The structure and expression of the FGF receptor-1 mRNA isoforms in rat tissues

Interorgan crosstalk mechanisms in disease: the case of acute kidney injury-induced remote lung injury

Homeostasis and health of multicellular organisms with multiple organs depends on interorgan communication. Tissue injury in one organ disturbs this homeostasis and can lead to disease in multiple organs, or multiorgan failure. Many routes of interorgan crosstalk during homeostasis are relatively well known, but interorgan crosstalk in disease still lacks understanding. In particular, how tissue injury in one organ can drive injury at remote sites and trigger multiorgan failure with high mortality is poorly understood. As examples, acute kidney injury can trigger acute lung injury and cardiovascular dysfunction; pneumonia, sepsis or liver failure conversely can cause kidney failure; lung transplantation very frequently triggers acute kidney injury. Mechanistically, interorgan crosstalk after tissue injury could involve soluble mediators and their target receptors, cellular mediators, in particular immune cells, as well as newly identified neuro-immune connections. In this review, I will focus the discussion of deleterious interorgan crosstalk and its mechanistic concepts on one example, acute kidney injury-induced remote lung injury.

Fibroblast Growth Factor 23 and αKlotho in Acute Kidney Injury: Current Status in Diagnostic and Therapeutic Applications

Fibroblast growth factor (FGF) 23 and αKlotho are circulating mineral regulatory substances that also have a very diverse range of actions. Acute kidney injury (AKI) is a state of high FGF23 and low αKlotho. Clinical association data for FGF23 are strong, but the basic pathobiology of FGF23 in AKI is rather sparse. Conversely, preclinical data supporting a pathogenic role of αKlotho in AKI are strong, but the human data are still being generated. This pair of substances can potentially serve as diagnostic and prognostic biomarkers. FGF23 blockade and αKlotho restoration can have prophylactic and therapeutic utility in AKI. The literature to date is briefly reviewed in this article.

Fibroblast Growth Factor 23 and Klotho in AKI

Acute kidney injury (AKI) is associated with many of the same mineral metabolite abnormalities that are observed in chronic kidney disease. These include increased circulating levels of the osteocyte-derived, vitamin D-regulating hormone, fibroblast growth factor 23 (FGF23), and decreased renal expression of klotho, the co-receptor for FGF23. Recent data have indicated that increased FGF23 and decreased klotho levels in the blood and urine could serve as novel predictive biomarkers of incident AKI, or as novel prognostic biomarkers of adverse outcomes in patients with established AKI. In addition, because FGF23 and klotho exert numerous classic as well as off-target effects on a variety of organ systems, targeting their dysregulation in AKI may represent a unique opportunity for therapeutic intervention. We review the pathophysiology, kinetics, and regulation of FGF23 and klotho in animal and human studies of AKI, and we discuss the challenges and opportunities involved in targeting FGF23 and klotho therapeutically.

Central Fibroblast Growth Factor 21 Browns White Fat via Sympathetic Action in Male Mice

Fibroblast growth factor 21 (FGF21) has multiple metabolic actions, including the induction of browning in white adipose tissue. Although FGF21 stimulated browning results from a direct interaction between FGF21 and the adipocyte, browning is typically associated with activation of the sympathetic nervous system through cold exposure. We tested the hypothesis that FGF21 can act via the brain, to increase sympathetic activity and induce browning, independent of cell-autonomous actions. We administered FGF21 into the central nervous system via lateral ventricle infusion into male mice and found that the central treatment increased norepinephrine turnover in target tissues that include the inguinal white adipose tissue and brown adipose tissue. Central FGF21 stimulated browning as assessed by histology, expression of uncoupling protein 1, and the induction of gene expression associated with browning. These effects were markedly attenuated when mice were treated with a β-blocker. Additionally, neither centrally nor peripherally administered FGF21 initiated browning in mice lacking β-adrenoceptors, demonstrating that an intact adrenergic system is necessary for FGF21 action. These data indicate that FGF21 can signal in the brain to activate the sympathetic nervous system and induce adipose tissue thermogenesis.

