Fibulin-5 binds urokinase-type plasminogen activator and mediates urokinase-stimulated β1-integrin-dependent cell migration

Effect of fibulin-5 on aldosterone-induced apoptosis in human ascending aortic smooth muscle cells

The aim of the current study was to investigate the effect of aldosterone on apoptosis in human aortic smooth muscle cells (HA-VSMC) and to determine the role of fibulin-5 in the aldosterone-induced apoptosis of HA-VSMC cells. Through the construction of a fibulin-5 eukaryotic overexpression vector and a short hairpin RNA interference plasmid, fibulin-5 was overexpressed and silenced, respectively. The role of fibulin-5 in the aldosterone-induced apoptosis of HA-VSMC was subsequently determined. The overexpression of fibulin-5 inhibited the apoptosis of cells, particularly at low concentrations of aldosterone; a smaller effect on apoptosis was induced by high concentrations of aldosterone. fibulin-5 knockdown promoted the apoptosis of cells induced by high concentrations of aldosterone but had a smaller effect on the apoptosis of cells induced by low concentrations of aldosterone. Therefore, the results of the current study indicate that fibulin-5 inhibits the aldosterone-induced apoptosis of HA-VSMC cells and that this effect may be altered by changing the aldosterone concentration.

Network-based analysis reveals novel gene signatures in the peripheral blood of patients with sporadic nonsyndromic thoracic aortic aneurysm

Thoracic aortic aneurysm (TAA), a serious cardiovascular disease that causes morbidity and mortality worldwide. At present, few biomarkers can accurately diagnose the appearance of TAA before dissection or rupture. Our research has the intention to investigate the developing applicable biomarkers for TAA promising clinically diagnostic biomarkers or probable regulatory targets for TAA. In our research, we built correlation networks utilizing the expression profile of peripheral blood mononuclear cell obtained from a public microarray data set (GSE9106). Furthermore, we chose the turquoise module, which has the strongest significance with TAA and was further analyzed. Fourteen genes that overlapped with differentially expressed proteins in the medial aortic layer were obtained. Subsequently, we verified the results applying quantitative polymerase chain reaction (Q-PCR) to our clinical specimen. In general, the Q-PCR results coincide with the majority of the expression profile. Fascinatingly, a notable change occurred in CLU, DES, MYH10, and FBLN5. In summary, using weighted gene coexpression analysis, our study indicates that CLU, DES, MYH10, and FBLN5 were identified and validated to be related to TAA and might be candidate biomarkers or therapeutic targets for TAA.

Functional Vascular Tissue Engineering Inspired by Matricellular Proteins

Modern regenerative medicine, and tissue engineering specifically, has benefited from a greater appreciation of the native extracellular matrix (ECM). Fibronectin, collagen, and elastin have entered the tissue engineer's toolkit; however, as fully decellularized biomaterials have come to the forefront in vascular engineering it has become apparent that the ECM is comprised of more than just fibronectin, collagen, and elastin, and that cell-instructive molecules known as matricellular proteins are critical for desired outcomes. In brief, matricellular proteins are ECM constituents that contrast with the canonical structural proteins of the ECM in that their primary role is to interact with the cell. Of late, matricellular genes have been linked to diseases including connective tissue disorders, cardiovascular disease, and cancer. Despite the range of biological activities, this class of biomolecules has not been actively used in the field of regenerative medicine. The intent of this review is to bring matricellular proteins into wider use in the context of vascular tissue engineering. Matricellular proteins orchestrate the formation of new collagen and elastin fibers that have proper mechanical properties-these will be essential components for a fully biological small diameter tissue engineered vascular graft (TEVG). Matricellular proteins also regulate the initiation of thrombosis via fibrin deposition and platelet activation, and the clearance of thrombus when it is no longer needed-proper regulation of thrombosis will be critical for maintaining patency of a TEVG after implantation. Matricellular proteins regulate the adhesion, migration, and proliferation of endothelial cells-all are biological functions that will be critical for formation of a thrombus-resistant endothelium within a TEVG. Lastly, matricellular proteins regulate the adhesion, migration, proliferation, and activation of smooth muscle cells-proper control of these biological activities will be critical for a TEVG that recellularizes and resists neointimal formation/stenosis. We review all of these functions for matricellular proteins here, in addition to reviewing the few studies that have been performed at the intersection of matricellular protein biology and vascular tissue engineering.

