Abstract A41: Regulation of Nrf2-dependent gene expression in aging

Abstract

Abstract Nrf2 is a transcription factor which controls induction of antioxidant and detoxification enzymes, and, therefore, plays an essential role in protection against chemical carcinogens. Here, we reported that expression of Nrf2 and its dependent genes was affected by age and became compromised in aged mouse livers. Detail analysis revealed that age-dependent Nrf2 expression was regulated primarily at transcriptional level. Accordingly, we cloned and characterized the promoter region of mouse Nrf2 gene. We identified multiple Sp1 binding sites and confirmed their binding activity by gel-shift and chromatin immunoprecipitation assay. We also showed that the identified Sp1 sites were functional since knockdown of Sp1 expression impaired Nrf2 promoter activity as well as expression of Nrf2-dependent genes. We then compared Sp1 expression and its binding activity to Nrf2 promoter in young and aged mouse liver tissues. While no significant change in Sp1 expression was found, Sp1 binding activity was severely impaired in aged tissues. Given that Sp1-binding sites are GC rich elements, we analyzed their methylation status in Nrf2 promoter, and found that Sp1 sites were highly methylated in aged tissues. In support of the role of methylation, treatment of a mouse hepatoma cell line with demethylase inhibitors indeed reduced Sp1 binding to Nrf2 promoter. We also cloned and analyzed human Nrf2 promoter. Multiple Sp1 binding sites were identified and shown to be equally functional as in mouse Nrf2 promoter. Thus, we propose that age-dependent expression of Nrf2 and its downstream genes is regulated by methylation. A strategy that targets methylation would help to restore Nrf2-mediated protection against oxidative stress or chemical carcinogens in aged tissues. Citation Information: Cancer Prev Res 2010;3(1 Suppl):A41.