Matrix-matrix interaction of cartilage oligomeric matrix protein and fibronectin.

Recent work indicates that cartilage oligomeric matrix protein (COMP) plays an important role in extracellular matrix assembly and matrix-matrix protein interactions. In order to identify the proteins in extracellular matrix that interact with COMP, we used an ELISA-based solid-phase binding assay, which revealed a specific, high-affinity interaction between COMP and fibronectin. This interaction is concentration-dependent and saturable, and appears to occur under physiologically relevant conditions. Electron microscopy after negative staining and fragment binding analysis using the solid-phase assay revealed a predominant binding site for the COMP C-terminal globular domain to a molecular domain approximately 14 nm from the N-terminal domain of fibronectin, which can be inhibited by the presence of a polyclonal antibody specific for the C-terminal heptadecapeptide of COMP. This interaction is further demonstrated in vivo by colocalization of both COMP and fibronectin in the chondrocyte pericellular matrix by laser confocal microscopy of chondrocytes grown in agarose culture, and by appositional and colocalization of these proteins in the growth plate of primates by immunohistochemistry.