IFN-gamma restricts the egress of melanoma cells to lymphatic vessels via Claudin-3 up-regulation in LECs

Tumor lymphatic invasion is an initial and key event in tumor lymphatic metastasis. IFN-gamma is well studied as a negative regulator for lymphangiogenesis, which is closely related to tumor lymphatic metastasis. However, whether IFN-gamma signaling in lymphatic endothelial cells (LECs) directly regulates tumor lymphatic invasion remains elusive. In this study, using LEC-specific IFN-gamma receptor (IFN-gammaR) knockout mice, we found that loss of IFN-gammaR in LECs elevated the dissemination of melanoma cells into the draining lymph node. Notably, both in vivo and in vitro assays revealed that IFN-gamma signaling in LECs restricted lymphatic invasion of melanoma cells. Further investigation showed that IFN-gamma up-regulated Claudin-3 expression in LECs. Knockdown of Claudin-3 in LECs abolished the inhibitory effect of IFN-gamma on melanoma cells trans-lymphatic endothelial migration activity, suggesting that IFN-gamma restricts lymphatic invasion of melanoma cells via the regulation of Claudin-3 in LECs. Mechanically, the AMPK signaling pathway was involved in the regulation of IFN-gamma on Claudin-3 in LECs. In conclusion, we report that IFN-gamma signaling in LECs is essential to restrict melanoma lymphatic invasion via upregulating the tight junction protein Claudin-3. This study provides new insight into how IFN-gamma modulates tight junctions in LECs to reduce metastasis and reveal new molecular mechanisms on tumor lymphatic invasion.