Static and Dynamic Assays of Cell Adhesion Relevant to the Vasculature

Methods are described for analyzing adhesion of isolated cells (such as leukocytes, tumor cells, or precursor cells) to purified adhesion receptors or cultured endothelial cells. "Static" assays (where cells are allowed to settle on the adhesive substrates) and flow-based assays (where cells are perfused over the substrates) are compared. Direct observations of the time course of adhesion and migration can be made when purified proteins or endothelial cells are cultured in plates, after cells are allowed to settle onto them for a desired period. In the flow-based assay, cells are perfused through coated glass capillaries, flow-channels incorporating coated plates, or commercially available preformed channels. Again, direct video-microscopic observations are made. In this assay various stages of capture, immobilization, and migration can be followed. In general, the static systems have higher throughput and greatest ease of use, but yield less detailed information, while the flow-based assay is most difficult to set up but is most physiologically relevant if one is interested in the dynamics of adhesion in the vasculature.

Anti-diabetic activity of recombinant irisin in STZ-induced insulin-deficient diabetic mice

In order to investigate the hypoglycemic effects and potential mechanism of recombinant irisin on diabetes, STZ-induced diabetic mice were established and treated with irisin. The results showed that daily water and food intake, and blood glucose significantly decreased after various concentrations of recombinant irisin treatment by intraperitoneal injection, of which 1.0 mg/kg was the optimal dose for lowering blood glucose. However, the body weight exhibited no significant difference during the treatment within groups, although the 0.9% NaCl treated group showed a trend of decreased body weight and the irisin treated groups showed a tendency of increasing weight. The oral glucose tolerance was improved, and serum insulin and circulating irisin content were significantly elevated in diabetic mice after 1.0 mg/kg irisin-injection treatment, compared to diabetic mice treated with 0.9% NaCl. 1.0 mg/kg irisin-injection also significantly increased the expression of energy and metabolism-related genes. In addition, oral administration of irisin lowered the blood glucose in diabetic mice. Our data suggested that irisin could lower blood glucose in insulin-deficient diabetic mice, to some extent, through irisin-mediated induction of energy and metabolic genes expression. These observations laid a foundation for the development of irisin-based therapy.

Shear-related fibrillogenesis of fibronectin

Biomechanical forces can induce the transformation of fibronectin (Fn) from its compact structure to an extended fibrillar state. Adsorption of plasma proteins onto metallic surfaces may also influence their conformation. We used a cone-plate rheometer to investigate the effect of shear and stainless steel on conformational changes of Fn. In control experiments, cones grafted once or twice with polyethylene glycol were used. Plasma Fn was added at concentrations of 50 or 100 μg/ml to bovine serum albumin (BSA)- or Fn-coated plates and subsequently exposed to dynamic shear rates stepwise increasing from 50 to 5000 s-1 within 5 min and subsequently decreasing from 5000 to 50 s-1 within 5 min. The viscosity (mPa s) of Fn solutions was recorded over 10 min. Upon exposure to shear, the viscosity in the sample increased, suggesting conformational changes in Fn. Western blotting and densitometric analyses demonstrated that conformational changes of plasma Fn depended both on shear and protein concentration. However, there was no significant difference in fibril formation between BSA- or Fn-coated plates, suggesting that physical properties of stainless steel and biomechanical forces such as shear can affect the molecular structure of Fn. Our model may provide useful information of surface- and flow-induced alterations of plasma proteins.

Adipose tissue metabolism in 2012: Adipose tissue plasticity and new therapeutic targets

2012 has been a rewarding year for adipocyte research. A new type of brown-like adipocyte—the beige adipocyte—and irisin, a previously unknown hormone that stimulates the formation of such cells, have been discovered. A bipotential adipocyte progenitor giving rise to both brown and white adipocytes has also been identified.

[Characteristic of carbohydrate components of chickens and human's fibronectins]

The paper presents new information about the carbohydrate structures of 39-days chicken's fibronectin. It is found out that chicken fibronectin contains mainly biantennary N-glycans with a core fucose and fucosylated O-glycans. It is shown that N-glycans of chicken fibronectin are poorly sialated, since this protein exhibits affinity for the PNA and weak binding to sialospecific SNA. A comparative analysis of lectin-binding activity of chicken and human fibronectins has shown that both glycoproteins differ in glycan composition.

Co-purified gelatinases alter the stability and biological activities of human plasma fibronectin preparations

BACKGROUND AND OBJECTIVE

Fibronectin (FN) is an important cell adhesion molecule that is used widely to characterize cell behavior. Preparations of FN purified from human plasma by gelatin-Sepharose affinity chromatography typically also contain gelatin-binding gelatinases that may cleave FN, reduce its stability and alter its biological activities. Available methods for separating gelatinases from FN are resource demanding. Therefore, our objective was to devise a time- and cost-efficient protocol for purification of gelatinase-free FN.

MATERIAL AND METHODS

Experiments tested the elution profiles for FN and gelatinases from gelatin-Sepharose using a concentration range (1-7%) of dimethyl sulfoxide (DMSO) and 4 m urea as eluants. Subsequently, we explored the sequential application of those eluants for differential elution of gelatinases and FN using a single affinity column. Finally, experiments characterized the stability of purified FN with or without contaminating gelatinases, as well as the effects of FN degradation on cell attachment and migration.

RESULTS

Assay optimization demonstrated that pre-elution with 3% DMSO efficiently eliminated gelatinases but not FN from gelatin-Sepharose, whereas subsequent elution with 4 m urea released FN. Sequential elutions with DMSO and urea produced gelatinase-free FN, which was more stable than FN eluted by urea only. Fibronectin degradation did not affect human gingival fibroblast attachment, but increased cell migration significantly.

CONCLUSION

The present experiments devised a time- and cost-efficient protocol for eliminating gelatinases during purification of human plasma FN. Gelatinase-free FN preparations had greater stability, which may be essential for experiments because FN fragments have altered biological activities compared with intact FN.

