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

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.

Heparin decreases activator protein-1 binding to DNA in part by posttranslational modification of Jun B

Heparin is a potent inhibitor of the proliferation and migration of vascular smooth muscle cells. This agent selectively inhibits the transcription of tissue-type plasminogen activator and interstitial collagenase, probably by decreasing the binding of activator protein-1 (AP-1) to phorbol ester-responsive elements in the promoters of these genes. Decreased AP-1 binding is not due to a direct inhibition by heparin, since heparinase digestion of nuclear extracts prepared from heparin-treated smooth muscle cells does not restore AP-1 binding activity. Treatment of cells with heparin suppresses the expression of Jun B, one of the components of AP-1. The major effect of heparin is at the level of posttranslational modification of Jun B. Results from pulse-chase labeling experiments show that the newly synthesized Jun B is rapidly converted to a higher-molecular-weight form and that conversion is suppressed by heparin. Evidence is presented suggesting that the heparin-inhibited event is phosphorylation of Jun B.

Molecular and structural analysis of nuclear localizing anti-DNA lupus antibodies

To determine the structure of three nuclear localizing lupus anti-DNA immunoglobulins (Igs) and to search for clues to mechanisms of cellular and/or nuclear access, their H- and L-chain variable region sequences were determined and subjected to three-dimensional modeling. Although the results indicate heterogeneity in their primary structures, the H chains are encoded by 3 members of the J558 VH gene family with a common tertiary conformation that is not shared by a J558-encoded nonnuclear localizing anti-DNA control Ig. Furthermore, at least two of the Igs share a conformational motif in the H-chain CDR3, and all three Igs contain multiple positively charged amino acids in their CDRs, resembling nuclear localization signals that direct protein nuclear import. Notably, each VH and VK gene is also found recurrently among previously described autoantibodies. Molecular analysis further indicates that both germline-encoded and significantly mutated V genes can generate nuclear localizing anti-DNA Ig.

Death of cultured postnatal rat CNS neurons by in vitro hypoxia with special reference to N-methyl-D-aspartate-related toxicity

We have established an in vitro hypoxia model using cultured central nervous system neurons from postnatal 4-day-old (P4) rats, in which death may be correlated with N-methyl-D-aspartate (NMDA)-related toxicity. P4 rat hippocampal and neocortical neurons in culture were prevented from death by the addition of MK-801, an NMDA receptor antagonist, and also partially by the removal of calcium ions from the medium, suggesting that NMDA receptors were associated with neuronal death in this in vitro hypoxia model. The neuronal death induced by the model was attenuated by the addition of alpha-tocopherol, indicating that free radicals emerged after hypoxia. This event seems similar to the hypoxia-reoxygenation phenomenon in in vitro hypoxia. Continuous treatment with basic fibroblast growth factor (bFGF) during hypoxia, and bFGF pretreatment for 6 h and removal before hypoxia induced the resistance to hypoxia-mediated cell death.

Expression of transforming growth factor alpha, amphiregulin and cripto-1 in human breast carcinomas

The expression of three epidermal growth factor (EGF)-related peptides, transforming growth factor alpha (TGF-alpha), amphiregulin (AR) and cripto-1 (CR-1), was examined by immunocytochemistry (ICC) in 68 primary infiltrating ductal (IDCs) and infiltrating lobular breast carcinomas (ILCs), and in 23 adjacent non-involved human mammary tissue samples. Within the 68 IDC and ILC specimens, 54 (79%) expressed immunoreactive TGF-alpha, 52 (77%) expressed AR and 56 (82%) expressed CR-1. Cytoplasmic staining was observed with all of the antibodies, and this staining could be eliminated by preabsorption of the antibodies with the appropriate peptide immunogen. Cytoplasmic staining with all of the antibodies was confined to the carcinoma cells, since no specific immunoreactivity could be detected in the surrounding stromal or endothelial cells. In addition to cytoplasmic reactivity, the AR antibody also exhibited nuclear staining in a number of the carcinoma specimens. No significant correlations were found between the percentage of carcinoma cells that were positive for TGF-alpha, AR or CR-1 and oestrogen receptor status, axillary lymph node involvement, histological grade, tumour size, proliferative index, loss of heterozygosity on chromosome 17p or overall patient survival. However, a highly significant inverse correlation was observed between the average percentage of carcinoma cells that expressed AR in individual tumours and the presence of a point-mutated p53 gene. Likewise, a significantly higher percentage of tumour cells in the ILC group expressed AR as compared with the average percentage of tumour cells that expressed AR in the IDC group. Of the 23 adjacent, non-involved breast tissue samples, CR-1 could be detected by ICC in only three (13%), while TGF-alpha was found in six (26%) and AR in ten (43%) of the non-involved breast tissues. These data demonstrate that breast carcinomas express multiple EGF-related peptides and show that the differential expression of CR-1 in malignant breast epithelial cells may serve as a potential tumour marker for breast cancer.

