Galectin-9 regulates dendritic cell contractility and migration via RhoA

Abstract To initiate adaptive immune responses, dendritic cells (DCs) migrate long distances to transport antigens from peripheral tissues to draining lymph nodes employing a so-called ameboid migration mode. Despite its critical importance, the specific molecular mechanisms that regulate DC migration are poorly characterised. Galectins, a family of β-galactoside-binding proteins, constitute a novel mechanism of membrane organisation at the cell surface and, in this way, exert crucial roles in multiple physiological and pathological processes. Nonetheless, the molecular mechanisms that underlie galectin functions are poorly described and their membrane interacting partners are mostly unknown. Here, we report that galectin-9 is required for the dynamic behaviour and motility of DCs. We demonstrate that galectin-9 deficiency results in impaired chemokine-driven and basal DC migration both in human and mouse, suggesting a conserved function for galectin-9. Deficiency in contractility was identified as the underlying mechanism, which could be rescued by restoring membrane-bound galectin-9 levels. Furthermore, we show that galectin-9 controls RhoA activity and downstream signalling, in turn causing rearrangements of the actin cytoskeleton at the cell rear that promote DC efficient migration. Galectin-9 interaction with the adhesion receptor CD44 was required for its function enhancing DC migration. Remarkably, analysis of DC motility in a 3D environment containing a tumour spheroid revealed galectin-9 is required for DC persistent migration towards the tumour and for DC infiltration. Moreover, exogenous galectin-9 rescued the motility of immunocompromised primary blood DCs, revealing a novel role for galectin-9 in the tumour microenvironment, with potential implications for DC-based immunotherapies.