90-kDa ribosomal S6 kinase is a direct target for the nuclear fibroblast growth factor receptor 1 (FGFR1): role in FGFR1 signaling

Nuclear receptor tyrosine kinase transport and functions in cancer

Signaling functions of plasma membrane-localized receptor tyrosine kinases (RTKs) have been extensively studied after they were first described in the mid-1980s. Plasma membrane RTKs are activated by extracellular ligands and cellular stress stimuli, and regulate cellular responses by activating the downstream effector proteins to initiate a wide range of signaling cascades in the cells. However, increasing evidence indicates that RTKs can also be transported into the intracellular compartments where they phosphorylate traditional effector proteins and non-canonical substrate proteins. In general, internalization that retains the RTK's transmembrane domain begins with endocytosis, and endosomal RTK remains active before being recycled or degraded. Further RTK retrograde transport from endosome-Golgi-ER to the nucleus is primarily dependent on membranes vesicles and relies on the interaction with the COP-I vesicle complex, Sec61 translocon complex, and importin. Internalized RTKs have non-canonical substrates that include transcriptional co-factors and DNA damage response proteins, and many nuclear RTKs harbor oncogenic properties and can enhance cancer progression. Indeed, nuclear-localized RTKs have been shown to positively correlate with cancer recurrence, therapeutic resistance, and poor prognosis of cancer patients. Therefore, understanding the functions of nuclear RTKs and the mechanisms of nuclear RTK transport will further improve our knowledge to evaluate the potential of targeting nuclear RTKs or the proteins involved in their transport as new cancer therapeutic strategies.

Thermal Bioprinting Causes Ample Alterations of Expression of LUCAT1, IL6, CCL26, and NRN1L Genes and Massive Phosphorylation of Critical Oncogenic Drug Resistance Pathways in Breast Cancer Cells

Bioprinting technology merges engineering and biological fields and together, they possess a great translational potential, which can tremendously impact the future of regenerative medicine and drug discovery. However, the molecular effects elicited by thermal inkjet bioprinting in breast cancer cells remains elusive. Previous studies have suggested that bioprinting can be used to model tissues for drug discovery and pharmacology. We report viability, apoptosis, phosphorylation, and RNA sequence analysis of bioprinted MCF7 breast cancer cells at separate timepoints post-bioprinting. An Annexin A5-FITC apoptosis stain was used in combination with flow cytometry at 2 and 24 h post-bioprinting. Antibody arrays using a Human phospho-MAPK array kit was performed 24 h post-bioprinting. RNA sequence analysis was conducted in samples collected at 2, 7, and 24 h post-bioprinting. The post-bioprinting cell viability averages were 77 and 76% at 24 h and 48 h, with 31 and 64% apoptotic cells at 2 and 24 h after bioprinting. A total of 21 kinases were phosphorylated in the bioprinted cells and 9 were phosphorylated in the manually seeded controls. The RNA seq analysis in the bioprinted cells identified a total of 12,235 genes, of which 9.7% were significantly differentially expressed. Using a ±2-fold change as the cutoff, 266 upregulated and 206 downregulated genes were observed in the bioprinted cells, with the following 5 genes uniquely expressed NRN1L, LUCAT1, IL6, CCL26, and LOC401585. This suggests that thermal inkjet bioprinting is stimulating large scale gene alterations that could potentially be utilized for drug discovery. Moreover, bioprinting activates key pathways implicated in drug resistance, cell motility, proliferation, survival, and differentiation.

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.

Oncogenic fusion protein BCR-FGFR1 requires the breakpoint cluster region-mediated oligomerization and chaperonin Hsp90 for activation

Mutation and translocation of fibroblast growth factor receptors often lead to aberrant signaling and cancer. This work focuses on the t(8;22)(p11;q11) chromosomal translocation which creates the breakpoint cluster region (BCR) fibroblast growth factor receptor1 (FGFR1) (BCR-FGFR1) fusion protein. This fusion occurs in stem cell leukemia/lymphoma, which can progress to atypical chronic myeloid leukemia, acute myeloid leukemia, or B-cell lymphoma. This work focuses on the biochemical characterization of BCR-FGFR1 and identification of novel therapeutic targets. The tyrosine kinase activity of FGFR1 is required for biological activity as shown using transformation assays, interleukin-3 independent cell proliferation, and liquid chromatography/mass spectroscopy analyses. Furthermore, BCR contributes a coiled-coil oligomerization domain, also essential for oncogenic transformation by BCR-FGFR1. The importance of salt bridge formation within the coiled-coil domain is demonstrated, as disruption of three salt bridges abrogates cellular transforming ability. Lastly, BCR-FGFR1 acts as a client of the chaperonin heat shock protein 90 (Hsp90), suggesting that BCR-FGFR1 relies on Hsp90 complex to evade proteasomal degradation. Transformed cells expressing BCR-FGFR1 are sensitive to the Hsp90 inhibitor Ganetespib, and also respond to combined treatment with Ganetespib plus the FGFR inhibitor BGJ398. Collectively, these data suggest novel therapeutic approaches for future stem cell leukemia/lymphoma treatment: inhibition of BCR oligomerization by disruption of required salt bridges; and inhibition of the chaperonin Hsp90 complex.

Differential regulation of fibroblast growth factor receptor 1 trafficking and function by extracellular galectins

Fibroblast growth factor receptors (FGFRs) are integral membrane proteins that transmit signals through the plasma membrane. FGFRs signaling needs to be precisely adjusted as aberrant FGFRs function is associated with development of human cancers or severe metabolic diseases. The subcellular localization, trafficking and function of FGFRs rely on the formation of multiprotein complexes. In this study we revealed galectins, lectin family members implicated in cancer development and progression, as novel FGFR1 binding proteins. We demonstrated that galectin-1 and galectin-3 directly bind to the sugar chains of the glycosylated extracellular part of FGFR1. Although both galectins compete for the same binding sites on FGFR1, these proteins elicit different impact on FGFR1 function and cellular trafficking. Galectin-1 mimics fibroblast growth factor as it efficiently activates FGFR1 and receptor-downstream signaling pathways that result in cell proliferation and apoptotic evasion. In contrast, galectin-3 induces extensive clustering of FGFR1 on the cell surface that inhibits constitutive internalization of FGFR1. Our data point on the interplay between extracellular galectins and FGFRs in the regulation of cell fate.

