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Open Access Research article

Inhibition of cathepsin B activity attenuates extracellular matrix degradation and inflammatory breast cancer invasion

Bernadette C Victor1, Arulselvi Anbalagan1, Mona M Mohamed2, Bonnie F Sloane13 and Dora Cavallo-Medved14*

Author Affiliations

1 Department of Pharmacology and Wayne State University, Detroit, Michigan 48201, USA

2 Department of Zoology, Faculty of Science, Cairo University, Giza, 12613 Egypt

3 Barbara Ann Karmanos Cancer Institute, Wayne State University, Detroit, Michigan 48201, USA

4 Department of Biological Sciences, University of Windsor, ON, N9B 3P4 Canada

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Breast Cancer Research 2011, 13:R115  doi:10.1186/bcr3058

Published: 17 November 2011

Abstract

Introduction

Inflammatory breast cancer (IBC) is an aggressive, metastatic and highly angiogenic form of locally advanced breast cancer with a relatively poor three-year survival rate. Breast cancer invasion has been linked to proteolytic activity at the tumor cell surface. Here we explored a role for active cathepsin B on the cell surface in the invasiveness of IBC.

Methods

We examined expression of the cysteine protease cathepsin B and the serine protease urokinase plasminogen activator (uPA), its receptor uPAR and caveolin-1 in two IBC cell lines: SUM149 and SUM190. We utilized a live cell proteolysis assay to localize in real time the degradation of type IV collagen by IBC cells. IBC patient biopsies were examined for expression of cathepsin B and caveolin-1.

Results

Both cell lines expressed comparable levels of cathepsin B and uPA. In contrast, levels of caveolin-1 and uPAR were greater in SUM149 cells. We observed that uPA, uPAR and enzymatically active cathepsin B were colocalized in caveolae fractions isolated from SUM149 cells. Using a live-cell proteolysis assay, we demonstrated that both IBC cell lines degrade type IV collagen. The SUM149 cells exhibit predominantly pericellular proteolysis, consistent with localization of proteolytic pathway constitutents to caveolar membrane microdomains. A functional role for cathepsin B was confirmed by the ability of CA074, a cell impermeable and highly selective cathepsin B inhibitor, to significantly reduce pericellular proteolysis and invasion by SUM149 cells. A statistically significant co-expression of cathepsin B and caveolin-1 was found in IBC patient biopsies, thus validating our in vitro data.

Conclusion

Our study is the first to show that the proteolytic activity of cathepsin B and its co-expression with caveolin-1 contributes to the aggressiveness of IBC.