CHARACTERIZATION OF CARTILAGE OLIGOMERIC MATRIX PROTEIN (COMP) IN HUMAN NORMAL AND PSEUDOACHONDROPLASIA MUSCULOSKELETAL TISSUES

Cartilage oligomeric matrix protein (COMP), the fifth member of the -t hrombospondin gene family, is an extracellular matrix calcium-binding protein. The importance of COMP is underscored by the finding that mut ations in COMP cause the human dwarfing condition, pseudoachondroplasi a (PSACH). Here, we report the results of human tissue distribution an d cell secretion studies of human COMP. COMP is expressed and secreted by cultured monolayer chondrocyte, tendon and ligament cells, and COM P secretion is not restricted to a differentiated chondrocyte phenotyp e. Whereas COMP is retained in the endoplasmic reticulum that accumula tes within PSACH chondrocytes in vivo, COMP is not retained intracellu larly in the dedifferentiated PSACH chondrocytes in cultures. These re sults lend further support to the hypothesis that retention of COMP is related to the terminal PSACH chondrocyte phenotype, processing of pr oteins related to extracellular matrix formation, and maintenance in c artilage.