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

FGF1 Suppresses Allosteric Activation of β3 Integrins by FGF2: A Potential Mechanism of Anti-Inflammatory and Anti-Thrombotic Action of FGF1

Several inflammatory cytokines bind to the allosteric site (site 2) and allosterically activate integrins. Site 2 is also a binding site for 25-hydroxycholesterol, an inflammatory lipid mediator, and is involved in inflammatory signaling (e.g., TNF and IL-6 secretion) in addition to integrin activation. FGF2 is pro-inflammatory and pro-thrombotic, and FGF1, homologous to FGF2, has anti-inflammatory and anti-thrombotic actions, but the mechanism of these actions is unknown. We hypothesized that FGF2 and FGF1 bind to site 2 of integrins and regulate inflammatory signaling. Here, we describe that FGF2 is bound to site 2 and allosterically activated β3 integrins, suggesting that the pro-inflammatory action of FGF2 is mediated by binding to site 2. In contrast, FGF1 bound to site 2 but did not activate these integrins and instead suppressed integrin activation induced by FGF2, indicating that FGF1 acts as an antagonist of site 2 and that the anti-inflammatory action of FGF1 is mediated by blocking site 2. A non-mitogenic FGF1 mutant (R50E), which is defective in binding to site 1 of αvβ3, suppressed β3 integrin activation by FGF2 as effectively as WT FGF1.

Significant Enhancement of Fibroblast Migration, Invasion, and Proliferation by Exosomes Loaded with Human Fibroblast Growth Factor 1

Exosomes possess several inherent properties that make them ideal for biomedical applications, including robust stability, biocompatibility, minimal immunogenicity, and the ability to cross biological barriers. These natural nanoparticles have recently been developed as drug delivery vesicles. To do so, therapeutic molecules must be efficiently loaded into exosomes first. Very recently, we developed a cell-penetrating peptide (CPP)-based platform for loading of nucleic acids and small molecules into exosomes by taking advantage of the membrane-penetration power of CPPs. Here, we extended this simple but effective platform by loading a protein cargo into exosomes isolated from either mesenchymal stem cells from three different sources or two different cancer cell lines. The protein cargo is a fusion protein YARA-FGF1-GFP through the covalent conjugation of a model CPP called YARA to human fibroblast growth factor 1 (FGF1) and green fluorescence protein (GFP). Loading of YARA-FGF1-GFP into exosomes was time-dependent and reached a maximum of about 1600 YARA-FGF1-GFP molecules in each exosome after 16 h. The ladened exosomes were effectively internalized by mammalian cells, and subsequently, the loaded protein cargo YARA-FGF1-GFP was delivered intracellularly. In comparison to YARA, YARA-FGF1-GFP, the unloaded exosomes, and the exosomes loaded with YARA, the exosomes loaded with YARA-FGF1-GFP substantially promoted the migration, proliferation, and invasion capabilities of mouse and human fibroblasts, which are important factors for wound repair. The work extended our CPP-based exosomal cargo loading platform and established a foundation for developing novel wound-healing therapies using exosomes loaded with FGF1 and other growth factors.

Large-Scale Preparation of Highly Stable Recombinant Human Acidic Fibroblast Growth Factor in Escherichia coli BL21(DE3) plysS Strain

In this study, the optimum human aFGF gene encoding haFGF₁₃₅ was cloned in pET3c and transferred to Escherichia coli BL21(DE3) plysS. To enhance the yield of fermentation and the expression level of the target protein, the fermentation parameters, including temperature, pH, dissolved oxygen, glucose concentration, ammonium chloride concentration, induction time, and inducer (IPTG) concentration, were optimized. The optimized fermentation parameters were used in large-scale fermentation (30 L). Ion-exchange and heparin-affinity column chromatography techniques were used for separation and purification of rhaFGF₁₃₅ protein. HPLC, isoelectric focusing electrophoresis, and mass spectrometry were used to detect the purity, isoelectric point, and molecular weight and peptide map of rhaFGF₁₃₅ protein, respectively. Mitogenic activity of rhaFGF₁₃₅ protein was detected in NIH-3T3 cells and a full-thickness injury wound diabetic rat model. The production and expression level of rhaFGF₁₃₅ in the 30-L scale fermentation reached 80.4 ± 2.7 g/L culture and 37.8% ± 1.8%, respectively. The RP-HPLC and SDS-PAGE purity of the final rhaFGF₁₃₅ product almost reached 100%, and the final pure protein yield was 158.6 ± 6.8 mg/L culture. Finally, the cell and animal experiments showed that rhaFGF₁₃₅ retained a potent mitogenic activity. The large-scale process of rhaFGF₁₃₅ production reported herein is relatively stable and time-saving, and thus, it can be used as an efficient and economic strategy for the synthesis of rhaFGF₁₃₅ at the industrial level.

Influence of the complex drug Cocarnit on the sciatic nerve in the development of diabetic polyneuropathy in rats

Ulcers and slow wound healing are common in diabetic polyneuropathy (DP), as well as shooting or burning pain, sensitivity to touch or lack of sensitivity, low oxygenation of nerve tissue, conductivity disorders and various vascular disorders. The mechanisms of DP development are complex and have not been completely studied. To take into account the role of B group vitamins, we investigated histological structure of nerve tissue, the level of different growth factors and the qualitative composition of active proteolytic enzymes in rats with DP and after the use of the metabolic drug Cocarnit for 9 days. This drug composition include nicotinamide, cocarboxylase, cyanocobalamin, adenosine triphosphate disodium trihydrate. We used an histological study of sciatic nerve; enzyme-linked immunosorbent assay and enzyme electrophoresis methods. In rats with DP, fragmentation of nerve tissue and their necrosis was established. Moreover, degraded forms of plasmin that has a fully functional serine proteinase domain are evident, and, therefore, it exhibits proteolytic properties. DP led to a decrease of neuron growth factor (NGF), vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). After treatment, the histological structure of nerve tissue was significantly improved, and the expression of growth factors NGF and bFGF was increased. Our study demonstrated that administration of Corcarnit brought about the complete restoration of the activation potential of plasmin and the almost disappearance of all degraded forms which were evident in the group with DP.

Systemic treatment with a novel basic fibroblast growth factor mimic small-molecule compound boosts functional recovery after spinal cord injury

Neurotrophic factors have been regarded having promising potentials for neuronal protection and regeneration, and thus promoting beneficial effects of kinesiological functions. They can be suspected to play important roles in cell/tissue grafting for various neural diseases. The clinical applications of such trophic factors to the central nervous system (CNS), however, have caused problematic side effects on account of the distinctive bioactive properties. In the course of developing synthetic compounds reflecting beneficial properties of basic fibroblast growth factor (bFGF), we conducted screening candidates that stimulate to trigger the intracellular tyrosine phosphorylation of FGF receptor and lead to the subsequent intracellular signaling in neurons. A small synthetic molecule SUN13837 was characterized by mimicking the beneficial properties of bFGF, which have been known as its specific activities when applied to CNS. What is more remarkable is that SUN13837 is eliminated the bioactivity to induce cell proliferation of non-neuronal somatic cells. On the bases of studies of pharmacology, behavior, physiology and histology, the present study reports that SUN13837 is characterized as a promising synthetic compound for treatment of devastating damages onto the rat spinal cord.

Intracellular partners of fibroblast growth factors 1 and 2 - implications for functions

Fibroblast growth factors 1 and 2 (FGF1 and FGF2) are mainly considered as ligands of surface receptors through which they regulate a broad spectrum of biological processes. They are secreted in non-canonical way and, unlike other growth factors, they are able to translocate from the endosome to the cell interior. These unique features, as well as the role of the intracellular pool of FGF1 and FGF2, are far from being fully understood. An increasing number of reports address this problem, focusing on the intracellular interactions of FGF1 and 2. Here, we summarize the current state of knowledge of the FGF1 and FGF2 binding partners inside the cell and the possible role of these interactions. The partner proteins are grouped according to their function, including proteins involved in secretion, cell signaling, nucleocytoplasmic transport, binding and processing of nucleic acids, ATP binding, and cytoskeleton assembly. An in-depth analysis of the network of these binding partners could indicate novel, non-classical functions of FGF1 and FGF2 and uncover an additional level of a fine control of the well-known FGF-regulated cellular processes.