Dynamic gene regulation by nuclear colony-stimulating factor 1 receptor in human monocytes and macrophages

Despite their location at the cell surface, several receptor tyrosine kinases (RTK) are also found in the nucleus, as either intracellular domains or full length proteins. However, their potential nuclear functions remain poorly understood. Here we find that a fraction of full length Colony Stimulating Factor-1 Receptor (CSF-1R), an RTK involved in monocyte/macrophage generation, migrates to the nucleus upon CSF-1 stimulation in human primary monocytes. Chromatin-immunoprecipitation identifies the preferential recruitment of CSF-1R to intergenic regions, where it co-localizes with H3K4me1 and interacts with the transcription factor EGR1. When monocytes are differentiated into macrophages with CSF-1, CSF-1R is redirected to transcription starting sites, colocalizes with H3K4me3, and interacts with ELK and YY1 transcription factors. CSF-1R expression and chromatin recruitment is modulated by small molecule CSF-1R inhibitors and altered in monocytes from chronic myelomonocytic leukemia patients. Unraveling this dynamic non-canonical CSF-1R function suggests new avenues to explore the poorly understood functions of this receptor and its ligands.

Receptor tyrosine kinases localize to the cell surface and have been suggested to also have nuclear function. Here the authors provide evidence that Colony Stimulating Factor-1 Receptor (CSF-1R) migrates to the nucleus upon CSF-1 stimulation in monocytes and that upon differentiation into macrophages, CSF-1R localizes to TSS, co-localizes with H3K4me3, and interacts with ELK and YY1.

Membrane-Associated, Not Cytoplasmic or Nuclear, FGFR1 Induces Neuronal Differentiation

The intracellular transport of receptor tyrosine kinases results in the differential activation of various signaling pathways. In this study, optogenetic stimulation of fibroblast growth factor receptor type 1 (FGFR1) was performed to study the effects of subcellular targeting of receptor kinases on signaling and neurite outgrowth. The catalytic domain of FGFR1 fused to the algal light-oxygen-voltage-sensing (LOV) domain was directed to different cellular compartments (plasma membrane, cytoplasm and nucleus) in human embryonic kidney (HEK293) and pheochromocytoma (PC12) cells. Blue light stimulation elevated the pERK and pPLCγ1 levels in membrane-opto-FGFR1-transfected cells similarly to ligand-induced receptor activation; however, no changes in pAKT levels were observed. PC12 cells transfected with membrane-opto-FGFR1 exhibited significantly longer neurites after light stimulation than after growth factor treatment, and significantly more neurites extended from their cell bodies. The activation of cytoplasmic FGFR1 kinase enhanced ERK signaling in HEK293 cells but not in PC12 cells and did not induce neuronal differentiation. The stimulation of FGFR1 kinase in the nucleus also did not result in signaling changes or neurite outgrowth. We conclude that FGFR1 kinase needs to be associated with membranes to induce the differentiation of PC12 cells mainly via ERK activation.

Targeting Cellular Trafficking of Fibroblast Growth Factor Receptors as a Strategy for Selective Cancer Treatment

Fibroblast growth factor receptors (FGFRs) in response to fibroblast growth factors (FGFs) transmit signals across the cell membrane, regulating important cellular processes, like differentiation, division, motility, and death. The aberrant activity of FGFRs is often observed in various diseases, especially in cancer. The uncontrolled FGFRs' function may result from their overproduction, activating mutations, or generation of FGFRs' fusion proteins. Besides their typical subcellular localization on the cell surface, FGFRs are often found inside the cells, in the nucleus and mitochondria. The intracellular pool of FGFRs utilizes different mechanisms to facilitate cancer cell survival and expansion. In this review, we summarize the current stage of knowledge about the role of FGFRs in oncogenic processes. We focused on the mechanisms of FGFRs' cellular trafficking-internalization, nuclear translocation, and mitochondrial targeting, as well as their role in carcinogenesis. The subcellular sorting of FGFRs constitutes an attractive target for anti-cancer therapies. The blocking of FGFRs' nuclear and mitochondrial translocation can lead to the inhibition of cancer invasion. Moreover, the endocytosis of FGFRs can serve as a tool for the efficient and highly selective delivery of drugs into cancer cells overproducing these receptors. Here, we provide up to date examples how the cellular sorting of FGFRs can be hijacked for selective cancer treatment.

Kinase-targeted cancer therapies: progress, challenges and future directions

The human genome encodes 538 protein kinases that transfer a γ-phosphate group from ATP to serine, threonine, or tyrosine residues. Many of these kinases are associated with human cancer initiation and progression. The recent development of small-molecule kinase inhibitors for the treatment of diverse types of cancer has proven successful in clinical therapy. Significantly, protein kinases are the second most targeted group of drug targets, after the G-protein-coupled receptors. Since the development of the first protein kinase inhibitor, in the early 1980s, 37 kinase inhibitors have received FDA approval for treatment of malignancies such as breast and lung cancer. Furthermore, about 150 kinase-targeted drugs are in clinical phase trials, and many kinase-specific inhibitors are in the preclinical stage of drug development. Nevertheless, many factors confound the clinical efficacy of these molecules. Specific tumor genetics, tumor microenvironment, drug resistance, and pharmacogenomics determine how useful a compound will be in the treatment of a given cancer. This review provides an overview of kinase-targeted drug discovery and development in relation to oncology and highlights the challenges and future potential for kinase-targeted cancer therapies.

