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A Siri

Publications and source records attributed to A Siri.

At least 37 records · Page 2Linked to original sources
PubMed1987

Demonstration of structural differences between the two subunits of human-plasma fibronectin in the carboxy-terminal heparin-binding domain.

Structural differences between the two subunits of human plasma fibronectin were studied by analyzing the carboxy-terminal heparin-binding domain (Hep-2). Two fragments (29 kDa and 38 kDa) derived from the Hep-2 domain were purified from thermolysin-digested human plasma fibronectin. Identical NH2-terminal sequences were obtained for both fragments through 16 Edman cycles. Neither domain contained the 90-amino-acid extra domain which is predicted by cDNA analysis of the cellular form of fibronectin. We have examined the primary structures of the 29-kDa and 38-kDa Hep-2 domains produced from the two chains of plasma fibronectin by analyzing the tryptic peptides by fast atom bombardment/mass spectrometry and comparison with the predicted fragments deduced from the corresponding cDNA-derived peptide sequences. Peptides that were unique to each domain were further characterized by microsequence analysis. The two domains showed identical amino acid sequences through 274 residues, followed by a region of variability. The 29-kDa domain contains 279 amino acids with an estimated relative molecular mass (Mr) of 30,460. This domain is located in the heavy chain of plasma fibronectin and contains three repeats of type III sequences plus a portion of the connecting segment (IIICS) region. The 38-kDa domain contains 359 amino acids and one O-linked glycosyl unit for an estimated Mr of 39,263. This domain is from the light chain of plasma fibronectin and contains four repeats of type III sequences with the deletion of the entire 120-amino-acid IIICS area. Secondary structure analysis by Chou/Fasman and circular dichroism reveals extensive beta-sheet structure for these domains. Key sulfhydryl and glycosylation sites are located near the mRNA splice junctions for the two chains. It is postulated that the splice junctions are adjacent to a flexible domain joining two regions of extensive beta-sheet structure.

Amino Acid Sequence↗
PubMed1987

Transformed human cells produce a new fibronectin isoform by preferential alternative splicing of a previously unobserved exon.

Purification and amino acid sequence analysis of a proteolytic fragment of fibronectin (FN) from transformed human cells demonstrated that a high percentage of these FN molecules contains an extra amino acid sequence which is present only in a very low percentage of FN molecules from normal fibroblasts and is undetectable in plasma FN. This new amino acid sequence introduces into the FN molecule a site very sensitive to a number of proteolytic enzymes. By analyzing the cellular mRNA and genomic clones, we have demonstrated that this sequence derives from a differential splicing pattern of the FN mRNA precursors, which leads in transformed cells to a high-level expression of an extra type III homology repeat (ED-B) coded for by a previously unobserved exon. Here we also report the complete sequence of this new exon. These results demonstrate that in malignant cells the mechanisms regulating the splicing of FN mRNA precursors are altered.

Amino Acid Sequence↗
PubMed1986

DNA-binding domains of human plasma fibronectin. pH and calcium ion modulation of fibronectin binding to DNA and heparin.

We have studied the binding of fibronectin and its thermolysin fragments to DNA and heparin. Elution of polypeptides bound to DNA-cellulose and heparin-Sepharose affinity chromatography columns was performed by NaCl linear gradients in buffers at different pH and in the presence and absence of calcium ions. The NaCl concentration required to elute fibronectin from both types of column increased as the pH decreased. Fibronectin was not retained on DNA-cellulose or heparin-Sepharose affinity chromatography columns using a buffer containing physiological concentrations of Ca2+, Mg2+ and NaCl, at pH 7.4. On the other hand at pH 6.4 in conditions of physiological ionic strength, fibronectin was retained by both columns, eluting from the DNA-cellulose at 280 mM NaCl and from the heparin-Sepharose column at 210 mM. Furthermore, we have studied the interaction of thermolysin-digested fibronectin both with DNA-cellulose and heparin-Sepharose using the above procedure. The results demonstrate that there are four distinct domains, which interact both with DNA and heparin. We also report here the modulation by pH and Ca2+ ions of the interaction with DNA and heparin of these different domains.

Amino Acid Sequence↗
PubMed1986

Large-scale procedure for the purification of fibronectin domains.

Human plasma fibronectin is composed of at least seven distinct domains, with affinities for different macromolecules and cell surfaces. Here we describe in detail a simple high-yield procedure for the purification of large amounts of fibronectin domains. This involves thermolysin digestion of the fibronectin molecule followed by the purification of the domain using mainly hydroxyapatite chromatography columns. This procedure represents a great simplification over those previously reported.

