Identifying the Role of the Type-II Transmembrane Serine Protease TMPRSS13 in Breast Cancer

摘要

Breast cancer is the most frequently diagnosed cancer and the second leading cause of cancer death in women in the United States. Breast cancer progression is accompanied by increased expression of extracellular and cell surface proteases that are capable of degrading the extracellular matrix as well as cleaving and activating downstream targets. These proteolytic processes are critically involved in modifying the tissue microenvironment of the breast, which is necessary for cancer cell invasion and eventual dissemination of cancer cells to other organs. Therefore, identifying novel proteases that promote tumor progression is critical to create new approaches for developing improved breast cancer therapeutics. Systematic in silico data analysis followed by experimental validation identified increased expression of the type-II transmembrane serine protease (TTSP) family member, TMPRSS13 (transmembrane protease, serine 13), in invasive ductal carcinoma (IDC) patient tissue samples compared to normal breast tissue. Immunohistochemical analysis revealed that the expression of TMPRSS13 is strictly confined to the malignant epithelial cells and not the surrounding tumor stroma. Currently, no studies have examined the role of TMPRSS13 in any cancer type. Additionally, the basic biochemical properties (i.e. activation, localization, and post translational modifications) have not yet been explored. Therefore to understand the potential role of TMPRSS13 in breast cancer, biochemical studies as well as thorough and comprehensive in vivo "loss-of-function" studies complemented by human cell culture models were performed. Biochemical characterization of TMPRSS13 show that TMPRSS13 is a glycosylated, active protease and that its own proteolytic activity mediates zymogen cleavage. Full-length, active TMPRSS13 exhibits impaired cell-surface expression in the absence of the cognate Kunitz-type serine protease inhibitors, hepatocyte growth factor activator inhibitor (HAI)-1 or HAI-2. Concomitant presence of TMPRSS13 with either HAI-1 or -2 mediates phosphorylation of residues in the intracellular domain of the protease, and it coincides with efficient transport of the protease to the cell surface and its subsequent shedding. Cell-surface labeling experiments indicate that the dominant form of TMPRSS13 on the cell surface is phosphorylated, whereas intracellular TMPRSS13 is predominantly non-phosphorylated.;Additionally, results from the breast cancer study indicates that genetic deletion of TMPRSS13 results in a significant decrease in overall tumor burden, growth rate, and a delayed detection of palpable mammary tumors (tumor latency), thereby indicating that TMPRSS13 plays a promotional role in breast cancer progression. Complementary studies using human cell culture models revealed that silencing TMPRSS13 expression decreases proliferation and induces apoptosis. Furthermore, silencing of TMPRSS13 in the invasive human breast cancer cell line BT20 attenuates its invasive potential. These studies are important to our understanding of novel proteolytic events that occur within the tumor microenvironment, and in determining whether TMPRSS13 may translate into a novel therapeutic target.