Abnormal expression of microRNA (miRNA) and aberration epigenetic regulation can both contribute to cancer development. miRNA expression can be changed by epigenetic regulation such as DNA methylation and histone acetylation, thereby regulates relative oncogenes and tumor-suppressor genes, and consequently leads to carcinogenesis.

Objective To analyze the differences in microRNA (miRNA) expression between A549 and A549/DDP cells and explore the association between miRNA expression and drug resistance in non-small cell lung cancer (NSCLC).Methods The drug resistance of A549/DDP cells was evaluated using CCK-8 assay and flow cytometry.Microarray technique and RT-PCR were used to analyze the differential expression of the miRNA between A549 and A549/DDP cells.Enforced or inhibited target miRNA expression in cisplatin resistant cell was used to investigate whether miRNA involve in modulating the sensitivity of NSCLC cells to chemotherapeutic agent,exploiting the emerging knowledge of miRNA for the development of new human therapeutic applications for overcoming anticancer drug resistance and trying to discover biomarkers that were better able to predict the cancer chemotherapy sensitivity.Results The drug resistance index of A549/DDP cells relative to the parental A549 cells was 18.Microarray analysis of A549 and A549/DDP cells identified 51 differentially expressed genes (≥4-fold),including 24 up-regulated and 27 down-regulated genes in A549/DDP cells.RT-PCR identified 9 miRNA that were differentially expressed between A549 and A549/DDP cells.Of these differentially expressed miRNA,miR-376c,miR-31,miR-29a,miR-221 showed significantly increased expression,and miR-196a,miR-20a,miR-20b,miR-17,miR-451 showed significantlylowered expression in A549/DDP cells as indicated by the results of microarray analysis and RT-PCR.DDP sensitivity was increased 11.7 ％ in A549/DDP cells transfected with miR-17,but the chemosensitivity was decreased when miR-451 was over-expressed or miR-29a was inhibited by selective inhibitor,the reduction was 15.5 ％,12.9 ％,respectively,whereas chemosensitivity did not change when miR-376c,miR-31,miR-221 were inhibited or miR-196a,miR-20b,miR-20a were over-expressed.Conclusion A549/DDP cells show a different miRNA expression profile from its parental A549 cells,suggesting the involvement of miRNA in tumor cell drug resistance.miR-17 has the potential to be an efficient agent for preventing and reversing DDP-resistance in NSCLC.These results provide a strong rationale for the development of miRNA-based therapeutic strategies aiming to overcome cancer cell resistance.