Transport of exogenous growth factors and cytokines to the cytosol and to the nucleus

Intracellular FGF1 protects cells from apoptosis through direct interaction with p53

Fibroblast growth factor 1 (FGF1) acts by activating specific tyrosine kinase receptors on the cell surface. In addition to this classical mode of action, FGF1 also exhibits intracellular activity. Recently, we found that FGF1 translocated into the cell interior exhibits anti-apoptotic activity independent of receptor activation and downstream signaling. Here, we show that expression of FGF1 increases the survival of cells treated with various apoptosis inducers, but only when wild-type p53 is present. The p53-negative cells were not protected by either ectopically expressed or translocated FGF1. We also confirmed the requirement of p53 for the anti-apoptotic intracellular activity of FGF1 by silencing p53, resulting in loss of the protective effect of FGF1. In contrast, in p53-negative cells, intracellular FGF1 regained its anti-apoptotic properties after transfection with wild-type p53. We also found that FGF1 directly interacts with p53 in cells and that the binding region is located in the DBD domain of p53. We therefore postulate that intracellular FGF1 protects cells from apoptosis by directly interacting with p53.

Exploring the Structural and Functional Diversity among FGF Signals: A Comparative Study of Human, Mouse, and Xenopus FGF Ligands in Embryonic Development and Cancer Pathogenesis

Fibroblast growth factors (FGFs) encode a large family of growth factor proteins that activate several intracellular signaling pathways to control diverse physiological functions. The human genome encodes 22 FGFs that share a high sequence and structural homology with those of other vertebrates. FGFs orchestrate diverse biological functions by regulating cellular differentiation, proliferation, and migration. Dysregulated FGF signaling may contribute to several pathological conditions, including cancer. Notably, FGFs exhibit wide functional diversity among different vertebrates spatiotemporally. A comparative study of FGF receptor ligands and their diverse roles in vertebrates ranging from embryonic development to pathological conditions may expand our understanding of FGF. Moreover, targeting diverse FGF signals requires knowledge regarding their structural and functional heterogeneity among vertebrates. This study summarizes the current understanding of human FGF signals and correlates them with those in mouse and Xenopus models, thereby facilitating the identification of therapeutic targets for various human disorders.

Secreted EMC10 is upregulated in human obesity and its neutralizing antibody prevents diet-induced obesity in mice

Secreted isoform of endoplasmic reticulum membrane complex subunit 10 (scEMC10) is a poorly characterized secreted protein of largely unknown physiological function. Here we demonstrate that scEMC10 is upregulated in people with obesity and is positively associated with insulin resistance. Consistent with a causal role for scEMC10 in obesity, Emc10-/- mice are resistant to diet-induced obesity due to an increase in energy expenditure, while scEMC10 overexpression decreases energy expenditure, thus promoting obesity in mouse. Furthermore, neutralization of circulating scEMC10 using a monoclonal antibody reduces body weight and enhances insulin sensitivity in obese mice. Mechanistically, we provide evidence that scEMC10 can be transported into cells where it binds to the catalytic subunit of PKA and inhibits its stimulatory action on CREB while ablation of EMC10 promotes thermogenesis in adipocytes via activation of the PKA signalling pathway and its downstream targets. Taken together, our data identify scEMC10 as a circulating inhibitor of thermogenesis and a potential therapeutic target for obesity and its cardiometabolic complications.

The Role of PDE11A4 in Social Isolation-Induced Changes in Intracellular Signaling and Neuroinflammation

Phosphodiesterase 11A (PDE11A), an enzyme that degrades cyclic nucleotides (cAMP and cGMP), is the only PDE whose mRNA expression in brain is restricted to the hippocampal formation. Previously, we showed that chronic social isolation changes subsequent social behaviors in adult mice by reducing expression of PDE11A4 in the membrane fraction of the ventral hippocampus (VHIPP). Here we seek extend these findings by determining 1) if isolation-induced decreases in PDE11A4 require chronic social isolation or if they occur acutely and are sustained long-term, 2) if isolation-induced decreases occur uniquely in adults (i.e., not adolescents), and 3) how the loss of PDE11 signaling may increase neuroinflammation. Both acute and chronic social isolation decrease PDE11A4 expression in adult but not adolescent mice. This decrease in PDE11A4 is specific to the membrane compartment of the VHIPP, as it occurs neither in the soluble nor nuclear fractions of the VHIPP nor in any compartment of the dorsal HIPP. The effect of social isolation on membrane PDE11A4 is also selective in that PDE2A and PDE10A expression remain unchanged. Isolation-induced decreases in PDE11A4 expression appear to be functional as social isolation elicited changes in PDE11A-relevant signal transduction cascades (i.e., decreased pCamKIIα and pS6-235/236) and behavior (i.e., increased remote long-term memory for social odor recognition). Interestingly, we found that isolation-induced decreases in membrane PDE11A4 correlated with increased expression of interleukin-6 (IL-6) in the soluble fraction, suggesting pro-inflammatory signaling for this cytokine. This effect on IL-6 is consistent with the fact that PDE11A deletion increased microglia activation, although it left astrocytes unchanged. Together, these data suggest that isolation-induced decreases in PDE11A4 may alter subsequent social behavior via increased neuroinflammatory processes in adult mice.

Impact of FGF1 on human periodontal ligament fibroblast growth, osteogenic differentiation and inflammatory reaction in vitro

PURPOSE

To investigate in vitro the impact of fibroblast growth factor 1 (FGF1) in comparison to ascorbic acid (AscA) on human periodontal ligament fibroblast (HPdLF) growth, their osteogenic differentiation, and modulation of their inflammatory reaction to mechanical stress.