1,10-Phenanthroline increases nuclear accumulation of insulin in response to inhibiting insulin degradation but has a biphasic effect on insulin's ability to increase mRNA levels

Previous reports demonstrated that insulin is translocated through the cytoplasm to the nucleus of H35 hepatoma cells and suggested that nuclear insulin may be involved in stimulating transcription of immediate-early genes. In a recent study, inhibition of insulin-degrading enzyme with 1,10-phenanthroline, a Zn2+ chelator, caused a significant increase in the nuclear accumulation of insulin. The present study characterized the effects of 1,10-phenanthroline and its nonchelating isomer, 1,7-phenanthroline, on insulin degradation, nuclear accumulation, and stimulation of immediate-early gene expression. 1,10- but not 1,7-phenanthroline inhibited insulin degradation and increased nuclear accumulation of insulin in a dose-dependent manner. 1,7-phenanthroline caused a dose-dependent decrease in the expression of insulin-stimulated immediate-early genes, but had no significant effect on alpha-tubulin mRNA levels. In the presence of insulin, Northern analysis revealed that 1,10-phenanthroline at all concentrations tested increased alpha-tubulin mRNA levels, but had a biphasic effect on insulin-stimulated immediate-early gene expression. At low concentrations (5-200 microM), 1,10-phenanthroline increased the expression of insulin-stimulated g33, c-fos, and Egr-1 mRNA. At concentrations greater than 1 mM, insulin-stimulated immediate-early gene expression was decreased similar to the effect seen with 1,7-phenanthroline. Nuclear run-on analysis demonstrated that high concentrations of 1,10-phenanthroline decreased insulin-stimulated immediate-early gene transcription but had no effect on transcription of alpha-tubulin. However, low concentrations of 1,10-phenanthroline did not increase transcription of any genes.(ABSTRACT TRUNCATED AT 250 WORDS)

Astrocyte growth is regulated by neuropeptides through Tis 8 and basic fibroblast growth factor

The important intracellular mechanisms of astrocyte growth are not well defined. Using an inhibitor of astrocyte proliferation, atrial natriuretic peptide (ANP), and the glial mitogen endothelin (ET-3), we sought a common pathway for growth regulation in these neural cells. In cultured fetal rat diencephalic astrocytes, ANP selectively and rapidly inhibited the Tis 8 immediate early gene and protein. After 4 h, ANP selectively inhibited the basic fibroblast growth factor (bFGF) gene and protein. ET-3 significantly stimulated both Tis 8 and bFGF mRNAs and protein, but also stimulated several other immediate early and growth factor/receptor genes. An antisense oligonucleotide to Tis 8 strongly prevented ET-stimulated thymidine incorporation, while the inhibitory action of ANP was enhanced. The Tis 8 antisense oligonucleotide also significantly reversed ET-stimulated bFGF transcription and enhanced the bFGF inhibition caused by ANP. In addition, an antisense oligonucleotide to bFGF significantly reversed the ET-stimulated thymidine incorporation and enhanced the ANP inhibition of DNA synthesis. The sequential modulation of Tis 8, followed by bFGF, provides a novel mechanism for both positive and negative regulation of astrocyte growth by endogenous neuropeptides.

Dual mode of signal transduction by externally added acidic fibroblast growth factor

Acidic fibroblast growth factor (aFGF), fused to diphtheria toxin and translocated into cells, stimulated DNA synthesis in toxin-resistant cells lacking functional aFGF receptors while having a high number of diphtheria toxin receptors. In NIH 3T3 cells that lack diphtheria toxin receptors, but have receptors for aFGF, both aFGF and the fusion protein induced tyrosine phosphorylation, but only aFGF as such entered the nuclei and stimulated DNA synthesis. The results indicate that signaling occurs partly through cell surface receptors and partly by transport of the growth factor into the cell.

Nuclear translocation of angiogenin in proliferating endothelial cells is essential to its angiogenic activity

The intracellular pathway of human angiogenin in calf pulmonary artery endothelial (CPAE) cells has been studied by immunofluorescence microscopy. Proliferating CPAE cells specifically endocytose native angiogenin and translocate it to the nucleus, where it accumulates in the nucleoli. Nuclear translocation of angiogenin does not occur in nonproliferative, confluent CPAE cells. These cells were previously found to express an angiogenin-binding protein (AngBP) that was identified as smooth muscle alpha-actin. Exogenous actin, an anti-actin antibody, heparin, and heparinase treatment all inhibit the internalization of angiogenin, suggesting the involvement of cell surface AngBP/actin and heparan sulfate proteoglycans in this process. It has been established that two regions of angiogenin are essential for its angiogenic activity, one is its endothelial cell binding site and the other its catalytic site capable of cleaving RNA. CPAE cells do not internalize four enzymatically active angiogenin derivatives whose cell binding site is modified, but they do internalize two enzymatically inactive mutants whose cell binding site is intact. Thus, the putative cell binding site of angiogenin is necessary for both endocytosis and nuclear translocation, but the catalytic site is not. Three other angiogenic molecules are also translocated to the nucleus of growing CPAE cells. Overall, the results suggest that nuclear translocation of angiogenin and other angiogenic molecules is a critical step in the process of angiogenesis.

Up-regulation of aFGF expression in quiescent cells is related to cell survival

Exogenously administrated acidic FGF modulates the proliferation of several cell types, controls cell differentiation, and promotes cell survival. Most cells that are sensitive to exogenous aFGF are also capable of expressing it at very low levels. Thus in order to establish the role of endogenous aFGF as a mitogenic, differentiation, or survival factor, we studied the regulation of aFGF expression by evaluating the level of mRNA by PCR amplification and the concentration of protein by Enzyme Immuno Assay (EIA). In the lens, the amount of aFGF transcripts in nondividing cells of the central epithelium and in the differentiated fiber cells located at the periphery of the lens is similar, suggesting that endogenous aFGF is not involved with lens differentiation. In cultures, depending on the growth conditions, the endogenous aFGF expressed by Bovine Epithelial Lens (BEL) cells is subject to modulation. Cells arrested either by contact inhibition or by serum deprivation express more aFGF transcripts and protein than in exponentially growing cells, implying that endogenous aFGF has no mitogenic role under these conditions. In serum-deprived cells, the addition of specific aFGF antisense primers inhibits endogenous aFGF expression and leads to the death of these cells. These results associated with the higher expression of aFGF in nondividing BEL cells, suggesting that, contrary to exogenous aFGF, endogenous aFGF is not a mitogenic factor but a survival factor.