Fibronectin modulates the morphology of osteoblast-like cells (MG-63) on nano-grooved substrates

Cell interactions with biomaterials are affected by surface topographic and chemical cues. Although it is well-known that nanometrical grooves/ridges structure modulates cellular spreading, elongation, and alignment, the combinational influence of surface topographic and chemical cues is not well studied. In this study, nano-textured silicon substrata with parallel ridges of 90, 250, or 500 nm wide, separated by grooves with equal width, were fabricated by electron beam lithography and dry etching techniques. Osteoblast-like cells, MG-63, were cultured on the patterned substrata with or without pre-adsorption of fibronectin. The cell morphology was imaged by scanning electron microscopy, and analyzed by image software. We found that FN coating initially modulated cellular spreading, length, and orientation on all types of grooved surfaces. However, after 24 h of culture, the cell morphology was not affected by FN coating on the 250-nm and 500-nm surfaces, while FN decreased cell alignment on the 90-nm surfaces. Our results suggest that surface chemical cues influence the initial cell-substratum contact, while the long-term cellular morphology is dictated by surface topographic cues.

Immunochemical Identification and Detection of Serum Fibronectin in Liver Fibrosis Patients with Chronic Hepatitis C

Serum tests measuring the dynamic processes of fibrogenesis and fibrolysis may reflect the severity of liver disease. Fibronectin plays a role in liver fibrosis. The aim of this study was to assess the diagnostic value of fibronectin in chronic HCV infection among Egyptian patients. Fibronectin was identified using specific monoclonal antibody and Western blot at 90-kDa in sera of HCV infected patients with liver fibrosis. The purified serum fibronectin showed one peak at 8 min when analyzed by capillary zone electrophoresis. Fibronectin was quantified in serum using ELISA. The mean (+/-SD) serum level of fibronectin (mg/L) in liver fibrosis patients were 450.9 (+/-170.3) and 230.5 (+/-90.3) in control individuals, respectively. There was a significant correlation between METAVIR score and serum fibronectin (r=0.401; P<0.0001). The area under the receiver operating characteristic (ROC) curve of fibronectin for discriminating patients with liver fibrosis from those with no fibrosis livers and its p value were 0.78 and P<0.0001. The efficiency of fibronectin for discriminating patients with liver fibrosis from those with non fibrosis livers was 75%. In conclusion, serum fibronectin can differentiate HCV infected patients with liver fibrosis from patients with non fibrosis.

Inhibitory effect of recombinant fibronectin polypeptide CH50 on invasion and metastasis of melanoma B16 cells

In order to investigate the inhibitory effect and mechanism of recombinant polypeptide CH50 on invasion and metastasis of melanoma B16 cells, the recombinant polypeptide CH50 was separated and purified by ion exchange chromatographic technique. The melanoma B16 cells treated with purified CH50 were cultured in vitro, the number was counted at 4, 24, 48 and 72 h and their morphological changes were observed in order to detect their adhesion and spreading abilities. In in vivo study, the melanoma B16 cells were labeled with CFSE and treated with CH50 and then they were injected into mice via mouse-tail veins. After 5 h, the lung tissues were fixed by frozen section. Accumulation and invasion abilities of B16 cells on lung tissues were observed under the fluorescent microscopy. The results showed that the morphological character of B16 cells treated with CH50 changed greatly and the number of B16 cells treated with CH50 decreased significantly (P<0.05). The adhesion and spreading abilities of B16 cells treated with CH50 were weakened obviously and the metastasis foci on lung tissues reduced. It was concluded that the recombinant polypeptide CH50 inhibited invasion and metastasis of melanoma B16 cells on tissues and could be a prospective bio-product in tumor general therapy.

Heparin-II domain of fibronectin is a vascular endothelial growth factor-binding domain: enhancement of VEGF biological activity by a singular growth factor/matrix protein synergism

We describe extracellular interactions between fibronectin (Fn) and vascular endothelial growth factor (VEGF) that influence integrin-growth factor receptor crosstalk and cellular responses. In previous work, we found that VEGF bound specifically to fibronectin (Fn) but not vitronectin or collagens. Herein we report that VEGF binds to the heparin-II domain of Fn and that the cell-binding and VEGF-binding domains of Fn, when physically linked, are necessary and sufficient to promote VEGF-induced endothelial cell proliferation, migration, and Erk activation. Using recombinant Fn domains, the C-terminal heparin-II domain of Fn (type III repeats 13 to 14) was identified as a key VEGF-binding site. Mutation of the heparin-binding residues on FnIII(13-14) abolished VEGF binding, and peptides corresponding to the heparin-binding sequences in FnIII(13-14) inhibited VEGF binding to Fn. Fn fragments containing both the alpha5beta1 integrin-binding domain (III 9 to 10) and the VEGF-binding domain (III 13 to 14) significantly enhanced VEGF-induced EC migration and proliferation and induced strong phosphorylation of the VEGF receptor and Erk. Neither the cell-binding or VEGF-binding fragment of Fn alone had comparable VEGF-promoting effects. These results suggest that the mechanism of VEGF/Fn synergism is mediated extracellularly by the formation of a novel VEGF/Fn complex requiring both the cell-binding and VEGF-binding domains linked in a single molecular unit. These data also highlight a new function for the Fn C-terminal heparin-binding domain that may have important implications for angiogenesis and tumor growth.

High-level expression of a recombinant fragment of human fibronectin containing the Cell I-Hep II-IIICS71 domain in Escherichia coli as a soluble protein

Fibronectin (FN) is a major matrix protein that is involved in multiple processes. Its Cell I-Hep II domain is potentially useful in tumor therapy. Here, a recombinant fragment of FN with the Cell I-Hep II-IIICS71 domain, CH/71, was expressed in Escherichia coli. The CH/71 fusion protein consists of Cell I-Hep II domain and 19th to 89th amino acids of IIICS domain of FN. The expression level of CH/71 in E. coli was very high after induction with IPTG. Furthermore, CH/71 protein was largely found in the soluble fraction. It was readily purified by one-step heparin-agarose affinity chromatograph. The ability of CH/71 binding cells was about 8-fold of that of Cell I-Hep II domain FN.