METHODS

The influence of different concentrations of FGF1 (12.5-200 ng/mL) on growth and proliferation of HPdLF cells was analyzed over 20 days by counting cell numbers and the percentage of Ki67-positive cells. Quantitative expression analysis of genes encoding the osteogenic markers alkaline phosphatase (ALPL), Runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), and osteopontin (OSP), as well as the fibroblast markers vimentin (VIM) and fibroblast-specific protein 1 (FSP1), was performed after 2 and 20 days of cultivation. Metabolic activity was determined by MTT assay. For comparison with AscA, 50 ng/mL FGF1 was used for stimulation for 2 and 20 days. Cell number, percentage of Ki67-positive cells, and expression of osteoblast- and fibroblast-specific genes were examined. Alkaline phosphatase activity was visualized by NBT/BCIP and calcium deposits were stained with alizarin red. Cytokine (IL‑6, IL‑8, COX2/PGE2) expression and secretion were analyzed by qPCR and ELISA in 6 h mechanically compressed HPdLF cultured for 2 days with FGF1 or ascorbic acid.

RESULTS

Higher concentrations of FGF1 promoted cell proliferation upon short-term stimulation, whereas prolonged treatment induced the expression of osteogenic markers even with low concentrations. AscA promotes cell growth more markedly than FGF1 in short-term cultures, whereas FGF1 induced osteogenic cell fate more strongly in long-term culture. Both factors induced an increased inflammatory response of HPdLF to mechanical compression.

CONCLUSION

Our data suggest that FGF1 promotes an osteogenic phenotype of HPdLF and limits inflammatory response to mechanical forces compared to AscA.

Aging triggers an upregulation of a multitude of cytokines in the male and especially the female rodent hippocampus but more discrete changes in other brain regions

BACKGROUND

Despite widespread acceptance that neuroinflammation contributes to age-related cognitive decline, studies comparing protein expression of cytokines in the young versus old brains are surprisingly limited in terms of the number of cytokines and brain regions studied. Complicating matters, discrepancies abound-particularly for interleukin 6 (IL-6)-possibly due to differences in sex, species/strain, and/or the brain regions studied.

METHODS

As such, we clarified how cytokine expression changes with age by using a Bioplex and Western blot to measure multiple cytokines across several brain regions of both sexes, using 2 mouse strains bred in-house as well as rats obtained from NIA. Parametric and nonparametric statistical tests were used as appropriate.

RESULTS

In the ventral hippocampus of C57BL/6J mice, we found age-related increases in IL-1α, IL-1β, IL-2, IL-3, IL-4, IL-6, IL-9, IL-10, IL-12p40, IL-12p70, IL-13, IL-17, eotaxin, G-CSF, interfeuron δ, KC, MIP-1a, MIP-1b, rantes, and TNFα that are generally more pronounced in females, but no age-related change in IL-5, MCP-1, or GM-CSF. We also find aging is uniquely associated with the emergence of a module (a.k.a. network) of 11 strongly intercorrelated cytokines, as well as an age-related shift from glycosylated to unglycosylated isoforms of IL-10 and IL-1β in the ventral hippocampus. Interestingly, age-related increases in extra-hippocampal cytokine expression are more discreet, with the prefrontal cortex, striatum, and cerebellum of male and female C57BL/6J mice demonstrating robust age-related increase in IL-6 expression but not IL-1β. Importantly, we found this widespread age-related increase in IL-6 also occurs in BALB/cJ mice and Brown Norway rats, demonstrating conservation across species and rearing environments.

CONCLUSIONS

Thus, age-related increases in cytokines are more pronounced in the hippocampus compared to other brain regions and can be more pronounced in females versus males depending on the brain region, genetic background, and cytokine examined.

Insights Into the Mechanisms of Brain Endothelial Erythrophagocytosis

The endothelial cells which form the inner cellular lining of the vasculature can act as non-professional phagocytes to ingest and remove emboli and aged/injured red blood cells (RBCs) from circulation. We previously demonstrated an erythrophagocytic phenotype of the brain endothelium for oxidatively stressed RBCs with subsequent migration of iron-rich RBCs and RBC degradation products across the brain endothelium in vivo and in vitro, in the absence of brain endothelium disruption. However, the mechanisms contributing to brain endothelial erythrophagocytosis are not well defined, and herein we elucidate the cellular mechanisms underlying brain endothelial erythrophagocytosis. Murine brain microvascular endothelial cells (bEnd.3 cells) were incubated with tert-butyl hydroperoxide (tBHP, oxidative stressor to induce RBC aging in vitro)- or PBS (control)-treated mouse RBCs. tBHP increased the reactive oxygen species (ROS) formation and phosphatidylserine exposure in RBCs, which were associated with robust brain endothelial erythrophagocytosis. TNFα treatment potentiated the brain endothelial erythrophagocytosis of tBHP-RBCs in vitro. Brain endothelial erythrophagocytosis was significantly reduced by RBC phosphatidylserine cloaking with annexin-V and with RBC-ROS and phosphatidylserine reduction with vitamin C. Brain endothelial erythrophagocytosis did not alter the bEnd.3 viability, and tBHP-RBCs were localized with early and late endosomes. Brain endothelial erythrophagocytosis increased the bEnd.3 total iron pool, abluminal iron levels without causing brain endothelial monolayer disruption, and ferroportin levels. In vivo, intravenous tBHP-RBC injection in aged (17–18 months old) male C57BL/6 mice significantly increased the Prussian blue-positive iron-rich lesion load compared with PBS-RBC-injected mice. In conclusion, RBC phosphatidylserine exposure and ROS are key mediators of brain endothelial erythrophagocytosis, a process which is associated with increased abluminal iron in vitro. tBHP-RBCs result in Prussian blue-positive iron-rich lesions in vivo. Brain endothelial erythrophagocytosis may provide a new route for RBC/RBC degradation product entry into the brain to produce iron-rich cerebral microhemorrhage-like lesions.

Fibroblast growth factor and kidney disease: Updates for emerging novel therapeutics

The discovery of fibroblast growth factors (FGFs) and fibroblast growth factor receptors (FGFRs) provided a profound new insight into physiological and metabolic functions. FGF has a large family by having divergent structural elements and enable functional divergence and specification. FGF and FGFRs are highly expressed during kidney development. Signals from the ureteric bud regulate morphogenesis, nephrogenesis, and nephron progenitor survival. Thus, FGF signaling plays an important role in kidney progenitor cell aggregation at the sites of new nephron formation. This review will summarize the current knowledge about functions of FGF signaling in kidney development and their ability to promote regeneration in injured kidneys and its use as a biomarker and therapeutic target in kidney diseases. Further studies are essential to determine the predictive significance of the various FGF/FGFR deviations and to integrate them into clinical algorithms.