Tumour-derived fibroblast growth factor-2 exerts lymphangiogenic effects through Akt/mTOR/p70S6kinase pathway in rat lymphatic endothelial cells

Fibroblast growth factor-2 (FGF-2) has been shown to induce both angiogenesis and lymphangiogenesis in the mouse corneum; however, the signalling mechanism underlying FGF-2-induced lymphangiogenesis remains unknown. Here we investigated the effect of FGF-2 on newly developed temperature-sensitive rat lymphatic endothelial (TR-LE) cells. The supernatant of PC-3 prostate cancer cells facilitated tube-like formation in TR-LE cells, and formation was inhibited by neutralising antibodies against FGF-2. The addition of FGF-2 stimulated tube-like formation as well as proliferation and chemotactic migration of TR-LE cells. Blockade of the Akt signalling pathway by LY294002 abolished the elongation of tubes induced by FGF-2, whereas inhibition of the extracellular signal-regulated kinase (ERK) signalling pathway had no effect. Rapamycin abrogated the phosphorylation of p70S6kinase and consistently inhibited the formation of tubes induced by FGF-2. Furthermore, tube-like formation induced by the supernatant of PC-3 cells was inhibited by LY294002 or rapamycin. These data suggest that FGF-2 exerts lymphangiogenic effects by activating the Akt/mammalian target of rapamycin (mTOR)/p70S6kinase pathway in lymphatic endothelial cells, and that the pathway provides a potent target for tumour lymphangiogenesis.

Regulation of epithelial cell growth factor receptor protein and gene expression using a rat periodontitis model

BACKGROUND AND OBJECTIVE

Regulation of epithelial cell behavior associated with periodontitis is not well elucidated but many responses will ultimately be regulated by growth factor receptors. Using a rat experimental periodontitis model, protein and gene expression of select growth factor receptors in junctional and pocket epithelium were examined.

MATERIAL AND METHODS

Periodontal disease was induced by daily topical application of lipopolysaccharide using an established protocol. Animals were killed at time 0 (control), and at 2 and 8 wk. Frozen tissue samples were collected from the right palatal gingival soft tissue, and the left periodontal tissues were decalcified and embedded in paraffin. Laser microdissection and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to quantify keratinocyte growth factor receptor (KGFR), hepatocyte growth factor receptor (HGFR), epidermal growth factor receptor (EGFR) and fibroblast growth factor receptor 1 (FGFR1) gene expression, and in situ RT-PCR localized these increases to specific epithelial cells. Receptor protein expression was examined immunohistochemically. In cell culture, induction of HGFR and KGFR protein expression by serum, lipopolysaccharide and pro-inflammatory cytokines were examined using flow cytometry.

RESULTS

Eight-week tissue samples exhibited histological changes consistent with periodontitis. KGFR and HGFR gene and protein expression were significantly induced at the 8 wk time point. KGFR expression was significantly up-regulated in basal and parabasal pocket epithelial cells, but HGFR was up-regulated throughout the pocket epithelium. In cell culture serum, lipopolysaccharide and pro-inflammatory cytokines, interleukin-1beta and tumour necrosis factor-alpha significantly induced KGFR protein receptor expression, but HGFR expression was only induced by serum.

CONCLUSION

KGFR and HGFR are highly up-regulated in this model of periodontal disease and may play a significant role in regulating the proliferation and migration of pocket epithelium.

Efficient use of a 'dead-end' GA 5' splice site in the human fibroblast growth factor receptor genes

We have investigated use of a conserved non-canonical GA 5' splice site present in vertebrate fibroblast growth factor receptor (FGFR) genes. Despite previous studies suggesting that GA at the beginning of an intron is incompatible with splicing, we observe efficient utilization of this splice site for human FGFR1 gene constructs. We show that use of the GA splice site is dependent on both a conventional splice site six nucleotides upstream and sequence elements within the downstream intron. Furthermore, our results are consistent with competition between the tandem 5' splice sites being mediated by U6 snRNP, rather than U1 snRNP. Thus the GA 5' splice site represents an extension of the adjacent conventional 5' splice site, the first natural example of such a composite 5' splice site.

