Long noncoding RNA-H19 (H19), an imprinted oncofetal gene, has a central role in carcinogenesis. Hitherto, the mechanism by which H19 regulates cancer stem cells, remains elusive. Here we show that breast cancer stem cells (BCSCs) express high levels of H19, and ectopic overexpression of H19 significantly promotes breast cancer cell clonogenicity, migration and mammosphere-forming ability. Conversely, silencing of H19 represses these BCSC properties. In concordance, knockdown of H19 markedly inhibits tumor growth and suppresses tumorigenesis in nude mice. Mechanistically, we found that H19 functions as a competing endogenous RNA to sponge miRNA let-7, leading to an increase in expression of a let-7 target, the core pluripotency factor LIN28, which is enriched in BCSC populations and breast patient samples. Intriguingly, this gain of LIN28 expression can also feedback to reverse the H19 loss-mediated suppression of BCSC properties. Our data also reveal that LIN28 blocks mature let-7 production and, thereby, de-represses H19 expression in breast cancer cells. Appropriately, H19 and LIN28 expression exhibits strong correlations in primary breast carcinomas. Collectively, these findings reveal that lncRNA H19, miRNA let-7 and transcriptional factor LIN28 form a double-negative feedback loop, which has a critical role in the maintenance of BCSCs. Consequently, disrupting this pathway provides a novel therapeutic strategy for breast cancer.

Morphine is an opioid analgesic drug commonly used for pain relief in cancer patients. Here, we report that morphine enhances the mammosphere forming capacity and increases the expression of stemness-related transcription factors Oct4, Sox2 and Nanog. Treatment with morphine leads to enrichment of a side population fraction in MCF-7 cells and the CD44+/CD24−/low population in BT549 cells. Consistently, morphine activates Wnt/β-catenin signaling to induce epithelial to mesenchymal transition and promotes metastasis. Moreover, morphine decreases the sensitivity of traditional anti-cancer drugs in breast cancer cells. Nalmefene, an antagonist of morphine, reverses morphine-induced cancer stem cell properties and chemoresistance in breast cancer. In addition, nalmefene abolishes morphine enhancing tumorigenesis in a NOD/SCID mouse model. In conclusion, our findings demonstrate that morphine contributes to chemoresistance via expanding the population of cancer stem cells and promotes tumor growth, thereby revealing a novel role of morphine and providing some new guides in clinical use of morphine.