Definition: A family of secreted proteins found associated with the EXTRACELLULAR MATRIX and cell surface receptors. They are believed to play a role in modulating the effects of a variety of GROWTH FACTORS and PROTEASES at the cell membrane extracellular matrix. The CCN protein family is named after three protypical members; CYSTEINE-RICH PROTEIN 61; CONNECTIVE TISSUE GROWTH FACTOR; and NEPHROBLASTOMA OVEREXPRESSED PROTEIN.