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

FASEB J. 2012 Dec;26(12):5172-81. doi: 10.1096/fj.12-205229. Epub 2012 Aug 16.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Cathepsin D / genetics
  • Cathepsin D / metabolism*
  • Cells, Cultured
  • Cystatin C / genetics
  • Cystatin C / metabolism*
  • Embryo, Mammalian / cytology
  • Enzyme Precursors / genetics
  • Enzyme Precursors / metabolism
  • Extracellular Space / metabolism
  • Female
  • Fibroblasts / cytology
  • Fibroblasts / metabolism*
  • Humans
  • Hydrogen-Ion Concentration
  • Immunoblotting
  • MCF-7 Cells
  • Mice
  • Mice, Knockout
  • Models, Biological
  • Molecular Sequence Data
  • Protein Binding
  • Proteolysis
  • RNA Interference
  • Tumor Microenvironment*
  • Two-Hybrid System Techniques

Substances

  • Cystatin C
  • Enzyme Precursors
  • procathepsin D
  • Cathepsin D