Nuclear action of FGF members in endocrine-related tissues and cancer: Interplay with steroid receptor pathways

Dysregulation of the fibroblast growth factors/fibroblast growth factor receptor (FGF/FGFR) pathway has been implicated in a wide range of human disorders and several members have been localized in the nuclear compartment. Hormone-activated steroid receptors or ligand independent activated receptors form nuclear complexes that activate gene transcription. This review aims to highlight the interplay between the steroid receptor and the FGF/FGFR pathways and focuses on the current knowledge on nuclear action of FGF members in endocrine-related tissues and cancer. The nuclear trafficking and targets of FGF/FGFR members and the available evidence on the interplay with steroid hormones and receptors is described. Finally, the data on aberrant FGF/FGFR signaling is summarized and the nuclear action of FGF members on endocrine resistant breast cancer is highlighted. Identifying the mechanisms underlying FGF-induced endocrine resistance will be important to understand how to efficiently target endocrine-related diseases and even enhance or restore endocrine sensitivity in hormone receptor positive tumors.

An oncogenic activity of PDGF-C and its splice variant in human breast cancer

Despite strong evidence for the involvement of PDGF signaling in breast cancer, little is known about the PDGF ligand responsible for PDGFR activation during breast cancer progression. Here, we found PDGF-C to be highly expressed in breast carcinoma cell lines. Immunohistochemical analysis of invasive breast cancer revealed an association between increased PDGF-C expression and lymph node metastases, Ki-67 proliferation index, and poor disease-free survival. We also identified a PDGF-C splice variant encoding truncated PDGF-C (t-PDGF-C) isoform lacking the signal peptide and the N-terminal CUB domain. While t-PDGF C homodimer is retained intracellularly, it can be secreted as a heterodimer with full-length PDGF-C (FL-PDGF-C). PDGF-C downregulation reduced anchorage-independent growth and matrigel invasion of MDA-MB-231 cells. Conversely, ectopic expression of t-PDGF-C enhanced phenotypic transformation and invasion in BT-549 cells expressing endogenous FL-PDGF-C. The present study provides new insights into the functional significance of PDGF-C and its splice variant in human breast cancer.

The FGF1/CPP-C chimera protein protects against intestinal adverse effects of C-ion radiotherapy without exacerbating pancreatic carcinoma

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C-ion radiotherapy is applied to pancreatic carcinoma in the abdominal cavity.

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The FGF1/CPP-C chimeric protein has an intracellular signaling mode.

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FGF1/CPP-C protects against C-ion-induced intestinal damage.

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FGF1/CPP-C inhibits the proliferation and metastasis of pancreatic carcinoma cells.

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FGF1/CPP-C may be useful for C-ion radiotherapy against pancreatic cancer.

Background and purpose

Carbon ion (C-ion) beams are concentrated to irradiate pancreatic carcinoma in the upper abdomen; however, this radiotherapy potentially causes adverse reactions in the gastrointestinal tract. FGF1 is a candidate radioprotector for radiation-induced intestinal damage, but may promote the malignancy of pancreatic cancer. An FGF1/CPP-C chimeric protein was created to enhance the intracellular signaling mode of FGF1 instead of FGFR signaling. The present study investigated the effects of FGF1/CPP-C on the intestinal adverse reactions of C-ion radiotherapy as well as its influence on the malignancy of pancreatic cancer.

Materials and methods

FGF1/CPP-C was administered intraperitoneally to BALB/c mice without heparin 12 h before total body irradiation (TBI) with low-LET C-ion (17 keV/μm) at 6–8 Gy. Several radioprotective effects were examined in the jejunum. The invasion and migration of the human pancreatic carcinoma cell lines MIAPaCa-2 and PANC-1 were assessed using Boyden chambers after cultures with FGF1/CPP-C.

Results

The FGF1/CPP-C treatment promoted crypt survival after C-ion irradiation at 7–8 Gy significantly more than the FGF1 treatment. FGF1/CPP-C also inhibited C-ion radiotherapy-induced apoptosis and reduced γH2AX foci in crypt cells more than FGF1. However, FGF1/CPP-C inhibited the downstream signaling pathways of FGFRs and suppressed the activation of cell-cycle regulatory molecules in the intestine until 4 h after TBI. Furthermore, IEC6 cells were arrested in G2M after cultures with FGF1/CPP-C or FGF1, suggesting that DNA repair after irradiation is promoted by FGF1/CPP-C-induced G2M arrest. In contrast, FGF1/CPP-C appeared to be internalized into MIAPaCa-2 and PANC-1 cells more efficiently than FGF1. Therefore, FGF1/CPP-C reduced the in vitro proliferation, invasion, and migration of MIAPaCa-2 and PANC-1 cells significantly more than FGF1 through the cellular internalization of FGF1.

Conclusion

These results suggest that the intracellular signaling mode of FGF1/CPP-C attenuates the intestinal adverse effects of C-ion radiotherapy without enhancing the malignancy of pancreatic carcinoma.

FGF1 induces resistance to chemotherapy in ovarian granulosa tumor cells through regulation of p53 mitochondrial localization

Ovarian cancer remains associated with a high mortality rate and relapse is too frequently seen after chemotherapeutic treatment of granulosa cell tumors (GCTs) or epithelial ovarian cancers (EOCs). It is thus of major importance to progress in the knowledge of the molecular mechanisms underlying chemoresistance of ovarian tumors. Overexpression of Fibroblast Growth Factor 1 (FGF1) is observed in various cancers, correlates with poor survival and could be responsible for resistance to platinum-based chemotherapy of serous ovarian cancers. How FGF1 promotes escape to chemotherapy remains unknown. In previous studies, we showed that FGF1 inhibits p53 transcriptional activities, leading to increased cell survival of neuronal or fibroblast cell lines. In this study, we show that FGF1 favors survival of COV434 cells upon treatment with etoposide and cisplatin, two common chemotherapeutic molecules used for ovarian cancer. Etoposide and cisplatin induced mitochondrial depolarization, cytochrome c release and caspase activation in COV434 cells. Overexpression of FGF1 counteracts these events and thus allows increased survival of ovarian cells. In this study, FGF1 had little effect on p53 stability and transcriptional activities. Etoposide induced p21 expression as expected, but p21 protein levels were even increased in the presence of FGF1. Using RNA interference, we showed that p21 exerts an anti-apoptotic activity in COV434 cells. However abrogating this activity was not sufficient to restore cell death of FGF1-overexpressing cells. We also show for the first time that p53 mitochondrial pathway is involved in the cell death of COV434 cells. Indeed, p53 accumulates at mitochondria upon etoposide treatment and inhibition of p53 mitochondrial localization using pifithrin-µ inhibits apoptosis of COV434 cells. FGF1 also decreases mitochondrial accumulation of p53 induced by etoposide. This constitutes a novel mechanism of action for FGF1 to promote cell survival in response to chemotherapy.

