Physical and methylation status of human papillomavirus 16 in asymptomatic cervical infections changes with malignant transformation.

AIMS

To evaluate how the genetic and epigenetic profile of human papillomavirus 16 (HPV16) changes from asymptomatic cervical infections to cervical cancer (CaCx) development.

METHODS

HPV16 physical status, methylation of its early-late promoters and its upstream enhancer sequences were analysed in samples from asymptomatic cervical infections (n=89), pre-neoplastic lesions (low and high grade squamous intraepithelial lesions LSIL/HSIL, n=28) and primary CaCx (n=98).

RESULTS

In asymptomatic infection (65%, 58/89) and LSIL/HSIL (57%, 16/28) samples, the episomal form of HPV16 was predominant whereas integration of HPV16 was significantly (p=0.01) higher in CaCx (59%, 57/98). The integrated viral form was also present in asymptomatic (27%, 24/89) and LSIL/HSIL (25%, 7/28) samples. The methylation of the enhancer region was comparable (29-34%) among asymptomatic, LSIL/HSIL and CaCx samples. The episomal form exhibited relatively higher methylation of the early promoter (52%) than that of the late promoter (40%) in asymptomatic infection but the integrated form in asymptomatic carriers showed the opposite methylation pattern (early promoter (42%) vs late-promoter (54%)). A similar pattern was observed in LSIL/HSIL samples, with comparable frequencies (44%) of early and late promoter methylation of the episomal form. However, irrespective of HPV16 physical status, higher methylation of late promoter than that of early promoter was observed in CaCx samples. An inverse correlation was observed between HPV16 integration and overall methylation of the early promoter-enhancer region in CaCx (p=0.05), LSIL/HSIL (p=0.09) and asymptomatic samples (p=0.09).

CONCLUSIONS

Our study indicates that integration of HPV16 along with changes in methylation pattern of early and late promoters is essential for neoplastic transformation of asymptomatic cervical infections.