Upregulation of MicroRNA-1246 Is Associated with BRAF Inhibitor Resistance in Melanoma Cells with Mutant BRAF

PURPOSE Intrinsic and acquired resistance limit the therapeutic benefits of inhibitors of oncogenic BRAF in melanoma. To identify microRNAs (miRNAs) associated with resistance to a BRAF inhibitor, we compared miRNA expression levels in three cell lines with different BRAF inhibitor sensitivity. MATERIALS AND METHODS miRNA microarray analysis was conducted to compare miRNA expression levels. Real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) was performed to confirm the expression of differentially expressed miRNAs. The cellular effects of miR-1246 were further examined by MTT assay, immunoblotting analysis, cell cycle analysis, flow cytometric assay of apoptosis, and autophagy assay. RESULTS The miRNA microarray analysis and qRT-PCR identified five miRNAs (miR-3617, miR-92a-1, miR-1246, miR-193b-3p, and miR-17-3p) with expression that was consistently altered in two BRAF inhibitor-resistant cell lines. Among the five miRNAs, a miR-1246 mimic significantly reduced the antiproliferative effects of the BRAF inhibitor PLX4720 in BRAF inhibitor-resistant A375P (A375P/Mdr) cells, suggesting that miR-1246 upregulation confers acquired resistance to BRAF inhibition. In particular, apoptosis was identified as a major type of cell death in miR-1246-transfected cells; however, necrosis predominated in mimic-control-transfected cells, indicating that the resistance to PLX4720 in miR-1246 mimic-transfected cells is predominantly due to a reduction in necrosis. Furthermore, we found that miR-1246 promoted G2/M arrest through autophagy as a way to escape cell death by necrosis and apoptosis in response to PLX4720. The promotion of BRAF inhibitor resistance by miR-1246 was associated with lowered levels of p-ERK. CONCLUSION These results suggest that miR-1246 may be a potential therapeutic target in melanoma with acquired resistance to BRAF inhibitors.