Cathepsin S Cannibalism of Cathepsin K as a Mechanism to Reduce Type I Collagen Degradation

• Published in: The Journal of biological chemistry 2012-08, Vol.287 (33), p.27723-27730
• Main Authors: Barry, Zachary T., Platt, Manu O.
• Format: Article
• Language: English
• Subjects: Cancer; Cathepsin K - chemistry; Cathepsin K - genetics; Cathepsin K - metabolism; Cathepsins - chemistry; Cathepsins - genetics; Cathepsins - metabolism; Cell Line; Collagen Type I - chemistry; Collagen Type I - genetics; Collagen Type I - metabolism; Computational Biology; Elastin - chemistry; Elastin - genetics; Elastin - metabolism; Enzyme Degradation; Enzyme Kinetics; Enzymology; Humans; Hydrolysis; Models, Chemical; Osteoporosis; Proteases; Proteolysis
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.332684

Cathepsins S and K are potent mammalian proteases secreted into the extracellular space and have been implicated in elastin and collagen degradation in diseases such as atherosclerosis and osteoporosis. Studies of individual cathepsins hydrolyzing elastin or collagen have provided insight into their binding and kinetics, but cooperative or synergistic activity between cathepsins K and S is less described. Using fluorogenic substrate assays, Western blotting, cathepsin zymography, and computational analyses, we uncovered cathepsin cannibalism, a novel mechanism by which cathepsins degrade each other as well as the substrate, with cathepsin S predominantly degrading cathepsin K. As a consequence of these proteolytic interactions, a reduction in total hydrolysis of elastin and type I collagen was measured compared with computationally predicted values derived from individual cathepsin assays. Furthermore, type I collagen was preserved from hydrolysis when a 10-fold ratio of cathepsin S cannibalized the highly collagenolytic cathepsin K, preventing its activity. Elastin was not preserved due to strong elastinolytic ability of both enzymes. Together, these results provide new insight into the combined proteolytic activities of cathepsins toward substrates and each other and present kinetic models to consider for more accurate predictions and descriptions of these systems. Background: Cathepsins K and S are powerful elastases and collagenases, but their combined activities toward each other and substrates are unclear. Results: Cathepsin S degrades cathepsin K even with elastin and collagen present. Conclusion: Cathepsin cannibalism is a novel mechanism describing protease interactions. Significance: Cannibalistic interactions reduce total substrate degradation and must be considered for accurate descriptions of proteolytic systems.