Human matriptase, encoded by the ST14 (suppression of tumorogenicity 14) gene, is also known as tumor associated differentially expressed gene 15 protein/TADG‑15), epithin, and membrane-type serine protease 1/MT-SP1 (1). Predicted to have a significant role in tumor biology, matriptase may be a novel target for anti-cancer therapy (2). However, expressed in most human epithelia, matriptase is also important in several physiological processes (1). For example, it activates prostasin to initiate a protease cascade that is essential for epidermal differentiation (3), and it converts a single-chain IGFBP-rp1 into the two-chain form (4).
Matriptase is a type II transmembrane serine protease with a complex modular structure (1). The 855 amino acid (aa) sequence of human matriptase consists of a cytoplasmic tail (aa 1-55), a transmembrane domain (aa 56-76), and an extracellular portion (aa 77-855). The latter contains the following domains: SEA (aa 86-201), two CUBs (aa 214-334 and 340-447), four LDLRAs (aa 452-486, 487-523, 524-560, and 566-603), and a serine protease (aa 615-855). The physiological activation of the single-chain zymogen requires the cleavage at the SEA domain within the ER or Golgi, association with HAI-1, which facilitates the transport of the protease to the cell surface, and auto-cleavage at QAR-V(615)VGG (1). The activated matriptase is inhibited by HAI-1, and the resulting HAI-1 complex can be shed from the cell surface (1). R&D Systems rhST14 corresponds to the catalytic domain, and is inhibited effectively by rhHAI-1 and rhHAI-2A (R&D Systems, Catalog # 1048-PI and 1106-PI).
