FGF signaling regulates salivary gland branching morphogenesis by modulating cell adhesion

Loss of FGF signaling leads to defects in salivary gland branching, but the mechanisms underlying this phenotype remain largely unknown. We disrupted expression of Fgfr1 and Fgfr2 in salivary gland epithelial cells and found that both receptors function coordinately in regulating branching. Strikingly, branching morphogenesis in double knockouts is restored by Fgfr1 and Fgfr2 (Fgfr1/2) knock-in alleles incapable of engaging canonical RTK signaling, suggesting that additional FGF-dependent mechanisms play a role in salivary gland branching. Fgfr1/2 conditional null mutants showed defective cell-cell and cell-matrix adhesion, both of which have been shown to play instructive roles in salivary gland branching. Loss of FGF signaling led to disordered cell-basement membrane interactions in vivo as well as in organ culture. This was partially restored upon introducing Fgfr1/2 wild-type or signaling alleles that are incapable of eliciting canonical intracellular signaling. Together, our results identify non-canonical FGF signaling mechanisms that regulate branching morphogenesis through cell-adhesion processes.

Single-Cell RNA Sequencing Technology Revealed the Pivotal Role of Fibroblast Heterogeneity in Angiotensin II-Induced Abdominal Aortic Aneurysms

The mechanism of abdominal aortic aneurysm (AAA) has not been fully elucidated. In this study, we aimed to map the cellular heterogeneity, molecular alteration, and functional transformation of angiotensin (Ang) II-induced AAA in mice based on single-cell RNA sequencing (sc-RNA seq) technology. sc-RNA seq was performed on suprarenal abdominal aorta tissue from male Apoe^-/- C57BL/6 mice of Ang II-induced AAA and shame models to determine the heterogeneity and phenotypic transformation of all cells. Immunohistochemistry was used to determine the pathophysiological characteristics of AAA. The single-cell trajectory was performed to predict the differentiation of fibroblasts. Finally ligand-receptor analysis was used to evaluate intercellular communication between fibroblasts and smooth muscle cells (SMCs). More than 27,000 cells were isolated and 25 clusters representing 8 types of cells were identified, including fibroblasts, macrophages, endothelial cells, SMCs, T lymphocytes, B lymphocytes, granulocytes, and natural killer cells. During AAA progression, the function and phenotype of different type cells altered separately, including activation of inflammatory cells, alternations of macrophage polarization, phenotypic transformation of vascular smooth muscle cells, and endothelial to mesenchymal transformation. The alterations of fibroblasts were the most conspicuous. Single-cell trajectory revealed the critical reprogramming genes of fibroblasts mainly enriched in regulation of immune system. Finally, the ligand-receptor analysis confirmed that disorder of collagen metabolism led by fibroblasts was one of the most prominent characteristics of Ang II-induced AAA. Our study revealed the cellular heterogeneity of Ang II-induced AAA. Fibroblasts may play a critical role in Ang II-induced AAA progression according to multiple biological functions, including immune regulation and extracellular matrix metabolic balance. Our study may provide us with a different perspective on the etiology and pathogenesis of AAA.

Exploring the FGF/FGFR System in Ocular Tumors: New Insights and Perspectives

Ocular tumors are a family of rare neoplasms that develop in the eye. Depending on the type of cancer, they mainly originate from cells localized within the retina, the uvea, or the vitreous. Even though current treatments (e.g., radiotherapy, transpupillary thermotherapy, cryotherapy, chemotherapy, local resection, or enucleation) achieve the control of the local tumor in the majority of treated cases, a significant percentage of patients develop metastatic disease. In recent years, new targeting therapies and immuno-therapeutic approaches have been evaluated. Nevertheless, the search for novel targets and players is eagerly required to prevent and control tumor growth and metastasis dissemination. The fibroblast growth factor (FGF)/FGF receptor (FGFR) system consists of a family of proteins involved in a variety of physiological and pathological processes, including cancer. Indeed, tumor and stroma activation of the FGF/FGFR system plays a relevant role in tumor growth, invasion, and resistance, as well as in angiogenesis and dissemination. To date, scattered pieces of literature report that FGFs and FGFRs are expressed by a significant subset of primary eye cancers, where they play relevant and pleiotropic roles. In this review, we provide an up-to-date description of the relevant roles played by the FGF/FGFR system in ocular tumors and speculate on its possible prognostic and therapeutic exploitation.

Pulling back the curtain: The hidden functions of receptor tyrosine kinases in development

Receptor tyrosine kinases (RTKs) are a conserved superfamily of transmembrane growth factor receptors that drive numerous cellular processes during development and in the adult. Upon activation, multiple adaptors and signaling effector proteins are recruited to binding site motifs located within the intracellular domain of the RTK. These RTK-effector interactions drive subsequent intracellular signaling cascades involved in canonical RTK signaling. Genetic dissection has revealed that alleles of Fibroblast Growth Factor receptors (FGFRs) that lack all canonical RTK signaling still retain some kinase-dependent biological activity. Here we examine how genetic analysis can be used to understand the mechanism by which RTKs drive multiple developmental processes via canonical signaling while revealing noncanonical activities. Recent data from both FGFRs and other RTKs highlight potential noncanonical roles in cell adhesion and nuclear signaling. The data supporting such functions are discussed as are recent technologies that have the potential to provide valuable insight into the developmental significance of these noncanonical activities.

Vitamin D Actions: The Lung Is a Major Target for Vitamin D, FGF23, and Klotho

Vitamin D is well known for its role as a calcium regulator and in maintenance of phosphate homeostasis in musculoskeletal health, and fibroblast growth factor 23 (FGF23) and its coreceptor α-klotho are known for their roles as regulators of serum phosphate levels. However, apart from these classical actions, recent data point out a relevant role of vitamin D and FGF23/klotho in lung health. The expression of the vitamin D receptor by different cell types in the lung and the fact that those cells respond to vitamin D or can locally produce vitamin D indicate that the lung represents a target for vitamin D actions. Similarly, the presence of the four FGF receptor isoforms in the lung and the ability of FGF23 to stimulate pulmonary cells support the concept that the lung is a target for FGF23 actions, whereas the contribution of klotho is still undetermined. This review will give an overview on how vitamin D or FGF23/klotho may act on the lung and interfere positively or negatively with lung health. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

The polyfunctional polysialic acid: A structural view

Polysialic acid (polySia), a homopolymer of α2,8-linked sialic acid residues, modifies a small number of proteins and has central functions in vertebrate signalling. Here, we review the regulatory functions of polySia in signalling processes and the immune system of adult humans, as well as functions based on their chemical properties. The main focus will be on the structure-function relationship of polySia with its interaction partners in humans. Recent studies have indicated that the degree of polymerisation is an important parameter that can guide the regulatory effect of polySia in addition to its binding to target proteins. Therefore, the structures of polySia in solution and bound to interaction partners are compared in order to identify the key factors that define binding specificity.

Fibroblast Growth Factor Signalling in the Diseased Nervous System

Fibroblast growth factors (FGFs) act as key signalling molecules in brain development, maintenance, and repair. They influence the intricate relationship between myelinating cells and axons as well as the association of astrocytic and microglial processes with neuronal perikarya and synapses. Advances in molecular genetics and imaging techniques have allowed novel insights into FGF signalling in recent years. Conditional mouse mutants have revealed the functional significance of neuronal and glial FGF receptors, not only in tissue protection, axon regeneration, and glial proliferation but also in instant behavioural changes. This review provides a summary of recent findings regarding the role of FGFs and their receptors in the nervous system and in the pathogenesis of major neurological and psychiatric disorders.