Cellular distribution, subcellular localization and possible functions of basic and acidic fibroblast growth factors

The distribution in the rat nervous system of acidic and basic fibroblast growth factors (FGFs) was analysed by a combination of biochemical and anatomical methods. Acidic FGF (aFGF) was found to be present exclusively in specific neuronal populations, such as motor neurons and basal forebrain cholinergic neurons. Basic FGF (bFGF) was found in astrocytes and in neurons in hippocampal area CA2. Within labelled astrocytes and CA2-neurons, bFGF was detected in both the cytoplasm and the nucleus. The levels of intracellular bFGF were manipulated by antisense oligonucleotide treatment of cultures of developing neural crest cells. Results indicated that the amount of melanogenesis in the cultures is likely to be regulated by intracellular, possibly nuclear bFGF.

Are fibroblast growth factors regulators of myogenesis in vivo?

Recent advances in understanding of skeletal muscle differentiation implicate fibroblast growth factors (FGFs) as regulators of myogenesis; however, the identity and actions of factors that repress myogenesis in vivo remain to be established. This review will focus on the fibroblast growth factor family and the evidence for its role in regulating myogenesis in culture and in vivo.

Expression of basic fibroblast growth factor in synovial tissues from patients with rheumatoid arthritis: detection by immunohistological staining and in situ hybridisation

OBJECTIVE

The distribution and production of basic fibroblast growth factor (bFGF) was examined on the synovium from patients with rheumatoid arthritis (RA) and osteoarthritis (OA).

METHODS

The localisation of bFGF was determined by an immunohistochemical staining procedure using anti-bFGF monoclonal antibody. The expression of bFGF mRNA was detected by nonradioactive in situ hybridisation using bFGF antisense oligo DNA.

RESULTS

The bFGF was found in the synovial lining cell, sublining stromal fibroblast-like cells, and vascular endothelial cells from patients with RA and OA. Little or no bFGF was found in non-inflamed synovium. Immunostaining of bFGF in the synovial cells was more extensive and intense in synovium of patients with RA than that of patients with OA. The nuclei of the synovial lining cell layer were also immunostained. These nuclear staining were more intense in the lining cell layer from RA patients with moderate or severe proliferation of synovial cells than in RA patients with mild proliferation. The bFGF mRNA was also detected in the synovial lining cell layer of the inflamed synovium.

CONCLUSION

The synovial lining cells produced bFGF. The proliferation of synovial cells in the inflamed joints may be the results of stimulation by the bFGF in autocrine manner.

Fibroblast growth factors and their receptors: an information network controlling tissue growth, morphogenesis and repair

The stimulation of cellular metabolism by the nine fibroblast growth factors (FGFs) is mediated by a dual-receptor system. This comprises a family of four receptor tyrosine kinases (FGFR) and heparan sulphate proteoglycans (HSPG). The stimulation of cell division by FGFs has an obligate requirement for both partners of the dual-receptor system. The binding of the nine FGFs to the FGFRs is marked by a pattern of overlapping specificity despite alternative splicing events generating a large number of FGFR proteins. Thus many of the FGFR isoforms bind several FGFs. It is likely that each FGF requires a different pattern of sulphation within the heparan sulphate chains for binding. Therefore, the HSPG receptors may provide additional specificity, allowing a cell to fine tune its response to the FGFs present in the extracellular milieu. The HSPG receptors also control the availability of FGFs and hence regulate the transport of FGFs within a tissue. FGF-stimulated cell division would appear to have a mandatory requirement for the FGFs to be translocated to the nucleus via the cytosol after interacting with the dual-receptor system. The consequences of the potential direct action of FGFs in stimulating cell division are examined in the light of current models of signal transduction.

Inhibitors of vacuolar-type H(+)-ATPase suppresses proliferation of cultured cells

We investigated effects of bafilomycin A1, a specific inhibitor of vacuolar-type H(+)-ATPase (V-ATPase), and its analogues on proliferation of various cultured cells. The proliferation of the various cell lines was suppressed by adding bafilomycin A1 to the culture medium. This inhibitory effect appeared at a concentration of nanomolar order and was dose dependent. Although the suppression was reversible, the drug exerted not only suppression of the proliferation but also death to some cell lines. Drug concentration required for 50% inhibition of the cell proliferation during 48 h differed markedly depending on cell species and the sensitivity appears to increase by the transformation of the cells. Two derivatives of concanamycin A, an analogue of bafilomycin A1, also inhibited strongly V-ATPase in vitro and in vivo, and simultaneously cell proliferation. Two concanamycin A derivatives which have lost inhibitory effect on V-ATPase lost inhibitory effect on cell proliferation as well. These results suggest that V-ATPase is involved in the machinery maintaining the cell proliferation.

Spatio-temporal distribution of acidic and basic FGF indicates a role for FGF in rat lens morphogenesis

As part of an investigation into the role of FGF in lens development, we have studied the distribution of both aFGF and bFGF during eye morphogenesis from embryonic days 10 to 18 (E10-E18) in the rat. For aFGF, reactivity was found only in ectoderm at E10, prior to contact between the optic vesicle and presumptive lens ectoderm. During lens placode formation (E11) there was a transient, diffuse reactivity for aFGF in anterior optic vesicle cells directly apposed to the labelled ectoderm of the lens placode. At E12 the diffuse reactivity of the lens placode had changed to a discrete localisation along the basolateral surfaces of differentiating cells in the lens pit. Similar reactivity was associated with neuroblasts along the inner margin of the optic cup. At the early lens vesicle stage (E13) the baso-lateral aFGF-like reactivity associated with elongating lens cells was more intense and extensive. From the late lens vesicle stage (E14) to E18, reactivity in the lens was increasingly restricted to the equatorial regions which incorporate the germinative and transitional zones. From E16 to E18, aFGF-like reactivity in the retina was predominantly localised in the peripheral regions corresponding to the developing ciliary body and iris and in the central retina associated with ganglion cell axons. For bFGF, weak reactivity was detectable as early as E13 in the developing lens capsule and increased in intensity during lens development with the posterior capsule reacting more intensely than the anterior capsule. Retinal bFGF-like reactivity was first detected at E14, associated with differentiating ganglion cells in the central retina. From E16 to E18 the retinal ganglion cells showed increasing reactivity and the pattern of reactivity followed the centro-peripheral pattern of retinal development. Thus reactivity for aFGF is first detected in presumptive lens ectoderm and subsequently in optic vesicle cells which are closely associated with lens ectoderm. This raises the possibility that aFGF may be involved in inductive interactions between presumptive lens ectoderm and optic vesicle. Furthermore the localisation patterns established for both aFGF and bFGF during lens and retina morphogenesis suggest an important role for FGF in regulating their morphogenesis and growth.

