Cloning and characterization of an androgen-induced growth factor essential for the androgen-dependent growth of mouse mammary carcinoma cells

The role of growth factors in vascular cell development and differentiation

The control of vascular growth and differentiation is a complex system of activity and interaction between positive and negative modulators of these processes. A number of important stimulators and inhibitors of both smooth muscle cells and endothelial cells have now been purified and biochemically characterized. Imbalances in the activity of these factors can result in serious pathologies. In this chapter, we briefly discuss the biology of blood vessel development and growth, review the current literature which describes these stimulators and inhibitors, and discuss current therapeutic strategies designed around these growth modulators.

Expression and functional activity of fibroblast growth factors and their receptors in human pancreatic cancer

We have analysed expression of the first 7 members of the family of heparin-binding fibroblast growth factor (FGFs) and their 4 high-affinity receptors (FGFRs) in human pancreatic carcinoma cell lines, both at the mRNA and protein levels. In cell lines expressing FGFRs, 2 typical patterns were observed: (i) expression of FGFR-I, -3 or -4 along with the expression of at least one FGF; (ii) co-expression of FGFR-3 and FGFR-4 in the absence of FGF expression. Using RT-PCR, transcripts representing multiple isoforms of both extracellular and intracellular domains of FGFR-I were detected in the cell line PT45. A novel extracellular domain variant of FGFR-I was predicted to encode the first immunoglobulin loop in a potentially secreted form. Protein expression of the splice variants of FGFR-I was confirmed by immunoprecipitation with specific antibodies in radiolabelled ligand cross-linking experiments. The type I carboxyl end and the alpha subtype extracellular domain were detected in the PANC-I cell line, while the type I carboxyl terminus and the gamma subtype extracellular domain were expressed in the PT45 cell line. Expression of FGF-2 in PT45 was also detected by immunoprecipitation using 3 different anti-FGF-2 antibodies. Apart from the 18-kDa product, higher molecular weight isoforms, namely 22- and 23-kDa isoforms, were expressed. In an assay of anchorage-independent growth, exogenous FGF-2 stimulated a maximum 15-fold and 10-fold increase in colony formation by the cell lines MIA PACA-2 and PANC-I respectively. Treatment of monolayer cultures of the same cell lines did not promote growth. However, a specific neutralising antibody against FGF-2 reduced cell proliferation of MIA PACA-2 cells by 50%.

Fibroblast growth factors in the nervous system

Fibroblast growth factors (FGFs) exhibit widespread mitogenic and neurotrophic activities. Nine members of the family are currently known, and FGF-1 and FGF-2 are present in relatively high levels in CNS. FGF-1 is expressed by a subset of neuronal populations, while FGF-2 is expressed by astrocytes. FGF-1 and FGF-2 lack signal peptides and appear to be present mainly in intracellular compartments. This suggests that the factors may act as initiators of a repair response after injury. Support for this notion comes from observations that FGF-1 and FGF-2 levels are low during critical phases of development, but high in the adult CNS. A family of transmembrane tyrosine kinase receptors (FGFRs) mediates the effects of FGFs. Four different genes coding for FGF receptors are currently known, three of which are expressed in cell type-specific patterns in the CNS. The main receptor variants present in this tissue, however, can by themselves not distinguish between FGF-1 and FGF-2. Additional selectivity may be established by interaction of the FGFs and their receptors with select heparan proteoglycans (HSPGs). Therefore, the precise physiological role of FGFs is determined by the combination of cell type-specific patterns of expression of FGFs, FGFRs and HSPGs together with the mechanisms that regulate the extracellular availability of FGFs.

Facilitation of autonomous phenotype acquisition in androgen-dependent Shionogi carcinoma 115 cells by transfection of androgen-induced growth factor expression vector

Androgen-induced growth factor (AIGF) is an autocrine growth factor for androgen-dependent SC-3 cells, which is induced by androgen stimuli. To elucidate the mechanism of the progression from hormone-dependent to -independent tumor, we transfected an expression vector of cDNA encoding AIGF into SC-3 cells and established a stable transfectant (A1) expressing AIGF. A1 cells showed enhanced DNA synthesis. This enhanced DNA synthesis was blocked by exposing the cells to AIGF antisense oligonucleotides, heparin, or suramin, indicating that enforced AIGF expression is responsible for the increase in DNA synthesis. However, A1 cells did not grow in serum-free medium unless stimulated with androgen. Recloning from A1 cells in semi-solid agar supplemented with fetal calf serum but without androgen quickly generated an autonomous subline that was able to grow rapidly in the serum-free medium irrespective of androgen stimulus. Mock-transfected SC-3 cells failed to form any colony under identical conditions. These results suggest that stable expression of AIGF alone is not sufficient for, but facilitates the conversion of SC-3 cells from androgen-dependent to -independent phenotype.

