miR-222 and miR-29a contribute to the drug-resistance of breast cancer cells

• We analyze miRNA expression profiles of the sensitive and resistant MCF-7 cells.
• miR-222 and miR-29a confer adriamycin and docetaxel resistance in MCF-7 cells.
• We use pathway mapping tools to analyze pathways affected by miR-222 and miR-29a.
• miR-222 and miR-29a regulate the expression of PTEN.

Adriamycin (Adr) and docetaxel (Doc) are two chemotherapeutic agents commonly used in the treatment of breast cancer. However, patients with breast cancer who are treated by the drugs often develop resistance to them and some other drugs. Recently studies have shown that microRNAs (miRNAs, miRs) play an important role in drug-resistance. In present study, miRNA expression profiles of MCF-7/S and its two resistant variant MCF-7/Adr and MCF-7/Doc cells were analyzed using microarray and the results were confirmed by real-time quantitative polymerase chain reaction. Here, 183 differentially expressed miRNAs were identified in the two resistant sublines compared to MCF-7/S. Then, five up-regulated miRNAs (miR-100, miR-29a, miR-196a, miR-222 and miR-30a) in both MCF-7/Adr and MCF-7/Doc were selected to explore their roles in acquisition of drug-resistance using transfection experiment. The results showed that miR-222 and miR-29a mimics and inhibitors had partially changed the drug-resistance of breast cancer cells, which was also confirmed by apoptosis assay. Western blot results suggested that miR-222 and -29a could regulate the expression of PTEN, maybe through which the two miRNAs conferred Adr and Doc resistance in MCF-7 cells. Finally, pathway mapping tools were employed to further analyze signaling pathways affected by the two miRNAs. In summary, this study demonstrates that altered miRNA expression pattern is involved in acquiring resistance to Adr and Doc in breast cancer MCF-7 cells, and that there are some miRNAs who displayed consistent up- or down-regulated expression changes in the two resistant sublines. The most importance is that we identify two miRNAs (miR-222 and miR-29a) involved in drug-resistance, at least in part via targeting PTEN.