Purification and characterization of the Caenorhabditis elegans HCF protein and domains of human HCF

The human cellular factor (HCF) is a multidomain protein that is implicated in processes of cell cycle progression, and it is recruited into a multicomponent assembly that triggers the expression of the herpes simplex virus genome. The amino-terminal domain of HCF has been proposed to form a "kelch" type beta-propeller fold, and the carboxy-terminal domain contains a repeat of a fibronectin-like motif. We describe the expression, purification, and characterization of the domains from the human HCF and of the full-length HCF from Caenorhabditis elegans. The purified recombinant C. elegans HCF can substitute for the human HCF in efficiently forming a multiprotein complex on a herpes simplex virus promoter element. As noted in earlier studies, a segment of human HCF encompassing the human kelch domain forms a stable complex on a viral promoter element. The purified fibronectin domain can also be recruited into this complex, but not into the stable complex formed with the minimal kelch domain. These results suggest that the fibronectin domain can interact with HCF in the transcriptional activating complex and that the association requires a region outside the putative beta-propeller.

Adsorption and interaction of fibronectin and human serum albumin at the liquid-liquid interface

The goal of this work was to investigate the dynamics of human plasma fibronectin (HFN) at the oil-water interface and to characterize its interactions with human serum albumin (HSA) by total internal reflection fluorescence microscopy (TIRFM). Among key results, we observed that fibronectin adsorption at the oil-water interface is rapid and essentially irreversible, even over short time scales. This may be due to the highly flexible nature of the protein, which allows its various domains to quickly attain energetically favorable conformations. On the other hand, HSA adsorption at the oil-water interface is relatively reversible at short times, and the protein is readily displaced by fibronectin even after HSA has been adsorbed at the interface for as long as 2 h. At longer adsorption times, HSA is able to more effectively resist complete displacement by fibronectin, although we observed significant fibronectin adsorption even under those conditions. Displacement of adsorbed fibronectin by HSA was negligible under all conditions. Fibronectin also adsorbs preferentially from a mixture of HFN and HSA, even when the concentration of HSA is substantially higher. This study is relevant to such emerging research thrusts as the development of biomimetic interfaces for a variety of applications, where there is a clear need for better understanding of the effects of interfacial competition, adsorption time scales, and extent of adsorption irreversibility on interfacial dynamics.

Isolation of fibronectin type III like peptide from human placental extract used as wound healer

A peptide of around 7.4 kDa has been purified from the aqueous extract of human placenta used as wound healer. Derived partial amino acid sequence from mass spectrometric analysis showed its homology with human fibronectin type III. Under nondenaturing condition, it formed aggregate, the elution pattern of which from reverse-phase HPLC was identical with that of fibronectin type III. Immuno-blot of the peptide with reference fibronectin type III-C showed strong cross reactivity. Since fibronectin type III plays important roles in wound healing, similar peptide in the extract is likely to take part in curing process.

The binding of fibrin sealant to collagen is influenced by the method of purification and the cross-linked fibrinogen–fibronectin (heteronectin) content of the ‘fibrinogen’ component

Two fibrinogen preparations, each an intermediate in the manufacture of the 'fibrinogen' component of a commercial human tissue sealant, were made from a common cryoprecipitate source. The first preparation, prepared according to the process described by Schwartz et al. had a higher ratio of clottable to total protein than the second preparation, prepared according to that by Martinowitz and Bal but a much lower ratio of fibronectin to fibrinogen. After clotting with thrombin and solubilization and reduction of the clots, sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a much higher content of high molecular weight polymers of fibrin(ogen) in the second preparation than in the first. The second preparation bound to collagen more strongly than did cryoprecipitate and much more strongly than did the first one. Experiments with highly purified proteins showed that fibronectin was essential in promoting progressive binding of fibrinogen to collagen under the action of activated factor XIII (transglutaminase). It was concluded that, because of their method of purification from cryoprecipitate, preparations of fibrinogen differ in their content of fibronectin and heteronectin. The binding of these proteins to collagen may improve the adhesion of tissue sealant clots to the extracellular matrix.

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.

Cryoprecipitate prepared from plasma treated with methylene blue plus light: increasing the fibrinogen concentration

When cryoprecipitate is prepared from plasma which has been treated with methylene blue plus light (MB) for the purpose of virus inactivation, clottable fibrinogen content is 40% lower compared with units prepared from untreated plasma. Initial studies showed that when frozen MB plasma units were removed to +2 to +6 degrees C for 4 h and then returned to -40 degrees C prior to cryoprecipitation, fibrinogen recoveries increased from 24 to 42%. Although fibrinogen yield improved when plasma units were stored at +2 to +6 degrees C for varying lengths of time, FVIII levels decreased with increasing time. Conditioning for 8 h was studied in more detail. Groups of two plasma units were mixed together, divided into two equal units, frozen/thawed and treated with MB. One of each pair was stored continually at -40 degrees C, whereas the other was removed to +2 to +6 degrees C for 8 h. Samples were assayed for fibrinogen, FVIII, VWF:Ristocetin cofactor activity (RCo), VWF:Ag and VWF:Collagen binding (CB). The cryoprecipitate fibrinogen content increased to a mean of 207 mg unit(-1). VWF:Ag, VWF:RCo and VWF:CB recoveries also increased. FVIII recovery decreased from 50 to 45% (mean 124 iu unit(-1)). Conditioning has been validated for routine production of cryoprecipitate from imported plasma.

Extraction of membrane proteins from a living cell surface using the atomic force microscope and covalent crosslinkers

The force curve mode of the atomic force microscope (AFM) was applied to extract intrinsic membrane proteins from the surface of live cells using AFM tips modified by amino reactive bifunctional covalent crosslinkers. The modified AFM tips were individually brought into brief contact with the living cell surface to form covalent bonds with cell surface molecules. The force curves recorded during the detachment process from the cell surface were often characterized by an extension of a few hundred nanometers followed mostly by a single step jump to the zero force level. Collection and analysis of the final rupture force revealed that the most frequent force values (of the force) were in the range of 0.4-0.6 nN. The observed rupture force most likely represented extraction events of intrinsic membrane proteins from the cell membrane because the rupture force of a covalent crosslinking system was expected to be significantly larger than 1.0 nN, and the separation force of noncovalent ligand-receptor pairs to be less than 0.2 nN, under similar experimental conditions. The transfer of cell surface proteins to the AFM tip was verified by recording characteristic force curves of protein stretching between the AFM tips used on the cell surface and a silicon surface modified with amino reactive bifunctional crosslinkers. This method will be a useful addition to bionanotechnological research for the application of AFM.