Induced Pluripotent Stem Cells Reveal Common Neurodevelopmental Genome Deprograming in Schizophrenia

Schizophrenia is a neurodevelopmental disorder characterized by complex aberrations in the structure, wiring, and chemistry of multiple neuronal systems. The abnormal developmental trajectory of the brain is established during gestation, long before clinical manifestation of the disease. Over 200 genes and even greater numbers of single nucleotide polymorphisms and copy number variations have been linked with schizophrenia. How does altered function of such a variety of genes lead to schizophrenia? We propose that the protein products of these altered genes converge on a common neurodevelopmental pathway responsible for the development of brain neural circuit and neurotransmitter systems. The results of a multichanneled investigation using induced pluripotent stem cell (iPSCs)- and embryonic stem cell (ESCs)-derived neuronal committed cells (NCCs) indicate an early (preneuronal) developmental-genomic etiology of schizophrenia and that the dysregulated developmental gene networks are common to genetically unrelated cases of schizophrenia. The results support a "watershed" mechanism in which mutations within diverse signaling pathways affect the common pan-ontogenic mechanism, integrative nuclear (n)FGFR1 signaling (INFS). Dysregulation of INFS in schizophrenia NCCs deconstructs coordinated gene networks and leads to formation of new networks by the dysregulated genes. This genome deprograming affects critical gene programs and pathways for neural development and functions. Studies show that the genomic deprograming reflect an altered nFGFR1-genome interactions and deregulation of miRNA genes by nFGFR1. In addition, changes in chromatin topology imposed by nFGFR1 may play a role in coordinate gene dysregulation in schizophrenia.

Evidence-Based Theory for Integrated Genome Regulation of Ontogeny--An Unprecedented Role of Nuclear FGFR1 Signaling

Genetic experiments have positioned the fgfr1 gene at the top of the gene hierarchy that governs gastrulation, as well as the subsequent development of the major body axes, nervous system, muscles, and bones, by affecting downstream genes that control the cell cycle, pluripotency, and differentiation, as well as microRNAs. Studies show that this regulation is executed by a single protein, the nuclear isoform of FGFR1 (nFGFR1), which integrates signals from development‐initiating factors, such as retinoic acid (RA), and operates at the interface of genomic and epigenomic information. nFGFR1 cooperates with a multitude of transcriptional factors (TFs), and targets thousands of genes encoding for mRNAs, as well as miRNAs in top ontogenic networks. nFGFR1 binds to the promoters of ancient proto‐oncogenes and tumor suppressor genes, in addition to binding to metazoan morphogens that delineate body axes, and construct the nervous system, as well as mesodermal and endodermal tissues. The discovery of pan‐ontogenic gene programming by integrative nuclear FGFR1 signaling (INFS) impacts our understanding of ontogeny, as well as developmental pathologies, and holds new promise for reconstructive medicine, and cancer therapy. J. Cell. Physiol. 231: 1199–1218, 2016. © 2016 The Authors. Journal of Cellular Physiology published by Wiley Periodicals, Inc.

Coalition of Nuclear Receptors in the Nervous System

A universal signaling module has been described which utilizes the nuclear form of Fibroblast growth Factor Receptor 1 (FGFR1) in a central role directing the post-mitotic development of neural cells through coordinated gene expression. In this review, we discuss in detail the current knowledge of FGFR1 nuclear interaction partners in three scenarios: (i) Engagement of FGFR1 in neuronal stem cells and regulation of neuronal differentiation; (ii) interaction with the orphan receptor Nurr1 in development of mesencephalic dopaminergic neurons; (iii) modulation of nuclear FGFR1 interactions downstream of nerve growth factor (NGF) signaling. These coalitions demonstrate the versatility of non-canonical, nuclear tyrosine kinase signaling in diverse cellular differentiation programs of neurons.

A new perspective on the role of the CREB family of transcription factors in memory consolidation via adult hippocampal neurogenesis

Adult neurogenesis is the process by which new neurons are generated in the brains of adults. Since its discovery 50 years ago, adult neurogenesis has been widely studied in the mammalian brain and has provided a new perspective on the pathophysiology of many psychiatric and neurodegenerative disorders, some of which affect memory. In this regard, adult hippocampal neurogenesis (AHN), which occurs in the subgranular zone (SGZ) of the dentate gyrus (DG), has been suggested to play a role in the formation and consolidation of new memories. This process involves many transcription factors, of which cyclic AMP (cAMP)-responsive element-binding protein (CREB) is a well-documented one. In the developing brain, CREB regulates crucial cell stages (e.g., proliferation, differentiation, and survival), and in the adult brain, it participates in neuronal plasticity, learning, and memory. In addition, new evidence supports the hypothesis that CREB may also participate in learning and memory through its involvement in AHN. This review examines the CREB family of transcription factors, including the different members and known signaling pathways. It highlights the role of CREB as a modulator of AHN, which could underlie its function in memory consolidation mechanisms.

Proteolytic cleavage, trafficking, and functions of nuclear receptor tyrosine kinases

Intracellular localization has been reported for over three-quarters of receptor tyrosine kinase (RTK) families in response to environmental stimuli. Internalized RTK may bind to non-canonical substrates and affect various cellular processes. Many of the intracellular RTKs exist as fragmented forms that are generated by γ-secretase cleavage of the full-length receptor, shedding, alternative splicing, or alternative translation initiation. Soluble RTK fragments are stabilized and intracellularly transported into subcellular compartments, such as the nucleus, by binding to chaperone or transcription factors, while membrane-bound RTKs (full-length or truncated) are transported from the plasma membrane to the ER through the well-established Rab- or clathrin adaptor protein-coated vesicle retrograde trafficking pathways. Subsequent nuclear transport of membrane-bound RTK may occur via two pathways, INFS or INTERNET, with the former characterized by release of receptors from the ER into the cytosol and the latter characterized by release of membrane-bound receptor from the ER into the nucleoplasm through the inner nuclear membrane. Although most non-canonical intracellular RTK signaling is related to transcriptional regulation, there may be other functions that have yet to be discovered. In this review, we summarize the proteolytic processing, intracellular trafficking and nuclear functions of RTKs, and discuss how they promote cancer progression, and their clinical implications.

Global Developmental Gene Programing Involves a Nuclear Form of Fibroblast Growth Factor Receptor-1 (FGFR1)

Genetic studies have placed the Fgfr1 gene at the top of major ontogenic pathways that enable gastrulation, tissue development and organogenesis. Using genome-wide sequencing and loss and gain of function experiments the present investigation reveals a mechanism that underlies global and direct gene regulation by the nuclear form of FGFR1, ensuring that pluripotent Embryonic Stem Cells differentiate into Neuronal Cells in response to Retinoic Acid. Nuclear FGFR1, both alone and with its partner nuclear receptors RXR and Nur77, targets thousands of active genes and controls the expression of pluripotency, homeobox, neuronal and mesodermal genes. Nuclear FGFR1 targets genes in developmental pathways represented by Wnt/β-catenin, CREB, BMP, the cell cycle and cancer-related TP53 pathway, neuroectodermal and mesodermal programing networks, axonal growth and synaptic plasticity pathways. Nuclear FGFR1 targets the consensus sequences of transcription factors known to engage CREB-binding protein, a common coregulator of transcription and established binding partner of nuclear FGFR1. This investigation reveals the role of nuclear FGFR1 as a global genomic programmer of cell, neural and muscle development.

