title: Long-term low-dose exposure of human urothelial cells to sodium arsenite activates lipocalin-2 via promoter hypomethylation.
abstract: We previously reported that the sustained exposure of human urothelial cells (HUCs) to low-dose sodium arsenite induces changes in the gene expression profile and neoplastic transformation. In this study, we used the HumanMethylation27 BeadChip to analyze genome-wide methylation profiles and 5-aza-2'-deoxycytidine to examine the involvement of promoter methylation in gene expression. Because the expression of lipocalin-2 (LCN2) was highly enhanced by promoter hypomethylation in inorganic arsenic (iAs)-HUCs cells as well as bladder cancer tissues, we further showed that mutations at the binding sequences for NF-κB and C/EBP-α significantly reduced LCN2 promoter activity. By chromatin immunoprecipitation assay, we demonstrated the significantly increased binding of RelA (p65) and NF-κB1 (p50) to the hypomethylated promoter of LCN2 in the iAs-HUCs. Furthermore, we also demonstrated that LCN2 overexpression was crucial for the neoplastic characteristics of the iAs-HUCs, such as enhanced anchorage-independent growth, resistance to serum deprivation and activation of NF-κB signaling. In addition, our results indicated that enhanced NF-κB activity in iAs-HUCs was via LCN2-mediated increase in intracellular iron and reactive oxygen species levels. Taken together, our results show that sustained low-dose arsenic exposure results in epigenetic changes and enhanced oncogenic potential via LCN2 overexpression.
authors.affiliation: Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan.
authors.forename: Hsiu-Hua
authors.initials: HH
authors.lastname: Wang
authors.forename: Meei-Maan
authors.initials: MM
authors.lastname: Wu
authors.forename: Michael W Y
authors.initials: MW
authors.lastname: Chan
authors.forename: Yeong-Shiau
authors.initials: YS
authors.lastname: Pu
authors.forename: Chien-Jen
authors.initials: CJ
authors.lastname: Chen
authors.forename: Te-Chang
authors.initials: TC
authors.lastname: Lee
mesh_terms: D000209:Acute-Phase Proteins / Q000235:genetics*; D018053:Arsenites / Q000633:toxicity*; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D018929:Cell Culture Techniques; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D047369:Chromatin Immunoprecipitation; D016895:Culture Media, Serum-Free; D019175:DNA Methylation / Q000187:drug effects / Q000235:genetics; D000077209:Decitabine; D004305:Dose-Response Relationship, Drug; D004785:Environmental Pollutants / Q000633:toxicity*; D020868:Gene Silencing; D055106:Genome-Wide Association Study; D006801:Humans; D000071068:Lipocalin-2; D054834:Lipocalins / Q000235:genetics*; D016297:Mutagenesis, Site-Directed; D016328:NF-kappa B / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D017670:Sodium Compounds / Q000633:toxicity*; D013997:Time Factors; D001749:Urinary Bladder Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D019459:Urothelium / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism
chemical_list: D000209:Acute-Phase Proteins; D018053:Arsenites; D016895:Culture Media, Serum-Free; D004785:Environmental Pollutants; C489506:LCN2 protein, human; D000071068:Lipocalin-2; D054834:Lipocalins; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D017670:Sodium Compounds; C017947:sodium arsenite; D000077209:Decitabine; D001374:Azacitidine