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

The control of lung branching morphogenesis

Branching morphogenesis generates epithelial trees which facilitate gas exchange, filtering, as well as secretion processes with their large surface to volume ratio. In this review, we focus on the developmental mechanisms that control the early stages of lung branching morphogenesis. Lung branching morphogenesis involves the stereotypic, recurrent definition of new branch points, subsequent epithelial budding, and lung tube elongation. We discuss current models and experimental evidence for each of these steps. Finally, we discuss the role of the mesenchyme in determining the organ-specific shape.

Dysregulated fibroblast growth factor (FGF) signaling in neurological and psychiatric disorders

The role of the fibroblast growth factor (FGF) system in brain-related disorders has received considerable attention in recent years. To understand the role of this system in neurological and psychiatric disorders, it is important to identify the specific members of the FGF family that are implicated, their location and the various mechanisms they can be modulated. Each disorder appears to impact specific molecular players in unique anatomical locations, and all of these could conceivably become targets for treatment. In the last several years, the issue of how to target this system directly has become an area of increasing interest. To date, the most promising therapeutics are small molecule inhibitors and antibodies that modulate FGF receptor (FGFR) function. Beyond attempting to modify the primary players affected by a given brain disorder, it may prove useful to target molecules, such as membrane-bound or extracellular proteins that interact with FGF ligands or FGFRs to modulate signaling.

Feedback, receptor clustering, and receptor restriction to single cells yield large Turing spaces for ligand-receptor-based Turing models

Turing mechanisms can yield a large variety of patterns from noisy, homogenous initial conditions and have been proposed as patterning mechanism for many developmental processes. However, the molecular components that give rise to Turing patterns have remained elusive, and the small size of the parameter space that permits Turing patterns to emerge makes it difficult to explain how Turing patterns could evolve. We have recently shown that Turing patterns can be obtained with a single ligand if the ligand-receptor interaction is taken into account. Here we show that the general properties of ligand-receptor systems result in very large Turing spaces. Thus, the restriction of receptors to single cells, negative feedbacks, regulatory interactions among different ligand-receptor systems, and the clustering of receptors on the cell surface all greatly enlarge the Turing space. We further show that the feedbacks that occur in the FGF10-SHH network that controls lung branching morphogenesis are sufficient to result in large Turing spaces. We conclude that the cellular restriction of receptors provides a mechanism to sufficiently increase the size of the Turing space to make the evolution of Turing patterns likely. Additional feedbacks may then have further enlarged the Turing space. Given their robustness and flexibility, we propose that receptor-ligand-based Turing mechanisms present a general mechanism for patterning in biology.

The control of branching morphogenesis

Many organs of higher organisms are heavily branched structures and arise by an apparently similar process of branching morphogenesis. Yet the regulatory components and local interactions that have been identified differ greatly in these organs. It is an open question whether the regulatory processes work according to a common principle and how far physical and geometrical constraints determine the branching process. Here, we review the known regulatory factors and physical constraints in lung, kidney, pancreas, prostate, mammary gland and salivary gland branching morphogenesis, and describe the models that have been formulated to analyse their impacts.

Embryonic coronary vasculogenesis and angiogenesis are regulated by interactions between multiple FGFs and VEGF and are influenced by mesenchymal stem cells

In embryonic hearts explanted on collagen gels, epicardial cells delaminate and form vascular tubes, thus providing a model for coronary tubulogenesis. Using this model, we show that fibroblast growth factors (FGFs) 1, 2, 4, 8, 9, and 18 contribute to tubulogenesis and that the availability of multiple FGFs provides the optimal tubulogenic response. Moreover, the FGF effects are vascular endothelial growth factor (VEGF) -dependent, while VEGF-induced tubulogenesis requires FGF signaling. The number of endothelial cells (ECs) is increased by all of the FGFs, while EC migration is significantly enhanced only by FGF-2 and FGF-18. Finally, addition of embryonic mesenchymal stem cells (EMSC) to the explants markedly enhances EC numbers and a 23-fold increase in stromal derived factor-1α (SDF-1α), which is FGF dependent. Both explants and EMSCs produce SDF-1α. In conclusion, coronary tubulogenesis of embryonic epicardium: (1) is responsive to many FGF family members, (2) requires both FGF and VEGFA signaling, and (3) is responsive to EMSCs.

Differential fibroblast growth factor 8 (FGF8)-mediated autoregulation of its cognate receptors, Fgfr1 and Fgfr3, in neuronal cell lines

Fibroblast growth factors (FGFs) mediate a vast range of CNS developmental processes including neural induction, proliferation, migration, and cell survival. Despite the critical role of FGF signaling for normal CNS development, few reports describe the mechanisms that regulate FGF receptor gene expression in the brain. We tested whether FGF8 could autoregulate two of its cognate receptors, Fgfr1 and Fgfr3, in three murine cell lines with different lineages: fibroblast-derived cells (3T3 cells), neuronal cells derived from hippocampus (HT-22 cells), and neuroendocrine cells derived from hypothalamic gonadotropin-releasing hormone (GnRH) neurons (GT1-7 cells). GnRH is produced by neurons in the hypothalamus and is absolutely required for reproductive competence in vertebrate animals. Several lines of evidence strongly suggest that Fgf8 is critical for normal development of the GnRH system, therefore, the GT1-7 cells provided us with an additional endpoint, Gnrh gene expression and promoter activity, to assess potential downstream consequences of FGF8-induced modulation of FGF receptor levels. Results from this study suggest that the autoregulation of its cognate receptor represents a common downstream effect of FGF8. Further, we show that Fgfr1 and Fgfr3 are differentially regulated within the same cell type, implicating these two receptors in different biological roles. Moreover, Fgfr1 and Fgfr3 are differentially regulated among different cell types, suggesting such autoregulation occurs in a cell type-specific fashion. Lastly, we demonstrate that FGF8b decreases Gnrh promoter activity and gene expression, possibly reflecting a downstream consequence of altered FGF receptor populations. Together, our data bring forth the possibility that, in addition to the FGF synexpression group, autoregulation of FGFR expression by FGF8 represents a mechanism by which FGF8 could fine-tune its regulatory actions.