"Nuclear FGF receptor-1 and CREB binding protein: an integrative signaling module"

In this review we summarize the current understanding of a novel integrative function of Fibroblast Growth Factor Receptor-1 (FGFR1) and its partner CREB Binding Protein (CBP) acting as a nuclear regulatory complex. Nuclear FGFR1 and CBP interact with and regulate numerous genes on various chromosomes. FGFR1 dynamic oscillatory interactions with chromatin and with specific genes, underwrites gene regulation mediated by diverse developmental signals. Integrative Nuclear FGFR1 Signaling (INFS) effects the differentiation of stem cells and neural progenitor cells via the gene-controlling Feed-Forward-And-Gate mechanism. Nuclear accumulation of FGFR1 occurs in numerous cell types and disruption of INFS may play an important role in developmental disorders such as schizophrenia, and in metastatic diseases such as cancer. Enhancement of INFS may be used to coordinate the gene regulation needed to activate cell differentiation for regenerative purposes or to provide interruption of cancer stem cell proliferation.

Compartmentalization of TNF-related apoptosis-inducing ligand (TRAIL) death receptor functions: emerging role of nuclear TRAIL-R2

Localized in the plasma membrane, death domain-containing TNF-related apoptosis-inducing ligand (TRAIL) receptors, TRAIL-R1 and TRAIL-R2, induce apoptosis and non-apoptotic signaling when crosslinked by the ligand TRAIL or by agonistic receptor-specific antibodies. Recently, an increasing body of evidence has accumulated that TRAIL receptors are additionally found in noncanonical intracellular locations in a wide range of cell types, preferentially cancer cells. Thus, besides their canonical locations in the plasma membrane and in intracellular membranes of the secretory pathway as well as endosomes and lysosomes, TRAIL receptors may also exist in autophagosomes, in nonmembraneous cytosolic compartment as well as in the nucleus. Such intracellular locations have been mainly regarded as hide-outs for these receptors representing a strategy for cancer cells to resist TRAIL-mediated apoptosis. Recently, a novel function of intracellular TRAIL-R2 has been revealed. When present in the nuclei of tumor cells, TRAIL-R2 inhibits the processing of the primary let-7 miRNA (pri-let-7) via interaction with accessory proteins of the Microprocessor complex. The nuclear TRAIL-R2-driven decrease in mature let-7 enhances the malignancy of cancer cells. This finding represents a new example of nuclear activity of typically plasma membrane-located cytokine and growth factor receptors. Furthermore, this extends the list of nucleic acid targets of the cell surface receptors by pri-miRNA in addition to DNA and mRNA. Here we review the diverse functions of TRAIL-R2 depending on its intracellular localization and we particularly discuss the nuclear TRAIL-R2 (nTRAIL-R2) function in the context of known nuclear activities of other normally plasma membrane-localized receptors.

A large-scale RNAi-based mouse tumorigenesis screen identifies new lung cancer tumor suppressors that repress FGFR signaling

To discover new tumor-suppressor genes (TSG), we developed a functional genomics approach in which immortalized but nontumorigenic cells were stably transduced with large-scale shRNA pools and tested for tumor formation in mice. Identification of shRNAs in resulting tumors revealed candidate TSGs, which were validated experimentally and by analyzing expression in human tumor samples. Using this approach, we identified 24 TSGs that were significantly downregulated in human lung squamous cell carcinomas (hLSCC). Amplification of fibroblast growth factor receptor 1 (FGFR1), which aberrantly increases FGFR signaling, is a common genetic alteration in hLSCCs. Remarkably, we found that 17 of the TSGs encode repressors of FGFR signaling. Knockdown of 14 of these TSGs transformed immortalized human bronchial epithelial cells and, in most cases, rendered them sensitive to FGFR inhibitors. Our results indicate that increased FGFR signaling promotes tumorigenesis in many hLSCCs that lack FGFR1 amplification or activating mutations.

SIGNIFICANCE

A functional genomics approach identifies new lung TSGs whose loss aberrantly increases FGFR signaling to promote tumorigenesis. These TSGs are frequently downregulated in hLSCCs, indicating that increased FGFR signaling promotes tumorigenesis in many hLSCCs lacking FGFR1 amplification or activating mutations.

The ins and outs of fibroblast growth factor receptor signalling

FGFR (fibroblast growth factor receptor) signalling plays critical roles in embryogensis, adult physiology, tissue repair and many pathologies. Of particular interest over recent years, it has been implicated in a wide range of cancers, and concerted efforts are underway to target different aspects of FGFR signalling networks. A major focus has been identifying the canonical downstream signalling pathways in cancer cells, and these are now relatively well understood. In the present review, we focus on two distinct but emerging hot topics in FGF biology: its role in stromal cross-talk during cancer progression and the potential roles of FGFR signalling in the nucleus. These neglected areas are proving to be of great interest clinically and are intimately linked, at least in pancreatic cancer. The importance of the stroma in cancer is well accepted, both as a conduit/barrier for treatment and as a target in its own right. Nuclear receptors are less acknowledged as targets, largely due to historical scepticism as to their existence or importance. However, increasing evidence from across the receptor tyrosine kinase field is now strong enough to make the study of nuclear growth factor receptors a major area of interest.

