal fragment of aFGF, aFGF-(1-15), was significantly inhibitory. Other amino-terminal fragments, aFGF-(1-20) and aFGF-(1-29), did not affect food intake. However, [Ala16]aFGF-(1-29), in which the cysteine residue at position 16 was replaced with alanine, significantly suppressed food intake. Infusions of functional antagonists for FGFs, anti-aFGF, anti-bFGF, and anti-aFGF-(1-15) IgGs, into the lateral hypothalamus significantly increased food intake. The results suggest that: aFGF, bFGF, and some amino-terminal peptides of aFGF participate in the central regulation of food intake; the lateral hypothalamus is involved in their feeding suppression actions; and these peptides may function as physiologically relevant substances in the adult central nervous system, other than as neurotrophic factors.