AbstractBackgroundCelastrol is a novel anti-tumor agent. Ways to further enhance this effect of celastrol has attracted much research attention.Methods and ResultsHere, we report that celastrol treatment can elevate miR-223 in human breast cancer cell line MCF-7 and prostate cancer PC3. Down-regulating miR-223 could increase the number of viable cells, yet it further reduced viable cells in samples that were treated by celastrol; up-regulation of miR-223 displayed opposite effects. Celastrol’s miR-223 induction might be due to NF-κB inhibition and transient mTOR activation: these two events occurred prior to miR-223 elevation in celastrol-treated cells. NF-κB inhibitor, like celastrol, could induce miR-223; the induction of miR-223 by NF-κB inhibitor or celastrol was reduced by the use of mTOR inhibitor. Finally and interestingly, miR-223 also could affect NF-κB and mTOR and the effects were different between cells treated or not treated with celastrol, thus providing an explanation for differing effects of miR-223 alteration on cellular viability in the presence of celastrol or not.ConclusionsFor the first time, we disclose that celastrol could induce miR-223 in breast and prostate cancer cells, and that inhibiting miR-223 could further reduce the living cells in celastrol-treated cancer cell lines. We thus provide a novel way to increase celastrol’s anti-cancer effects.