It has been reported that the melanogenic activity can be inhibited by antioxidants, like a-tocopherol and hydrocoumarins, 1) and that reduced glutathione (GSH), an important biological reductant, plays a role in the modulation of the melanogenic process.
2)Melanogenesis, which is catalyzed enzymatically by the key enzyme, tyrosinase, is also influenced by other non-enzymatic factors such as ultraviolet rays and a-melanocytestimulating hormone (a-MSH).3) In the case of a-MSH-induced melanogenesis, the enhancement of tyrosinase activity, tyrosinase mRNA, and intracellular cyclic AMP (cAMP) were observed.
4)The requirement of cAMP for melanogenesis is quite clear for pigmentation. cAMP also increases tyrosinase mRNA and promotes increased microphthalmia transcription factor (MITF) expression. MITF is a melanocyte-specific transcription factor crucial for melanocyte survival, development and differentiation through the activation of protein kinase A (PKA).5) PKA is a serine/threonine kinase that is an inactive tetramer consisting of two regulatory subunits and two catalytic subunits, and its activation occurs by the binding of cAMP to its regulatory subunits and then releasing its catalytic subunits from the regulatory subunits.
6)Recently, we reported that 4,4Ј-dihydroxybiphenyl (44Ј-BP) has a melanogenesis inhibitory effect through the inhibition of tyrosinase and reduction of melanin content.7) However, the underlying process by which tyrosinase activity and melanogenesis were inhibited by 44Ј-BP was not elucidated. In this current study, we attempted to investigate the effect of 44Ј-BP on major cellular regulators involved in melanogenesis in B16 melanoma cells (B16 cells). The analysis was carried out by quantifying amounts of tyrosinase and MITF proteins, cAMP levels, phosphorylated PKA, and GSH and oxidized glutathione (GSSG) levels. Cell Culture System B16 cells (from Korean Cell Line Bank) were cultured in DMEM with 10% fetal bovine serum (FBS; Gibco) and penicillin/streptomycin (100 IU/50 mg/ml) in a humidified atmosphere containing 5% CO 2 in air at 37°C. B16 cells were cultured in 24-well plates for each assay.
MATERIALS AND METHODS
MaterialsAll the experiments were determined in triplicate and repeated three times to ensure reproducibility.GSH and GSSG Assay Assays for GSH and GSSG were carried out by the method of Pandey and Katiyar.
8)Twenty-five percent of the meta-phosphoric acid-added cell pellets were centrifuged at 12000 rpm for 10 min, and the supernatant was taken for assay. For GSH, 1 mM EDTA-50 mM phosphate buffer was added to the supernatant followed by ophthaladehyde. After 20 min at room temperature, the fluorescence was measured at excitation wavelength of 360 nm and emission wavelength of 460 nm. GSSG was assayed after preincubated with N-ethylmaleimide for 20 min and 0.1 M NaOH was substituted for 1 mM EDTA-50 mM phosphate buffer.Quantitation of cAMP To measure intracellular cAMP levels, an enzyme immunoassay kit was used. In brief, B16 cells (7ϫ10 4 ) were lyzed in 0.1 M of HCl to inh...