Modulation of annexin I and cyclooxygenase-2 in smokeless tobacco-induced inflammation and oral cancer
Smokeless tobacco usage is a growing public health concern in the United States. Epidemiological evidence shows a correlation between use of chewing tobacco, lesions of the oral cavity and the incidence of oral and other cancers. However, the molecular mechanism(s) underlying the oral cancer causation are yet unknown. The major constituents of tobacco are known to cause inflammation, DNA damage and cell death. We propose modulation of inflammatory mediators by smokeless tobacco as a novel mechanism for the development of oral cancer. Exposure of hamster cheek pouches to smokeless tobacco extract (STE) results in cleavage of the anti-inflammatory peptide from the anti-inflammatory protein annexin I. Annexin I is produced from cultured oral epithelial cells and its expression is modulated by STE. We further show that STE exposure of oral epithelial cells results in upregulation of the pro-inflammatory protein COX-2. COX-2 is also upregulated in immortalized human oral epithelial cells, human squamous cell carcinoma cells and in primary tumor tissues from head and neck cancer. In summary, we find that exposure to smokeless tobacco results in loss of the anti-inflammatory activity of annexin I and upregulation of the pro-inflammatory COX-2 in oral cells. The dual effect of these regulatory events leads the cells down the carcinogenic pathway.
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