Negative Regulation of FGFR (Fibroblast Growth Factor Receptor) Signaling

FGFR (fibroblast growth factor receptor) signaling controls fundamental processes in embryonic, fetal and adult human life. The magnitude, duration, and location of FGFR signaling must be strictly controlled in order to induce the correct biological response. Uncontrolled receptor signaling has been shown to lead to a variety of diseases, such as skeletal disorders and cancer. Here we review the numerous cellular mechanisms that regulate and turn off FGFR signaling, once the receptor is activated. These mechanisms include endocytosis and endocytic sorting, phosphatase activity, negative regulatory proteins and negative feedback phosphorylation events. The mechanisms act together simultaneously or sequentially, controlling the same or different steps in FGFR signaling. Although more work is needed to fully understand the regulation of FGFR signaling, it is clear that the cells in our body have evolved an extensive repertoire of mechanisms that together keep FGFR signaling tightly controlled and prevent excess FGFR signaling.

FHA domain of AGGF1 is essential for its nucleocytoplasmic transport and angiogenesis

Angiogenic factor with G-patch and FHA domains 1 (AGGF1) exhibits a dynamic distribution from the nucleus to the cytoplasm in endothelial cells during angiogenesis, but the biological significance and underlying mechanism of this nucleocytoplasmic transport remains unknown. Here, we demonstrate that the dynamic distribution is essential for AGGF1 to execute its angiogenic function. To search the structural bases for this nucleocytoplasmic transport, we characterized three potential nuclear localization regions, one potential nuclear export region, forkhead-associated (FHA), and G-patch domains to determine their effects on nucleocytoplasmic transport and angiogenesis, and we show that AGGF1 remains intact during the dynamic subcellular distribution and the region from 260 to 288 amino acids acts as a signal for its nuclear localization. The distribution of AGGF1 in cytoplasm needs both FHA domain and 14-3-3α/β. Binding of AGGF1 via FHA domain to 14-3-3α/β is required to complete the transport. Thus, we for the first time established structural bases for the nucleocytoplasmic transport of AGGF1 and revealed that the FHA domain of AGGF1 is essential for its nucleocytoplasmic transport and angiogenesis.

Involvement of Syndecan-1 and Heparanase in Cancer and Inflammation

The cell surface heparan sulfate proteoglycan Syndecan-1 acts as an important co-receptor for receptor tyrosine kinases and chemokine receptors, and as an adhesion receptor for structural glycoproteins of the extracellular matrix. It serves as a substrate for heparanase, an endo-β-glucuronidase that degrades specific domains of heparan sulfate carbohydrate chains and thereby alters the functional status of the proteoglycan and of Syndecan-1-bound ligands. Syndecan-1 and heparanase show multiple levels of functional interactions, resulting in mutual regulation of their expression, processing, and activity. These interactions are of particular relevance in the context of inflammation and malignant disease. Studies in animal models have revealed a mechanistic role of Syndecan-1 and heparanase in the regulation of contact allergies, kidney inflammation, multiple sclerosis, inflammatory bowel disease, and inflammation-associated tumorigenesis. Moreover, functional interactions between Syndecan-1 and heparanase modulate virtually all steps of tumor progression as defined in the Hallmarks of Cancer. Due to their prognostic value in cancer, and their mechanistic involvement in tumor progression, Syndecan-1 and heparanase have emerged as important drug targets. Data in preclinical models and preclinical phase I/II studies have already yielded promising results that provide a translational perspective.

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.

FHF1 is a bona fide fibroblast growth factor that activates cellular signaling in FGFR-dependent manner

Abstract

Fibroblast growth factors (FGFs) via their receptors (FGFRs) transduce signals from the extracellular space to the cell interior, modulating pivotal cellular processes such as cell proliferation, motility, metabolism and death. FGF superfamily includes a group of fibroblast growth factor homologous factors (FHFs), proteins whose function is still largely unknown. Since FHFs lack the signal sequence for secretion and are unable to induce FGFR-dependent cell proliferation, these proteins were considered as intracellular proteins that are not involved in signal transduction via FGFRs. Here we demonstrate for the first time that FHF1 directly interacts with all four major FGFRs. FHF1 binding causes efficient FGFR activation and initiation of receptor-dependent signaling cascades. However, the biological effect of FHF1 differs from the one elicited by canonical FGFs, as extracellular FHF1 protects cells from apoptosis, but is unable to stimulate cell division. Our data define FHF1 as a FGFR ligand, emphasizing much greater similarity between FHFs and canonical FGFs than previously indicated.

Noncanonical IFN Signaling, Steroids, and STATs: A Probable Role of V-ATPase

A small group of only seven transcription factors known as STATs (signal transducer and activator of transcription) are considered to be canonical determinants of specific gene activation for a plethora of ligand/receptor systems. The activation of STATs involves a family of four tyrosine kinases called JAK kinases. JAK1 and JAK2 activate STAT1 in the cytoplasm at the heterodimeric gamma interferon (IFNγ) receptor, while JAK1 and TYK2 activate STAT1 and STAT2 at the type I IFN heterodimeric receptor. The same STATs and JAKs are also involved in signaling by functionally different cytokines, growth factors, and hormones. Related to this, IFNγ-activated STAT1 binds to the IFNγ-activated sequence (GAS) element, but so do other STATs that are not involved in IFNγ signaling. Activated JAKs such as JAK2 and TYK2 are also involved in the epigenetics of nucleosome unwrapping for exposure of DNA to transcription. Furthermore, activated JAKs and STATs appear to function coordinately for specific gene activation. These complex events have not been addressed in canonical STAT signaling. Additionally, the function of noncoding enhancer RNAs, including their role in enhancer/promoter interaction is not addressed in the canonical STAT signaling model. In this perspective, we show that JAK/STAT signaling, involving membrane receptors, is essentially a variation of cytoplasmic nuclear receptor signaling. Focusing on IFN signaling, we showed that ligand, IFN receptor, the JAKs, and the STATs all undergo endocytosis and ATP-dependent nuclear translocation to promoters of genes specifically activated by IFNs. We argue here that the vacuolar ATPase (V-ATPase) proton pump probably plays a key role in endosomal membrane crossing by IFNs for receptor cytoplasmic binding. Signaling of nuclear receptors such as those of estrogen and dihydrotestosterone provides templates for making sense of the specificity of gene activation by closely related cytokines, which has implications for lymphocyte phenotypes.

