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

ilaria giusti, Sandra D'Ascenzo, Danilo Millimaggi, Giulia Taraboletti, Gaspare Carta, Nicola Franceschini, antonio pavan and vincenza dolo

Year 2008, Volume 10, Issue 5

Abstract

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 MMP-9 and MMP-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 acid pH values. Inhibition of protease activity by the cysteine protease inhibitor, E-64, and treatment of ovarian cancer cells with siRNA 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.

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