Methylation status of the long control region of HPV 16 in clinical cervical specimens

Abstract

DNA methylation is one of the regulatory pathways that modulate human papillomavirus (HPV) gene expression. To obtain detailed methylation information on crucial areas of the long control region (LCR) of HPV 16 and to clarify the significance of methylation in clinical cervical lesions, 80 clinical samples were examined to determine the methylation status of the HPV 16 promoter and enhancer core using bisulfite modification and pyrosequencing. Seventy samples [26 of cervical carcinoma (CC), 13 of cervical intraepithelia neoplasia (CIN) III, 17 of CIN I-II and 14 of asymptomatic HPV 16 infection] were successfully examined. Analysis of the general methylation status of HPV 16 LCR in the 70 clinical specimens revealed 43 (61.4%) with methylation in the promoter and/or enhancer core of HPV 16. The proportion of methylated samples was highest in CC specimens (84.6%), followed by asymptomatic infection (71.4%) and CIN III (46.2%), while the proportion of methylated samples was lowest in CIN I-II specimens (29.4%). The methylation status of eight CpGs in HPV 16 LCR was determined in detail. In general, the methylation of CpGs was more common in the promoter than in the enhancer core region. The methylation frequencies of the eight CpGs ranged from 14.6±7.2 to 33.7±23.0% in individual methylated CpG cases. The methylation pattern of all eight CpGs methylated in the promoter and enhancer core was more common in CC, and the pattern of scattered methylated CpGs was relatively more prevalent in asymptomatic infections. Our study demonstrates that DNA methylation is a common phenomenon in HPV 16 LCR clinical specimens, and may function as a host defense mechanism. While hypomethylation is probably associated with the initiation of neoplasia, hypermethylation in cervical cancer may be a reflection of the host defense mechanism. In the regulation of transcription, methylation is of more importance in the HPV 16 promoter than in the enhancer core.