A rapid method for fibronectin purification on nitrocellulose membranes suitable for tissue culture

We have developed a simple method for plasma fibronectin purification based on the well-known gelatin binding property of fibronectin. In this procedure we immobilize the melted gelatin to nitrocellulose membranes; these are then used to affinity-purify the fibronectin from the plasma sample. The fibronectin is eluted from the membrane by treatment with 8 M urea. The procedure described here gives a yield of up to 60% (from presumed fibronectin concentration) and the fibronectin obtained is homogeneous in SDS-PAGE and biologically active, as assessed by a cell migration assay. The method is rapid, simple, inexpensive, does not require the use of chromatographic equipment and is suitable for tissue culture applications.

Fibrin sealant produced by the CryoSealR FS System: product chemistry, material properties and possible preparation in the autologous preoperative setting

BACKGROUND AND OBJECTIVES

The CryoSeal FS has been introduced as an automated device for the production of fibrin sealant from small volumes of plasma. We tested this device and compared the product with commercially available fibrin sealants and with the requirements of the European Pharmacopoeia.

MATERIALS AND METHODS

The CP3 program and disposables required were used to manufacture fibrin sealant. The chemistry and mechanical properties of the product were investigated.

RESULTS

The cryoprecipitate generated with CryoSeal contains concentrated fibrinogen and critical clotting factors. The efficiency of the production process is poor, but the production procedure itself is simple and not time-consuming. The volume of plasma required allows application in the preoperative autologous setting.

CONCLUSIONS

The CryoSeal FS is an automated device for cryoprecipitation and production of thrombin. It can be implemented easily in the clinical routine, although, owing to product specifications, the efficacy of the CryoSeal fibrin sealant requires further clinical trials.

Purification of a plant cell wall fibronectin-like adhesion protein involved in plant response to salt stress

The structural role of extracellular-matrix (ECM) has been recognized in both plants and animals as a support and anchorage-inducing cell behavior. Unlike the animal ECM proteins, the proteins that have been identified in plant ECM have not yet been purified from whole plants and cell wall. As several immunological data indicate the presence of animal ECM-like proteins in plants cell wall, especially under salt stress or water deficit, we propose a protocol to purify a fibronectin-like protein from the cell wall of epicotyls of young germinating peas. The process consists of a combination of gelatin and heparin affinity chromatography, close to the classical one used for human blood plasma fibronectin purification. Proteins with affinity for gelatin and heparin, immunologically related to human fibronectin, are found in the cell wall of epicotyls grown under salt stress or not. Total amount of purified proteins is 3-4 times more enriched in salt stressed epicotyls. SDS-PAGE and Western blot with antibodies directed against human blood plasma fibronectin give evidence that the cell wall proteins purified by gelatin/heparin affinity chromatography are closely related to human fibronectin. The present protocol leads us to purify 17 (control) or 65 (salt stress) micrograms of protein per g of fresh starting material. Our results suggest that plant cell wall proteins can provide better anchorage of the cell to its cell-wall during salt stress or water deficit and could be considered not only as cell adhesion but also as signaling molecules.

Crosslinked glass fiber affinity membrane chromatography and its application to fibronectin separation

Macroporous glass membranes were prepared from glass fiber filters via chemical crosslinking and modification, and used for the membrane affinity chromatography of fibronectin from human blood plasma. The filters were first treated with a piranha solution (a concentrated solution of H2SO4 + H2O2 in water), and then crosslinked with bifunctional organosilanes and modified to introduce amino or aniline moieties. Ligand immobilizations via diazotization and glutaraldehyde pathways were carried out and compared. Characterization of the membranes was performed using bovine serum albumin and trypsin as test ligands. By using a cartridge containing gelatin immobilized affinity membranes followed by another cartridge containing heparin immobilized membranes, fibronectin from human blood plasma could be separated.

[Study on preparation of a wound healing agent: fibronectin]

In search of the optimal preparation method for large-scale purification of human plasma fibronectin, we adopted affinity chromatography with gelatin and the Sepharose 4B activated with cyanogen bromide to purify fibronectin from type "C" plasma of healthy males, and scanned the best method under the conditions of different amount of plasma loading and different residence time in column. In a given column volume of gelatin, the absorbent was related with the plasma residence time in column and the total amount of plasma loaded. As a result, the optimal loading amount of plasma is 150 ml, and the residence time is 20 minutes. The preparation method, herein, has been proved to require small amount of plasma and yield large amount of fibronectin.

Control of von Willebrand factor multimer size by a fibronectin-related substance

Fraction (F) II and FIII obtained by heparin-Sepharose after digestion of partially purified fibronectin (FN) with cathepsin D and F3, obtained like FIII but from untreated FN, exerted activity (arFN) on unfolded purified von Willebrand factor (vWF) that controls vWF multimer size. Our aim was to evaluate the arFN of F from commercial FN, commercial 30 kDa (with heparin affinity), 45 kDa (gelatin affinity) and 70 kDa FN fragments (gelatin and heparin affinity) and whole FN. The arFN was detected in FII, FIII, F2, F3, 30 kDa, 45 kDa and 70 kDa fragments. The least contaminated sample was the 30 kDa commercial fragment. Characterization studies of this sample revealed two bands: a blurred band of approximately 60 kDa and a sharp major band of 32 +/- 6 kDa. The 32 +/- 6 kDa band fragment failed to produce arFN because it was stronger than in F2 and FIII band fragments at the same position and with the same arFN. Our data suggest that a fragment of approximately 60 kDa that co-purified with FN, with affinity to heparin and gelatin, has the arFN that controls vWF multimer size.

