Structural Analysis of the α2 Integrin I Domain/Procollagenase-1 (Matrix Metalloproteinase-1) Interaction

Outside-in signals delivered by matrix metalloproteinase-1 regulate platelet function

Matrix metalloproteinases (MMPs) are proteolytic enzymes that degrade extracellular matrix proteins. These enzymes are implicated in a variety of physiological and pathological events characterized by extracellular matrix remodeling. Recent studies suggest that MMPs may have a signaling capacity, but direct evidence supporting this concept is lacking. In the present study, we demonstrate that outside-in signals delivered by exogenous MMP-1 (interstitial collagenase) markedly increase the number of tyrosine-phosphorylated proteins in platelets. Active MMP-1 also targets beta(3) integrins to areas of cell contact and primes platelets for aggregation. Examination of the endogenous enzyme demonstrated that activated platelets process latent MMP-1 into its active form. Neutralization of MMP-1 activity with MMP inhibitors or specific blocking antibodies markedly attenuates agonist-induced phosphorylation of intracellular proteins, movement of beta(3) integrins to cell contact points, and intercellular aggregation. The finding that MMP-1 is rapidly activated in platelets and controls functional responses identifies a new role for this metalloproteinase as a signaling molecule that regulates thrombotic events.

Matrix metalloproteinases and angiogenesis

Angiogenesis is a prominent feature of numerous diseases, including cancer and arthritis, and appears to play an important role in kidney disease and hypertension. The matrix metalloproteinases, especially matrix metalloproteinase-2, play a vital role during angiogenesis by degrading the surrounding extracellular matrix and allowing endothelial cell invasion. Membrane type 1 matrix metalloproteinase directly degrades matrix components as well as activating matrix metalloproteinase-2 on the cell surface. The integrin receptors, particularly alpha(v)beta(3), can recruit and possibly activate matrix metalloproteinases to localized microdomains on the cell membrane. This restricts matrix metalloproteinase activity to the pericellular region, preventing excessive matrix degradation which would otherwise impede endothelial invasion. Inhibitors of matrix metalloproteinase activity may actually promote cell invasion by preventing uncontrolled matrix degradation. In addition to degrading the matrix, matrix metalloproteinases produce protein fragments that impede their angiogenic action. These multiple regulatory pathways permit fine control over cell invasion during angiogenesis and provide new, precise strategies for targeting abnormal angiogenesis, through control of matrix metalloproteinase activity.

Processing of integrin alpha(v) subunit by membrane type 1 matrix metalloproteinase stimulates migration of breast carcinoma cells on vitronectin and enhances tyrosine phosphorylation of focal adhesion kinase

Recently, we have shown that membrane type 1 matrix metalloproteinase (MT1-MMP) exhibits integrin convertase activity. Similar to furin-like proprotein convertases, MT1-MMP directly processes a single chain precursor of alpha(v) integrin subunit (pro-alpha(v)) into the heavy and light alpha-chains connected by a disulfide bridge. To evaluate functionality of MT1-MMP-processed integrins, we examined breast carcinoma MCF7 cells co-expressing alpha(v)beta(3) integrin with either the wild type or mutant MT1-MMP in a variety of migration and adhesion tests. Specific inhibitors of proprotein convertases and MMP were employed in our cell system to attenuate the individual pathways of pro-alpha(v) maturation. We present evidence that MT1-MMP cleavage of pro-alpha(v) in the cells did not affect RGD-ligand binding of the resulting alpha(v)beta(3) integrin but enhanced outside-in signal transduction through a focal adhesion kinase pathway. Enhanced tyrosine phosphorylation of focal adhesion kinase in cells co-expressing MT1-MMP and alpha(v)beta(3) integrin contributed to efficient adhesion and, especially, migration of cells on vitronectin, a ligand of alpha(v)beta(3) integrin. These mechanisms underscore the significance of a coordinated interplay between MT1-MMP and alpha(v)beta(3) integrin in tumor cells and identify downstream signaling pathways resulting from their interactions. Regulation of integrin maturation and functionality may be an important role of MT1-MMP in tumor cells.

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.