Identification of two distinct regions of the type III connecting segment of human plasma fibronectin that promote cell type-specific adhesion

Lnc-ABCA12-8 confers acquired resistance to gefitinib in non-small cell lung cancer by regulating the alternative splicing of fibronectin 1 in the IIICS region

Acquired resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), such as gefitinib, has dramatically impaired the clinical outcomes in non-small cell lung cancer (NSCLC) patients, but the mechanisms are still unclear in substantial cases. In our previous study, we demonstrated that a novel long non-coding RNA (lncRNA), lnc-ABCA12-8, was overexpressed in gefitinib-resistant NSCLC cells, but the exact function is unknown. In this study, we confirmed that lnc-ABCA12-8 was significantly upregulated both in NSCLC cell lines and the plasma samples of NSCLC patients with acquired resistance to gefitinib. Downregulation of lnc-ABCA12-8 could reverse gefitinib resistance both in vitro and in vivo. Mechanistically, lnc-ABCA12-8 interacted with alternative splicing factor/splicing factor 2 (ASF/SF2), promoted the binding of ASF/SF2 to the IIICS exon of fibronectin 1 (FN1) gene and enhanced the IIICS region inclusion during fibronectin 1 (FN1) alternative splicing, resulting in the upregulation of entire IIICS region, and enhanced cell proliferation, migration, invasion, and adhesion. Taken together, our study suggest that lnc-ABCA12-8 is involved in the acquired resistance to gefitinib, and may be a novel biomarker and therapeutic target for monitoring and overcoming gefitinib resistance in NSCLC.

Monocyte Recruitment for Vascular Tissue Regeneration

A strategy to recruit monocytes (MCs) from blood to regenerate vascular tissue from unseeded (cell-free) tissue engineered vascular grafts is presented. When immobilized on the surface of vascular grafts, the fusion protein, H2R5 can capture blood-derived MC under static or flow conditions in a shear stress dependent manner. The bound MC turns into macrophages (Mϕ) expressing both M1 and M2 phenotype specific genes. When H2R5 functionalized acellular-tissue engineered vessels (A-TEVs) are implanted into the mouse aorta, they remain patent and form a continuous endothelium expressing both endothelial cell (EC) and MC specific proteins. Underneath the EC layer, multiple cells layers are formed coexpressing both smooth muscle cell (SMC) and MC specific markers. Lineage tracing analysis using a novel CX3CR1-confetti mouse model demonstrates that fluorescently labeled MC populates the graft lumen by two and four weeks postimplantation, providing direct evidence in support of MC/Mϕ recruitment to the graft lumen. Given their abundance in the blood, circulating MCs may be a great source of cells that contribute directly to the endothelialization and vascular wall formation of acellular vascular grafts under the right chemical and biomechanical cues.

Fibronectin: Molecular Structure, Fibrillar Structure and Mechanochemical Signaling

The extracellular matrix (ECM) plays a key role as both structural scaffold and regulator of cell signal transduction in tissues. In times of ECM assembly and turnover, cells upregulate assembly of the ECM protein, fibronectin (FN). FN is assembled by cells into viscoelastic fibrils that can bind upward of 40 distinct growth factors and cytokines. These fibrils play a key role in assembling a provisional ECM during embryonic development and wound healing. Fibril assembly is also often upregulated during disease states, including cancer and fibrotic diseases. FN fibrils have unique mechanical properties, which allow them to alter mechanotransduction signals sensed and relayed by cells. Binding of soluble growth factors to FN fibrils alters signal transduction from these proteins, while binding of other ECM proteins, including collagens, elastins, and proteoglycans, to FN fibrils facilitates the maturation and tissue specificity of the ECM. In this review, we will discuss the assembly of FN fibrils from individual FN molecules; the composition, structure, and mechanics of FN fibrils; the interaction of FN fibrils with other ECM proteins and growth factors; the role of FN in transmitting mechanobiology signaling events; and approaches for studying the mechanics of FN fibrils.

Improvement of wound healing by the development of ECM-inspired biomaterial coatings and controlled protein release

Implant design has evolved from biochemically inert substrates, minimizing cell and protein interaction, towards sophisticated bioactive substrates, modulating the host response and supporting the regeneration of the injured tissue. Important aspects to consider are the control of cell adhesion, the discrimination of bacteria and non-local cells from the desired tissue cell type, and the stimulation of implant integration and wound healing. Here, the extracellular matrix acts as a role model providing us with inspiration for sophisticated designs. Within this scope, small bioactive peptides have proven to be miscellaneously deployable for the mediation of surface, cell and matrix interactions. Combinations of adhesion ligands, proteoglycans, and modulatory proteins should guide multiple aspects of the regeneration process and cooperativity between the different extracellular matrix components, which bears the chance to maximize the therapeutic efficiency and simultaneously lower the doses. Hence, efforts to include multiple of these factors in biomaterial design are well worth. In the following, multifunctional implant coatings based on bioactive peptides are reviewed and concepts to implement strong surface anchoring for stable cell adhesion and a dynamic delivery of modulator proteins are discussed.

Discovering Cell-Adhesion Peptides in Tissue Engineering: Beyond RGD

As an alternative to natural extracellular matrix (ECM) macromolecules, cell-adhesion peptides (CAPs) have had tremendous impact on the design of cell culture platforms, implants, and wound dressings. However, only a handful of CAPs have been utilized. The discrepancy in ECM composition strongly affects cell behavior, so it is paramount to reproduce such differences in synthetic systems. This Opinion article presents strategies inspired from high-throughput screening techniques implemented in drug discovery to exploit the potential of a growing CAP library. These strategies are expected to promote the use of a broader spectrum of CAPs, which in turn could lead to improved cell culture models, implants, and wound dressings.

Mono vs multilayer fibronectin coatings on polar/hydrophobic/ionic polyurethanes: Altering surface interactions with human monocytes

Monocyte interactions with materials that are biofunctionalized with fibronectin (Fn) are of interest because of the documented literature which associates this protein with white blood cell function at implant sites. A degradable-polar hydrophobic ionic polyurethane (D-PHI), has been reported to promote an anti-inflammatory response from human monocytes. The aim of the current work was to study the influence of intrinsic D-PHI material chemistry on Fn adsorption (mono and multi-layer structures), and to investigate the influence of such chemistry on the structural state of the Fn, as well as the latter's influence on the activity of human monocytes on the protein coated substrates. Significant differences in Fn adsorption, surface hydrophobicity and the availability of defined peptide sequences (N terminal, C terminal or Cell Binding Domain) for the Fn in mono vs multilayer structures were observed as a function of the changes in intrinsic material chemistry. A D-PHI-formulated polyurethane substrate with subtle changes in anionic and hydrophobic domain content relative to the polar non-ionic urethane/carbonate groups within the polymer matrix promoted the lowest activation of monocytes, in the presence of multi-layer Fn constructs. These results highlight the importance of chemical heterogeneity as a design parameter for biomaterial surfaces, and establishes a desired strategy for controlling human monocyte activity at the surface of devices, when these are coated with multi-layer Fn structures. The latter is an important step towards functionalizing the materials with multi-layer protein drug carriers as interventional therapeutic agents.

