N-Glycosylation Regulates Chitinase 3-like-1 and IL-13 Ligand Binding to IL-13 Receptor α2

Chitinase 3-like-1 (Chi3l1) and IL-13 are both ligands of IL-13 receptor alpha 2 (IL-13R alpha 2). The binding of the former activates mitogen-activated protein kinase, AKT, and Wnt/beta-catenin signaling, and plays important roles in innate and adaptive immunity, cellular apoptosis, oxidative injury, allergic inflammation, tumor metastasis and wound healing, fibrosis, and repair in the lung. In contrast, the latter binding is largely a decoy event that diminishes the effects of IL-13. Here, we demonstrate that IL-13R alpha 2 N-glycosylation is a critical determinant of which ligand binds. Structure-function evaluations demonstrated that Chi3l1-IL-13R alpha 2 binding was increased when sites of N-glycosylation are mutated, and studies with tunicamycin and Peptide:N-glycosidase F (PNGase F) demonstrated that Chi3l1-IL13R alpha 2 binding and signaling were increased when N-glycosylation was diminished. In contrast, structure-function experiments demonstrated that IL-13 binding to IL-13R alpha 2 was dependent on each of the four sites of N-glycosylation in IL-13R alpha 2, and experiments with tunicamycin and PNGase F demonstrated that IL-13-IL-13R alpha 2 binding was decreased when IL-13R alpha 2 N-glycosylation was diminished. Studies with primary lung epithelial cells also demonstrated that Chi3l1 inhibited, whereas IL-13 stimulated, N-glycosylation as evidenced by the ability of Chi3l1 to inhibit and IL-13 to stimulate the subunits of the oligosaccharide complex A and B (STT3A and STT3B). These studies demonstrate that N-glycosylation is a critical determinant of Chi3l1 and IL-13 binding to IL-13R alpha 2, and highlight the ability of Chi3l1 and IL-13 to alter key elements of the N-glycosylation apparatus in a manner that would augment their respective binding.