OBJECTIVETo analyze the difference in microRNAs expression between MCF-7 and MCF-7/ADR cells and explore the association between microRNA and drug resistance of breast cancer.

METHODSThe drug resistance of MCF-7/ADR cells was evaluated using MTT assay and flow cytometry. Microarray technique and RT-PCR were used to analyze the differential expressions of the microRNA between MCF-7 and MCF-7/ADR cells.

RESULTSThe drug resistance index of MCF-7/ADR cells relative to the parental MCF-7 cells was 33.2. The percentages of the side population in MCF-7/ADR and MCF-7 cells were (9.50-/+0.9)% and (0.85-/+0.2)%, respectively. Microarray analysis of MCF-7 to MCF-7/ADR cells identified 36 differentially expressed genes, including 16 up-regulated and 20 down-regulated genes in MCF-7/ADR cells. RT-PCR identified 14 microRNAs that were differentially expressed between MCF-7 and MCF-7/ADR cells, including 7 up-regulated and 7 down-regulated ones in MCF-7/ADR cells. Of these differentially expressed microRNAs, mir-221, mir222, mir-130a, and mir-155 showed significantly increased expression, and mir200a, mir-200b, mir-200c, and mir-421 showed significantly lowered expression in MCF-7/ADR cells as indicated by the results of microarray analysis and RT-PCR.

CONCLUSIONMCF-7/ADR cells show a different microRNA expression profile from its parental MCF-7 cells, suggesting the involvement of microRNAs in tumor cell drug resistance. This finding provides a experimental basis for further study of mechanism underlying the drug resistance of breast cancer.