STATEMENT OF SIGNIFICANCE

The control of the behavior of monocytes, especially migration and activation, is of crucial interest to modulate the inflammatory response at the site of implanted biomaterial. Several studies report the influence of adsorbed serum proteins on the behavior of monocytes on biomaterials. However, few studies show the influence of surface chemical group distribution on the controlled adsorption and the subsequent induced conformation- of mono versus multi-layer assembled structures generated from specific proteins implicated in wound repair. The current research considered the role of Fn adsorption and conformation in thin films while interacting with the intrinsic chemistry of segmented block polyurethanes; and the influence of the former on modulation and activation of human monocytes.

Targeting the Hemopexin-like Domain of Latent Matrix Metalloproteinase-9 (proMMP-9) with a Small Molecule Inhibitor Prevents the Formation of Focal Adhesion Junctions

A lack of target specificity has greatly hindered the success of inhibitor development against matrix metalloproteinases (MMPs) for the treatment of various cancers. The MMP catalytic domains are highly conserved, whereas the hemopexin-like domains of MMPs are unique to each family member. The hemopexin-like domain of MMP-9 enhances cancer cell migration through self-interaction and heterointeractions with cell surface proteins including CD44 and α4β1 integrin. These interactions activate EGFR-MAP kinase dependent signaling that leads to cell migration. In this work, we generated a library of compounds, based on hit molecule N-[4-(difluoromethoxy)phenyl]-2-[(4-oxo-6-propyl-1H-pyrimidin-2-yl)sulfanyl]-acetamide, that target the hemopexin-like domain of MMP-9. We identify N-(4-fluorophenyl)-4-(4-oxo-3,4,5,6,7,8-hexahydroquinazolin-2-ylthio)butanamide, 3c, as a potent lead (K_d = 320 nM) that is specific for binding to the proMMP-9 hemopexin-like domain. We demonstrate that 3c disruption of MMP-9 homodimerization prevents association of proMMP-9 with both α4β1 integrin and CD44 and results in the dissociation of EGFR. This disruption results in decreased phosphorylation of Src and its downstream target proteins focal adhesion kinase (FAK) and paxillin (PAX), which are implicated in promoting tumor cell growth, migration, and invasion. Using a chicken chorioallantoic membrane in vivo assay, we demonstrate that 500 nM 3c blocks cancer cell invasion of the basement membrane and reduces angiogenesis. In conclusion, we present a mechanism of action for 3c whereby targeting the hemopexin domain results in decreased cancer cell migration through simultaneous disruption of α4β1 integrin and EGFR signaling pathways, thereby preventing signaling bypass. Targeting through the hemopexin-like domain is a powerful approach to antimetastatic drug development.

The α4β1/EMILIN1 interaction discloses a novel and unique integrin-ligand type of engagement

EMILIN1, a homo-trimeric adhesive ECM glycoprotein, interacts with the α4β1 integrin through its gC1q domain. Uniquely among the C1q family members, the EMILIN1 gC1q presents only nine-stranded β-sandwich fold and the missing strand is substituted by a disordered 19-residue long segment spanning from Y927 to G945 at the apex of the gC1q domain. This unstructured loop exposes to the solvent the acidic residue E933, which plays a key role in the α4β1 integrin mediated interaction. Here, we experimentally determined that the three E933 residues (one from each monomer) are all required for ligand binding. By docking the NMR structure of the gC1q to a virtual α4β1 crystal structure based on the known structures of α4β7 and α5β1 integrins we built a model of α4β1-gC1q complex where three E933 residues are smoothly forced to coordinate the Mg²⁺ ion at the βI MIDAS site of the integrin. By bringing the three E933 close in space, the trimeric supramolecular organization of gC1q allows the formation of a proper 3D geometry and suggests a quaternary-structure-dependent mode of interaction. Furthermore, we experimentally identified R904 as a synergistic residue for cell adhesion. Accordingly, the model showed that this residue is able to form potential stabilizing intra-chain salt bridges with residues E928 and E930. This mode of interaction likely accounts for a more stable and durable α4β1-gC1q interaction in comparison with the prototypic CS1 ligand. To our knowledge, this is the first report describing the simultaneous involvement of all the three acidic residues of a trimeric ligand in the formation of a dimeric complex with the integrin βI domain.

Fibronectin connecting segment-1 peptide inhibits pathogenic leukocyte trafficking and inflammatory demyelination in experimental models of chronic inflammatory demyelinating polyradiculoneuropathy

The molecular determinants of pathogenic leukocyte migration across the blood-nerve barrier (BNB) in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) are unknown. Specific disease modifying therapies for CIDP are also lacking. Fibronectin connecting segment-1 (FNCS1), an alternatively spliced fibronectin variant expressed by microvascular endothelial cells at sites of inflammation in vitro and in situ, is a counterligand for leukocyte α₄ integrin (also known as CD49d) implicated in pathogenic leukocyte trafficking in multiple sclerosis and inflammatory bowel disease. We sought to determine the role of FNCS1 in CIDP patient leukocyte trafficking across the BNB in vitro and in severe chronic demyelinating neuritis in vivo using a representative spontaneous murine CIDP model. Peripheral blood mononuclear leukocytes from 7 untreated CIDP patients were independently infused into a cytokine-treated, flow-dependent in vitro BNB model system. Time-lapse digital video microscopy was performed to visualize and quantify leukocyte trafficking, comparing FNCS1 peptide blockade to relevant controls. Fifty 24-week old female B7-2 deficient non-obese diabetic mice with spontaneous autoimmune peripheral polyneuropathy (SAPP) were treated daily with 2mg/kg FNCS1 peptide for 5days via intraperitoneal injection with appropriate controls. Neurobehavioral measures of disease severity, motor nerve electrophysiology assessments and histopathological quantification of inflammation and morphometric assessment of demyelination were performed to determine in vivo efficacy. The biological relevance of FNCS1 and CD49d in CIDP was evaluated by immunohistochemical detection in affected patient sural nerve biopsies. 25μM FNCS1 peptide maximally inhibited CIDP leukocyte trafficking at the human BNB in vitro. FNCS1 peptide treatment resulted in significant improvements in disease severity, motor electrophysiological parameters of demyelination and histological measures of inflammatory demyelination. Microvessels demonstrating FNCS1 expression and CD49d+ leukocytes were seen within the endoneurium of patient nerve biopsies. Taken together, these results imply a role for FNCS1 in pathogenic leukocyte trafficking in CIDP, providing a potential target for therapeutic modulation.