Laminin- and fibronectin-like molecules produced by periodontal ligament fibroblasts under serum-free culture are potent chemoattractants for gingival epithelial cells

Previously, we revealed that hepatocyte growth factor (HGF) or an HGF-like factor secreted by periodontal ligament fibroblasts (PLF) and gingival fibroblasts cultured in the presence of serum was a major chemoattractant for gingival epithelial cells, and suggested that it might play a role in epithelial invasion. However, our recent study showed that serum-free culture of PLF and gingival fibroblasts produced potent chemoattractants other than HGF for gingival epithelial cells. To identify these chemoattractants, PLF-conditioned medium (PLF-CM) from serum-free cultures was obtained, concentrated, and separated by gel filtration column chromatography, and the chemotactic activity for gingival epithelial cells of each eluted fraction was monitored by a modified Boyden chamber assay. The chemoattractant activity was eluted at a molecular mass of around 600 kDa, which would include laminin and fibronectin, but not HGF, determined by ELISA. The chemotactic activity was reduced by treatment with antilaminin and/or antifibronectin polyclonal antibodies. Western blots using both antibodies revealed that the PLF-CM contained laminin- and fibronectin-like molecules. Along with HGF, these large glycoprotein molecules produced by PLF may be involved in the pathogenesis and progression of periodontitis by inducing the apical migration of epithelial cells.

Several regions of the repeat domain of the Staphylococcus caprae autolysin, AtlC, are involved in fibronectin binding

The autolysin AtlC is the only known fibronectin-binding protein in Staphylococcus caprae strain 96007. The fibronectin-binding domain of AtlC consists of three repeats (AtlCR(1)R(2)R(3)), which are located between the two enzymatic domains. The AtlCR(1)R(2)R(3) domain and the AtlCR(1)R(2) and AtlCR(3) subdomains were expressed separately as His(6)-tagged proteins. In Western affinity blots, only AtlCR(1)R(2)R(3) and AtlCR(3) but not AtlCR(1)R(2) appeared to recognise fibronectin; however, in ELISA and Biacore experiments, all three bound fibronectin. The interaction between AtlCR(1)R(2)R(3) and fibronectin is multivalent and involves high- and low-affinity sites that are present in a 2:1 ratio. These distinct classes of binding sites may be situated on either or on both ligands.

Recruitment of mammalian cell fibronectin to the surface of Chlamydia trachomatis

Pathogenic bacteria exploit the presence of various host cell molecules in order to colonize new tissues. Fibronectin is involved in a wide range of cell functions in vivo, and staphylococci, streptococci, and gonococci have evolved mechanisms to utilize this glycoprotein to mediate host cell binding. We show that elementary bodies (EB) from two biovars of Chlamydia trachomatis recruit fibronectin to their surfaces upon lysis of the host cell. We also demonstrate that a heparan sulfate lyase-sensitive molecule on chlamydial EB is responsible for binding at least a portion of this fibronectin.

Fibronectin purification from human plasma in a packed-bed column system with gelatin immobilized PHEMA microspheres

Bioaffinity chromatography has a unique and powerful role that is used as a purification tool in the production of therapeutic plasma protein derivatives. In this study, a bioaffinity-ligand, i.e. gelatin, was covalently immobilized with PHEMA microspheres (150-200 microm in diameter). The affinity sorbent carrying 7.5 mg gelatin g(-1) polymer was then used to separate fibronectin from human plasma in a packed-bed column system. Fibronectin separation from human plasma on unmodified PHEMA microspheres was 0.45 mg g(-1), while much higher adsorption values, up to 21.8 mg g(-1), were obtained with gelatin-immobilized microspheres. The fibronectin adsorption capacity of the microspheres decreased with an increase in the recirculation rate of plasma. Fibronectin adsorption increased with decreasing temperature, and the maximum adsorption achieved at 4 degrees C (26.3 mg fibronectin g(-1)). Up to 94.7% of the adsorbed fibronectin was desorbed by using 2 M urea in the presence of 1 M sodium chloride as elution agent. The adsorption-desorption cycle was repeated ten times using the same affinity column. There was no remarkable reduction in the adsorption capacity of the gelatin-immobilized PHEMA microspheres.

Specific lectin binding to beta1 integrin and fibronectin on the apical membrane of madin-darby canine kidney cells

Although lectins have previously been used to identify specific cell types in the kidney and various other tissues, the proteins labeled were not identified. We hypothesized that fluorescently labeled lectins could provide a useful tool for direct labeling of membrane-associated glycoproteins. Protein fractions from Madin-Darby canine kidney (MDCK) cells were exposed to a panel of 16 fluorescently labeled lectins to identify suitable lectin-protein pairs. Peanut agglutinin (PNA) selectively bound a 220-240 kDa O-linked glycoprotein with a slightly acidic isoelectric point, while Sambucus nigra agglutinin (SNA) labeled a 130 kDa glycoprotein with a highly acidic isoelectric point. Both proteins were readily labeled by lectins applied to the apical surface of living confluent cells. The proteins were isolated by lectin affinity columns and identified by mass spectrometry. Peptides from the PNA-binding protein shared molecular weight and amino acid composition with fibronectin. Fragments of the SNA-binding protein showed amino-acid identity with peptides from beta1 integrin. The identities of these proteins were validated by Western blotting. Binding of PNA to a 220 kDa protein was inhibited by an anti-fibronectin antibody, and binding of a 130 kDa protein by SNA was diminished by an anti-beta1 integrin antibody. We conclude that PNA and SNA can be used as specific markers for fibronectin and beta1 integrin, respectively, in MDCK cells.

Buffalo plasma fibronectin: a physico-chemical study

Plasma fibronectin (FN) of buffalo (Babulis babulis) was purified to apparent homogeneity, using gelatin-Sepharose and heparin-Sepharose affinity columns. It was found to have two subunits of molecular mass 246 kDa and 228 kDa, on SDS-gel. Its immunological cross-reactivity with anti-human plasma FN was confirmed by Western blotting. The amino acid composition was found to be similar to that of human and bovine plasma FNs. Buffalo plasma FN contained 2.23% neutral hexoses and 1.18% sialic acids. No titrable sulfhydryl group could be detected in the absence of denaturant. Reaction with DTNB indicated 3.4 sulfhydryl groups in the molecule, whereas BDC-OH titration gave a value of 3.8 -SH groups in buffalo plasma FN. Stoke's radius, intrinsic viscosity, diffusion coefficient and frictional ratio indicated that buffalo plasma FN did not have a compact globular conformation at physiological pH and ionic strength. Molecular dimensions (average length, 120 nm; molar mass to length ratio, 3950 nm(-1) and mean diameter, 2.4 nm) as revealed by rotary shadowing electron microscopy further supported the extended conformation of buffalo plasma FN. These results show that buffalo plasma FN has similar properties as that of human plasma FN.