Heparin inhibits DNA synthesis and gene expression in alveolar type II cells

Responses of isolated type II alveolar cells to fibroblast growth factors (FGF) have been shown to be sensitive to the level of sulfation in extracellular matrix (ECM) substrata. These observations may reflect the specific in situ distribution and level of sulfation of ECM within the alveolar basement membranes (ABM) associated with type II cells. The goal of this study was to determine if the model sulfated ECM heparin modified DNA synthesis and gene expression by type II cells in a concentration dependent-manner. Isolated rat type II cells were exposed to different concentrations of heparin (0.005-500 micro g/ml) in serum-free medium for 1-3 d with or without FGF-1 or FGF-2. The effects of heparin were examined by [(3)H]thymidine incorporation into DNA, total cell protein, cell number, and selected gene expression. Results indicated that heparin inhibited [(3)H]thymidine uptake in a concentration-dependent manner. Total protein, cell number, and FGF-2 protein expression and mRNA of FGF-1, -2, and FGF receptor-2 detected by reverse transcriptase-polymerase chain reaction were decreased by heparin. These results demonstrate that sulfated molecules in the ABM may play important regulatory role(s) in selected type II cell activities during normal cell homeostasis, turnover, and repair after lung injury.

Fibroblast growth factor receptors and their ligands in the adult rat kidney

BACKGROUND

Fibroblast growth factors (FGFs) are a family of at least 21 heparin-binding proteins involved in many biological processes, both during development and in the adult, including cell proliferation, differentiation, and angiogenesis. FGFs mediate their effects through high-affinity tyrosine kinase receptors (FGFRs), which are encoded by four genes. The aims of the present study were to localize FGFR-1 through FGFR-3 in the normal adult rat kidney and to determine which functional FGFR variants and FGFs were expressed.

METHODS

Avidin-biotin-enhanced horseradish peroxidase immunohistochemistry was used on paraffin sections of rat kidney to localize FGFR-1 through FGFR-3, whereas reverse transcriptase-polymerase chain reaction was used to examine expression of the receptor variants and also of FGF-1 through FGF-10 in cortex, outer medulla, and inner medulla.

RESULTS

By immunohistochemistry, each receptor was localized to distinct and overlapping nephron segments, such that one or more FGFRs were localized to all nephron and collecting duct epithelia. FGFR-1 and FGFR-3 were localized to glomeruli, FGFR-3 to proximal tubules and FGFR-1 to thin limbs. FGFR-1 through FGFR-3 were localized to distal straight tubules, with FGFR-1 and FGFR-3 localized to distal convoluted tubules. FGFR-1 and FGFR-3 were localized to medullary collecting ducts. In addition, FGFR-1 was localized to the smooth muscle of renal arteries. All seven FGFR variants were expressed in the cortex and outer medulla, with fewer FGFRs in the inner medulla. FGF-1, FGF-2, FGF-7, FGF-8, and FGF-9 were expressed in the kidney, with FGF-10 expression found only in the cortex.

CONCLUSIONS

Mapping of these receptors is critical to the determination of the effects of FGF ligands in discrete regions of the kidney. The distributions of the FGFRs in the normal adult kidney and the restricted expression of FGF ligands suggest that specific FGFs have distinct and important roles in the maintenance of normal kidney structure and function.

TGF-beta1 and fibroblast growth factor-1 modify fibroblast growth factor-2 production in type II cells

Fibroblast growth factor (FGF)-2, which stimulates DNA synthesis by type II cells in the lung, has been shown to be regulated by transforming growth factor (TGF)-beta1, an important inflammatory cytokine, in vascular epithelium. The goal of this study was to determine if FGF-2 production by alveolar type II cells is modulated by TGF-beta1 or FGF-1, which also stimulates DNA synthesis by type II cells. Isolated rat type II cells were exposed to 0-40 ng/ml of TGF-beta1 or 0-500 ng/ml of FGF-1 in serum-free medium for 1-5 days. With a specific immunoassay, significant increases of FGF-2 protein in type II cell lysates to levels above those in control cells were achieved after 1 day of exposure to 100 ng/ml of FGF-1 and after 3 days of treatment with 8 ng/ml of TGF-beta1. Similarly, transcripts for FGF-2 were dramatically increased above those in control cells with TGF-beta1 or FGF-1, as were those for FGF receptor-1. These results demonstrate important regulatory links between FGF-2 and both TGF-beta1 and FGF-1 in the alveolar epithelium that could contribute to the regulation of normal cell turnover, development, and the repair processes after injury in the lung.

