Tobacco smoke induces polyeomb-mediated repression of Dickkopf-1 in lung cancer cells

Mustafa Hussain, Mahadev Rao, Ashley E. Humphries, Julie A. Hong, Fang Liu, Maocheng Yang, Diana Caragacianu, David S. Sehrump

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Limited information is available about epigenetic mechanisms by which cigarette smoke enhances the initiation and progression of lung cancer. To examine this issue, A549 and Calu-6 lung cancer cells were cultured in normal media with or without tobacco smoke condensate (TSC) under clinically relevant exposure conditions. Ten-day TSC exposure dramatically increased the tumorigenicity of lung cancer cells in nude mice. Microarray and quantitative reverse transcription-PCR (RT-PCR) experiments revealed that this phenomenon coincided with diminished expression of Dickkopf-1 (Dkk-1). Western blot, chromatin immunoprecipitation, methylation-specific PCR, and pyrosequencing experiments showed that repression of Dkk-1 coincided with decreased H4K16Ac, increased H3K27me3, and recruitment of SirTl, EZH2, SUZ12, and Bmil without DNA hypermethylation within the Dkk-1 promoter despite prolonged TSC exposures. Removal of TSC from culture media resulted in loss of promoter-associated polycomb repressor complexes and reexpression of Dkk-1. siRNA-mediated knockdown of EZH2 and SirT1 partially abrogated TSC-mediated inhibition of Dkk-1 expression. Western blot and quantitative RT-PCR array experiments showed that TSC exposure as well as knockdown of Dkk-1 activated Wnt signaling and significantly up-regulated Wnt5a in lung cancer cells. Knockdown of Dkk-1 recapitulated the dramatic protumorigenic effects of TSC exposure in Calu-6 cells. Despite the transient nature of Dkk-1 repression following TSC exposure in vitro, Dkk-1 remained silenced in tumor xenografts derived from TSC-treated Calu-6 cells. Collectively, these data provide evidence that cigarette smoke directly engages polycomb machinery to activate a signaling network implicated in maintenance of cancer stem cells.

Original languageEnglish
Pages (from-to)3570-3578
Number of pages9
JournalCancer Research
Issue number8
Publication statusPublished - 15-04-2009

All Science Journal Classification (ASJC) codes

  • Medicine(all)
  • Oncology
  • Cancer Research

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    Hussain, M., Rao, M., Humphries, A. E., Hong, J. A., Liu, F., Yang, M., Caragacianu, D., & Sehrump, D. S. (2009). Tobacco smoke induces polyeomb-mediated repression of Dickkopf-1 in lung cancer cells. Cancer Research, 69(8), 3570-3578.