title: Reversal and prevention of arsenic-induced human bronchial epithelial cell malignant transformation by microRNA-200b.
abstract: Arsenic is a well-recognized human carcinogen, yet the mechanism by which it causes human cancer has not been elucidated. MicroRNAs (miRNAs) are a big family of small noncoding RNAs and negatively regulate the expression of a large number of protein-coding genes. We investigated the role of miRNAs in arsenic-induced human bronchial epithelial cell malignant transformation and tumor formation. We found that prolonged exposure of immortalized p53-knocked down human bronchial epithelial cells (p53(low)HBECs) to low levels of arsenite (NaAsO₂, 2.5 μM) caused malignant transformation that was accompanied by epithelial to mesenchymal transition (EMT) and reduction in the levels of miR-200 family members. Stably reexpressing miR-200b in arsenite-transformed cells (As-p53(low)HBECs) completely reversed their transformed phenotypes, as evidenced by inhibition of colony formation in soft agar and prevention of xenograft tumor formation in nude mice. Moreover, stably expressing miR-200b alone in parental nontransformed p53(low)HBECs was sufficient to completely prevent arsenite exposure from inducing EMT and malignant transformation. Further mechanistic studies showed that depletion of miR-200 in arsenite-transformed cells involved induction of the EMT-inducing transcription factors zinc-finger E-box-binding homeobox factor 1 (ZEB1) and ZEB2 and increased methylation of miR-200 promoters. Stably expressing ZEB1 alone in parental nontransformed p53(low)HBECs was sufficient to deplete miR-200, induce EMT and cause cell transformation, phenocopying the oncogenic effect of 16-week arsenite exposure. These findings establish for the first time a causal role for depletion of miR-200b expression in human cell malignant transformation and tumor formation resulting from arsenic exposure.
authors.affiliation: Department of Physiology, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Zhishan
authors.initials: Z
authors.lastname: Wang
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhao
authors.forename: Eric
authors.initials: E
authors.lastname: Smith
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Goodall
authors.forename: Paul A
authors.initials: PA
authors.lastname: Drew
authors.forename: Thomas
authors.initials: T
authors.lastname: Brabletz
authors.forename: Chengfeng
authors.initials: C
authors.lastname: Yang
mesh_terms: D000818:Animals; D001151:Arsenic / Q000633:toxicity*; D001483:Base Sequence; D001980:Bronchi / Q000187:drug effects* / Q000473:pathology; D002471:Cell Transformation, Neoplastic; D019175:DNA Methylation; D017931:DNA Primers; D004847:Epithelial Cells / Q000187:drug effects / Q000473:pathology; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D035683:MicroRNAs / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; D035683:MicroRNAs; D001151:Arsenic