Cathepsin B mediates the pH-dependent proinvasive activity of tumor-shed microvesicles

Neoplasia. 2008 May;10(5):481-8. doi: 10.1593/neo.08178.


Vesicles shed by cancer cells are known to mediate several tumor-host interactions. Tumor microenvironment may, in turn, influence the release and the activity of tumor-shed microvesicles. In this study, we investigated the molecular mediators of the pH-dependent proinvasive activity of tumor-shed vesicles. Gelatinase zymography showed increased microvesicle activity of matrix metalloproteinases 9 and 2 as a result of acid exposure (pH 5.6) compared to pH 7.4. Thus, we reasoned that the cysteine protease cathepsin B might play a role in mediating the pH-dependent activation of gelatinases. Cathepsin B expression in tumor-shed microvesicles was confirmed by Western blot analysis and zymography. The activity of vesicle-associated cathepsin B measured using Z-Arg-Arg-pNA as substrate was significantly increased at acidic pH values. Inhibition of protease activity by the cysteine protease inhibitor, E-64, and treatment of ovarian cancer cells with small interfering RNA against cathepsin B suppressed the ability of tumor-shed microvesicles to stimulate both gelatinase activation and the invasiveness of endothelial cells observed at low pH values. We conclude that microvesicle shedding is a major secretory pathway for cathepsin B release from tumor cells. Hence, the acidic microenvironment found in most solid tumors may contribute to cathepsin B-mediated proinvasive capabilities of tumor-shed vesicles.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cathepsin B / genetics
  • Cathepsin B / metabolism*
  • Cell Line, Tumor
  • Cell Movement
  • Culture Media, Conditioned / pharmacology
  • Enzyme Activation
  • Female
  • Humans
  • Hydrogen-Ion Concentration
  • Matrix Metalloproteinase 2 / metabolism
  • Matrix Metalloproteinase 9 / metabolism
  • Membrane Microdomains / metabolism*
  • Membrane Microdomains / pathology*
  • Neoplasm Invasiveness
  • Ovarian Neoplasms / enzymology*
  • Ovarian Neoplasms / genetics
  • Ovarian Neoplasms / pathology
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA, Small Interfering / pharmacology
  • Reverse Transcriptase Polymerase Chain Reaction


  • Culture Media, Conditioned
  • RNA, Messenger
  • RNA, Small Interfering
  • Cathepsin B
  • Matrix Metalloproteinase 2
  • Matrix Metalloproteinase 9