FGFR-1 is required by epicardium-derived cells for myocardial invasion and correct coronary vascular lineage differentiation

Critical steps in coronary vascular formation include the epithelial-mesenchyme transition (EMT) that epicardial cells undergo to become sub-epicardial; the invasion of the myocardium; and the differentiation of coronary lineages. However, the factors controlling these processes are not completely understood. Epicardial and coronary vascular precursors migrate to the avascular heart tube during embryogenesis via the proepicardium (PE). Here, we show that in the quail embryo fibroblast growth factor receptor (FGFR)-1 is expressed in a spatially and temporally restricted manner in the PE and epicardium-derived cells, including vascular endothelial precursors, and is up-regulated in epicardial cells after EMT. We used replication-defective retroviral vectors to over-express or knock-down FGFR-1 in the PE. FGFR-1 over-expression resulted in increased epicardial EMT. Knock-down of FGFR-1, however, did not inhibit epicardial EMT but greatly compromised the ability of PE progeny to invade the myocardium. The latter could, however, contribute to endothelia and smooth muscle of sub-epicardial vessels. Correct FGFR-1 levels were also important for correct coronary lineage differentiation with, at E12, an increase in the proportion of endothelial cells amongst FGFR-1 over-expressing PE progeny and a decrease in the proportion of smooth muscle cells in antisense FGFR-1 virus-infected PE progeny. Finally, in a heart explant system, constitutive activation of FGFR-1 signaling in epicardial cells resulted in increased delamination from the epicardium, invasion of the sub-epicardium, and invasion of the myocardium. These data reveal novel roles for FGFR-1 signaling in epicardial biology and coronary vascular lineage differentiation, and point to potential new therapeutic avenues.

Cellular analysis of S100Beta and fibroblast growth factor-2 in the dorsal root ganglia and sciatic nerve of rodents. focus on paracrine actions of activated satellite cells after axotomy

The role of satellite cells, a type of peripheral glia, in the paracrine mechanisms related to neuronal maintenance and plasticity in the dorsal root ganglia (DRG) needs to be further investigated. This study employed immunohistochemistry and image analysis to investigate basic fibroblast growth factor (bFGF, FGF-2) and S100Beta immunoreactivities in the DRG and sciatic nerve of the rat and mouse. Well-characterized antibodies against bovine (residues 1-24) and rat (residues 1-23) FGF-2 were employed. Furthermore, the state of satellite cell reaction and changes in the FGF-2/S100Beta immunoreactivity were analyzed after axotomy of rat sciatic nerve. Scattered neurons and the majority of the satellite cells of the rat DRG and also Schwann cells of the rat sciatic nerve stained for S100Beta. In the mouse, strong S100Beta was encountered in the majority of sensory neurons and Schwann cells. Moderate FGF-2 (residues 1-24) immunoreactivity was found in scattered small size neurons of the rat DRG. A strong FGF-2 (residues 1-23) immunoreactivity was achieved in the satellite cells of rat DRG. Both FGF-2 antisera showed strong labeling in the mouse DRG sensory neurons. Activated satellite cells of the axotomized DRG possessed increased amount of FGF-2 and S100Beta immunoreactivity as demonstrated by quantitative image analysis. The proximal stump of the lesioned rat sciatic nerve showed increased FGF-2 (residues 1-24 and 1-23) in the Schwann cells, myelin sheaths, and neuronal fibers, without changes in the level of S100Beta immunoreactivity. Results suggested a possible interaction between FGF-2 and S100Beta in activated satellite cells of the DRG, which might trigger paracrine actions in the axotomized sensory neurons.

Identification of c-Jun as a critical mediator for the intracrine 24 kDa FGF-2 isoform-induced cell proliferation

Tumor cells frequently synthesize an N-terminally extended the FGF-2 isoform of 24 kDa devoid of signal peptide but that contains a functional nuclear localization sequence (NLS). Although the signaling pathways elicited by secreted FGF-2 are well described, the molecular mechanisms involved in the growth promoting action of nuclearized 24 kDa FGF-2 remain unknown. The cancer cell line AR4-2J was engineered to stably express only the 24 kDa FGF-2 isoform and cDNA microarrays were used to identify targets implicated in the intracrine-induced cell proliferation. Levels of 27 transcripts were found either upregulated or downregulated compared to control cells. Among the 18 upregulated genes was c-jun, which is often involved in cell proliferation. Real-time PCR and Western blot analyses confirmed c-jun induction at both mRNA and protein levels. The c-jun antisense oligonucleotide strategy pointed out the involvement of c-Jun in the 24 kDa FGF-2-induced cell proliferation. The mitogenic effect was found to depend on ERK pathway and not on phosphoinositide 3-kinase, p38 MAPK, c-Jun NH2-terminal kinase signal transducers. In addition, the MEK inhibitor PD98059 reduced the 24 kDa FGF-2-dependent c-Jun level. These data show that intracrine FGF-2-mediated regulation of cell growth involves ERK activation and consequent c-Jun expression. Thus, despite its incapacity to be secreted, the intracellular-localized 24 kDa FGF-2 can activate a growth-related signaling pathway normally elicited by cell surface receptors.