Activation of developmental nuclear fibroblast growth factor receptor 1 signaling and neurogenesis in adult brain by α7 nicotinic receptor agonist

Reactivation of endogenous neurogenesis in the adult brain or spinal cord holds the key for treatment of central nervous system injuries and neurodegenerative disorders, which are major health care issues for the world's aging population. We have previously shown that activation of developmental integrative nuclear fibroblast growth factor receptor 1 (FGFR1) signaling (INFS), via gene transfection, reactivates neurogenesis in the adult brain by promoting neuronal differentiation of brain neural stem/progenitor cells (NS/PCs). In the present study, we report that targeting the α7 nicotinic acetylcholine receptors (α7nAChRs) with a specific TC-7020 agonist led to a robust accumulation of endogenous FGFR1 in the cell nucleus. Nuclear FGFR1 accumulation was accompanied by an inhibition of proliferation of NS/PCs in the subventricular zone (SVZ) and by the generation of new neurons. Neuronal differentiation was observed in different regions of the adult mouse brain, including (a) βIII-Tubulin-expressing cortical neurons, (b) calretinin-expressing hippocampal neurons, and (c) cells in substantia nigra expressing the predopaminergic Nurr1+ phenotype. Furthermore, we showed that in vitro stimulation of neural stem/progenitor cells with α7nAChR agonist directly activated INFS and neuronal-like differentiation. TC-7020 stimulation of the βIII-Tubulin gene was accompanied by increased binding of FGFR1, CREB binding protein, and RNA polymerase II to a Nur77 targeted promoter region. TC-7020 augmented Nur77-dependent activation of nerve growth factor inducible-B protein responsive element, indicating that α7nAChR upregulation of βIII-Tubulin involves neurogenic FGFR1-Nur signaling. The reactivation of INFS and neurogenesis in adult brain by the α7nAChR agonist may offer a new strategy to treat brain injuries, neurodegenerative diseases, and neurodevelopmental diseases.

NGF-induced cell differentiation and gene activation is mediated by integrative nuclear FGFR1 signaling (INFS)

Nerve growth factor (NGF) is the founding member of the polypeptide neurotrophin family responsible for neuronal differentiation. To determine whether the effects of NGF rely upon novel Integrative Nuclear FGF Receptor-1 (FGFR1) Signaling (INFS) we utilized the PC12 clonal cell line, a long-standing benchmark model of sympathetic neuronal differentiation. We demonstrate that NGF increases expression of the fgfr1 gene and promotes trafficking of FGFR1 protein from cytoplasm to nucleus by inhibiting FGFR1 nuclear export. Nuclear-targeted dominant negative FGFR1 antagonizes NGF-induced neurite outgrowth, doublecortin (dcx) expression and activation of the tyrosine hydroxylase (th) gene promoter, while active constitutive nuclear FGFR1 mimics the effects of NGF. NGF increases the expression of dcx, th, βIII tubulin, nurr1 and nur77, fgfr1and fibroblast growth factor-2 (fgf-2) genes, while enhancing binding of FGFR1and Nur77/Nurr1 to those genes. NGF activates transcription from isolated NurRE and NBRE motifs. Nuclear FGFR1 transduces NGF activation of the Nur dimer and raises basal activity of the Nur monomer. Cooperation of nuclear FGFR1 with Nur77/Nurr1 in NGF signaling expands the integrative functions of INFS to include NGF, the first discovered pluripotent neurotrophic factor.

FGFR1 cleavage and nuclear translocation regulates breast cancer cell behavior

FGFR1 cleavage by Granzyme B induces its nuclear translocation, in which it stimulates cell migration through effects on gene expression.

FGF-10 and its receptors, FGFR1 and FGFR2, have been implicated in breast cancer susceptibility and progression, suggesting that fibroblast growth factor (FGF) signaling may be co-opted by breast cancer cells. We identify a novel pathway downstream of FGFR1 activation, whereby the receptor is cleaved and traffics to the nucleus, where it can regulate specific target genes. We confirm Granzyme B (GrB) as the protease responsible for cleavage and show that blocking GrB activity stopped FGFR1 trafficking to the nucleus and abrogates the promigratory effect of FGF stimulation. We confirm the in vivo relevance of our findings, showing that FGFR1 localized to the nucleus specifically in invading cells in both clinical material and a three-dimensional model of breast cancer. We identify target genes for FGFR1, which exert significant effects on cell migration and may represent an invasive signature. Our experiments identify a novel mechanism by which FGF signaling can regulate cancer cell behavior and provide a novel therapeutic target for treatment of invasive breast cancer.

T-cadherin is located in the nucleus and centrosomes in endothelial cells

T-cadherin (H-cadherin, cadherin 13) is upregulated in vascular proliferative disorders and in tumor-associated neovascularization and is deregulated in many cancers. Unlike canonical cadherins, it lacks transmembrane and intracellular domains and is attached to the plasma membrane via a glycosylphosphatidylinositol anchor. T-cadherin is thought to function in signaling rather than as an adhesion molecule. Some interactive partners of T-cadherin at the plasma membrane have recently been identified. We examined T-cadherin location in human endothelial cells using confocal microscopy and subcellular fractionation. We found that a considerable proportion of T-cadherin is located in the nucleus and in the centrosomes. T-cadherin colocalized with a centrosomal marker gamma-tubulin uniformly throughout the cell cycle at least in human umbilical vein endothelial cells. In the telophase, T-cadherin transiently concentrated in the midbody and was apparently degraded. Its overexpression resulted in an increase in the number of multinuclear cells, whereas its downregulation by small interfering RNA led to an increase in the number of cells with multiple centrosomes. These findings indicate that deregulation of T-cadherin in endothelial cells may lead to disturbances in cytokinesis or centrosomal replication.

Monoclonal antibodies with selective specificity towards different glycosylation isoforms of FGFR1

Fibroblast growth factor receptor 1 (FGFR1) is a member of the FGFR family of receptor tyrosine kinases, whose function has been implicated in diverse biological processes including cell proliferation, differentiation, survival, and tumorigenesis. This diversity is possibly mediated by the existence of multiple FGFR1 isoforms, generated by alternative splicing and post-translational modifications, mainly through glycosylation. In this study we report the generation and characterization of a panel of monoclonal antibodies directed towards FGFR1. To achieve this, we used as an antigen a fragment of FGFR1, corresponding to loop II-III of the extracellular domain, which shares low homology to other members of the FGFR family and possesses numerous antigentic determinants. Two rounds of ELISA screening and Western blot analysis allowed us to isolate a panel of monoclonal antibodies, which recognize specifically recombinant FGFR1 loop II-III. The ability of generated antibodies to recognize endogenous FGFR1 was examined in 3T3 L1 cells, which are known to express FGFR1, but not other members of FGFR family. Immunoblot analysis of 3T3 L1 cell lysates with hybridoma media of selected clones revealed a different, but overlapping pattern of immunoreactive bands, which might represent splicing and post-translationally modified forms of FGFR1. Furthermore, we also tested the cross-reactivity of generated antibodies towards recombinant full-length FGFR3 and their ability to recognize FGFR1 in 3T3 L1 cells by cyto- and immunocytochemistry. In summary, generated antibodies should be useful as tools for examining the expression pattern and biological functions of FGFR1 in normal and pathological tissues.

