A rapid and highly sensitive solid-phase enzyme immunoassay specific for human fibronectin using a characterized monoclonal antibody

Fibronectin in formation and degradation of the pericellular matrix

Fibronectin is a large multifunctional glycoprotein present both in soluble form in plasma and other body fluids and in an insoluble form in interstitial connective tissues and in association with most basement membranes. The protein seems to provide a link between circulating body fluids, cell surfaces and the extracellular matrix. At sites of injury, fibronectin, covalently cross-linked to the fibrin clot, may provide a growth substratum for the invading cells and appears through its multiple interactions with other matrix components and cell surfaces to be involved in the organization of the matrix that will replace the clot. Fibronectin deposition may serve as a useful early marker for connective tissue formation in pathological processes and its fragmentation may serve as an indicator of pathological conditions involving proteolytic events.

FAK-independent alphavbeta3 integrin-EGFR complexes rescue from anoikis matrix-defective fibroblasts

Extracellular matrix (ECM) binding to integrin receptors regulates cell cycle progression and survival. In adherent cells, ECM disassembly induces anoikis, the apoptotic pathway switched on by loss of adhesion. ECM-deficient Ehlers-Danlos syndrome (EDS) fibroblasts, to adhere to rare fibronectin (FN) fibrils, and to proliferate, only organize, as FN receptor, the alphavbeta3 integrin. We report that in EDS cells the alphavbeta3 integrin is bound to talin and vinculin, but not to tensin, and that actin cytoskeleton is disorganized. Furthermore, in EDS cells Bcl-2 is down-regulated and caspases are active. We provide evidence that the antibody-mediated alphavbeta3 integrin or the FN inhibition induces anoikis in EDS cells. The alphavbeta3 integrin transduces survival signals to pp60src-mediated tyrosine phosphorylated paxillin, instead than to FAK, and interacts with EGF receptor (EGFR). This complex, when activated by EGF and FN, signals for the rescue of EDS cells from anoikis. Therefore, EDS cells, through the alphavbeta3 integrin-EGFR complexes, engage a paxillin- but not FAK-mediated pathway of cell survival.

The FN13 peptide inhibits human tumor cells invasion through the modulation of αvβ3 integrins organization and the inactivation of ILK pathway

We report the effect of the stable expression of a 13 amino acid human fibronectin (FN) peptide (FN13) on the organization of the FN extracellular matrix (ECM) and of FN integrin receptors (FNRs), in relationship with the inhibition of cellular invasion, in three FN-ECM defective human tumor-derived cell lines: SK-Hep1C3, hepatoma, ACN, neuroblastoma, and SK-OV-3, ovary carcinoma. All these cell lines stably expressing the FN13 peptide, organized an FN-ECM, disorganized alpha v beta 1 integrins and inactivated the ILK pathway, with the loss of secretion of MMP-9. This was associated with the inhibition of cell invasion in Matrigel matrix only in SK-Hep1C3 and ACN, but not in SK-OV-3 cells. Analysis of the integrin receptors organization showed that the FN13 expressing cells SK-Hep1C3 and ACN organized alpha v beta 3 integrins, whereas SK-OV-3 organized alpha v beta 5 dimers. The functional block of alpha v beta 5 integrins, with an inactivating anti-alpha v beta 5 antibody, led to the induction of alpha v beta 3 integrins also in SK-OV-3 cells, and to the inhibition of cell invasion. These data show that in the human tumor cells studied FN13 inhibits the in vitro invasion through the dissociation of alpha v beta 1 dimers, leading to ILK pathway inactivation, only when the organization of alpha v beta 3 integrins is induced in the plasma membrane.