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

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

Integrative nuclear FGFR1 signaling (INFS) as a part of a universal ?feed-forward-and-gate? signaling module that controls cell growth and differentiation

A novel signaling mechanism is described through which extracellular signals and intracellular signaling pathways regulate proliferation, growth, differentiation, and other functions of cells in the nervous system. Upon cell stimulation, fibroblast growth factor receptor-1 (FGFR1), a typically plasma membrane-associated protein, is released from ER membranes into the cytosol and translocates to the cell nucleus by an importin-beta-mediated transport pathway along with its ligand, FGF-2. The nuclear accumulation of FGFR1 is activated by changes in cell contacts and by stimulation of cells with growth factors, neurotransmitters and hormones as well as by a variety of different second messengers and thus was named integrative nuclear FGFR1 signaling (INFS). In the nucleus, FGFR1 localizes specifically within nuclear matrix-attached speckle-domains, which are known to be sites for RNA Pol II-mediated transcription and co-transcriptional pre-mRNA processing. In these domains, nuclear FGFR1 colocalizes with RNA transcription sites, splicing factors, modified histones, phosphorylated RNA Pol II, and signaling kinases. Within the nucleus, FGFR1 serves as a general transcriptional regulator, as indicated by its association with the majority of active nuclear centers of RNA synthesis and processing, by the ability of nuclear FGFR1 to activate structurally distinct genes located on different chromosomes and by its stimulation of multi-gene programs for cell growth and differentiation. We propose that FGFR1 is part of a universal "feed-forward-and-gate" signaling module in which classical signaling cascades initiated by specific membrane receptors transmit signals to sequence specific transcription factors (ssTFs), while INFS elicited by the same stimuli feeds the signal forward to the common coactivator, CREB-binding protein (CBP). Activation of CBP by INFS, along with the activation of ssTFs by classical signaling cascades brings about coordinated responses from structurally different genes located at different genomic loci.

Activation of phosphorylating-p38 mitogen-activated protein kinase and its relationship with localization of intestinal stem cells in rats after ischemia-reperfusion injury

AIM: To investigate the expression of phosphorylating p38 mitogen-activated protein kinase (MAPK) in rat small intestine after ischemia-reperfusion (I/R) insult and its relationship with the localization of intestinal stem cells.

METHODS: Forty-eight Wistar rats were divided randomly into three groups, namely intestinal ischemia-reperfusion group (R), intestinal ischemia group (I) and sham-operated control group (C). In group I, the animals were killed 45 minutes after superior mesenteric artery (SMA) occlusion, while in group R the rats sustained SMA occlusion for 45 minutes and reperfusion for 2, 6, 12 or 24 h respectively. In sham-operated control group, SMA was separated, but without occlusion. The activity of plasma diamine oxidase (DAO) was determined. Intestinal tissue samples were also taken for histological analysis and immunohistochemical analysis of MAPK p38 detection and intestinal stem cell localization.

RESULTS: The changes in histological structure and plasma DAO levels indicated that the intestinal barrier was damaged after intestinal I/R injury. In group C and I, each crypt contained 5-6 p38 MAPK positive cells, which were mainly located in the lower region of the crypts. This was consistent with the distribution of intestinal stem cells. The presence of positive cells in crypts increased with the time of reperfusion and reached its peak at 12 h after reperfusion (35.6%).

CONCLUSION: After intestinal I/R injury, the expression of phosphorylating-p38 MAPK in small intestine increased with the duration of reperfusion, and its distribution coincided with that of intestinal stem cells and their daughter cells, indicating that phosphorylating-p38 might be a possible marker of intestinal stem cells.

Role and regulation of the fibroblast growth factor axis in human thyroid follicular cells

Thyroidal levels of fibroblast growth factor-2 (FGF-2) and fibroblast growth factor receptor 1 (FGFR1) are elevated in human thyroid hyperplasia. To understand the significance of this, effects of FGFR1 activation on normal human thyrocyte growth and function in vitro and the regulation of FGF-2 and FGFR1 expression have been examined. FGF-2 stimulated cell growth, as measured by cell counting, and inhibited thyroid function as measured by 125I uptake. Sensitivity to FGF-2 disappeared after 7 days, although FGFR1 expression was maintained. Thyroid-stimulating hormone (TSH, 300 mU/l) increased FGFR1 mRNA expression within 4 h and protein expression by 8 h. Exogenous FGF-2 decreased FGFR1 protein. Endogenous FGF-2 levels were low (approximately 1-2 pg/microg protein), and TSH treatment decreased these by 50%. Protein kinase C (PKC) activation increased FGF-2 mRNA and FGF-2 secretion within 2 h. This effect was enhanced (4.4-fold) when cells were cultured in TSH. We conclude that TSH stimulates FGFR1 but not FGF-2 expression. PKC activation stimulates FGF-2 synthesis and secretion, and TSH synergizes with PKC activators. Increases in FGFR1 or FGF-2 or in both may contribute to goitrogenesis.

Rapid mitogen-activated protein kinase by basic fibroblast growth factor in rat intestine after ischemia/reperfusion injury

AIM: Previous studies showed that exogenous basic fibroblast growth factor (bFGF or FGF-2) could improve physiological dysfunction after intestinal ischemia/reperfusion (I/R) injury. However, the mechanisms of this protective effect of bFGF are still unclear. The present study was to detect the effect of bFGF on the activities of mitogen-activated protein kinase (MAPK) signaling pathway in rat intestine after I/R injury, and to investigate the protective mechanisms of bFGF on intestinal ischemia injury.

