CYR61 Stimulates Human Skin Fibroblast Migration through Integrin αvβ5 and Enhances Mitogenesis through Integrin αvβ3, Independent of Its Carboxyl-terminal Domain

Abstract CYR61, an angiogenic factor and a member of the CCN protein family, is an extracellular matrix-associated, heparin-binding protein that mediates cell adhesion, promotes cell migration, and enhances growth factor-stimulated cell proliferation. CYR61 induces angiogenesis and promotes tumor growth in vivo and is expressed in dermal fibroblasts during cutaneous wound healing. It has been demonstrated recently that adhesion of primary skin fibroblasts to CYR61 is mediated through integrin α6β1 and cell surface heparan sulfate proteoglycans, resulting in adhesive signaling and up-regulation of matrix metalloproteinases 1 and 3. CYR61 is composed of four discrete structural domains that bear sequence similarities to the insulin-like growth factor-binding proteins, von Willebrand factor type C repeat, thrombospondin type 1 repeat, and a carboxyl-terminal (CT) domain that resembles cysteine knots found in some growth factors. In this study, we show that a CYR61 mutant (CYR61ΔCT) that has the CT domain deleted is unable to support adhesion of primary human skin fibroblasts but is still able to stimulate chemotaxis and enhance basic fibroblast growth factor-induced mitogenesis similar to wild type. In addition, fibroblast migration to CYR61 is mediated through integrin αvβ5 but not integrins α6β1 or αvβ3. Furthermore, we show that CYR61 binds directly to purified integrin αvβ5 in vitro. By contrast, CYR61 enhancement of basic fibroblast growth factor-induced DNA synthesis is mediated through integrin αvβ3, a known receptor for CYR61 that mediates CYR61-dependent cell adhesion and chemotaxis in vascular endothelial cells. Thus, CYR61 promotes primary human fibroblast adhesion, migration, and mitogenesis through integrins α6β1, αvβ5, and αvβ3, respectively. Together, these findings establish CYR61 as a novel ligand for integrin αvβ5 and show that CYR61 interacts with distinct integrins to mediate disparate activities in a cell type-specific manner.