The CNC-family transcription factor Nrf3 coordinates the melanogenesis cascade through macropinocytosis and autophagy regulation.

Melanin is a pigment produced from the amino acid L-tyrosine in melanosomes. The CNC-family transcription factor Nrf3 is expressed in the basal layer of the epidermis, where melanocytes reside, but its melanogenic function is unclear. Here, we show that Nrf3 regulates macropinocytosis and autophagy to coordinate melanogenesis cascade. In response to an exogenous inducer of melanin production, forskolin, Nrf3 upregulates the core melanogenic gene circuit, which includes Mitf, Tyr, Tyrp1, Pmel, and Oca2. Furthermore, Nrf3 induces the gene expression of Cln3, an autophagosome-related factor, for melanin precursor uptake by macropinocytosis. Ulk2 and Gabarapl2 are also identified as Nrf3-target autophagosome-related genes for melanosome formation. In parallel, Nrf3 prompts autolysosomal melanosome degradation for melanocyte survival. An endogenous melanogenic inducer αMSH also activates Nrf3-mediated melanin production, whereas it is suppressed by an HIV-1 protease inhibitor, nelfinavir. These findings indicate the significant role of Nrf3 in the melanogenesis and the anti-melanogenic potential of nelfinavir.

Aryl hydrocarbon receptor activation and CYP1A induction by cooked food-derived carcinogenic heterocyclic amines in human HepG2 cell lines.

The ability of nine cooked food-derived heterocyclic aromatic amines (HCAs), such as 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-amino-6-methylpyrido[12-a:3',2'-d]imidazole (Glu-P-1), 2-amino-pyrido[12-a:3',2'-d]imidazole hydrochloride (Glu-P-2), 2-amino-9H-pyrido[2,3-b]indole (AαC), 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeAαC), 2-amino-3-methylimidazo[4,5-f]quinolone (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenyl-1H-imidazo[4,5-b]pyridine (PhIP), to activate human aryl hydrocarbon receptor (hAhR) was examined using a HepG2-A10 cell line, which has previously established from human hepatocarcinoma-derived HepG2 cells for use in hAhR-based luciferase reporter gene assays. Trp-P-1, Trp-P-2, AαC, MeAαC, IQ and MeIQx showed a definite ability to induce not only luciferase (hAhR activation) in HepG2-A10 cells but also cytochrome P450 (CYP)1A1/1A2 mRNAs in HepG2 cells, while such the ability of Glu-P-1, Glu-P-2, and PhIP was very low. In addition, all the HCAs examined, especially MeAαC and MeIQx, had a definite capacity for inhibiting the activity of ethoxyresorfin O-deethylase (CYP1As, especially CYP1A1). The present findings demonstrate that all the HCAs examined have the ability to activate hAhR and its target genes, and further confirm that these HCAs become good substrates for human CYP1A subfamily enzyme(s).