Role of Fibroblast Growth Factors Receptors (FGFRs) in Brain Tumors, Focus on Astrocytoma and Glioblastoma

Despite pharmacological treatments and surgical practice options, the mortality rate of astrocytomas and glioblastomas remains high, thus representing a medical emergency for which it is necessary to find new therapeutic strategies. Fibroblast growth factors (FGFs) act through their associated receptors (FGFRs), a family of tyrosine kinase receptors consisting of four members (FGFR1-4), regulators of tissue development and repair. In particular, FGFRs play an important role in cell proliferation, survival, and migration, as well as angiogenesis, thus their gene alteration is certainly related to the development of the most common diseases, including cancer. FGFRs are subjected to multiple somatic aberrations such as chromosomal amplification of FGFR1; mutations and multiple dysregulations of FGFR2; and mutations, translocations, and significant amplifications of FGFR3 and FGFR4 that correlate to oncogenesis process. Therefore, the in-depth study of these receptor systems could help to understand the etiology of both astrocytoma and glioblastoma so as to achieve notable advances in more effective target therapies. Furthermore, the discovery of FGFR inhibitors revealed how these biological compounds improve the neoplastic condition by demonstrating efficacy and safety. On this basis, this review focuses on the role and involvement of FGFRs in brain tumors such as astrocytoma and glioblastoma.

Leucocyte-Rich Platelet-Rich Plasma Enhances Fibroblast and Extracellular Matrix Activity: Implications in Wound Healing

Background: Platelet-rich plasma (PRP) is an autologous blood product that contains a high concentration of platelets and leucocytes, which are fundamental fibroblast proliferation agents. Literature has emerged that offers contradictory findings about leucocytes within PRP. Herein, we elucidated the effects of highly concentrated leucocytes and platelets on human fibroblasts. Methods: Leucocyte-rich, PRP (LR-PRP) and leucocyte-poor, platelet-poor plasma (LP-PPP) were compared to identify their effects on human fibroblasts, including cell proliferation, wound healing and extracellular matrix and adhesion molecule gene expressions. Results: The LR-PRP exhibited 1422.00 ± 317.21 × 10³ platelets/µL and 16.36 ± 2.08 × 10³ white blood cells/µL whilst the LP-PPP demonstrated lower concentrations of 55.33 ± 10.13 × 10³ platelets/µL and 0.8 ± 0.02 × 10³ white blood cells/µL. LR-PRP enhanced fibroblast cell proliferation and cell migration, and demonstrated either upregulation or down-regulation gene expression profile of the extracellular matrix and adhesion molecules. Conclusion: LR-PRP has a continuous stimulatory anabolic and ergogenic effect on human fibroblast cells.

Polysialylation and disease

Polysialic acid (polySia, PSA) is a unique constituent of the glycocalyx on the surface of bacterial and vertebrate cells. In vertebrates, its biosynthesis is highly regulated, not only in quantity and quality, but also in time and location, which allows polySia to be involved in various important biological phenomena. Therefore, impairments in the expression and structure of polySia sometimes relate to diseases, such as schizophrenia, bipolar disorder, and cancer. Some bacteria express polySia as a tool for protecting themselves from the host immune system during invasion. PolySia is proven to be a biosafe material; polySia, as well as polySia-recognizing molecules, are key therapeutic agents. This review first comprehensive outlines the occurrence, features, biosynthesis, and functions of polySia and subsequently focuses on the related diseases.

RET-independent signaling by GDNF ligands and GFRα receptors

The discovery in the late 1990s of the partnership between the RET receptor tyrosine kinase and the GFRα family of GPI-anchored co-receptors as mediators of the effects of GDNF family ligands galvanized the field of neurotrophic factors, firmly establishing a new molecular framework besides the ubiquitous neurotrophins. Soon after, however, it was realized that many neurons and brain areas expressed GFRα receptors without expressing RET. These observations led to the formulation of two new concepts in GDNF family signaling, namely, the non-cell-autonomous functions of GFRα molecules, so-called trans signaling, as well as cell-autonomous functions mediated by signaling receptors distinct from RET, which became known as RET-independent signaling. To date, the best studied RET-independent signaling pathway for GDNF family ligands involves the neural cell adhesion molecule NCAM and its association with GFRα co-receptors. Among the many functions attributed to this signaling system are neuronal migration, neurite outgrowth, dendrite branching, spine formation, and synaptogenesis. This review summarizes our current understanding of this and other mechanisms of RET-independent signaling by GDNF family ligands and GFRα receptors, as well as their physiological importance.

Global responses to tris(1-chloro-2-propyl)phosphate (TCPP) in rockfish Sebastes schlegeli using integrated proteomic and metabolomic approach

As alternatives of brominated flame retardants, organophosphate flame retardants (OPFRs) can be detected in multiple marine environmental media. Tris(1-chloro-2-propyl)phosphate (TCPP) was one of the most frequently and abundantly detected OPFRs in the Bohai Sea. Exposure to TCPP has been shown to induce abnormal behavior in zebrafish as well as neurotoxicity in Caenorhabditis elegans. However, there is a lack of mechanism investigations on the toxic effects of TCPP at molecular levels. In this work, proteomics and metabolomics were integrated to analyze the proteome and metabolome responses in rockfish Sebastes schlegeli treated with TCPP (10 and 100 nM) for 15 days. A total of 143 proteins and 8 metabolites were significantly altered in rockfish following TCPP treatments. The responsive proteins and metabolites were predominantly involved in neurotransmission, neurodevelopment, signal transduction, cellular transport, cholesterol metabolism, bile acid synthesis, and detoxification. Furthermore, a hypothesized network of proteins, metabolites, and pathways in rockfish was summarized based on the combination of proteomic and metabolomic results, showing some key molecular events in response to TCPP. Overall, the present study unraveled the molecular responses at protein and metabolite levels, which provided a better understanding of toxicological effects and mechanisms of TCPP in marine teleost.

NCAM1/FGF module serves as a putative pleuropulmonary blastoma therapeutic target

Pleuropulmonary blastoma (PPB) is a rare pediatric lung neoplasm that recapitulates developmental pathways of early embryonic lungs. As lung development proceeds with highly regulated mesenchymal-epithelial interactions, a DICER1 mutation in PPB generates a faulty lung differentiation program with resultant biphasic tumors composed of a primitive epithelial and mesenchymal stroma with early progenitor blastomatous cells. Deciphering of PPB progression has been hampered by the difficulty of culturing PPB cells, and specifically progenitor blastomatous cells. Here, we show that in contrast with in-vitro culture, establishment of PPB patient-derived xenograft (PDX) in NOD-SCID mice selects for highly proliferating progenitor blastoma overexpressing critical regulators of lung development and multiple imprinted genes. These stem-like tumors were sequentially interrogated by gene profiling to show a FGF module that is activated alongside Neural cell adhesion molecule 1 (NCAM1). Targeting the progenitor blastoma and these transitions with an anti-NCAM1 immunoconjugate (Lorvotuzumab mertansine) inhibited tumor growth and progression providing new paradigms for PPB therapeutics. Altogether, our novel in-vivo PPB xenograft model allowed us to enrich for highly proliferating stem-like cells and to identify FGFR and NCAM1 as two key players that can serve as therapeutic targets in this poorly understood and aggressive disease.

