MicroRNA-26a inhibits the growth and invasiveness of malignant melanoma and directly targets on MITF gene

Metastatic melanoma is the most aggressive form of skin cancer and is refractory to therapy. MicroRNAs have been recently discovered as novel molecules that provide therapeutic benefits against melanoma. This work aims to examine the effects of miR-26a and let-7a on the growth and invasiveness of malignant melanoma in vitro and in vivo. In addition, we elucidate the mechanism of action by identifying the target gene of miR-26a. Both miR-26a and let-7a inhibited proliferation and invasiveness and halted the cell cycle at the G(1)/G(0) phase in SKMEL-28 and WM1552C malignant melanoma cell lines. Moreover, miR-26a potently induced apoptosis and downregulated the expressions of microphthalmia-associated transcription factor (MITF) and MAP4K3 in both cell lines. The luciferase reporter assay demonstrated that miR-26a suppresses MITF expression by binding the 3′-UTR, suggesting that MITF is a bona fide target of miR-26a. SiRNA knockdown of the MITF gene confirmed that miR-26a reduced cell viability and induced apoptosis by regulating MITF. Using a murine model, we also found miR-26a significantly retarded the growth of melanoma tumors in vivo. In conclusion, miR-26a and let-7a suppressed the growth and invasiveness of melanoma cells, suggesting that miR-26a and let-7a may represent novel therapies for malignant melanoma.