IFT20 regulates lymphatic endothelial cell-cell junctions via endocytic trafficking of VE-cadherin

Intraflagellar transport (IFT) proteins are required for the assembly and function of primary cilia. They also regulate non-ciliary polarized vesicular traffic, such as T cell receptor recycling. We recently reported that lymphatic endothelial cells assemble primary cilia and express IFT proteins. Here, we report that IFT20 regulates vascular endothelial cadherin (VE-cadherin) localization at adherens junctions. IFT20 deletion caused discontinuous, button-like interendothelial junctions. This resulted in excessive lymphangiogenesis and impaired lymph drainage in mice. In vitro, VEGF-C treatment of IFT20 KD primary human dermal lymphatic endothelial cells caused accumulation of VE-cadherin in RAB5+ endosomes and enhanced and sustained VEGFR-3 signaling. Our findings are consistent with a model in which IFT20 promotes recycling of VE-cadherin to the adherens junction where it sequesters VEGFR-3 at the cell surface, thereby limiting pro-lymphangiogenic signaling. In the absence of IFT20, intercellular junctions are destabilized, pro-lymphangiogenic VEGFR-3 signaling is enhanced, and lymph transport is impaired by intracellular sequestration of VE-cadherin. This study elucidates the function of an IFT protein in lymphatic endothelial cells and provides mechanistic insight into the processes that regulate lymphatic endothelial cell-cell junctions and lymphangiogenic signaling.