Amino Acids↗
PubMed1986

Transformed human cells release different fibronectin variants than do normal cells.

Fibronectin molecules are dimers composed of subunits whose primary structures may differ. This is due to alternative splicing in at least two regions (ED and IIICS) of the pre-mRNA. Using two monoclonal antibodies specific for two different epitopes of domain 5 (high affinity for heparin), we have quantitatively analyzed the expression of the IIICS sequence in human fibronectins from different sources. The results demonstrated that the percentage of fibronectin subunits containing the IIICS is higher in fibronectins from tumor-derived or simian virus 40-transformed human cells than in fibronectins from human plasma or normal human fibroblasts. Furthermore, we observed that 45-65% of fibronectin subunits from transformed cells or normal embryonic fibroblasts are sialylated on the heparin-binding domain 5, whereas this occurs in only 24-28% of fibronectin subunits from normal adult fibroblasts. On the contrary, no sialylation was observed on domain 5 in fibronectin from human plasma.

Amino Acid Sequence↗
PubMed1985

Primary structure of a DNA- and heparin-binding domain (Domain III) in human plasma fibronectin.

The complete amino acid sequence of a DNA- and heparin-binding domain isolated by limited thermolysin digestion of human plasma fibronectin has been obtained. The domain contains 90 amino acids with a calculated molecular weight of 10,225. The apparent molecular mass of this domain is 14 kDa when analyzed by sodium dodecyl sulfate-gel electrophoresis. The anomalously high molecular size estimation may be due to the inaccuracy of this method in the low range. The structure was established from microsequence analysis of the chymotryptic, tryptic, and Staphylococcus aureus protease peptides. The molecular ion of each of the chymotryptic peptides was obtained by fast atom bombardment mass spectrometry. The domain has a preponderance of basic residues with a net charge of +5 at neutral pH. The basic nature of the domain may account for its affinity for the polyanions, DNA and heparin. The predicted secondary structure is beta-sheet, in common with all of the type III internal sequence homology structures obtained for fibronectin so far. The location of the domain in fibronectin was made possible by limited thermolysin digestion and identification of the fragments and by comparison of the sequence of the 14-kDa fragment with the partial structure of bovine plasma fibronectin. The domain comprises residues 585-675 and defines a region immediately adjacent to the collagen-binding domain. Numbering domains beginning at the amino terminus, this domain is Domain III after the fibrin/heparin/actin/S. aureus binding Domain I and the collagen-binding Domain II. The domain was obtained from a larger precursor (56 kDa) which bound heparin, DNA, and gelatin. Further digestion of the 56-kDa fragment gave rise to a 40-kDa fragment which only bound gelatin, and a 14-kDa fragment which only bound heparin or DNA. The 14-kDa fragment (Domain III) marks the beginning of the type III homology region in fibronectin, for there may be up to 15 repeats of 90 amino acids. The size of this domain corresponds to one repeat of 90 amino acids and it has some sequence homology to the other type III sequences found thus far in fibronectin.

Amino Acid Sequence↗
PubMed1985

Differences in domain structure between human fibronectins isolated from plasma and from culture supernatants of normal and transformed fibroblasts. Studies with domain-specific antibodies.

The domain structure of human fibronectins isolated from plasma and from the conditioned medium of normal and transformed fibroblasts was analyzed by limited proteolysis and S-cyanylation followed by immunostaining of released fragments with five kinds of antibodies, each specific for one functional domain. The results indicate that all three human fibronectins are composed of the same set of functional domains aligned in the same topological order. However, the following clear differences were found in specific fragments released from plasma fibronectin (pFN) and those released from fibronectin of normal (N-cFN) and transformed fibroblasts (T-cFN). Two fragments (Mr = 70,000 and 60,000) were released from the COOH-terminal region of pFN by cathepsin D. These fragments represent the COOH-terminal heparin-binding (Hep-2) and fibrin-binding (Fib-2) domains. The corresponding fragments released from both N-cFN and T-cFN by cathepsin D had much larger molecular weights (Mr = 100,000 and 83,000-74,000) than those from pFN. The fragments from the Fib-2 domain alone, however, did not show any difference among all three FNs. The internal region, from the gelatin-binding (Gel) domain through the Hep-2 domain, of N-cFN and T-cFN was released as a Mr = 210,000 fragment upon mild trypsin digestion. The corresponding fragment from pFN was released as a Mr = 185,000 fragment. The COOH-terminal half, including the Hep-2 domain, of both N-cFN and T-cFN was released by S-cyanylation as Mr = 160,000-145,000 fragments, which are 25,000-20,000 larger than the corresponding fragments of pFN. These results clearly indicate that the Hep-2 domain of N-cFN and T-cFN is 30,000-20,000 daltons larger than the same domain of pFN. Although various fragments released from N-cFN and T-cFN showed a similar pattern, there were minor differences. Thermolysin fragments derived from the Hep-2 domain of N-cFN were clearly distinguishable from those from T-cFN. Three groups of fragments with Mr = 40,000, 35,000-32,000, and 30,000 were released from N-cFN, while only the 35,000-32,000 fragment was released from T-cFN. The Mr = 44,000/60,000 thermolysin fragments representing the Gel domain and the Mr = 210,000/165,000 tryptic fragments representing the internal domains of T-cFN were slightly, but consistently, larger than those of N-cFN.(ABSTRACT TRUNCATED AT 400 WORDS)