Glutamate-stimulated proliferation of rat retinal pigment epithelial cells

We investigated the effects of glutamate on cell proliferation and the expression of basic fibroblast growth factor (bFGF) and its receptor (FGF-R1) mRNA in cultured rat retinal pigment epithelial (RPE) cells. The number of primary RPE cells was significantly higher after treatment with 0.2 to 1.0 mM glutamate (maximum at 1.0 mM) for 7 days than in controls. Glutamate-stimulated cell proliferation was abolished by (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801), but not by 6,7-dinitroquinoxaline-2,3-dione or L(+)-2-amino-3-phosphonopropionic acid. Proliferation was increased to a similar extent by N-methyl-D-aspartate (NMDA), but not by kainate, alpha-amino-3-hydroxy-3-methyl-4-isoxazolepropionic acid or trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid. NMDA-receptor-like immunoreactivity was detected in most cells cultured. Treatment of cells with glutamate increased the level of bFGF mRNA and, to a lesser extent, that of FGF-R1 mRNA, which peaked 2 and 4 days, respectively, after glutamate was added. The increase in bFGF mRNA induced by glutamate was inhibited by MK-801. These findings suggest that glutamate might stimulate proliferation of RPE cells through activation of NMDA receptors and expression of bFGF and further suggest that glutamate may be involved in the proliferative changes of RPE cells in retinal wound healing.

Critical periods of basic fibroblast growth factor and brain-derived neurotrophic factor in the development of the chicken cochleovestibular ganglion in vitro

The temporal roles of brain-derived neurotrophic factor (BDNF) and fibroblast growth factor-2 (FGF-2) in the development of sensory neurons have been studied in a cell culture preparation which models normal embryonic inner ear development (normocytic). Previous studies showed that FGF-2 stimulated migration and differentiation of ganglion cells for the first 2 days in vitro, but after 5 days led to degeneration, implicating other factors in their later development. To see if BDNF could be such a factor, otocysts were explanted from white leghorn embryos at the time when ganglion cell precursors normally start migrating from the otic epithelium. Cultures were grown in a defined medium, either with or without human recombinant FGF-2 for 2 days or with BDNF. On Day 3, FGF-2 was replaced either with BDNF in defined medium or with defined medium only. Measurements of neuroblast migration and neurite outgrowth were made by time-lapse imaging in living cultures. In cultures receiving BDNF on Day 3, cell migration and neurite outgrowth from the explant increased for more than 3 weeks but not in cultures receiving only defined medium from Day 3. Cultures did not survive more than 3-4 days when receiving either BDNF in defined medium or defined medium alone from the first day. A neutralizing antibody to BDNF inhibited neuronal migration and neurite outgrowth, and it also blocked the effects of exogenous BDNF. BDNF did not enhance the effects of FGF-2 by interacting with it. These experiments defined a temporal sequence in which FGF-2 acts early in development, while BDNF affects a later stage.

Embryonic expression pattern of H218, a G-protein coupled receptor homolog, suggests roles in early mammalian nervous system development

Heterologous expression studies employing mammalian cell tissue culture techniques and in vivo studies of lower eukaryotes suggest that G-protein coupled receptors may play critical roles in regulating early stages of vertebrate nervous system development. Previous work suggests that H218, a rat G-protein coupled receptor homolog, could serve such a role. Most importantly, northern blot data indicate that whole brain H218 mRNA levels are highest during embryogenesis. In the present studies we raised, affinity-purified and characterized several anti-H218, polyclonal antisera and immunohistochemically mapped the expression of H218 during the early stages of rat embryonic nervous system development. The resulting data indicate that H218 is preferentially expressed in young, differentiating neuronal cell bodies and axons. Moreover, the expression is temporally regulated such that highest H218 levels are found in neuronal cell bodies during their early stages of differentiation and in axons during their outgrowth. Therefore, we propose that H218 signal transduction may widely participate in the regulation of some of the first steps in neuronal differentiation including axon outgrowth.

