| Hinokitiol (b-thujaplicin) is a tropolone-related compound which has been reported to have several biological effects including anti-microbe, anti-inflammation and anti-tumor activity. Cancer stem/progenitor cells (CSCs) are a subpopulation of cancer cells with tumor initiation, chemoresistant and metastatic properties and have been considered as the important therapeutic target in future cancer therapy. We have previously demonstrated that hinokitiol exhibits anti-cancer activity in against murine tumor cells through the induction of autophagy. Here we discovered that hinokitiol suppressed the self-renewal capability of human breast CSCs (BCSCs) and inhibited the expression of Bmi1 in protein level without suppressing its mRNA. Treatment of hinokitiol in mammospheres induced the expression of miR-494-3p and inhibition of miR-494-3p expression in BCSCs abolished the suppressive effect of hinokitiol in mammosphere formation and Bmi1 expression. We further demonstrated that Bmi1 is a target of miR-494-3p by luciferase-based 3'UTR reporter assay. Overexpression of miR-494-3p in BCSCs caused the down-regulation of Bmi1 protein, inhibition of mammosphere formation capability and suppression of their tumorigenicity. We also found that miR-494-3p expression was significantly and inversely correlated with patient survival in two independent public database sets. Furthermore, in vivo treatment of hinokitiol suppressed the growth of xenograft human breast tumors as well as the expression of Bmi1 and ALDH1A1 in xenograft tumors. In conclusion, our data suggest that hinokitiol could target BCSCs through the miR-494-3p mediated down-modulation of Bmi1 expression. |
