Abstract 1994: Tobacco carcinogen-induced transformation of HBECs is associated with chromatin-mediated reprogramming of the epigenome

An in vitro model, hTERT/cdk4, immortalized human bronchial epithelial cells (HBECs), was used to identify key molecular changes driving cell transformation and the clonal outgrowth of preneoplastic lung epithelial cells. Low-dose weekly treatment (12 weeks) of HBECs with genotoxic, but not cytotoxic doses of the carcinogens methylnitrosourea (MNU), benzo(a)pyrene-diolepoxide 1 (BPDE), or both induced transformation. Transformation efficiency (0.2-3%) differed between HBECs and was associated with DNA repair capacity, increased levels of DNMT1 protein, promoter hypermethylation, EMT, and stem-like cell phenotype. Agilent 44K arrays were used to determine genome-wide changes in gene expression associated with transformation. Comparison of expression between HBEC1 and HBEC2 to cells transformed by BPDE, MNU, or the combination revealed 287-321 and 320-493 genes with increased or decreased (≥ 3-fold change) expression. Approximately 214 and 331 of the genes with decreased expression in HBEC1 and HBEC2 had CpG islands that extended through their transcriptional start site. HBEC2 MNU/BPDE transformed cells were treated with DAC or TSA to assess globally whether chromatin remodeling alone, or in combination with DNA methylation mediated gene silencing. Only 128 of 331 silenced genes in HBEC2 MNU/BPDE transformed cells responded to DAC alone. Promoter methylation arrays and genome-wide ChIP-chip for inactive chromatin marks were used to elucidate mechanisms of global gene silencing in HBEC2 MNU/BPDE transformed cells. Array analysis revealed 216 genes with reduced expression are enriched for H3K27me3 and 23 novel genes with reduced expression are hypermethylated in HBEC2 MNU/BPDE transformed cells. Our in vitro model suggests that the re-programming of the epigenome during carcinogen-induced transformation is initially mediated by chromatin remodeling with ensuing DNA methylation sustaining gene silencing. The authors’ work is supported by a research grant from National Institutes of Health (R01 ES008801). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1994. doi:10.1158/1538-7445.AM2011-1994