The Role of Fibroblast Growth Factor 23 in Inflammation and Anemia

In patients with chronic kidney disease (CKD), adverse outcomes such as systemic inflammation and anemia are contributing pathologies which increase the risks for cardiovascular mortality. Amongst these complications, abnormalities in mineral metabolism and the metabolic milieu are associated with chronic inflammation and iron dysregulation, and fibroblast growth factor 23 (FGF23) is a risk factor in this context. FGF23 is a bone-derived hormone that is essential for regulating vitamin D and phosphate homeostasis. In the early stages of CKD, serum FGF23 levels rise 1000-fold above normal values in an attempt to maintain normal phosphate levels. Despite this compensatory action, clinical CKD studies have demonstrated powerful and dose-dependent associations between FGF23 levels and higher risks for mortality. A prospective pathomechanism coupling elevated serum FGF23 levels with CKD-associated anemia and cardiovascular injury is its strong association with chronic inflammation. In this review, we will examine the current experimental and clinical evidence regarding the role of FGF23 in renal physiology as well as in the pathophysiology of CKD with an emphasis on chronic inflammation and anemia.

Fibroblast Growth Factor Receptor Functions in Glioblastoma

Glioblastoma is the most lethal brain cancer in adults, with no known cure. This cancer is characterized by a pronounced genetic heterogeneity, but aberrant activation of receptor tyrosine kinase signaling is among the most frequent molecular alterations in glioblastoma. Somatic mutations of fibroblast growth factor receptors (FGFRs) are rare in these cancers, but many studies have documented that signaling through FGFRs impacts glioblastoma progression and patient survival. Small-molecule inhibitors of FGFR tyrosine kinases are currently being trialed, underlining the therapeutic potential of blocking this signaling pathway. Nevertheless, a comprehensive overview of the state of the art of the literature on FGFRs in glioblastoma is lacking. Here, we review the evidence for the biological functions of FGFRs in glioblastoma, as well as pharmacological approaches to targeting these receptors.

Cross-Talk between Fibroblast Growth Factor Receptors and Other Cell Surface Proteins

Fibroblast growth factors (FGFs) and their receptors (FGFRs) constitute signaling circuits that transmit signals across the plasma membrane, regulating pivotal cellular processes like differentiation, migration, proliferation, and apoptosis. The malfunction of FGFs/FGFRs signaling axis is observed in numerous developmental and metabolic disorders, and in various tumors. The large diversity of FGFs/FGFRs functions is attributed to a great complexity in the regulation of FGFs/FGFRs-dependent signaling cascades. The function of FGFRs is modulated at several levels, including gene expression, alternative splicing, posttranslational modifications, and protein trafficking. One of the emerging ways to adjust FGFRs activity is through formation of complexes with other integral proteins of the cell membrane. These proteins may act as coreceptors, modulating binding of FGFs to FGFRs and defining specificity of elicited cellular response. FGFRs may interact with other cell surface receptors, like G-protein-coupled receptors (GPCRs) or receptor tyrosine kinases (RTKs). The cross-talk between various receptors modulates the strength and specificity of intracellular signaling and cell fate. At the cell surface FGFRs can assemble into large complexes involving various cell adhesion molecules (CAMs). The interplay between FGFRs and CAMs affects cell–cell interaction and motility and is especially important for development of the central nervous system. This review summarizes current stage of knowledge about the regulation of FGFRs by the plasma membrane-embedded partner proteins and highlights the importance of FGFRs-containing membrane complexes in pathological conditions, including cancer.

Endocytosis and Transport of Growth Factor Receptors in Peripheral Axon Regeneration: Novel Lessons from Neurons Expressing Lysine-Deficient FGF Receptor Type 1 in vitro

In the course of peripheral nerve regeneration, axons encounter different extracellular growth factors secreted by non‐neuronal cells at the injury site and retrogradely transported after binding to neuronal membrane receptor tyrosine kinases. The present study reviews the role of receptor transport in peripheral axon outgrowth and provides novel data on trafficking of fibroblast growth factor receptor type 1 (FGFR1). Differences in receptor transport are determined by different numbers of lysine residues acting as ubiquitination sites in the intracellular receptor domain. We previously demonstrated that overexpression of mutant FGFR1‐25R (25 out of 29 intracellular lysines replaced with arginine) results in enhanced receptor recycling as compared to wild‐type FGFR1 followed by strong stimulation of elongative axon growth in vitro. Here, the effects of lysine‐deficient FGFR1 (FGFR1‐29R lacking all 29 cytoplasmic lysine residues) or of only 15 lysine mutations (FGFR1‐15R) on axon outgrowth and concomitant changes in signal pathway activation were investigated by immunocytochemistry and morphometry of cultured primary neurons. Overexpression of FGFR1‐15R in adult sensory neurons resulted in enhanced receptor recycling, which was accompanied by increased axon elongation without stimulating axon branching. By contrast, FGFR1‐29R was neither endocytosed nor axon outgrowth affected. Although overexpression of FGFR1‐15R or FGFR1‐25Ra strongly promoted elongation, we did not detect increased signal pathway activation (ERK, AKT, PLC, or STAT3) in neurons expressing mutant FGFR1 as compared with wild‐type neurons raising the possibility that other signaling pathways or signaling independent mechanisms may be involved in the axon outgrowth effects of recycled FGF receptors. Anat Rec, 302:1268–1275, 2019. © 2019 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Number and brightness analysis reveals that NCAM and FGF2 elicit different assembly and dynamics of FGFR1 in live cells

Both fibroblast growth factor-2 (FGF2) and neural cell adhesion molecule (NCAM) trigger FGF receptor 1 (FGFR1) signaling; however, they induce remarkably distinct receptor trafficking and cellular responses. The molecular basis of such a dichotomy and the role of distinct types of ligand-receptor interaction remain elusive. Number of molecules and brightness (N&B) analysis revealed that FGF2 and NCAM promote different FGFR1 assembly and dynamics at the plasma membrane. NCAM stimulation elicits long-lasting cycles of short-lived FGFR1 monomers and multimers, a behavior that might reflect a rapid FGFR1 internalization and recycling. FGF2, instead, induces stable dimerization at the dose that stimulates cell proliferation. Reducing the occupancy of FGFR1 in response to low FGF2 doses causes a switch towards cyclically exposed and unstable receptor dimers, consistently with previously reported biphasic response to FGF2 and with the divergent signaling elicited by different ligand concentrations. Similar instability was observed upon altering the endocytic pathway. Thus, FGF2 and NCAM induce differential FGFR1 clustering at the cell surface, which might account for the distinct intracellular fate of the receptor and, hence, for the different signaling cascades and cellular responses.

