dna repair 7 ( 2 0 0 8 ) 1352–1363 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/dnarepair Promoter methylation of O 6 -methylguanine-DNA- methyltransferase in lung cancer is regulated by p53 Ji-Ching Lai a , Ya-Wen Cheng b,d , Yih-Gang Goan f,g,h , Jinghua Tsai Chang a , Tzu-Chin Wu c,d , Chih-Yi Chen e , Huei Lee a,d,* a Institute of Medical & Molecular Toxicology, Chung Shan Medical University, Taichung, Taiwan, ROC b Institute of Medicine, Chung Shan Medical University, Taichung, Taiwan, ROC c Department of Internal Medicine, Chung Shan Medical University, Taichung, Taiwan, ROC d Lung Cancer Research Center, Chung Shan Medical University, Taichung, Taiwan, ROC e Department of Surgery, China Medical University, Taichung, Taiwan, ROC f Department of Surgery, Kaohsiung Veterans General Hospital, Taiwan, ROC g Department of Surgery, National Yang-Ming University, Taipei, Taiwan, ROC h Department of Biological Sciences, National Sun Yat-Sen University, Kaohsiung, Taiwan, ROC article info Article history: Received 28 January 2008 Received in revised form 30 April 2008 Accepted 30 April 2008 Published on line 13 June 2008 Keywords: Promoter methylation O 6 -Methylguanine-DNA- methyltransferase p53 Mutation Lung cancer abstract Methylation of the O 6 -methylguanine-DNA-methyltransferase (MGMT) promoter is asso- ciated with G:C to A:T transitions in the p53 gene in various human cancers, including lung cancer. In tumors with p53 mutation, MGMT promoter methylation is more common in advanced tumors than in early tumors. However, in tumors with wild-type p53, MGMT promoter methylation is independent of tumor stage. To elucidate whether p53 partici- pates in MGMT promoter methylation, we engineered three cell models: A549 cells with RNA interference (RNAi)-mediated knockdown of p53, and p53 null H1299 cells transfected with either wild-type p53 (WT-p53) or mutant-p53 (L194R, and R249S-p53). Knockdown of endogenous p53 increased MGMT promoter methylation in A549 cells, and transient expres- sion of WT-p53 in p53 null H1299 cells diminished MGMT promoter methylation, whereas the MGMT promoter methylation status were unchanged by expression of mutant-p53. Pre- vious work showed that p53 modulates DNA-methyltransferase 1 (DNMT1) expression; we additionally examined chromatin remodeling proteins expression levels of histone deacety- lase 1 (HDAC1). We found that p53 knockdown elevated expression of both DNMT1 and HDAC1 in A549 cells. Conversely, expressing WT-p53 in p53 null H1299 cells reduced DNMT1 and HDAC1 expression, but the reduction of both proteins was not observed in expressing mutant-p53 H1299 cells. CHIP analysis further showed that DNMT1 and HDAC1 binding to the MGMT promoter was increased by MGMT promoter methylation and decreased by MGMT promoter demethylation. In conclusion, MGMT promoter methylation modu- lated by p53 status could partially promote p53 mutation occurrence in advanced lung tumors. © 2008 Elsevier B.V. All rights reserved. ∗ Corresponding author at: Institute of Medical & Molecular Toxicology, Chung Shan Medical University, No. 110, Sec. 1, Chien-Kuo N. Road, Taichung, Taiwan. Tel.: +886 4 24759400; fax: +886 4 24720407. E-mail address: hl@csmu.edu.tw (H. Lee). 1568-7864/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.dnarep.2008.04.016