Importin α: functions as a nuclear transport factor and beyond

Nucleocytoplasmic transport is an essential process in eukaryotes. The molecular mechanisms underlying nuclear transport that involve the nuclear transport receptor, small GTPase Ran, and the nuclear pore complex are highly conserved from yeast to humans. On the other hand, it has become clear that the nuclear transport system diverged during evolution to achieve various physiological functions in multicellular eukaryotes. In this review, we first summarize the molecular mechanisms of nuclear transport and how these were elucidated. Then, we focus on the diverse functions of importin α, which acts not merely an import factor but also as a multi-functional protein contributing to a variety of cellular functions in higher eukaryotes.

Distinctive actions of connexin 46 and connexin 50 in anterior pituitary folliculostellate cells

Folliculostellate cell gap junctions establish a network for the transmission of information within the anterior pituitary. Connexins make up gap junction channels. Changes in connexin (Cx) turnover modify gap junction-mediated intercellular communication. We have reported that cytokines and hormones influence Cx43 turnover and coupling in folliculostellate cells and in the folliculostellate cell line TtT/GF. In addition, the expression of different connexins alters intercellular communication and connexins may have functions besides cell coupling. Here we assessed the expression, turnover and subcellular localization of Cx46 and Cx50 in the anterior pituitary and TtT/GF cells. Then, we assessed the impact of various natural (lactation, annual reproductive cycle, bFGF) and pathological (autoimmune orchitis, diabetes/obesity) conditions associated with altered anterior pituitary hormone secretion on Cx46 and Cx50. Anterior pituitary Cx46 and Cx50 expression and subcellular distribution were cell-dependent. Cx46 was expressed by folliculostellate, TtT/GF and endocrine cells. In the cytoplasm, Cx46 was chiefly associated with lysosomes. Variously sized Cx46 molecules were recovered exclusively in the TtT/GF cell nuclear fraction. In the nucleus, Cx46 co-localized with Nopp-140, a nucleolar factor involved in rRNA processing. Neither cytoplasmic nor nuclear Cx46 and Cx43 co-localized. Cx50 localized to folliculostellate and TtT/GF cells, and to the walls of blood capillaries, not to endocrine cells. Cx50 was cytoplasmic and associated with the cell membrane, not nuclear. Cx50 did not co-localize with Cx46 but it co-localized in the cytoplasm and co-immunoprecipitated with Cx43. Cx46 and Cx50 responses to various physiological and pathological challenges were different, often opposite. Cx46 and Cx43 expression and phosphorylation profiles differed in the anterior pituitary, whereas Cx50 and Cx43 were similar. The data suggest that Cx46 participates to cellular growth and proliferation and that Cx50, together with Cx43, contributes to folliculostellate cell coupling.

Cytotoxic Conjugates of Fibroblast Growth Factor 2 (FGF2) with Monomethyl Auristatin E for Effective Killing of Cells Expressing FGF Receptors

Antibody-drug conjugates (ADCs) are a new class of anticancer therapeutics that combine the selectivity of targeted treatment, ensured by monoclonal antibodies, with the potency of the cytotoxic agent. Here, we applied an analogous approach, but instead of an antibody, we used fibroblast growth factor 2 (FGF2). FGF2 is a natural ligand of fibroblast growth factor receptor 1 (FGFR1), a cell-surface receptor reported to be overexpressed in several types of tumors. We developed and characterized FGF2 conjugates containing a defined number of molecules of highly cytotoxic drug monomethyl auristatin E (MMAE). These conjugates effectively targeted FGFR1-expressing cells, were internalized upon FGFR1-mediated endocytosis, and, in consequence, revealed high cytotoxicity, which was clearly related to the FGFR1 expression level. Among the conjugates tested, the most potent was that bearing three MMAE molecules, showing that the cytotoxicity of protein-drug conjugates in vitro is directly dependent on drug loading.

Noncanonical IFN Signaling: Mechanistic Linkage of Genetic and Epigenetic Events

The canonical model of cytokine signaling via the JAK/STAT pathway dominates our view of signal transduction but provides no insight into the significance of the simultaneous presence of activated JAKs and STATs in the nucleus of cells treated with cytokines. Such a mechanistic shortcoming challenges the usefulness of the model in its present form. Focusing on the interferon (IFN) cytokines, we have developed a noncanonical model of IFN signaling that naturally connects activated JAKs and STATs at or near response elements of genes that are activated by the IFNs. Specifically, cells treated with IFNγ showed association of activated STAT1α and JAK2 at the GAS element of genes activated by IFNγ. For IFNα treated cells, the association involved activated STAT1α and TYK2 JAK kinase at the ISRE promoter. The power of the noncanonical model is that it provides mechanistic insight into specific gene activation at the level of the associated epigenetics, akin to that of steroid/steroid receptor signaling.

An S116R Phosphorylation Site Mutation in Human Fibroblast Growth Factor-1 Differentially Affects Mitogenic and Glucose-Lowering Activities

Fibroblast growth factor-1 (FGF-1), a potent human mitogen and insulin sensitizer, signals through both tyrosine kinase receptor-mediated autocrine/paracrine pathways as well as a nuclear intracrine pathway. Phosphorylation of FGF-1 at serine 116 (S116) has been proposed to regulate intracrine signaling. Position S116 is located within a ∼17 amino acid C-terminal loop that contains a rich set of functional determinants including heparin∖heparan sulfate affinity, thiol reactivity, nuclear localization, pharmacokinetics, functional half-life, nuclear ligand affinity, stability, and structural dynamics. Mutational targeting of specific functionality in this region without perturbing other functional determinants is a design challenge. S116R is a non-phosphorylatable variant present in bovine FGF-1 and other members of the human FGF family. We show that the S116R mutation in human FGF-1 is accommodated with no perturbation of biophysical or structural properties, and is therefore an attractive mutation with which to elucidate the functional role of phosphorylation. Characterization of S116R shows reduction in NIH 3T3 fibroblast mitogenic stimulation, increase in fibroblast growth factor receptor-1c activation, and prolonged duration of glucose lowering in ob/ob hyperglycemic mice. A novel FGF-1/fibroblast growth factor receptor-1c dimerization interaction combined with non-phosphorylatable intracrine signaling is hypothesized to be responsible for these observed functional effects.

