title: Promoter demethylation of nuclear factor-erythroid 2-related factor 2 gene in drug-resistant colon cancer cells.
abstract: The mechanisms underlying drug resistance in colorectal cancer (CRC) treatment remain to be fully elucidated. Therefore, the present study aimed to investigate the underlying mechanism resistance to a widely used anticancer drug, 5-Fluorouracil (5-FU). Nuclear factor-erythroid 2-related factor 2 (Nrf2) is an important transcription factor involved in cellular protection. In the present study, it was hypothesized that the epigenetic modification of Nrf2 may be a potential target for 5-FU resistance in CRC treatment. Protein and messenger RNA levels of Nrf2, heme oxygenase-1 (HO-1), DNA methylases and DNA methyltransferases were determined and DNA methylation analysis for the Nrf2 promoter was performed in a human CRC control (SNU-C5) and resistant (SNU-C5R) cell line. The results demonstrated that Nrf2 expression levels, nuclear translocation and promoter binding were significantly increased in SNU-C5R cells compared with SNU-C5 cells. Elevated levels of activated Nrf2 in SNU-C5R cells resulted in the increased protein expression and activity of HO-1. In addition, increased production of reactive oxygen species (ROS) and upregulation of ten-eleven translocation (TET)1 were observed in SNU-C5R cells compared with SNU-C5 cells. Furthermore, methylation analysis revealed Nrf2 promoter cytosine-phosphate-guanine island hypomethylation in 5-FU-treated cells. In conclusion, the results indicated that 5-FU-induced ROS production resulted in the upregulation of TET1 expression and function. In addition, these results indicated that TET-dependent demethylation of the Nrf2 promoter upregulated Nrf2 and HO-1 expression, which induced cellular protection mechanisms, ultimately leading to drug resistance.
authors.affiliation: Department of Digestive Diseases, Shandong Provincial Hospital Affiliated to Shandong University, Jinan, Shandong 250021, P.R. China.
authors.forename: Xiao-Qian
authors.initials: XQ
authors.lastname: Zhao
authors.affiliation: Department of Gastrointestinal Surgery, Yantai Yuhuangding Hospital Affiliated to Medical College of Qingdao University, Yantai, Shandong 264000, P.R. China.
authors.forename: Yi-Fei
authors.initials: YF
authors.lastname: Zhang
authors.affiliation: Department of Medical Imaging, The Sixth People's Hospital of Jinan City, Jinan, Shandong 250200, P.R. China.
authors.forename: Yi-Fang
authors.initials: YF
authors.lastname: Xia
authors.affiliation: Department of Child Medicine, Taian Central Hospital, Taian, Shandong 271000, P.R. China.
authors.forename: Zhong-Mei
authors.initials: ZM
authors.lastname: Zhou
authors.affiliation: Department of Anorectal Surgery, Taian Central Hospital, Taian, Shandong 271000, P.R. China.
authors.forename: Ying-Qing
authors.initials: YQ
authors.lastname: Cao
keywords: 5-fluorouracil; SNU-C5 cells; colorectal cancer; cytosine-phosphate-guanine islands; epigenetics