Expression of fibroblast growth factors and their receptors in rat glomeruli

Fibroblast growth factors (FGFs) regulate cell proliferation and differentiation, and are also important regulators of extracellular matrix. They are among the most potent angiogenic factors known. Evidence suggests the FGFs play a role in glomerular development and pathology. The aim of the present study was to determine whether FGF-1 (acidic FGF) and FGF-2 (basic FGF) and their receptors (FGFRs) were expressed in normal adult rat glomeruli, using reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. For RT-PCR studies, the kidneys of 200 g female Sprague-Dawley rats were perfused with buffer and glomeruli isolated using conventional sieving techniques followed by micropipetting. FGF-1 and FGF-2 were expressed in cortex and in glomeruli. All seven receptor isoforms assayed (FGFR1, 2 and 3 IIIb and IIIc splice variants, and FGFR4) were expressed in whole cortex. However, only the IIIc variants and FGFR4 were expressed in glomeruli. The relative levels of glomerular expression of these isoforms were determined using a semiquantitative RT-PCR assay using primers designed against three transmembrane regions; FGFR1 (100%); FGFR2 (0.1%); and FGFR4 (6%). Immunohistochemistry revealed specific immunostaining for all four FGFRs within glomeruli. The differential expression pattern of FGFR isoforms between glomeruli and whole cortex, and the mutually exclusive nature of the expression of IIIc but not IIIb isoforms within glomeruli, indicates that FGFR expression and thereby FGF activity is tightly regulated in glomeruli. These findings have important implications for the roles of the FGFs in glomerular health and disease.

Sequence requirements for regulated RNA splicing of the human fibroblast growth factor receptor-1 alpha exon

Progression of astrocytes from a benign to a malignant phenotype is accompanied by a change in the RNA processing of the fibroblast growth factor receptor 1 (FGFR-1) gene. The level of a high affinity form of the FGFR-1 is dramatically elevated as a result of alpha-exon skipping during RNA splicing. In this paper we have been able to duplicate this tumor-specific RNA processing pathway by transfection of a chimeric minigene containing a 4-kilobase fragment of the human FGFR-1 gene (including the alpha-exon) into a variety of cell lines. In a transfected human astrocytoma cell line, alpha-exon skipping was consistently observed for RNA transcripts derived from both the chimeric minigene and endogenous gene expression. This exon skipping phenotype was dependent on the size of the flanking intron as deletions which reduced the introns to less than approximately 350 base pairs resulted in enhanced alpha-exon inclusion. Increased exon inclusion was not sequence-specific as exon skipping could be restored with insertion of nonspecific sequence. Cell-specific exon recognition was maintained with a 375-nucleotide sequence inclusive and flanking the alpha-exon, provided that intron size was maintained. These results identify the minimal cis-regulatory sequence requirements for exclusion of FGFR-1 alpha-exon in astrocytomas.

Structure and expression of the rat mRNA encoding a novel member of the fibroblast growth factor family

We isolated the cDNA encoding a novel member of the fibroblast growth factor (FGF) family from rat embryos by homology-based polymerase chain reaction. The FGF-related cDNA encodes a protein of 215 amino acids (approximately 24 kDa), which has a conserved approximately 120-amino acid core with approximately 30-60% amino acid sequence identity with the FGF family. This protein with a hydrophobic amino terminus appears to be a secreted protein. The cDNA was translated in a coupled in vitro transcription-translation system. The molecular mass of the translation product was observed to be approximately 26 kDa. The expression of the FGF-related mRNA in the rat embryo and adult tissues was determined by Northern analysis and in situ hybridization. The mRNA was expressed in several discrete regions of the embryo. In adult tissues, the mRNA was preferentially expressed in the lung. The expression profile of the FGF-related mRNA was different from those of other FGF family mRNAs. As this protein is the 10th documented protein related to FGFs, we tentatively term this protein FGF-10.

An RT-PCR analysis of mRNA for growth factor receptors in damaged and control sensory epithelia of rat utricles

Sensory epithelia from normal rat utricles and those cultured with and without neomycin treatment were assayed for the presence of growth factor receptor mRNAs by RT-PCR (reverse transcriptase-polymerase chain reaction). Both undamaged and damaged utricles showed mRNA for Insulin receptor, IGF-I receptor, FGF receptor 1, EGF receptor, and PDGF alpha receptor. Neomycin-damaged sensory epithelia showed less PDGF alpha receptor mRNA than undamaged epithelia, suggesting that this message by expressed at higher copy levels in hair cells than in supporting cells. Consistent with that hypothesis, immunohistochemistry revealed much stronger PDGF alpha receptor staining in the hair cells than in the supporting cells. Preliminary evidence suggests that IGF-I receptor message also may be lowered in neomycin-damaged epithelia.