Inhibition of cell growth by bafilomycin A1, a selective inhibitor of vacuolar H(+)-ATPase

Bafilomycin A1, a potent selective inhibitor of vacuolar H(+)-ATPase, inhibited the growth of a variety of cultured cells dose-dependently, including golden hamster embryo and NIH-3T3 fibroblasts, whether or not they were transformed, and PC12 and HeLa cells. The concentration of bafilomycin A1 for 50% inhibition of cell growth ranged from 10 to 50 nM. The dose response was nearly parallel with that of the bafilomycin A1-induced lysosomal pH increase. The degree of pH increase for growth inhibition produced by bafilomycin A1 was similar to that produced by NH4Cl in which little difference was recognized in effect among cell types.

Retroviral expression of FGF-2 (bFGF) affects patterning in chick limb bud

To investigate the role of fibroblast growth factor-2 (basic fibroblast growth factor) in chick limb development, we constructed a replication-defective spleen necrosis virus to ectopically express fibroblast growth factor-2 in stage 20–22 chick limb bud. Because infecting cells in vivo proved to be inefficient, limb bud cells were dissociated, infected in vitro, and then grafted back into host limbs. This procedure caused duplications of anterior skeletal elements, including proximal humerus, distal radius, and digits 2 and 3. Eighty-nine percent of host wings receiving infected grafts at their anterior borders had duplications of one or more of these elements. The frequency of duplication declined dramatically when infected cells were grafted to progressively more posterior sites of host limb buds, and grafting to the posterior border had no effect at all. Several techniques were used to determine the role of infected tissue in forming skeletal duplications. First, staining with an fibroblast growth factor-2 specific monoclonal antibody showed higher than endogenous levels of fibroblast growth factor-2 expression associated with extra elements. Second, the host/donor composition of duplicated elements was determined by simultaneously infecting donor cells with viruses encoding fibroblast growth factor-2 or beta-galactosidase; donor tissue was then visualized by X-gal staining. Patterns of ectopic fibroblast growth factor-2 expression and X-gal staining confirmed the presence of infected donor tissue near duplicated structures, but the duplicated skeletal elements themselves showed very little staining. Similar results were obtained in duplications caused by infected quail wing bud cells grafted to the chick wing bud. These observations suggest that fibroblast growth factor-2-expressing donor tissue induced host tissue to form normally patterned extra elements. In support of this conclusion, implanting beads containing fibroblast growth factor-2 caused partial duplications of digit 2. These data provide the first direct evidence that fibroblast growth factor-2 plays a role in patterning in the limb bud.

Schwannoma-derived growth factor must be transported into the nucleus to exert its mitogenic activity

Schwannoma-derived growth factor (SDGF) is a mitogen and neurotrophic protein which belongs to the epidermal growth factor (EGF) family. There are two basic amino acid clusters in the SDGF molecule which are homologous to the nuclear targeting signal of the simian virus 40-encoded large tumor antigen. Mutational analysis of these clusters showed that they function as nuclear targeting signals, and a gel retardation assay showed that SDGF binds to A+T-rich DNA sequences. Both the wild-type SDGF and a mutant defective in the nuclear targeting signals activate the immediate early genes NGFI-A and c-fos. The wild-type SDGF is a mitogen for Swiss mouse 3T3 fibroblasts, but the mutant defective in the nuclear targeting signals is not mitogenic. Moreover, wild-type SDGF potentiates [3H]thymidine incorporation in NIH mouse 3T3 cells bearing an EGF receptor defective in the kinase domain, whereas the mutant SDGF does not stimulate DNA synthesis. These results suggest that transport into the nucleus is required for SDGF to induce a mitogenic response.

Growth factors: regulation of normal and neoplastic growth

This paper presents an overview of current trends in growth factor research. The first part of the review considers the current classification of growth factors and their receptors. A model of cell proliferation regulation by growth factors is then presented. The final section reviews the latest concepts of the involvement of growth factors in the development of neoplasia.

aFGF binding to low and high affinity receptors induces both aFGF and aFGF receptors dimerization