Inhibition of Tumor Metastasis by a Synthetic Polymer Containing a Cell-Adhesive RGDS Peptide

A water soluble polymer containing cell adhesive Arg-Gly-Asp- Ser (RGDS) sequence, i.e., poly(carboxyethylmethacrylamide-RGDS) conjugate [poly(CEMA-RGDS)], was synthesized. Poly(CEMA-RGDS) inhibited lung metastasis of B16-BL6 melanoma cells in a dose-dependent manner (20-1000 μg) and liver metastasis of L5178YML25 lymphoma cells. A mixture of poly- (CEMA) and RGDS peptide or poly(CEMA) alone did not show any inhibitory effect on lung metastasis. The Gly-Arg-Gly-Asp-Ser (GRGDS) peptide required high doses (3000 μ g) to obtain a sufficient antimetastatic effect. An in vitro study showed that poly(CEMA-RGDS) as well as RGDS + poly(CEMA) gave similar inhibition of B16-BL6 cell invasion into reconstituted basement mem brane Matrigel. Intermittent i.v. administration of poly(CEMA-RGDS) after in oculation with B16-BL6 cells caused significant inhibition of spontaneous lung metastasis as compared with the multiple administration of RGDS, poly- (CEMA) or untreated control. These results demonstrate that the conjugation

Identification of important long non-coding RNAs and highly recurrent aberrant alternative splicing events in hepatocellular carcinoma through integrative analysis of multiple RNA-Seq datasets

Hepatocellular carcinoma (HCC) is an aggressive and deadly cancer. The molecular pathogenesis of the disease remains poorly understood. To better understand HCC biology and explore potential biomarkers and therapeutic targets, we investigated the whole transcriptome of HCC. Considering the genetic heterogeneity of HCC, four datasets from four studies consisting of 15 pairs of HCC and adjacent normal samples were analyzed. We observed that the number of lncRNAs expressed in each HCC sample was consistently greater than the adjacent normal sample. Moreover, 15 lncRNAs were identified expressed in five to seven HCC tissues but were not detected in any adjacent normal tissue. Differential expression analysis detected 35 up- and 80 down-regulated lncRNAs in HCC samples compared with adjacent normal samples. In addition, five differentially expressed lncRNAs were predicted to play a role in oxidation and reduction process. With regard to splicing alterations, we identified nine highly recurrent differential splicing events belonging to eight genes USO1, RPS24, CCDC50, THNSL2, NUMB, FN1 (two events), SLC39A14 and NR1I3. Of them, splicing alterations of SLC39A14 and NR1I3 were reported for the association with HCC for the first time. The splicing dysregulation in HCC may be influenced by three splicing factors ESRP2, CELF2 and SRSF5 which were significantly down-regulated in HCC samples. This study revealed uncharacterized aspects of HCC transcriptome and identified important lncRNAs and splicing isoforms with the potential to serve as biomarkers and therapeutic targets for the disease.

Hybrid hydrogels based on keratin and alginate for tissue engineering

Novel hybrid hydrogels based on alginate and keratin were successfully produced for the first time. The self-assembly properties of keratin, and its ability to mimic the extracellular matrix were combined with the excellent chemical and mechanical stability and biocompatibility of alginate to produce 2D and 3D hybrid hydrogels. These hybrid hydrogels were prepared using two different approaches: sonication, to obtain 2D hydrogels, and a pressure-driven extrusion technique to produce 3D hydrogels. All results indicated that the composition of the hydrogels had a significant effect on their physical properties, and that they can easily be tuned to obtain materials suitable for biological applications. The cell-material interaction was assessed through the use of human umbilical vein endothelial cells, and the results demonstrated that the alginate/keratin hybrid biomaterials supported cell attachment, spreading and proliferation. The results proved that such novel hybrid hydrogels might find applications as scaffolds for soft tissue regeneration.

Epithelial wound healing on keratin film, amniotic membrane and polystyrene in vitro

PURPOSE

Corneal epithelial wound healing is a major issue in ocular surface (OS) reconstruction. Aim of this study was to evaluate parameters of epithelial wound healing in vitro on transparent keratin films (KFs) derived from human hair in comparison with amniotic membrane (AM) and polystyrene.

MATERIALS AND METHODS

The human corneal epithelial cell line (HCE-T) was expanded on KF, AM and commercially available 24-well polystyrene cell culture plates in vitro to compare cell proliferation, migration and attachment by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, scratch-wound healing and adhesion assay. Cells cultured on KF and AM at an air-liquid interface for 14 d were stained with hematoxylin and eosin for histology.

RESULTS

The highest proliferation of HCE-T cells was observed on polystyrene at all time points (p < 0.05). At a seeding density of 5 × 10(3) cells/well, no difference in proliferation was found between AM and KF after 24 h and 72 h (p = 0.582 and p = 0.066), while higher proliferation was observed on AM compared to KF after 48 h (p = 0.005). At a seeding density of 1 × 10(4) cells/well, no difference was found between AM and KF after 24 h (p = 0.252), while higher proliferation was observed on AM compared to KF after 48 h and 72 h (p = 0.001 and p = 0.003). The significantly fastest cell migration was observed on polystyrene at all time points (p < 0.01). Cell migration was significantly higher on KF compared to AM at 48 h (p < 0.05). After 30 min, there were significantly more cells attached to AM compared to polystyrene and KF (p = 0.032 and p = 0.001). No significant difference in cell attachment was observed between KF and polystyrene (p = 0.147). Histology demonstrated that HCE-T cells cultured on KF and AM at an air-liquid interface for 14 d form a multilayered epithelium similar to normal human corneal epithelium.

CONCLUSION

Transparent KFs derived from human hair support proliferation, migration, adhesion and differentiation of HCE-T cells in vitro. Therefore, it could be a promising alternative to AM for OS reconstruction.

Toxicity study of isolated polypeptide from wool hydrolysate

The cytotoxicity of wool polypeptide has been evaluated by both cell and animal models. Wool was dissolved in sodium hydroxide solution, the pH value of the solution was adjusted to 5.55 and the precipitate was harvested as wool polypeptide. The spray-dried polypeptide was collected as powders and characterized by SEM, FTIR and TG-DSC. The cell culturing results showed that wool polypeptide had no obvious negative effect on cell viability in vitro. Both acute oral toxicity and subacute 30-day oral toxicology studies showed that wool polypeptide had no influence on body weight, feed consumption, blood chemistry, and hematology at any dose levels. There were no treatment related findings on gross or detailed necroscopy, organ weights, organ/body weight ratios and histology. Our study indicated the absence of toxicity in wool polypeptide and supported its safe use as a food ingredient or drug carrier.