FGF1 protects neuroblastoma SH-SY5Y cells from p53-dependent apoptosis through an intracrine pathway regulated by FGF1 phosphorylation

Neuroblastoma, a sympathetic nervous system tumor, accounts for 15% of cancer deaths in children. In contrast to most human tumors, p53 is rarely mutated in human primary neuroblastoma, suggesting impaired p53 activation in neuroblastoma. Various studies have shown correlations between fgf1 expression levels and both prognosis severity and tumor chemoresistance. As we previously showed that fibroblast growth factor 1 (FGF1) inhibited p53-dependent apoptosis in neuron-like PC12 cells, we initiated the study of the interaction between the FGF1 and p53 pathways in neuroblastoma. We focused on the activity of either extracellular FGF1 by adding recombinant rFGF1 in media, or of intracellular FGF1 by overexpression in human SH-SY5Y and mouse N2a neuroblastoma cell lines. In both cell lines, the genotoxic drug etoposide induced a classical mitochondrial p53-dependent apoptosis. FGF1 was able to inhibit p53-dependent apoptosis upstream of mitochondrial events in SH-SY5Y cells by both extracellular and intracellular pathways. Both rFGF1 addition and etoposide treatment increased fgf1 expression in SH-SY5Y cells. Conversely, rFGF1 or overexpressed FGF1 had no effect on p53-dependent apoptosis and fgf1 expression in neuroblastoma N2a cells. Using different FGF1 mutants (that is, FGF1^K132E, FGF1^S130A and FGF1^S130D), we further showed that the C-terminal domain and phosphorylation of FGF1 regulate its intracrine anti-apoptotic activity in neuroblastoma SH-SY5Y cells. This study provides the first evidence for a role of an intracrine growth factor pathway on p53-dependent apoptosis in neuroblastoma, and could lead to the identification of key regulators involved in neuroblastoma tumor progression and chemoresistance.

Trimodal rescue of hind limb ischemia with growth factors, cells, and nanocarriers: fundamentals to clinical trials

Peripheral artery disease is a severe medical condition commonly characterized by critical or acute limb ischemia. Gradual accumulation of thrombotic plaques in peripheral arteries of the lower limb may lead to intermittent claudication or ischemia in muscle tissue. Ischemic muscle tissue with lesions may become infected, resulting in a non-healing wound. Stable progression of the non-healing wound associated with severe ischemia might lead to functional deterioration of the limb, which, depending on the severity, can result in amputation. Immediate rescue of ischemic muscles through revascularization strategies is considered the gold standard to treat critical limb ischemia. Growth factors offer multiple levels of protection in revascularization of ischemic tissue. In this review, the basic mechanism through which growth factors exert their beneficial properties to rescue the ischemic limb is extensively discussed. Moreover, clinical trials based on growth factor and stem cell therapy to treat critical limb ischemia are considered. The clinical utility of stem cell therapy for the treatment of limb ischemia is explained and recent advances in nanocarrier technology for selective growth factor and stem cell supplementation are summarized.

Characterization of FN1-FGFR1 and novel FN1-FGF1 fusion genes in a large series of phosphaturic mesenchymal tumors

Phosphaturic mesenchymal tumors typically cause paraneoplastic osteomalacia, chiefly as a result of FGF23 secretion. In a prior study, we identified FN1-FGFR1 fusion in 9 of 15 phosphaturic mesenchymal tumors. In this study, a total of 66 phosphaturic mesenchymal tumors and 7 tumors resembling phosphaturic mesenchymal tumor but without known phosphaturia were studied. A novel FN1-FGF1 fusion gene was identified in two cases without FN1-FGFR1 fusion by RNA sequencing and cross-validated with direct sequencing and western blot. Fluorescence in situ hybridization analyses revealed FN1-FGFR1 fusion in 16 of 39 (41%) phosphaturic mesenchymal tumors and identified an additional case with FN1-FGF1 fusion. The two fusion genes were mutually exclusive. Combined with previous data, the overall prevalence of FN1-FGFR1 and FN1-FGF1 fusions was 42% (21/50) and 6% (3/50), respectively. FGFR1 immunohistochemistry was positive in 82% (45/55) of phosphaturic mesenchymal tumors regardless of fusion status. By contrast, 121 cases of potential morphologic mimics (belonging to 13 tumor types) rarely expressed FGFR1, the main exceptions being solitary fibrous tumors (positive in 40%), chondroblastomas (40%), and giant cell tumors of bone (38%), suggesting a possible role for FGFR1 immunohistochemistry in the diagnosis of phosphaturic mesenchymal tumor. With the exception of one case reported in our prior study, none of the remaining tumors resembling phosphaturic mesenchymal tumor had either fusion type or expressed significant FGFR1. Our findings provide insight into possible mechanisms underlying the pathogenesis of phosphaturic mesenchymal tumor and imply a central role of the FGF1-FGFR1 signaling pathway. The novel FN1-FGF1 protein is expected to be secreted and serves as a ligand that binds and activates FGFR1 to achieve an autocrine loop. Further study is required to determine the functions of these fusion proteins.

Cell surface localization of importin α1/KPNA2 affects cancer cell proliferation by regulating FGF1 signalling

Importin α1 is involved in nuclear import as a receptor for proteins with a classical nuclear localization signal (cNLS). Here, we report that importin α1 is localized to the cell surface in several cancer cell lines and detected in their cultured medium. We also found that exogenously added importin α1 is associated with the cell membrane via interaction with heparan sulfate. Furthermore, we revealed that the cell surface importin α1 recognizes cNLS-containing substrates. More particularly, importin α1 bound directly to FGF1 and FGF2, secreted cNLS-containing growth factors, and addition of exogenous importin α1 enhanced the activation of ERK1/2, downstream targets of FGF1 signalling, in FGF1-stimulated cancer cells. Additionally, anti-importin α1 antibody treatment suppressed the importin α1-FGF1 complex formation and ERK1/2 activation, resulting in decreased cell growth. This study provides novel evidence that functional importin α1 is located at the cell surface, where it accelerates the proliferation of cancer cells.

FGF1 C-terminal domain and phosphorylation regulate intracrine FGF1 signaling for its neurotrophic and anti-apoptotic activities

Fibroblast growth factor 1 (FGF1) is a prototypic member of the FGFs family overexpressed in various tumors. Contrarily to most FGFs, FGF1 lacks a secretion peptide signal and acts mainly in an intracellular and nuclear manner. Intracellular FGF1 induces cell proliferation, differentiation and survival. We previously showed that intracellular FGF1 induces neuronal differentiation and inhibits both p53- and serum-free-medium-induced apoptosis in PC12 cells. FGF1 nuclear localization is required for these intracellular activities, suggesting that FGF1 regulates p53-dependent apoptosis and neuronal differentiation by new nuclear pathways. To better characterize intracellular FGF1 pathways, we studied the effect of three mutations localized in the C-terminal domain of FGF1 (i.e., FGF1^K132E, FGF1^S130A and FGF1^S130D) on FGF1 neurotrophic and anti-apoptotic activities in PC12 cells. The change of the serine 130 to alanine precludes FGF1 phosphorylation, while its mutation to aspartic acid mimics phosphorylation. These FGF1 mutants kept both a nuclear and cytosolic localization in PC12 cells. Our study highlights for the first time the role of FGF1 phosphorylation and the implication of FGF1 C-terminal domain on its intracellular activities. Indeed, we show that the K132E mutation inhibits both the neurotrophic and anti-apoptotic activities of FGF1, suggesting a regulatory activity for FGF1 C terminus. Furthermore, we observed that both FGF1^S130A and FGF1^S130D mutant forms induced PC12 cells neuronal differentiation. Therefore, FGF1 phosphorylation does not regulate FGF1-induced differentiation of PC12 cells. Then, we showed that only FGF1^S130A protects PC12 cells against p53-dependent apoptosis, thus phosphorylation appears to inhibit FGF1 anti-apoptotic activity in PC12 cells. Altogether, our results show that phosphorylation does not regulate FGF1 neurotrophic activity but inhibits its anti-apoptotic activity after p53-dependent apoptosis induction, giving new insight into the poorly described FGF1 intracrine/nuclear pathway. The study of nuclear pathways could be crucial to identify key regulators involved in neuronal differentiation, tumor progression and resistances to radio- and chemo-therapy.