Acidic Fibroblast Growth Factor (aFGF) binds on two classes of fibroblast growth factor receptors, the high affinity receptors (HAR) a family of four known transmembrane tyrosine kinases and the low affinity receptors (LAR), related to cell surface heparan sulfate proteoglycan (HSPG). We analysed the relationship between the binding of aFGF on the HAR and on the LAR in bovine lens epithelial (BEL) cells in the presence of heparin or suramin. Through Northern blotting analysis we demonstrated that the three immunoglobulin-like transcript of FGF receptor type 1 (FGF-R1) is the major expressed high affinity receptor in BEL cells. On the contrary, HAR-aFGF complexes are present in two forms (150 kDa and 135 kDa) revealed by cross-linking experiments with 125I aFGF. Moreover 125I aFGF binding to BEL cell surface induces the spontaneous formation of a 125I aFGF dimer (31 kDa) which is then internalized and degraded in the cells as the 15.5 kDa aFGF native form is. It has been observed that heparin at 10 micrograms/ml (1) in cross-linking experiments, reduces by half the total number of HAR complexes by preventing the formation of the 150 kDa complex but does not affect the 135 kDa complex, (2) in binding experiments, suppress the spontaneous formation of the 125I aFGF dimer bound to LAR, and then its internalization and degradation in the cells. Moreover, we demonstrate that (1) only HAR contributes specifically and directly to the aFGF internalization process, (2) HAR internalization is ligand concentration and time saturable, (3) there is no desensitization of aFGF internalization induced by ligand binding to HAR, (4) a FGF dimerization process is highly dependent on the apparent affinity of FGF for heparin, since aFGF mutant with a reduced affinity for heparin does not promote the dimerization. These data strongly suggest that a heteroreceptor-aFGF complex (150 kDa) is formed by one molecule of HAR (FGF-R1) associated to one molecule of LAR through their respective interactions with a very stable aFGF homodimer. Such a three component receptor induced by FGF dimerization may be a process involved in the mechanism of action of FGFs which could explain the diversity of the biological response of FGF depending on the presence of the HSPG on the extra cellular matrix. In addition prebinding of unlabelled aFGF to the cells induces a 4 fold increase in the affinity of HAR to 125IaFGF concomitant with its down regulation by 80% and initiates the formation of the HAR homodimer.(ABSTRACT TRUNCATED AT 400 WORDS)

Acidic fibroblast growth factor gene 5' non-coding exon and flanking region from hamster DDT1 cells: identification of the promoter region and transcriptional regulation by testosterone and aFGF protein

Selected clones of Syrian hamster DDT1-MF2 cells are responsive to testosterone for growth. Heparin binding growth factor 1 (HBGF-1) or acidic fibroblast growth factor (aFGF) can replace testosterone (T) in the stimulation of growth in these cells. This phenomena is correlated with testosterone's ability to elevate aFGF mRNA two- to threefold in DDT1 cells. To better understand the possible mechanisms of regulation of aFGF mRNA by steroids and other growth factors, we isolated the aFGF 5' non-coding exon and its flanking region from a EMBL3 DDT1 genomic library, using a 5' non-coding exon 69 bp DDT1 aFGF cDNA probe. Clones spanning 30 kb of genomic DNA were isolated. After restriction mapping and DNA sequence analysis, the clones were shown to contain all of the 5' non-coding exon included in the cDNA and approximately 10 kb of 5' flanking region. RNase protection and primer extension assays confirmed that the 5' non-coding exon is included in the DDT1 aFGF mRNA and that a major transcription start site is approximately 136 bp upstream of the 5' non-coding splice junction of this exon. The 5' flanking region DNA was inserted into pBLCAT3 reporter gene and transfected into DDT1 cells. Chloramphenicol acetyltransferase (CAT) assays demonstrated that there are promoter elements in the -1645/-392 and -392/+131 regions of the aFGF gene in the context of DDT1 cells. NIH 3T3 cells, on the other hand, show no CAT activity with these aFGF-CAT plasmids. CAT assays also demonstrated that addition of testosterone (T) or aFGF to DDT1 cells increased CAT activity threefold. This activity was mapped to -1645 to -4 bp region of this DDT1 aFGF gene promoter.

Subcellular localization and biological activity of M(r) 18,000 basic fibroblast growth factor: site-directed mutagenesis of a putative nuclear translocation sequence

Residues 27-31 (Lys-Asp-Pro-Lys-Arg) of the 155-amino acid form of basic fibroblast growth factor (bFGF) are in good agreement with a consensus sequence for nuclear translocation. To evaluate the role of this sequence in mediating the intracellular localization and biological activity of bFGF, basic residues Lys-27, Lys-30, and Arg-31 were changed to neutral glutamine residues by site-directed mutagenesis of the human bFGF cDNA. The bFGF mutant (M1Q-bFGF) was expressed in eukaryotic cells and in prokaryotic cells, from which it was purified to homogeneity. Transient expression of bFGF cDNA and of M1Q-bFGF cDNA in simian COS-1 cells followed by immunolocalization and by subcellular fractionation indicated that both molecules localize in the nucleus, as well as in the cytoplasm of transfected cells, and interact with nuclear chromatin and with eukaryote DNA in a similar manner. Prokaryotic expression of M1Q-bFGF cDNA yields a polypeptide endowed with a receptor-binding capacity and mitogenic activity similar to that exerted by wild-type bFGF. However, recombinant M1Q-bFGF showed a drastically reduced capacity to induce the production of urokinase-type plasminogen activator (uPA) in endothelial cells. The uPA-inducing activity of M1Q-bFGF was fully restored by the presence of soluble heparin in the culture medium. In conclusion, the sequence bFGF(27-31) does not appear to represent a nuclear translocation and/or retention sequence for bFGF. However, neutralization of its basic residues seems to modify the tertiary structure of the growth factor, thus affecting some of its biological properties.