Sialic Acids in Neurology

Sialic acid (Sia) is involved in many biological activities and commonly occurs as a monosialyl residue at the nonreducing terminal end of glycoconjugates. The loss of activity of UDP-GlcNAc2-epimerase/ManNAc kinase, which is a key enzyme in Sia biosynthesis, is lethal to the embryo, which clearly indicates the importance of Sia in embryogenesis. Occasionally, oligo/polymeric Sia structures such as disialic acid (diSia), oligosialic acid (oligoSia), and polysialic acid (polySia) occur in glycoconjugates. In particular, polySia, a well-known epitope that commonly occurs in neuroinvasive bacteria and vertebrate brains, is one of the most well-known and biologically/neurologically important glycotopes in vertebrates. The biological effects of polySia, especially on neural cell-adhesion molecules, have been well studied, and in-depth knowledge regarding polySia has been accumulated. In addition, the importance of diSia and oligoSia epitopes has been reported. In this chapter, the recent advances in the study of diSia, oligoSia, and polySia residues in glycoproteins in neurology, and their history, definition, occurrence, analytical methods, biosynthesis, and biological functions evaluated by phenotypes of gene-targeted mice, biochemical features, and related diseases are described.

GDNF/GFRα1 Complex Abrogates Self-Renewing Activity of Cortical Neural Precursors Inducing Their Differentiation

The balance between factors leading to proliferation and differentiation of cortical neural precursors (CNPs) determines the correct cortical development. In this work, we show that GDNF and its receptor GFRα1 are expressed in the neocortex during the period of cortical neurogenesis. We show that the GDNF/GFRα1 complex inhibits the self-renewal capacity of mouse CNP cells induced by fibroblast growth factor 2 (FGF2), promoting neuronal differentiation. While GDNF leads to decreased proliferation of cultured cortical precursor cells, ablation of GFRα1 in glutamatergic cortical precursors enhances its proliferation. We show that GDNF treatment of CNPs promoted morphological differentiation even in the presence of the self-renewal-promoting factor, FGF2. Analysis of GFRα1-deficient mice shows an increase in the number of cycling cells during cortical development and a reduction in dendrite development of cortical GFRα1-expressing neurons. Together, these results indicate that GDNF/GFRα1 signaling plays an essential role in regulating the proliferative condition and the differentiation of cortical progenitors.

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GFRα1 receptor is expressed in the neocortex during the period of neurogenesis

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GDNF/GFRα1 complex inhibits self-renewing of cortical neuronal precursors

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GDNF and GFRα1 promote neurogenic differentiation of cortical neural progenitors

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Requirement of GFRα1 for proper dendrite development of cortical neurons

FGF23 Actions on Target Tissues-With and Without Klotho

Fibroblast growth factor (FGF) 23 is a phosphaturic hormone whose physiologic actions on target tissues are mediated by FGF receptors (FGFR) and klotho, which functions as a co-receptor that increases the binding affinity of FGF23 for FGFRs. By stimulating FGFR/klotho complexes in the kidney and parathyroid gland, FGF23 reduces renal phosphate uptake and secretion of parathyroid hormone, respectively, thereby acting as a key regulator of phosphate metabolism. Recently, it has been shown that FGF23 can also target cell types that lack klotho. This unconventional signaling event occurs in an FGFR-dependent manner, but involves other downstream signaling pathways than in "classic" klotho-expressing target organs. It appears that klotho-independent signaling mechanisms are only activated in the presence of high FGF23 concentrations and result in pathologic cellular changes. Therefore, it has been postulated that massive elevations in circulating levels of FGF23, as found in patients with chronic kidney disease, contribute to associated pathologies by targeting cells and tissues that lack klotho. This includes the induction of cardiac hypertrophy and fibrosis, the elevation of inflammatory cytokine expression in the liver, and the inhibition of neutrophil recruitment. Here, we describe the signaling and cellular events that are caused by FGF23 in tissues lacking klotho, and we discuss FGF23's potential role as a hormone with widespread pathologic actions. Since the soluble form of klotho can function as a circulating co-receptor for FGF23, we also discuss the potential inhibitory effects of soluble klotho on FGF23-mediated signaling which might-at least partially-underlie the pleiotropic tissue-protective functions of klotho.

Cooperation of HIF- and NCAM-mediated mechanisms in cell viability of hippocampal cultures after oxygen-glucose deprivation

Neurodegenerative diseases of different genesis are the result of cellular damages including those caused by oxygen and glucose deficit. Neuronal survival or death in brain pathologies depends on a variety of interrelated molecular mechanisms. A key role in modulation of neuron viability belongs to HIF (hypoxia-inducible factor) and NCAM (neural cell adhesion molecules) signaling pathways. In this work, we used organotypic and dissociated hippocampal cultures to analyze cell viability and HIF-1α immunopositive (HIF-1α⁺ ) signal after 30 min oxygen-glucose deprivation (OGD) followed by 24 h of reoxygenation in the presence of FGL (synthetic NCAM-derived mimetic peptide). According to LDH- and MTS-assay of cell viability, FGL showed a neuroprotective effect, which was attributed to the association with FGFR. We showed that these effects correlated with changes of the HIF-1α⁺ level suggesting the communications of HIF and NCAM signaling pathways. These data extend our knowledge of neurodegeneration mechanisms and open additional potential for the development of neuroprotection strategies.

Gene expression profile in human induced pluripotent stem cells: Chondrogenic differentiation in vitro, part A

Human induced pluripotent stem cells (hiPSCs) offer promise in regenerative medicine, however more data are required to improve understanding of key aspects of the cell differentiation process, including how specific chondrogenic processes affect the gene expression profile of chondrocyte-like cells and the relative value of cell differentiation markers. The main aims of the present study were as follows: To determine the gene expression profile of chondrogenic-like cells derived from hiPSCs cultured in mediums conditioned with HC-402-05a cells or supplemented with transforming growth factor β3 (TGF-β3), and to assess the relative utility of the most commonly used chondrogenic markers as indicators of cell differentiation. These issues are relevant with regard to the use of human fibroblasts in the reprogramming process to obtain hiPSCs. Human fibroblasts are derived from the mesoderm and thus share a wide range of properties with chondrocytes, which also originate from the mesenchyme. Thus, the exclusion of dedifferentiation instead of chondrogenic differentiation is crucial. The hiPSCs were obtained from human primary dermal fibroblasts during a reprogramming process. Two methods, both involving embryoid bodies (EB), were used to obtain chondrocytes from the hiPSCs: EBs formed in a chondrogenic medium supplemented with TGF-β3 (10 ng/ml) and EBs formed in a medium conditioned with growth factors from HC-402-05a cells. Based on immunofluorescence and reverse transcription-quantiative polymerase chain reaction analysis, the results indicated that hiPSCs have the capacity for effective chondrogenic differentiation, in particular cells differentiated in the HC-402-05a-conditioned medium, which present morphological features and markers that are characteristic of mature human chondrocytes. By contrast, cells differentiated in the presence of TGF-β3 may demonstrate hypertrophic characteristics. Several genes [paired box 9, sex determining region Y-box (SOX) 5, SOX6, SOX9 and cartilage oligomeric matrix protein] were demonstrated to be good markers of early hiPSC chondrogenic differentiation: Insulin-like growth factor 1, Tenascin-C, and β-catenin were less valuable. These observations provide valuable data on the use of hiPSCs in cartilage tissue regeneration.