Low Density Receptor-Related Protein 1 Interactions With the Extracellular Matrix: More Than Meets the Eye

The extracellular matrix (ECM) is a biological substrate composed of collagens, proteoglycans and glycoproteins that ensures proper cell migration and adhesion and keeps the cell architecture intact. The regulation of the ECM composition is a vital process strictly controlled by, among others, proteases, growth factors and adhesion receptors. As it appears, ECM remodeling is also essential for proper neuronal and glial development and the establishment of adequate synaptic signaling. Hence, disturbances in ECM functioning are often present in neurodegenerative diseases like Alzheimer’s disease. Moreover, mutations in ECM molecules are found in some forms of epilepsy and malfunctioning of ECM-related genes and pathways can be seen in, for example, cancer or ischemic injury. Low density lipoprotein receptor-related protein 1 (Lrp1) is a member of the low density lipoprotein receptor family. Lrp1 is involved not only in ligand uptake, receptor mediated endocytosis and lipoprotein transport—functions shared by low density lipoprotein receptor family members—but also regulates cell surface protease activity, controls cellular entry and binding of toxins and viruses, protects against atherosclerosis and acts on many cell signaling pathways. Given the plethora of functions, it is not surprising that Lrp1 also impacts the ECM and is involved in its remodeling. This review focuses on the role of Lrp1 and some of its major ligands on ECM function. Specifically, interactions with two Lrp1 ligands, integrins and tissue plasminogen activator are described in more detail.

Multifaced Roles of the Urokinase System in the Regulation of Stem Cell Niches

Proliferation, subsequent migration to the damaged area, differentiation into appropriate cell types, and/or secretion of biologically active molecules and extracellular vesicles are important processes that underlie the involvement of stem/progenitor cells in the repair and regeneration of tissues and organs. All these functions are regulated through the interaction between stem cells and the microenvironment in the tissue cell niches that control these processes through direct cell-cell interactions, production of the extracellular matrix, release of extracellular vesicles, and secretion of growth factors, cytokines, chemokines, and proteases. One of the most important proteolytic systems involved in the regulation of cell migration and proliferation is the urokinase system represented by the urokinase plasminogen activator (uPA, urokinase), its receptor (uPAR), and inhibitors. This review addresses the issues of urokinase system involvement in the regulation of stem cell niches in various tissues and analyzes the possible effects of this system on the signaling pathways responsible for the proliferation, programmed cell death, phenotype modulation, and migration properties of stem cells.

Dysregulation of fibulin-5 and matrix metalloproteases in epithelial ovarian cancer

Fibulin 5 (FBLN5) is an extracellular matrix glycoprotein that suppresses matrix metalloprotease 9 (MMP-9), angiogenesis and epithelial cell motility. Here, we investigated the regulation and function of FBLN5 in epithelial ovarian cancer (EOC). FBLN5 mRNA was down-regulated 5-fold in EOC relative to benign ovary. Not surprisingly, MMP9 mRNA and enzyme activity were increased significantly, and inversely correlated with FBLN5 gene expression. FBLN5 degradation products of 52.8 and 41.3 kDa were increased substantially in EOC. We identified two candidate proteases (serine elastase and MMP-7, but not MMP-9) that cleave FBLN5. MMP-7, but not neutrophil elastase, gene expression was increased dramatically in EOC. Recombinant FBLN5 significantly inhibited adhesion of EOC cells to both laminin and collagen I. Finally, using immunohistochemistry, we found immunoreactive FBLN5 within tumor macrophages throughout human EOC tumors. This work indicates that FBLN5 is degraded in EOC most likely by proteases enriched in macrophages of the tumor microenvironment. Proteolysis of FBLN5 serves as a mechanism to promote cell adhesion and local metastasis of ovarian cancer cells. Promotion of a stable ECM with intact FBLN5 in the tumor matrix may serve as a novel therapeutic adjunct to prevent spread of ovarian cancer.