Matrix assembly induction and cell migration and invasion inhibition by a 13-amino acid fibronectin peptide

Fibronectin (FN) is an extracellular matrix (ECM) protein involved in tumor growth and metastasis. Five human FN cDNA segments encoding for FN fragments, all starting with the II1 repeat and ending with different C-terminal extensions, have been stably expressed in chick embryo fibroblasts (CEF). These FN cDNAs induce the formation of an organized ECM in CEF as long as they retain a sequence coding for a 13-amino acid stretch (FN13), with collagen binding activity, localized between type II2 and I7 repeats. An FN13 synthetic peptide induces in control CEF the assembly of an FN-ECM comparable with that observed in CEF-expressing FN fragments. The activity of FN13 is specific for its amino acid sequence, although the cysteine present in the 6th position can be substituted with a polar serine without affecting the induction of a fibrillar FN-ECM. A less fibrillar matrix is induced by FN13-modified peptides in which the cysteine is methylated or substituted by a non-polar alanine. FN13 induces the assembly of an FN-ECM also in Rous sarcoma virus-transformed CEF lacking the ECM and in hepatoma (SK-Hep1) and fibrosarcoma (HT-1080) human cell lines. FN13 also promotes the adhesion of CEF and Rous sarcoma virus-CEF at levels comparable with those obtained with purified intact FN. Finally, FN13 inhibits the migratory and invasive properties of tumorigenic cells, whereas intact FN favors their migration. All FN13-modified peptides show similar effects, although with reduced efficiency. None of these activities is supported by a scrambled peptide. These data suggest a possible role of FN13 in tumor growth and metastasis inhibition and its possible use as anti-tumorigenic agent.

Induction of fibronectin mRNA by urokinase- and tissue-type plasminogen activator in human skin fibroblasts: differential role of u-PA and t-PA at the fibronectin protein level

Plasminogen activators of the urokinase- and tissue-type and fetal calf serum (u-PA, t-PA, FCS) exert their mitogenic effect on quiescent human dermal fibroblasts and modulate the mRNA expression of cell-cycle related genes. The present study deals with the effects of PAs on the expression of fibronectin (FN), a heterodimeric extracellular matrix (ECM) protein that can be modulated in different ways by various mitogens. The kinetics of FN gene response was examined in quiescent fibroblasts upon PA stimulation (30 min -24 h). The results obtained evidenced that: (i) all mitogens tested (u-PA, t-PA and FCS) led to an increase of FN mRNA expression in early G1, as shown by the analysis of two sequences, III-9, common to all FN mRNAs, and EDA+, present only in the EDA+FN isoform; (ii) the kinetic profiles of FN mRNA stimulation were comparable for the three mitogens, although the effects on the FN-ECM assembly were distinct; (iii) t-PA and FCS led to FN assembly in the ECM, which was absent or decreased in u-PA-treated cultures. Immunobiochemical analysis of total FN and EDA+ FN showed that FN induced by t-PA was mainly dimeric (450-500 kDa), whereas FN induced by u-PA was mainly monomeric (230-250 kDa). These differences are probably due to the differential enzymatic action of t-PA and u-PA on FN, which might be related to a differential role of the two PAs in several physiopathological conditions.

A comparison of performances of four enzymes used in ELISA with special reference to beta-lactamase

Horse radish peroxidase, alkaline phaosphatase and beta-D-galactosidase are widely used as labels in the development of enzyme immunoassays (EIAs). Enzyme beta-lactamase, though introduced as a label in late seventies has not yet become very popular inspite of having the necessary features of an enzyme to be used in EIAs. The present article reviews assays developed with this enzyme, highlights its salient features and brings out an argument in favour of its wide spread use in EIAs.

Assessment of plasma fibronectin in malnourished Nigerian children

BACKGROUND

Severe malnutrition is associated with septic infections. The concentrations of fibronectin, albumin, and transferrin in plasma were measured in three groups of children with protein-energy malnutrition, aged 1-3 years, each group comprising 20 children. The aim of which was to test whether plasma fibronectin, being an opsonic protein, was reduced in such children, and if it was a useful index for assessing the severity of malnutrition.

METHODS

The concentrations of fibronectin, albumin, and transferrin in plasma were studied by enzyme immunoassay/ immunoblotting, spectrophotometry and immunoturbidimetry respectively.

RESULTS

All values were significantly lower in the patients with malnutrition than in the age- and sex-matched well-nourished Nigerian reference children. Within the malnourished group, the fibronectin value was evenly reduced in all subgroups. Albumin and transferrin values were lowest in the patients with kwashiorkor, highest in the marasmic patients, and intermediate in the patients with marasmic kwashiorkor; the values correlated mutually in individual cases as well, but not with the fibronectin levels. Neither plasma fibronectin fragmentation nor tissue fibronectin was detected in any patient with malnutrition or in the reference subjects.

