Kallikrein-related peptidase 14 activates zymogens of membrane type matrix metalloproteinases (MT-MMPs) - a CleavEx library-based analysis

Kallikrein-related peptidases (KLKs) and matrix metalloproteinases (MMPs) are secretory proteinases known to proteolytically process components of the extracellular matrix (ECM), thus modulating the pericellular environment in physiology and excessively in pathologies like cancer. However, the interconnection between these groups of proteases remains elusive. To test this hypothesis, we have developed a peptide library-based exposition system (Cleavage of exposed amino acid sequences, CleavEx) aiming at investigating the potential of KLK14 to recognize and hydrolyze proMMP sequences specifically. Initial assessment of the library identified a total of ten MMP activation domain sequences which were validated by Edman degradation. The CleavEx analysis revealed that membrane-type (MT) MMPs are likely targeted by KLK14 for activation. Correspondingly, commercially available proMT-MMPs, namely proMMP14-17 were investigated in vitro and found to be effectively processed by KLK14. Again, the expected neo-N-termini of the activated MT MMPs were yielded and confirmed by Edman degradation. In addition, the productivity of proMMP activation was analyzed by gelatin zymography, which indicated the release of fully active, mature MT-MMPs upon KLK14 treatment. Lastly, MMP14 was shown to be processed on the cell surface by KLK14 using murine fibroblasts stably overexpressing human MMP14. Herein, we propose KLK14-mediated selective activation of cell-membrane located MT-MMPs as an additional layer of their regulation within the ECM. As both, KLKs and MT-MMPs are implicated in cancer, the activation described herein may constitute an important factor in tumor progression and metastasis.