A 17-residue sequence from the matrix metalloproteinase-9 (MMP-9) hemopexin domain binds α4β1 integrin and inhibits MMP-9-induced functions in chronic lymphocytic leukemia B cells

We previously showed that pro-matrix metalloproteinase-9 (proMMP-9) binds to B chronic lymphocytic leukemia (B-CLL) cells and contributes to B-CLL progression by regulating cell migration and survival. Induction of cell survival involves a non-proteolytic mechanism and the proMMP-9 hemopexin domain (PEX9). To help design specific inhibitors of proMMP-9-cell binding, we have now characterized B-CLL cell interaction with the isolated PEX9. B-CLL cells bound soluble and immobilized GST-PEX9, but not GST, and binding was mediated by α4β1 integrin. The ability to recognize PEX9 was observed in all 20 primary samples studied irrespective of their clinical stage or prognostic marker phenotype. By preparing truncated forms of GST-PEX9 containing structural blades B1B2 or B3B4, we have identified B3B4 as the primary α4β1 integrin-interacting region within PEX9. Overlapping synthetic peptides spanning B3B4 were then tested in functional assays. Peptide P3 (FPGVPLDTHDVFQYREKAYFC), a sequence present in B4 or smaller versions of this sequence (peptides P3a/P3b), inhibited B-CLL cell adhesion to GST-PEX9 or proMMP-9, with IC(50) values of 138 and 279 μm, respectively. Mutating the two aspartate residues to alanine rendered the peptides inactive. An anti-P3 antibody also inhibited adhesion to GST-PEX9 and proMMP-9. GST-PEX9, GST-B3B4, and P3/P3a/P3b peptides inhibited B-CLL cell transendothelial migration, whereas the mutated peptide did not. B-CLL cell incubation with GST-PEX9 induced intracellular survival signals, namely Lyn phosphorylation and Mcl-1 up-regulation, and this was also prevented by the P3 peptides. The P3 sequence may, therefore, constitute an excellent target to prevent proMMP-9 contribution to B-CLL pathogenesis.

Neisseria gonorrhoeae pilin glycan contributes to CR3 activation during challenge of primary cervical epithelial cells

Expression of type IV pili by Neisseria gonorrhoeae plays a critical role in mediating adherence to human epithelial cells. Gonococcal pilin is modified with an O-linked glycan, which may be present as a di- or monosaccharide because of phase variation of select pilin glycosylation genes. It is accepted that bacterial proteins may be glycosylated; less clear is how the protein glycan may mediate virulence. Using primary, human, cervical epithelial (i.e. pex) cells, we now provide evidence to indicate that the pilin glycan mediates productive cervical infection. In this regard, pilin glycan-deficient mutant gonococci exhibited an early hyper-adhesive phenotype but were attenuated in their ability to invade pex cells. Our data further indicate that the pilin glycan was required for gonococci to bind to the I-domain region of complement receptor 3, which is naturally expressed by pex cells. Comparative, quantitative, infection assays revealed that mutant gonococci lacking the pilin glycan did not bind to the I-domain when it is in a closed, low-affinity conformation and cannot induce an active conformation to complement receptor 3 during pex cell challenge. To our knowledge, these are the first data to directly demonstrate how a protein-associated bacterial glycan may contribute to pathogenesis.

A high throughput micro-array system of polymer surfaces for the manipulation of primary pancreatic islet cells

We developed a high throughput micro-arrayed polymer system for the study of polymer surfaces for islet cell culture. A micro-arrayed library with 496 different polymers was synthesized and used to examine attachment and insulin expression of islet cells. While most polymers were not supportive, several related polymers were identified as suitable ("hit's"). The "hit" arrays composed of "hit" polymers with 36 replicates were fabricated to confirm their capacities to support the attachment of islet cells, and these capacities were further validated in large surfaces. Notably, the attachment of islet cells on these synthetic polymeric films has been found to be as supportive as 804G supernatant coated tissue culture polystyrene dishes, one of the most extensively used substrates for the islet cell attachment. Interestingly, the polymeric surfaces optimal for a different cell type, hES derived cells, were distinct, highlighting the utility of these approaches for identifying cell type specific surfaces.

The CS1 segment of fibronectin is involved in human OSCC pathogenesis by mediating OSCC cell spreading, migration, and invasion

Background

The alternatively spliced V region or type III connecting segment III (IIICS) of fibronectin is important in early development, wound healing, and tumorigenesis, however, its role in oral cancer has not been fully investigated. Thus, we investigated the role of CS-1, a key site within the CSIII region of fibronectin, in human oral squamous cell carcinoma (OSCC).

Methods

To determine the expression of CS-1 in human normal and oral SCC tissue specimens immunohistochemical analyses were performed. The expression of CS1 was then associated with clinicopathological factors. To investigate the role of CS-1 in regulating OSCC cell spreading, migration and invasion, OSCC cells were assayed for spreading and migration in the presence of a CS-1 peptide or a CS-1 blocking peptide, and for invasion using Matrigel supplemented with these peptides. In addition, integrin α4siRNA or a focal adhesion kinase (FAK) anti-sense oligonucleotide was transfected into OSCC cells to examine the mechanistic role of integrin α4 or FAK in CS1-mediated cell spreading and migration, respectively.

Results

CS-1 expression levels were significantly higher in OSCC tissues compared to normal tissues (p < 0.05). Also, although, high levels of CS-1 expression were present in all OSCC tissue samples, low-grade tumors stained more intensely than high grade tumors. OSCC cell lines also expressed higher levels of CS-1 protein compared to normal human primary oral keratinocytes. There was no significant difference in total fibronectin expression between normal and OSCC tissues and cells. Inclusion of CS-1 in the in vitro assays enhanced OSCC cell spreading, migration and invasion, whereas the CS1 blocking peptide inhibited these processes. Suppression of integrin α4 significantly inhibited the CS1-mediated cell spreading. Furthermore, this migration was mediated by focal adhesion kinase (FAK), since FAK suppression significantly blocked the CS1-induced cell migration.

Conclusion

These data indicate that the CS-1 site of fibronectin is involved in oral cancer pathogenesis and in regulating OSCC cell spreading, migration and invasion.

Development and characterization of a novel human in vitro blood-nerve barrier model using primary endoneurial endothelial cells

There are phenotypic and functional differences between vascular endothelium from different tissues and between microvascular and macrovascular endothelial cells (ECs) from the same tissue. Relatively little is known about the human blood-nerve barrier (BNB). We report the development of an in vitro BNB model using primary human endoneurial ECs freshly isolated and purified from decedent sciatic nerves via endoneurial stripping, connective tissue enzymatic digestion, and density centrifugation. Primary human endoneurial ECs are spindle shaped and contact inhibited. They rapidly differentiate to form capillary-like networks and microvessels, bind Ulex Europaeus Agglutinin 1 lectin, express von Willebrand factor, and endocytose acetylated low-density lipoprotein. They also express specific transport and cellular adhesion molecules and tight junction proteins, consistent with cells that form a highly restrictive endothelial barrier similar to the blood-brain barrier. When cultured on collagen-coated transwell inserts, the primary human endoneurial ECs develop an in vitro BNB with high transendothelial electrical resistances (160 Omega x cm(2); maximal 12 days after seeding) and low solute permeability coefficient to fluoresceinated high-molecular weight (70 kDa) dextran (2.75 x 10(-3) cm/minute). This in vitro BNB model retains essential known or expected characteristics of the human BNB and has many potential applications for studies of solute, macromolecule, microbial, virus, and leukocyte interactions with this highly specialized endothelial barrier.

