Transgenic mice expressing targeted HPV-18 E6 and E7 oncogenes in the epidermis develop verrucous lesions and spontaneous, rasHa-activated papillomas.

In order to create a transgenic model for human papilloma virus (HPV)-associated carcinogenesis, we have used the regulatory elements of a human keratin K1 (HK1) gene to target the expression of the E6 and E7 oncogenes of HPV-18 exclusively to the epidermis. All murine expressors were viable and lived normal lifetimes; older mice (> 1 year) possessed numerous small lesions with a verrucous (wart-like) histotype. Analysis of newborn epidermis and lesions revealed that the HPV-18 E6/E7 genes were being expressed with a predominance of the E6*/E7 transcript over the full length E6/E7 message. The long latency in lesion appearance may reflect the low level of intact E6 transcripts and the requirement for additional genetic or epigenetic events before production of an overt lesion. In agreement with this proposal, spontaneous papillomas developed that expressed an activated rasHa oncogene (codon 61, A-->T; codon 13, G-->T). All lesions expressed keratin genes K1, K6, and K13 in a fashion characteristic of hyperproliferative or benign tumors with no evidence of malignant conversion. Our results demonstrate that the mouse epidermis represents a relevant in vivo model system to analyze the interaction between HPV and cellular genes in neoplasia.