Abstract
MicroRNA (miR) are a class of small non-coding RNA that are able to inhibit gene expression by directly binding to the 3' untranslated region (UTR) of their target mRNA and thus promote translational repression or mRNA degradation. Recently, miR-9 was reported to have a suppressive role in malignant melanoma; however, the underlying mechanism remains largely unclear. In the present study, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting were used to examine the mRNA and protein expression levels in malignant melanoma tissues and cell lines. The MTT assay and wound healing assay were used to examine the cell viability, proliferation and migratory capacities. Bioinformatics prediction and luciferase reporter assay were performed to investigate the relationship between miR-9 and its potential target gene. The present data revealed that miR-9 expression was significantly downregulated in malignant melanoma tissues when compared with their matched adjacent non-tumor tissues. Furthermore, the expression levels of miR-9 were reduced in malignant melanoma cell lines when compared with human normal skin HACAT cells. Moreover, the ectopic expression of miR-9 significantly suppressed the proliferation and migration of malignant melanoma cells, accompanied with a remarkable decrease in the protein expression levels of sirtuin 1 (SIRT1), which were markedly upregulated in malignant melanoma tissues and cell lines. Additionally, restoration of SIRT1 reversed the suppressive effects of miR-9 on the proliferation and migration of malignant melanoma cells. Luciferase reporter assay data further identified SIRT1 as a direct target gene of miR-9. To conclude, the present findings indicate that miR-9 has a suppressive role in malignant melanoma cell viability and migration, at least in part, via directly inhibiting the protein expression of its target gene, SIRT1. Therefore, miR-9 may serve as a potential candidate for the treatment of malignant melanoma.