Human CYP2A6 is responsible for the metabolism of nicotine and coumarin as well as the metabolic activation of tobacco-related nitrosamines. Earlier studies revealed that CYP2A6 activity was increased by dietary cadmium or cruciferous vegetables, but the underlying mechanisms remain to be clarified. In the present study, we investigated the possibility that Nrf2 might be involved in the regulation of CYP2A6. Real-time RT-PCR analysis revealed that the CYP2A6 mRNA level in human hepatocytes was significantly (P<0.01, 1.4-fold) induced by 10μM sulforaphane (SFN), a typical activator of Nrf2. A computer-based search identified three putative antioxidant response elements (AREs) in the 5'-flanking region of the CYP2A6 gene at positions -1212, -2444, and -3441, termed ARE1, ARE2, and ARE3, respectively. Electrophoretic mobility shift assays demonstrated that Nrf2 bound only to ARE1. Luciferase assays using HepG2 cells revealed that the overexpression of Nrf2 significantly increased the reporter activities of the constructs containing a 30-bp fragment that included ARE1. However, the activity of the construct containing the intact 5'-flanking region (-1 to -1395) including ARE1 was not increased by the overexpression of Nrf2. In contrast, when the reporter construct was injected into mice via the tail vein, the reporter activity in the liver was significantly (P<0.05, 1.9-fold) increased by SFN (1mg/head) administration. In conclusion, we found that human CYP2A6 is regulated via Nrf2, suggesting that CYP2A6 is induced under oxidative stress.
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