Laia Querol Cano, Annemiek van Spriel and colleagues, theme Cancer development and immune defense, have discovered how galectin-9, a sugar-binding membrane organiser, governs dendritic cell function by intracellularly modulating actin cytoskeleton. These findings are published in the latest issue of iScience.
Endogenous extracellular Galectins constitute a novel mechanism of membrane protein organization at the cell surface. Although Galectins are also highly expressed intracellularly, their cytosolic functions are poorly understood. They investigated the role of Galectin-9 in dendritic cell (DC) surface organization and function. By combining functional, super-resolution and atomic force microscopy experiments to analyze membrane stiffness, they identified intracellular Galectin-9 to be indispensable for plasma membrane integrity and structure in DCs. Galectin-9 knockdown studies revealed intracellular Galectin-9 to directly control cortical membrane structure by modulating Rac1 activity, providing the underlying mechanism of Galectin-9-dependent actin cytoskeleton organization. Consequent to its role in maintaining plasma membrane structure, phagocytosis studies revealed that Galectin-9 was essential for C-type-lectin receptor-mediated pathogen uptake by DCs. This was confirmed by the impaired phagocytic capacity of Galectin-9-null murine DCs. Together, this study demonstrates a novel role for intracellular Galectin-9 in modulating DC function, which may be evolutionarily conserved.