Heparan sulfate proteoglycans as transducers of FGF-2 signalling

The fibroblast growth factor-2 (FGF-2) low-affinity binding sites, heparan sulfate proteoglycans (HSPGs), function as modulators of FGF-2 activity. It is noteworthy that HSPG binding protects FGF-2 from denaturation and proteolytic degradation, provides a matrix-bound or cell-surface reservoir of this factor for the cells and is required for the activation of FGF high-affinity receptors. In our study we investigated the biological meaning of FGF-2 internalization mediated through its low-affinity binding sites, HSPGs. Using as model system L6 myoblasts lacking endogenous FGF receptors (FGFRs), we demonstrated that these cells internalize FGF-2 efficiently through an HSPG-mediated pathway. FGF-2 internalization occurring through HSPGs was paralleled by an increase in the activity of urokinase plasminogen activator (u-PA). The u-PA-inducing activity of FGF-2 was strictly correlated to its internalization, as chlorate treatment, which causes a strong inhibition of FGF-2 internalization, abrogated the u-PA-inducing activity of FGF-2. In addition, expression of functional FGF high-affinity receptors (FGFR-1) did not enhance u-PA in L6 myoblasts upon FGF-2 stimulation. According to our results we propose that FGF-2 internalization mediated through HSPGs may transduce FGF-2 signalling such as u-PA-activity stimulation. Thus, HSPGs may act as direct transducers of FGF signalling and indeed, different FGF-signalling pathways must exist.

Alternative splicing of fibroblast growth factor 1 (FGF-1) transcripts: a cellular dilemma in determining exon selection and exclusion

During reverse transcription and polymerase chain reaction (RT-PCR) of kidney RNA using fibroblast growth factor 1 (FGF-1) gene-specific primers, we amplified five fragments with the sizes of 507, 410, 310, 285, and 216 bp. Cloning of the 507-, 310-, and 216-bp fragments revealed that the latter two share the same sequences to the 507-bp DNA but missing 197 and 291 bp, respectively. Characterization of the corresponding genomic DNA sequences showed that the three cDNA are alternative splicing products of the same gene. We further showed that these three transcripts are also present in brain in similar proportions albeit in a much lesser extent. Repeated attempts to clone the 410-bp fragment resulted in isolation of three additional cDNA clones; each has the inclusion of a distinct novel exon. Because each novel exon is delimited by the splicing donor and acceptor sequences, these cDNA clones are not likely to be RT-PCR artifacts. Yet their mRNA levels are extremely low, because we could not detect the corresponding PCR products on ethidium bromide-stained gels nor by Southern hybridization. These novel exons may be routinely used in different tissues. The nature of the 410- and 285-bp products was shown to be heteroduplexing among the 507-, 310-, and 216-bp PCR products. Identification of the three novel FGF-1 exons, which we designate exons -1B, -1E, and -1F, will facilitate the studies of the mechanisms of regulated alternative splicing.

Induction of keratinocyte growth factor expression is reduced and delayed during wound healing in the genetically diabetic mouse

We have recently demonstrated induction of expression of several members of the fibroblast growth factor family during wound healing, particularly for keratinocyte growth factor, which was more than 150-fold induced within 24 h after injury. To assess whether wound-healing disorders are associated with a defect in fibroblast growth factor regulation, we have now investigated the expression of these mitogens as well as their receptors in normal and wounded skin of genetically diabetic db/db mice, which are characterized by their impaired wound healing. We demonstrate that induction of keratinocyte growth factor expression in these mice is significantly reduced and delayed compared to normal mice. Induction of acidic fibroblast growth factor (FGF) and basic FGF expression was earlier in diabetic mice than in normal mice, but by 3 d after injury expression of these mitogens had already returned to the basal levels. In contrast, elevated levels of acidic FGF and basic FGF transcripts were detected within the first 5 d in wounds from normal mice. Thus, FGFs seem to be expressed in a limited fashion in the wound tissue of db/db mice during the period when re-epithelialization and granulation tissue formation normally occur. These findings provide an explanation for the beneficial effect of exogenous FGF in the treatment of impaired wound healing in these animals and suggest that induction of KGF early in repair may be critical for the rapid re-epithelialization in normal wound healing.

In vivo and in vitro effects of androgen on fibroblast growth factor-2 concentrations in the human prostate

Prostatic growth is primarily regulated by dihydrotestosterone (DHT). Recent studies have demonstrated that a large number of growth factors are present in the human benign prostatic hyperplasia (BPH) prostate, including epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), transforming growth factor beta (TGF-beta), insulin-like growth factor (IGF), and basic fibroblast growth factor (bFGF) (FGF-2). DHT may mediate its mitogenic effects in the prostate by regulating growth factors. To test this hypothesis, we have utilized a histoculture androgen sensitivity assay (HASA) in which 3H-thymidine incorporation is measured in aliquots of BPH tissue in histoculture with either added DHT or hydroxyflutamide (HF). The resulting DHT/HF ratio is an expression of the androgen sensitivity of the tissue. In this study, we have compared the DHT/HF ratio for 3H-thymidine incorporation to the DHT/HF ratio for FGF-2 measured in the histocultured prostates. The DHT/HF ratio for the HASA studies of 3H-thymidine incorporation averaged 2.68 compared to the DHT/HF ratio for FGF-2 in the same specimens of 1.01. These values were significantly different, therefore indicating no relationship between DHT stimulation and FGF-2 levels. In addition, FGF-2 levels were measured in human BPH prostates from patients medically castrated with megesterol acetate and estradiol 17-beta prior to surgery. These values were not significantly different, and therefore do not suggest any effect of DHT on the concentration of prostatic FGF-2. Although these studies did not show any effect of DHT on the regulation of prostatic FGF-2, they do indicate that the HASA assay is feasible and appropriate to use in the study of relationships between DHT and various growth factors.