Antibodies, Monoclonal↗
PubMed1985

Elution of fibronectin proteolytic fragments from a hydroxyapatite chromatography column. A simple procedure for the purification of fibronectin domains.

Human plasma fibronectin is composed of at least five distinct domains which we refer to as Hep-1/Fib-1, Gel, Cell, Hep-2 and Fib-2 depending on their affinity for heparin (Hep), gelatin (Gel), the cell surface (Cell) or fibrin (Fib). These domains are aligned from the NH2 to the COOH terminus in the above order and can be separated from each other by mild proteolytic digestion. We have studied the elution of fibronectin thermolysin digest from a hydroxyapatite column using a linear gradient (0.5-190 mM) of sodium phosphate buffer. The five major fibronectin domains were eluted from the hydroxyapatite chromatography column in the following order: Gel, Fib-2, Cell, Hep-1/Fib-1 and Hep-2. They were identified on the basis of their molecular mass, affinity to different macromolecules and reaction with domain-specific monoclonal antibodies. All domains except the Cell and Hep-2 domains eluted as single homogeneous peaks. The Cell domain eluted as two different peaks and the Hep-2 domain eluted as four different peaks. This is the first time that heterogeneity of these two domains has been observed. Since chromatography of a fibronectin thermolysin digest on a hydroxyapatite column provides a good separation of the five major fibronectin domains, we have elaborated a procedure in which each fibronectin domain is purified by no more than two steps; hydroxyapatite and molecular exclusion chromatography. Fractionation of fibronectin proteolytic digest on a hydroxyapatite chromatography column should be of great value in the comparative analysis of fibronectin from different sources and in the study of fibronectin heterogeneity. Its use in combination with molecular exclusion chromatography offers a simple and high-yield method for the purification of large amounts of fibronectin domains.

Chemical Phenomena↗
PubMed1984

Fibronectin concentrations in pleural effusions of patients with malignant and non-malignant diseases.

We have determined the amount of fibronectin in pleural fluids and plasma of 131 patients suffering from pleurisy of malignant and non-malignant etiology. We observed a significantly higher concentration of fibronectin in pleural fluids of a few patients with mesothelioma as compared with that found in pleural fluids of patients with pleurisies of different etiology. In these patients the pleural fluid fibronectin concentration was higher than that measured in plasma, suggesting local synthesis of fibronectin.

Adult↗
PubMed1983

Differences in domain structure between pericellular matrix and plasma fibronectins as revealed by domain-specific antibodies combined with limited proteolysis and S-cyanylation: a preliminary note.

Differences in domain structure between human fibronectins obtained from pericellular matrix and plasma have been revealed by limited proteolysis and S-cyanylation, followed by identification of each domain with domain-specific antibodies. Although the overall domain structure is similar between pericellular and plasma fibronectins, the fragments derived from the COOH-terminal region of these fibronectins, which were defined by specific antibodies, exhibited clear differences in their molecular weights and protease susceptibility, suggesting that the structure near the COOH-terminal region is significantly different between these two proteins.

Antibodies↗
PubMed1983

Increased plasma fibronectin concentrations in tumor bearing mice.

Fibronectin concentration was studied in plasma of mice at different times after inoculation of 3 different experimental tumors, Colon 26 adenocarcinoma, mFS6 fibrosarcoma and B16 melanoma. A significant increase in fibronectin concentrations 10-30 days after inoculation of all tumors was found. Highest and earliest fibronectin increases were observed in BALB/c mice inoculated with Colon 26 adenocarcinoma cells. Control animals inoculated with previously irradiated cells (5000 rad) showed neither tumor growth nor significant variations in plasma fibronectin levels.