METHODS: Rat intestinal I/R injury was produced by clamping the superior mesenteric artery (SMA) for 45 min and followed by reperfusion for 48 h. Seventy-eight Wistar rats were used and divided randomly into sham-operated group (A), normal saline control group (B), bFGF antibody pre-treated group (C), and bFGF treated group (D). In group A, SMA was separated without occlusion. In groups B, C and D, SMA was separated and occluded for 45 min, then, released for reperfusion for 48 h. After the animals were sacrificed, blood and tissue samples were taken from the intestine 45 min after ischemia in group A and 2, 6, 24, and 48 h after reperfusion in the other groups. Phosphorylated forms of p42/p44 MAPK, p38 MAPK and stress activated protein kinase/C-Jun N-terminal kinase (SAPK/JNK) were measured by immunohistochemistry. Plasma levels of D-lactate were examined and histological changes were observed under the light microscope.

RESULTS: Intestinal I/R injury induced the expression of p42/p44 MAPK, p38 MAPK, and SAPK/JNK pathways and exogenous bFGF stimulated the early activation of p42/p44 MAPK and p38 MAPK pathways. The expression of phosphorylated forms of p42/p44 MAPK was primarily localized in the nuclei of crypt cells and in the cytoplasm and nuclei of villus cells. The positive expression of p38 MAPK was localized mainly in the nuclei of crypt cells, very few in villus cells. The activities of p42/p44 MAPK and p38 MAPK peaked 6 h after reperfusion in groups B and C, while SAPK/JNK peaked 24 h after reperfusion. The activities of p42/p44 MAPK and p38 MAPK peaked 2 h after reperfusion in group D and those of SAPK/JNK were not changed in group B. D-lactate levels and HE staining showed that the intestinal barrier was damaged severely 6 h after reperfusion; however, histological structures were much improved 48 h after reperfusion in group D than in the other groups.

CONCLUSION: The results indicate that intestinal I/R injury stimulates the activities of MAPK pathways, and that p42/p44 MAPK and p38MAPK activities are necessary for the protective effect of exogenous bFGF on intestinal I/R injury. The protective effect of bFGF on intestinal dysfunction may be mediated by the early activation of p42/p44 MAPK and p38 MAPK signaling pathways.

Inhibitory role of the somatostatin receptor SST2 on the intracrine-regulated cell proliferation induced by the 210-amino acid fibroblast growth factor-2 isoform: implication of JAK2

The fibroblast growth factor (FGF)-2 isoform of 210 amino acids (HMW FGF-2) contains a nuclear localization sequence (NLS) and is targeted to the nucleus. This FGF-2 isoform allows cells to grow in low serum concentrations through still unknown mechanisms called intracrine regulations. Different peptide hormones and cytokines have been found to be nuclearized through NLS and to induce cell proliferation. The existence of molecules acting as negative regulators of the intracrine-induced cell growth has not been explored. Pancreatic cells AR4-2J were stably transfected to express selectively the HMW FGF-2. We demonstrated that activation of the somatostatin receptor subtype SST2 by the somatostatin analogue RC-160 in serum-deprived medium inhibits the mitogenic effect of the HMW FGF-2, without affecting growth of control cells. The signaling pathway implicates Galphai/JAK2/SHP-1. The Galphai inhibitor pertussis toxin and the JAK2 inhibitor AG490 abrogate the inhibitory effect of RC-160 on HMW FGF-2-induced cell growth. Co-immunoprecipitation studies demonstrate the constitutive association of JAK2 and SHP-1, and RC-160 induces a rapid activation of both proteins followed by the dissociation of the complex. AG490 prevents the RC-160 induced SHP-1 activation indicating the implication of JAK2 in this process. JAK2 and SHP-1 are immunoprecipitated with SST2 in basal conditions indicating the existence of a functional signaling complex at the receptor level. In summary, these data provide the following evidence: 1) the intracrine-induced proliferation can be reversed by extracellular acting polypeptides; 2) SST2 inhibitory signaling may involve the JAK2/SHP-1 pathway.

Translokin is an intracellular mediator of FGF-2 trafficking

Basic fibroblast growth factor (bFGF or FGF-2) exerts its pleiotropic activities both as an exogenous and an intracellular factor. FGF-1 and FGF-2 are prototypes for this dual signalling, but the mechanisms of their intracellular actions remain unknown. Here we show that Translokin, a cytoplasmic protein of relative molecular mass 55,000 (M(r) 55K), interacts specifically with the 18K form of FGF-2. Translokin is ubiquitously expressed and colocalizes with the microtubular network. As Translokin does not interact with FGF-1, we used a strategy based on FGF-1-FGF-2 chimaeras to map the interacting regions in FGF-2 and to generate Nb1a2, a non-interacting variant of FGF-2. Although most of the FGF-2 properties are preserved in Nb1a2, this variant is defective in intracellular translocation and in stimulating proliferation. The fusion of a nuclear localization signal to Nb1a2 restores its mitogenic activity and its nuclear association. Inhibiting Translokin expression by RNA interference reduces the translocation of FGF-2 without affecting the intracellular trafficking of FGF-1. Our data show that the nuclear association of internalized FGF-2 is essential for its mitogenic activity and that Translokin is important in this translocation pathway.

Smad mediates BMP-2-induced upregulation of FGF-evoked PC12 cell differentiation

We previously reported that bone morphogenetic protein (BMP)-2 augments fibroblast growth factor (FGF)-induced neuronal differentiation of PC12 cells by selectively upregulating FGF receptor (FGFR)-1 expression. Here we describe the underlying mechanism. BMP-2 activated Smad proteins in PC12 cells. Overexpression of Smad7 or Smad1, inhibitory and receptor-regulated isoforms, respectively, suppressed or enhanced BMP-2-induced upregulation of FGFR-1 expression. Smad 7 also inhibited the FGF-induced PC12 differentiation. Our findings indicate that activation of a Smad signaling pathway is required for upregulation of FGFR-1 expression by BMP-2 and for the synergistic induction of PC12 differentiation by BMP-2 and FGF.

