Ultraviolet (UV) irradiation is the leading factor in the development of skin cancer, which is the most common form of cancer in the United States. Discovering novel chemopreventive agents against this disease is extremely important. Kaempferol, a natural flavonol isolated from tea, broccoli, grapes, apples and other plant sources, is known to have anticancer activity, but its molecular mechanisms and direct target(s) in cancer chemoprevention are still unclear. In this study, our pull-down assay results showed that RSK2 and MSK1 directly interact with kaempferol in both ex vivo and in vitro systems. ATP competition and in vitro kinase assay data revealed that kaempferol interacts with RSK2 and MSK1 at the ATP-binding pocket and inhibits their respective kinase activities. Mechanistic investigations determined that kaempferol acts as an inhibitor of RSK2 and MSK1 kinase activities to attenuate solar UV-induced phosphorylation in mitogen-activated protein kinase signaling cascades in JB6 P+ mouse skin epidermal cells. In a mouse skin tumorigenesis study, kaempferol significantly suppressed solar UV-induced skin carcinogenesis. Further analysis showed that the kaempferol-treated group had a substantial reduction in solar UV-induced phosphorylation of CREB and c-Fos in mouse skin. Taken together, our results identify kaempferol as a safe and novel chemopreventive agent against solar UV-induced skin carcinogenesis that acts by targeting RSK2 and MSK1.

Citation Format: Ke Yao, Hanyong Chen, Mee-Hyun Lee, Alyssa Langfald, Myoung Ok Kim, Dong Hoon Yu, Kangdong Liu, Wei-Ya Ma, Ann M. Bode, Ziming Dong, Zigang Dong. Kaempferol suppresses solar ultraviolet radiation-induced skin cancers by targeting RSK2 and MSK1. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1241. doi:10.1158/1538-7445.AM2014-1241