Potential mechanisms regulating the extracellular activities of basic fibroblast growth factor (FGF-2)

Basic fibroblast growth factor (FGF-2) is nearly ubiquitous in its distribution, leading numerous investigators to propose that there must exist highly specific mechanisms to regulate its bioavailability. Moreover, in each of the tissues where it can be localized, numerous cells are its potential target. The identification of these mechanisms could serve as an important step in developing novel strategies to inhibit FGF action. It could be possible to block such FGF-dependent activities as angiogenesis, tumor growth, reproduction, and selected diseases of cell proliferation. Over the course of the past several years, we have attempted to describe some of the processes that might regulate a target cell's ability to activate FGF-2 in its local milieu.

Expression and function of FGF-4 in peri-implantation development in mouse embryos

One of the earliest events in mammalian embryogenesis is the formation of the inner cell mass (ICM) and the subsequent delamination of primitive endoderm. We have found that mRNA for fibroblast growth factor (FGF)-4, but not FGF-3, is expressed in preimplantation mouse blastocysts and that the FGF-4 polypeptide is present in ICM cells. ICM-like embryonal carcinoma cells and embryonic stem cells also express FGF-4. Conversely, differentiated embryonal carcinoma cells in the endoderm lineage express FGF-3, but not FGF-4 mRNA. Although mouse embryos expressed FGF-4 mRNA from the 1-cell stage, embryos cultured from the 2-cell through the blastocyst stage in the presence of recombinant FGF-4 did not respond mitogenically. However, when ICMs that were isolated by immunosurgery were cultured with FGF-4, the number of morphologically distinct, differentiated parietal endoderm cells growing out onto the coverslip increased, without an increase in the number of undifferentiated ICM cells. ICM outgrowths cultured with FGF-4 increased their secretion of 92 × 10(3) M(r) gelatinase and tissue plasminogen activator, a hallmark of migrating cells. Receptors for FGF-4 (FGFR-3 and FGFR-4) are expressed in all cells of the mouse blastocyst. These findings indicate that FGF-4 produced by undifferentiated ICM cells acts in the peri-implantation period of embryogenesis to influence the production and behavior of endoderm cells derived from them.

Keratinocyte growth factor is a growth factor for mammary epithelium in vivo. The mammary epithelium of lactating rats is resistant to the proliferative action of keratinocyte growth factor

Keratinocyte growth factor (KGF) is a member of the fibroblast growth factor (FGF) family. KGF is secreted by stromal cells and affects epithelial but not mesenchymal cell proliferation. KGF injected intravenously was found to cause dramatic proliferation of mammary epithelium in the mammary glands of rats. KGF causes ductal neogenesis and intraductal epithelial hyperplasia but not lobular differentiation in nulliparous female rats. KGF causes ductal and lobular epithelial hyperplasia in male rats. KGF causes proliferation of ductal and acinar cells in the mammary glands of pregnant rats. On the other hand, the ductal epithelium of lactating postpartum rats is resistant to the proliferative action of KGF. The mammary glands of lactating rats did not express less KGF receptor mRNA than the glands of pregnant rats, suggesting that the resistance of the ductal epithelium to KGF during lactation is not related to KGF receptor mRNA down-regulation. The mammary glands of both pregnant and postpartum lactating rats express KGF mRNA with more KGF present in the glands of lactating rats. In conclusion, the KGF and KGF receptor genes are expressed in rat mammary glands and recombinant KGF is a potent growth factor for mammary epithelium.

T lymphocytes synthesize and export heparin-binding epidermal growth factor-like growth factor and basic fibroblast growth factor, mitogens for vascular cells and fibroblasts: differential production and release by CD4+ and CD8+ T cells

T lymphocytes infiltrate wounds, tumors, and atherosclerotic plaques, pathophysiological processes characterized by the migration and proliferation of vascular cells and fibroblasts. Although T lymphocytes are known to produce cytokines for inflammatory cells, it has not been demonstrated that they synthesize growth factors that are mitogenic for vascular cells and fibroblasts. We demonstrate that cultured T lymphocytes isolated from normal human peripheral blood synthesize and export two well-characterized growth factors, heparin-binding epidermal growth factor-like growth factor (HB-EGF) and basic fibroblast growth factor (bFGF). This conclusion is based on mRNA expression analysis, heparin-affinity chromatography profiles, target-cell specificity, and functional inhibition by specific neutralizing antibodies. Atypically, a substantial amount of T-cell-derived bFGF-like activity appears to be constitutively released into conditioned medium, almost as much as is associated with T-cell lysates. bFGF is synthesized and exported by purified CD4+ and CD8+ T cells, whereas HB-EGF is synthesized and exported primarily by CD4+ T cells. The T-cell-derived HB-EGF and bFGF activities are potent mitogens for fibroblasts and smooth muscle cells, and the bFGF-like activity is also mitogenic for endothelial cells. These results suggest that T lymphocytes may play key roles in mediating smooth muscle hyperplasia associated with atherosclerosis and in angiogenesis associated with wound healing and tumor growth by acting locally to deliver vascular-cell growth factors to tissues.

