Backgrounds: Acquired resistance is a significant clinical challenge in targeted therapy of melanomas using BRAF inhibitors. We previously identified that downregulation of miR-92a-1-5p confers acquired resistance to BRAF inhibition using an miRNA array platform.
Objective: In this study, we investigated the target genes of miR-92a-1-5p and their functional significance in BRAF inhibitor resistance.
Methods: The miRNA target prediction data were combined with RNA-Seq data to identify possible target genes for miR-92a-1-5p. Cellular effects of target genes were further examined using siRNA knockdown, WST-1 assay, and immunoblotting analysis.
Results: We selected S100 calcium-binding protein A9 (S100A9) as a possible target gene for functional validation. S100A9 knockdown abrogated resistance to PLX4720 in A375P/Mdr cells. This result was similar to those described earlier for miR-92a-1-5p, indicating that miR-92a-1-5p inhibits cell viability by targeting S100A9. S100A9 overexpression partially conferred PLX4720 resistance to A375P cells. We also demonstrated that MAPK re-activation does not contribute to the promotion of BRAF inhibitor resistance by S100A9.
Conclusion: Taken together, our results indicate that S100A9 might be functionally involved in development of resistance to BRAF inhibitors and might be a target for melanoma therapy in the future.
Keywords: BRAF inhibitor; Drug resistance; RNA-Seq analysis; S100A9; miRNA.