Fibulin-5 promotes airway smooth muscle cell proliferation and migration via modulating Hippo-YAP/TAZ pathway

Asthma is a common chronic disease mainly occurs from childhood. Increased airway smooth muscle mass is involved in the pathogenesis of asthma. Fibulin-5 was upregulated in the lung tissues of patients with COPD and idiopathic pulmonary fibrosis. This study aimed to investigate Fibulin-5 expression in asthmatic patients and the effect and mechanism of Fibulin-5 on the proliferation and migration of airway smooth muscle cells (ASMCs). The expression of Fibulin-5, YAP, and TAZ in the induced sputum of 38 asthmatic children (19 mild and 19 moderate asthmatics) and 19 healthy controls was determined. The effects and mechanisms of Fibulin-5 on the proliferation and migration of ASMCs were analyzed through upregulating Fibulin-5. We found compared with healthy controls, the expression of Fibulin-5, YAP, and TAZ was increased in the induced sputum of asthmatic children and much higher in moderate asthmatics. Fibulin-5 overexpression promoted the proliferation and migration of ASMCs, upregulated the expression of YAP and TAZ, and reduced the levels of p-YAP and p-TAZ. YAP inhibitor (Peptide 17) abrogated the proliferation and migration of ASMCs induced by Fibulin-5 overexpression in a dose-dependent manner. Additionally, Fibulin-5 overexpression enhanced its binding capacity of β1 integrin, and β1 integrin blocking antibody partly reversed the effect of Fibulin-5 overexpression on the levels of YAP and TAZ. In conclusion, Fibulin-5 expression is correlated with the pathogenesis of childhood asthma. It may function at least partly through binding to β1 integrin and modulating Hippo-YAP/TAZ pathway to promote the proliferation and migration of ASMCs.

Identification of the matricellular protein Fibulin-5 as a target molecule of glucokinase-mediated calcineurin/NFAT signaling in pancreatic islets

Glucokinase-mediated glucose signaling induces insulin secretion, proliferation, and apoptosis in pancreatic β-cells. However, the precise molecular mechanisms underlying these processes are not clearly understood. Here, we demonstrated that glucokinase activation using a glucokinase activator (GKA) significantly upregulated the expression of Fibulin-5 (Fbln5), a matricellular protein involved in matrix-cell signaling, in isolated mouse islets. The islet Fbln5 expression was induced by ambient glucose in a time- and dose-dependent manner and further enhanced by high-fat diet or the deletion of insulin receptor substrate 2 (IRS-2), whereas the GKA-induced increase in Fbln5 expression was diminished in Irs-2-deficient islets. GKA-induced Fbln5 upregulation in the islets was blunted by a glucokinase inhibitor, K_ATP channel opener, Ca²⁺ channel blocker and calcineurin inhibitor, while it was augmented by harmine, a dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) 1 A inhibitor. Although deletion of Fbln5 in mice had no significant effects on the glucose tolerance or β-cell functions, adenovirus-mediated Fbln5 overexpression increased glucose-stimulated insulin secretion in INS-1 rat insulinoma cells. Since the islet Fbln5 expression is regulated through a glucokinase/K_ATP channel/calcineurin/nuclear factor of activated T cells (NFAT) pathway crucial for the maintenance of β-cell functions, further investigation of Fbln5 functions in the islets is warranted.

[Inflammation inhibits vascular fibulin-5 expression: Involvement of transcription factor SOX9]

INTRODUCTION

Fibulin-5 (FBLN5) is an elastogenic protein critically involved in extracellular matrix (ECM) remodelling, a key process in abdominal aortic aneurysm (AAA). However, the possible contribution of FBLN5 to AAA development has not been addressed.

METHODS

Expression levels were determined by real-time PCR and Western blot in human abdominal aorta from patients with AAA or healthy donors, as well as in human aortic vascular smooth muscle cells (VSMC). Lentiviral transduction, transient transfections, and chromatin immunoprecipitation (ChIP) assays were also performed.

