Glycobiology Advance Access originally published online on October 11, 2008
Glycobiology 2009 19(1):29-37; doi:10.1093/glycob/cwn100
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The role of integrin glycosylation in galectin-8-mediated trabecular meshwork cell adhesion and spreading
2 New England Eye Center, Departments of Ophthalmology
3 Biochemistry
4 Anatomy and Cell Biology, Tufts University School of Medicine, Boston, MA 02111, USA
5 Section of Microbiology, Immunology and Glycobiology (MIG), Lund University, 223 62 Lund, Sweden
1 To whom correspondence should be addressed: Tel: +1-617-636-6776; Fax: +1-617-636-0348; e-mail: Noorjahan.Panjwani{at}tufts.edu
Received on April 2, 2008; revised on August 30, 2008; accepted on September 28, 2008
Primary open angle glaucoma (POAG) is a major blindness-causing disease, characterized by elevated intraocular pressure due to an insufficient outflow of aqueous humor. The trabecular meshwork (TM) lining the aqueous outflow pathway modulates the aqueous outflow facility. TM cell adhesion, cell–matrix interactions, and factors that influence Rho signaling in TM cells are thought to play a pivotal role in the regulation of aqueous outflow. In a recent study, we demonstrated that galectin-8 (Gal8) modulates the adhesion and cytoskeletal arrangement of TM cells and that it does so through binding to β1 integrins and inducing Rho signaling. The current study is aimed at the characterization of the mechanism by which Gal8 mediates TM cell adhesion and spreading. We demonstrate here that TM cells adhere to and spread on Gal8-coated wells but not on galectin-1 (Gal1)- or galectin-3 (Gal3)-coated wells. The adhesion of TM cells to Gal8-coated wells was abolished by a competing sugar, β-lactose, but not by a noncompeting sugar, sucrose. Also, a trisaccharide, NeuAc
2-3Galβ1-4GlcNAc, which binds specifically to the N-CRD of Gal8, inhibited the spreading of TM cells to Gal8-coated wells. In contrast, NeuAc2-6Galβ1-4GlcNAc which lacks affinity for Gal8 had no effect. Affinity chromatography of cell extracts on a Gal8-affinity column and binding experiments with plant lectins, Maakia Amurensis and Sambucus Nigra, revealed that 3β1, 5β1, and vβ1 integrins are major counterreceptors of Gal8 in TM cells and that TM cell β1 integrins carry predominantly 2-3-sialylated glycans, which are high-affinity ligands for Gal8 but not for Gal1 or Gal3. These data lead us to propose that Gal8 modulates TM cell adhesion and spreading, at least in part, by interacting with 2-3-sialylated glycans on β1 integrins.
Key words: cell adhesion / galectin-8 / glaucoma / integrins / trabecular meshwork