Membrane type-1 matrix metalloproteinase (MT1-MMP) degrades the extracellular matrix, initiates the activation pathway of soluble MMPs and regulates the functionality

MT1-MMP is a prototypic member of a membrane-anchored MMP subfamily (Egeblad and Werb, 2002; Holmbeck et al., 2004). This subfamily consists of the six individual enzymes that share a significant peptide sequence homology. MT1-MMP is associated with the cell membrane by a transmembrane domain followed by a cytoplasmic tail (Hernandez-Barrantes et al., 2002) and is synthesized as a latent zymogen that requires N-terminal proteolytic processing to generate a proteolytically potent, mature, membrane-tethered enzyme. Once activated, MT1-MMP can be inhibited by tissue inhibitors of metalloproteinases-2, -3 and -4 (TIMP-2, -3 and -4) but not by TIMP-1 (Baker et al., 2002). A potent and multifunctional proteinase, MT1-MMP functions in cancer cells as the main mediator of proteolytic events on the cell surface. MT1-MMP degrades a broad spectrum of the extracellular matrix (ECM) substrata including fibronectin, vitronectin, proteoglycan, collagen and laminin (d’Ortho et al., 1997; Ohuchi et al., 1997; Osenkowski et al., 2004), initiates the activation cascade of soluble MMPs (Cowell et al., 1998; Knauper et al., 1996; Sato et al., 1994; Toth et al., 2003), and is directly involved in the cleavage of cell surface receptors including tissue transglutaminase (Belkin et al., 2001), CD44 (Mori et al., 2002), prov integrin (Deryugina et al., 2002a), syndecan-1 (Endo et al., 2003), low-density lipoprotein receptor-related protein (Rozanov et al., 2004b) and -glycan (Velasco-Loyden et al., 2004). The MT1-MMP-mediated pericellular proteolytic events modulate cell attachment and motility, and allow cell functioning to adjust to the continuously changing tissue microenvironment (Katayama et al., 2004; Seiki, 2003; Zucker et al., 2003). Consistent with its role in the migration and invasion of malignant cells, MT1MMP is frequently overexpressed in aggressive, metastatic neoplasms (Katayama et al., 2004; Seiki, 2003). Recently, we have demonstrated that MT1-MMP either naturally expressed by the cells or the overexpressed recombinant constructs were trafficked to the pericentrosomal compartment and, as a result, accumulated in the centrosomes (Golubkov et al., 2005). To demonstrate that the microtubular trafficking of MT1-MMP to the pericentrosomal compartment is a general cellular phenomenon, we extended these studies by performing an examination of the trafficking and internalization pathways of MT1-MMP in several cell types. Accordingly, this work was intended to confirm and reinforce the evidence presented in our earlier publication (Golubkov et al., 2005). Here, we report that MT1-MMP employs the 4975