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© The Rockefeller University Press, 0021-9525/1997//1159 $5.00
The Journal of Cell Biology, Volume 138, Number 5, , 1997 1159-1167

Article

Integrin {alpha}2β1 Is a Receptor for the Cartilage Matrix Protein Chondroadherin



Lisbet Camper, Dick Heinegård, and Evy Lundgren-Åkerlund

Department of Cell and Molecular Biology, Section for Connective Tissue Biology, Lund University, S-221 00 Lund, Sweden

Chondroadherin (the 36-kD protein) is a leucine-rich, cartilage matrix protein known to mediate adhesion of isolated chondrocytes. In the present study we investigated cell surface proteins involved in the interaction of cells with chondroadherin in cell adhesion and by affinity purification. Adhesion of bovine articular chondrocytes to chondroadherin-coated dishes was dependent on Mg2+ or Mn2+ but not Ca2+. Adhesion was partially inhibited by an antibody recognizing β1 integrin subunit. Chondroadherin-binding proteins from chondrocyte lysates were affinity purified on chondroadherin-Sepharose. The β1 integrin antibody immunoprecipitated two proteins with molecular mass ~110 and 140 kD (nonreduced) from the EDTA-eluted material. These results indicate that a β1 integrin on chondrocytes interacts with chondroadherin. To identify the {alpha} integrin subunit(s) involved in interaction of cells with the protein, we affinity purified chondroadherin-binding membrane proteins from human fibroblasts. Immunoprecipitation of the EDTA-eluted material from the affinity column identified {alpha}2β1 as a chondroadherin-binding integrin. These results are in agreement with cell adhesion experiments where antibodies against the integrin subunit {alpha}2 partially inhibited adhesion of human fibroblast and human chondrocytes to chondroadherin. Since {alpha}2β1 also is a receptor for collagen type II, we tested the ability of different antibodies against the {alpha}2 subunit to inhibit adhesion of T47D cells to collagen type II and chondroadherin. The results suggested that adhesion to collagen type II and chondroadherin involves similar or nearby sites on the {alpha}2β1 integrin. Although {alpha}2β1 is a receptor for both collagen type II and chondroadherin, only adhesion of cells to collagen type II was found to mediate spreading.

Please address all correspondence to Dr. Evy Lundgren-Åkerlund, Department of Cell and Molecular Biology, Section for Connective Tissue Biology, Lund University, P.O. Box 94, S-221 00 Lund, Sweden. Tel.: (46) 46-222-3311; FAX: (46) 46-211-3417.

1. Abbreviation used in this paper: CHAD, chondroadherin.

Grants were obtained from the Swedish Medical Research Council, the Medical Faculty, Lund University, Anna-Greta Crafoord's stiftelse, Crafoord's stiftelser, Gustav V's 80-års fond, Axel och Margaret Ax:son Johnson's stiftelse, Greta och Johan Kock's stiftelse, Kungliga fysiografiska sällskapets stiftelse, Riksföreningen mot reumatism, Åke Wiberg's stiftelse, Thelma Zoe'ga's ‘fond, and Alfred Österlund's stiftelse.


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