Coptis chinensis inhibits melanogenesis increasing miR-340-mediated suppression of microphathalmia-associated transcription factor

Background: Coptis chinensis (C. chinensis) contains various antioxidants, including berberine, epiberberlin, ferulic acid, magnoflorine, palmatine, and worenine, which have antibacterial, anti-inflammatory, haemostatic, hypotensive, and anticancer effects. In the present study, the melanogenesis-inhibiting effects of C. chinensis were investigated and the molecular mechanisms were elucidated. Methods: The melanogenesis-inhibiting effect of C. chinensis was verified by measuring melanin contents, melanogenesisrelated tyrosinase activities, and mRNA and protein expression levels of tyrosinase and microphthalmia-associated transcription factor (MITF). In addition, changes in miR-340 expression by C. chinensis were verified, and the activity of the miR-340 binding site of the target MITF gene was determined using luciferase reporter assays. Results: Assays of melanin contents showed that C. chinensis had a skin-whitening effect and controlled mRNA and protein expression levels of tyrosinase. However, C. chinensis controlled protein levels of MITF without affecting mRNA levels. Determinations of miR-340 expression, which directly influences MITF translation, showed increased miR-340 mRNA levels in the presence of C. chinensis. Finally, luciferase reporter assays of the binding site on MITF showed that C. chinensis inhibits melanogenesis by directly controlling the miR-340–MITF axis. Conclusions: The results of the present study verified the skin-whitening effect of C. chinensis and its molecular mechanisms and indicated that C. chinensis has high potential as an ingredient in skin-whitening cosmetics.