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.

Carcinogenic Parasite Secretes Growth Factor That Accelerates Wound Healing and Potentially Promotes Neoplasia

Infection with the human liver fluke Opisthorchis viverrini induces cancer of the bile ducts, cholangiocarcinoma (CCA). Injury from feeding activities of this parasite within the human biliary tree causes extensive lesions, wounds that undergo protracted cycles of healing, and re-injury over years of chronic infection. We show that O. viverrini secreted proteins accelerated wound resolution in human cholangiocytes, an outcome that was compromised following silencing of expression of the fluke-derived gene encoding the granulin-like growth factor, Ov-GRN-1. Recombinant Ov-GRN-1 induced angiogenesis and accelerated mouse wound healing. Ov-GRN-1 was internalized by human cholangiocytes and induced gene and protein expression changes associated with wound healing and cancer pathways. Given the notable but seemingly paradoxical properties of liver fluke granulin in promoting not only wound healing but also a carcinogenic microenvironment, Ov-GRN-1 likely holds marked potential as a therapeutic wound-healing agent and as a vaccine against an infection-induced cancer of major public health significance in the developing world.

Nuclear envelope-associated endosomes deliver surface proteins to the nucleus

Endocytosis directs molecular cargo along three main routes: recycling to the cell surface, transport to the Golgi apparatus or degradation in endolysosomes. Pseudomonas exotoxin A (PE) is a bacterial protein that typically traffics to the Golgi and then the endoplasmic reticulum before translocating to the cytosol. Here we show that a substantial fraction of internalized PE is also located in nuclear envelope-associated endosomes (NAE), which display limited mobility, exhibit a propensity to undergo fusion and readily discharge their contents into the nuclear envelope. Electron microscopy and protein trapping in the nucleus indicate that NAE mediate PE transfer into the nucleoplasm. RNAi screening further revealed that NAE-mediated transfer depends on the nuclear envelope proteins SUN1 and SUN2, as well as the Sec61 translocon complex. These data reveal a novel endosomal route from the cell surface to the nucleoplasm that facilitates the accumulation of extracellular and cell surface proteins in the nucleus.

The Fibroblast Growth Factor signaling pathway

The signaling component of the mammalian Fibroblast Growth Factor (FGF) family is comprised of eighteen secreted proteins that interact with four signaling tyrosine kinase FGF receptors (FGFRs). Interaction of FGF ligands with their signaling receptors is regulated by protein or proteoglycan cofactors and by extracellular binding proteins. Activated FGFRs phosphorylate specific tyrosine residues that mediate interaction with cytosolic adaptor proteins and the RAS-MAPK, PI3K-AKT, PLCγ, and STAT intracellular signaling pathways. Four structurally related intracellular non-signaling FGFs interact with and regulate the family of voltage gated sodium channels. Members of the FGF family function in the earliest stages of embryonic development and during organogenesis to maintain progenitor cells and mediate their growth, differentiation, survival, and patterning. FGFs also have roles in adult tissues where they mediate metabolic functions, tissue repair, and regeneration, often by reactivating developmental signaling pathways. Consistent with the presence of FGFs in almost all tissues and organs, aberrant activity of the pathway is associated with developmental defects that disrupt organogenesis, impair the response to injury, and result in metabolic disorders, and cancer. For further resources related to this article, please visit the WIREs website.

Nuclear localization of vascular endothelial growth factor-D and regulation of c-Myc-dependent transcripts in human lung fibroblasts

Lymphangiogenesis and angiogenesis are processes that are, in part, regulated by vascular endothelial growth factor (VEGF)-D. The formation of lymphatic structures has been implicated in multiple lung diseases, including pulmonary fibrosis. VEGF-D is a secreted protein produced by fibroblasts and macrophages, which induces lymphangiogenesis by signaling via VEGF receptor-3, and angiogenesis through VEGF receptor-2. VEGF-D contains a central VEGF homology domain, which is the biologically active domain, with flanking N- and C-terminal propeptides. Full-length VEGF-D (∼ 50 kD) is proteolytically processed in the extracellular space, to generate VEGF homology domain that contains the VEGF-D receptor-binding sites. Here, we report that, independent of its cell surface receptors, full-length VEGF-D accumulated in nuclei of fibroblasts, and that this process appears to increase with cell density. In nuclei, full-length VEGF-D associated with RNA polymerase II and c-Myc. In cells depleted of VEGF-D, the transcriptionally regulated genes appear to be modulated by c-Myc. These findings have potential clinical implications, as VEGF-D was found in fibroblast nuclei in idiopathic pulmonary fibrosis, a disease characterized by fibroblast proliferation. These findings are consistent with actions of full-length VEGF-D in cellular homeostasis in health and disease, independent of its receptors.

Nuclear translocation of heparan sulfate proteoglycans and their functional significance

BACKGROUND

Heparan sulfate proteoglycans (HSPGs) are important constituents of the cell membrane and they act as co-receptors for cellular signaling. Syndecan-1, glypican and perlecan also translocate to the nucleus in a regulated manner. Similar nuclear transport of growth factors and heparanase indicate a possible co-regulation and functional significance.

SCOPE OF REVIEW

In this review we dissect the structural requirement for the nuclear translocation of HSPGs and their functional implications.s

MAJOR CONCLUSIONS

The functions of the nuclear HSPGs are still incompletely understood. Evidence point to possible functions in hampering cell proliferation, inhibition of DNA topoisomerase I activity and inhibition of gene transcription.