Integration of gene expression and methylation to unravel biological networks in glioblastoma patients

The vast amount of heterogeneous omics data, encompassing a broad range of biomolecular information, requires novel methods of analysis, including those that integrate the available levels of information. In this work, we describe Regression2Net, a computational approach that is able to integrate gene expression and genomic or methylation data in two steps. First, penalized regressions are used to build Expression-Expression (EEnet) and Expression-Genomic or Expression-Methylation (EMnet) networks. Second, network theory is used to highlight important communities of genes. When applying our approach, Regression2Net to gene expression and methylation profiles for individuals with glioblastoma multiforme, we identified, respectively, 284 and 447 potentially interesting genes in relation to glioblastoma pathology. These genes showed at least one connection in the integrated networks ANDnet and XORnet derived from aforementioned EEnet and EMnet networks. Although the edges in ANDnet occur in both EEnet and EMnet, the edges in XORnet occur in EMnet but not in EEnet. In-depth biological analysis of connected genes in ANDnet and XORnet revealed genes that are related to energy metabolism, cell cycle control (AATF), immune system response, and several cancer types. Importantly, we observed significant overrepresentation of cancer-related pathways including glioma, especially in the XORnet network, suggesting a nonignorable role of methylation in glioblastoma multiforma. In the ANDnet, we furthermore identified potential glioma suppressor genes ACCN3 and ACCN4 linked to the NBPF1 neuroblastoma breakpoint family, as well as numerous ABC transporter genes (ABCA1, ABCB1) suggesting drug resistance of glioblastoma tumors.

Immunophenotyping Reveals the Diversity of Human Dental Pulp Mesenchymal Stromal Cells In vivo and Their Evolution upon In vitro Amplification

Mesenchymal stromal/stem cells (MSCs) from human dental pulp (DP) can be expanded in vitro for cell-based and regenerative dentistry therapeutic purposes. However, their heterogeneity may be a hurdle to the achievement of reproducible and predictable therapeutic outcomes. To get a better knowledge about this heterogeneity, we designed a flow cytometric strategy to analyze the phenotype of DP cells in vivo and upon in vitro expansion with stem cell markers. We focused on the CD31⁻ cell population to exclude endothelial and leukocytic cells. Results showed that the in vivo CD31⁻ DP cell population contained 1.4% of CD56⁺, 1.5% of CD146⁺, 2.4% of CD271⁺ and 6.3% of MSCA-1⁺ cells but very few Stro-1⁺ cells (≤ 1%). CD56⁺, CD146⁺, CD271⁺, and MSCA-1⁺ cell subpopulations expressed various levels of these markers. CD146⁺MSCA-1⁺, CD271⁺MSCA-1⁺, and CD146⁺CD271⁺ cells were the most abundant DP-MSC populations. Analysis of DP-MSCs expanded in vitro with a medicinal manufacturing approach showed that CD146 was expressed by about 50% of CD56⁺, CD271⁺, MSCA-1⁺, and Stro-1⁺ cells, and MSCA-1 by 15–30% of CD56⁺, CD146⁺, CD271⁺, and Stro-1⁺ cells. These ratios remained stable with passages. CD271 and Stro-1 were expressed by <1% of the expanded cell populations. Interestingly, the percentage of CD56⁺ cells strongly increased from P1 (25%) to P4 (80%) both in all sub-populations studied. CD146⁺CD56⁺, MSCA-1⁺CD56⁺, and CD146⁺MSCA-1⁺ cells were the most abundant DP-MSCs at the end of P4. These results established that DP-MSCs constitute a heterogeneous mixture of cells in pulp tissue in vivo and in culture, and that their phenotype is modified upon in vitro expansion. Further studies are needed to determine whether co-expression of specific MSC markers confers DP cells specific properties that could be used for the regeneration of human tissues, including the dental pulp, with standardized cell-based medicinal products.

ZDHHC3 Tyrosine Phosphorylation Regulates Neural Cell Adhesion Molecule Palmitoylation

The neural cell adhesion molecule (NCAM) mediates cell-cell and cell-matrix adhesion. It is broadly expressed in the nervous system and regulates neurite outgrowth, synaptogenesis, and synaptic plasticity. Previous in vitro studies revealed that palmitoylation of NCAM is required for fibroblast growth factor 2 (FGF2)-stimulated neurite outgrowth and identified the zinc finger DHHC (Asp-His-His-Cys)-containing proteins ZDHHC3 and ZDHHC7 as specific NCAM-palmitoylating enzymes. Here, we verified that FGF2 controlled NCAM palmitoylation in vivo and investigated molecular mechanisms regulating NCAM palmitoylation by ZDHHC3. Experiments with overexpression and pharmacological inhibition of FGF receptor (FGFR) and Src revealed that these kinases control tyrosine phosphorylation of ZDHHC3 and that ZDHHC3 is phosphorylated by endogenously expressed FGFR and Src proteins. By site-directed mutagenesis, we found that Tyr18 is an FGFR1-specific ZDHHC3 phosphorylation site, while Tyr295 and Tyr297 are specifically phosphorylated by Src kinase in cell-based and cell-free assays. Abrogation of tyrosine phosphorylation increased ZDHHC3 autopalmitoylation, enhanced interaction with NCAM, and upregulated NCAM palmitoylation. Expression of ZDHHC3 with tyrosine mutated in cultured hippocampal neurons promoted neurite outgrowth. Our findings for the first time highlight that FGFR- and Src-mediated tyrosine phosphorylation of ZDHHC3 modulates ZDHHC3 enzymatic activity and plays a role in neuronal morphogenesis.

The IgLON Family Member Negr1 Promotes Neuronal Arborization Acting as Soluble Factor via FGFR2

IgLON proteins are GPI anchored adhesion molecules that control neurite outgrowth. In particular, Negr1 down-regulation negatively influences neuronal arborization in vitro and in vivo. In the present study, we found that the metalloprotease ADAM10 releases Negr1 from neuronal membrane. Ectodomain shedding influences several neuronal mechanisms, including survival, synaptogenesis, and the formation of neurite trees. By combining morphological analysis and virus-mediated selective protein silencing in primary murine cortical neurons, we found that pharmacologically inhibition of ADAM10 results in an impairment of neurite tree maturation that can be rescued upon treatment with soluble Negr1. Furthermore, we report that released Negr1 influences neurite outgrowth in a P-ERK1/2 and FGFR2 dependent manner. Together our findings suggest a role for Negr1 in regulating neurite outgrowth through the modulation of FGFR2 signaling pathway. Given the physiological and pathological role of ADAM10, Negr1, and FGFR2, the regulation of Negr1 shedding may play a crucial role in sustaining brain function and development.

ACAM, a novel member of the neural IgCAM family, mediates anterior neural tube closure in a primitive chordate

The neural IgCAM family of cell adhesion molecules, which includes NCAM and related molecules, has evolved via gene duplication and alternative splicing to allow for a wide range of isoforms with distinct functions and homophilic binding properties. A search for neural IgCAMs in ascidians (Ciona intestinalis, Ciona savignyi, and Phallusia mammillata) has identified a novel set of truncated family members that, unlike the known members, lack fibronectin III domains and consist of only repeated Ig domains. Within the tunicates this form appears to be unique to the ascidians, and it was designated ACAM, for Ascidian Cell Adhesion Molecule. In C. intestinalis ACAM is expressed in the developing neural plate and neural tube, with strongest expression in the anterior sensory vesicle precursor. Unlike the two other conventional neural IgCAMs in C. intestinalis, which are expressed maternally and throughout the morula and blastula stages, ACAM expression initiates at the gastrula stage. Moreover, C. intestinalis ACAM is a target of the homeodomain transcription factor OTX, which plays an essential role in the development of the anterior central nervous system. Morpholino (MO) knockdown shows that ACAM is required for neural tube closure. In MO-injected embryos neural tube closure was normal caudally, but the anterior neuropore remained open. A similar phenotype was seen with overexpression of a secreted version of ACAM. The presence of ACAM in ascidians highlights the diversity of this gene family in morphogenesis and neurodevelopment.