RESULTS

The expression of FBLN5 in human AAA was significantly lower than in healthy donors. FBLN5 mRNA and protein levels and their secretion to the extracellular environment were down-regulated in VSMC exposed to inflammatory stimuli. Interestingly, FBLN5 transcriptional activity was inhibited by TNFα and lipopolysaccharide (LPS), and depends on a SOX response element. In fact, SOX9 expression was reduced in VMSC induced by inflammatory mediators and in human AAA, and correlated with that of FBLN5. Furthermore, SOX9 over-expression limited the reduction of FBLN5 expression induced by cytokines in VSMC. Finally, it was observed that SOX9 interacts with FBLN5 promoter, and that this binding was reduced upon TNFα exposure.

CONCLUSIONS

FBLN5 downregulation in human AAA could contribute to extracellular matrix remodelling induced by the inflammatory component of the disease.

Guidance Receptors in the Nervous and Cardiovascular Systems

Blood vessels and nervous fibers grow in parallel, for they express similar receptors for chemokine substances. Recently, much attention is being given to studying guidance receptors and their ligands besides the growth factors, cytokines, and chemokines necessary to form structures in the nervous and vascular systems. Such guidance molecules determine trajectory for growing axons and vessels. Guidance molecules include Ephrins and their receptors, Neuropilins and Plexins as receptors for Semaphorins, Robos as receptors for Slit-proteins, and UNC5B receptors binding Netrins. Apart from these receptors and their ligands, urokinase and its receptor (uPAR) and T-cadherin are also classified as guidance molecules. The urokinase system mediates local proteolysis at the leading edge of cells, thereby providing directed migration. T-cadherin is a repellent molecule that regulates the direction of growing axons and blood vessels. Guidance receptors also play an important role in the diseases of the nervous and cardiovascular systems.

Urokinase-type Plasminogen Activator (uPA) Promotes Angiogenesis by Attenuating Proline-rich Homeodomain Protein (PRH) Transcription Factor Activity and De-repressing Vascular Endothelial Growth Factor (VEGF) Receptor Expression

Urokinase-type plasminogen activator (uPA) regulates angiogenesis and vascular permeability through proteolytic degradation of extracellular matrix and intracellular signaling initiated upon its binding to uPAR/CD87 and other cell surface receptors. Here, we describe an additional mechanism by which uPA regulates angiogenesis. Ex vivo VEGF-induced vascular sprouting from Matrigel-embedded aortic rings isolated from uPA knock-out (uPA(-/-)) mice was impaired compared with vessels emanating from wild-type mice. Endothelial cells isolated from uPA(-/-) mice show less proliferation and migration in response to VEGF than their wild type counterparts or uPA(-/-) endothelial cells in which expression of wild type uPA had been restored. We reported previously that uPA is transported from cell surface receptors to nuclei through a mechanism that requires its kringle domain. Intranuclear uPA modulates gene transcription by binding to a subset of transcription factors. Here we report that wild type single-chain uPA, but not uPA variants incapable of nuclear transport, increases the expression of cell surface VEGF receptor 1 (VEGFR1) and VEGF receptor 2 (VEGFR2) by translocating to the nuclei of ECs. Intranuclear single-chain uPA binds directly to and interferes with the function of the transcription factor hematopoietically expressed homeodomain protein or proline-rich homeodomain protein (HHEX/PRH), which thereby lose their physiologic capacity to repress the activity of vehgr1 and vegfr2 gene promoters. These studies identify uPA-dependent de-repression of vegfr1 and vegfr2 gene transcription through binding to HHEX/PRH as a novel mechanism by which uPA mediates the pro-angiogenic effects of VEGF and identifies a potential new target for control of pathologic angiogenesis.

Fibulin-5 inhibits hepatocellular carcinoma cell migration and invasion by down-regulating matrix metalloproteinase-7 expression

Background

Fibulin-5 has been considered as a tumor suppressor through inhibiting tumor growth and invasion. Reduced expression of Fibulin-5 is frequently observed in various human cancers. In this study, we investigate the clinical significance of Fibulin-5 and its role in hepatocellular carcinoma (HCC) cell migration and invasion.

Methods

The expression of Fibulin-5 was evaluated by qRT-PCR and immunoblotting in HCC and matched noncancerous tissues. Fibulin-5 was over-expressed or knocked down by a retrovirus-mediated expression plasmid or a specific siRNA in HCC cells. Boyden chamber and Transwell assays were used to test HCC cell migration and invasion. Immunostaining was performed to determine matrix metalloproteinase-7 (MMP-7) expression in HCC specimens. MMP-7 retroviruses and siRNA were used to alter MMP-7 expression in HCC cells.