A fetal rat urogenital sinus mesenchymal cell line (rUGM): accelerated growth and conferral of androgen-induced growth responsiveness upon a human bladder cancer epithelial cell line in vivo

A cell-cell interaction model was developed to examine the intercellular communication between mesenchymal and epithelial cells in vivo, and to define the role of androgen and paracrine growth factors in promoting growth and differentiation of the target epithelial cells. Using this model system, we have demonstrated that, in the presence of androgenic steroids, a fetal urogenital sinus mesenchymal cell line exhibited androgen-induced growth responses which resulted in an induction of growth of a non-androgen target epithelial cell line derived from human urinary bladder. Our results show that: (1) a rat fetal urogenital sinus mesenchyme-derived cell line (rUGM) accelerated growth and conferred androgen-induced growth responsiveness upon a non-androgen target cell line, WH, derived from a human bladder transitional-cell carcinoma (TCC); this induction of epithelial tumor growth in vivo occurred in a fibroblast-specific manner; (2) live fetal rUGM cells are required to promote WH tumor growth in vivo, which suggests that continuous production of factors that may serve as mediators for paracrine/autocrine pathways are responsible for androgen stimulation of WH tumor growth in vivo; and (3) although WH tumor growth, mediated by the presence of rUGM cells, was markedly accelerated by the presence of androgen in vivo, androgen and rUGM cells failed to promote the expression of a human prostate-specific antigen (PSA) by WH tumors in vivo. Our results emphasize the importance of organ-specific fibroblasts that promote tumor growth and mediate androgen-induced growth responses; the accelerated growth of the bladder epithelium was not accompanied by the expression of PSA, a known differentiated gene product produced by human prostatic epithelial cells. This report also discusses the potential significance of mesenchymal-epithelial cellular interaction which mediates androgen action and may play an important role by influencing human prostate tumor growth, progression and differentiation.

Keratinocyte growth factor functions in epithelial induction during seminal vesicle development

Development of the seminal vesicle (SV) is elicited by androgens and is dependent on epithelial-mesenchymal interactions. Androgenic signal transmission from the androgen-receptor-positive mesenchyme to the epithelium has been postulated to involve paracrine factors. Keratinocyte growth factor (KGF), a member of the fibroblast growth factor family, is produced by stromal/mesenchymal cells and acts specifically on epithelial cells. The KGF transcript was detected by reverse transcription-polymerase chain reaction in newborn mouse SVs and by Northern blot analysis of RNA from cultured neonatal SV mesenchymal cells. Newborn SVs placed in organ culture undergo androgen-dependent growth and differentiation. Addition of a KGF-neutralizing monoclonal antibody to this system caused striking inhibition of both SV growth and branching morphogenesis. This inhibition was due to a decline in epithelial proliferation and differentiation, as the mesenchymal layer was not affected by anti-KGF treatment. When KGF (100 ng/ml) was substituted for testosterone in the culture medium, SV growth was approximately 50% that observed with an optimal dose of testosterone (10(-7) M). All of these findings suggest that KGF is present during a time of active SV morphogenesis and functions as an important mediator of androgen-dependent development.

Transfected MCF-7 cells as a model for breast-cancer progression

The MCF-7 human breast carcinoma cell line has been used as a recipient for eukaryotic plasmid expression vectors to determine the effects of growth factor and growth factor receptor overexpression on the estrogen-dependent, antiestrogen sensitive and poorly metastatic phenotypes exhibited by this line. Overexpression of some members of the erbB family of ligands and receptors were found to have some effects on these phenotypes. However, only when two members of the fibroblast growth factor family, FGF-1 and FGF-4, were overexpressed was progressive in vivo growth observed is either ovariectomized nude mice without estrogen supplementation or in mice that received tamoxifen treatment. FGF transfected cells also exhibited an increased ability to form micrometastases. The implications of these results with regard to the possible role of the paracrine and autocrine effects of angiogenic growth factor production in breast cancer progression are discussed.

Growth factor regulation of mouse primordial germ cell development

This chapter focused on three key regulators of PGC survival and proliferation; SLF, LIF, and bFGF. The survival of all animal cells may require multiple polypeptide factors and PGCs seem to be no exception (Fig. 7). A number of lines of evidence suggest that membrane-bound forms of SLF may be required for PGC survival. These data suggest an exquisite mechanism for controlling both PGC survival and migration. Thus PGCs that stray from the normal migratory pathway might be eliminated through programmed cell death. SLF, together with LIF, can stimulate PGC proliferation in culture and it seems likely that LIF or a related cytokine may function in vivo to regulate PGC survival and proliferation. Animals doubly deficient in LIF and its relatives may soon allow the roles of these cytokines in PGC development to be determined. Although bFGF is a potent PGC mitogen in vitro, whether PGCs ever encounter bFGF in vivo remains questionable since in culture it alters both the proliferative and developmental potential of PGCs. TGF beta or MIS may be important negative regulators of PGC development, and mice lacking these factors should allow their role in PGC development to be assessed.

