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Osteopontin overexpression in breast cancer: Knowledge gained and possible implications for clinical management

Authors

  • Alan B. Tuck,

    Corresponding author
    1. London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada
    2. Department of Pathology, University of Western Ontario, London, Ontario, Canada
    3. Department of Oncology, University of Western Ontario, London, Ontario, Canada
    • Department of Pathology, London Health Sciences Centre, University Campus, P.O. Box 5339, STN. B, London, Ont., Canada N6A 5A5.
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  • Ann F. Chambers,

    1. London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada
    2. Department of Pathology, University of Western Ontario, London, Ontario, Canada
    3. Department of Oncology, University of Western Ontario, London, Ontario, Canada
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  • Alison L. Allan

    1. London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada
    2. Department of Oncology, University of Western Ontario, London, Ontario, Canada
    3. Department of Anatomy & Cell Biology, University of Western Ontario, London, Ontario, Canada
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Abstract

Osteopontin (OPN) is a secreted protein that is overexpressed in a number of human cancers, and has been associated with increased metastatic burden and poor prognosis in breast cancer patients. The OPN protein contains several conserved structural elements including heparin- and calcium-binding domains, a thrombin-cleavage site, a CD44 binding site, and two integrin-binding sites. Experimental studies have shown that the ability of OPN to interact with a diverse range of factors, including cell surface receptors (integrins, CD44), secreted proteases (matrix metalloproteinases, urokinase plasminogen activator), and growth factor/receptor pathways (TGFα/EGFR, HGF/Met) is central to its role in malignancy. These complex signaling interactions can result in changes in gene expression, which ultimately lead to alterations in cell properties involved in malignancy such as adhesion, migration, invasion, enhanced tumor cell survival, tumor angiogenesis, and metastasis. Therefore, OPN is not merely associated with cancer, but rather it plays a multi-faceted functional role via complex molecular cross-talk with other factors. This review will focus on the role of OPN in breast cancer, in particular on the malignancy-promoting aspects of OPN that may reveal opportunities for new approaches to the clinical management of breast cancer. J. Cell. Biochem. 102: 859–868, 2007. © 2007 Wiley-Liss, Inc.

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