Cpc attenuated α-MSH-stimulated melanogenesis and elevated the abundance of intracellular cAMP. Cells were pretreated with 20 nM α-MSH for 30 mins, and then treated with Cpc (0.05, 0.1, 0.2 mg/mL) for 72 hrs. (A) Tyrosinase activity (black) and melanin content (grey) were measured. (B) The expression of tyrosinase was determined by immunoblotting analysis (black) and RT-PCR (grey), using β-actin and GAPDH as internal standards, respectively. (C) The cAMP concentration was measured by enzyme immunoassay at assigned time intervals (10, 30, 60 min) after Cpc treatment. Data were expressed at mean ± SD from three different experiments. The asterisk (*) indicates a significant difference from control group (*, P < 0.05).