GENERAL SIGNIFICANCE

HSPGs influence the behavior of malignant tumors in many different ways. Modulating their functions may offer powerful tools to control fundamental biological processes and provide the basis for subsequent targeted therapies in cancer. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

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.

Impacts of the apoptosis inhibitor of macrophage (AIM) on obesity-associated inflammatory diseases

Obesity is associated with various metabolic and cardiovascular diseases caused by chronic, low-grade inflammation that is initially observed in obese adipose tissue. In addition, many etiological studies in humans have shown a strong correlation between obesity and inflammatory autoimmune diseases. In this review, we focus on the involvement of apoptosis inhibitor of macrophage (AIM), a macrophage-derived blood protein, in both types of immune response. Through differential mechanisms, AIM thereby plays key roles in the pathogenesis of atherosclerosis, metabolic diseases, and obesity-associated autoimmune diseases. Thus, the regulation of blood AIM levels or AIM function has the potential to serve as a next-generation therapy against these inflammatory diseases brought about by modern lifestyle.

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.

Challenges, expectations and limits for nanoparticles-based therapeutics in cancer: a focus on nano-albumin-bound drugs

Improving the efficacy-toxicity balance of anticancer agents remains an ongoing challenge in oncology. Beside the ever-growing development of innovative drugs addressing newly discovered molecular targets, nanotechnologies provide today a promising and exciting strategy to achieve this goal. The idea of carrying active compounds to their respective targets so as to improve their efficacy while sparing healthy tissue and reducing side-effects is not new. However, this area of research is in constant rise, and benefits from the latest advances in the field of biopharmaceutics, medicinal chemistry and nanomedicine. In addition to anthracyclines already widely present as liposomal drugs on the shelves, a variety of anticancer drugs can be now encapsulated into different chemical of structures so as to enhance their specificity toward malignant cells, mainly through improved pharmacokinetics profiles. Indeed, the recent advances in chemistry allow now a wide variety of scaffolds to be used as drug-carriers, so as optimize the delivery of cytotoxics. Even more recently, conjugated-drugs such as nanoalbumin (Nab) conjugates have emerged as a new promising alternative to improve both anticancer drugs distribution in the body and efficacy/toxicity balance eventually. This review covers the achievements and current limits of nanoparticles in oncology, with a special focus on nab-paclitaxel as a paradigmatic drug for this new generation of conjugated entities.

Realizing the clinical potential of cancer nanotechnology by minimizing toxicologic and targeted delivery concerns

Nanotechnology has the potential to make smart drugs that would be capable of targeting cancer but not normal cells and to load combinations of cooperating agents into a single nanosized particle to more effectively treat this disease. However, to realize the full potential of this technology, the negative aspects associated with these nanoparticles need to be overcome. This review discusses concerns in the field limiting realization of the full clinical potential of this technology, which are toxicity and targeted delivery. Strategies to overcome these hurdles are also reviewed, which could lead to attainment of the full clinical potential of this exciting technology.

Blood vessels as targets in tumor therapy

The landmark papers published by Judah Folkman in the early 1970s on tumor angiogenesis and therapeutic implications promoted the rapid development of a very dynamic field where basic scientists, oncologists, and pharmaceutical industry joined forces to determine the molecular mechanisms in blood vessel formation and find means to exploit this knowledge in suppressing tumor vascularization and growth. A wealth of information has been collected on angiogenic growth factors, and in 2004 the first specific blood vessel-targeted cancer therapy was introduced: a neutralizing antibody against vascular endothelial growth factor (VEGF). Now (2011) we know that suppression of tumor angiogenesis may be a double-edged sword and that the therapy needs to be further refined and individualized. This review describes the hallmarks of tumor vessels, how different angiogenic growth factors exert their function, and the perspectives for future development of anti-angiogenic therapy.

Urokinase receptor associates with myocardin to control vascular smooth muscle cells phenotype in vascular disease

OBJECTIVE

The urokinase-type plasminogen activator (uPA) and its specific receptor (uPAR) are a potent multifunctional system involved in vascular remodeling. The goal of the study was to unravel the mechanisms of uPA/uPAR-directed vascular smooth muscle cell (VSMC) differentiation.

METHODS AND RESULTS

Using cultured human primary VSMCs, we identified a new molecular mechanism controlling phenotypic modulation in vitro and in vivo. We found that the urokinase-type plasminogen activator receptor (uPAR) acts together with the transcriptional coactivator myocardin to regulate the VSMC phenotype. uPAR, a glycosylphosphatidylinositol-anchored cell-surface receptor family member, undergoes ligand-induced internalization and nuclear transport in VSMCs. Platelet-derived growth factor receptor β and SUMOylated RanGAP1 mediate this trafficking. Nuclear uPAR associates with myocardin, which is then recruited from the promoters of serum response factor target genes and undergoes proteasomal degradation. This chain of events initiates the synthetic VSMC phenotype. Using mouse carotid artery ligation model, we show that this mechanism contributes to adverse vascular remodeling after injury in vivo. We then cultured cells on a microstructured biomaterial and found that substrate topography induced uPAR-mediated VSMC differentiation.

CONCLUSIONS

These findings reveal the transcriptional activity of uPAR, controlling the differentiation of VSMCs in a vascular disease model. They also suggest a new role for uPAR as a therapeutic target and as a marker for VSMC phenotyping on prosthetic biomaterials.

Pigment epithelium-derived factor (PEDF) interacts with transportin SR2, and active nuclear import is facilitated by a novel nuclear localization motif

PEDF (Pigment epithelium-derived factor) is a non-inhibitory member of the serpin gene family (serpinF1) that displays neurotrophic and anti-angiogenic properties. PEDF contains a secretion signal sequence, but although originally regarded as a secreted extracellular protein, endogenous PEDF is found in the cytoplasm and nucleus of several mammalian cell types. In this study we employed a yeast two-hybrid interaction trap screen to identify transportin-SR2, a member of the importin-β family of nuclear transport karyopherins, as a putative PEDF binding partner. The interaction was supported in vitro by GST-pulldown and co-immunoprecipitation. Following transfection of HEK293 cells with GFP-tagged PEDF the protein was predominantly localised to the nucleus, suggesting that active import of PEDF occurs. A motif (YxxYRVRS) shared by PEDF and the unrelated transportin-SR2 substrate, RNA binding motif protein 4b, was identified and we investigated its potential as a nuclear localization signal (NLS) sequence. Site-directed mutagenesis of this helix A motif in PEDF resulted in a GFP-tagged mutant protein being excluded from the nucleus, and mutation of two arginine residues (R67, R69) was sufficient to abolish nuclear import and PEDF interaction with transportin-SR2. These results suggest a novel NLS and mechanism for serpinF1 nuclear import, which may be critical for anti-angiogenic and neurotrophic function.

