Glycoside oleandrin downregulates toll-like receptor pathway genes and associated miRNAs in human melanoma cells.

Melanoma accounts for the majority of skin cancer-related deaths. Nerium oleander is a plant known to be toxic and consumed due to the cardiac glycosides it contains. Oleandrin is a cardiac glycoside obtained from of N. oleander. Beside capable of inhibiting proliferation and metastasis of cancer cells, cardiac glycoside derivative compounds cause cardiovascular side effects. Because of cardiovascular toxicity of clinically used cardiac glycosides, it is necessary to investigate cardiac glycoside derivative compounds capable of inhibiting proliferation and metastasis of cancer cells. It is known that oleandrin has anticarcinogenic effects in other cancers. Previous studies have shown that toll-like receptors (TLRs) and their related microRNAs (miRNAs) are associated with cancer. Therefore, aim was to investigate the effect of oleandrin on genes and miRNAs associated with TLRs in A375 melanoma cells in this study. The effects of oleandrin on cell viability, cytokines, apoptosis were evaluated using XTT, ELISA and TUNEL analyses, respectively. The effect of oleandrin on expression of TLR genes and 5 associated miRNAs in A375 cells has been determined by qRT-PCR. In addition, the levels of MyD88, TLR2 and TLR4 proteins were analyzed by western blot method. ELISA indicated that oleandrin treatment (47 nM at 48 h) reduced the level of proinflammatory cytokine IFNG. TUNEL analysis showed that apoptosis rate was significantly increased in the oleandrin dose group. According to qRT-PCR results, there was a significant decrease in IRAK1, IRAK4, MyD88, TLR2-TLR7 and TRAF3 expressions in the oleandrin treated group compared to the control (untreated cell). Also, a significant decrease in TLR4 protein expression has been observed. In addition, oleandrin significantly downregulated the levels of hsa-miRNA-146a-5p and hsa-miRNA-21-5p. In conclusion, it has been observed that oleandrin has an effect on TLR pathway-related genes and miRNAs in melanoma cells. We show that TLRs pathways and hsa-miR-146a-5p and hsa-miR-21-5p can participate in the oleandrin molecular mechanism of action.