Decorin is a member of the widely expressed family of small leucine-rich proteoglycans. In addition to a primary role as a modulator of extracellular matrix protein fibrillogenesis, decorin can inhibit the cellular response to growth factors. Decorin expression is induced in endothelial cells during angiogenesis, but not when migration and proliferation are stimulated. Thus, decorin may support the formation of the fibrillar pericellular matrix that stabilizes the differentiated endothelial phenotype during the later stages of angiogenesis. Therefore, we tested whether constitutive decorin expression alone could modify endothelial cell migration and proliferation or affect pericellular matrix formation. To this end, replication-defective retroviral vectors were used to stably express bovine decorin, which was detected by Northern and Western blotting. The migration of endothelial cells that express decorin is significantly inhibited in both monolayer outgrowth and microchemotaxis chamber assays. The inhibition of cell migration by decorin was not accompanied by decreased proliferation. In addition, endothelial cells that express decorin assemble an extensive fibrillar fibronectin matrix more rapidly than control cells as assessed by immunocytochemical and fibronectin fibrillogenesis assays. These observations suggest that cell migration may be modulated by the influence of decorin on the assembly of the cell-associated extracellular matrix.Migration and proliferation of endothelial cells and the subsequent establishment of a stable monolayer are critical events in the repair of injured vessels and in angiogenesis and vasculogenesis during development, tumor growth, and tissue repair. Cell migration and proliferation are controlled by growth factors and cell adhesive interactions, which are mediated by cell surface receptors, such as integrins (1) and syndecan-4 (2, 3). Thus, control of cell migration may involve a change in cell-matrix interaction characterized by extracellular matrix remodeling and changes in signaling generated by receptors for both soluble and matrix ligands.Proteoglycans (PGs) 1 are a heterogeneous group of protein families that bear anionic glycosaminoglycan (GAG) chains covalently bound to core proteins. These molecules are prominent constituents of both the extracellular matrix and the cell surface, where they are proposed to play roles in cell adhesion, growth factor interactions, and matrix assembly (4, 5). Decorin is a member of the small leucine-rich PG family (6 -8). The association of decorin with collagen fibrils has long been recognized (9, 10), and experimental studies indicated that decorin regulates collagen fibrillogenesis (11,12). In addition, decorin may affect cell migration and proliferation both by modulation of interactions of cell surface receptors with their matrix ligands, such as fibronectin and thrombospondin (13-15), or by an influence on the availability (16, 17) and function (18, 19) of growth factors that direct these cellular processes.We have previously report...