Smokeless tobacco increases aneuploidy in oral HPV16 E6/E7-transformed keratinocytes in vitro

The scope of this work was to study synergism between human papillomavirus (HPV) infection and tobacco in vitro, both known to be independent risk factors for oral cancer.

HPV-positive and HPV-negative oral keratinocytes and oral HPV-negative fibroblasts were exposed to smokeless tobacco extract (STE) prepared from the Scandinavian (STE1) and US-type (STE2) snuff. Cell cycle profiles were determined with flow cytometry, and HPV E6/E7 mRNA expression in HPV-positive cells was assayed using RT-qPCR.

The exposure of HPV-positive keratinocytes with STE2 increased the number of aneuploid cells from 27% to 80% of which 44% were in S-phase, while none of the diploid cells were in S-phase. The changes after STE1 exposure were less than seen after STE2: from 27% to 31% of which 34% were in S-phase. STE had no effect on HPV16 E6/E7 expression in HPV-positive keratinocytes. In oral spontaneously transformed, HPV-negative keratinocytes, the number of aneuploid cells at G2-M stage increased after STE1 and STE2 exposure from 3% to 9% and 7%, respectively. In HPV-negative oral fibroblasts, the number of cells at G2-M phase increased from 11% to 21% after STE1 and 29% after STE2 exposure.

The effect of STE varied in the cell lines studied. STE2 increased significantly the proportion of aneuploid cells in HPV-positive oral keratinocytes, but not HPV16 E6/E7 expression. This indicates that tobacco products may enhance the effects of HPV 16 and the risk of DNA aneuploidy increasing risk to malignant transformation.