Galectin-lattice sustains function of cationic amino acid transporter and insulin secretion of pancreatic β cells

Maintenance of cell surface residency and function of glycoproteins by lectins is essential for regulating cellular functions. Galectins are beta-galactoside-binding lectins and form a galectin-lattice, which regulates stability, clustering, membrane sub-domain localization, and endocytosis of plasmalemmal glycoproteins. We have previously reported that galectin-2 forms a complex with cationic amino acid transporter 3, CAT3, in pancreatic beta cells, although the biological significance of the molecular interaction between galectin-2 and CAT3 has not been elucidated. In the present study, we demonstrated that the structure of N-glycan of CAT3 was either tetra- or tri- antennary branch structure carrying beta-galactosides, which works as galectin ligands. Indeed, CAT3 bound to galectin-2 using beta-galactoside epitope. Moreover, the disruption of the glycan-mediated bindings between galectins and CAT3 significantly reduced cell surface expression levels of CAT3. The reduced cell surface residency of CAT3 attenuated the cellular arginine uptake activities and subsequently reduced nitric oxide production, and thus impaired the arginine-stimulated insulin secretion of pancreatic beta cells. These results indicate that galectin-lattice stabilizes CAT3 by preventing endocytosis to sustain the arginine-stimulated insulin secretion of pancreatic beta cells. This provides a novel cell biological insight into the endocrinological mechanism of nutrition metabolism and homeostasis.