Association of Cell Surface Mucins with Galectin-3 Contributes to the Ocular Surface Epithelial Barrier

Abstract

Maintenance of an intact mucosal barrier is critical to preventing damage to and infection of wet-surfaced epithelia. The mechanism of defense has been the subject of much investigation, and there is evidence now implicating O-glycosylated mucins on the epithelial cell surface. Here we investigate a new role for the carbohydrate-binding protein galectin-3 in stabilizing mucosal barriers through its interaction with mucins on the apical glycocalyx. Using the surface of the eye as a model system, we found that galectin-3 colocalized with two distinct membrane-associated mucins, MUC1 and MUC16, on the apical surface of epithelial cells and that both mucins bound to galectin-3 affinity columns in a galactosedependent manner. Abrogation of the mucin-galectin interaction in four different mucosal epithelial cell types using competitive carbohydrate inhibitors of galectin binding, ␤-lactose and modified citrus pectin, resulted in decreased levels of galectin-3 on the cell surface with concomitant loss of barrier function, as indicated by increased permeability to rose bengal diagnostic dye. Similarly, down-regulation of mucin O-glycosylation using a stable tetracycline-inducible RNA interfering system to knockdown c1galt1 (T-synthase), a critical galactosyltransferase required for the synthesis of core 1 O-glycans, resulted in decreased cell surface O-glycosylation, reduced cell surface galectin-3, and increased epithelial permeability. Taken together, these results suggest that galectin-3 plays a key role in maintaining mucosal barrier function through carbohydrate-dependent interactions with cell surface mucins.

The Inhibitory Effects of a Rhamnogalacturonan Ι (RG-I) Domain from Ginseng Pectin on Galectin-3 and Its Structure-Activity Relationship

“…Galectin-3 is involved in various biological processes, such as cell-cell interactions, proliferation, differentiation, apoptosis, and mRNA splicing, and is associated with different pathologic conditions including cancer (1,3,7,8). Galectin-3 is highly expressed in a subset of metastatic cancer cells in comparison with benign or normal cells and is a potential diagnostic and/or prognostic marker for some types of cancers (9).…”

Clusterin in the eye: An old dog with new tricks at the ocular surface

“…Bridging of membrane-associated mucins by LGALS3 has been shown as essential for exclusion of the clinical dye rose-bengal [181]. MMPs and other proteinases can cleave the multimerization domain from the body of LGALS3, reducing self-association [168][169][170]; truncated LGALS3 interferes with network formation and rose-bengal exclusion [182].…”

CA-125 of fetal origin can act as a ligand for dendritic cell-specific ICAM-3-grabbing non-integrin

“…Distinct types of human lectin with different specificities and binding requirements were demonstrated to recognize CA-125. The siglecs (sialic-acid Ig-like lectins), which are a subgroup of I-type lectins, and the galectins (beta-galactoside-binding lectins) were found to interact with MUC16 [9][10][11][12]. Specifically, siglec-9 was identified as a ligand for MUC16 on human NK cells, B cells, and monocytes [11].…”

“…Specifically, siglec-9 was identified as a ligand for MUC16 on human NK cells, B cells, and monocytes [11]. Galectin-1 (gal-1) and galectin-3 (gal-3) were shown to be receptors for MUC16 on membrane-associated fragments of HeLa cell lysates and on the ocular epithelial cell surface [9,10]. In addition, MUC16 expressed by metastatic pancreatic cancer cells was identified as a ligand for E-and L-selectin [13].…”