title: Localization of beta 1-integrins in human cartilage and their role in chondrocyte adhesion to collagen and fibronectin.
abstract: In the past, proteins have been described that may be involved in chondrocyte interactions with extracellular collagen, but little is known about the role of integrins in chondrocyte-collagen interactions. Here we report on the analysis of beta 1-integrin distribution in human fetal cartilage and on the expression of integrins on fetal chondrocytes, using monoclonal and polyclonal antibodies to integrin alpha- and beta-chains. We show the presence of alpha 2-, alpha 5-, alpha 6-, alpha v-, and beta 1-chains on freshly isolated chondrocytes by surface immunofluorescence in the fluorescence-activated cell sorter and by surface iodination followed by immunoprecipitation. Affinity chromatography of bovine chondrocyte membrane proteins on a collagen-Sepharose column followed by immunoprecipitation confirmed the presence of the collagen-binding alpha 2 beta 1-integrin on chondrocytes. Chondrocyte adhesion on native collagens I and II, on fibronectin, and on laminin was completely blocked by anti-beta 1; anti-alpha 2 reduced chondrocyte binding to collagen by only 40-50%; similarly, anti-alpha 1-antibodies were also able to reduce chondrocyte binding to collagen, although alpha 1 could not be unequivocally identified on chondrocytes. Chondrocyte adhesion to fibronectin was Mg(2+)- and Ca(2+)-dependent and could be inhibited by anti-alpha 5 and by RGD peptides. Chondrocyte adhesion to native collagens is Mg(2+)-, but not Ca(2+)-dependent and RGD-independent. Interestingly, although these data point to a role of alpha 2 beta 1 in chondrocyte-collagen interactions in vitro, alpha 2 could not be visualized in sections of human fetal cartilage, in contrast to the beta 1-, alpha v-, and alpha 5-chains which were present. This suggests that alpha 2 beta 1-integrin may be involved in the assembly of a pericellular collagen matrix in vitro, but may not be required for chondrocyte-collagen interactions in intact cartilage.
authors.affiliation: Clinical Research Unit for Rheumatology, University of Erlangen-Nürnberg, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Dürr
authors.forename: S
authors.initials: S
authors.lastname: Goodman
authors.forename: A
authors.initials: A
authors.lastname: Potocnik
authors.forename: H
authors.initials: H
authors.lastname: von der Mark
authors.forename: K
authors.initials: K
authors.lastname: von der Mark
mesh_terms: D000818:Animals; D000906:Antibodies; D002118:Calcium / Q000494:pharmacology; D002356:Cartilage / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D002417:Cattle; D002448:Cell Adhesion / Q000502:physiology; D002846:Chromatography, Affinity; D003094:Collagen / Q000378:metabolism*; D005353:Fibronectins / Q000378:metabolism*; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006023:Glycoproteins / Q000032:analysis / Q000502:physiology; D006801:Humans; D019012:Integrin beta1; D016023:Integrins / Q000032:analysis* / Q000276:immunology / Q000502:physiology*; D008274:Magnesium / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D011233:Precipitin Tests; D019096:Vitronectin
chemical_list: D000906:Antibodies; D005353:Fibronectins; D006023:Glycoproteins; D019012:Integrin beta1; D016023:Integrins; D009842:Oligopeptides; D019096:Vitronectin; C047981:arginyl-glycyl-aspartic acid; D003094:Collagen; D008274:Magnesium; D002118:Calcium