Localization of beta 1-integrins in human cartilage and their role in chondrocyte adhesion to collagen and fibronectin

Exp Cell Res. 1993 Aug;207(2):235-44. doi: 10.1006/excr.1993.1189.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies
  • Calcium / pharmacology
  • Cartilage* / chemistry
  • Cartilage* / cytology
  • Cartilage* / metabolism
  • Cattle
  • Cell Adhesion / physiology
  • Chromatography, Affinity
  • Collagen / metabolism*
  • Fibronectins / metabolism*
  • Flow Cytometry
  • Fluorescent Antibody Technique
  • Glycoproteins / analysis
  • Glycoproteins / physiology
  • Humans
  • Integrin beta1
  • Integrins / analysis*
  • Integrins / immunology
  • Integrins / physiology*
  • Magnesium / pharmacology
  • Oligopeptides / pharmacology
  • Precipitin Tests
  • Vitronectin

Substances

  • Antibodies
  • Fibronectins
  • Glycoproteins
  • Integrin beta1
  • Integrins
  • Oligopeptides
  • Vitronectin
  • arginyl-glycyl-aspartic acid
  • Collagen
  • Magnesium
  • Calcium