Characterization of the nuclear translocation of acidic fibroblast growth factor

The subcellular localization of human acidic FGF (aFGF; FGF-1) expressed to high levels by using a bacteriophage T7 RNA polymerase-driven vaccinia virus expression system was studied in BHK21 and HeLa cells. Acidic FGF was detected by immunoblotting or immunofluorescence using an affinity-purified rabbit polyclonal antibody. The nuclei of most transfected cells, but not nuclei of control cells, were strongly immunoreactive. The nuclear accumulation of aFGF was confirmed by subcellular fractionation and immunoblotting, indicating that about 50% of the expressed protein was located in the nuclei at 12 h after transfection. It has previously been reported that a putative N-terminal nuclear localization sequence (NLS) in aFGF is required for full mitogenic activity (Imamura et al., Science 249, 1567–1570, 1990). We found that deletion of the first 27 residues including the putative NLS did not prevent the nuclear translocation of aFGF in either cell type. This observation suggests that the putative NLS sequence is not essential for targeting aFGF to the cell nucleus. To analyze further the mechanism of nuclear import, purified aFGF was microinjected into the cytoplasm of growing BHK21 cells under various conditions. In chilled (4 degrees C) or ATP-depleted cells, the injected aFGF entered the nucleus with similar efficiency to that in control cells at 37 degrees C. This suggests that aFGF, which has a molecular mass of only 16,500, enters the cell nucleus by free diffusion, and possibly becomes trapped by binding to some nuclear structures. When added exogenously to growing BHK21 cells, aFGF was not localized to the nucleus. Instead, a punctate staining pattern in the cytosol was observed, reminiscent of that in the endosomal-lysosomal compartments. In addition, a diffuse extracellular surface-staining was evident. This result demonstrates that receptor-mediated endocytosis of aFGF does not result in its translocation to the nucleus, as has been reported for basic FGF.

Internalization of basic fibroblast growth factor (bFGF) in cultured endothelial cells: role of the low affinity heparin-like bFGF receptors

We have shown (Presta et al., Cell Regul., 2:719-726, 1991) that a long-lasting interaction of basic fibroblast growth factor (bFGF) with endothelial GM 7373 cells is required to induce cell proliferation. In the present work, we have investigated the interaction of 125I-bFGF with GM 7373 cells, its pathway of internalization, and its intracellular fate under the same experimental conditions previously utilized to assess the mitogenic activity of the growth factor. Cell cultures were incubated with 10 ng/ml 125I-bFGF for 2 h at 4 degrees C. Then, cells were shifted to 37 degrees C without changing the medium. A rapid down-regulation of high affinity sites, paralleled by a rapid internalization of 125I-bFGF, was observed during the first 1-2 h at 37 degrees C. After 6-8 h, also low affinity sites down-regulate. This was paralleled by a continuous internalization of 125I-bFGF and by a slow disappearance of the growth factor from the culture medium. This suggests that GM 7373 cells activate, when exposed to bFGF for a long period of time, a late internalization pathway mediated by low affinity sites. This hypothesis was supported by the following experimental evidence: 1) soluble heparin inhibited the prolonged internalization of 125I-bFGF and its binding to low affinity sites with the same potency; 2) treatment of GM 7373 cells with heparinase, which removes most of the low affinity sites, also inhibited the prolonged internalization of 125I-bFGF. 125I-bFGF internalized via low affinity sites was partially protected from lysosomal degradation. This was the case also when 125I-bFGF was internalized in the presence of soluble heparin, suggesting that the complexes bFGF-cell surface glycosaminoglycan and bFGF-soluble heparin are maintained during the internalization of the growth factor. Moreover, the capacity of soluble heparin to inhibit the mitogenic activity of bFGF also when added to cell cultures several hours after the growth factor indicates that the requirement for a prolonged interaction of bFGF with GM 7373 cells in order to induce cell proliferation might be related to the late internalization of the growth factor via low affinity sites.

Release and subcellular localization of acidic fibroblast growth factor expressed to high levels in HeLa cells

Acidic fibroblast growth factor (aFGF) lacks a classical signal sequence for secretion via the exocytic pathway but yet has to be released from cells in order to interact with high affinity receptors on the cell surface. To study the release process, we have expressed human aFGF in HeLa cells using a T7 RNA polymerase-driven vaccinia virus system. The high level of expression in combination with an efficient antibody allowed us to analyze the release of aFGF by pulse-chase experiments, and to immunolocalize the protein in transfected cells. In the absence of heparin, only negligible amounts of aFGF were detected in the medium during a 15 hr chase period. However, if heparin was present during the chase, readily detectable amounts (about 10-20% of total) of aFGF were found in the medium during the 15 hr chase. Extracellular aFGF was first detected at 8 hr and increased during the chase. Concomitantly, only small amounts of lactate dehydrogenase activity, used as a cytoplasmic marker, was released from the cells. Further analyses indicated that heparin both stabilized the protein from degradation and prevented the binding of released aFGF to extracellular heparan-sulfate proteoglycans. Thus, both factors contributed to the increased recovery of aFGF in the presence of heparin. The slow and inefficient release of aFGF is consistent with our previous results obtained in insect cells expressing aFGF to a very high level, as well as with those obtained by others in cultured cells producing FGF. Immunolocalization using an affinity purified antibody made against native aFGF, showed strong fluorescence in the nuclei in most cells, while staining in the cytoplasm was usually weaker and varied between cells. The nuclear localization was confirmed by subcellular fractionation and immunoblot analysis. At an early time point following transfection (4 hr), aFGF was preferentially localized to the nuclei, while the distribution of the protein between cytoplasm and nuclei was about equal at later time points (12 hr). Thus, we conclude that aFGF is capable of efficiently entering the nucleus and apparently becoming trapped there.

Identification of a cysteine-rich receptor for fibroblast growth factors

The fibroblast growth factor (FGF) family consists of seven members whose activities are thought to be mediated by multiple receptors. Here we describe the cDNA cloning, expression, and characterization of a cysteine-rich FGF receptor (CFR) that is distinct from previously identified FGF receptors. The deduced amino acid sequence for CFR suggests that it is an integral membrane protein containing a large extracellular domain comprising 16 cysteine-rich repeated units and an intracellular domain of 13 amino acids. No reported sequences exhibit significant homologies to either the repeated extracellular motif or to the entire CFR amino acid sequence. Several CFR transcripts are present in embryonic chick tissue, suggesting that CFR undergoes alternate mRNA splicing or that related genes are present. Chinese hamster ovary cells transfected with the CFR cDNA express a 150-kDa polypeptide that binds FGF-1, FGF-2, and FGF-4 but does not bind several non-FGF family members. The high degree of evolutionary conservation among vertebrate CFRs and its ability to bind three different FGFs with high affinity suggest that this unique receptor plays an important role in FGF biology.