Adenocarcinoma↗
PubMed1982

Species-specific monoclonal antibodies in the assignment of the gene for human fibronectin to chromosome 2.

Using three different species-specific monoclonal antibodies we have studied, in human-mouse and human-hamster somatic cell hybrids, the correlation between the presence of different human chromosomes and the ability to release human fibronectin into the tissue culture medium. Presence of human fibronectin was determined by an affinity-radioimmunoassay. In addition, tissue culture media of the different hybrids were separated on SDS-polyacrylamide gels, the proteins were blotted onto a nitrocellulose sheet and human fibronectin visualized by an immunoenzymatic technique. Karyology and determination of isoenzyme markers of specific human chromosomes show that the ability to produce human fibronectin segregated with the presence of human chromosome 2.

Animals↗
PubMed1980

Somatic cell hybrids producing antibodies specific to human fibronectin.

We have produced somatic cell hybrids between mouse plasocytoma cells deficient in hypoxanthine phosphoribosyltransferase (P3 x 63 Ag8) and spleen cells derived from mice immunized with purified human plasma fibronectin. We report herein the properties of monoclonal anti-fibronectin antibodies released by eight different clones.

Animals↗
PubMed1980

A simplified procedure for the preparation of antibodies to serum fibronectin.

In the present paper we describe in detail a simple procedure for the preparation of monospecific antisera to human and mouse serum fibronectin. A similar procedure could also be used to prepare antibodies to fibronectin from other species. The procedure, based on the recently reported affinity of fibronectin for gelatin, essentially consists of two steps (1) Immunization of rabbits with fibronectin purified from serum by affinity chromatography using gelatin coupled to CNBr-activated Sepharose 4B. (2) Absorption of the antiserum obtained by an immunoabsorbent prepared using fibronectin-free serum proteins that remained after absorbing serum with gelatin-Sepharose. The antisera obtained were monospecific, as determined by immunoelectrophoresis and did not show any difference with respect to antisera prepared by different procedures.

Animals↗
PubMed1980

Antireticulin antibodies in psoriasis.

Antireticulin antibodies were studied in the sera of 32 patients affected by various clinical forms of psoriasis. The indirect immunofluorescence method was used on histological sections of human kidney and mouse liver and kidney. This method was also used with sera from children with coeliac disease and from healthy controls. In 10 these antibodies were positive, while in 22 they were negative, the intensity of the titres varying with the extent of the disease. These results support the notion that immunological phenomena may be involved in the physiopathological mechanisms of psoriasis.

Adolescent↗
PubMed1979

Fibronectin: a chromatin-associated protein?

We have previously reported that chromatin preparations from human cultured fibroblasts contain a single homologous serum protein. In this paper we present evidence, based on immunological identity and physicochemical properties, that this serum protein is fibronectin. Furthermore, using a radioimmunoassay system, we have estimated that fibronectin represents about 0.7% of the total protein in both chromatin preparations and whole fibroblasts. Using a nitrocellulose filter assay system, we also show that fibronectin is a DNA-binding protein having an equilibrium constant of 4.6 x 10(-6) M. Equilibrium competition experiments have demonstrated that fibronectin has the ability to differentiate among nucleotides, indicating that fibronectin-DNA interaction is at least partially specific, and that a minimum polymer length of 12-18 nucleotides is required for effective binding to occur. Fibronectin has been isolated readily from plasma using DNA-affinity chromatography. We do not have direct evidence that fibronectin is an actual nonhistone chromosomal protein, but fibronectin is a DNA-binding protein (at least under in vitro assay conditions) and appears to be a normal constituent of chromatin as chromatin is currently isolated from cell nuclei.

Antibody Specificity↗
PubMed1976

A serum protein associated with chromatin of cultured fibroblasts.

Antibodies to chromatin proteins from human and mouse fibroblasts which have been cultured for more than 25 generations with heterologous serum show specificity for a homologous alpha-serum protein. These results indicate that among the chromatin-associated proteins there is one (or more) which has extensive structural similarity to a serum protein. This is the first direct evidence that a serumlike protein or proteins could be chromatin associated in vivo, as has been suggested by experiments showing in vitro interaction between DNA and certain serum proteins.

Binding Sites↗