Cell Adhesion Molecules and Ubiquitination-Functions and Significance

Cell adhesion molecules of the immunoglobulin (Ig) superfamily represent the biggest group of cell adhesion molecules. They have been analyzed since approximately 40 years ago and most of them have been shown to play a role in tumor progression and in the nervous system. All members of the Ig superfamily are intensively posttranslationally modified. However, many aspects of their cellular functions are not yet known. Since a few years ago it is known that some of the Ig superfamily members are modified by ubiquitin. Ubiquitination has classically been described as a proteasomal degradation signal but during the last years it became obvious that it can regulate many other processes including internalization of cell surface molecules and lysosomal sorting. The purpose of this review is to summarize the current knowledge about the ubiquitination of cell adhesion molecules of the Ig superfamily and to discuss its potential physiological roles in tumorigenesis and in the nervous system.

Markers of epithelial to mesenchymal transition in association with survival in head and neck squamous cell carcinoma (HNSCC)

BACKGROUND

Elucidating the molecular phenotype of cancers with high metastatic potential will facilitate the development of novel therapeutic approaches to the disease. Gene expression profiles link epithelial to mesenchymal transition (EMT) phenotype with high-risk HNSCC. We sought to determine the role of protein biomarkers of EMT in head and neck squamous carcinoma (HNSC) prognosis.

METHODS

Protein expression analysis of EGFR, β-catenin and E-cadherin was performed on a cohort of 102 patients with HNSCC recruited between 1992 and 2005 using automated quantitative protein analysis (AQUA). We evaluated associations with clinicopathological parameters and prognosis.

RESULTS

There were 67 patients with primary squamous cell carcinoma of the head and neck in this cohort who met inclusion criteria and for whom we had complete E-cadherin, beta-catenin and EGFR expression data. High E-cadherin expressers had longer 5-year progression-free survival (PFS) compared to those with low E-cadherin (59.7% versus 40.6%, p = 0.04) and overall survival (OS) (69.6% versus 44.3%, p  = 0.05). Kaplan-Meier analysis showed that patients with low beta-catenin-expressing tumors trended toward worse 5-year PFS (p = 0.057). High EGFR expressers had inferior OS compared to low EGFR expressers (27.7% vs. 54%, p = 0.029). In the multivariable analysis context, E-cadherin remained an independent predictor of improved OS (HR = 0.204, 95% CI 0.043 to 0.972, p = 0.046) while EGFR trended towards significance for OS.

CONCLUSIONS

The putative markers of EMT defined within a panel of HNSCC using AQUA are associated with tumors of poor prognosis.

Perivascular macrophage-like melanocyte responsiveness to acoustic trauma--a salient feature of strial barrier associated hearing loss

Tissue perivascular resident macrophages (PVM/Ms), a hybrid cell type with characteristics of both macrophages and melanocytes, are critical for establishing and maintaining the endocochlear potential (EP) required for hearing. The PVM/Ms modulate expression of tight- and adherens-junction proteins in the endothelial barrier of the stria vascularis (intrastrial fluid-blood barrier) through secretion of a signaling molecule, pigment epithelium growth factor (PEDF). Here, we identify a significant link between abnormalities in PVM/Ms and endothelial barrier breakdown from acoustic trauma to the mouse ear. We find that acoustic trauma causes activation of PVM/Ms and physical detachment from capillary walls. Concurrent with the detachment, we find loosened tight junctions between endothelial cells and decreased production of tight- and adherens-junction protein, resulting in leakage of serum proteins from the damaged barrier. A key factor in the intrastrial fluid-blood barrier hyperpermeability exhibited in the mice is down-regulation of PVM/M modulated PEDF production. We demonstrate that delivery of PEDF to the damaged ear ameliorates hearing loss by restoring intrastrial fluid-blood barrier integrity. PEDF up-regulates expression of tight junction-associated proteins (ZO-1 and VE-cadherin) and PVM/M stabilizing neural cell adhesion molecule (NCAM-120). These studies point to the critical role PVM/Ms play in regulating intrastrial fluid-blood barrier integrity in healthy and noise-damaged ears.

The 140-kD isoform of CD56 (NCAM1) directs the molecular pathogenesis of ischemic cardiomyopathy

Despite recent advances in understanding the relevance of cell adhesion-related signaling in the pathogenesis of ischemic cardiomyopathy (ICM) in animal models, substantial questions remain unanswered in the human setting. We have previously shown that the neural cell adhesion molecule CD56 [neural cell adhesion molecule (NCAM1)] is specifically overexpressed in ICM; it was the aim of the current study to further elucidate the role of CD56 in the pathogenesis of human ICM. We used quantitative real-time PCR and IHC in human ICM and a rat model of coronary obstruction to demonstrate that CD56(140kD), the only extraneuronally expressed NCAM1 isoform with a cytoplasmic protein domain capable of inducing intracellular signaling, is the only up-regulated CD56 isoform in failing cardiomyocytes in human ICM in vivo. In subsequent analyses of the cellular effects of CD56(140kD) overexpression in the development of ICM using differential whole transcriptome expression analyses and functional in vitro cardiomyocyte cell culture assays, we further show that the up-regulation of CD56(140kD) is associated with profound gene expression changes, increased apoptosis, and reduced Ca(2+) signaling in failing human cardiomyocytes. Because apoptosis and Ca(2+)-related sarcomeric dysfunction are molecular hallmarks of ICM in humans, our results provide strong evidence that CD56(140kD) up-regulation plays a pivotal role in the pathogenesis of ICM and may be a target for future immunotherapeutic strategies in the treatment of this common and often fatal disease.

CD146 is a coreceptor for VEGFR-2 in tumor angiogenesis

CD146 is a novel endothelial biomarker and plays an essential role in angiogenesis; however, its role in the molecular mechanism underlying angiogenesis remains poorly understood. In the present study, we show that CD146 interacts directly with VEGFR-2 on endothelial cells and at the molecular level and identify the structural basis of CD146 binding to VEGFR-2. In addition, we show that CD146 is required in VEGF-induced VEGFR-2 phosphorylation, AKT/p38 MAPKs/NF-κB activation, and thus promotion of endothelial cell migration and microvascular formation. Furthermore, we show that anti-CD146 AA98 or CD146 siRNA abrogates all VEGFR-2 activation induced by VEGF. An in vivo angiogenesis assay showed that VEGF-promoted microvascular formation was impaired in the endothelial conditional knockout of CD146 (CD146EC-KO). Our animal experiments demonstrated that anti-CD146 (AA98) and anti-VEGF (bevacizumab) have an additive inhibitory effect on xenografted human pancreatic and melanoma tumors. The results of the present study suggest that CD146 is a new coreceptor for VEGFR-2 and is therefore a promising target for blocking tumor-related angiogenesis.