Nonreceptor mediated nuclear accumulation of insulin in H35 rat hepatoma cells

We previously demonstrated that insulin accumulated in the nucleus in several cell types and partially characterized the uptake mechanisms and pathways in H35 rat hepatoma cells. Nuclear accumulation of insulin was energy independent, time, temperature, and insulin concentration dependent, but apparently nonsaturable. This study investigated further the initial endocytotic pathways that contribute to the nuclear accumulation of insulin using trypsin treatment of the cells to prevent insulin binding to its plasma membrane receptor. Total cell-associated, intracellular, and nuclear insulin were compared in control and trypsin-treated H35 hepatoma cells. Trypsin treatment markedly decreased total cell-associated and intracellular insulin as well as the nuclear accumulation of insulin when cells were incubated with 2.8 ng/ml insulin. When the cells were incubated with 100 ng/ml insulin, trypsin treatment totally inhibited insulin binding to the plasma membrane for at least 90 min. However, intracellular accumulation of insulin was reduced by only 50% at 60 min, and trypsin treatment failed to inhibit the nuclear accumulation of insulin. Chemical extraction and Sephadex G-50 chromatography revealed nuclear associated insulin in trypsin-treated cells was identical to that in control cells incubated with either 2.8 or 100 ng/ml insulin. These results suggest that a nonreceptor mediated uptake pathway, i.e., fluid-phase endocytosis, contributed significantly to the nuclear accumulation of insulin at high insulin concentrations, but at lower insulin concentrations the receptor-mediated pathway predominated. No matter which initial endocytotic route was used to internalize insulin, the insulin apparently associated with the same nuclear matrix proteins. This association of insulin with the nuclear matrix may be involved in regulation of nuclear events such as cell growth and differentiation or gene transcription.

Identification of a cysteine-rich receptor for fibroblast growth factors

The fibroblast growth factor (FGF) family consists of seven members whose activities are thought to be mediated by multiple receptors. Here we describe the cDNA cloning, expression, and characterization of a cysteine-rich FGF receptor (CFR) that is distinct from previously identified FGF receptors. The deduced amino acid sequence for CFR suggests that it is an integral membrane protein containing a large extracellular domain comprising 16 cysteine-rich repeated units and an intracellular domain of 13 amino acids. No reported sequences exhibit significant homologies to either the repeated extracellular motif or to the entire CFR amino acid sequence. Several CFR transcripts are present in embryonic chick tissue, suggesting that CFR undergoes alternate mRNA splicing or that related genes are present. Chinese hamster ovary cells transfected with the CFR cDNA express a 150-kDa polypeptide that binds FGF-1, FGF-2, and FGF-4 but does not bind several non-FGF family members. The high degree of evolutionary conservation among vertebrate CFRs and its ability to bind three different FGFs with high affinity suggest that this unique receptor plays an important role in FGF biology.

Possible activity of acidic fibroblast growth factor as a progression factor rather than a transforming factor

Acidic and basic fibroblast growth factors (aFGF and bFGF) are mitogens for mesoderm- and neuroectoderm-derived cells. The facts that FGF-related proteins are oncogenic and that FGFs are expressed in a variety of tumor cell lines or tumor tissues suggest the transforming activities of FGFs. To examine such an activity of aFGF, we introduced a human aFGF expression vector into two populations of Rat-1 cells; one was non-transformed (nRat-1), the other was partially-transformed (tRat-1). tRat-1 cells transfected with aFGF cDNA formed larger colonies in soft agar and produced larger and more malignant tumors in nude mice than those of parental cells. In contrast, nRat-1 cells transfected with aFGF cDNA neither formed colonies in soft agar nor produced tumors in nude mice. Our results suggest that high expression of aFGF may enhance a tumorigenic potential of Rat-1 cells rather than confer such a potential de novo.

Analysis of endogenous and exogenous nuclear translocation of fibroblast growth factor-1 in NIH 3T3 cells

Nuclear localization of fibroblast growth factors (FGF) have been reported by many laboratories. We demonstrate here that FGF-1, the precursor for acidic FGF contains a putative nuclear translocation sequence (NTS) NYKKPKL, which is able to direct the expression of the bacterial beta galactosidase (beta gal) gene to the nucleus of transfected NIH 3T3 cells. However, this NTS is unable to target either FGF-1 itself or a FGF-1-beta gal fusion protein into the nucleus, suggesting that FGF-1 may contain an additional sequence which prevents endogenously expressed FGF-1 from being translocated into the nucleus. Indeed, when FGF-1 was fused to the NTS derived from the yeast histone 2B gene, the chimeric construct also failed to be transported into the nucleus either by itself or as a beta gal fusion protein. Interestingly, when 125I-FGF-1 was used to stimulate quiescent NIH 3T3 cells, a significant amount of internalized 125I-FGF-1 (approximately 10%) was found within the nucleus and the nuclear localization of FGF-1 through the exogenous pathway could be significantly reduced by suramin, an inhibitor of the interaction of FGF-1 with its receptor. These data suggest that while FGF-1 contains a NTS, nuclear translocation requires an exogenous and not an endogenous pathway.

