Regulation of the human papillomavirus type 11 E6 promoter by viral and host transcription factors in primary human keratinocytes.

Human papillomavirus (HPV) type 11 is strictly trophic for epithelial cells and induces benign condylomata of the external genitalia and also causes laryngeal papillomas. Primary keratinocytes are the appropriate hosts for studies of HPV gene regulation, but they are not frequently used, owing to difficulties in culturing and low transfection efficiencies. By modifying a Polybrene transfection procedure, we achieved consistently high transfection efficiencies in primary human foreskin keratinocytes and characterized the HPV type 11 enhancer in the context of the homologous E6 promoter. Contrary to previous studies with immortalized human cervical carcinoma C-33A cells, constitutive enhancer element II in the upstream regulatory region conferred no enhancer activity and did not abrogate repression by the homologous E2 protein. Rather, repression was strong, ranging from 5.6- to 20-fold for the various enhancer deletion mutations. By deletion analysis, a strong enhancer that included three nuclear factor 1 sites and one nuclear factor 1-associated factor-binding site was localized to a 45-bp region within constitutive enhancer element I, and it showed some degree of tissue specificity.