Targeting novel integrative nuclear FGFR1 signaling by nanoparticle-mediated gene transfer stimulates neurogenesis in the adult brain

Neurogenesis, the process of differentiation of neuronal stem/progenitor cells (NS/PC) into mature neurons, holds the key to the treatment of various neurodegenerative disorders, which are a major health issue for the world's aging population. We report that targeting the novel integrative nuclear FGF Receptor 1 signaling (INFS) pathway enhances the latent potential of NS/PCs to undergo neuronal differentiation, thus promoting neurogenesis in the adult brain. Employing organically modified silica (ORMOSIL)-DNA nanoplexes to efficiently transfect recombinant nuclear forms of FGFR1 and its FGF-2 ligand into the brain subventricular zone, we find that INFS stimulates the NS/PC to withdraw from the cell cycle, differentiate into doublecortin expressing migratory neuroblasts and neurons that migrate to the olfactory bulb, subcortical brain regions and in the brain cortex. Thus, nanoparticle-mediated non-viral gene transfer may be used to induce selective differentiation of NS/PCs, providing a potentially significant impact on the treatment of a broad range of neurological disorders.

A novel interaction between fibroblast growth factor receptor 3 and the p85 subunit of phosphoinositide 3-kinase: activation-dependent regulation of ERK by p85 in multiple myeloma cells

Ectopic activation of fibroblast growth factor receptor 3 (FGFR3) is associated with several cancers, including multiple myeloma (MM). FGFR3 inhibition in these cells inhibits proliferation and induces apoptosis, validating FGFR3 signaling as a therapeutic target in t(4;14) MM cases. We have identified the PI3K regulatory subunit, p85alpha, as a novel interactor of FGFR3 by yeast two-hybrid, and confirmed an interaction with both p85alpha and p85beta in mammalian cells. The interaction of FGFR3 with p85 is dependent upon receptor activation. In contrast to the Gab1-mediated association of FGFRs with p85, the FGFR3-p85 interaction we observed requires FGFR3 Y760, previously identified as a PLCgamma binding site. The interaction of p85 with FGFR3 does not require PLCgamma, suggesting the p85 interaction is direct and independent of PLCgamma binding. FGFR3 and p85 proteins also interact in MM cell lines which consistently express p85alpha and p85beta, but not p50 or p55 subunits. siRNA knockdown of p85beta in MM cells caused an increased ERK response to FGF2. These data suggest that an endogenous negative regulatory role for the p85-FGFR3 interaction on the Ras/ERK/MAPK pathway may exist in response to FGFR3 activity and identifies a novel therapeutic target for MM.

Fibroblast growth factor receptor-1 (FGFR1) nuclear dynamics reveal a novel mechanism in transcription control

Nuclear FGFR1 acts as a developmental gene regulator in cooperation with FGF-2, RSK1, and CREB-binding protein (CBP). FRAP analysis revealed three nuclear FGFR1 populations: i) a fast mobile, ii) a slower mobile population reflecting chromatin-bound FGFR1, and iii) an immobile FGFR1 population associated with the nuclear matrix. Factors (cAMP, CBP) that induce FGFR1-mediated gene activation shifted FGFR1 from the nuclear matrix (immobile) to chromatin (slow) and reduced the movement rate of the chromatin-bound population. Transcription inhibitors accelerated FGFR1 movement; the content of the chromatin-bound slow FGFR1 decreased, whereas the fast population increased. The transcriptional activation appears to involve conversion of the immobile matrix-bound and the fast nuclear FGFR1 into a slow chromatin-binding population through FGFR1's interaction with CBP, RSK1, and the high-molecular-weight form of FGF-2. Our findings support a general mechanism in which gene activation is governed by protein movement and collisions with other proteins and nuclear structures.

Targeting cancer with small molecule kinase inhibitors

Deregulation of kinase activity has emerged as a major mechanism by which cancer cells evade normal physiological constraints on growth and survival. To date, 11 kinase inhibitors have received US Food and Drug Administration approval as cancer treatments, and there are considerable efforts to develop selective small molecule inhibitors for a host of other kinases that are implicated in cancer and other diseases. Herein we discuss the current challenges in the field, such as designing selective inhibitors and developing strategies to overcome resistance mutations. This Review provides a broad overview of some of the approaches currently used to discover and characterize new kinase inhibitors.

Genome-wide prediction of SH2 domain targets using structural information and the FoldX algorithm

Current experiments likely cover only a fraction of all protein-protein interactions. Here, we developed a method to predict SH2-mediated protein-protein interactions using the structure of SH2-phosphopeptide complexes and the FoldX algorithm. We show that our approach performs similarly to experimentally derived consensus sequences and substitution matrices at predicting known in vitro and in vivo targets of SH2 domains. We use our method to provide a set of high-confidence interactions for human SH2 domains with known structure filtered on secondary structure and phosphorylation state. We validated the predictions using literature-derived SH2 interactions and a probabilistic score obtained from a naive Bayes integration of information on coexpression, conservation of the interaction in other species, shared interaction partners, and functions. We show how our predictions lead to a new hypothesis for the role of SH2 domains in signaling.

Understanding the functional role of every protein in the cell is a long-standing goal of cellular biology. An important step in this direction is to discover how and when proteins interact inside the cell to accomplish their tasks. Many of the cellular functions depend on reversible protein modifications like phosphorylation. To sense these modifications, cells have protein domains capable of binding phosphorylated proteins such as the SH2 domain. In this work, we show that it is possible to use the three-dimensional structure of protein domains to predict its binding preferences. Using a computational tool called FoldX, we have predicted the binding specificity of several human SH2 domains. These predictions, based on the computational analysis of the 3-D structure, were shown to be of similar accuracy as those obtained from experimental binding assays. We show here that it is also possible to understand how a mutation changes the binding preference of protein binding domains, opening the way for better understanding of some disease causing mutations. The combination of this novel computational approach with other sources of information allowed us to provide a set of high-confidence novel interactions for the proteins here studied.