Integrin alpha(v)beta(3) on human endothelial cells binds von Willebrand factor strings under fluid shear stress

Acutely secreted von Willebrand factor (VWF) multimers adhere to endothelial cells, support platelet adhesion, and may induce microvascular thrombosis. Immunofluorescence microscopy of live human umbilical vein endothelial cells showed that VWF multimers rapidly formed strings several hundred micrometers long on the cell surface after stimulation with histamine. Unexpectedly, only a subset of VWF strings supported platelet binding, which depended on platelet glycoprotein Ib. Electron microscopy showed that VWF strings often consisted of bundles and networks of VWF multimers, and each string was tethered to the cell surface by a limited number of sites. Several approaches implicated P-selectin and integrin alpha(v)beta(3) in anchoring VWF strings. An RGDS peptide or a function-blocking antibody to integrin alpha(v)beta(3) reduced the number of VWF strings formed. In addition, integrin alpha(v) decorated the VWF strings by immunofluorescence microscopy. Furthermore, lentiviral transduction of shRNA against the alpha(v) subunit reduced the expression of cell-surface integrin alpha(v)beta(3) and impaired the ability of endothelial cells to retain VWF strings. Soluble P-selectin reduced the number of platelet-decorated VWF strings in the absence of Ca(2+) and Mg(2+) but had no effect in the presence of these cations. These results indicate that VWF strings bind specifically to integrin alpha(v)beta(3) on human endothelial cells.

Alpha4beta1 integrin and 190-kDa CD44v constitute a cell surface docking complex for gelatinase B/MMP-9 in chronic leukemic but not in normal B cells

As B-cell chronic lymphocytic leukemia (B-CLL) progresses, malignant cells extravasate and infiltrate lymphoid tissues. Several molecules, including gelatinase B/MMP-9, contribute to these processes. Although mainly a secreted protease, some MMP-9 is present at the B-CLL cell surface and the function, mode of anchoring, and interactions of this MMP-9 are unknown. Here we show that anti-MMP-9 antibodies immunoprecipitated a 190-kDa CD44v isoform and alpha4beta1 integrin from B-CLL cells, but not from normal B cells. Function-blocking antibodies to alpha4beta1 or CD44, or transfection with specific siRNAs, decreased cell-associated proMMP-9 and increased the secreted form. B-CLL cells attached to and bound proMMP-9 and active MMP-9, and this was inhibited by blocking the expression or function of alpha4beta1 or CD44. The MMP-9 hemopexin domain was critical in these interactions. alpha4beta1 and 190-kDa CD44v (but not CD44H) formed a complex at the cell surface, since they both coimmunoprecipitated with anti-alpha4, anti-beta1, or anti-CD44 antibodies. Immunofluorescence analyses confirmed that alpha4beta1 and CD44v colocalized with MMP-9. Binding of proMMP-9 inhibited B-CLL cell migration, and this required MMP-9 proteolytic activity. Thus, we have identified alpha4beta1 and CD44v as a novel proMMP-9 cell surface docking complex and show that cell-associated MMP-9 may regulate B-CLL cell migration and arrest.

Purification of fibronectin

This unit describes the purification of the multifunctional adhesive glycoprotein fibronectin from plasma or of cell-derived fibronectin from cell surfaces and from conditioned medium. Fibronectin can be used in cell adhesion and migration assays, and can be obtained in relatively high purity using simple affinity chromatography techniques.

Peptides Derived from Fibronectin Type III Connecting Segments Promote Endothelial Cell Adhesion but Not Platelet Adhesion: Implications in Tissue-Engineered Vascular Grafts

The development of a completely tissue-engineered small-caliber prosthesis suitable for incorporation into an in vivo vascular network is fraught with many challenges, including overcoming resistance to endothelialization and susceptibility to thrombogenesis. In this work, recombinant human fibronectin-derived low-molecular-weight peptide fragments were studied for their ability to promote cell type-specific alpha(4) integrin-mediated adhesion. Two populations of primary human endothelial cells were examined and found to express alpha(4) integrin receptors on their surfaces; on the contrary, human platelets were not found to be expressers of alpha(4) integrins. A peptide fragment isolated from the variably spliced human fibronectin type III connecting segment-1 (CS-1) domain was determined to mediate statistically significant endothelial cell alpha(4) integrin-mediated adhesion. In contrast, the fibronectin type III CS-1 fragment did not support human platelet adhesion under physiological fluid shear conditions, although fully intact human fibronectin molecules supported shear-induced platelet adhesion. This suggests that platelets bind to fibronectin in regions not encompassing the CS-1 domain. In conclusion, this work has demonstrated that the low-molecular-weight peptide CS-1 could serve as a cell-selective adhesion mediator in the engineering of a more-compatible small-caliber vascular graft lumen interface.

Surface presentation of bioactive ligands in a nonadhesive background using DOPA-tethered biotinylated poly(ethylene glycol)

We have developed surfaces for the selective presentation of biotinylated peptides and proteins in a background that resists nonspecific protein adsorption; controlled amounts of biotinylated poly(ethylene glycol) (MW 3400 Da; PEG3400) anchored to titanium-dioxide-coated surfaces via an adhesive tri-peptide sequence of L-3,4-dihydroxyphenylalanine (DOPA3-PEG3400-biotin; DPB) were incorporated within a DOPA3-PEG2000 background. Using optical waveguide lightmode spectroscopy, we found that the amounts of sequentially adsorbed NeutrAvidin and singly biotinylated molecules increased proportionally with the amount of DPB in the surface. Biotinylated peptides (MW approximately 2000 Da) were able to fill all three of the remaining avidin-binding sites, while only one molecule of biotinylated PEG5000 or stem cell factor bound to each avidin. The resulting biotin-avidin-biotin linkages were stable for prolonged periods under continuous perfusion, even in the presence of excess free biotin. Hematopoietic M07e cells bound to immobilized peptide ligands for alpha5beta1 (cyclic RGD) and alpha4beta1 (cylic LDV) integrins in a DPB-dose-dependent manner, with near-maximal binding to cylic LDV for surfaces containing 1% DPB. Multiple ligands were adsorbed in a controlled manner by incubating NeutrAvidin with the respective ligands in the desired molar ratio and then adding the resulting complexes to DPB-containing surfaces. Cell adhesion to surfaces containing both cylic LDV and cyclic RGD increased in an additive manner compared to that for the individual ligands. The bioactivity of adsorbed biotinylated stem cell factor was retained, as demonstrated by DPB-dose-dependent M07e cell adhesion and ERK1/2 activation.