Differential regulation of fibroblast growth factor (FGF) receptor-1 mRNA and protein by two molecular forms of basic FGF. Modulation of FGFR-1 mRNA stability

To evaluate possible functional differences between basic fibroblast growth factor (FGF) 2 isoforms we analyzed the effects of the 18-kDa FGF-2 which mainly localizes in the cytosol and that of the nuclear-targeted 22.5-kDa form on FGF receptors (FGFR) expression. These peptides were expressed at low amounts through a retroviral-infection system. Point mutated FGF-2 cDNAs under the control of the beta-actin promoter were used to infect a pancreatic cell line (AR4 2J) which does not produce FGF-2. Saturation and competition binding studies with 125I-FGF-2 revealed a 3-fold increase in both high and low affinity receptors in cells expressing the 22.5-kDa form and a 2-fold increase only in the high affinity receptors in cells producing the 18-kDa form. Kd values and molecular weights of the high affinity receptors were unaffected. Increasing cell densities or cell treatment with exogenous FGF-2 resulted in FGFR down-regulation as in control cells. Neutralizing anti-FGF-2 antibodies and suramin did not affect receptor density in control and in cells producing the 22.5-kDa form but further increased by 60 and 80%, respectively, the receptor level in cells synthesizing the 18-kDa form. These data suggest the involvement of the intracellular stored FGF-2 in FGFR up-regulation. Although all cells expressed FGFR-1, -2, and -3 mRNA only the FGFR-1 transcript was found increased, 6-fold in 22.5-kDa expressing cells and 3-fold in cell producing the shortest secreted isoform. The increase in FGFR-1 mRNA levels in the 22.5-kDa expressing cells was due to enhanced stability of the transcript. Confocal microscopy detected the presence of FGFR-1 at the cell surface whereas secretory isoforms of the receptor were not observed. Reverse transcriptase-polymerase chain reaction did not reveal significant differences in the expression of FGFR-1 variants. In the 22.5-kDa expressing cells exogenous FGF-2 evoked a stronger translocation of the calcium-phospholipid-dependent PKC. These results indicate that the transfected FGF-2 isoforms up-regulated FGFR-1 mRNA and protein. The 22.5-kDa form acted by increasing FGFR-1 mRNA stability enhancing cell responses to exogenous FGF-2.

Cloning of a fibroblast growth factor receptor 1 splice variant from Xenopus embryos that lacks a protein kinase C site important for the regulation of receptor activity

A cDNA clone, predicted to encode a variant form of the type 1 fibroblast growth factor receptor (FGFR1) containing a dipeptide Val-Thr (VT) deletion at amino acid positions 423 and 424 located within the juxtamembrane region, was isolated from a Xenopus embryo (stage 8 blastula) library. Sequence analysis of genomic DNA encoding a portion of the FGFR1 juxtamembrane region demonstrated that this variant form arises from use of an alternative 5' splice donor site. RNase protection analysis revealed that both VT- and VT+ forms of the FGFR1 were expressed throughout embryonic development, the VT+ being the major form. Amino acid position 424 is located within a consensus sequence for phosphorylation by a number of Ser/Thr kinases. We demonstrate that a VT+ peptide was specifically phosphorylated by protein kinase C (PKC) in vitro, but not by protein kinase A (PKA). A VT- peptide, on the other hand, was not a substrate for either enzyme. Phosphorylation levels of in vitro synthesized FGFR-VT+ protein by PKC were twice that of FGFR-VT- protein. In a functional assay, Xenopus oocytes expressing FGFR-VT- or FGFR-VT+ protein were equally able to mobilize intracellular Ca2+ in response to basic fibroblast growth factor (bFGF). However, pretreatment with phorbol 12-myristate 13-acetate significantly reduced this mobilization in oocytes expressing FGFR-VT+ while having little effect on oocytes expressing FGFR-VT-. These findings demonstrate that alternative splicing of Val423-Thr424 generates isoforms which differ in their ability to be regulated by phosphorylation and thus represents an important mechanism for regulating FGFR activity.