Differential expression of specific FGF ligand and receptor isoforms during angiogenesis associated with prostate cancer progression

BACKGROUND

The aim of this study was to elucidate how changes in temporal and spatial expression patterns of individual components of the fibroblast growth factor (FGF) signaling axis correlate with prostate cancer-associated angiogenesis to contribute to the progression of this disease.

METHODS

The temporal and spatial expression patterns of specific FGF ligands and receptors were characterized by immunoblot, in situ hybridization, and immunohistochemical analyses in the transgenic adenocarcinoma of the mouse prostate (TRAMP) model.

RESULTS

We detected expression of high molecular weight isoform of FGF-2 in PIN lesions and detected both high and low molecular weight isoforms of FGF-2 in advanced tumors. Expression of the mRNA encoding the FGFR1iiib isoform was found to be specifically and differentially expressed in tumor vasculature in TRAMP but was not detected in prostate-associated vasculature in nontransgenic mice. Expression of the FGFR2iiic isoform was observed to be elevated in the epithelial component of PIN lesions in TRAMP mice.

CONCLUSION

By using the TRAMP model, the expression of FGFR1iiib in intraductal vasculature and expression of FGF-2 protein were found to be concomitant with the emergence of PIN. These observations implicate specific changes in the FGF axis with the initiation and progression of prostate cancer and underscore the utility of animal models to identify specific molecular changes in early disease.

Long-term follow-up and prognostic significance of angiogenic basic fibroblast growth factor (bFGF) expression in patients with breast cancer

The development of distant metastasis in breast cancer patients is the key step towards worse prognosis. The angiogenic basic fibroblast growth factor (bFGF) has been associated with tumorigenesis and metastasis in several human cancers. Therefore, bFGF expression was studied by immunohistochemistry in 111 patients with primary breast cancer. The results were correlated with prognostically relevant clinico-pathological features. such as tumor stage, grading. nodal stage and survival. bFGF was expressed in approximately 70% of the breast cancer tissues; 30% of the tumors showed strongly positive staining. With the exception of histological grading (p < 0.05), no correlation was found between the extent of bFGF expression and prognostic parameters. Analysis of survival showed a significantly (p < 0.05) prolonged survival for patients with a concomitant absence of axillary lymph node metastasis and bFGF immunoreactivity. Our data suggest that increased bFGF expression is a novel parameter for worse prognosis in nodal-negative breast cancer patients.

Integrative nuclear FGFR1 signaling (INFS) pathway mediates activation of the tyrosine hydroxylase gene by angiotensin II, depolarization and protein kinase C

The integrative nuclear FGFR1 signaling (INFS) pathway functions in association with cellular growth, differentiation, and regulation of gene expression, and is activated by diverse extracellular signals. Here we show that stimulation of angiotensin II (AII) receptors, depolarization, or activation protein kinase C (PKC) or adenylate cyclase all lead to nuclear accumulation of fibroblast growth factor 2 (FGF-2) and FGFR1, association of FGFR1 with splicing factor-rich domains, and activation of the tyrosine hydroxylase (TH) gene promoter in bovine adrenal medullary cells (BAMC). The up-regulation of endogenous TH protein or a transfected TH promoter-luciferase construct by AII, veratridine, or PMA (but not by forskolin) is abolished by transfection with a dominant negative FGFR1TK-mutant which localizes to the nucleus and plasma membrane, but not by extracellularly acting FGFR1 antagonists suramin and inositolhexakisphosphate (IP6). Mechanism of TH gene activation by FGF-2 and FGFR1 was further investigated in BAMC and human TE671 cultures. TH promoter was activated by co-transfected HMW FGF-2 (which is exclusively nuclear) but not by cytoplasmic FGF-1 or extracellular FGFs. Promoter transactivation by HMWFGF-2 was accompanied by an up-regulation of FGFR1 specifically in the cell nucleus and was prevented FGFR1(TK-) but not by IP6 or suramin. The TH promoter was also transactivated by co-transfected wild-type FGFR1, which localizes to both to the nucleus and the plasma membrane, and by an exclusively nuclear, soluble FGFR1(SP-/NLS) mutant with an inserted nuclear localization signal. Activation of the TH promoter by nuclear FGFR1 and FGF-2 was mediated through the cAMP-responsive element (CRE) and was associated with induction of CREB- and CBP/P-300-containing CRE complexes. We propose a new model for gene regulation in which nuclear FGFR1 acts as a mediator of CRE transactivation by AII, cell depolarization, and PKC.

Expression of the high molecular weight fibroblast growth factor-2 isoform of 210 amino acids is associated with modulation of protein kinases C delta and epsilon and ERK activation

The high molecular weight (HMW) fibroblast growth factor (FGF)-2 isoform of 210 amino acids initiated at a CUG start codon possesses a nuclear localization sequence and is not secreted. In contrast, the low molecular weight (LMW) isoform of 155 amino acids initiated at the AUG start codon can be secreted and activates the cell surface FGF receptors. The two isoforms possess different biological properties; however, little is known about the intracrine regulatory mechanisms involved in the biological effects of the HMW FGF-2 isoform. Using pancreatic cells stably transfected with cDNAs leading to the expression of either the HMW FGF-2 (A3 cells) or the LMW form (A5 cells), we provide evidence that the two FGF-2 isoforms differentially modulate PKC levels. The LMW FGF-2 up-regulated the PKC epsilon levels by 1.6-fold; by contrast the HMW isoform down-regulated the level of this PKC isotype by about 3-fold and increased the amount of PKC delta by 1.7-fold. PKC mRNAs were also modified, suggesting that PKC expression was regulated at a pretranslational level. Additionally, expression of different levels of the HMW FGF-2 with an inducible expression system confirmed the role of this isoform on PKC delta and epsilon expressions. Increased activation of ERK-1 and -2 was also observed in cells expressing the HMW FGF-2. By using different PKC inhibitors and a dominant negative PKC delta, it was found that ERK activation was PKC delta-dependent. These data indicate that expression of HMW FGF-2 can modify PKC levels by acting at the intracellular level and that the overexpression of PKC delta induces ERK-1/2 activation. The expression of a dominant negative FGFR1 did not reduce ERK-1/2 activation by the HMW FGF-2, suggesting that ERK activation does not require FGFR activity. The signaling cascade downstream of ERK might be involved in the known mitogenic effect exerted by this FGF-2 isoform.