The cell interaction sites of fibronectin in tumour metastasis

Adhesion to specific extracellular matrix molecules appears to be an important prerequisite for successful target organ colonization by metastasizing tumour cells. Interference in the adhesive function of malignant cells with antiadhesive agents is therefore one potential approach for preventing metastasis. Recently, synthetic peptides taken from the cell interaction sites of fibronectin have been characterized as inhibitors of cellular adhesion in vitro. Using these antiadhesive probes we have examined the role of cell adhesion to fibronectin in tumour metastasis using the B16-F10 murine melanoma model system. Two sequences from the IIICS cell-binding domain, the 25-mer CS1 peptide and the tetrapeptide Arg-Glu-Asp-Val (REDV), had no detectable activity, but the pentapeptide Gly-Arg-Gly-Asp-Ser (GRGDS), an active sequence from the central cell-binding domain, exhibited potent, dose-dependent inhibition, indicating a role for this cell recognition determinant in tumour metastasis. Under appropriate conditions GRGDS treatment afforded remarkable protection to the host; mice injected with melanoma cells and peptide were still alive 15 months after injection whereas mice injected with melanoma cells alone died within six weeks. Kinetic analyses of the retention of tumour cells in the lungs and of the vascular clearance rate of labelled GRGDS predict an early time frame of activity for the peptide. From the results of a variety of in vitro invasion and migration assays it appears that GRGDS may interfere with multiple, fibronectin-mediated adhesive and migratory events at different points of the metastatic cascade. In preliminary studies designed to optimize the therapeutic usefulness of GRGDS-like agents, peptide conjugates have been found to possess enhanced antiadhesive activity as well as an extended vascular clearance rate. In the future, therefore, these or related peptide derivatives may be potentially useful agents for the prevention of tumour metastasis.

Mechanisms of VCAM-1 and fibronectin binding to integrin alpha 4 beta 1: implications for integrin function and rational drug design

Integrin alpha 4 beta 1 can mediate both cell-cell and cell-extracellular matrix adhesion by binding to either fibronectin or vascular cell adhesion molecule 1 (VCAM-1). Both interactions are important for extravasation of leukocytes from the blood implying that rationally designed inhibitors of alpha 4 beta 1 function may be useful for treating a various inflammatory conditions. The mechanisms of ligand binding by alpha 4 beta 1 are complicated by the fact that alternative splicing can generate different isoforms of the receptor-binding domains in both fibronectin and VCAM-1. Therefore, in addition to developing alpha 4 beta 1 antagonists, we have also been interested in identifying isoform-specific functions. Recombinant ligand variants have been tested in adhesion and direct receptor-binding assays and each molecule was found to have a different inherent affinity for alpha 4 beta 1 that endows them with different adhesive activities. This suggests that alternative splicing may regulate alpha 4 beta 1-dependent motility in vivo. The initial strategy that we have adopted to develop alpha 4 beta 1 inhibitors has been to identify key amino acid residues and peptide sequences participating in the receptor-ligand binding event and to use this information to generate synthetic mimetics. Three active sites have been identified in fibronectin by testing truncated proteins, expressing recombinant fragments and screening synthetic peptides. Two of these sites employ versions of a novel integrin-binding motif, LDVP/IDAP. A key active site in VCAM-1 has been identified by similar approaches as the related sequence IDSP. Since IDSP-like sequences are probably used by other integrin-binding immunoglobulins, derivatives of these peptides may turn out to be the forerunners of a new generation of therapeutic agents with multiple applications.

Determinants of CCL5-driven mononuclear cell migration across the blood-brain barrier. Implications for therapeutically modulating neuroinflammation

Chemokine receptors and adhesion molecules are used selectively for the transmigration of leukocytes across the blood-brain barrier (BBB) during neuroinflammation. We established an activated in vitro BBB (aIVBBB) using physiological concentrations of cytokines. We studied CCL5-driven migration as a model to determine how chemokine receptors and adhesion molecules regulate T-cell and monocyte migration across the aIVBBB. Increased expression of CCL5 and its receptors, CCR1 and CCR5 have been described in the perivascular space of multiple sclerosis (MS) lesions. Elucidating the determinants of CCL5-mediated mononuclear cell migration may clarify appropriate targets for therapeutic modulation in neuroinflammatory conditions. In response to CCL5, there was a significant increase in total mononuclear cell migration across the aIVBBB. Neutralizing monoclonal antibodies to CCR1 and CCR5 abrogated CCL5-driven transmigration, suggestive of non-redundant receptor usage in mononuclear cell migration to this chemokine in vitro. CCL5-driven transmigration was also dependent on alpha(4)beta(1) integrin/fibronectin connecting segment-1 (FN CS-1) and alpha(L)beta(2) integrin/intercellular adhesion molecule (ICAM-1) interactions. Monocyte migration to CCL5 was solely dependent on alpha(4)beta(1) integrin/FN CS-1 while T-cell migration required both alpha(L)beta(2) integrin/ICAM-1 and alpha(4)beta(1) integrin/FN CS-1 interactions. These findings provide plausible molecular targets for the selective inhibition of mononuclear cell trafficking during the acute immune effector phases of MS and other neuroinflammatory diseases.

Culture of human cervical cancer cells, SiHa, in the presence of fibronectin activates MMP-2

PURPOSE

Several studies indicate that integrin receptors are involved in the regulation of matrix metalloproteinase (MMP) expression. Integrin-ECM ligand interaction leads to phosphorylation of focal adhesion kinase (FAK) and activation of mitogen activated protein kinase pathways. In this present communication, we cultured human cervical cancer cells, SiHa, in the presence of fibronectin to study fibronectin-integrin mediated modulation of MMP activity.

METHODS

SiHa cells were cultured in serum-free medium (SFCM) in the presence of fibronectin, SFCM was collected and gelatin zymography was performed. Western blot, RT-PCR and immunocytochemistry were performed with SiHa cells cultured in the presence of fibronectin.

RESULTS

The culture of SiHa cells in the presence of 50 microg/1.5 ml fibronectin led to expression of pro-MMP-9 and activation of MMP-2 within 2 h. When cells were treated with ERK inhibitor (PD98059) and grown in the presence of fibronectin MMP-2 activation was partially inhibited, but when cells were treated with PI-3K inhibitor (LY294002) and grown in the presence of fibronectin MMP-2 activation was appreciably reduced. Tyrosine phosphorylation of FAK, PI-3K and ERK and nuclear trafficking of ERK were increased in SiHa cells grown in the presence of fibronectin. Increased MT1-MMP mRNA expression and processing of MT1-MMP were also observed in SiHa cells grown in the presence of fibronectin.

