MT-SP1 is a mediator of cell signaling as shown by substrate identification

Membrane type serine protease 1 (MT-SP1) is a type II transmembrane protease that is poised to serve as a mediator between the extracellular and intracellular compartments of complex multicellular organisms. Its multidomain structure includes a highly active trypsin-fold serine protease domain covalently complexed to multiple protein-protein interaction domains located on the cell surface. This unique modular architecture likely allows for optimization of both catalytic activity and substrate specificity in an independent manner. MT-SPl is upregulated in many epithelial cancers and cleaves several cancer-associated proteins such as the urokinase type plasminogen activator (uPA) and the hepatocyte growth factor (HGF). As MT-SP1 has no homologs in model eukaryotic organisms, the effort to physiologically characterize the enzyme relies heavily on a biochemical, as opposed to a genetic approach.; In order to gain an understanding of the biological function of MT-SP1 interacting proteins and downstream targets of proteolysis were identified using biochemical, cell biological, and genomic profiling approaches. Transcriptional coexpression identified the urokinase type plasminogen activator receptor (uPAR) as a potential binding partner of MT-SP1. Immunoprecipitation and inhibitor studies lead to the identification of a new cancer-associated, MT-SP1 substrate involved in adhesion signaling, Trask. Using a combination of the aforementioned transcriptional coexpression strategy and biochemical specificity profiling of the catalytic domain of MT-SP1, both the macrophage stimulating protein 1 (MSP-1) and the vascular endothelial growth factor receptor 2 (VEGFR-2) were identified as downstream components of the MT-SP1 signaling pathway.