Galectin-9 interacts with Vamp-3 to regulate cytokine secretion in dendritic cells

Intracellular vesicle transport is essential to maintain cellular homeostasis and is known to be mediated by the endosomal pathway and SNARE proteins. Endosomal-mediated transport to the plasma membrane ensures cytokine secretion in dendritic cells (DCs) and the initiation of effector immune responses. Despite the critical importance of this process, the specific molecular agents that regulate DC cytokine secretion are poorly characterised. Galectin-9, a ß-galactoside-binding protein, has emerged as novel modulator of numerous cellular processes although its exact functions remain to be elucidated. In particular, its intracellular roles in regulating (immune) cell homeostasis and cytosolic transport are virtually unknown. Here, we investigated galectin-9 function in cytokine secretion in primary human DCs, and report that galectin-9 is essential for intracellular trafficking of cytokines to the cell surface. Galectin-9 depletion resulted in the accumulation of cytokine-containing vesicles in the Golgi complex that eventually underwent lysosomal degradation. We observed galectin-9 to molecularly interact with Vamp-3 using unbiased immunoprecipitation-mass spectrometry technology, and identified that galectin-9 was required for rerouting of Vamp-3-containing endosomes to the plasma membrane for cargo release upon DC activation as the underlying mechanism. Overall, this study identifies galectin-9 as a necessary mechanistic component for intracellular trafficking. This may impact our general understanding of vesicle machinery and transport and shed new light into the multiple roles galectin and glycan-mediated interactions play in governing cell function.