Identification and characterization of a novel fibronectin in zebrafish

Sequence analysis of zebrafish fibronectin (FN) cDNAs indicates that at least two forms of the protein exist in fish. One form (FN1) is very similar to FNs identified in other vertebrates possessing 12 type I, 2 type II, and 17 type III repeats including two alternative splice sites (EIIIA and EIIIB) and a variable region (V). Zebrafish FN1 contains the RGD cell adhesion site in type III(10) and a second cell-binding site (LDV) in the V region. In addition to this conserved form of FN, a novel truncated form of zebrafish FN (FN2) was identified. The predicted structure of FN2 is identical to FN1 at the N-terminal region possessing 9 type I, 2 type II, and the first 3 type III repeats. Following III(3), FN2 contains a unique 20-amino-acid C-terminal tail that is different from the C-terminus of FN1, lacking the two cysteines that are usually involved in the formation of interchain disulfide bonds. Genomic sequence analysis has revealed that FN2 is generated by an alternative RNA splicing pattern that has not been described for FN in other organisms. Reverse transcription-polymerase chain reaction analysis and RNase protection assays reveal that FN2 mRNA is present in the zebrafish embryo throughout development as well as in cultures of an established liver cell line. Experiments conducted with recombinant FN2 synthesized in insect cells demonstrate that the protein promotes the attachment and spreading of fish embryo cells in culture.

A 10-kda fragment of fibronectin type III domain is a neutrophil chemoattractant purified from conditioned medium of rat granulation tissue

A neutrophil chemoattractant has been purified from the conditioned medium of granulation tissue obtained from carrageenan-induced inflammation in rats. The purified chemoattractant was a basic protein with a molecular mass of 10 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing and non-reducing conditions. NH2-terminal amino acid sequence of the purified 10-kDa protein was identical with the sequence of rat fibronectin starting from the residue Thr585, indicating that the purified 10-kDa chemoattractant is a fragment derived from the NH2-terminal type III domain of rat fibronectin.

Radiolabeled peptides in the detection of deep venous thrombosis

Venous thrombosis and pulmonary embolism are major clinical problems that result in significant morbidity and mortality. It is estimated that 600,000 cases of pulmonary embolism occur each year in the United States, resulting in the death of approximately 100,000 patients. Most of these pulmonary emboli arise from deep venous thrombosis (DVT). The clinical diagnosis of DVT is unreliable. Only a third of patients with a clinical suspicion of DVT have objective evidence of the disease, and half of patients with proven DVT do not have any clinical symptoms. Although ascending contrast venography is the present standard for the diagnosis of DVT, duplex ultrasonography, which is increasingly used in combination with color Doppler flow imaging, is accepted as a useful clinical afternative to contrast venography. Both contrast venography and ultrasonography are imaging procedures that detect changes in venous anatomy that are caused by the presence of an intraluminal thrombus that is sufficiently formed either to reduce vascular filling with contrast medium or to resist compression. However, these imaging procedures do not reflect the metabolic activity of the clot, and therefore, they may overestimate the presence of active clots. The sensitivity of ultrasonography is also limited by various disease-related and technical factors. An alternative approach to the diagnosis of acute DVT is to detect a molecular marker of acute DVT that is not present in old, organized DVT. Recent advances in biotechnology permit the use of highly specific synthetic peptide or small molecular markers, which are involved in the acute stages of DVT formation and can be labeled efficiently with 99mTc. 99mTc-apcitide, a glycoprotein (GP IIb/IIIa) receptor antagonist previously known as 99mTc-P280, has been approved recently by the Food and Drug Administration for the clinical detection of acute DVT. Two other agents are currently under clinical investigation: 99mTc-DMP 444, which is another GP IIb/IIIa receptor antagonist, and 99mTc-Fibrin-Binding Domain (FBD), a radio-labeled fibrin-binding domain of fibronectin. Different clinical studies have shown a high diagnostic accuracy with these synthetic 99mTc-labeled peptides in the detection of acute DVT. Although further studies are needed to fully appreciate all of the diagnostic potential of these radiopharmaceuticals, the clinical introduction of 99mTcapcitide scintigraphy will certainly be helpful in expanding the use of nuclear medicine in a specific field in which it used to play a relatively marginal role.

Specific affinity depletion of cell adhesion molecules and growth factors from serum

Serum is a common component of most in vitro cell culture media, particularly of primary cells. Studies of cellular responses to particular adhesion molecules or growth factors are often confounded by the presence of these molecules in the serum supplement. We describe a combined affinity protocol for removing vitronectin and fibronectin from serum. This protocol can also be used to purify these molecules. We also describe the removal of growth-promoting elements using heparin-Sepharose. As vitronectin and fibronectin each bind to heparin, these molecules are removed first and the heparin-Sepharose depletion occurs last in the sequence. This protocol provides a detailed step-by-step guide to achieve quantitative depletion of serum in an optimised format, with additional information on pitfalls and problems. It should be of use to people who wish to accurately determine the relationship between cells, extracellular matrix molecules and growth factors.

A very-high-purity von Willebrand factor preparation containing high-molecular-weight multimers

BACKGROUND AND OBJECTIVES

We investigated large-scale production of very-high-purity von Willebrand factor (vWf) containing high-molecular-weight vWf multimers, using chromatography alone.

MATERIALS AND METHODS

Factor VIII (FVIII)-containing vWf was produced by initial separation of vWf from plasma by gel filtration followed by two ion exchange steps. Two virus inactivation steps were incorporated in the process.

RESULTS

The process resulted in FVIII-containing vWf preparations with a mean specific activity of 82 U vWf: collagen-binding activity per milligram protein (excluding added albumin) and with almost intact vWf multimer distributions.

CONCLUSIONS

Very-high-purity, double virus-inactivated vWf preparations containing high molecular weight multimers were obtained on a production scale.

