Cyr61, also known as CCN1,is a 40-45 kDa matricellular glycoprotein that plays an important role in cellular adhesion and migration. Cyr61 consists of an IGFBP domain, a VWF type C domain, a TSP type I domain, and a cysteine knot domain. Mature human Cyr61 shares 93% amino acid sequence identity with mouse and rat Cyr61. It is widely expressed during development and in adult tissues (2, 3). Cyr61 associates with the extracellular matrix (ECM) and with many cell surface molecules including Integrins alpha V beta 3, alpha V beta 5, alpha M beta 2, and alpha 6 beta 1, Syndecan-4, and heparan sulfate proteoglycans. Cyr61 mediates the adhesion and migration of multiple cell types and also promotes vascular endothelial cell tubule formation. Plasmin cleavage of ECM-bound Cyr61 releases a 28 kDa N-terminal fragment which retains the ability to promote endothelial cell migration. Cyr61 exhibits both tumorigenic and tumor suppressor properties.