Involvement of basic fibroblast growth factor NH2 terminus in nuclear accumulation

The human basic Fibroblast Growth Factor (bFGF) gene was shown to encode four polypeptides by an alternative use of initiation codons (three CUG and one AUG). In this report, we present a comparative study of the fate and intracellular localization of individual bFGF isoforms. For this purpose, we have produced the various bFGF isoforms in E. coli and purified them to homogeneity: the 210 amino acid form initiated at CUG1 that contains a nuclear localization sequence (NLS), the 155 amino acid form (AUG-mediated initiation) and the 146 amino acid form (processed form extracted from tissues). While the different bFGFs were taken up by the cell with equal efficiency, more of the 210 amino acid form accumulated in the nucleus and represented 36% of the internalized bFGF compared with 15% in the others. A chimeric protein containing the minimal SV40 Large T NLS (SV40NLS) fused to the 155 amino acid bFGF form (SVbFGF) behaves like the native 155 amino acid form, indicating that nuclear accumulation of exogenous bFGF is not mediated by the NLS-associated function. These results suggest that the amino-terminal part of the 210 amino acid bFGF contains a sequence responsible for its nuclear retention. Bioactivities of the different forms were tested on adult bovine aortic endothelial (ABAE) cells. The bFGF degradation pathways, mitogenic activity and stimulation of rRNA synthesis appeared to be the same for all bFGFs but the stimulation of plasminogen activator was enhanced by the 210 amino acid form and correlated with nuclear accumulation.

The immunolocalization of basic fibroblast growth factor in the mouse uterus during the initial stages of embryo implantation

Mammalian embryo implantation involves a series of complex interactions between maternal and embryonic cells. Uterine polypeptide growth factors may play critical roles in these cell interactions. Basic fibroblast growth factor (basic FGF) is a member of a family of growth factors. This growth factor may be potentially important for the process of embryo implantation because it (a) is stored within the extracellular matrix and is thus easily available during embryo invasion, (b) is a potent modulator of cell proliferation and differentiation and (c) stimulates angiogenesis. The immunolocalization of basic FGF in the uterus during the peri-implantation period of pregnancy is presented in this study. Uterine tissue samples were obtained on days 6-9 of pregnancy with day 1 of pregnancy being the day of a vaginal copulatory plug. Uterine samples were fixed in Bouin's fluid for no longer than 18 h. Following fixation and paraffin embedding, sections were exposed to primary antisera made in rabbits against either (a) human recombinant basic FGF or (b) 1-24 synthetic fragment of bovine basic FGF. The primary antibody was followed by biotinylated goat anti-rabbit IgG and a biotin-avidin-peroxidase complex. There were no differences in the immunolocalization of basic FGF using either source of primary antibody. Our results demonstrated both temporal and spatial changes in the localization of immunoreactive basic FGF within the implantation chamber during days 6-9 of pregnancy. Inter-implantation sites resembled the non-pregnant uterus with basic FGF present in extracellular matrices including basal laminae. On day 6 of pregnancy, decidual cells within the primary decidual zone lacked both intracellular and pericellular basic FGF while non-decidualized uterine stroma resembled inter-implantation sites. By days 7-8 of pregnancy, the secondary decidual zone had formed and was characterized by the distinct pericellular localization of basic FGF around individual decidual cells. By day 9 of pregnancy, the mesometrial region was forming and contained cords of decidual cells and a labyrinth of maternal blood vessels. The decidual cells contained diffuse intracellular basic FGF. Trophoblast cells were devoid of basic FGF at all times examined. These results indicate that basic FGF is present within the implantation chamber on days 6-9 of pregnancy and may be involved in the decidual cell response, trophoblast cell invasion and angiogenesis.

Characteristics of FGF-receptors expressed by stromal and epithelial cells cultured from normal and hyperplastic prostates

Three fibroblast growth factors (FGFs), acidic FGF (FGF1), basic FGF (FGF2), and keratinocyte growth factor (FGF7) have been identified in prostate. To understand how FGFs regulate growth of the prostate, and to determine if regulation is altered in benign prostatic hyperplasia (BPH), the mitogenic potential of FGFs, receptor binding, and FGF-receptor (FGFR) gene expression of stromal (PS) and epithelial cells (PE) cultured from normal human prostate and BPH where determined. FGF1 and FGF2, but not FGF7, were mitogens for PS. FGF1 and FGF7 were potent mitogens for PE, but FGF2 was a weak mitogen for these cells. Both PS and PE exhibited high affinity binding (pM K) of iodinated-FGF2. The K was 4-fold and 12-fold higher for PS than for PE cultured from normal prostate and BPH, respectively. Northern analysis indicated that PS, but not PE, expressed FGFR type 1 (FGFR1) mRNA. The reverse transcriptase polymerase chain reaction (RT-PCR) was used to evaluate FGFR type 2 (FGFR2) expression. The size of amplified DNA fragments, and nucleotide sequences, indicated that PS also expressed transcripts for the exon IIIc RNA splice variant of FGFR2. A RT-PCR product with the FGFR2 exon IIIb nucleotide sequence joined with the exon IIIc sequence was amplified with poly A+ RNA from PE and primers spanning both exons. Thus, PE did not alternatively splice mRNA for FGFR2 exon IIIb and exon IIIc. No differences in the mitogenic potential of FGFs, receptor binding (K or number of sites), or FGFR gene expression were found in cells cultured from normal prostate and BPH.

