Expressions of miR-181a and miR-20a in RPMI8226 cell line and their potential as biomarkers for multiple myeloma.

Multiple myeloma (MM) is characterized by clonal proliferation of malignant plasma cells in the bone marrow. The anti-tumor activity of bortezomib (a proteosome inhibitor) in MM is challenged by emergence of drug resistance. MicroRNAs (miR) regulate and orchestrate multiple cellular pathways. We investigate the contribution miR-181a and miR-20a expressions' on cell proliferation and apoptosis in RPMI8226 cell line and their influence on bortezomib treatment. RNA isolation, quantitative real-time PCR (qRT-PCR), cell proliferation assay, cell cycle analysis, and cell apoptosis assay were done. Statistical analysis was performed using SPSS 17.0 software (SPSS, Chicago, IL, USA). P values of less than 0.05 were considered statistically significant. RPMI8226 cells seeded in 96-well plates and treated for 24 h with different concentrations of bortezomib showed dose-dependent growth inhibition; expression of both miR-181a and miR-20a were inhibited by bortezomib. We found decrease of miR-181a (60%) and miR-20a (30%) in cells transfected with 20-nM inhibitor. A relative increase of 14-fold in miR-181a and 11-fold in miR-20a was observed in cells transfected with mimics of the same concentration. Transient low expression of miR-181a/20a inhibited proliferation at day 4, and overexpression of miR-181a promoted proliferation. Cells transfected with miR-181a/20a inhibitor within day 4 showed lower survival rate, and low expression of miR-181a on the fourth day after transfection promoted apoptosis. Our findings suggest that miR-181a/20a has a higher expression in MM. miR-181-a expression is proportional to MM tumor burden and could be a biomaker for monitoring treatment. miR-20a shows the potential of a diagnostic biomarker.