Mechanisms Regulating Protein Localization

Cellular functions are dictated by protein content and activity. There are numerous strategies to regulate proteins varying from modulating gene expression to post-translational modifications. One commonly used mode of regulation in eukaryotes is targeted localization. By specifically redirecting the localization of a pool of existing protein, cells can achieve rapid changes in local protein function. Eukaryotic cells have evolved elegant targeting pathways to direct proteins to the appropriate cellular location or locations. Here, we provide a general overview of these localization pathways, with a focus on nuclear and mitochondrial transport, and present a survey of the evolutionarily conserved regulatory strategies identified thus far. We end with a description of several specific examples of proteins that exploit localization as an important mode of regulation.

Fibroblast Growth Factor Signaling in Metabolic Regulation

The prevalence of obesity is a growing health problem. Obesity is strongly associated with several comorbidities, such as non-alcoholic fatty liver disease, certain cancers, insulin resistance, and type 2 diabetes, which all reduce life expectancy and life quality. Several drugs have been put forward in order to treat these diseases, but many of them have detrimental side effects. The unexpected role of the family of fibroblast growth factors in the regulation of energy metabolism provides new approaches to the treatment of metabolic diseases and offers a valuable tool to gain more insight into metabolic regulation. The known beneficial effects of FGF19 and FGF21 on metabolism, together with recently discovered similar effects of FGF1 suggest that FGFs and their derivatives carry great potential as novel therapeutics to treat metabolic conditions. To facilitate the development of new therapies with improved targeting and minimal side effects, a better understanding of the molecular mechanism of action of FGFs is needed. In this review, we will discuss what is currently known about the physiological roles of FGF signaling in tissues important for metabolic homeostasis. In addition, we will discuss current concepts regarding their pharmacological properties and effector tissues in the context of metabolic disease. Also, the recent progress in the development of FGF variants will be reviewed. Our goal is to provide a comprehensive overview of the current concepts and consensuses regarding FGF signaling in metabolic health and disease and to provide starting points for the development of FGF-based therapies against metabolic conditions.

A model to explain specific cellular communications and cellular harmony:- a hypothesis of coupled cells and interactive coupling molecules

BACKGROUND

The various cell types and their relative numbers in multicellular organisms are controlled by growth factors and related extracellular molecules which affect genetic expression pathways. However, these substances may have both/either inhibitory and/or stimulatory effects on cell division and cell differentiation depending on the cellular environment. It is not known how cells respond to these substances in such an ambiguous way. Many cellular effects have been investigated and reported using cell culture from cancer cell lines in an effort to define normal cellular behaviour using these abnormal cells.A model is offered to explain the harmony of cellular life in multicellular organisms involving interacting extracellular substances.

METHODS

A basic model was proposed based on asymmetric cell division and evidence to support the hypothetical model was accumulated from the literature. In particular, relevant evidence was selected for the Insulin-Like Growth Factor system from the published data, especially from certain cell lines, to support the model. The evidence has been selective in an attempt to provide a picture of normal cellular responses, derived from the cell lines.

RESULTS

The formation of a pair of coupled cells by asymmetric cell division is an integral part of the model as is the interaction of couplet molecules derived from these cells. Each couplet cell will have a receptor to measure the amount of the couplet molecule produced by the other cell; each cell will be receptor-positive or receptor-negative for the respective receptors. The couplet molecules will form a binary complex whose level is also measured by the cell. The hypothesis is heavily supported by selective collection of circumstantial evidence and by some direct evidence. The basic model can be expanded to other cellular interactions.

CONCLUSIONS

These couplet cells and interacting couplet molecules can be viewed as a mechanism that provides a controlled and balanced division-of-labour between the two progeny cells, and, in turn, their progeny. The presence or absence of a particular receptor for a couplet molecule will define a cell type and the presence or absence of many such receptors will define the cell types of the progeny within cell lineages.

Nucleolin regulates phosphorylation and nuclear export of fibroblast growth factor 1 (FGF1)

Extracellular fibroblast growth factor 1 (FGF1) acts through cell surface tyrosine kinase receptors, but FGF1 can also act directly in the cell nucleus, as a result of nuclear import of endogenously produced, non-secreted FGF1 or by transport of extracellular FGF1 via endosomes and cytosol into the nucleus. In the nucleus, FGF1 can be phosphorylated by protein kinase C δ (PKCδ), and this event induces nuclear export of FGF1. To identify intracellular targets of FGF1 we performed affinity pull-down assays and identified nucleolin, a nuclear multifunctional protein, as an interaction partner of FGF1. We confirmed a direct nucleolin-FGF1 interaction by surface plasmon resonance and identified residues of FGF1 involved in the binding to be located within the heparin binding site. To assess the biological role of the nucleolin-FGF1 interaction, we studied the intracellular trafficking of FGF1. In nucleolin depleted cells, exogenous FGF1 was endocytosed and translocated to the cytosol and nucleus, but FGF1 was not phosphorylated by PKCδ or exported from the nucleus. Using FGF1 mutants with reduced binding to nucleolin and a FGF1-phosphomimetic mutant, we showed that the nucleolin-FGF1 interaction is critical for the intranuclear phosphorylation of FGF1 by PKCδ and thereby the regulation of nuclear export of FGF1.

IFN signaling: how a non-canonical model led to the development of IFN mimetics

The classical model of cytokine signaling dominates our view of specific gene activation by cytokines such as the interferons (IFNs). The importance of the model extends beyond cytokines and applies to hormones such as growth hormone (GH) and insulin, and growth factors such as epidermal growth factor (EGF) and fibroblast growth factor (FGF). According to this model, ligand activates the cell via interaction with the extracellular domain of the receptor. This results in activation of receptor or receptor-associated tyrosine kinases, primarily of the Janus activated kinase (JAK) family, phosphorylation and dimerization of the signal transducer and activator of transcription (STAT) transcription factors, which dissociate from the receptor cytoplasmic domain and translocate to the nucleus. This view ascribes no further role to the ligand, JAK kinase, or receptor in either specific gene activation or the associated epigenetic events. The presence of dimeric STATs in the nucleus essentially explains it all. Our studies have resulted in the development of a non-canonical, more complex model of IFNγ signaling that is akin to that of steroid hormone (SH)/steroid receptor (SR) signaling. We have shown that ligand, receptor, activated JAKs, and STATs are associated with specific gene activation, where the receptor subunit IFNGR1 functions as a co-transcription factor and the JAKs are involved in associated epigenetic events. We found that the type I IFN system functions similarly. The fact that GH receptor, insulin receptor, EGF receptor, and FGF receptor undergo nuclear translocation upon ligand binding suggests that they may also function similarly. The SH/SR nature of type I and II IFN signaling provides insight into the specificity of signaling by members of cytokine families. The non-canonical model could also provide better understanding to more complex cytokine families such as those of IL-2 and IL-12, whose members often use the same JAKs and STATs, but also have different functions and properties.

IGFBP-2 nuclear translocation is mediated by a functional NLS sequence and is essential for its pro-tumorigenic actions in cancer cells

IGFBP-2 is highly expressed in both the serum and tumor tissues of most cancers, and is considered one of the most significant genes in the signature of major cancers. IGFBP-2 mainly modulates IGF actions in the pericellular space; however, there is considerable evidence to suggest that IGFBP-2 may also act independently of the IGFs. These IGF-independent actions of IGFBP-2 are exerted either via interactions at the cell surface or intracellularly, via interaction with cytoplasmic or nuclear-binding partners. The precise mechanism underlying the intracellular/intranuclear localization of IGFBP-2 remains unclear. In this study, we investigated IGFBP-2 nuclear localization in several common cancer cells with the aim of dissecting the mechanism of its nuclear trafficking. IGFBP-2 is detected in the nuclei of common cancer cells, including breast, prostate and several neuroblastoma cell lines, using cell fractionation and confocal microscopy. Via nuclear import assays, we show that nuclear entry of IGFBP-2 is mediated by the classical nuclear import mechanisms, primarily through importin-α, as demonstrated by the use of blocking, competition and co-immunoprecipitation assays. Bioinformatics analysis of the IGFBP-2 protein sequence with PSORT II identified a classical nuclear localization signal (cNLS) sequence at 179PKKLRPP185, within the IGFBP-2 linker domain, mutagenesis of which abolishes IGFBP-2 nuclear import. Accordingly, the NLSmutIGFBP-2 fails to activate the VEGF promoter, which would otherwise occur in the presence of wild-type IGFBP-2. As a consequence, no activation of angiogenic processes were observed in NLSmutIGFBP-2 expressing SHEP cells when implanted onto our in vivo quail chorio-allantoic membrane model. Taken together, these data show for the first time that IGFBP-2 possesses a functional NLS sequence and that IGFBP-2 actively translocates into the nucleus by a classical nuclear import mechanism, involving formation of IGFBP-2 complexes with importin-α. Nuclear IGFBP-2 is required for the activation of VEGF expression and consequent angiogenesis.