Plasma fibronectin: three steps to purification and stability

Large amounts of soluble fibronectin were easily purified from cryoprecipitated or fresh citrated human blood plasma by a three-step combination of gelatin and heparin-cellufine affinity chromatography. The elution conditions were optimized to obtain a homogeneous fraction on SDS-PAGE and Western blot under reducing condition. No proteolytic activities were detected by zymography at acidic or neutral pH. Furthermore, the fibronectin preparation was stable over time up to 456 h at 37 degrees C in the presence of calcium, zinc, or mercury. This preparation of very stable fibronectin, called highly purified fibronectin (hpFN), gave a yield of 7.00 +/- 0.77 mg of fibronectin per gram of cryoprecipitated plasma and 0.16 mg of fibronectin per milliliter of fresh citrated, giving a yield of 32 to 53% (from presumed fibronectin concentration). This preparation may be useful for cellular tests and interaction analysis.

Inhibition of human and mouse complement-dependent hemolytic activity by mouse fibronectin

Not only does mouse complement (C) have low hemolytic activity, but mouse serum has an inhibiting effect on hemolysis by human C. To purify and identify the putative mouse serum factor inhibiting human C activity, a sequential procedure of fractionated precipitation by PEG, followed by chromatographies with a heparin-Sepharose column, a phenyl-Sepharose column, a Protein G column, and a gel-filtration column was performed. The amino acid sequence analyses of two polypeptides obtained by digestion of the purified serum factor with TPCK-trypsin revealed that it was mouse fibronectin (FN). Highly purified mouse FN, but not human FN, has an inhibiting effect on human C-dependent hemolysis. Moreover, the hemolysis of sensitized rabbit erythrocytes by mouse C was also inhibited by the addition of mouse FN in a dose-dependent fashion, but not by the addition of human FN. These results suggest that FN is the putative internal C inhibitor in the mouse system.

Proliferation of endothelial cells on surface-immobilized albumin-heparin conjugate loaded with basic fibroblast growth factor

Seeding of endothelial cells (ECs) on the luminal surface of small-diameter vascular grafts is a promising method to avoid occlusion of these prostheses. Immobilization of basic fibroblast growth factor (bFGF) to substrates used to coat or fill porous prostheses may enhance the formation of a confluent monolayer of ECs. Human umbilical vein endothelial cells (HUVECs) were grown on bFGF-loaded albumin-heparin conjugate bound to CO2 gas-plasma-treated polystyrene. In the order of 2-3 ng/cm2 bFGF had to be immobilized to form a confluent monolayer of HUVECs. The most prominent effect of surface-immobilized bFGF was stimulation of the proliferation shortly after seeding, resulting within 3 days in confluent cell monolayers with high density. In contrast, in cultures with 0.3 ng/mL bFGF in the medium instead of bFGF bound to the surface, it took almost a week before the cell layers reached confluency. Binding of bFGF to heparin and the biological activity of bFGF towards ECs were not influenced by the (radio-)labeling of bFGF with iodine. However, only a minor part of the bFGF used in this study displayed heparin affinity. Furthermore, degradation and multimerization of labeled bFGF in time occurred when the growth factor was stored at 20 degrees -37 degrees C. This limits the use of labeled bFGF to short-term (hours) experiments. In conclusion, bFGF loading of vascular graft surfaces through complexation of bFGF with a heparin-containing matrix probably will lead to more rapid formation of a confluent monolayer of ECs on graft surfaces upon seeding of the cells.

High-molecular-weight fibronectin synthesized by adenoid cystic carcinoma cells of salivary gland origin

To understand the morphogenesis of characteristic cribriform structures and the frequent invasion of salivary adenoid cystic carcinomas (ACC) along such basement membrane-rich structures as peripheral nerves, we have isolated fibronectin (FN) from the culture media of ACC3 cells established from a parotid ACC and characterized its glycosylation and alternative splicing status. FN isolated from ACC3 cells (ACC-FN) showed a molecular mass of 315 kDa in SDS-PAGE and was less heterogeneous and larger than plasma FN (pFN) or FNs from other cell sources. Differential enzymatic treatments of immunoprecipitated ACC-FN with neuraminidase, peptide-N-glycosidase F and endo-alpha-N-acetylgalactosaminidase revealed that ACC-FN was composed of a polypeptide chain of 270 kDa, with 10 kDa each of N-linked and O-linked oligosaccharide chains. Reverse transcription polymerase chain reaction (RT-PCR), in-situ hybridization, and immunofluorescence studies showed that most ACC-FNs contained ED-A, ED-B and IIICS regions in the molecules. This alternative splicing status of ACC-FN seemed to contribute to its less heterogeneous and larger molecular form. Cell attachment assay demonstrated that ACC-FN was more potent than pFN in adhesion of ACC3 cells. The results indicated that ACC-FN may function as a substrate for attachment of ACC3 cells, or that ACC3 cells trap and retain ACC-FN in their pericellular space. This isoform of FN may play an important role in the mode of invasion of ACC and the formation of stromal pseudocysts in the characteristic cribriform structure of ACC.

Expression of extracellular matrix components fibronectin and laminin in the human fetal heart

It has been well documented that the extracellular matrix components fibronectin and laminin promote or regulate morphogenesis of the myocardial cells in mammalian heart. However, their chronological change of expression (or localization) in the human heart remains elusive. In this study, fibronectin and laminin in the left ventricle of forty-two human fetuses aged from 8 to 26 weeks gestation and left ventricular tissues obtained from a 2-week old infant and two adults were investigated by Western blot analyses and indirect immunofluorescence technique with monoclonal antibodies. In the fetal heart, fibronectins were present along the endocardium, epicardium, and linings of larger blood vessels. In 14-16 weeks gestation, fibronectin immunofluorescence became stronger but not evenly dispersed in the interstitium. After 24 weeks gestation, they were strongly positive only in the relatively larger blood vessels, as well as those in the infant and adult cardiac tissues. Laminins were strongly positive along the endocardium and basement membrane of the myocardial cells and fibroblasts during fetal life. After birth, laminins formed fine fibrillar network along the basement membrane in association with the transverse tubules of myocardial cell; these morphological characteristics remained in the adult cardiac tissues. These results indicate that fibronectin expression is relatively constant during fetal life but decreases after birth; in contrast, laminin expression is not age-dependent and constant throughout the life.

