title: Dual inhibition of γ-oryzanol on cellular melanogenesis: inhibition of tyrosinase activity and reduction of melanogenic gene expression by a protein kinase A-dependent mechanism.
abstract: The in vitro effects on melanogenesis of γ-oryzanol (1), a rice bran-derived phytosterol, were investigated. The melanin content in B16F1 cells was significantly and dose-dependently reduced (-13% and -28% at 3 and 30 μM, respectively). Tyrosinase enzyme activity was inhibited by 1 both in a cell-free assay and when analyzed based on the measurement of cellular tyrosinase activity. Transcriptome analysis was performed to investigate the biological pathways altered by 1, and it was found that gene expression involving protein kinase A (PKA) signaling was markedly altered. Subsequent analyses revealed that 1 stimulation in B16 cells reduced cytosolic cAMP concentrations, PKA activity (-13% for cAMP levels and -40% for PKA activity), and phosphorylation of the cAMP-response element binding protein (-57%), which, in turn, downregulated the expression of microphthalmia-associated transcription factor (MITF; -59% for mRNA and -64% for protein), a key melanogenic gene transcription factor. Accordingly, tyrosinase-related protein 1 (TRP-1; -69% for mRNA and -82% for protein) and dopachrome tautomerase (-51% for mRNA and -92% for protein) in 1-stimulated B16F1 cells were also downregulated. These results suggest that 1 has dual inhibitory activities for cellular melanogenesis by inhibiting tyrosinase enzyme activity and reducing MITF and target genes in the PKA-dependent pathway.
authors.affiliation: Division of Food Bioscience and Technology, College of Life Sciences and Biotechnology, Korea University, Seoul 136-713, Republic of Korea.
authors.forename: Hee-jin
authors.initials: HJ
authors.lastname: Jun
authors.forename: Ji Hae
authors.initials: JH
authors.lastname: Lee
authors.forename: Bo-Ram
authors.initials: BR
authors.lastname: Cho
authors.forename: Woo-Duck
authors.initials: WD
authors.lastname: Seo
authors.forename: Hang-Won
authors.initials: HW
authors.lastname: Kang
authors.forename: Dong-Woo
authors.initials: DW
authors.lastname: Kim
authors.forename: Kang-Jin
authors.initials: KJ
authors.lastname: Cho
authors.forename: Sung-Joon
authors.initials: SJ
authors.lastname: Lee
mesh_terms: D000242:Cyclic AMP / Q000032:analysis / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D019746:Intramolecular Oxidoreductases / Q000235:genetics; D008543:Melanins / Q000235:genetics* / Q000378:metabolism; D015394:Molecular Structure; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012275:Oryza / Q000737:chemistry* / Q000235:genetics; D010666:Phenylpropionates / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D008543:Melanins; D010666:Phenylpropionates; D000242:Cyclic AMP; D014442:Monophenol Monooxygenase; D017868:Cyclic AMP-Dependent Protein Kinases; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase; C013172:gamma-oryzanol