Developmentally regulated expression of fibroblast growth factor receptor genes and splice variants by murine embryonic stem and embryonal carcinoma cells

The expression of the four fibroblast growth factor receptor (FGF-R) genes was examined in murine embryonic stem (ES) cells, embryonal carcinoma (EC) cells, and their differentiated derivatives. FGF-R1 and FGF-R4 were found to be expressed constitutively in all samples examined. The expression of FGF-R2 and FGF-R3 was, however found to increase significantly upon differentiation of both ES and EC cells. Examination of splice variants of the third immunoglobulin domain (IgIII) of the extracellular region of the FGF-R2 revealed that whilst IgIIIc transcripts were expressed upon ES cell differentiation, IgIIIb transcripts (which confer specificity for the ligand FGF-7) were expressed in both ES cells and their differentiated progeny. FGF-R3 transcripts were also expressed in ES cells, but variant FGF-R3 transcripts containing the IgIIIb region were expressed upon differentiation. The findings suggest that the repertoire of FGF-R expression in embryonic cell types is developmentally regulated at the level of both gene expression, and alternative splicing and different members of the FGF-R family can exhibit distinct patterns of both gene and splice variant expression.

Progression of androgen-sensitive mouse tumor (Shionogi carcinoma 115) to androgen-insensitive tumor after long-term removal of testosterone

Shionogi Carcinoma 115 (SC115) is an androgen-sensitive transplantable mouse tumor. To study the mode of progression from androgen-sensitive to -insensitive tumor, cloned SC115 cells were serially cultured without androgen. Shortly after withdrawal of androgen, SC115 cells showed markedly decreased growth, but growth resumed gradually with loss of response to androgen and the cells 60 weeks after androgen removal [A(-)60 cells] grew faster than SC115 cells cultured in the presence of androgen. A(-)60 cells showed malignant phenotype with morphological changes and tumorigenicity in male and female mice. Although mRNA and binding capacity of androgen receptor were maintained, the cells after removal of androgen rapidly lost expression of mouse mammary tumor virus-related gene and the loss was irreversible in A(-)60 cells. The stimulating effect of basic fibroblast growth factor (bFGF) temporarily decreased, then recovered to the initial level after long-term androgen removal. This fluctuation of response to bFGF was accompanied with changes in the number of bFGF receptors and amount of bFGF-like substance(s) secreted. The substance(s) seemed to be an FGF-like growth factor different from known factors. It was concluded that progression of SC115 cells to androgen-insensitive ones under an androgen-deprived condition proceeded with adaptation by means of increases in production of an FGF-like growth factor and in binding capacity to this factor.

Identification of positive and negative regulatory elements involved in the retinoic acid/cAMP induction of Fgf-3 transcription in F9 cells

The proto-oncogene Fgf-3 has been implicated as an important signalling molecule in vertebrate development. In the mouse, it is expressed for a limited time at a multitude of sites from embryonic day 7 to birth. Transcription of Fgf-3 initiates at three promoter regions resulting in the generation of various mRNAs which nevertheless all encode the same protein products. A 1.7kb DNA fragment which encompasses these regions was joined to the CAT reporter gene and shown to function as a promoter in embryonal carcinoma cells. In stable transfectants the promoter retains its retinoic acid inducibility, initiating transcription at the same cap-sites as the endogenous gene. In differentiated F9 cells, transient transfection of progressive and targeted deletion mutants of the promoter region has revealed at least two positive and three negative regulatory elements. With one exception, loss of these elements was shown to dramatically affect promoter activity in stable transfectants of F9 cells. However the promoter remained inducible by retinoic acid to differing degrees, apart from deletions encompassing PS-4A which essentially abolished promoter activity in both undifferentiated and differentiated cells. The sequences of these potential regulatory regions were further defined using DNase-I footprinting, revealing some similarities to consensus binding sites for known transcription factors.

Basic fibroblast growth factor promotes adhesive interactions of neuroepithelial cells from chick neural tube with extracellular matrix proteins in culture

Fibroblast growth factors have been increasingly assigned mitogenic and trophic roles in embryonic and postnatal development of the nervous system. Little is known, however, of their functional roles in early embryonic neural development at the neural tube stage. We have examined the effect of basic fibroblast growth factor (bFGF) on the adhesive behavior in culture of dissociated brachio-thoracic neural tube cells from 26- to 30-somite stage chick embryos. Cells plated on collagen-coated substratum at a low density attach to the substratum but show poor cell spreading. Addition of bFGF markedly promotes cell spreading, yielding an epithelial morphology. This effect becomes discernible 6–8 hours after cell plating with bFGF and is completed by 24 hours, with half-maximal and maximal effects attained at around 0.4 and 10 ng/ml, respectively. The number of cells remain largely constant up to 24 hours, and then cell survival and/or mitogenic effects of bFGF become apparent. The cell spreading effect is abolished by cycloheximide treatment, inhibited by the anti-beta 1-integrin antibody CSAT, and accompanied by about twofold increases in the expression of beta 1-integrin and vinculin, components of focal adhesion complexes. Cells cultured with bFGF for 24 hours exhibit enhanced cell attachment and cell spreading with little time lag following cell plating. In earlier embryonic stages, developmentally less mature cells depend much more on bFGF for their cell spreading and survival, while in later stages the cell spreading response to bFGF becomes undetectable as neural tube develops to spinal cord. The cell spreading effect of bFGF is realized on specific extracellular matrix proteins including laminin, fibronectin and collagen, but not on vitronectin, arg-gly-asp peptide (PepTite-2000), poly-L-ornithine or others. These results suggest that, in an early stage of neural tube development, bFGF is involved in the developmental regulation of adhesive interactions between neuroepithelial cells and the extracellular matrix, thereby controlling their proliferation, migration and differentiation.