Demonstration of fibroblast growth factor receptor-I in human prostate by polymerase chain reaction and immunohistochemistry

The expression and localization of fibroblast growth factor receptor-1 were investigated in human prostatic tissues with or without benign hyperplasia. Using a polymerase chain reaction method, we were able to demonstrate that prostatic tissues with benign hyperplasia expressed a significantly higher level of fibroblast growth factor receptor-1 mRNA than normal prostatic tissues (P < 0.01 by Anova). Western blot analysis using an antiserum against the receptor gave 2 bands with molecular weights of about 140 kDa and 80 kDa; these correspond to the expected sizes of the long and secreted forms of the fibroblast growth factor receptor-1, respectively. An immunohistochemical study using the same antiserum further demonstrated that the immunoreactive staining occurred mainly in the basal cells of the glandular epithelium and occasionally in the stromal cells. These results suggest that fibroblast growth factors may influence, at least in part, the proliferation of the epithelial cells seen in benign hyperplasia of human prostate.

Characterization of fibroblast growth factor receptor 1 RNA expression in the embryonic mouse heart

We used reverse transcriptase-polymerase chain reaction (RT-PCR) to clone fibroblast growth factor receptor (FGFR) 1 isoforms from embryonic mouse heart and as a more sensitive method to characterize FGFR1 RNA expression in embryonic and adult mouse hearts. We describe the cloning of both full-length short (2259 base pairs) and long (2526 base pairs) FGFR1 isoform cDNAs which generated 86 and 102 kilodalton proteins, respectively, following in vitro translation. An assessment of FGFR1 RNA indicates that FGFR1-IIIc is the major form in both the embryonic and adult heart but there is an approximately 8.5-fold decrease in RNA levels in the adult. Differential RNA blotting as well as RT-PCR analyses are consistent with a switch in the relative expression of the short versus long FGFR1 isoforms during heart development. The long isoforms are more abundant in the embryo and the short isoforms predominate in the adult. This may be important in the regulation of growth and development of the heart.

Apoptosis occurs in the oligodendroglial lineage, and is prevented by basic fibroblast growth factor

During the perinatal period, oligodendroglial precursor cells proliferate rapidly, then cease dividing and differentiate into oligodendroglia. Many of these newly formed oligodendroglia are destined to die. We now demonstrate that oligodendroglia generated in passaged cultures of rat forebrain oligodendroglial precursor cells after removal of basic fibroblast growth factor (basic FGF) from the medium often undergo internucleosomal DNA nicking and nuclear fragmentation, features characteristic of apoptosis. These alterations are rare in cultures maintained continuously in basic FGF. As in many other cellular lineages susceptible to apoptosis, these degenerative changes can be prevented by treatment with the endonuclease antagonist, aurintricarboxylic acid, or by inhibiting de novo RNA or protein synthesis. Supplementation of the basic FGF-free medium with insulin, insulin-like growth factor-1, platelet-derived growth factor, or ciliary neuronotrophic growth factor also diminishes DNA nicking. Both oligodendroglial differentiation and DNA nicking are induced in basic FGF-treated cultures by inhibiting DNA synthesis with aphidicholin or excess thymidine, thus suggesting a close linkage between the anti-apoptotic, anti-differentiation, and mitogenic effects of basic FGF on the oligodendroglial lineage.

A common mutation in the fibroblast growth factor receptor 1 gene in Pfeiffer syndrome

Pfeiffer syndrome (PS) is one of the classic autosomal dominant craniosynostosis syndromes with craniofacial anomalies and characteristic broad thumbs and big toes. We have previously mapped one of the genes for PS to the centromeric region of chromosome 8 by linkage analysis. Here we present evidence that mutations in the fibroblast growth factor receptor-1 (FGFR1) gene, which maps to 8p, cause one form of familial Pfeiffer syndrome. A C to G transversion in exon 5, predicting a proline to arginine substitution in the putative extracellular domain, was identified in all affected members of five unrelated PS families but not in any unaffected individuals. FGFR1 therefore becomes the third fibroblast growth factor receptor to be associated with an autosomal dominant skeletal disorder.