CONCLUSIONS

The reduced plasma fibronectin values in these patients may be due to reduced synthesis by the liver, as evidenced by the equally reduced albumin and transferrin concentrations and/or to the multiple infections characteristic of the patients.

Degradation of human plasma and extracellular matrix fibronectin by tissue type plasminogen activator and urokinase

Fibronectins and plasminogen activators, both tissue and urokinase types, are involved in the physiopathological degradation of the extracellular matrix. Previous reports indicate that fibronectin can be degraded by urokinase without plasminogen. Also, we have shown that tissue-type plasminogen activator can cleave fibronectin, without plasminogen, generating fragments of 30 and 220-250 kDa detectable by immunoblotting analysis. A comparison with urokinase-induced degradation indicates that the cleavage sites are the same for both plasminogen activators. One is close to the carboxyl-terminal, disrupting the fibronectin dimeric structure, and one is near the amino-terminal, generating a 30 kDa fragment. In solution, the activity of tissue-type plasminogen activator was prevalent on the amino-terminal site, while urokinase activity was prevalent on the carboxyl-terminal site. On fibronectin immobilized onto a gelatin coated surface, only the 30 kDa fragment was released when treated with both plasminogen activators. Plasminogen activators also were active on fibronectin assembled into the extracellular matrix of cultured fibroblasts. Urokinase caused the complete disappearance of extracellular matrix fibronectin, together with the release of the 30 and the 220-250 kDa fibronectin fragments, but left a flat morphology, while tissue-type plasminogen activator induced the release of the 30 kDa fragment associated with changes in cellular morphology. The plasminogen-independent fibronectin degradation exerted by tissue-type plasminogen activator and urokinase is 100 times lower than that exerted by plasmin. This may provide a mechanism for localized and limited degradation of fibronectin preventing the generalized proteolysis associated with plasminogen activation.

ED-A region-containing isoform of cellular fibronectin is present in dentin matrix in dentinogenesis imperfecta associated with osteogenesis imperfecta

To elucidate the defective dentin formation in osteogenesis imperfecta (OI), we analyzed the expression of selected fibronectin (FN) isoforms in the dentin matrix of a patient with dentinogenesis imperfecta (DI) associated with OI, and in normal teeth. Frozen tooth sections were immunostained with three monoclonal antibodies (MAbs). The MAb recognizing the major cell-binding region (f-33), shared by plasma FN (pFN) and cellular FN (cFN), stained the pulp of normal adult permanent teeth intensely, while no reactivity was present in predentin, (demineralized) dentin, or dental cementum. The periodontal ligament stained unevenly. The dentin matrix of the patient with OI displayed reactive zones, alternating layerwise or concentrically with non-reactive ones. Staining throughout the connective tissue of adult oral mucosa, analyzed for the form of FN present, was intense, and in dermis, which was also studied, it was moderate. Reactivities in dental tissues with the MAb specific for the ED-A region (IST-9), included in cFN but not pFN, were similar to those with MAb f-33. The mucosal connective tissue stained weakly and dermis was negative, except that nerves and endothelia of some large blood vessels stained clearly. The MAb specific for the ED-B segment (BC-1), also included in cFN only, did not stain any of the tissues analyzed. The results suggest that, unlike mucosal and dermal FNs, FNs in the dental tissues are largely cellular, and also that dentin formation in OI may be completed by successive generations of pulpal fibroblasts differentiated into hard-tissue-forming cells.