Steroid-like signalling by interferons: making sense of specific gene activation by cytokines

Many cytokines, hormones and growth factors use the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) pathway for cell signalling and specific gene activation. In the classical model, ligand is said to interact solely with the receptor extracellular domain, which triggers JAK activation of STATs at the receptor cytoplasmic domain. Activated STATs are then said to carry out nuclear events of specific gene activation. Given the limited number of STATs (seven) and the activation of the same STATs by cytokines with different functions, the mechanism of the specificity of their signalling is not obvious. Focusing on IFNγ (interferon γ), we have shown that ligand, receptor and activated JAKs are involved in nuclear events that are associated with specific gene activation, where the receptor subunit IFNGR1 (IFNγ receptor 1) functions as a transcription/co-transcription factor and the JAKs are involved in key epigenetic events. RTKs (receptor tyrosine kinases) such as EGFR [EGF (epidermal growth factor) receptor] and FGFR [FGF (fibroblast growth factor) receptor] also undergo nuclear translocation in association with their respective ligands. EGFR and FGFR, like IFNGR1, have been shown to function as transcription/co-transcription factors. The RTKs also regulate other kinases that have epigenetic effects. Our IFNγ model, as well as the RTKs EGFR and FGFR, have similarities to that of steroid receptor signalling. These systems consist of ligand-receptor-co-activator complexes at the genes that they activate. The co-activators consist of transcription factors and kinases, of which the latter play an important role in the associated epigenetics. It is our view that signalling by cytokines such as IFNγ is but a variation of specific gene activation by steroid hormones.

Nuclear translocation of FGF8 and its implication to induce Sprouty2

Fibroblast growth factor 8 (FGF8) functions as a local organizing signal for the tectum and cerebellum. FGF8 activates Ras-ERK signaling pathway to induce cerebellar development. We paid attention to the difference in the expression pattern of the molecules that are induced by FGF8 in the mid-hind brain region during normal development and after FGF8 misexpression; some are expressed in the area corresponding to the ERK activation domain but the others are expressed corresponding to the Fgf8 expression domain. Since some of the FGF family members are localized in the nucleus, we wondered if FGF8 could localize in the nuclei and function in the nucleus. We first show that in cultured NIH3T3 cells transfected FGF8b could localize in the nucleus. Transfected FGF8b could also localize in the nucleus of the cells in the chick neural tube. In mouse embryonic neural tube, we detected endogenous FGF8 in the nuclei. Implantation of an FGF8b-soaked bead showed that exogenous FGF8b could be translocated to the nuclei in the isthmus. Furthermore, signal-peptide-deletion mutant of FGF8b mainly localized in the nuclei, and induced Sprouty2 without activating ERK in the mesencephalon. Signal-peptide-deletion mutant of FGF8b could not induce Pax2 expression. Taken together, we concluded that FGF8b could be translocated to the nuclei, and that the nuclear FGF8 could function as transcriptional regulator to induce Sprouty2 in the isthmus.

Fibroblast growth factor-12 (FGF12) translocation into intestinal epithelial cells is dependent on a novel cell-penetrating peptide domain: involvement of internalization in the in vivo role of exogenous FGF12

The extracellular effect of fibroblast growth factor-12 (FGF12) remains unknown because FGF12 cannot activate any fibroblast growth factor receptors (FGFRs), and FGF12 is not currently thought to be released from cells. We reported previously that FGF12 plays an intracellular role in the inhibition of radiation-induced apoptosis. In this study, we demonstrated that recombinant FGF12 was able to be internalized into the cytoplasm of a rat intestinal epithelial cell line, IEC6, and this process was dependent on two novel cell-penetrating peptide (CPP) domains (CPP-M and CPP-C). In particular, CPP-C, composed of ∼10 amino acids, was identified as a specific domain of FGF12 and its subfamily in the C-terminal region (residues 140-149), although CPP-M was a common domain in the internal region of the FGF family. The absence of CPP-C from FGF12 or a mutation (E142L) in the CPP-C domain drastically reduced the internalization of FGF12 into cells. Therefore, CPP-C played an essential role in the internalization of FGF12. In addition, CPP-C was able to deliver other polypeptides into cells as a CPP because an FGF1/CPP-C chimeric protein was internalized into IEC6 cells more efficiently than wild-type FGF1. Finally, intraperitoneally added FGF12 inhibited radiation-induced apoptosis in the intestinal epithelial cells of BALB/c mice, and deletion of the CPP-C domain decreased the inhibition of the apoptosis. These findings suggest that exogenous FGF12 can play a role in tissues by translocating into cells through the plasma membrane, and the availability of this novel CPP provides a new tool for the intracellular delivery of bioactive molecules.

Molecular level interaction of the human acidic fibroblast growth factor with the antiangiogenic agent, inositol hexaphosphate

Acidic fibroblast growth factor (FGF1) regulates a wide array of important biological phenomena such as angiogenesis, cell differentiation, tumor growth, and neurogenesis. Generally, FGFs are known for their strong affinity for the glycosaminoglycan heparin, as a prerequisite for recognition of a specific tyrosine kinase on the cell surface and are responsible for the cell signal transduction cascade. Inositol hexaphosphate (IP6) is a natural antioxidant and is known for its antiangiogenic role, in addition to its ability to control tumor growth. In the present study, we investigated the interaction of IP6 with the acidic fibroblast growth factor (FGF1) using various biophysical techniques including isothermal calorimetry, circular dichroism, and multidimensional NMR spectroscopy. Herein, we have reported the three-dimensional solution structure of the FGF1-IP6 complex. These data show that IP6 binds FGF1 and enhances its thermal stability. In addition, we also demonstrate that IP6 acts as an antagonist to acidic fibroblast growth factor by inhibiting its receptor binding and subsequently decreasing the mitogenic activity. The inhibition likely results in the ability of IP6 to antagonize the angiogenic and mitogenic activity of FGF1.

Post treatment with an FGF chimeric growth factor enhances epithelial cell proliferation to improve recovery from radiation-induced intestinal damage

PURPOSE

A fibroblast growth factor (FGF) 1-FGF2 chimera (FGFC) was created previously and showed greater structural stability than FGF1. This chimera was capable of stimulating epithelial cell proliferation much more strongly than FGF1 or FGF2 even without heparin. Therefore FGFC was expected to have greater biologic activity in vivo. This study evaluated and compared the protective activity of FGFC and FGF1 against radiation-induced intestinal injuries.

METHODS AND MATERIALS

We administered FGFC and FGF1 intraperitoneally to BALB/c mice 24 h before or after total-body irradiation (TBI). The numbers of surviving crypts were determined 3.5 days after TBI with gamma rays at doses ranging from 8 to 12 Gy.