Fibroblast growth factor-9 modulates the expression of myelin related proteins and multiple fibroblast growth factor receptors in developing oligodendrocytes

The effect of fibroblast growth factor (FGF)-9 on the expression of FGF receptors (FGFR) and the major myelin proteins was examined in cultures of developing rat brain oligodendrocytes (OLs), using immunological techniques. FGFR-1, -3, and -4 were expressed at all developmental stages but were not present in isolated myelin fractions. By contrast, FGFR-2 protein was predominantly localized to differentiating cells and myelin. FGF-9 altered FGFR and myelin protein levels during OL differentiation; there was increased expression of FGFR-1 and decreased levels of both FGFR-2 and myelin proteins. Further, FGF-9 stimulated mitogen-associated protein kinase (MAPK) phosphorylation. The effect of FGF-9 on MAPK, however, was transient and less robust in progenitor cells than in differentiated oligodendrocytes. The effects of FGF-9 and FGF-2 on FGFR and myelin protein levels were comparable; both up-regulated FGFR-1, and down-regulated FGFR-2, CNP, PLP and MBP. These findings suggest that FGF-9 may be important for glial cell development.

The Ser252Trp fibroblast growth factor receptor-2 (FGFR-2) mutation induces PKC-independent downregulation of FGFR-2 associated with premature calvaria osteoblast differentiation

We recently showed that the Apert Ser252Trp fibroblast growth factor receptor-2 (FGFR-2) mutation causes premature osteoblast differentiation and increased subperiosteal calvaria bone matrix formation. To gain further insight into the cellular mechanisms involved in these effects, we examined the effects of the mutation on the expression of FGFRs in relation to cell proliferation and differentiation markers in vivo and in vitro, and we analyzed the underlying signaling pathways in mutant cells. Immunohistochemical analysis of the Apert calvaria suture showed that the Ser252Trp FGFR-2 mutation increased type 1 collagen, osteocalcin, and osteopontin expression in preosteoblasts compared to normal, whereas cell growth was not affected. The premature osteoblast differentiation induced by the mutation was associated with lower than normal FGFR-2 immunolabeling, whereas FGFR-1 and FGFR-3 levels were not decreased. Immunocytochemical analysis in osteoblasts isolated from Apert coronal suture showed that the Ser252Trp mutation induced constitutive downregulation of FGFR-2 in mutant cells. Western blot analysis of FGFRs in immortalized mutant osteoblastic cells confirmed that the mutation induced FGFR-2 downregulation. FGFR-2 mRNA levels were not altered in mutant cells, indicating that FGFR-2 downregulation resulted from receptor internalization rather than from changes in receptor mRNA. The signaling pathway involved in FGFR-2 downregulation was studied using specific inhibitors of FGF signaling molecules. The selective PKC inhibitor calphostin C markedly reduced FGFR-2 protein levels in mutant cells, in contrast to the p38 MAP kinase inhibitor SB 203580 or the Erk 1,2 MAP kinase inhibitor PD-98059, showing that PKC is involved in FGFR-2 regulation, but not in FGFR-2 downregulation in mutant cells. The results indicate that the premature osteoblast differentiation induced by the FGFR-2 Ser252Trp mutation is associated with a PKC-independent downregulation of FGFR-2 in human calvaria cells.

The high molecular weight isoforms of basic fibroblast growth factor (FGF-2): an insight into an intracrine mechanism

Basic fibroblast growth factor (FGF-2) is an important modulator of cell growth and differentiation under both physiological and pathological conditions. Until recently, most investigations into the FGF-2 signalling pathway were concerned with its interaction with specific membrane receptors. Nevertheless, while a 18 kDa protein of FGF-2 is cytosolic, there are also co-translated high molecular weight (HMW) isoforms that are predominantly located in the cell nucleus. An increasing amount of data strongly argue in favour of distinct biological functions depending on the subcellular location of the FGF-2 species. This review describes the evidence concerning the strictly intracellular mode of action of the HMW isoforms of FGF-2.

The expression of basic fibroblast growth factor (bFGF) in tumor-associated stromal cells and vessels is inversely correlated with non-small cell lung cancer progression

Tumor progression results from complex interactions between tumor and tumor-associated host tissue. Basic fibroblast growth factor (bFGF), via activation of its receptor, FGFR-1, has been postulated to be an important inducer of host stromal response and angiogenesis. To assess the putative role of tumor-associated stromal cells and vessels in tumor progression, we studied non-small cell lung cancer (NSCLC) from 84 patients, including 51 squamous cell carcinomas and 33 nonsquamous cell carcinomas, by immunohistochemical detection. bFGF and FGFR-1 immunoreactivity was observed in tumor and in tumor-associated stromal cells and vessels. The expression of bFGF and FGFR-1 in stromal cells was higher in squamous than in non-squamous cell carcinomas (respectively, P = .007 and P = .0004). We found that bFGF and FGFR-1 expression in tumor and tumor-associated stromal cells and vessels was directly correlated with host stromal response, as assessed by intratumoral extension of stroma, but not with angiogenic response, as assessed by microvessel count. Although FGFR-1 expression of tumor cells was directly correlated with T-stage (P = .03), bFGF expressions of tumor-associated stromal cells and vessels were inversely correlated with lymph node metastasis (respectively, P = .0001 and P = .0002) and advanced pathological stage (respectively, P = .03 and P = .01). These findings suggest that bFGF might mediate host stromal response in NSCLC and that the expression of bFGF in tumor-associated stromal cells and vessels might have an inhibitory role in NSCLC progression.