Nuclear trafficking of secreted factors and cell-surface receptors: new pathways to regulate cell proliferation and differentiation, and involvement in cancers

Secreted factors and cell surface receptors can be internalized by endocytosis and translocated to the cytoplasm. Instead of being recycled or proteolysed, they sometimes translocate to the nucleus. Nuclear import generally involves a nuclear localization signal contained either in the secreted factor or its transmembrane receptor, that is recognized by the importins machinery. In the nucleus, these molecules regulate transcription of specific target genes by direct binding to transcription factors or general coregulators. In addition to the transcription regulation, nuclear secreted proteins and receptors seem to be involved in other important processes for cell life and cellular integrity such as DNA replication, DNA repair and RNA metabolism.

Nuclear secreted proteins and transmembrane receptors now appear to induce new signaling pathways to regulate cell proliferation and differentiation. Their nuclear localization is often transient, appearing only during certain phases of the cell cycle. Nuclear secreted and transmembrane molecules regulate the proliferation and differentiation of a large panel of cell types during embryogenesis and adulthood and are also potentially involved in wound healing. Secreted factors such as CCN proteins, EGF, FGFs and their receptors are often detected in the nucleus of cancer cells. Nuclear localization of these molecules has been correlated with tumor progression and poor prognosis for patient survival. Nuclear growth factors and receptors may be responsible for resistance to radiotherapy.

Fibroblast growth factor receptor signaling affects development and function of dopamine neurons - inhibition results in a schizophrenia-like syndrome in transgenic mice

Developing and mature midbrain dopamine (DA) neurons express fibroblast growth factor (FGF) receptor-1 (FGFR1). To determine the role of FGFR1 signaling in the development of DA neurons, we generated transgenic mice expressing a dominant negative mutant [FGFR1(TK-)] from the catecholaminergic, neuron-specific tyrosine hydroxylase (TH) gene promoter. In homozygous th(tk-)/th(tk-) mice, significant reductions in the size of TH-immunoreactive neurons were found in the substantia nigra compacta (SNc) and the ventral tegmental area (VTA) at postnatal days 0 and 360. Newborn th(tk-)/th(tk-) mice had a reduced density of DA neurons in both SNc and VTA, and the changes in SNc were maintained into adulthood. The reduced density of DA transporter in the striatum further demonstrated an impaired development of the nigro-striatal DA system. Paradoxically, the th(tk-)/th(tk-) mice had increased levels of DA, homovanilic acid and 3-methoxytyramine in the striatum, indicative of excessive DA transmission. These structural and biochemical changes in DA neurons are similar to those reported in human patients with schizophrenia and, furthermore, these th(tk-)/th(tk-) mice displayed an impaired prepulse inhibition that was reversed by a DA receptor antagonist. Thus, this study establishes a new developmental model for a schizophrenia-like disorder in which the inhibition of FGF signaling leads to alterations in DA neurons and DA-mediated behavior.

Impact of basic FGF expression in astrocytes on dopamine neuron synaptic function and development

Behavioural sensitization to amphetamine (AMPH) requires action of the drug in the ventral midbrain where dopamine (DA) neurons are located. In vivo studies suggest that AMPH sensitization requires enhanced expression of basic fibroblast growth factor (bFGF) in the nucleus of midbrain astrocytes. One idea is that the AMPH-induced increase in bFGF expression in astrocytes leads to enhanced secretion of this peptide and to long-term plasticity in DA neurons. To study directly the effects of astrocytic expression of bFGF on DA neurons, we established a cell-culture model of mesencephalic astrocytes and DA neurons. Immunolabelling showed that even in the absence of a pharmacological stimulus, the majority of mesencephalic astrocytes in culture express bFGF at a nuclear level. Arguing against the idea that bFGF was secreted, bFGF was undetectable in the extracellular medium (below 10 pg/mL). However, supplementing culture medium with exogenous bFGF at standard concentrations (20 ng/mL) led to a dramatic change in the morphology of astrocytes, increased spontaneous DA release, and inhibited synapse formation by individual DA neurons. RNA interference (siRNA) against bFGF mRNA, caused a reduction in DA release but produced no change in synaptic development. Together these data demonstrate that under basal conditions (in the absence of a pharmacological stimulus such as amphetamine) bFGF is not secreted even though there is abundant nuclear expression in astrocytes. The effects of bFGF seen here on DA neurons are thus likely to be mediated through more indirect glial-neuronal interactions, leading to enhanced DA release without a necessary change in synapse number.

Factors controlling fibroblast growth factor receptor-1's cytoplasmic trafficking and its regulation as revealed by FRAP analysis

Biochemical and microscopic studies have indicated that FGFR1 is a transmembrane and soluble protein present in the cytosol and nucleus. How FGFR1 enters the cytosol and subsequently the nucleus to control cell development and associated gene activities has become a compelling question. Analyses of protein synthesis, cytoplasmic subcompartmental distribution and movement of FGFR1-EGFP and FGFR1 mutants showed that FGFR1 exists as three separate populations (a) a newly synthesized, highly mobile, nonglycosylated, cytosolic receptor that is depleted by brefeldin A and resides outside the ER-Golgi lumen, (b) a slowly diffusing membrane receptor population, and (c) an immobile membrane pool increased by brefeldin A. RSK1 increases the highly mobile cytosolic FGFR1 population and its overall diffusion rate leading to increased FGFR1 nuclear accumulation, which coaccumulates with RSK1. A model is proposed in which newly synthesized FGFR1 can enter the (a) "nuclear pathway," where the nonglycosylated receptor is extruded from the pre-Golgi producing highly mobile cytosolic receptor molecules that rapidly accumulate in the nucleus or (b) "membrane pathway," in which FGFR1 is processed through the Golgi, where its movement is spatially restricted to trans-Golgi membranes with limited lateral mobility. Entrance into the nuclear pathway is favored by FGFR1's interaction with kinase active RSK1.

