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Cancer progression is often accompanied by increased levels of extracellular proteases capable of remodeling the extracellular matrix and promoting pro-cancerous signaling pathways by activating growth factors and receptors. The type II transmembrane serine protease (TTSP) family encompasses several proteases that play critical roles in cancer progression; however, the expression or function of the TTSP TMPRSS13 in carcinogenesis has not been examined. In the present study, we found TMPRSS13 to be differentially expressed at both the transcript and protein levels in human colorectal cancer (CRC). Immunohistochemical analyses revealed consistent high expression of TMPRSS13 protein on the cancer cell surface in CRC patient samples; in contrast, the majority of normal colon samples displayed no detectable expression. On a functional level, TMPRSS13 silencing in CRC cell lines increased apoptosis and impaired invasive potential. Importantly, transgenic overexpression of TMPRSS13 in CRC cell lines increased tolerance to apoptosis-inducing agents, including paclitaxel and HA14-1. Conversely, TMPRSS13 silencing rendered CRC cells more sensitive to these agents. Together, our findings suggest that TMPRSS13 plays an important role in CRC cell survival and in promoting resistance to drug-induced apoptosis; we also identify TMPRSS13 as a potential new target for monotherapy or combination therapy with established chemotherapeutics to improve treatment outcomes in CRC patients.

TMPRSS13 is a member of the type II transmembrane serine protease (TTSP) family. Here we characterize a novel post-translational mechanism important for TMPRSS13 function: proteolytic cleavage within the extracellular TMPRSS13 stem region located between the transmembrane domain and the first site of N-linked glycosylation at asparagine (N)-250 in the scavenger receptor cysteine rich (SRCR) domain. Importantly, the catalytic competence of TMPRSS13 is essential for stem region cleavage, suggesting an autonomous mechanism of action. Site-directed mutagenesis of the 10 basic amino acids (four arginine and six lysine residues) in this region abrogated zymogen activation and catalytic activity of TMPRSS13, as well as phosphorylation, cell surface expression, and shedding. Mutation analysis of individual arginine residues identified R223, a residue located between the low-density lipoprotein receptor class A domain and the SRCR domain, as important for stem region cleavage. Mutation of R223 causes a reduction in the aforementioned functional processing steps of TMPRSS13. These data provide further insight into the roles of different post-translational modifications as regulators of the function and localization of TMPRSS13. Additionally, the data suggest the presence of complex interconnected regulatory mechanisms that may serve to ensure the proper levels of cell-surface and pericellular TMPRSS13-mediated proteolysis under homeostatic conditions.