Though smoking remains one of the established risk factors of
esophageal squamous cell carcinoma, there is limited data on molecular alterations associated with cigarette
smoke exposure in esophageal cells. To investigate molecular alterations associated with chronic exposure to cigarette
smoke, non-neoplastic human esophageal epithelial cells were treated with cigarette
smoke condensate (CSC) for up to 8 months. Chronic treatment with CSC increased cell proliferation and invasive ability of non-neoplastic esophageal cells. Whole exome sequence analysis of CSC treated cells revealed several mutations and copy number variations. This included loss of high mobility group nucleosomal binding domain 2 (
HMGN2) and a missense variant in
mediator complex subunit 1 (MED1). Both these genes play an important role in DNA repair. Global proteomic and phosphoproteomic profiling of CSC treated cells lead to the identification of 38 differentially expressed and 171 differentially phosphorylated
proteins. Bioinformatics analysis of differentially expressed
proteins and
phosphoproteins revealed that most of these
proteins are associated with DNA damage response pathway. Proteomics data revealed decreased expression of
HMGN2 and hypophosphorylation of MED1. Exogenous expression of
HMGN2 and MED1 lead to decreased proliferative and invasive ability of
smoke exposed cells. Immunohistochemical labeling of
HMGN2 in primary ESCC
tumor tissue sections (from smokers) showed no detectable expression while strong to moderate staining of
HMGN2 was observed in normal esophageal tissues. Our data suggests that cigarette
smoke perturbs expression of
proteins associated with DNA damage response pathways which might play a vital role in development of ESCC.