Delineating mechanisms of tobacco induced cellular transformation using an integrated approach

H Gowda

Institute of Bioinformatics, Bangalore, India

Tobacco in its smoking as well as chewing form is known to be a risk factor for a number of cancers. A causal relationship has been established between smoking and cancers of different tissues including lung, oral cavity, esophagus, bladder and pancreas. Mechanism by which cigarette smoke causes cancer is extensively studied and is attributed to several carcinogenic compounds that exist in tobacco and some that are produced during combustion. These studies have been mainly carried out using acute treatment models. However, molecular mechanisms underlying chewing tobacco induced cellular transformation is not well understood. We have developed chronic treatment models by treating non-neoplastic esophageal and oral keratinocyte cell lines with condensed cigarette smoke and aqueous extract of tobacco over a period of 12 months. Both smoke treated and chewing tobacco treated cells acquired oncogenic phenotype in 6-8 months and showed increased proliferation and invasion capability. We carried out quantitative proteomic profiling to evaluate protein expression and phosphorylation pattern to systematically map molecular changes that are influenced by tobacco exposure. We observed distinct changes in cigarette smoke exposed and chewing tobacco exposed cell models. Proteins involved in DNA damage response pathways were found to be elevated in cigarette smoke treated cells. This is in agreement with previous studies where DNA damage has been reported to be one of the major ways in which cigarette smoke induces cellular transformation. On the contrary, chewing tobacco treated cells showed increased expression of proteins involved in β-oxidation, TCA cycle and oxidative phosphorylation and decreased expression of proteins involved in glycolysis. This metabolic reprogramming was further evaluated by mass spectrometry based metabolomics studies. Chewing tobacco treated cells also showed elevated expression of cancer stem cell markers. Our studies provide detailed insights into mechanisms that are associated with tobacco induced cellular transformation. These insights would be valuable to identify biomarkers relevant for risk assessment and to develop therapeutic intervention strategies for cancers associated with tobacco usage.