HPV 16 E2 binding sites 1 and 2 become more methylated than E2 binding site 4 during cervical carcinogenesis.

Abstract

E2 protein binding to the four E2 binding sites (E2BSs) at the long control region of Human Papillomavirus (HPV) 16/18 genome may exert either transcriptional activation/repression on E6 and E7 oncoproteins. Methylation status at the E2BSs may affect the relative binding of E2 protein to them. In this study, methylation percentage at E2BS 1, 2 (promoter-proximal), and 4 (promoter-distal) were assessed by pyrosequencing and compared among HPV 16/18-positive cervical cancer, high-grade, and low-grade Cervical Intraepithelial Neoplasia, Atypical Squamous Cells of Undetermined Significance, and normal cervical epithelium. HPV 16 E2BS1&2 were more methylated than HPV 16 E2BS4 in cervical cancer whereas in cervical premalignant lesions and normal epithelium, HPV 16 E2BS1&2 were less methylated than HPV 16 E2BS4. HPV 18 E2BS1&2 remained more methylated than E2BS4 in all histological groups. HPV 16 E2BS1&2 methylation increased from high-grade lesions to cervical cancer (P < 0.001). HPV 16 E2BS4 methylation increased from low-grade to high-grade premalignant lesions (P = 0.041). Both HPV 18 E2BS1&2 and E2BS4 methylation increased from low-grade to high-grade Cervical Intraepithelial Neoplasia (P = 0.019 and 0.001 respectively) and further increased form high-grade lesions to cervical cancer (P < 0.001 and 0.005 respectively). Conclusively, HPV 16 E2BS1&2 (for transcriptional repression of E6/E7 oncoproteins) became more heavily methylated than E2BS4 (for transcriptional activation of E6/E7) in cervical cancer, favouring the differential binding of E2 protein to E2BS4. Increasing methylation at HPV 16/18 E2BSs are potentially useful adjunctive molecular markers for predicting progression from low-grade to high-grade cervical premalignant lesions and from high-grade lesions to cervical cancer.