AIMing at metabolic syndrome. -Towards the development of novel therapies for metabolic diseases via apoptosis inhibitor of macrophage (AIM).-

Metabolic syndrome (MetS) is a cascade of metabolic diseases, starting with obesity and progressing to atherosclerosis, and is often fatal because of serious cardiovascular problems such as heart/brain infarction and hemorrhage. Accumulating evidence has revealed a critical involvement of inflammatory responses triggered by lesional macrophages in the pathogenesis of MetS. Importantly, we found that macrophages are associated with disease progression, not only in the induction of inflammation but also in the production of apoptosis inhibitor of macrophages (AIM), which we initially identified as a soluble factor expressed by macrophages. In atherosclerotic plaques, AIM is highly expressed by foam macrophages and inhibits apoptosis of these cells, which results in the accumulation of macrophages, causing inflammatory responses within the lesion, and ultimately disease progression. In adipose tissue, macrophage-derived AIM is incorporated into adipocytes through CD36-mediated endocytosis, thereby reducing the activity of cytosolic fatty acid synthase. This unique response stimulates lipolysis, resulting in a decrease in adipocyte size, which is physiologically relevant to the prevention of obesity. The lipolytic response also stimulates inflammation of adipocytes in association with the induction of metabolic disorders subsequent to obesity. Thus, AIM is involved in the progression of MetS in both an advancing and inhibitory fashion. Regulation of AIM could therefore be therapeutically applicable for MetS.

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.

CCN5, a novel transcriptional repressor of the transforming growth factor β signaling pathway

CCN5 is a member of the CCN (connective tissue growth factor/cysteine-rich 61/nephroblastoma overexpressed) family and was identified as an estrogen-inducible gene in estrogen receptor-positive cell lines. However, the role of CCN5 in breast carcinogenesis remains unclear. We report here that the CCN5 protein is localized mostly in the cytoplasm and in part in the nucleus of human tumor breast tissue. Using a heterologous transcription assay, we demonstrate that CCN5 can act as a transcriptional repressor presumably through association with histone deacetylase 1 (HDAC1). Microarray gene expression analysis showed that CCN5 represses expression of genes associated with epithelial-mesenchymal transition (EMT) as well as expression of key components of the transforming growth factor β (TGF-β) signaling pathway, prominent among them TGF-βRII receptor. We show that CCN5 is recruited to the TGF-βRII promoter, thereby providing a mechanism by which CCN5 restricts transcription of the TGF-βRII gene. Consistent with this finding, CCN5, we found, functions to suppress TGF-β-induced transcriptional responses and invasion that is concomitant with EMT. Thus, our data uncovered CCN5 as a novel transcriptional repressor that plays an important role in regulating tumor progression functioning, at least in part, by inhibiting the expression of genes involved in the TGF-β signaling cascade that is known to promote EMT.

Macrophage-derived AIM is endocytosed into adipocytes and decreases lipid droplets via inhibition of fatty acid synthase activity

Macrophages infiltrate adipose tissue in obesity and are involved in the induction of inflammation, thereby contributing to the development of obesity-associated metabolic disorders. Here, we show that the macrophage-derived soluble protein AIM is endocytosed into adipocytes via CD36. Within adipocytes, AIM associates with cytosolic fatty acid synthase (FAS), thereby decreasing FAS activity. This decreases lipid droplet size, stimulating the efflux of free fatty acids and glycerol from adipocytes. As an additional consequence of FAS inhibition, AIM prevents preadipocyte maturation. In vivo, the increase in adipocyte size and fat weight induced by high-fat diet (HFD) was accelerated in AIM-deficient (AIM(-)(/-)) mice compared to AIM(+/+) mice. Moreover, injection of recombinant AIM in AIM(-)(/-) mice suppresses the increase in fat mass induced by HFD. Interestingly, metabolic rates are comparable in AIM(-)(/-) and AIM(+/+) mice, suggesting that AIM specifically influences adipocyte status. Thus, this AIM function in adipocytes may be physiologically relevant to obesity progression.

Expression and function of fibroblast growth factor 18 in the ovarian follicle in cattle

Fibroblast growth factors (FGF) are involved in paracrine signaling between cell types in the ovarian follicle. FGF8, for example, is secreted by oocytes and controls cumulus cell metabolism. The closely related FGF18 is also expressed in oocytes in mice. The objective of this study was to assess the potential role of FGF18 in follicle growth in a monovulatory species, the cow. Messenger RNA encoding FGF18 was detected primarily in theca cells, and in contrast to the mouse, FGF18 was not detected in bovine oocytes. Addition of FGF18 protein to granulosa cell cultures inhibited estradiol and progesterone secretion as well as the abundance of mRNA encoding steroidogenic enzymes and the follicle-stimulating hormone receptor. In vivo, onset of atresia of the subordinate follicle was associated with increased thecal FGF18 mRNA levels and FGF18 protein in follicular fluid. In vitro, FGF18 altered cell cycle progression as measured by flow cytometry, resulting in increased numbers of dead cells (sub-G1 peak) and decreased cells in S phase. This was accompanied by decreased levels of mRNA encoding the cell cycle checkpoint regulator GADD45B. Collectively, these data point to a unique role for this FGF in signaling from theca cells to granulosa cells and suggest that FGF18 influences the process of atresia in ovarian follicles.

