Src kinase activation is mandatory for MDA-9/syntenin-mediated activation of Nuclear Factor-κB

The scaffolding PDZ-domain containing protein MDA-9/syntenin is a tandem PDZ protein overexpressed in human melanoma, and breast and gastric cancer cells. MDA-9/syntenin affects cancer cell motility and invasion through distinct biochemical and signaling pathways, including focal adhesion kinase (FAK) and p38 mitogen-activated protein kinase (MAPK), resulting in activation of the NFκ B pathway. MDA9/syntenin also promotes melanoma metastasis by activating c-Src, but how c-Src regulates NFκ B activation is unclear. Using a human melanoma model, we document that MDA-9/syntenin/c-Src interactions are positive regulators of NFκ B activation. Inhibition of c-Src by PP2 treatment, by blocking c-Src or mda-9/syntenin expression with siRNA, or in c-Src (−/−) knockout cell lines, reduces NFκ B activation following overexpression of mda-9/syntenin or c-Src. Deletion or point mutations of the PDZ binding motif preventing MDA-9/syntenin association with c-Src reveals that both PDZ domains, with PDZ2 being the dominant module, are required for activating downstream signaling pathways, including p38 MAPK and NFκ B. We also document that MDA-9/syntenin/c-Src complexes functionally cooperate with NFκ B to promote anchorage-independent growth, motility and invasion of melanoma cells. These findings underscore PDZ domains of MDA-9/syntenin as promising potential therapeutic targets for intervening in a decisive component of cancer progression, namely metastatic tumor spread.