RESUMO
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.