Distribution of FGF-2 suggests it has a role in chick limb bud growth

We developed and characterized antibodies specific for FGF-2 and used them to locate FGF-2 during chick embryo development. A series of micrographs demonstrated the progression of FGF-2 staining during development of the different tissues and organs. FGF-2 was present in the ectoderm covering the entire embryo, muscle cells, nervous system, neural crest cells, and mesonephros. FGF-2 was also present in the limb from initiation of budding through differentiation. The limb ectoderm and subjacent mesoderm showed the strongest immunostaining, with lower levels in the center of the bud. However, the distribution of FGF-2 positive cells in the mesoderm was not homogeneous. This heterogeneity was not due to cell cycle specific distribution of FGF-2 protein, as flow cytometric analysis showed that FGF-2-positive cells were distributed throughout the cell cycle. However, the amount of anti-FGF-2 fluorescence varied most during G1, consistent with the possibility that FGF-2 is low after M phase and increases during G1. A bioassay was used to demonstrate FGF-2 levels in the wing ectoderm were approximately 2.7-fold greater than in the mesoderm. We propose that the location of FGF-2 in the embryo is consistent with a role in epithelial-mesenchymal interactions; in the limb bud it may prevent differentiation and permit limb outgrowth and subsequent expression of patterning events.

Heterogeneity in the expression of fibroblast growth factor receptors during limb regeneration in newts (Notophthalmus viridescens)

Two closely related fibroblast growth factor receptors, FGFR1 and FGFR2, have been cloned from a newt (Notophthalmus viridescens) limb blastema cDNA library. Sequence analysis revealed that we have isolated both the bek and KGFR variants of FGFR2. These two variants differ only in the second half of the last of their three Ig-like domains. The expression patterns of FGFR1 and FGFR2 during limb regeneration have been determined by in situ hybridization. During the preblastema stages of regeneration, FGFR2 expression is observed in the basal layer of the wound epithelium and in the cells of the periosteum. As regeneration progresses to the blastema stages, FGFR2 expression continues to be observed in the basal layer of the wound epithelium with additional hybridization seen in the blastema mesenchyme closely associated with the bisected bones. From the early bud to the mid-bud blastema stage, FGFR1 expression is observed throughout the blastema mesenchyme but, unlike FGFR2, is distinctly absent from the wound epithelium. In the differentiation stages of regeneration, the mesenchymal expression of FGFR2 becomes restricted to the cells of the condensing cartilage and later to the perichondrium. During these later stages of regeneration, the wound epithelium hybridization to the FGFR2 probe is no longer observed. The expression patterns of these receptors suggest that FGFR1 and FGFR2 have distinct roles in limb regeneration, despite their sharing a number of the FGF ligands. Further investigation regarding the potential sources of the FGF ligands will help establish the role that FGFs and FGFRs play in limb regeneration.

Molecular cloning of a novel cytokine cDNA encoding the ninth member of the fibroblast growth factor family, which has a unique secretion property

Glia-activating factor (GAF) is a novel heparin-binding growth factor purified from the culture supernatant of a human glioma cell line. It shows a spectrum of activity slightly different from those of other known growth factors. We have isolated the cDNA which encodes human GAF. A homology search revealed that GAF would be the ninth member of the FGF family, and we therefore call it FGF-9. The human FGF-9 cDNA cloned by using oligonucleotide probes encoded a polypeptide consisting of 208 amino acids. Sequence similarity to other members of the FGF family was estimated to be around 30%. Two cysteine residues and other consensus sequences in family members were also well conserved in the FGF-9 sequence. FGF-9 was found to have no typical signal sequence in its N terminus like those in acidic FGF and basic FGF. Acidic FGF and basic FGF are known not to be secreted from cells in a conventional manner. However, FGF-9 was found to be secreted from cells after synthesis despite its lack of a typical signal sequence. It could be detected exclusively in the culture medium of cDNA-transfected COS cells. The amino acid sequence of proteins purified from culture supernatant of the CHO cell line, which was cDNA transfected and selected as a high producer of FGF-9, showed that no peptides were cleaved from the N terminus except the initiation methionine. The rat FGF-9 cDNA was also cloned, and the structural analysis indicated that the PGF-9 gene is highly conserved. Expression of the FGF-9 gene could be detected in the brain and kidney of the adult rat. Restricted gene expression in organs and the unique secretion nature of the protein suggest that FGF-9 plays a physiological role which differs from those of well-characterized acidic FGF and basic FGF.