Results

In our study, the expression levels of Fibulin-5 protein and mRNA were down-regulated in HCC tissues as compared with those in matched noncancerous tissues. Reduced expression of Fibulin-5 was observed in all HCC cell lines (HepG2, SMMC-7721, MHCC97L, Hep3B, MHCC97H and HCC-LM3) as compare with that in a non-transformed hepatic cell line (LO2). Low expression of Fibulin-5 was significantly correlated with poor prognostic features including multiple tumor nodes, venous infiltration, high Edmondson-Steiner grading and advanced tumor-node-metastasis (TNM) tumor stage. Furthermore, we demonstrated that Fibulin-5 was a novel independent prognostic marker for predicting 5-year survival of HCC patients. Our in vitro studies showed that Fibulin-5 overexpression inhibited HCC cell migration and invasion. While Fibulin-5 knockdown increased the number of migrated and invaded HCC cells. Fibulin-5 negatively regulated MMP-7 abundance in HCC cells. Moreover, the inverse correlation between Fibulin-5 and MMP-7 expressions was observed in HCC tissues. Mechanistically, we disclosed that MMP-7 knockdown reduced the number of migrated and invaded HCC cells. Restoring MMP-7 expression abrogated the suppressive effect of Fibulin-5 on HCC cell migration and invasion in vitro, suggesting that Fibulin-5 exerted its anti-metastatic function, at least in part, by down-regulating the expression of MMP-7 in HCC cells.

Conclusions

These results indicate that Fibulin-5 may serve as a prognostic biomarker and inhibits HCC invasion and metastasis by suppressing MMP-7 expression.

The C. elegans HGF/plasminogen-like protein SVH-1 has protease-dependent and -independent functions

Hepatocyte growth factor (HGF) and fibrinolytic serine protease plasminogen may have evolved from a common ancestor in vertebrates. This has been hard to ascertain, as no ancestral form has been identified in other lineages. In Caenorhabditis elegans, an HGF/plasminogen-like protein SVH-1 regulates axon regeneration via the HGF receptor homolog SVH-2. In this study, we report that both the svh-1 and svh-2 genes are conserved in many invertebrates. We also show that SVH-1 has an additional function, independent of SVH-2, which controls larval growth. SVH-1 protease activity is essential for larval growth, but not for axon regeneration. Deletion of svh-1 causes abnormal accumulation of FBL-1 protein, an extracellular matrix (ECM) component fibulin, around the pharynx, and this growth defect is partially suppressed by FBL-1 depletion. These results suggest that SVH-1 acts as both a growth factor and a protease, and they also provide insights into the evolution of HGF/plasminogen in animals.

Expression of fibulin-6 in failing hearts and its role for cardiac fibroblast migration

AIMS

The cardiac extracellular matrix (ECM) undergoes a dynamic transition following myocardial infarction. Fibulin-6 is expressed in cell junctions particularly in tissues subjected to significant mechanical stress. Fibulin-6 deficiency results in defective cell migration in nematodes and early embryonic lethality in mice. The role of fibulin-6 in healthy and failing myocardium is unknown. We have examined the expression and distribution pattern of fibulin-6 during myocardial remodelling (MR) and detailed its effect on the migratory function of cardiac fibroblasts (CFs) in response to TGF-β1.

METHODS AND RESULTS

In healthy murine myocardium, fibulin-6 expression is largely confined to larger coronary arteries. It is induced during the early and the late phase of remodelling after infarction in murine hearts predominantly in the scar-muscle junction. Similar results are obtained in human ischaemic cardiomyopathy. Fibulin-6 is mostly expressed in close vicinity to vimentin-positive cells and is also abundantly expressed in vitro in cultured neonatal CF. TGF-β1 does not induce smooth muscle actin in fibroblasts deficient of fibulin-6, which also compromised their migration. Cells that had migrated expressed more fibulin-6 compared with stationary cells. Plated on fibulin-6-depleted matrix, stress fibre induction in fibroblast in response to TGF-β1 was impaired. In ex vivo explant cultures from post-infarct myocardium, the number of emigrating fibroblasts was also significantly reduced by fibulin-6 siRNA knockdown.

