Exome-seq analysis of human bronchial epithelial cells (HBEC3KT) cells pre and post treatment with DMSO (Control) or 10 µg/ml cigarette smoke condensate (CSC) for 15 months and tumor xenografts obtained with 15 month CSC treated cells expressing KRASV12

We define how chronic cigarette smoke-induced time-dependent epigenetic alterations can sensitize human bronchial epithelial cells (HBEC) for transformation by a single oncogene. The smoke-induced, chromatin changes include initial repressive polycomb marking of genes later manifesting abnormal DNA methylation by 10 months. At this time, cells manifest epithelial to mesenchymal changes, anchorage-independent growth and upregulated RAS/MAPK signaling with silencing of hyper-methylated genes normally inhibiting these pathways and which are associated with smoking related NSCLC. These cells, in the absence of any driver gene mutations, now transform by introducing a single KRAS mutation and form adeno-squamous lung carcinomas in mice. Thus, epigenetic abnormalities may prime for changing oncogene senescence to addiction for a single key oncogene involved in lung cancer initiation. Overall design: HBEC cells treated with DMSO (Control) or 10 µg/ml CSC for 15 months. Xenografts were obtained by subcutaneously injecting 15 month CSC treated cells expressing KRASV12 in NSG mice.