Cutaneous Human Papillomavirus E7 Type-Specific Effects on Differentiation and Proliferation of Organotypic Skin Cultures

Background: A role for cutaneous human β-papillomavirus (HPV) types as co-factors in the development of non-melanoma skin cancer has been postulated. Here we have investigated the effects of E7 expression on keratinocyte differentiation, proliferation and cell-cycle proteins in organotypic skin cultures. Methods: Recombinant retroviruses containing the E7 genes from cutaneous HPV types 1, 4, 5, 8, 20, 38 and RTRX7 were produced that include types associated with benign and malignant lesions. Adult human primary keratinocytes were transduced with these recombinant retroviruses and differentiated into skin-equivalents using de-epidermalised human dermis. Results: Expression patterns of the basal keratinocyte marker cytokeratin 14 (CK14) were not altered by any of the viral E7 types analysed. However, expression of the early and late differentiation markers CK10 and involucrin were markedly altered in HPV 1, 4 and 38 cultures. The highest proliferation rates in basal cell layers, as judged by BrdU and Ki67 staining, were observed in HPV 1, 4 and 38 cultures. Interestingly, co-expression of cyclin E and p16(INK4a) within the same cell of the suprabasal cell layers was observed only in cultures generated using E7 of HPV 5 or HPV 8. Conclusion: HPV types associated with either benign or malignant lesions perturb keratinocyte proliferation and differentiation in different ways. Moreover, expression of E7 from HPV 5 or HPV 8 seem able to overcome p16(INK4a) induced cell cycle arrest in a subset of keratinocytes.