Membrane type 1 matrix metalloproteinase (MT1-MMP) is a transmembrane MMP that plays important roles in migratory processes underlying tumor invasion and angiogenesis. In addition to its matrix degrading activity, MT1-MMP also contains a short cytoplasmic domain whose involvement in cell locomotion seems important but remains poorly understood. In this study, we show that MT1-MMP is phosphorylated on the unique tyrosine residue located within this cytoplasmic sequence (Tyr The degradation of extracellular matrix (ECM)3 proteins by members of the matrix metalloproteinases (MMPs) plays a crucial role in several biological processes, including cell attachment, cell migration, invasiveness, cell proliferation, apoptosis, and angiogenesis (1-4). Among the various MMPs described to date, there is now considerable evidence that MMPs that are intrinsically associated with the plasma membrane because of the presence of a transmembrane domain within their sequence, the so-called membrane type MMPs, represent key components involved in pericellular proteolysis and subsequent cell locomotion and invasion (5, 6). The prototypical member of this family, MT1-MMP, actively participates in the remodeling of the pericellular ECM by acting as a cellular receptor and activator of proMMP-2 (7) and as a potent matrixdegrading protease that proteolyses a broad spectrum of ECM proteins (8 -10) as well as a number of cell surface-associated adhesion receptors (11,12). These events are likely to be important in vivo because MT1-MMP null mice fail to thrive and have a markedly reduced lifespan (13,14).In addition to its role in normal physiology, MT1-MMP is also overexpressed in many types of tumors (15, 16), and this overexpression appears crucial for tumor cell migration and invasion. For example, MT1-MMP-mediated degradation of some ECM proteins, such as the laminin-5␥2 chain (17), stimulates migration, whereas proteolysis of the dense, cross-linked meshwork of type I collagen fibrils by the enzyme confers neoplastic cells with tissueinvasive activity (18) and sustains tumor cell growth in otherwise growth-restrictive three-dimensional matrices (19).Despite its importance to normal physiology and in the development of malignancy, the mechanisms underlying MT1-MMP-mediated cell invasion remain incompletely understood. During cell migration, MT1-MMP localizes predominantly to the cell adherent edge at the migration front, an appropriate location for the degradation of the ECM barrier (20). In addition, we and others have shown that MT1-MMP is preferentially localized into caveolae, specialized domains of the plasma membrane (21,22), and this localization may contribute to the spatiotemporal regulation of its proteolytic activity by controlling adequate endocytosis and recycling of the enzyme (23,24).In addition to the importance of MT1-MMP-mediated proteolytic breakdown of ECM proteins for the induction of cell migration, recent studies suggested that the cytoplasmic domain of the enzyme may also play a role in this process. For example...

Pericellular proteolysis of the extracellular matrix by membrane type 1-matrix metalloproteinase (MT1-MMP) confers tumor cells with the ability to proliferate within three-dimensional (3D) matrices and sustains tumor growth in mice. In this study, we show that in addition to its matrix-degrading activity, phosphorylation of MT1-MMP on its unique tyrosine residue located within its cytoplasmic sequence (Tyr573) may also participate to these processes. Fibrosarcoma cells expressing a proteolytically active but non-phosphorylable mutant of MT1-MMP showed a markedly reduced proliferation rate when embedded within 3D type I collagen matrices, this antiproliferative effect being correlated with arrest in the G(0)/G(1) phase of the cell cycle. Impaired tyrosine phosphorylation of MT1-MMP also inhibits anchorage-independent growth of HT-1080 cells in soft agar as well as their invasion of collagen barriers, two prominent attributes of tumor cells, suggesting a broad inhibitory effect of the MT1-MMP mutant on tumorigenesis. Accordingly, whereas HT-1080 cells formed well-vascularized tumors containing tyrosine-phosphorylated MT1-MMP, tumor growth was completely abolished by expression of the non-phosphorylable MT1-MMP mutant. These findings thus indicate a close co-operation between the matrix-degrading activity of MT1-MMP and tyrosine phosphorylation of its intracellular domain for tumor cell invasion and proliferation and suggest that the targeting of the intracellular signaling pathways leading to tyrosine phosphorylation of MT1-MMP may represent an unexpected alternative strategy for the inhibition of this enzyme.

Membrane-type 1 matrix metalloproteinase (MT1-MMP) plays an important role in sphingosine-1-phosphate(S1P)-dependent migration of endothelial cells but the underlying mechanisms remain largely unknown. Herein, we show that S1P promotes the relocalization of MT1-MMP to peripheral actin-rich membrane ruffles that is coincident with its association with the adaptor protein p130Cas at the leading edge of migrating cells. Immunoprecipitation and confocal microscopy analyses suggest that this interaction required the tyrosine phosphorylation of p130Cas and also involves S1P-dependent phosphorylation of MT1-MMP within its cytoplasmic sequence. The interaction of MT1-MMP with p130Cas at the cell periphery suggests the existence of a close interplay between pericellular proteolysis and signaling pathways involved in EC migration.