Partial reduction in neural cell adhesion molecule (NCAM) in heterozygous mice induces depression-related behaviour without cognitive impairment

The neural cell adhesion molecule (NCAM) plays an important role in brain plasticity. Using mice deficient in all isoforms of NCAM we have previously demonstrated that constitutive deficiency in the NCAM gene (NCAM-/-) resulted in cognitive impairment, anhedonic behaviour and a reduced ability to cope with stress. This was accompanied by reduced basal phosphorylation of the fibroblast growth factor receptor 1 (FGFR1) and reduced phosphorylation of calcium-calmodulin kinase (CaMK) II and IV and cAMP response element binding protein (CREB). The present study was aimed to investigate how partial deficiency in NCAM in mice (NCAM+/-) affected phenotype. We found that NCAM+/- mice showed a longer period of immobility in the tail suspension test, increased latency to feed in the novelty-suppressed feeding test and reduced preference for sucrose in sucrose preference test. Both NCAM+/- and NCAM-/- mice showed reduced extinction of contextual fear. In contrast to NCAM-/- mice, NCAM+/- mice did not demonstrate memory impairment in either object recognition or contextual fear conditioning tests. Levels of phosphorylated FGFR1 in the hippocampus and prefrontal/frontal cortex of NCAM+/- mice were partially reduced and no changes in the phosphorylation of CaMKII, CaMKIV or CREB in the hippocampus were found. We conclude that a constitutive partial reduction in NCAM proteins results in a behavioural phenotype related to depression without impairment in cognitive functions, also affecting the level of FGFR1 phosphorylation without major alterations in CaMKII and CaMKIV intracellular signalling. Partial reduction in FGFR1 phosphorylation might explain the observed behavioural phenotype in NCAM+/- mice.

Novel regulation of fibroblast growth factor 2 (FGF2)-mediated cell growth by polysialic acid

Polysialic acid (polySia) is a unique polysaccharide that modifies neural cell adhesion molecule (NCAM) spatiotemporally. Recently, we demonstrated that polySia functions as a reservoir for several neurotrophic factors and neurotransmitters. Here, we showed the direct interaction between polySia and fibroblast growth factor-2 (FGF2) by native-PAGE, gel filtration, and surface plasmon resonance. The minimum chain length of polySia required for the interaction with FGF2 was 17. Compared with heparan sulfate, a well known glycosaminoglycan capable of forming a complex with FGF2, polySia formed a larger complex with distinct properties in facilitating oligomerization of FGF2, as well as in binding to FGF receptors. In polySia-NCAM-expressing NIH-3T3 cells, which were established by transfecting cells with either of the plasmids for the expression of the polysialyltransferases ST8SiaII/STX and ST8SiaIV/PST that can polysialylate NCAM, FGF2-stimulated cell growth, but not cell survival, was inhibited. Taken together, these results suggest that polySia-NCAM might be involved in the regulation of FGF2-FGF receptor signaling through the direct binding of FGF2 in a manner distinct from heparan sulfate.

The interplay between NCAM and FGFR signalling underlies ovarian cancer progression

Epithelial ovarian carcinoma (EOC) is an aggressive neoplasm, which has often disseminated to peritoneal cavity at the time of diagnosis. In order to better understand the molecular mechanisms behind EOC progression, we investigated the expression and functional role of neural cell adhesion molecule (NCAM) in this tumour type.

Polysialic acid controls NCAM signals at cell–cell contacts to regulate focal adhesion independent from FGF receptor activity

The polysialic acid (polySia) modification of the neural cell adhesion molecule NCAM is a key regulator of cell migration. Yet its role in NCAM-dependent or NCAM-independent modulation of motility and cell–matrix adhesion is largely unresolved. Here, we demonstrate that loss of polySia attenuates tumour cell migration and augments the number of focal adhesions in a cell–cell contact- and NCAM-dependent manner. In the presence or absence of polySia, NCAM never colocalised with focal adhesions but was enriched at cell–cell contacts. Focal adhesion of polySia- and NCAM-negative cells was enhanced by incubation with soluble NCAM or by removing polySia from heterotypic contacts with polySia–NCAM-positive cells. Focal adhesion was compromised by the src-family kinase inhibitor PP2, whereas loss of polySia or exposure to NCAM promoted the association of p59Fyn with the focal adhesion scaffolding protein paxillin. Unlike other NCAM responses, NCAM-induced focal adhesion was not prevented by inhibiting FGF receptor activity and could be evoked by NCAM fragments comprising immunoglobulin domains three and four but not by the NCAM fibronectin domains alone or by an NCAM-derived peptide known to interact with and activate FGF receptors. Together, these data indicate that polySia regulates cell motility through NCAM-induced but FGF-receptor-independent signalling to focal adhesions.

Beyond VEGF: inhibition of the fibroblast growth factor pathway and antiangiogenesis

Fibroblast growth factor (FGF) signaling regulates cell proliferation, differentiation, survival, angiogenesis, and wound healing. Compelling evidence for deregulated FGF signaling in tumorigenesis continues to emerge, and a growing body of research suggests that FGF may also play an integral role in the resistance to anti-VEGF therapy. Although agents targeting FGF signaling are early in development, the potential to target both the VEGF and FGF pathways may translate into improvements in the clinical care of cancer patients.

The adhesion molecule NCAM promotes ovarian cancer progression via FGFR signalling

Epithelial ovarian carcinoma (EOC) is an aggressive neoplasm, which mainly disseminates to organs of the peritoneal cavity, an event mediated by molecular mechanisms that remain elusive. Here, we investigated the expression and functional role of neural cell adhesion molecule (NCAM), a cell surface glycoprotein involved in brain development and plasticity, in EOC. NCAM is absent from normal ovarian epithelium but becomes highly expressed in a subset of human EOC, in which NCAM expression is associated with high tumour grade, suggesting a causal role in cancer aggressiveness. We demonstrate that NCAM stimulates EOC cell migration and invasion in vitro and promotes metastatic dissemination in mice. This pro-malignant function of NCAM is mediated by its interaction with fibroblast growth factor receptor (FGFR). Indeed, not only FGFR signalling is required for NCAM-induced EOC cell motility, but targeting the NCAM/FGFR interplay with a monoclonal antibody abolishes the metastatic dissemination of EOC in mice. Our results point to NCAM-mediated stimulation of FGFR as a novel mechanism underlying EOC malignancy and indicate that this interplay may represent a valuable therapeutic target.

Adhesion molecule signalling: not always a sticky business

The signalling activity of cell adhesion molecules (CAMs) such as cadherins, immunoglobulin-like CAMs or integrins has long been considered to be a direct consequence of their adhesive properties. However, there are physiological and pathological processes that reduce or even abrogate the adhesive properties of CAMs, such as cleavage, conformational changes, mutations and shedding. In some cases these 'adhesion deficient' CAMs still retain signalling properties through their cytoplasmic domains and/or their mutated or truncated extracellular domains. The ability of CAMs to activate signal transduction cascades in the absence of cell adhesion significantly extends their range of biological activities.