Fibronectin in plasma and CSF: evidence for its intrathecal synthesis

A new methodology, using electroimmunodiffusion, has been described for the determination of fibronectin (Fn) in plasma and CSF. Fn was determined in the plasma of 35 normal subjects, and in the plasma and the CSF of 86 patients: 10 controls, 17 definite MS, 15 other inflammatory processes, 11 degenerative diseases, 13 peripheral neuropathies and 20 other neurological diseases. The normal mean was 354 +/- 53 micrograms/ml in plasma, not influenced by sex or age, and in the CSF 2.3 +/- 0.85 micrograms/ml. A significant increase of plasma Fn was observed in each of the patients-group. In the CSF an increase of Fn was observed predominantly in inflammatory processes but not in MS. An intrathecal synthesis of Fn was established in 24/76 patients, most often in inflammatory (9/15) processes but rarely (3/17) in MS. The intrathecal synthesis was suspected from the CSF Fn/CSF Albumin ratio and calculated using a formula derived from the principles previously described for IgG intrathecal synthesis. It represents the principal source of Fn increase in the CSF. In all inflammatory processes (including MS) the eventual influence of corticoids, immunosuppressive or anti-inflammatory drugs has not been established. The significance of the CSF Fn level in MS is discussed with regard to the recent demonstration of its presence within MS lesions and on macrophages in plaques.

Time-resolved immunofluorometric assays with measurement of a europium chelate in solution: application for sensitive determination of fibronectin

A novel detection principle applicable for sensitive measurement of molecules of biological interest by time-resolved fluorescence spectrophotometry is described. Our method is based on the quantification of the Eu3+ chelator 4,7-bis(chlorosulfophenyl)-1,10-phenanthroline-2,9-dicarboxylic acid (BCPDA) in solution in presence of an excess of Eu3+ ions. BCPDA-labeled solid phase complexes obtained by conventional immunoassay procedures are transferred into solution using urea/SDS/Eu3+ as dissociating and fluorescent lanthanide ion reagent. Two 'sandwich-type' assay variants based on the above methodology were realized for the determination of small amounts of fibronectin (FN) in biological fluids. FN is captured from solution by solid phase coated gelatin or a monoclonal antibody, respectively. Rabbit anti-FN antiserum used as second antibody is detected with a biotinylated anti-rabbit IgG antibody. Fluoresence is measured after incubation with streptavidin-BCPDA and dissociation of solid phase complexes as described. Both assays have a detection limit (blank + 3 x SD) of less than 0.5 ng/ml FN, a dynamic range of up to 300 ng/ml, and intraserial coefficients of variation of 4.4 and 6.3%, respectively. Median FN concentrations in saliva of healthy individuals were 104 (gelatin) and 36 ng/ml (double antibody), respectively.

Procollagen-III in serum, plasminogen activation and fibronectin in bronchoalveolar lavage fluid during and following irradiation of human lung

In the search for predictors of late radiation-induced lung injury we studied procollagen type III peptide concentration (P-III-P) in serum as well as fibronectin and plasminogen activation in bronchoalveolar lavage (BAL) fluid during and following irradiation of human lung. The patients received either high-dose hemithorax irradiation for pleural mesothelioma (11 patients) or high-dose irradiation with individually shaped fields for non-small cell lung cancer (12 patients). The severity of radiation fibrosis was assessed clinically from CT scans 6 months and 12 months after treatment. Four scores were used: severe, moderate, mild, or normal. Radiological lung injury varied from "severe" (9 patients) to near absence of injury-"normal" (6 patients). Serum levels of P-III-P, when measured weekly during the 5-week period of radiotherapy or at several time-points after treatment, did not show consistent changes, nor did the levels correlate with the score for radiation fibrosis as assessed by CT scanning. Changes in fibronectin levels or in markers of plasminogen activation in BAL fluid did not correlate with the development of late lung injury. The levels of BAL fluid plasmin and plasminogen activator as assessed zymographically, but not the free net enzyme values, showed a tendency to be elevated in patients with severe radiation-induced lung injury, suggesting a possible role for inhibitors of the plasminogen activation cascade in the process of radiation-induced lung injury.