CONCLUSIONS

Our findings indicate that the culture of SiHa cells in SFCM in the presence of fibronectin perhaps generates a signalling cascade which leads to the expression of pro-MMP-9 and the activation of MMP-2 within 2 h. The signalling pathways activated seem to be the FAK/ERK/PI-3K pathway.

The monoclonal antibody SM5-1 recognizes a fibronectin variant which is widely expressed in melanoma

Background

Previously we have generated the monoclonal antibody SM5-1 by using a subtractive immunization protocol of human melanoma. This antibody exhibits a high sensitivity for primary melanomas of 99% (248/250 tested) and for metastatic melanoma of 96% (146/151 tested) in paraffin embedded sections. This reactivity is superior to the one obtained by HMB-45, anti-MelanA or anti-Tyrosinase and is comparable to anti-S100. However, as compared to anti-S100, the antibody SM5-1 is highly specific for melanocytic lesions since 40 different neoplasms were found to be negative for SM5-1 by immunohistochemistry. The antigen recognized by SM5-1 is unknown.

Methods

In order to characterize the antigen recognized by mAb SM5-1, a cDNA library was constructed from the metastatic human melanoma cell line SMMUpos in the Uni-ZAP lambda phage and screened by mAb SM5-1. The cDNA clones identified by this approach were then sequenced and subsequently analyzed.

Results

Sequence analysis of nine independent overlapping clones (length 3100–5600 bp) represent fibronectin cDNA including the ED-A, but not the ED-B region which are produced by alternative splicing. The 89aa splicing variant of the IIICS region was found in 8/9 clones and the 120aa splicing variant in 1/9 clones, both of which are included in the CS1 region of fibronectin being involved in melanoma cell adhesion and spreading.

Conclusion

The molecule recognized by SM5-1 is a melanoma associated FN variant expressed by virtually all primary and metastatic melanomas and may play an important role in melanoma formation and progression. This antibody is therefore not only of value in immunohistochemistry, but potentially also for diagnostic imaging and immunotherapy.

Molecular determinants of biocompatibility

The biocompatibility of medical implants dictates the fate of almost all medical devices. It is well established that medical devices trigger a variety of adverse tissue responses, such as inflammation, fibrosis, infection and thrombosis. However, the mechanisms involved in biomaterial-mediated tissue responses remain largely unknown. The lack of such knowledge hinders the development of biomaterials with better biocompatibility and safety. The aim of this review is to summarize our current understanding of the processes governing foreign body reactions to tissue-contact devices. Obviously, this information is urgently needed for assisting the rational design of materials or medical devices to minimize undesirable tissue reactions upon implantation and, in addition, to promote the wound healing process.

The role of fibronectin in fibroblast migration during tissue repair

Fibronectin is known to stimulate cell growth and migration, but research does not provide a complete picture of all the mechanisms involved. Further studies are needed before practitioners can apply in vitro results to in vivo environments.

Cell-Binding Domain Context Affects Cell Behavior on Engineered Proteins

A family of artificial extracellular matrix proteins developed for application in small-diameter vascular grafts is used to examine the importance of cell-binding domain context on cell adhesion and spreading. The engineered protein sequences are derived from the naturally occurring extracellular matrix proteins elastin and fibronectin. While each engineered protein contains identical CS5 cell-binding domain sequences, the lysine residues that serve as cross-linking sites are either (i) within the elastin cassettes or (ii) confined to the ends of the protein. Endothelial cells adhere specifically to the CS5 sequence in both of these proteins, but cell adhesion and spreading are more robust on proteins in which the lysine residues are confined to the terminal regions of the chain. These results may be due to altered protein conformations that affect either the accessibility of the CS5 sequence or its affinity for the alpha(4)beta(1) integrin receptor on the endothelial cell surface. Amino acid choice outside the cell-binding domain can thus have a significant impact on the behavior of cells cultured on artificial extracellular matrix proteins.

Increased angiogenic response in aortic explants of collagen XVIII/endostatin-null mice

Endostatin, a proteolytic fragment of basement membrane-associated collagen XVIII, has been shown to be a potent angiogenesis inhibitor both in vivo and in vitro when given at high concentrations. The precise molecular mechanisms by which it functions and whether or not it plays a role in physiological regulation of angiogenesis are not clear. In mice with targeted null alleles of Col18a1, there appears to be no major abnormality in vascular patterns or capillary density in most organs. Furthermore, the growth of experimental tumors is not increased. However, a detailed analysis of induced angiogenesis in these mice has not been performed. Therefore, we compared the angiogenic responses induced by in vitro culture of aortic explants from collagen XVIII/endostatin-null mice (ko) to wild-type (wt) littermates. We found a twofold increase in microvessel outgrowth in explants from ko mice, relative to wt explants. This increased angiogenesis was reduced to the wt level by the addition of low levels (0.1 microg/ml) of recombinant mouse or human endostatin during the culture period. To address cellular/molecular mechanisms underlying this difference in angiogenic response between ko and wt mice, we isolated endothelial cells from both strains and compared their biological behavior. Proliferation assays showed no difference between the two types of endothelial cells. In contrast, adhesion assays showed a striking difference in their ability to adhere to fibronectin suggesting that collagen XVIII/endostatin may regulate interactions between endothelial cells and underlying basement membrane-associated components, including fibronectin, such that in the absence of collagen XVIII/endostatin, endothelial cells are more adhesive to fibronectin. In the aortic explant assay, characterized by dynamic processes of microvessel elongation and regression, this may result in stabilization of newly formed vessels, reduced regression, and a net increase in microvessel outgrowth in explants from ko mice compared to the wt littermates.

Multiple binding sites in fibrinogen for integrin alphaMbeta2 (Mac-1)

The leukocyte integrin alphaMbeta2 (Mac-1) is a multiligand receptor that mediates a range of adhesive reactions of leukocytes during the inflammatory response. This integrin binds the coagulation protein fibrinogen providing a key link between thrombosis and inflammation. However, the mechanism by which alphaMbeta2 binds fibrinogen remains unknown. Previous studies indicated that a model in which two fibrinogen gammaC domain sequences, P1 (gamma190-202) and P2 (gamma377-395), serve as the alphaMbeta2 binding sites cannot fully account for recognition of fibrinogen by integrin. Here, using surface plasmon resonance, we examined the interaction of the ligand binding alphaMI-domain of alphaMbeta2 with the D fragment of fibrinogen and showed that this ligand is capable of associating with several alphaMI-domain molecules. To localize the alternative alphaMI-domain binding sites, we screened peptide libraries covering the complete sequences of the gammaC and betaC domains, comprising the majority of the D fragment structure, for alphaMI-domain binding. In addition to the P2 and P1 peptides, the alphaMI-domain bound to many other sequences in the gammaC and betaC scans. Similar to P1 and P2, synthetic peptides derived from gammaC and betaC were efficient inhibitors of alphaMbeta2-mediated cell adhesion and were able to directly support adhesion suggesting that they contain identical recognition information. Analyses of recognition specificity using substitutional peptide libraries demonstrated that the alphaMI-domain binding depends on basic and hydrophobic residues. These findings establish a new model of alphaMbeta2 binding in which the alphaMI-domain interacts with multiple sites in fibrinogen and has the potential to recognize numerous sequences. This paradigm may have implications for mechanisms of promiscuity in ligand binding exhibited by integrin alphaMbeta2.

