title: Alternative splicing of the angiogenesis associated extra-domain B of fibronectin regulates the accessibility of the B-C loop of the type III repeat 8.
abstract: BACKGROUND
  Fibronectin (FN) is a multi-domain molecule involved in many cellular processes, including tissue repair, embryogenesis, blood clotting, and cell migration/adhesion. The biological activities of FN are mediated by exposed loops located mainly at the interdomain interfaces that interact with various molecules such as, but not only, integrins. Different FN isoforms arise from the alternative splicing of the pre-mRNA. In malignancies, the splicing pattern of FN pre-mRNA is altered; in particular, the FN isoform containing the extra-domain B (ED-B), a complete FN type III repeat constituted by 91 residues, is undetectable in normal adult tissues, but exhibits a much greater expression in fetal and tumor tissues, and is accumulated around neovasculature during angiogenic processes, thus making ED-B one of the best markers and targets of angiogenesis. The functions of ED-B are still unclear; however, it has been postulated that the insertion of an extra-domain such as ED-B modifies the domain-domain interface and may unmask loops that are otherwise cryptic, thus giving FN new potential activities.
  
  
  METHODS
  We used the mAb C6, which reacts with ED-B containing FN, but not with ED-B-free FN and various recombinant FN fragments containing mutations, to precisely localize the epitopes recognized by the mAb C6.
  
  
  CONCLUSIONS
  We formally demonstrated that the inclusion of the alternatively spliced angiogenesis-associated ED-B leads to the unmasking of the FNIII 8 B-C loop that is cryptic in FN molecules lacking ED-B. Thus, the mAb C6, in addition to providing a new reagent for angiogenesis targeting, represents a new tool for the study of the potential biological functions of the B-C loop of the repeat FNIII 8 that is unmasked during angiogenic processes.
authors.affiliation: Laboratory of Recombinant Therapeutic Proteins, CBA - Advanced Biotechnology Centre, Genoa, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Ventura
authors.forename: Francesca
authors.initials: F
authors.lastname: Sassi
authors.forename: Arianna
authors.initials: A
authors.lastname: Parodi
authors.forename: Enrica
authors.initials: E
authors.lastname: Balza
authors.forename: Laura
authors.initials: L
authors.lastname: Borsi
authors.forename: Patrizia
authors.initials: P
authors.lastname: Castellani
authors.forename: Barbara
authors.initials: B
authors.lastname: Carnemolla
authors.forename: Luciano
authors.initials: L
authors.lastname: Zardi
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D018604:Epitope Mapping; D000939:Epitopes / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D005353:Fibronectins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D009154:Mutation; D009369:Neoplasms / Q000098:blood supply; D009389:Neovascularization, Pathologic / Q000235:genetics / Q000276:immunology; D018919:Neovascularization, Physiologic / Q000235:genetics / Q000276:immunology; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics; D017434:Protein Structure, Tertiary; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D005353:Fibronectins; D020033:Protein Isoforms