Molecular cloning of a novel cytokine cDNA encoding the ninth member of the fibroblast growth factor family, which has a unique secretion property

Glia-activating factor (GAF) is a novel heparin-binding growth factor purified from the culture supernatant of a human glioma cell line. It shows a spectrum of activity slightly different from those of other known growth factors. We have isolated the cDNA which encodes human GAF. A homology search revealed that GAF would be the ninth member of the FGF family, and we therefore call it FGF-9. The human FGF-9 cDNA cloned by using oligonucleotide probes encoded a polypeptide consisting of 208 amino acids. Sequence similarity to other members of the FGF family was estimated to be around 30%. Two cysteine residues and other consensus sequences in family members were also well conserved in the FGF-9 sequence. FGF-9 was found to have no typical signal sequence in its N terminus like those in acidic FGF and basic FGF. Acidic FGF and basic FGF are known not to be secreted from cells in a conventional manner. However, FGF-9 was found to be secreted from cells after synthesis despite its lack of a typical signal sequence. It could be detected exclusively in the culture medium of cDNA-transfected COS cells. The amino acid sequence of proteins purified from culture supernatant of the CHO cell line, which was cDNA transfected and selected as a high producer of FGF-9, showed that no peptides were cleaved from the N terminus except the initiation methionine. The rat FGF-9 cDNA was also cloned, and the structural analysis indicated that the PGF-9 gene is highly conserved. Expression of the FGF-9 gene could be detected in the brain and kidney of the adult rat. Restricted gene expression in organs and the unique secretion nature of the protein suggest that FGF-9 plays a physiological role which differs from those of well-characterized acidic FGF and basic FGF.

Structural and functional specificity of FGF receptors

Fibroblast growth factors (FGFs) represent a group of polypeptide mitogens eliciting a wide variety of responses depending on the target cell type. The knowledge of the cell surface receptors mediating the effects of FGFs has recently expanded remarkably. Perhaps not surprisingly, the complexity of the FGF family and FGF induced responses is reflected in the diversity and redundancy of the FGF receptors. The molecular cloning of the signal transducing receptors for fibroblast growth factors has revealed a tyrosine kinase gene family with at least four members. Differential splicing and polyadenylation creates further diversity in the FGF receptor system. These numerous receptor forms have both distinct and redundant properties. We are only now beginning to understand how the different receptors are activated by the various FGFs and how they are expressed by various cells and tissues. FGF binding to the tyrosine kinase receptors needs the assistance of heparan sulphate side chains of proteoglycans present at the cell surface and in the extracellular matrix. As several other growth factors share the heparin binding property of FGFs, the dual receptor system for FGFs might be an example of a more widely used principle.

Amplification of fgfr4 gene in human breast and gynecological cancers

We have investigated gene amplification of fibroblast growth factor receptor-4 (FGFR4) gene in 30 primary breast tumor samples and 15 gynecological tumor samples. Ten percent of the breast tumors showed 2- to 4-fold amplification. Amplification was found more frequently in estrogen- and progesterone-receptor-positive tumors and in tumors with high lymph-node involvement. Breast tumor samples were also analyzed for the amplification of fgfr3 and erbB2 genes and the chromosome 11q13 located genes hst1/int2/bcl1/sea. erbB2 gene was amplified 2- to 13-fold in 13% of the cases, but no amplification of int2/hst1/bcl1/sea amplicon was found. Gynecological tumors were also analyzed for the amplification of fgfr4 and fgfr3 genes and for int2 and hst1 oncogenes. Eleven of the 15 gynecological tumors were ovarian neoplasms including 2 benign tumors; the remainder comprised 1 ovarian metastasis of breast cancer; 1 endometrial cancer; 1 uterine leiomyosarcoma and 1 carcinosarcoma of the fallopian tube. In gynecological tumors, fgfr4 gene was found to be amplified in 2 ovarian tumors. Amplification of hst1 was found in 1 benign ovarian tumor. Thus, the fgfr4 gene may be involved in breast and ovarian tumorigenesis.

Ectopic expression of Fgf-4 in chimeric mouse embryos induces the expression of early markers of limb development in the lateral ridge

The biological consequences of constitutive fibroblast growth factor-4 (fgf-4) expression were investigated in chimeric embryos prepared between wild-type host embryos and murine ES cells transfected with a construct in which expression of the murine fgf-4 gene was directed by the phosphoglycerate kinase (PGK-1) promoter. The embryos exhibit abnormalities of the limbs and the anterior central nervous system (CNS). The limb phenotype comprised the induction of outgrowth along the lateral ridge between the definitive fore and hind limbs resembling the early phases of limb development. The CNS defects comprised a complete absence, or marked reduction in forebrain and midbrain structures and rudimentary or absent eye development. Constitutive expression of fgf-4 was also accompanied by ectopic expression of the sonic hedgehog (shh) and msx-1 genes in the lateral ridge. These findings indicate that FGF exhibits multiple activities in early development which include the ability to induce the expression of early markers of limb development in the lateral ridge.