title: Epigenetic inactivation of the dioxin-responsive cytochrome P4501A1 gene in human prostate cancer.
abstract: 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD; dioxin) is a toxic environmental contaminant that works through dioxin response elements (DRE) to activate gene expression. We tested the hypothesis that cancer-related epigenetic changes suppress dioxin activation of the cytochrome P4501A1 (CYP1A1) gene. 5-Aza-2'-deoxycytidine (5-aza-CdR), an inhibitor of DNA methylation, increases TCDD-inducible CYP1A1 mRNA expression in cancerous LNCaP cells but not in noncancerous PWR-1E and RWPE-1 cells (all human prostate cell lines). Bisulfite DNA sequencing shows that the TCDD-responsive CYP1A1 enhancer is highly methylated in LNCaP cells but not in RWPE-1 cells. In vivo footprinting experiments reveal that unmethylated DRE sites do not bind protein in response to TCDD in LNCaP cells, whereas inducible DRE occupancy occurs in RWPE-1 cells. Pretreatment of LNCaP cells with 5-aza-CdR partially restores TCDD-inducible DRE occupancy, showing that DNA methylation indirectly suppresses DRE occupancy. Chromatin immunoprecipitation experiments reveal that LNCaP cells lack trimethyl histone H3 lysine 4, a mark of active genes, on the CYP1A1 regulatory region, whereas this histone modification is prevalent in PWR-1E and RWPE-1 cells. We also analyzed CYP1A1 enhancer methylation in human prostate tissue DNA. We do not detect CYP1A1 enhancer methylation in 30 DNA samples isolated from noncancerous prostate tissue. In contrast, 11 of 30 prostate tumor DNA samples have detectable CYP1A1 enhancer methylation, indicating that it is hypermethylated in prostate tumors. This is the first report that shows that CYP1A1 is aberrantly hypermethylated in human prostate cancer and has an altered, inaccessible chromatin structure that suppresses its dioxin responsiveness.
authors.affiliation: Department of Urology, San Francisco Veterans Affairs Medical Center 4150 Clement Street, San Francisco, CA 94121, USA. steveokino@gmail.com
authors.forename: Steven T
authors.initials: ST
authors.lastname: Okino
authors.forename: Deepa
authors.initials: D
authors.lastname: Pookot
authors.forename: Long-Cheng
authors.initials: LC
authors.lastname: Li
authors.forename: Hong
authors.initials: H
authors.lastname: Zhao
authors.forename: Shinji
authors.initials: S
authors.lastname: Urakami
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Shiina
authors.forename: Mikio
authors.initials: M
authors.lastname: Igawa
authors.forename: Rajvir
authors.initials: R
authors.lastname: Dahiya
mesh_terms: D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D002843:Chromatin / Q000187:drug effects / Q000378:metabolism; D018899:CpG Islands; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis / Q000235:genetics*; D019175:DNA Methylation / Q000187:drug effects; D004273:DNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D000077209:Decitabine; D004147:Dioxins / Q000494:pharmacology*; D004742:Enhancer Elements, Genetic; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000201:enzymology* / Q000235:genetics*; D020218:Response Elements
chemical_list: D002843:Chromatin; D004273:DNA, Neoplasm; D004147:Dioxins; D000077209:Decitabine; D019363:Cytochrome P-450 CYP1A1; D001374:Azacitidine