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Molecular and Cellular Biology, April 2006, p. 3181-3193, Vol. 26, No. 8
0270-7306/06/$08.00+0 doi:10.1128/MCB.26.8.3181-3193.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Jacky G. Goetz,1,2,
Pam Cheung,3
Avraham Raz,4
James W. Dennis,3 and
Ivan R. Nabi1,2*
Department of Pathology and Cell Biology, Université de Montréal, Québec, Canada,1 Department of Cellular and Physiological Sciences, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada,2 Samuel Lunenfeld Research Institute, Toronto, Ontario, Canada,3 Karmanos Cancer Institute, Detroit, Michigan4
Received 22 September 2005/ Returned for modification 1 November 2005/ Accepted 21 January 2006
Oncogenic signaling stimulates the dynamic remodeling of actin microfilaments and substrate adhesions, essential for cell spreading and motility. Transformation is associated with increased expression of ß1,6GlcNAc-branched N-glycans, products of Golgi ß1,6-acetylglucosaminyltransferase V (Mgat5) and the favored ligand for galectins. Herein we report that fibronectin fibrillogenesis and fibronectin-dependent cell spreading are deficient in Mgat5/ mammary epithelial tumor cells and inhibited in Mgat5+/+ cells by blocking Golgi N-glycan processing with swainsonine or by competitive inhibition of galectin binding. At an optimum dosage, exogenous galectin-3 added to Mgat5+/+ cells activates focal adhesion kinase (FAK) and phosphatidylinositol 3-kinase (PI3K), recruits conformationally active
5ß1-integrin to fibrillar adhesions, and increases F-actin turnover. RGD peptide inhibits PI3K-dependent fibronectin matrix remodeling and fibronectin-dependent cell motility, while galectin-3 stimulates and overrides the inhibitory effects of RGD. Antibodies to the galectin-3 N-terminal oligomerization domain stimulate
5ß1 activation and recruitment to fibrillar adhesions in Mgat5+/+ cells, an effect that is blocked by disrupting galectin-glycan binding. Our results demonstrate that fibronectin polymerization and tumor cell motility are regulated by galectin-3 binding to branched N-glycan ligands that stimulate focal adhesion remodeling, FAK and PI3K activation, local F-actin instability, and
5ß1 translocation to fibrillar adhesions.
These authors contributed equally.
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