RESULTS

The effect of FGFC was equal to or slightly superior to FGF1 with heparin. However, FGFC was significantly more effective in promoting crypt survival than FGF1 (p < 0.01) when 10 μg of each FGF was administered without heparin before irradiation. In addition, FGFC was significantly more effective at promoting crypt survival (p < 0.05) than FGF1 even when administered without heparin at 24 h after TBI at 10, 11, or 12 Gy. We found that FGFC post treatment significantly promoted 5-bromo-2'-deoxyuridine incorporation into crypts and increased crypt depth, resulting in more epithelial differentiation. However, the number of apoptotic cells in FGFC-treated mice decreased to almost the same level as that in FGF1-treated mice.

CONCLUSIONS

These findings suggest that FGFC strongly enhanced radioprotection with the induction of epithelial proliferation without exogenous heparin after irradiation and is useful in clinical applications for both the prevention and post treatment of radiation injuries.

Expression and possible role of fibroblast growth factor family members in porcine antral follicles during final maturation

The aim of this study was to investigate the possible participation of fibroblast growth factor (FGF) family members (FGF1, FGF2 and FGF7 and their receptors) in porcine follicles (polyovulatory species) under special consideration for FGF2 during final growth. A classification of follicles was done by size and follicular fluid content of oestradiol-17β, progesterone and prostaglandin F2α. The mRNA expression of examined factors was analysed by real-time PCR. The hormone concentration was estimated by enzyme immunoassay, protein characterisation by western blotting and localisation by immunohistochemistry. Follicle tissue separated in theca interna and granulosa cells was extracted and tested for mRNA of FGF1, FGF2, FGF7 and receptors (FGFR1IIIc, FGFRIIIb and FGFR2IIIc). Additionally, the mRNA expression of FSHR, LHR and aromatase cytochrome P450 for further characterisation of follicles was analysed. Significantly, higher FGF2 protein levels were measured in stroma when compared with total follicle or corpus luteum tissue. This result was confirmed by western blot with two strong bands. Immunological localisation of FGF2 only in stroma (fibroblasts) confirms the protein measurements. The results show a clear difference for FGF2 protein expression during final growth of follicles if monovulatory (bovine) and polyovulatory (porcine) species are compared. FGF2 protein in porcine ovary may be (due to localisation and concentration in stroma) important for support of angiogenesis of more follicles (polyovulatory species) and not of a single follicle like in cows.

Cooperation of salivary protein histatin 3 with heat shock cognate protein 70 relative to the G1/S transition in human gingival fibroblasts

Histatins, a family of salivary proteins, have antimicrobial activity. Candida albicans, which is killed by histatins, induces oral candidiasis in individuals with compromised immune systems. Although the functional significance of histatins has been documented, their biological and physiological functions against host cells have not been clarified. In this study, we found that histatin 3, a member of the histatin family, binds to heat shock cognate protein 70 (HSC70). These proteins were co-localized in the cytoplasm and nucleus in human gingival fibroblasts following non-heat and heat shock. Histatin 3 induced stimulation of DNA synthesis and cell survival in human gingival fibroblasts in a dose-dependent manner. This DNA synthesis was found to be dependent on HSC70 by knockdown experiments. The effect of heat shock on DNA synthesis induced by histatin 3 was approximately 2-fold higher than that of non-heat shock. When the histatin 3 uptake into cells was inhibited by monodansylcadaverine or when histatin 3 binding to HSC70 was precluded by 15-deoxyspergualin, DNA synthesis by histatin 3 was approximately 2-fold less than that without monodansylcadaverine or 15-deoxyspergualin. Although HSC70 directly bound to p27(Kip1) (a cyclin-dependent kinase inhibitor), histatin 3 increased the binding between those proteins but not with a peptide capable of binding to HSC70. Moreover histatin 3 prevented ATP-dependent dissociation of HSC70-p27(Kip1). ATP was unable to form a histatin 3-HSC70(D10N)-p27(Kip1) complex (HSC70(D10N) is a mutant attenuating ATPase activity). These findings suggest that histatin 3 may be involved in cell proliferation through the regulation of HSC70 and p27(Kip1) in oral cells.

FGF-1 induces expression of LXRalpha and production of 25-hydroxycholesterol to upregulate the apoE gene in rat astrocytes

Fibroblast growth factor 1 (FGF-1) enhances apolipoprotein E (apoE) expression and apoE-HDL biogenesis in autocrine fashion in astrocytes (Ito, J., Y. Nagayasu, R. Lu, A. Kheirollah, M. Hayashi, and S. Yokoyama. Astrocytes produce and secrete FGF-1, which promotes the production of apoE-HDL in a manner of autocrine action. J. Lipid Res. 2005. 46: 679-686) associated with healing of brain injury (Tada,T., J-i. Ito, M. Asai, and S. Yokoyama. Fibroblast growth factor 1 is produced prior to apolipoprotein E in the astrocytes after cryo-injury of mouse brain. Neurochem. Int. 2004. 45: 23-30). FGF-1 stimulates mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK) to increase cholesterol biosynthesis and phosphatidylinositol 3-OH kinase (PI3K)/Akt to enhance apoE-HDL secretion (Ito, J., Y. Nagayasu, K. Okumura-Noji, R. Lu, T. Nishida, Y. Miura, K. Asai, A. Kheirollah, S. Nakaya, and S. Yokoyama. Mechanism for FGF-1 to regulate biogenesis of apoE-HDL in astrocytes. J. Lipid Res. 2007. 48: 2020-2027). We investigated the mechanism for FGF-1 to upregulate apoE transcription. FGF-1 increased apoE and liver X receptor alpha (LXRalpha) mRNAs in rat astrocytes. Increase of LXRalpha mRNA was suppressed by inhibition of the FGF-1 receptor-1 and MEK/ERK but not by inhibition of PI3K/Akt. The increases of apoE mRNA and apoE-HDL secretion were both inhibited by downregulation or inhibition of LXRalpha, while they were partially suppressed by inhibiting cholesterol biosynthesis. We identified the liver X receptor element responsible for activation of the rat apoE promoter by FGF-1 located between -450 and -320 bp, and the direct repeat 4 (DR4) element in this region (-448 to -433 bp) was responsible for the activation. Chromatin immunoprecipitation analysis supported that FGF-1 enhanced association of LXR with the rat apoE promoter. FGF-1 partially activated the apoE promoter even in the presence of an MEK inhibitor that inhibits the FGF-1-mediated enhancement of cholesterol biosynthesis. On the other hand, FGF-1 induced production of 25-hydroxycholesterol by MEK/ERK as an sterol regulatory element-dependent reaction besides cholesterol biosynthesis. We concluded that FGF-1-induced apoE expression in astrocytes depends on LXRalpha being mediated by both LXRalpha expression and an LXRalpha ligand biosynthesis.

Midkine translocated to nucleoli and involved in carcinogenesis

Midkine (MK) is a heparin-binding growth factor with its gene first identified in embryonal carcinoma cells at early stages of retinoic acid-induced differentiation. MK is frequently and highly expressed in a variety of human carcinomas. Furthermore, the blood MK level is frequently elevated with advance of human carcinomas, decreased after surgical removal of the tumors. Thus, it is expected to become a promising marker for evaluating the progress of carcinomas. There is mounting evidence that MK plays a significant role in carcinogenesis-related activities, such as proliferation, migration, anti-apoptosis, mitogenesis, transforming, and angiogenesis. In addition, siRNA and anti-sense oligonucleotides for MK have yielded great effects in anti-tumor activities. Therefore, MK appears to be a potential candidate molecular target of therapy for human carcinomas. In this paper, we review MK targeting at nucleoli in different tumor cells and its role in carcinogenesis to deepen our understanding of the mechanism of MK involved in carcinogenesis.

Effects of acidic fibroblast growth factor fragments on nocturnal feeding in rats by intracerebroventricular and hypodermic injection

AIM: To investigate the active region of aFGF responsible for food intake by calculating nocturnal food consumption to examine the efficacy of peripheral administration of the active fragments.