Comparative Cell Response to Artificial Extracellular Matrix Proteins Containing the RGD and CS5 Cell-Binding Domains

This study addresses endothelial cell adhesion and spreading on a family of artificial extracellular matrix (aECM) proteins designed for application in small-diameter vascular grafts. The aECM proteins contain domains derived from elastin and from fibronectin. aECM 1 contains the RGD sequence from the tenth type III domain of fibronectin; aECM 3 contains the fibronectin CS5 cell-binding domain. Negative control proteins aECM 2 and 4 are scrambled versions of aECM 1 and 3, respectively. Competitive peptide inhibition studies and comparisons of positive and negative control proteins confirm that adhesion of HUVECs to aECM proteins 1 and 3 is sequence specific. When subjected to a normal detachment force of 780 pN, 3-fold more HUVECs remained adherent to aECM 1 than to aECM 3. HUVECs also spread more rapidly on aECM 1 than on aECM 3. These results (i) indicate that cellular responses to aECM proteins can be modulated through choice of cell-binding domain and (ii) recommend the RGD sequence for applications that require rapid endothelial cell spreading and matrix adhesion.

Fibroblast migration on fibronectin requires three distinct functional domains

Mesenchymal cell movement is normally constrained; however, fibronectin can provide a pathway for stromal cell migration during embryogenesis, morphogenesis, and wound healing. Cells can adhere to fibronectin via integrin and nonintegrin receptors, which bind multiple unique peptide sequences. Synthetic peptides and recombinant proteins were used to delineate the functional domains needed for human fibroblast migration over fibronectin. The 9th and 10th fibronectin type III repeats, which contain RGD and PHSRN synergy cell attachment sequences, support almost maximal fibroblast attachment, but not migration of primary dermal fibroblasts. Specific sequences within the heparin domain and the IIICS region are also required for migration. These findings predict and additional data confirm the necessity for the cooperation of multiple integrin and nonintegrin receptors for fibroblast migration on fibronectin. Such stringency of migration most likely imposes an immense constraint on normal mesenchymal cell mobility in unperturbed tissue. Loss of such restraint may be critical for the migration cancer cells through the extracellular matrix.

Recombinant Expression and Characterization of a Novel Fibronectin Isoform Expressed in Cartilaginous Tissues

A novel fibronectin (FN) isoform lacking the segment from IIICS (type III connecting segment) through the I-10 module is expressed predominantly in normal cartilaginous tissues. We expressed and purified recombinant cartilage-type FN using a mammalian expression system and characterized its molecular and biological properties. Although FNs have been shown to be secreted as disulfide-bonded dimers, cartilage-type FN was secreted mainly as a monomer. It was less potent than plasma-type FN in promoting cell adhesion and binding to integrin alpha5beta1, although it was more active than plasma-type FN in binding to chondroitin sulfate E. When added exogenously, cartilage-type FN was poorly assembled into the fibrillar FN matrix, mostly because of its monomeric structure. Given that cartilage is characterized by its non-fibrillar matrix with abundant chondroitin sulfate-containing proteoglycans, it is likely that cartilage-type FN has evolved to adapt itself to the non-fibrillar structure of the cartilage matrix through acquisition of a novel mechanism of alternative pre-mRNA splicing.

Integrin-specific signaling pathways controlling focal adhesion formation and cell migration

The fibronectin (FN)-binding integrins alpha4beta1 and alpha5beta1 confer different cell adhesive properties, particularly with respect to focal adhesion formation and migration. After analyses of alpha4+/alpha5+ A375-SM melanoma cell adhesion to fragments of FN that interact selectively with alpha4beta1 and alpha5beta1, we now report two differences in the signals transduced by each receptor that underpin their specific adhesive properties. First, alpha5beta1 and alpha4beta1 have a differential requirement for cell surface proteoglycan engagement for focal adhesion formation and migration; alpha5beta1 requires a proteoglycan coreceptor (syndecan-4), and alpha4beta1 does not. Second, adhesion via alpha5beta1 caused an eightfold increase in protein kinase Calpha (PKCalpha) activation, but only basal PKCalpha activity was observed after adhesion via alpha4beta1. Pharmacological inhibition of PKCalpha and transient expression of dominant-negative PKCalpha, but not dominant-negative PKCdelta or PKCzeta constructs, suppressed focal adhesion formation and cell migration mediated by alpha5beta1, but had no effect on alpha4beta1. These findings demonstrate that different integrins can signal to induce focal adhesion formation and migration by different mechanisms, and they identify PKCalpha signaling as central to the functional differences between alpha4beta1 and alpha5beta1.

Monocyte adhesion to mesangial matrix modulates cytokine and metalloproteinase production

BACKGROUND

Monocytes migrate into the glomerular mesangium during acute inflammatory renal disease, differentiate into macrophages, and may play a key role in the development and progression of glomerular scarring. Treatment strategies that inhibit monocyte infiltration ameliorate glomerular injury in animal models. Mesangial matrix contains several potential monocyte-binding domains that may contribute to monocyte entrapment and modulate cell activation.

METHODS

Adhesion of peripheral blood-derived monocytes to matrix synthesized by human mesangial cells and to individual matrix proteins was assessed by colorimetry of nuclear staining with crystal violet. Monoclonal antibodies were used to identify the cell-surface integrins and matrix ligands involved. Monocyte proliferation was assessed by 3H-thymidine incorporation and cytokine production using enzyme-linked immunosorbent assay (ELISA). Secretion of metalloproteinases and their inhibitors was determined by zymography and ELISA, respectively.

RESULTS

Monocytes bound to matrix synthesized by mesangial cells. Prestimulation of mesangial cells with tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) enhanced matrix fibronectin content (P < 0.001) and monocyte binding (P < 0.001). Blocking antibodies to fibronectin, as well as to the integrins very late antigen-4 (VLA-4) and VLA-5, reduced monocyte adhesion to mesangial matrix by approximately 50%. Incubation of monocytes with matrix, fibronectin, laminin and collagen IV enhanced production of interleukin-1beta (IL-1beta), interleukin-6 (IL-6), TNF-alpha and metalloproteinase-9 (MMP-9) when compared to cells incubated in plastic wells. However, there was no apparent difference in proliferation rate and no change in production of metalloproteinase inhibitors.

CONCLUSION

Monocyte activation within the glomerulus may be mediated by binding to mesangial matrix components, particularly fibronectin. Matrix-mediated activation enhances production of inflammatory cytokines and matrix-degrading enzymes.