Up-regulation of the fibroblast growth factor 8 subfamily in human hepatocellular carcinoma for cell survival and neoangiogenesis

Fibroblast growth factors (FGFs) and their high-affinity receptors [fibroblast growth factor receptors (FGFRs)] contribute to autocrine and paracrine growth stimulation in several non-liver cancer entities. Here we report that at least one member of the FGF8 subfamily (FGF8, FGF17, and FGF18) was up-regulated in 59% of 34 human hepatocellular carcinoma (HCC) samples that we investigated. The levels of the corresponding receptors (FGFR2, FGFR3, and FGFR4) were also elevated in the great majority of the HCC cases. Overall, 82% of the HCC cases showed overexpression of at least one FGF and/or FGFR. The functional implications of the deregulated FGF/FGFR system were investigated by the simulation of an insufficient blood supply. When HCC-1.2, HepG2, or Hep3B cells were subjected to serum withdrawal or the hypoxia-mimetic drug deferoxamine mesylate, the expression of FGF8 subfamily members increased dramatically. In the serum-starved cells, the incidence of apoptosis was elevated, whereas the addition of FGF8, FGF17, or FGF18 impaired apoptosis, which was associated with phosphorylation of extracellular signal-regulated kinase 1/2 and ribosomal protein S6. In contrast, down-modulation of FGF18 by small interfering RNA (siRNA) significantly reduced the viability of the hepatocarcinoma cells. siRNA targeting FGF18 also impaired the cells' potential to form clones at a low cell density or in soft agar. With respect to the tumor microenvironment, FGF17 and FGF18 stimulated the growth of HCC-derived myofibroblasts, and FGF8, FGF17, and FGF18 induced the proliferation and tube formation of hepatic endothelial cells.

CONCLUSION

FGF8, FGF17, and FGF18 are involved in autocrine and paracrine signaling in HCC and enhance the survival of tumor cells under stress conditions, malignant behavior, and neoangiogenesis. Thus, the FGF8 subfamily supports the development and progression of hepatocellular malignancy.

Unique intracellular trafficking processes associated with neural cell adhesion molecule and its intracellular signaling

Homophilic binding of the neural cell adhesion molecule (NCAM) results in intracellular signaling, which also involves heterophilic engagement of coreceptors such as the fibroblast growth factor receptor (FGFR) and receptor protein tyrosine phosphatase-α (RPTPα). NCAM's own cellular dynamic itinerary includes endocytosis and recycling to the plasma membrane. Recent works suggest that NCAM could influence the trafficking of other receptor molecules that it associates with, particularly the FGFR. Furthermore, it was demonstrated that NCAM could undergo proteolytic processing upon activation. A processed fragment of NCAM, together with an N-terminal fragment of focal adhesion kinase (FAK), is translocated into the nucleus. Here, the authors discuss these rather unique (though not without precedence and analogues) receptor trafficking activities that are associated with NCAM and NCAM signaling.

Cell adhesion molecules in context: CAM function depends on the neighborhood

Cell adhesion molecules (CAMs) are now known to mediate much more than adhesion between cells and between cells and the extracellular matrix. Work by many researchers has illuminated their roles in modulating activation of molecules such as receptor tyrosine kinases, with subsequent effects on cell survival, migration, and process extension. CAMs also are known to serve as substrates for proteases which can create diffusible fragments capable of signaling independently from the CAM. The diversity of interactions is further modulated by membrane rafts, which can co-localize or separate potential signaling partners to affect the likelihood of a given signaling pathway being activated. Given the ever-growing number of known CAMs and the fact that their heterophilic binding in cis or in trans can affect their interactions with other molecules, including membrane-bound receptors, one would predict a wide range of effects attributable to a particular CAM in a particular cell at a particular stage of development. The function(s) of a given CAM must therefore be considered in the context of the history of the cell expressing it and the repertoire of molecules expressed both by that cell and its neighbors.

Gene expression of axon growth promoting factors in the deer antler

The annual regeneration cycle of deer (Cervidae, Artiodactyla) antlers represents a unique model of epimorphic regeneration and rapid growth in adult mammals. Regenerating antlers are innervated by trigeminal sensory axons growing through the velvet, the modified form of skin that envelopes the antler, at elongation velocities that reach one centimetre per day in the common deer (Cervus elaphus). Several axon growth promoters like NT-3, NGF or IGF-1 have been described in the antler. To increase the knowledge on the axon growth environment, we have combined different gene-expression techniques to identify and characterize the expression of promoting molecules not previously described in the antler velvet. Cross-species microarray analyses of deer samples on human arrays allowed us to build up a list of 90 extracellular or membrane molecules involved in axon growth that were potentially being expressed in the antler. Fifteen of these genes were analysed using PCR and sequencing techniques to confirm their expression in the velvet and to compare it with the expression in other antler and skin samples. Expression of 8 axon growth promoters was confirmed in the velvet, 5 of them not previously described in the antler. In conclusion, our work shows that antler velvet provides growing axons with a variety of promoters of axon growth, sharing many of them with deer's normal and pedicle skin.

Expression of nestin, vimentin, and NCAM by renal interstitial cells after ischemic tubular injury

This work explores the distribution of various markers expressed by interstitial cells in rat kidneys after ischemic injury (35 minutes) during regeneration of S3 tubules of outer stripe of outer medulla (OSOM). Groups of experimental animals (n = 4) were sacrificed every two hours during the first 24 hours post-ischemia as well as 2, 3, 7, 14 days post-ischemia. The occurrence of lineage markers was analyzed on kidney sections by immunohistochemistry and morphometry during the process of tubular regeneration. In postischemic kidneys, interstitial cell proliferation, assessed by 5-bromo-2'-deoxyuridine (BrdU) and Proliferating Cell Nuclear Antigen (PCNA) labeling, was prominent in outer medulla and reach a maximum between 24 and 72 hours after reperfusion. This population was characterized by the coexpression of vimentin and nestin. The density of -Neural Cell Adhesion Molecule (NCAM) positive interstitial cells increased transiently (18-72 hours) in the vicinity of altered tubules. We have also localized a small population of alpha-Smooth Muscle Actin (SMA)-positive cells confined to chronically altered areas and characterized by a small proliferative index. In conclusion, we observed in the postischemic kidney a marked proliferation of interstitial cells that underwent transient phenotypical modifications. These interstitial cells could be implicated in processes leading to renal fibrosis.

The binding of NCAM to FGFR1 induces a specific cellular response mediated by receptor trafficking

Neural cell adhesion molecule (NCAM) associates with fibroblast growth factor (FGF) receptor-1 (FGFR1). However, the biological significance of this interaction remains largely elusive. In this study, we show that NCAM induces a specific, FGFR1-mediated cellular response that is remarkably different from that elicited by FGF-2. In contrast to FGF-induced degradation of endocytic FGFR1, NCAM promotes the stabilization of the receptor, which is recycled to the cell surface in a Rab11- and Src-dependent manner. In turn, FGFR1 recycling is required for NCAM-induced sustained activation of various effectors. Furthermore, NCAM, but not FGF-2, promotes cell migration, and this response depends on FGFR1 recycling and sustained Src activation. Our results implicate NCAM as a nonconventional ligand for FGFR1 that exerts a peculiar control on the intracellular trafficking of the receptor, resulting in a specific cellular response. Besides introducing a further level of complexity in the regulation of FGFR1 function, our findings highlight the link of FGFR recycling with sustained signaling and cell migration and the critical role of these events in dictating the cellular response evoked by receptor activation.