Fibronectin concentration in cerebrospinal fluid reflects early central nervous system involvement in children with acute lymphoblastic leukemia

We measured concentrations of fibronectin (FN) in the cerebrospinal fluid (CSF) in long-term follow-up patients with acute lymphoblastic leukemia (ALL). In 11 patients with neuroleukemia the CSF-FN level was elevated already at the time of diagnosis of ALL, 3.8 +/- 0.6 mg/l, increased during therapy to 4.7 +/- 0.5 mg/l, and at the time of concurrent blast cell finding it was 5.5 +/- 1.0 mg/l. In 11 patients with no subsequent CNS leukemia, the mean CSF-FN level was 2.4 +/- 0.6 mg/l at the time of diagnosis of ALL and 2.8 +/- 0.6 mg/l during therapy, and increased to 3.2 +/- 0.8 mg/l. The neuroleukemia rate was 43% in patients with initial CSF-FN levels greater than 2 mg/l, compared with 5% in patients with CSF-FN levels less than or equal to 2 mg/l (p less than 0.005) in a group of 45 long-term follow-up patients with ALL. Regression analysis on the 21 clinical or laboratory parameters studied showed that the only variable independently associated with CSF-FN was the total protein concentration in the CSF; this, however, explained only 14% of the observed variation in the CSF-FN concentration and did not show any correlation with CNS involvement. We conclude that the CSF-FN test at diagnosis of ALL showed significant differences between groups of patients with and without CNS leukemia, and may prove to be a new early marker for neuroleukemia.

Elevated cerebrospinal fluid fibronectin concentration at diagnosis indicates poor prognosis in children with acute lymphoblastic leukemia

We investigated whether the concentration of fibronectin (FN) in the cerebrospinal fluid (CSF) could be used for identifying patients with subclinical blast-cell infiltration in the central nervous system (CNS) and an increased risk of CNS relapse later in the course of their leukemia. Our series comprised 36 children with newly diagnosed acute lymphoblastic leukemia (ALL). The mean follow-up time was 54 months (range 5 to 96 months). The median concentration of CSF-FN at diagnosis was 2.24 mg/l (range 0.78 to 7.04 mg/l). The 3-year continuous complete remission rate for the 16 patients with CSF-FN concentrations less than or equal to 2 mg/l was 93% as compared with 37% for the 19 patients with CSF-FN greater than 2 mg/l (p = 0.001). When multivariate analysis was performed, the CSF-FN concentration retained its prognostic significance. When all relapses were considered as failures, the relative risks of relapse for patients with CSF-FN less than or equal to 2 mg/l and greater than 2 mg/l were I and 15.8 (95% confidence limits 1.8-135.6, p less than 0.02), respectively. If only CNS relapses (isolated and combined) were considered as failures, relative risks for the above-mentioned groups were I and 11.6 (1.4-99.5, p less than 0.05), respectively. We conclude that determination of the CSF-FN concentration may provide a new means of evaluating the CSF in children with ALL and may prove to be a sensitive indicator of leukemic CNS infiltration.

Increased fibronectin production by cell lines from hypertrophic scar and keloid

Primary cell lines of fibroblasts from 8 tissues were established--three from hypertrophic scars (HS), one keloid (K) and four from the normal uninvolved dermis adjacent to each lesion. The objective was to quantify and compare all eight cell lines on the basis of fibronectin (FN) produced per cell and per total protein (PR). Two hypertrophic scars and their adjacent skin cell lines were evaluated by the ELISA method for FN and a micro Lowry assay for PR. The scar lines showed statistically significant increases in the amount of FN/cell compared to the cell lines from their adjacent normal dermis. The third hypertrophic scar and the keloid with their adjacent skin cell lines were assayed for FN and PR by radioimmunoprecipitation. Subconfluent cells were metabolically labeled with 35S-methionine for 20 hours. Harvested media and cell monolayers were assayed for radioactivity incorporated into FN and PR. The percentage of FN/PR was significantly higher in media for HS and K compared to the adjacent normal skin lines in the three passages tested. These results support our previous immunofluorescence studies and demonstrate that a fibroblast-type cell line from a hypertrophic scar or keloid produces more FN/PR over time than the normal fibroblast-type cell line from adjacent uninvolved dermis.

