Overexpression of miR-381 and miR-539 represses MITF expression and function. (A) Western blot shows an increase in MITF protein with SCF treatment in primary BMMCs. Retroviral overexpression of miR-381 and miR-539 (miR cluster) represses MITF expression at baseline and blunts up-regulation with SCF treatment. (B) PCR analysis shows overexpression of miR-381 and miR-539 in miR cluster-expressing BMMCs. miR-16 expression is not significantly changed. (C) Overexpression of miR-381 and miR-539 in HMC-1 cells (miR cluster) impairs colony-forming capacity. **P < .005. P values are calculated with Student t test; all experiments performed in triplicate. (D) Western blot shows decrease of MITF protein in miR cluster-expressing HMC-1 cells. (E) PCR analysis demonstrates overexpression of miR-539 and miR-381 in HMC cells transduced with the miR cluster compared with vector-transduced cells. miR-16 expression is not significantly changed.