Specific blockade of basic fibroblast growth factor gene expression in endothelial cells by antisense oligonucleotide

The migration and proliferation of endothelial cells play a pivotal role in various vascular diseases. To elucidate the role of endogenous basic fibroblast growth factor (bFGF) produced within endothelial cells on cell growth, we introduced the antisense oligonucleotide complementary to bFGF mRNA into cultured bovine aortic endothelial cells by cationic liposome to block the production of autocrine bFGF. The treatment of the endothelial cells with the specific antisense oligomer efficiently inhibited the synthesis of bFGF with the concomitant suppression of endothelial proliferation, indicating the significant role of bFGF as an endothelial growth promotor. The neutralizing antibody against bFGF had no inhibition on basal DNA synthesis of the endothelial cells, in contrast to marked suppressive action of bFGF antisense oligomer. The results provide the new analytic and therapeutic implications in the use of the antisense methodology for the study of vascular biology.

Heat shock induces the release of fibroblast growth factor 1 from NIH 3T3 cells

Fibroblast growth factor 1 (FGF-1) is a potent angiogenic and neurotrophic factor whose structure lacks a classical signal sequence for secretion. Although the initiation of these biological activities involves the interaction between FGF-1 and cell surface receptors, the mechanism responsible for the regulation of FGF-1 secretion is unknown. We report that murine NIH 3T3 cells transfected with a synthetic gene encoding FGF-1 secrete FGF-1 into their conditioned medium in response to heat shock. The form of FGF-1 released by NIH 3T3 cells in response to increased temperature (42 degrees C, 2 hr) in vitro is not biologically active and does not associate with either heparin or the extracellular NIH 3T3 monolayer matrix. However, it was possible to derive biologically active FGF-1 from the conditioned medium of heat-shocked NIH 3T3 cell transfectants by ammonium sulfate fractionation. The form of FGF-1 exposed by ammonium sulfate fractionation is similar in size to cytosolic FGF-1 and can bind and be eluted from immobilized heparin similarly to the recombinant human FGF-1 polypeptide. Further, the release of FGF-1 by NIH 3T3 cell transfectants in response to heat shock is reduced significantly by both actinomycin D and cycloheximide. These data indicate that increased temperature may upregulate the expression of a factor responsible for the secretion of FGF-1 as a biologically inactive complex that requires an activation step to exhibit the biological activity of the extracellular polypeptide mitogen.

Preparation of fluorescent basic fibroblast growth factor: localization in living retinal microvascular endothelial cells

A biologically active fluorescent derivative of recombinant human basic fibroblast growth factor (bFGF) was prepared by immobilization on heparin-Sepharose 4B (HS) and derivatization with the fluorophore, Texas Red (TR). TR-bFGF was separated from free dye and carrier protein by elution from HS using 1.5 M NaCl. TR-bFGF contained an average of two dye molecules bound per bFGF, retained its mitogenic activity and was visible using a fluorescence microscope equipped with silicon intensified target camera (SIT). TR-bFGF stimulated the growth of bovine aortic endothelial cells (BAEC), microvessel endothelial cells (MVEC) and BHK-21 cells grown in culture. BAEC, MVEC and BHK-21 cells treated with 20 ng ml-1 (1 nM) TR-bFGF for 72 hr were stimulated over serum controls by 87, 26 and 6%, respectively. TR-bFGF stimulated EC growth was inhibited in a dose-dependent fashion when cells were coincubated with microM chloroquine. When EC were treated with TR-bFGF at 4 degrees C and then monitored at 37 degrees C, bright, focal, cytoplasmic spots were observed, which accumulated as punctate, perinuclear fluorescence. EC internalization of TR-bFGF was inhibited 80% by the addition of 100-fold molar excess unlabeled bFGF or by maintaining cultures at 4 degrees C. TR-bFGF colocalized with an EC lysosomal marker, but TR-bFGF was not detected in the nucleus. Results of these localization studies suggest that TR-bFGF stimulates EC proliferation without entering the nucleus.

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

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

Identification of the hepatocyte mitogen in bovine spleen as heparin-binding growth factors

Growth promoting activity for rat hepatocytes in bovine spleen was identified as three heparin-binding growth factors. All the features tested, such as heparin affinity, molecular mass, cross reactivity with antibody, and partial amino acid sequence, indicated that one of the three factors was identical to FGF-1 (fibroblast growth factor-1, acidic FGF), another one was related to FGF-2 (fibroblast growth factor-2, basic FGF), whereas it was more potent for hepatocytes than the FGF-2 purified from bovine brain. The third one was eluted from heparin-Sepharose column at 0.75M NaCl, of which activity was not abolished by anti-FGF-1 or FGF-2 antibodies. In addition, the mitogenic effect of this factor was synergistic with that of HGF (hepatocyte growth factor), a known potent hepatocyte mitogen, suggesting that it is a novel growth factor for hepatocytes.

Subcellular localization of bFGF in human retinal pigment epithelium in vitro

Basic fibroblast growth factor is a polypeptide mitogen with potential biological roles in angiogenesis, differentiation, and the survival of neurons. To study the expression and subcellular distribution of basic fibroblast growth factor in human retinal pigment epithelium in vitro, affinity-purified antipeptide antibodies were generated against a 15 amino acid sequence in the amino-terminus of this growth factor. Analysis of the cross reactivity and specificity of the affinity-purified antibodies demonstrated no ability to recognize acidic fibroblast growth factor and the ability to label specifically the major known forms of basic fibroblast growth factor in whole-cell lysates of retinal pigment epithelium in vitro. Examination of paraformaldehyde- or glutaraldehyde-fixed pigment epithelium at the light and electron microscopic levels revealed prominent localization of basic fibroblast growth factor to the nucleus and nucleolus. In cells fixed with organic reagents, prominent cytoplasmic staining was noted in addition to the nuclear staining seen in aldehyde fixed cells. Investigation of subcellular fractions by Western blot analysis indicated cytosolic as well as nuclear localization of the basic fibroblast growth factor. These analyses, however, demonstrated that the higher molecular weight forms of basic fibroblast growth factor predominate in the nucleus.

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

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