Pro-collagenase-1 (matrix metalloproteinase-1) binds the α2β1 integrin upon release from keratinocytes migrating on type I collagen

In injured skin, collagenase-1 (matrix metalloproteinase-1 (MMP-1)) is induced in migrating keratinocytes. This site-specific expression is regulated by binding of the alpha (2)beta (1) integrin with dermal type I collagen, and the catalytic activity of MMP-1 is required for keratinocyte migration. Because of this functional association among substrate/ligand, receptor, and proteinase, we assessed whether the integrin also directs the compartmentalization of MMP-1 to its matrix target. Indeed, pro-MMP-1 co-localized to sites of alpha (2)beta (1) contacts in migrating keratinocytes. Furthermore, pro-MMP-1 co-immunoprecipitated with alpha (2)beta (1) from keratinocytes, and alpha (2)beta (1) co-immunoprecipitated with pro-MMP-1. No other MMPs bound alpha (2)beta (1) and no other integrins interacted with MMP-1. Pro-MMP-1 also provided a substrate for alpha (2)beta (1)-dependent adhesion of platelets. Complex formation on keratinocytes was most efficient on native type I collagen and reduced or ablated on denatured or cleaved collagen. Competition studies suggested that the alpha (2) I domain interacts with the linker and hemopexin domains of pro-MMP-1, not with the pro-domain. These data indicate that the interaction of pro-MMP-1 with alpha (2)beta (1) confines this proteinase to points of cell contact with collagen and that the ternary complex of integrin, enzyme, and substrate function together to drive and regulate keratinocyte migration.