Local delivery of a collagen-binding FGF-1 chimera to smooth muscle cells in collagen scaffolds for vascular tissue engineering

We investigated the delivery of R136K-CBD (a collagen-binding mutant chimera of fibroblast growth factor-1) with a type I collagen scaffold as the delivery vehicle to smooth muscle cells (SMCs) for vascular tissue engineering. The binding affinity of R136K-CBD to 3-D collagen scaffolds was investigated both in the presence and absence of cells and/or salts. 2-D and 3-D visualization of delivery of R136K-CBD into SMCs were accomplished by combined fluorescent and reflection confocal microscopy. The mitogenic effect of collagen-immobilized R136K-CBD on SMCs in 3-D collagen was studied by Cyquant assay at different time intervals. In the group devoid of salt and cells, no detectable release of R136K-CBD into overlying culture media was found, compared with burst-and-continuous release of R136K and FGF-1 over a 14-day period in all other groups. The release rate of R136K-CBD was 1.7 and 1.6-fold less than R-136K and FGF-1 when media was supplemented with 2m salt (P<0.0001), and 2.6 and 2.5-fold less in cell-populated collagen hydrogels (P<0.0001), respectively. R136K-CBD showed essentially uniform binding to collagen and its distribution was dependent on that of the collagen scaffold. Internalization of R136K-CBD into SMCs was documented by confocal microscopy. 3-D local delivery of collagen-immobilized R136K-CBD increased the proliferation of SMCs in the collagen matrix to significantly greater levels and for a significantly greater duration than R136K or FGF-1, with 2.0 and 2.1-fold more mitogenicity than R136K and FGF-1 respectively (P<0.0001) at day 7. The results suggest that our collagen-binding fusion protein is an effective strategy for growth factor delivery for vascular tissue engineering.

Increased protein stability of FGF1 can compensate for its reduced affinity for heparin

Human FGF1 (fibroblast growth factor 1) is a powerful signaling molecule with a short half-life in vivo and a denaturation temperature close to physiological. Binding to heparin increases the stability of FGF1 and is believed to be important in the formation of FGF1.fibroblast growth factor receptor (FGFR) active complex. In order to reveal the function of heparin in FGF1.FGFR complex formation and signaling, we constructed several FGF1 variants with reduced affinity for heparin and with diverse stability. We determined their biophysical properties and biological activities as well as their ability to translocate across cellular membranes. Our study showed that increased thermodynamic stability of FGF1 nicely compensates for decreased binding of heparin in FGFR activation, induction of DNA synthesis, and cell proliferation. By stepwise introduction of stabilizing mutations into the K118E (K132E) FGF1 variant that shows reduced affinity for heparin and is inactive in stimulation of DNA synthesis, we were able to restore the full mitogenic activity of this mutant. Our results indicate that the main role of heparin in FGF-induced signaling is to protect this naturally unstable protein against heat and/or proteolytic degradation and that heparin is not essential for a direct FGF1-FGFR interaction and receptor activation.

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.

Trafficking of receptor tyrosine kinases to the nucleus

It has been known for at least 20 years that growth factors induce the internalization of cognate receptor tyrosine kinases (RTKs). The internalized receptors are then sorted to lysosomes or recycled to the cell surface. More recently, data have been published to indicate other intracellular destinations for the internalized RTKs. These include the nucleus, mitochondria, and cytoplasm. Also, it is recognized that trafficking to these novel destinations involves new biochemical mechanisms, such as proteolytic processing or interaction with translocons, and that these trafficking events have a function in signal transduction, implicating the receptor itself as a signaling element between the cell surface and the nucleus.

Basic fibroblast growth factor-binding peptide as a novel targeting ligand of drug carrier to tumor cells

Drug systems targeting tumor cells using basic fibroblast growth factor (bFGF) have been widely reported. In this study, the peptide KRTGQYKLC (bFGFp), containing cysteine at the carboxyl termination of the bFGF-derived peptide, was applied as a novel ligand targeting tumor cells. bFGFp was conjugated with bovine serum albumin (BSA) and liposomes. The peptide was shown to inhibit the binding of bFGF to FGF receptor-1 (FGFR1). Interestingly, the binding study using surface plasmon resonance (SPR) assay revealed that the bFGFp-BSA was not bound to FGFR1, but was selectively bound to bFGF. Furthermore, the SPR assay showed that bFGFp-BSA is capable of binding to FGFR1 following the pretreatment with bFGF. The confocal microscopy study indicated that the uptake of bFGFp-BSA by NIH3T3 cells, which highly express FGFRs, was significantly enhanced by pretreatment with bFGF. Then, PEGylated liposomes containing bFGFp (bFGFp-liposome) were prepared by conjugating maleimide-PEG-PE with bFGFp. Following the pretreatment of bFGF, the uptake of bFGFp-liposomes by NIH3T3 cells was significantly enhanced. These results suggest that bFGFp-BSA and bFGFp-liposomes are taken by NIH3T3 cells via binding with bFGF. In addition, both bFGFp-BSA and bFGFp-liposomes had no effect on the proliferation of NIH3T3 cells. This strategy can be used as a novel system for targeting tumors highly expressing FGFRs without a proliferation effect.

Changes in bone morphogenetic protein receptor-IB localisation regulate osteogenic responses of human bone cells to bone morphogenetic protein-2

Cell responses to bone morphogenetic proteins (BMP) depend on the expression and surface localisation of transmembrane receptors BMPR-IA, -IB and -II. The present study shows that all three antigens are readily detected in human bone cells. However, only BMPR-II was found primarily at the plasma membrane, whereas BMPR-IA was expressed equally in the cytoplasm and at the cell surface. Notably, BMPR-IB was mainly intracellular, where it was associated with a number of cytoplasmic structures and possibly the nucleus. Treatment with transforming growth factor beta1 (TGF-beta1) caused rapid translocation of BMPR-IB to the cell surface, mediated via the p38 mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) pathways. The TGF-beta1-induced increase in surface BMPR-IB resulted in significantly elevated BMP-2 binding and Smad1/5/8 phosphorylation, although the receptor was subsequently internalised and the functional response to BMP-2 consequently down-regulated. The results show, for the first time, that BMPR-IB is localised primarily in intracellular compartments in bone cells and that TGF-beta1 induces rapid surface translocation from the cytoplasm to the cell surface, resulting in increased sensitivity of the cells to BMP-2.