The Human Papillomavirus Type 16 E6 Gene Alone Is Sufficient To Induce Carcinomas in Transgenic Animals

Abstract

High-risk human papillomaviruses (HPVs) are the causative agents of certain human cancers. HPV type 16 (HPV16) is the papillomavirus most frequently associated with cervical cancer in women. The E6 and E7 genes of HPV are expressed in cells derived from these cancers and can transform cells in tissue culture. Animal experiments have demonstrated that E6 and E7 together cause tumors. We showed previously that E6 and E7 together or E7 alone could induce skin tumors in mice when these genes were expressed in the basal epithelia of the skin. In this study, we investigated the role that the E6 gene plays in carcinogenesis. We generated K14E6 transgenic mice, in which the HPV16 E6 gene was directed in its expression by the human keratin 14 promoter (hK14) to the basal layer of the epidermis. We found that E6 induced cellular hyperproliferation and epidermal hyperplasia and caused skin tumors in adult mice. Interestingly, the tumors derived from E6 were mostly malignant, as opposed to the tumors from E7 mice, which were mostly benign. This result leads us to hypothesize that E6 may contribute differently than E7 to HPV-associated carcinogenesis; whereas E7 primarily contributes to the early stages of carcinogenesis that lead to the formation of benign tumors, E6 primarily contributes to the late stages of carcinogenesis that lead to malignancy.

Transcriptional profiling of dysplastic lesions in K14‐HPV16 transgenic mice using laser microdissection

“…A broad range of pathology, mostly restricted to the squamous epithelium, was observed in the K14-HPV16 mice as described previously (5)(6)(7)(8). Figure 1 shows a comparative phenotype of a wild-type FVB/N mouse and a K14-HPV16 transgenic mouse at 9 months of age.…”

“…Previous studies (5)(6)(7)(8) have clearly shown that the lesions in the K14-HPV16 transgenic mouse model show characteristic neoplastic progression in the squamous epithelium with advancing age. We examined biopsies from the ears of transgenic mice, since the ears consistently develop increasingly severe lesions, as described previously (5)(6)(7)(8) . Figure 2A shows the ear epithelium of an adult wild-type FVB/N mouse.…”

“…2J) or welldifferentiated squamous cell carcinomas. Some high-grade, poorly differentiated carcinomas that were locally invasive were also observed at low frequency (5)(6)(7)(8). Metastasis was not observed in older animals because most animals were killed 1 month after onset of visible tumors because of perceived discomfort.…”

“…One of the transgenic mouse models of HPV16-associated neoplasia that is currently available is the K14-HPV16 transgenic model (5)(6)(7)(8). One of these transgenic lines carries HPV16 sequences from nucleotides (nt) 97 to 6152, including the E6, E7, E1, E2, E4, and E5 open reading frames (ORFs) of the HPV16 genome driven by the human keratin-14 promoter (5,6).…”

“…All of the K14-HPV16 transgenic animals develop hyperplastic and/or dysplastic lesions in several inbred backgrounds. Malignant squamous cell carcinomas are typically observed on the epidermis of the ear, the chest, and the truncal skin (5)(6)(7)(8). Because this transgene construct contains the E2 gene (5), we predicted that it might be a useful model to test our E2-driven gene therapy approach.…”