Isosakuranetin, a 4′-O-methylated flavonoid, stimulates melanogenesis in B16BL6 murine melanoma cells

AimsThe beneficial effects of 4′-O-methylated flavonoids on induction of melanogenesis are well established. Here, we report the effect of isosakuranetin (Iso) on melanogenesis in B16BL6 melanoma cells and an analysis of the signaling pathways involved in this activity.MethodsB16BL6 melanoma cells were treated with several concentrations of Iso and melanin content was measured. Activation and expression of factors involved in melanogenesis were assessed via western blotting.Key findingsIso (15 and 30 μmol/L) strongly stimulated melanogenesis in a dose-dependent manner. Iso increased tyrosinase activity and up-regulated tyrosinase (Tyr), tyrosinase related protein 1 (TRP1), and tyrosinase related protein 2 (TRP2) in a time-dependent manner. Iso decreased B16 cell proliferation at a concentration above 45 μmol/L, and had no effect on cell viability as revealed by MTT and trypan blue assays. Iso up-regulated expression of microphthalmia transcription factor (MITF), with a maximum effect after 12 h. H89, a specific inhibitor of PKA, showed that MITF up-regulation is mediated through PKA/CREB activation. Furthermore, Iso decreased phosphorylation of MITF at Ser73 after 24 h and 48 h of exposure, activating MITF and leading to up-regulation of Tyr, TRP1, and TRP2. Iso inhibited phosphorylation and activation of ERK1/2 after 12 h, while no significant effects on p38 and JNK phosphorylation were observed. Iso inhibited AKT phosphorylation and led to activation of GSK3β.SignificanceIso stimulates melanogenesis in B16 melanoma cells via up-regulation of MITF. Furthermore, Iso-induced inhibition of ERK1/2 and PI3K/AKT signaling pathways activate MITF and subsequent expression of Tyr, TRP1, and TRP2.

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