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Biomedical subjects

R Brentani

Publications and source records attributed to R Brentani.

12 recordsLinked to original sources

Collagen binding site in collagenase can be determined using the concept of sense-antisense peptide interactions.

Tissue degradation and invasion are hallmarks of the metastatic phenotype. While several extracellular matrix components can be digested by proteases, degradation of interstitial collagen is selectively initiated by collagenase. It is obvious that inhibitors of collagenase activity would be extremely useful in preventing tissue destruction and tumor cell invasion and thus prove invaluable therapeutic agents. We describe here the possible development of such inhibitors through the use of the principle of complementary hydropathy. A peptide was deduced from the nucleotide sequence complementary to that coding for the region in interstitial collagen surrounding the bond between Gly775 and Ile776 which is cleaved by the enzyme. Labeled collagen binds specifically and quantitatively to this peptide. A polyclonal mouse serum raised against this peptide recognized purified human collagenase, was able to immunoprecipitate collagenase from cultured human keratinocyte supernatants and was effective in inhibiting collagenolytic activity with a K(iapp) = 0.3 microM.

Amino Acid Sequence

A monoclonal antibody (IID510g52) for the determination of functional domains within integrin cell surface receptors.

Monoclonal antibodies against cell surface receptors can be useful for the study of structural and biochemical features involved in protein interactions underlying platelet adhesion and aggregation. We report here the characterization of a monoclonal antibody, IID510g52 (hereafter referred to as IID5), which has been selected based on its specific binding properties against the platelet membrane glycoprotein IIIa. Characterization of the reactive epitope, including evolutionary conservation and identification of related IID5 target antigens in tumor cells, suggest that the IID5 epitope is implicated in the ligand-binding function of integrin receptors. Indeed, we show that this MoAb acts as a potent inhibitor of platelet aggregation and cell adhesion. Taken together, these results indicate that such a monoclonal may be a strategic tool for better understanding multiple integrin-mediated adhesive reactions, as well as the determination of interacting recognition sites.

Adult

Anti-platelet autoantibodies from ITP patients recognize an epitope in GPIIb/IIIa deduced by complementary hydropathy.

Idiopathic thrombocytopenic purpura (ITP) is a frequent platelet disorder due to the presence of anti-platelet autoantibodies. Recently a fibronectin/fibrinogen receptor in platelets, integrin GPIIb/IIIa, has been implicated as the antigen in chronic ITP. To examine the epitopes involved in the autoimmune response against GPIIb/IIIa we have used concepts from the complementary hydropathy principle. We used the peptide Trp-Thr-Val-Pro-Thr-Ala, WTVPTA (deduced from the complementary nucleotide sequence to that which codes for the Arg-Gly-Asp, RGD, domain in fibronectin), to test the immunologic activity of ITP sera. Sera from 31 patients with clinically defined ITP were tested in ELISA for reactivity towards WTVPTA and affinity purified GPIIb/IIIa. Seventeen sera (57%) reacted strongly with the glycoprotein complex, five of which reacted with the peptide. By affinity chromatography of one of these sera, we were able to show that antibodies that bind to the peptide are within the population that binds to GPIIb/IIIa. Liquid phase competition experiments revealed that binding of ITP serum to WTVPTA was inhibited only by a hydropathically compatible peptide. Our data indicate that autoantibodies can bind to hydropathically generated antigenic determinants and thus, render these peptides clinically important as diagnostic tools.

Adolescent

Integrins and metastases: an overview.

Metastasis, the major cause of cancer deaths, is represented by a complex, multistep cascade of events characterized by the interaction between neoplastic cells and host tissue elements (cells and extracellular matrix components). These interactions are mediated by specific receptors; among them are members of a growing family of heterodimeric cell surface glycoproteins, called integrins. The role of integrins along tumor progression key steps, as well as their value as diagnostic and prognostic markers are discussed herein. Emphasis on the nature of integrin-ligand interaction is given; in particular, concerning the role of carbohydrate moieties on the generation of diversity in integrin specificity and varying affinity states.

Animals

Differences in human laminin B2 sequences.

A cDNA clone encoding the B2 chain of laminin has been isolated from a human endothelial lambda gt11 cDNA library. The nucleotide and deduced amino acid sequences of the clone were determined and showed one amino acid substitution (Ser1519 instead of Asn) when compared to lung laminin B2 chain and one silent nucleotide change (G4200 instead of A) in relation to the human placenta laminin B2 chain. Other differences in the 3'-untranslated region were also found.

Amino Acid Sequence

Differential staining of collagens type I, II and III by Sirius Red and polarization microscopy.

Organs of fish, amphibian, reptile, bird and mammals when stained by Sirius Red and studied with polarization microscopy present different colors in regions where collagens I, II and III have been described. Collagen type I presented a yellow, orange or red color while collagen type III appeared green. Collagen type II, present in cartilage and chondrosarcoma showed a variable color according to the tissue and the species. Its color and morphology however always permitted its clear distinction from collagens type I and type III.

Animals

Further studies on collagen mRNA: partial chemical characterization and polyadenylic acid sequence.

Collagen mRNA has already been purified and characterized by us. Its purity has now been enhanced by two different methods. Gel electrophoresis shows in either method, a single peak with the same mobility already reported: 1.05 X 10(6) daltons. Base composition analyses of collagen mRNA purified by either method were almost identical. Chemical analyses of the isolated polyadenylic acid stretch show that it is, 0.48 X 10(5) daltons-long, (about 140 nucleotides-long), contains 75% AMP, and is located at the 3' end of the polymer.

Animals

Isolation and characterization of collagen-synthesizing polysomes from chick embryos.

Collagen-synthesizing polysomes were isolated by low-speed centrifugation of the post-mitochondrial supernatant of chick homogenates. Electron microscopy of the fraction thus isolated shows it to be exclusively composed of ribosomes. Amino acid incorporation in vitro showed that these particles were efficient in the incorporation of proline, but not tryptophan, as opposed to ribosomes obtained from the supernatant of the low-speed centrifugation. The incorporation process was highly dependent on GTP, and exibited an optimal Mg2+concentration of 5.6mM. The reaction was inhibited by RNase, elongation inhibitors as anysomycin, sparsomycin, fusidic acid and GDPCP. It was also moderately inhibited by initiation inhibitors such as aurintricarboxilic acid and pyrocatechol violet. The product of the incorporation was characterized as collagen by its sensitivity towards purified collagenase, lack of tryptophan, chromatography in CM-cellulose and molecular sieve chromatography in Sephadex G-200.

Animals

Isolation and characterization of collagen messenger RNA*.

Chick embryo collagen-synthesizing polysomes were isolated by differential centrifugation. RNA extracted from these particles was chromatographed in oligo(dT)-cellulose solumns and the mRNA thus obtained characterized as collagen mRNA by its electrophoetical mobility in acrylamide gels (equivalent to 1.05 x 10-6 daltons) and its effect upon a cell-free system derived from Krebs ascites tumor cells. The incorporation of 3H-proline was markedly dependent upon rabbit reticulocyte initiation factors and inhibited by initiation inhibitors such as aurintricaboxilate and pyrocatechol violet. The incorporation product was characterized as collagen by its lack of tryptophan, digestibility by purified bacterial collagenase, and by its co-chromatography with unlabled chick collagen in Sephadex G-200 and CM-cellulose columns.

Animals