Proteolysis of cystatin C by cathepsin D in the breast cancer microenvironment

Abstract

The aspartic protease cathepsin D, a poor prognostic indicator of breast cancer, is abundantly secreted as procathepsin D by human breast cancer cells and self‐activates at low pH in vitro , giving rise to catalytically active cathepsin D. Due to a lower extracellular pH in tumor microenvironments compared to normal tissues, cathepsin D may cleave pathophysiological substrates contributing to cancer progression. Here, we show by yeast 2‐hybrid and degradomics analyses that cystatin C, the most potent natural secreted inhibitor of cysteine cathepsins, both binds to and is a substrate of extracellular procathepsin D. The amount of cystatin C in the extracellular environment is reduced in the secretome of mouse embryonic fibroblasts stably transfected with human cathepsin D. Cathepsin D extensively cleaved cystatin C in vitro at low pH. Cathepsin D secreted by breast cancer cells also processed cystatin C at the pericellular pH of tumors and so enhancing extracellular proteolytic activity of cysteine cathepsins. Thus, tumor derived cathepsin D assists breast cancer progression by reducing cystatin C activity, which, in turn, enhances cysteine cathepsin proteolytic activity, revealing a new link between protease classes in the protease web.—Laurent‐Matha, V., Huesgen, P. F., Masson, O., Derocq, D., Prébois, C., Gary‐Bobo, M., Lecaille, F., Rebière, B., Meurice, G., Oréar, C., Hollingsworth, R. E., Abrahamson, M., Lalmanach, G., Overall, C. M., Liaudet‐Coopman, E. Proteolysis of cystatin C by cathepsin D in the breast cancer microenvironment. FASEB J. 26, 5172–5181 (2012). www.fasebj.org