Inhibitory effects on melanogenesis by thymoquinone are mediated through the β-catenin pathway in B16F10 mouse melanoma cells

Thymoquinone (TQ) is a component found in the seeds of Nigella sativa, an annual plant growing on the Mediterranean coast, and is known for its anticancer and anti-inflammatory effects. However, to date, at least to the best of our knowledge, limited studies are available examining the molecular mechanisms through which TQ inhibits melanogenesis. Accordingly, this study aimed to treat B16F10 mouse melanoma cells with TQ to investigate its apparent effects and its molecular regulatory mechanisms. Treatment of the B16F10 cells with 10, 15 and 20 mu M of TQ for 48 h resulted in a dose-dependent decrease in the expression of microphthalmia-associated transcription factor (MITF), tyrosinase expression and tyrosinase activity, and these treatments simultaneously led to a decrease in the protein expression and transcription of beta -catenin, a Wnt signaling pathway protein. Pre-treatment of the cells with the proteasome inhibitor, MG132, to confirm the inhibition of melanogenesis through the beta -catenin pathway by TQ treatment resulted in an increase in the expression of beta -catenin that was initially reduced by TQ, and the expression and activity of MITF and tyrosinase also increased. Pre-treatment with LiCl, which is known to inactivate glycogen synthase kinase 3 beta (GSK3 beta) by inducing the phosphorylation of the Ser-9 site, resulted in an increased phospho-GSK3 beta expression accompanied by beta -catenin that was initially reduced by TQ, and the recovery of the expression and activity of tyrosinase was also confirmed. The transfection of S37A cDNA into B16F10 cells that overexpress beta -catenin resulted in the recovery of beta -catenin expression that was initially reduced by TQ, and this treatment also recovered the expression and activity of tyrosinase. When zebrafish eggs were treated with 1, 2.5 and 5 mu M of TQ at 10 h following fertilization, their melanin content decreased in a dose-dependent manner. On the whole, these findings demonstrated that the inhibition of melanogenesis in B16F10 mouse melanoma cells by TQ treatment resulted from the inhibition of the beta -catenin pathway and confirmed that TQ treatment inhibited melanogenesis in zebrafish.