Alternative splicing in fibroblast growth factor receptor 2 is associated with induced epithelial-mesenchymal transition in rat bladder carcinoma cells

We described previously that acidic fibroblast growth factor (aFGF), but not basic fibroblast growth factor (bFGF), can induce the rat carcinoma cell line NBT-II to undergo a rapid and reversible transition from epithelial to mesenchymal phenotype (EMT). We now find that NBT-II EMT is stimulated by keratinocyte growth factor (KGF) in cells grown at low density. Accordingly, a high-affinity receptor showing 98% homology to mouse FGF receptor 2b/KGF receptor was cloned and sequenced from NBT-II cells. Northern analysis indicated that mRNA for FGF receptor 2b/KGF receptor was drastically down-regulated within 1 wk in aFGF-induced mesenchymal NBT-II cells. This decrease coincided with an up-regulation of FGF receptor 2c/Bek, a KGF-insensitive, alternatively spliced form of FGF receptor 2b/KGF receptor. Functional studies confirmed that KGF could not maintain EMT induction on mesenchymal NBT-II cells. FGF receptor 1 and FGF receptor 2c/Bek could also support EMT induction when transfected into NBT-II cells in response to aFGF or bFGF. Such transfected cells could bind bFGF as well as aFGF. Therefore, EMT can be induced through different FGF receptors, but EMT may also regulate FGF receptor expression itself.

Immunohistochemical localization in the rat brain of an epitope corresponding to the fibroblast growth factor receptor-1

The localization of fibroblast growth factor receptor-1 was investigated in rat brain by immunohistochemistry using a polyclonal antibody against an acidic peptide sequence of chicken fibroblast growth factor receptor-1. For raising the antisera in rabbits, we synthesized the oligopeptide EDDDDEDDSSSEEKEAD which is a highly acidic region of chicken fibroblast growth factor receptor-1. The oligopeptide was used as a haptenic antigen by conjugating with poly-L-glutamate as a carrier protein. On immunospot assay, the best antiserum was capable of detecting 15.7 pmols of both the chicken and its analogous human oligopeptides but failed to react even with up to 1 nmol of poly-L-glutamate. When rat brain homogenate was examined by Western blots, the antiserum revealed two bands with molecular weights of 145,000 and 75,000 corresponding to known sizes of the membrane-bound and secreted forms of the rat receptor, respectively. Immunohistochemistry in rat brain demonstrated that putative fibroblast growth factor receptor-1 immunoreactivity sites were present mainly in neurons but also in tanycytes and ependymal cells. Positive neurons were distributed widely in various brain regions, but were particularly abundant in such regions as the lateral hypothalamus, substantia nigra, locus coeruleus and raphe nuclei. The present study suggests that fibroblast growth factor receptor-1 is expressed preferentially in certain neuronal systems that appear to be under the influence of fibroblast growth factors in the normal brain. The result should facilitate study of the functional significance of fibroblast growth factors in these brain neurons.

Differential expression patterns of mRNAs for members of the fibroblast growth factor receptor family, FGFR-1-FGFR-4, in rat brain

We have examined the region-specific expression of mRNAs for four members of rat FGF receptor family, FGFR-1, FGFR-2 FGFR-3, and FGFR-4, in rat brain by in situ hybridization. The FGFR-1, FGFR-2, and FGFR-3 mRNAs were expressed widely but differentially in the brain. However, the FGFR-4 mRNA was not expressed in the brain. The FGFR-1 mRNA was strongly expressed in several regions including the hippocampus, cerebellum, and pedunculopotine tegmental nucleus. The FGFR-2 mRNA expression was high in the choroid plexus, and moderate in the fiber-rich regions (the corpus callosum, external capsule, and internal capsule) and the olfactory bulb. The FGFR-3 mRNA was expressed diffusely in the brain. We have also examined the cellular localization of these mRNAs in the brain. Although the FGFR-1 mRNA was expressed preferentially in neurons, the FGFR-2 and FGFR-3 mRNAs were expressed preferentially in glial cells. The present findings that the FGFR-1, FGFR-2, and FGFR-3 mRNAs were expressed widely but with region- and cell-specificity in the brain indicate that these receptors have different roles in the brain.

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.