FGF-2 enhances intestinal stem cell survival and its expression is induced after radiation injury

Fibroblast growth factors (FGFs) have mitogenic activity toward a wide variety of cells of mesenchymal, neuronal, and epithelial origin and regulate events in normal embryonic development, angiogenesis, wound repair, and neoplasia. FGF-2 is expressed in many normal adult tissues and can regulate migration and replication of intestinal epithelial cells in culture. However, little is known about the effects of FGF-2 on intestinal epithelial stem cells during either normal epithelial renewal or regeneration of a functional epithelium after injury. In this study, we investigated the expression of FGF-2 in the mouse small intestine after irradiation and determined the effect of exogenous FGF-2 on crypt stem cell survival after radiation injury. Expression of FGF-2 mRNA and protein began to increase at 12 h after gamma-irradiation, and peak levels were observed from 48 to 120 h after irradiation. At all times after irradiation, the higher molecular mass isoform ( approximately 24 kDa) of FGF-2 was the predominant form expressed in the small intestine. Immunohistochemical analysis of FGF-2 expression after radiation injury demonstrated that FGF-2 was predominantly found in the mesenchyme surrounding regenerating crypts. Exogenous recombinant human FGF-2 (rhFGF-2) markedly enhanced crypt stem cell survival when given before irradiation. We conclude that expression of FGF-2 is induced by radiation injury and that rhFGF-2 can enhance crypt stem cell survival after subsequent injury.

FGF-2 dimerization involvement in growth factor mediated cell proliferation but not cell differentiation

Dimerization is a prerequisite for many growth factors in their receptor activation leading to cellular response. FGF-1 and FGF-2, members of the Fibroblast Growth Factor (FGF) family, were shown to form non-covalent dimers and oligomers in vitro. Using the two-hybrid system as an in vivo binding assay we show here that of three representative members of the FGF family, only FGF-2 is able to homodimerize. Moreover the FGF-2 isoforms could heterodimerize. Two single-point mutants (T121F and W123R), defective in their dimerization capability, were isolated through random mutagenesis and were used to study the role of FGF-2 dimerization with regard to its biological activity. Remarkably, these mutant proteins were still able to induce cell differentiation, but were strongly affected in their capacity to promote cell proliferation. This study thus highlights the uncoupling between proliferation and differentiation FGF-2 signaling pathways and the crucial role of FGF-2 dimerization in the mitogenic activity of this factor.

Fibroblast growth factor (FGF) soluble receptor 1 acts as a natural inhibitor of FGF2 neurotrophic activity during retinal degeneration

Fibroblast growth factors (FGF) 1 and 2 and their tyrosine kinase receptor (FGFR) are present throughout the adult retina. FGFs are potential mitogens, but adult retinal cells are maintained in a nonproliferative state unless the retina is damaged. Our work aims to find a modulator of FGF signaling in normal and pathological retina. We identified and sequenced a truncated FGFR1 form from rat retina generated by the use of selective polyadenylation sites. This 70-kDa form of soluble extracellular FGFR1 (SR1) was distributed mainly localized in the inner nuclear layer of the retina, whereas the full-length FGFR1 form was detected in the retinal Muller glial cells. FGF2 and FGFR1 mRNA levels greatly increased in light-induced retinal degeneration. FGFR1 was detected in the radial fibers of activated retinal Muller glial cells. In contrast, SR1 mRNA synthesis followed a biphasic pattern of down- and up-regulation, and anti-SR1 staining was intense in retinal pigmented epithelial cells. The synthesis of SR1 and FGFR1 specifically and independently regulated in normal and degenerating retina suggests that changes in the proportion of various FGFR forms may control the bioavailability of FGFs and thus their potential as neurotrophic factors. This was demonstrated in vivo during retinal degeneration when recombinant SR1 inhibited the neurotrophic activity of exogenous FGF2 and increased damaging effects of light by inhibiting endogenous FGF. This study highlights the significance of the generation of SR1 in normal and pathological conditions.

Fibroblast growth factors as multifunctional signaling factors

The fibroblast growth factor (FGF) family consists of at least 15 structurally related polypeptide growth factors. Their expression is controlled at the levels of transcription, mRNA stability, and translation. The bioavailability of FGFs is further modulated by posttranslational processing and regulated protein trafficking. FGFs bind to receptor tyrosine kinases (FGFRs), heparan sulfate proteoglycans (HSPG), and a cysteine-rich FGF receptor (CFR). FGFRs are required for most biological activities of FGFs. HSPGs alter FGF-FGFR interactions and CFR participates in FGF intracellular transport. FGF signaling pathways are intricate and are intertwined with insulin-like growth factor, transforming growth factor-beta, bone morphogenetic protein, and vertebrate homologs of Drosophila wingless activated pathways. FGFs are major regulators of embryonic development: They influence the formation of the primary body axis, neural axis, limbs, and other structures. The activities of FGFs depend on their coordination of fundamental cellular functions, such as survival, replication, differentiation, adhesion, and motility, through effects on gene expression and the cytoskeleton.

