Abstract
MicroRNAs (miRs) may induce mRNA degradation or inhibit protein translation by directly binding to the 3'-untranslational region of target mRNAs. It has been reported that miR-138 is downregulated in malignant melanoma (MM) cells. However, the role of miR-138 in MM cell proliferation, invasion and energy metabolism remains unknown. These were investigated using reverse transcription-quantitative polymerase chain reaction was used to evaluate the expression of miR-138 and the mRNA expression of hypoxia-inducible factor-1α (HIF-1α), as HIF-1α serves a crucial role in glycolysis, which is important for tumor growth. In addition, western blot analysis was used to detected the protein expression of HIF-1α, while MTT and Transwell assays evaluated cell proliferation and invasion, respectively. Furthermore, glucose consumption and lactic acid production were assessed. These tests were conducted using the normal human melanocyte cell line HM and the MM cell line WM451, which was transfected variously with scramble miR mimics, miR-138 mimics, miR-138 inhibitor, non-specific small interfering (si)RNA, HIF-1α siRNA, or co-transfected with miR-138 mimics and pc-DNA3.1(+)-HIF-1α plasmid. The results showed that miR-138 was significantly downregulated in MM WM451 cells compared to a normal melanocyte cell line HM. Overexpression of miR-138 significantly inhibited the proliferation and invasion of WM451 cells. These effects were similar to those induced by the siRNA-mediated knockdown of HIF-1α, a direct target of miR-138. Further investigation found that miR-138 negatively regulated the protein expression of HIF-1α in WM451 cells. Moreover, upregulation of miR-138 notably inhibited the glycolysis level, as demonstrated by reduced glucose consumption and lactic acid production, which could be reversed by the overexpression of HIF-1α. In summary, the present study demonstrated that miR-138 is able to inhibit proliferation, invasion and glycolysis in MM cells, potentially by directly targeting HIF-1α.