METHODS: For intracerebroventricular infusion, a guide cannula made of stainless steel tubing was fixed into the third cerebral ventricle one week before the experiments. Under no anesthesia seven synthesized aFGF fragments aFGF-(1-15), [D-Trp⁶]-aFGF-(1-15), [desaminoPhe1.D-Trp⁶]-aFGF-(1-15), [desaminoPhe1.Lys (ε-myristyl)¹⁶]-aFGF-(1-16), [Lys (ε-myristyl)¹⁶]-aFGF-(1-16), [D-Trp6.Lys (ε-myristyl)¹⁶]-aFGF-(1-16) and [Ala16] aFGF-(1-29) were injected into the third ventricle of rats during the period from 18:30 to 19:00. Powdered food in the animal food boxes were weighed at 19:00, 22:00, and 7:00 for calculating food consumption by rats in 3 hours and 12 hours. Then the two active aFGF fragments aFGF-(1-15) and [Ala¹⁶] aFGF-(1-29) were injected into the subcutaneous tissue of rats during the period from 18:30 to 19:00, to calculate nocturnal food consumption.

RESULTS: For intracerebroventricular infusion, aFGF-(1-15) (per rat 200 ng) had no effect on the feeding, while aFGF-(1-15) (per rat 400 ng) suppressed the food intake (3 h: 3.0 ± 0.2 vs 2.1 ± 0.2; 12 h: 18.5 ± 0.5 vs 16.1 ± 0.5, both P < 0.01). As for [Ala¹⁶] aFGF-(1-29), not only per rat 200 ng (3 h: 4.9 ± 0.2 vs 3.4 ± 0.2; 12 h: 19.3 ± 1.2 vs 17.3 ± 1.1, both P < 0.01) but also per rat 400 ng (3 h: 3.6 ± 0.1 vs 1.6 ± 0.2; 12 h: 19.9 ± 0.8 vs 16.4 ± 1.6, both P < 0.01) suppressed the food intake. Other five aFGF fragments had no effect on the feeding in the dose of per rat 200 ng and per rat 400 ng. For hypodermic injection, [Ala¹⁶] aFGF-(1-29) (300 mg/kg) suppressed the food intake (3 h: 3.9 ± 0.2 vs 2.1 ± 0.3; 12 h: 19.8 ± 0.5 vs 11.2 ± 0.8, both P < 0.01), while others had no effect.

CONCLUSION: These findings suggest the amino-terminal portion of aFGF is active in food intake suppression. The replacement of cysteine residue by alanine is important in some amino-terminal aFGF fragments. Other aFGF fragments, in which glycine at position 6 was replaced with D-tryptophane, phenylalanine at position 1 with desaminoPhe, and cysteine at position 16 with Lys (ε-myristyl) has no effect on nocturnal feeding in rats. Peripheral administration of one fragment is also effective on nocturnal feeding in rats.

Fibroblast growth factor receptor 1 is a key regulator of early adipogenic events in human preadipocytes

Cell number is an important determinant of adipose tissue mass, and the coordinated proliferation and differentiation of preadipocytes into mature lipid-laden adipocytes underpins the increased adipose tissue mass associated with obesity. Despite this, the molecular cues governing such adipose tissue expansion are poorly understood. We previously reported that fibroblast growth factor-1 (FGF-1) promotes both proliferation and differentiation of human preadipocytes and that the major adipogenic effect of FGF-1 occurs during proliferation, priming the cells for adipose conversion. In the current study, we examined whether this effect was linked to the mitogenic action of FGF-1 by investigating the mitogenic and adipogenic potential of other growth factors, platelet-derived growth factor (PDGF; AA and BB) and vascular endothelial growth factor. Although PDGF-AA and PDGF-BB showed comparable mitogenic potential to FGF-1, only FGF-1 treatment resulted in priming and subsequent differentiation. Pharmacological inhibition of FGF receptor (FGFR) tyrosine kinase activity, using the FGFR-specific inhibitors PD-173074 and SU-5402, revealed an obligate requirement for FGFR activity in these processes. A combination of biochemical and genetic approaches revealed an important role for FGFR1. Knock down of FGFR1 expression by small-interfering RNA reduced FGF-1-stimulated signaling events, proliferation, and priming. Together these data highlight the unique nature of the role of FGF-1 during the earliest stages of adipogenesis and establish a role for FGFR1 in human adipogenesis, identifying FGFR1 as a potential therapeutic target to reduce obesity.

Involvement of intracellular expression of FGF12 in radiation-induced apoptosis in mast cells

Several fibroblast growth factors (FGFs) are able to reduce and improve radiation-induced tissue damage through the activation of surface fibroblast growth factor receptors (FGFRs). In contrast, some FGFs lack classical signal sequences, which play roles in the release of FGFs, and the intracellular function of these FGFs is not well clarified. In this study, we evaluated the transcript levels of 22 FGFs in a human mast cell line, HMC-1, using quantitative RT-PCR and found that FGF2 and FGF12 were expressed in HMC-1 cells. FGF12 not only lacks classical signal sequences but also fails to activate FGFRs. HMC-1 cells were transfected with an expression vector of FGF12 to clarify the intracellular function of FGF12 after irradiation. The overexpression of FGF12 in HMC-1 cells decreased ionizing radiation-induced apoptosis, and siRNA-mediated repression of FGF12 expression augmented apoptosis in HMC-1 cells. The overexpression of FGF12 strongly suppressed the marked augmentation of apoptosis induced by inhibition of the MEK/ERK pathway with PD98059. In contrast, the mitogen-activated protein kinase (MAPK) scaffold protein islet brain 2 (IB2), which was reported to bind to FGF12, did not interfere with the anti-apoptotic effect of FGF12. The expression of FGF12 transcripts was also detected in murine cultured mast cells derived from bone marrow or fetal skin. These findings suggest that FGF12 intracellularly suppresses radiation-induced apoptosis in mast cells independently of IB2.

An FGF1:FGF2 chimeric growth factor exhibits universal FGF receptor specificity, enhanced stability and augmented activity useful for epithelial proliferation and radioprotection

Structural instability of wild-type fibroblast growth factor (FGF)-1 and its dependence on exogenous heparin for optimal activity diminishes its potential utility as a therapeutic agent. Here we evaluated FGFC, an FGF1:FGF2 chimeric protein, for its receptor affinity, absolute heparin-dependence, stability and potential clinical applicability. Using BaF3 transfectants overexpressing each FGF receptor (FGFR) subtype, we found that, like FGF1, FGFC activates all of the FGFR subtypes (i.e., FGFR1c, FGFR1b, FGFR2c, FGFR2b, FGFR3c, FGFR3b and FGFR4) in the presence of heparin. Moreover, FGFC activates FGFRs even in the absence of heparin. FGFC stimulated keratinocytes proliferation much more strongly than FGF2, as would be expected from its ability to activate FGFR2b. FGFC showed greater structural stability, biological activity and resistance to trypsinization, and less loss in solution than FGF1 or FGF2. When FGFC was intraperitoneally administered to BALB/c mice prior to whole body gamma-irradiation, survival of small intestine crypts was significantly enhanced, as compared to control mice. These results suggest that FGFC could be useful in a variety of clinical applications, including promotion of wound healing and protection against radiation-induced damage.