CONCLUSION

Fibulin-6, a fibroblast-released ECM protein, may play an important role during MR by imparting an effect on CF migration in close and complementary interplay with TGF-β1 signalling.

Fibulin-4 and fibulin-5 in elastogenesis and beyond: Insights from mouse and human studies

The fibulin family of extracellular matrix/matricellular proteins is composed of long fibulins (fibulin-1, -2, -6) and short fibulins (fibulin-3, -4, -5, -7) and is involved in protein-protein interaction with the components of basement membrane and extracellular matrix proteins. Fibulin-1, -2, -3, -4, and -5 bind the monomeric form of elastin (tropoelastin) in vitro and fibulin-2, -3, -4, and -5 are shown to be involved in various aspects of elastic fiber development in vivo. In particular, fibulin-4 and -5 are critical molecules for elastic fiber assembly and play a non-redundant role during elastic fiber formation. Despite manifestation of systemic elastic fiber defects in all elastogenic tissues, fibulin-5 null (Fbln5(-/-)) mice have a normal lifespan. In contrast, fibulin-4 null (Fbln4(-/-)) mice die during the perinatal period due to rupture of aortic aneurysms, indicating differential functions of fibulin-4 and fibulin-5 in normal development. In this review, we will update biochemical characterization of fibulin-4 and fibulin-5 and discuss their roles in elastogenesis and outside of elastogenesis based on knowledge obtained from loss-of-function studies in mouse and in human patients with FBLN4 or FBLN5 mutations. Finally, we will evaluate therapeutic options for matrix-related diseases.

Fibulin-3, -4, and -5 are highly susceptible to proteolysis, interact with cells and heparin, and form multimers

Extracellular short fibulins, fibulin-3, -4, and -5, are components of the elastic fiber/microfibril system and are implicated in the formation and homeostasis of elastic tissues. In this study, we report new structural and functional properties of the short fibulins. Full-length human short fibulins were recombinantly expressed in human embryonic kidney cells and purified by immobilized metal ion affinity chromatography. All three fibulins showed various levels of degradation after the purification procedure. N-terminal sequencing revealed that all three fibulins are highly susceptible to proteolysis within the N-terminal linker region of the first calcium-binding epidermal growth factor domain. Proteolytic susceptibility of the linker correlated with its length. Exposure of these fibulins to matrix metalloproteinase (MMP)-1, -2, -3, -7, -9, and -12 resulted in similar proteolytic fragments with MMP-7 and -12 being the most potent proteases. Fibulin-3 proteolysis was almost completely inhibited in cell culture by the addition of 25 μm doxycycline (a broad spectrum MMP inhibitor). Reducible fibulin-4 dimerization and multimerization were consistently observed by SDS-PAGE, Western blotting, and mass spectrometry. Atomic force microscopy identified monomers, dimers, and multimers in purified fibulin-4 preparations with sizes of ∼10-15, ∼20-25, and ∼30-50 nm, respectively. All short fibulins strongly adhered to human fibroblasts and smooth muscle cells. Although only fibulin-5 has an RGD integrin binding site, all short fibulins adhere at a similar level to the respective cells. Solid phase binding assays detected strong calcium-dependent binding of the short fibulins to immobilized heparin, suggesting that these fibulins may bind cell surface-located heparan sulfate.

The dual role of fibulins in tumorigenesis

The human fibulin family consists of seven complex extracellular glycoproteins originally characterized as components of elastic fibers in connective tissue. However, beyond its structural role, fibulins are involved in complex biological processes such as cell adhesion, migration or proliferation. Indeed, they have proved to be essential elements in normal physiology, as shown by mouse models lacking these proteins, that evidence several developmental abnormalities and pathological features. Their relevance is also apparent in tumorigenesis, an aspect that has started to be intensely studied. Distinct fibulins are expressed in both tumor and stromal cells and are subjected to multiple expression regulations with either anti or pro-tumor effects. The mechanistic insights that underlie these observations are now commencing to emerge, portraying these proteins as very versatile and active constituents of connective tissue. The aim of this review is to highlight the most relevant connections between fibulins and cancer.