Overexpression of the FGF-2 24-kDa isoform up-regulates IL-6 transcription in NIH-3T3 cells

We have isolated NIH-3T3 cell lines overexpressing the nuclear 24-kDa isoform of fibroblast growth factor (FGF)-2 and characterized its regulatory effect on the expression of interleukin-6 (IL-6) in these cells. The clone pRF5 expressing the highest level was able to grow in 1% serum medium to a high saturation density and acquired a radioresistance advantage. In pRF5 and another clone pRF1, IL-6 RNA levels were markedly increased. Studies with IL-6 promoter constructs revealed that IL-6 gene up-regulation occurred at the transcriptional level and did not involve the AP-1 binding site. Exogenously added 18-kDa isoform of FGF-2 (100 ng/ml) produced down-regulation of IL-6 involving an AP-1 binding site, thus suggesting a receptor-independent pathway for the intracellular 24-kDa isoform.

Endogenous FGF1-induced activation and synthesis of extracellular signal-regulated kinase 2 reduce cell apoptosis in retinal-pigmented epithelial cells

Retinal-pigmented epithelial (RPE) cell survival is critical to the maintenance of the function of the neural retinal and in the development of various retina degenerations. We investigated molecular mechanisms involved in this function by assessing apoptosis in RPE cells following serum deprivation. Apoptosis induced by serum withdrawal is lower in aged RPE cells because of higher endogenous acidic fibroblast growth factor (FGF1) synthesis and secretion. These experiments examined several aspects of FGF signaling and the contribution of endogenous FGF1 to activation of the extracellular signal-regulated kinase 2 (ERK2). In aged RPE cells, FGFR1 was rapidly activated, and its autophosphorylation followed the kinetics of endogenous FGF1 secretion, before the onset of apoptosis. ERK2 phosphorylation, activity, and de novo synthesis increased at the same time. In marked contrast, no de novo JNK1 synthesis was observed. MEK1 inhibition resulted in lower levels of ERK2 activation and synthesis and higher levels of apoptosis. Treatment with neutralizing anti-FGF1 or blocking anti-FGFR1 antibodies mimics these effects. Thus, this study strongly suggests that the survival-increasing effect of FGF1 in aged RPE cells is because of an autocrine/paracrine loop in which the ERK2 cascade plays a pivotal role.

A functional fibroblast growth factor-1 immunoglobulin fusion protein

Proteins of the fibroblast growth factor (FGF) family play diverse roles in embryonic development, angiogenesis, and wound healing. The most well studied targets of FGF activity typically are cells of mesodermal and neuroectodermal origin; in addition, expression of FGF-1 (acidic FGF) is increased at several sites of chronic immunologic injury, and recent studies show that FGF-1 also may interact with cells of the immune system. In some human T cells, FGF-1 can induce signals necessary for production of interleukin-2, a key cytokine required for T cell proliferation. To better characterize the interaction of FGF-1 with FGF receptors on T cells, a fusion protein was constructed containing a portion of the constant region of human IgG1 (Fc) at the amino terminus of FGF-1. The Fc-FGF-1 fusion protein retained FGF function as determined by stimulation of tyrosine phosphorylation and DNA synthesis in NIH 3T3 cells. Binding of the intact fusion protein to FGF receptor 1 (FGFR1) on T cells was demonstrated by immunoprecipitation of the receptor bound to Fc-FGF-1 and by flow cytometry showing binding of fusion protein to T cells expressing FGFR1. This functional Fc-FGF-1 protein should prove useful in identifying FGFR-expressing cells.

Suppression of fibroblast growth factor receptor signaling inhibits pancreatic cancer growth in vitro and in vivo

BACKGROUND & AIMS

Fibroblast growth factors (FGFs) are mitogenic polypeptides that activate specific cell surface FGF receptors (FGFRs). Pancreatic cancers overexpress basic FGF (bFGF) and the type I FGF receptor (FGFR-1), and overexpression of bFGF has been correlated with decreased patient survival. The aim of this study was to examine the effects of abrogation of FGFR-1-dependent signaling on pancreatic cancer cell growth.

METHODS

PANC-1 human pancreatic cancer cells were transfected with a truncated FGFR-1 complementary DNA (FGFR405), resulting in the expression of a kinase-deficient receptor. Activation of endogenous FGFR-1 was assessed in immunoblot studies with antiphosphotyrosine and anti-active mitogen-activated protein (MAP) kinase antibodies. Effects on cell growth were determined in vitro and in nude mice.

RESULTS

PANC-1 clones expressing the truncated receptor showed attenuated receptor tyrosine phosphorylation and MAP kinase activation in response to bFGF, decreased basal cell growth, and a marked decrease in tumor-forming potential in vivo. Confirmatory experiments with MIA PaCa-2 pancreatic cancer cells indicated that FGFR405 also attenuated FGF-dependent MAP kinase activation in this cell line.

CONCLUSIONS

The findings suggest that FGFR-dependent signaling is crucial for pancreatic cancer growth and raise the possibility that inhibition of FGFR signaling may ultimately prove useful as a therapeutic option in patients with pancreatic cancer.

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.

Inherited retinal degeneration: basic FGF induces phagocytic competence in cultured RPE cells from RCS rats

In RCS rats, the retinal pigment epithelium (RPE) is defective in phagocytosis of photoreceptor membranes. We have previously shown reduced expression of basic fibroblast growth factor (bFGF) in the RPE of 7-10-day-old RCS rats. This study using primary RPE cultures from rats of this age demonstrates that the phagocytic defect in the mutant RPE can be overcome by treatment with bFGF, by a mechanism involving gene transcription and that normal RPE phagocytosis, also requiring transcription, is blocked by a bFGF neutralizing antibody. The combined data point to a role for bFGF in the normal mechanism of RPE phagocytosis and the RCS defect.