Phosphorylation of fibroblast growth factor (FGF) receptor 1 at Ser777 by p38 mitogen-activated protein kinase regulates translocation of exogenous FGF1 to the cytosol and nucleus

Exogenous fibroblast growth factor 1 (FGF1) signals through activation of transmembrane FGF receptors (FGFRs) but may also regulate cellular processes after translocation to the cytosol and nucleus of target cells. Translocation of FGF1 occurs across the limiting membrane of intracellular vesicles and is a regulated process that depends on the C-terminal tail of the FGFR. Here, we report that translocation of FGF1 requires activity of the alpha isoform of p38 mitogen-activated protein kinase (MAPK). FGF1 translocation was inhibited after chemical inhibition of p38 MAPK or after small interfering RNA knockdown of p38alpha. Translocation was increased after stimulation of p38 MAPK with anisomycin, mannitol, or H2O2. The activity level of p38 MAPK was not found to affect endocytosis or intracellular sorting of FGF1/FGFR1. Instead, we found that p38 MAPK regulates FGF1 translocation by phosphorylation of FGFR1 at Ser777. The FGFR1 mutation S777A abolished FGF1 translocation, while phospho-mimetic mutations of Ser777 to Asp or Glu allowed translocation to take place and bypassed the requirement for active p38 MAPK. Ser777 in FGFR1 was directly phosphorylated by p38alpha in a cell-free system. These data demonstrate a crucial role for p38alpha MAPK in the regulated translocation of exogenous FGF1 into the cytosol/nucleus, and they reveal a specific role for p38alpha MAPK-mediated serine phosphorylation of FGFR1.

Therapeutic angiogenesis in cardiovascular disease

Atherosclerotic disease of the arteries is a major cause of coronary artery disease, peripheral vascular disease and stroke. Some patients are however not candidate for the standard treatment of angioplasty or bypass surgery. Hence there is tremendous enthusiasm for the utilization of angiogenesis as a therapeutic modality for atherosclerotic arterial disease. This augmentation of physiological neo-vascularization in cardiovascular disease can be achieved through different pathways. In this article we are reviewing the Use of Gene therapy, Protein therapy and cellular therapy.

High-level expression and purification of Tat-haFGF19-154

Human acidic fibroblast growth factor (haFGF) stimulates repair and regeneration of central and peripheral nerves after various injuries. However, it is unable to cross the blood-brain barrier (BBB). To produce a therapeutic haFGF with cell-permeable activity, we fused the haFGF(19-154) gene with Tat-PTD. After its construction by a single-step insertion of a polymerase chain reaction (PCR)-amplified coding sequence, the vector pTat-haFGF(19-154)-His was expressed in Escherichia coli BL21 (DE3) cells. The optimal expression level of the soluble fusion protein was up to 36.7% of the total cellular protein. The recombinant Tat-haFGF(19-154)-His was purified by a combination of Ni-NTA affinity, Sephadex G-25, and heparin affinity chromatography to 95% as detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The final yield was 171 mg/l culture. Purified Tat-haFGF(19-154)-His had distinct mitogenic activity in Balb/c 3T3 cells, as measured by methylthiazoletetrazolium (MTT) assay and its ED(50) was 3.931 x 10(-4) micromol/l. Tat-haFGF(19-154)-His protein intravenously injected at the dose of 10 mg/kg could be detected in the pallium and hippocampi.

A nuclear export sequence located on a beta-strand in fibroblast growth factor-1

Receptor-bound and endocytosed fibroblast growth factor-1 (FGF-1) is able to cross the vesicle membrane and translocate to cytosol and nucleus. This suggests an intracellular role of FGF-1, which also signals by activating transmembrane FGF receptors. Phosphorylation of internalized FGF-1 by nuclear protein kinase C delta induces rapid export from the nuclei by a leptomycin B-sensitive pathway. In the present work, we have searched for and identified a Leu-rich nuclear export sequence (NES) at the C terminus of FGF-1 required for its nuclear export and able to confer nuclear export activity to a reporter protein in an in vivo system. Mutants where hydrophobic amino acids within the NES were exchanged for alanine exhibited reduced or abolished nuclear export. As demonstrated in co-immunoprecipitation experiments, a complex containing FGF-1, exportin-1, and its co-factor Ran-GTP, was formed in vitro. Formation of this complex in vivo was demonstrated by a peroxisomal targeting assay. Formation of the FGF-1-exportin-1-Ran-GTP complex in vitro as well as nuclear export of FGF-1 in vivo was dependent on phosphorylation of FGF-1, and it was abolished by leptomycin B. The FGF-1 NES was found to be situated along a beta-strand, which has not been reported before, since NESs usually are alpha-helical.

Fibroblast Growth Factor 1 inhibits p53-dependent apoptosis in PC12 cells

The survival activity of FGF1 and the pro-apoptotic activity of p53 were characterized in vitro and/or in vivo for different types of neurons after different stresses and in different neurodegenerative pathologies. To investigate whether or not FGF1 and p53 pathways interact in neuronal cells, we studied the effect of FGF1 on p53-dependent apoptosis in PC12 cells. We first characterized p53-dependent PC12 cell death induced by etoposide (a DNA damaging agent). We showed that etoposide increased p53 stabilization, phosphorylation (Ser-15), nuclear translocation and transcriptional activity. In particular, p53 promoted mdm2, p21, puma and noxa expression in PC12 cells. The activation of p53 initiated a classical mitochondrial apoptosis process associated with caspases activation and nuclear degradation. We demonstrated that FGF1 protected PC12 cells from p53-dependent apoptosis upstream from mitochondrial and nuclear events. FGF1 inhibited etoposide-induced p53 phosphorylation, stabilization, nuclear translocation and transcriptional activity. This study presents the first evidence that FGF1 and p53 pathways interact in neuronal cells, and that FGF1 protects neuronal cells from p53-dependent apoptosis, suggesting that alterations of FGF1/p53 crosstalk could be involved in a large range of neurons and in neurological disorders.

Dual localization: proteins in extracellular and intracellular compartments

The goal of this article is to provide a comprehensive catalog of those proteins documented to exhibit dual localization, being found in both the extracellular compartment (cell surface and extracellular medium) as well as the intracellular compartment (cytosol and nucleus). A large subset of these proteins that show dual localization is found both in the nucleus and outside of cells. Proteins destined to be secreted out of the cell or to be expressed at the cell surface usually enter the endomembrane pathway on the basis of a signal sequence that targets them into the endoplasmic reticulum. Proteins destined for import into the nucleus, on the other hand, usually carry a nuclear localization signal. We have organized our catalog in terms of the presence and absence of these trafficking signals: (a) proteins that contain a signal sequence but no nuclear localization signal; (b) proteins that contain both a signal sequence as well as a nuclear localization signal; (c) proteins that contain a nuclear localization signal but lack a signal sequence; and (d) proteins containing neither a signal sequence nor a nuclear localization signal. Novel insights regarding the activities of several classes of proteins exhibiting dual localization can be derived when one targeting signal is experimentally abrogated. For example, the mitogenic activity of both fibroblasts growth factor-1 and schwannoma-derived growth factor clearly requires nuclear localization, independent of the activation of the receptor tyrosine kinase signaling pathway. In addition, there is a growing list of integral membrane receptors that undergo translocation to the nucleus, with bona fide nuclear localization signals and transcription activation activity. The information provided in this descriptive catalog will, hopefully, stimulate investigations into the pathways and mechanisms of transport between these compartments and the physiological significance of dual localization.

fgf1 is required for normal differentiation of erythrocytes in zebrafish primitive hematopoiesis

Hematopoiesis in vertebrate development involves an embryonic, primitive wave and a later, definitive wave in which embryonic blood cells are replaced with adult blood cells. We here show that zebrafish fgf1 is involved in vivo in primitive hematopoiesis. Fibroblast growth factor-1 (FGF1) morpholino knockdown leads to abnormal accumulation of blood cells in the posterior intermediate cell mass at 32 hr postfertilization. Expression of the erythroid markers gata1 and ika, normally diminishing in differentiating erythrocytes at this stage, is maintained at abnormally high levels in primitive blood cells. The onset of erythrocyte differentiation as assessed by o-dianisidine staining is severely delayed. Most fgf1 morphants later recover to wild-type appearance, and primitive erythrocytes eventually differentiate. Zebrafish fgf1 is syntenic to human FGF1, which maps to a critically deleted region in human del(5q) syndrome posing an increased risk of leukemia to patients. As its knockdown in zebrafish changes expression of gata1, a gene involved in hematopoietic stem cell decisions, FGF1 should be considered to play a role in the pathogenesis of del(5q) syndrome.