Activation of distinct alpha5beta1-mediated signaling pathways by fibronectin's cell adhesion and matrix assembly domains

The interaction of cells with fibronectin generates a series of complex signaling events that serve to regulate several aspects of cell behavior, including growth, differentiation, adhesion, and motility. The formation of a fibronectin matrix is a dynamic, cell-mediated process that involves both ligation of the alpha5beta1 integrin with the Arg-Gly-Asp (RGD) sequence in fibronectin and binding of the amino terminus of fibronectin to cell surface receptors, termed "matrix assembly sites," which mediate the assembly of soluble fibronectin into insoluble fibrils. Our data demonstrate that the amino-terminal type I repeats of fibronectin bind to the alpha5beta1 integrin and support cell adhesion. Furthermore, the amino terminus of fibronectin modulates actin assembly, focal contact formation, tyrosine kinase activity, and cell migration. Amino-terminal fibronectin fragments and RGD peptides were able to cross-compete for binding to the alpha5beta1 integrin, suggesting that these two domains of fibronectin cannot bind to the alpha5beta1 integrin simultaneously. Cell adhesion to the amino-terminal domain of fibronectin was enhanced by cytochalasin D, suggesting that the ligand specificity of the alpha5beta1 integrin is regulated by the cytoskeleton. These data suggest a new paradigm for integrin-mediated signaling, where distinct regions within one ligand can modulate outside-in signaling through the same integrin.

Development of the selective adsorbent for EDA containing fibronectin using heparin immobilized cellulose

We have noticed that extra domain A containing fibronectin (EDA(+)FN) is closely related to inflammatory diseases and accordingly investigated a selective adsorbent to remove EDA(+)FN, which may increase the severity of the symptoms, from the plasma of rheumatoid arthritis (RA) patients. Three types of heparin immobilized cellulose (HC) were prepared and their adsorptive properties were evaluated by batchwise adsorption tests. The results showed that EDA(+)FN was adsorbed more efficiently than total FN on HC. In particular HC in which heparin was immobilized to amino residue had an excellent capacity. The adsorption rates of EDA(+)FN, total FN and antithrombin-III were 89, 15 and 17% respectively. This adsorbent is extremely useful in selectively removing EDA(+)FN from plasma.

The 67-kDa enzymatically inactive alternatively spliced variant of beta-galactosidase is identical to the elastin/laminin-binding protein

Our previous studies showed immunological and functional similarities, as well as partial sequence homology, between the enzymatically inactive alternatively spliced variant of human beta-galactosidase (S-gal) and the 67-kDa elastin/laminin-binding protein (EBP) from sheep. To define the genetic origin of the EBP further, a full-length human S-gal cDNA clone was constructed and subjected to in vitro transcription/translation. The cDNA was also transfected into COS-1 cells and into the EBP-deficient smooth muscle cells (SMC) from sheep ductus arteriosus (DA). In vitro translation yielded an unglycosylated form of the S-gal protein, which immunoreacted with anti-beta-galactosidase antibodies and bound to elastin and laminin affinity columns. S-gal cDNA transfections into COS-1 and DA SMC increased expression of a 67-kDa protein that immunolocalized intracellularly and to the cell surface and, when extracted from the cells, bound to elastin. The S-gal-transfected cells displayed increased adherence to elastin-covered dishes, consistent with the cell surface distribution of the newly produced S-gal-encoded protein. Transfection of DA SMC additionally corrected their impaired elastic fiber assembly. These results conclusively identify the 67-kDa splice variant of beta-galactosidase as EBP.

A miniaturized arrayed assay format for detecting small molecule-protein interactions in cells

BACKGROUND

Two complementary approaches to studying the cellular function of proteins involve alteration of function either by mutating protein-encoding genes or by binding a small molecule to the protein. A mutagen can generate millions of genetic mutations; correspondingly, split-pool synthesis can generate millions of unique ligands attached to individual beads. Genetic screening of mutations is relatively straightforward but, in contrast, split-pool synthesis presents a challenge to current methods of screening for compounds that alter protein function. The methods used to screen natural products are not feasible for large libraries composed of covalently immobilized compounds on synthesis beads. The sheer number of compounds synthesized by split-pool synthesis, and the small quantity of individual compound attached to each bead require assay miniaturization for efficient screening.

RESULTS

We present a miniaturized cell-based technique for the screening of ligands prepared by split-pool synthesis. Spatially defined droplets with uniform volumes of approximately 50-150 nanoliters (depending on well dimensions) are arrayed on plastic devices prepared using a combination of photolithography and polymer molding. Using this microtechnology, approximately 6,500 assays using either yeast cells or mammalian tissue culture can be performed within the dimensions of a standard 10 cm petri dish. We demonstrate that the biological effect of a small molecule prepared by split-pool synthesis can be detected in this format following its photorelease from a bead.

CONCLUSIONS

The miniaturized format described here allows uniformly sized nanodroplets to be arrayed on plastic devices. The design is amenable to a large number of biological assays and the spatially arrayed format ensures uniform and controlled ligand concentrations and should facilitate automation of assays. The screening method presented here provides an efficient means of rapidly screening large numbers of ligands made by split-pool synthesis in both yeast and mammalian cells.

Establishment of a standardized assay system of fibronectin activity using fibronectin-mediated cell adhesion

An in vitro assay of fibronectin (FN) was established based on the adhesion of baby hamster kidney (BHK) cells through the cell-binding domain of FN. Each well of a microtiter plate was coated with samples or various concentrations of standard FN. Bovine serum albumin was further coated to prevent the non-specific adhesion of the cells. Various numbers of BHK cells were plated and incubated. After washing out the non-attached cells, the number of attached cells was measured using neutral red (NR)-staining. The conditions for the assay were optimal when 1 x 10(5) cells/well were plated and incubated for 90 min. The linear relationship between the concentration of FN coated and the absorbance of NR was observed in the range of 0.1-1.0 micro/ml of FN. The inhibition of cell binding by the peptides containing an Arg-Gly-Asp (RGD) sequence demonstrated that this assay system depended on FN-mediated cell adhesion through the major cell-binding domain.