Characterization of fibronectin metabolites in normal rat urine

Fibronectin fragments showing immunoreactivity against an anti-rat plasma fibronectin antibody were detected in normal rat urine. Untreated urine showed immunoreactivity and this reactivity could not be dialyzed. These rat urinary fibronectin-related substances (RUF) were adsorbed on heparin-immobilized gel but hardly at all on gelatin-immobilized gel. They were separated into three fractions by DEAE-Sephadex ion exchange chromatography and each fraction was further purified by heparin-Sepharose affinity chromatography. The partially purified preparations, RUF-1, RUF-2 and RUF-3, were analyzed by the sandwich-type enzyme-linked immunosorbent assay (ELISA) method, and it was found their maximum reactivities were about 30%, 45% and 20% that of the intact plasma fibronectin, respectively. Plasma fibronectin was digested with elastase and then analyzed by the ELISA method to elucidate the patterns shown by the fragments. The fragments showed almost the same patterns on ELISA analysis, and the maximum immunoreactivity decreased in parallel with the degradation. On SDS-polyacrylamide gel electrophoresis, the RUF preparations were found to be composed of multiple forms of molecules, Mr 15,000-100,000, which reacted with the antibody. These results suggest that various forms of fibronectin metabolites are excreted in normal rat urine.

Sensitive two-site sandwich enzyme immunoassay with antipeptide antibodies for detection of viral antigens

Two-site sandwich ELISAs with antipeptide antibodies were developed for measuring the amounts of polyoma virus medium T and SV40 virus large T antigen in extracts from virus infected and transformed cells. In order to exclude crossreactive proteins, two antipeptide antibodies directed against different regions of the antigen were used in series. Both antigenic determinants have to be recognized for the assay to score positive. A positive signal was obtained with as little as 10 microliter of polyoma virus infected cell lysate and 100 microliter of extract prepared from medium T antigen-transformed FR18-1 cells which were shown to contain 37 and 15 pg of medium T antigen, respectively. This two-site sandwich ELISA is a sensitive tool to detect novel or closely related proteins.

Fibronectin-binding 36 kDa protein in human fibroblasts

A 36 kDa fibronectin-binding protein was identified from electrophoretically separated proteins of the deoxycholate-soluble fraction of cultured fibroblasts by blotting with fibronectin and using poly- or monoclonal antibodies and immunoperoxidase staining to detect the bound fibronectin. The 36 kDa protein was purified by preparative electrophoresis and used to raise specific antibodies. Solid-phase 36 kDa protein bound plasma and fibroblast fibronectins equally well. The 36 kDa protein is an amphipathic protein with pI 5.9. It is monomeric with a tendency to dimerize and appears to be distinct from the cell surface fibronectin receptors which interact with the Arg-Gly-Asp recognition site in the fibronectin molecule.

Fibronectin-plasma membrane interaction in the adhesion of hemopoietic cells

Many hemopoietic cell lines were examined for their ability to adhere to culture dishes coated with extracellular matrix proteins. Adhesion assay was performed with murine and human leukemic cell lines representative of different stages of differentiation along both erythroid and myeloid lineages. All the hemopoietic cell lines tested adhered to fibronectin but not to laminin, types I, III, and IV collagen, serum-spreading factor, and cartilage proteoglycans. In addition to immortalized cell lines, immature erythroid and myeloid mouse bone marrow cells adhered to fibronectin. To define the fibronectin region involved in hemopoietic cell adhesion, proteolytic fragments, monoclonal antibodies, and synthetic peptides were used. Among different fibronectin fragments tested, only a 110-kD polypeptide, corresponding to the fibroblast attachment domain, was active in promoting adhesion. Moreover, a monoclonal antibody to the cell binding site located within this domain prevented hemopoietic cell adhesion. Finally, the tetrapeptide Arg-Gly-Asp-Ser, which corresponds to the fibronectin sequence recognized by fibroblastic cells, specifically and competitively inhibited attachment of hemopoietic cells to this molecule. The cell surface molecule involved in the interaction of mouse hemopoietic cells with fibronectin was identified as a 145,000-D membrane glycoprotein by adhesion-blocking antibodies. This glycoprotein was found to be antigenically and functionally related to the GP135 membrane glycoprotein involved in the adhesion of fibroblasts to fibronectin (Giancotti, F. G., P. M. Comoglio, and G. Tarone, 1986, Exp. Cell Res., 163:47-62). On the basis of these data, we conclude that interaction of hemopoietic cells with fibronectin involves a specific fibronectin sequence and a 145,000-D cell surface glycoprotein. We speculate that this property might be relevant for the interaction of hemopoietic cells with the bone marrow stroma, which represents the natural site of hemopoiesis.