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Circulating Galectin-3 Promotes Metastasis by Modifying MUC1 Localization on Cancer Cell Surface

¹ Gastroenterology Research Unit, School of Clinical Sciences, University of Liverpool, Liverpool, United Kingdom; ² Department of Pharmacology, School of Pharmacy, Shandong University, Shandong, China; ³ Division of Medical Sciences, School of Medicine, University of Birmingham, Birmingham, United Kingdom; and ⁴ Division of Molecular Genetics, the Netherlands Cancer Institute, Amsterdam, the Netherlands

Requests for reprints: Lu-Gang Yu, The Henry Wellcome Laboratory, School of Clinical Sciences, University of Liverpool, Liverpool L69 3GE, United Kingdom. Phone: 44-151-794-6820; Fax: 44-151-794-6825; E-mail: lgyu{at}liv.ac.uk.

Key Words: circulating galectin-3 • MUC1 • cell adhesion • metastasis • glycosylation

Adhesion of circulating tumor cells to the blood vessel endothelium is a critical step in cancer metastasis. We show in this study that galectin-3, the concentration of which is greatly increased in the circulation of cancer patients, increases cancer cell adhesion to macrovascular and microvascular endothelial cells under static and flow conditions, increases transendothelial invasion, and decreases the latency of experimental metastasis in athymic mice. These effects of galectin-3 are shown to be a consequence of its interaction with cancer-associated MUC1, which breaks the "protective shield" of the cell-surface MUC1 by causing MUC1 polarization, leading to exposure of smaller cell-surface adhesion molecules/ligands including CD44 and ligand(s) for E-selectin. Thus, the interaction in the bloodstream of cancer patients between circulating galectin-3 and cancer cells expressing MUC1 bearing the galectin-3 ligand TF (Galβ1,3GalNAc-) promotes metastasis. This provides insight into the molecular regulation of metastasis and has important implications for the development of novel therapeutic strategies for prevention of metastasis. [Cancer Res 2009;69(17):6799–806]