Role of anchorin CII, a 31,000-mol-wt membrane protein, in the interaction of chondrocytes with type II collagen.

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Abstract
The isolation of a hydrophobic, type-II collagen-binding glycoprotein of MW 31,000 (31,000-MW protein) from chick chondrocyte membranes was reported. The function of this protein in anchoring pericellular type II collagen to the chondrocyte surface was inferred from its ability to bind native type-II collagen either when detergent solubilized or when inserted into liposomes. Specific antibodies were used to localize this protein, which are now called anchorin CII, to the surface of chondrocytes in both cartilage sections, and in cell culture. In immunofluorescence studies of isolated chondrocytes a dense, punctate distribution of anchorin CII was observed on the cell surface when chondrocytes were enclosed by a pericellular type II collagen matrix. Removal of the pericellular matrix with trypsin also removed anchorin CII. The membrane protein character of anchorin CII was indicated by the demonstration of antibody-induced patching and capping on the chondrocyte surface at 22.degree. and 37.degree. C, respectively. In monolayer culture, the amount of anchorin CII appeared reduced on flattened chondrocytes lacking a pericellular type II collagen matrix but was prominent upon intercellular cell processes. Fab'' fragments prepared from either anchorin CII antiserum or an antiserum directed against the entire chondrocyte membrane inhibited the attachment of chondrocytes to a type II collagen substrate. In each case, the inhibition of attachment was neutralized by preincubation of Fab'' fragments with purified anchorin CII.