Melanoma suppression by quercein is correlated with RIG-I and type I interferon signaling

Melanoma is a life-threatening cancer with limited treatments. Retinoic acid-inducible gene I (RIG-I) is a cytosolic pattern recognition receptor (PRR) crucial to RNA virus sensing, interferon production, and tumor suppression. Quercetin, a natural flavonoid, has particularly therapeutic interests to prevent and treat cancer, for its pharmacological effects against oxidant, inflammation, and angiogenesis. Quercetin was investigated for its anti-melanoma activity and potential mechanisms in this study. We found that quercetin inhibited mouse melanoma growth in vivo, and suppressed proliferation and promoted apoptosis of both B16 and A375 cells in vitro. Quercetin upregulated IFN-alpha and IFN-beta expression through activating RIG-I promoter in B16 cells. The induction of IFN-alpha and IFN-beta, which could be severely impaired by silencing RIG-I induced interferon stimulated genes (ISGs). Moreover, RIG-I likely amplifies antitumor effects by activating signal transduction and activator of transcription 1 (STAT1) in the IFN-JAK-STAT pathway in an autocrine and paracrine manner. Our study provided novel insights regarding biological and anti-proliferative activities of quercetin against melanoma, and we identified RIG-I as a potential target in anti-tumor therapies.