The IA-2 interactome

AIMS/HYPOTHESIS

Islet antigen-2 (IA-2), a major autoantigen in type 1 diabetes, is an enzymatically inactive member of the transmembrane protein tyrosine phosphatase (PTP) family. IA-2 is located in dense-core secretory vesicles and is involved in the regulation of insulin secretion. The present experiments were initiated to identify those proteins that interact with IA-2 (i.e. the IA-2 interactome) as a first step towards elucidating the mechanism(s) by which IA-2 influences insulin secretion and serves as an autoantigen.

MATERIALS AND METHODS

To determine the proteins with which IA-2 interacts, a yeast two-hybrid system was used to screen a human foetal library, and deletion mutants were used to determine the binding sites. Positive interactions were confirmed by immunoprecipitation pull-down experiments using cell lysate from transfected mammalian cell lines.

RESULTS

Six new interacting proteins were identified by this approach: mitogen-activated protein kinase-activating death domain (MADD), the MADD isoform IG20, PTPrho, PTPsigma, sorting nexin 19 (SNX19) and cyclophilin A. Using a series of IA-2 deletion mutants, we identified the regions on the IA-2 molecule to which five of the interacting proteins bound. Amino acids 744-979 of IA-2 were required for the maximum binding of MADD, IG20 and SNX19, whereas amino acids 602-907 of IA-2 were required for the maximum binding of PTPrho and PTPsigma. Pull-down experiments with cell lysate from transfected mammalian cells confirmed the binding of the interacting proteins to IA-2.

CONCLUSIONS/INTERPRETATION

The IA-2 interactome based on, pull-down experiments, currently consists of 12 proteins. The identification of these interacting proteins provides clues as to how IA-2 exerts its biological functions.

Organically modified silica nanoparticles: a nonviral vector for in vivo gene delivery and expression in the brain

This article reports on the application of organically modified silica (ORMOSIL) nanoparticles as a nonviral vector for efficient in vivo gene delivery. Highly monodispersed, stable aqueous suspension of nanoparticles, surface-functionalized with amino groups for binding of DNA, were prepared and characterized. Stereotaxic injections of nanoparticles, complexed with plasmid DNA encoding for EGFP, into the mouse ventral midbrain and into lateral ventricle, allowed us to fluorescently visualize the extensive transfection of neuronal-like cells in substantia nigra and areas surrounding the lateral ventricle. No ORMOSIL-based toxicity was observed 4 weeks after transfection. The efficiency of transfection equaled or exceeded that obtained in studies using a viral vector. An in vivo optical imaging technique (a fiber-based confocal fluorescent imaging system) provided an effective means to show the retention of viability of the transfected cells. The ORMOSIL-mediated transfections also were used to manipulate the biology of the neural stem/progenitor cells in vivo. Transfection of a plasmid expressing the nucleus-targeting fibroblast growth factor receptor type 1 resulted in significant inhibition of the in vivo incorporation of bromodeoxyuridine into the DNA of the cells in the subventricular zone and the adjacent rostral migratory stream. This in vivo approach shows that the nuclear receptor can control the proliferation of the stem/progenitor cells in this region of the brain. The results of this nanomedicine approach using ORMOSIL nanoparticles as a nonviral gene delivery platform have a promising future direction for effective therapeutic manipulation of the neural stem/progenitor cells as well as in vivo targeted brain therapy.

Nuclear Translocation of Cell-Surface Receptors: Lessons from Fibroblast Growth Factor

The nuclear localization of a number of growth factors, cytokine ligands and their receptors has been reported in various cell lines and tissues. These include members of the fibroblast growth factor (FGF), epidermal growth factor and growth hormone families. Accordingly, a number of nuclear functions have begun to emerge for these protein families. The demonstration of functional interactions of these proteins with the nuclear import machinery has further supported their functions as nuclear signal transducers. Here, we review the membrane- trafficking machinery and pathways demonstrated to regulate this cell surface to nucleus-trafficking event and highlight the many remaining unanswered questions. We focus on the FGF family, which is providing many of the clues as to the process of this unusual phenomenon.

Control of CREB-binding Protein Signaling by Nuclear Fibroblast Growth Factor Receptor-1

In integrative nuclear fibroblast growth factor receptor-1 (FGFR1) signaling a newly synthesized FGFR1 translocates to the nucleus to stimulate cell differentiation and associated gene activities. The present study shows that FGFR1 accumulates and interacts with the transcriptional co-activator CREB-binding protein (CBP) in nuclear speckle domains in the developing brain and in neural progenitor-like cells in vitro, which accompanies differentiation and postmitotic growth. Cell differentiation and gene activation by nuclear FGFR1 do not require tyrosine kinase activity. Instead, FGFR1 stimulates transcription in cooperation with CBP by increasing recruitment of RNA polymerase II and histone acetylation at the active gene promoter. FGFR1 is a multifactorial protein whose N terminus interacts with CBP and C terminus with ribosomal S6 kinase 1 (RSK1). Nuclear FGFR1 augments CBP-mediated transcription by 1) releasing the CBP C-terminal domain from RSK1 inhibition and 2) activating the CBP N-terminal domain. The interaction of FGFR1 with CBP and RSK1 allows activation of gene transcription and may play a role in cell differentiation.

Exogenously Added Fibroblast Growth Factor 2 (FGF-2) to NIH3T3 CellsInteracts with Nuclear Ribosomal S6 Kinase 2 (RSK2) in a Cell Cycle-dependentManner

Fibroblast growth factor 2 (FGF-2) has been detected in the nuclei of many tissues and cell lines. Here we demonstrate that FGF-2 added exogenously to NIH3T3 cells enters the nucleus and interacts with the nuclear active 90-kDa ribosomal S6 kinase 2 (RSK2) in a cell cycle-dependent manner. By using purified proteins, FGF-2 is shown to directly interact through two separate domains with two RSK2 domains on both sides of the hydrophobic motif, namely the NH2-terminal kinase domain (residues 360-381) by amino acid Ser-117 and the COOH-terminal kinase domain (residues 388-400) by amino acids Leu-127 and Lys-128. Moreover, this interaction leads to maintenance of the sustained activation of RSK2 in G1 phase of the cell cycle. FGF-2 mutants (FGF-2 S117A, FGF-2 L127A, and FGF-2 K128A) that fail to interact in vitro with RSK2 fail to maintain a sustained RSK2 activity in vivo.