Identification, cellular tropism and in vitro transforming properties of ovine papillomaviruses

To date, about 150 animal papillomaviruses (PV) have been identified in benign and malignant lesions of the skin and mucosa in 75 vertebrate host species. In sheep, three ovine PV types have been described so far, namely OaPV1, OaPV2, and OaPV3. All of them infect skin epithelium, but while OaPV1, OaPV2 belong to the Delta-genus and cause benign fibropapillomas, OaPV3 is part of the distant Dyokappa-genus and has been detected in squamous cell carcinomas (SCC). This research aims to identify and genetically characterize novel ovine papillomaviruses types, and to investigate their role in skin carcinogenesis. The identification of OaPV4, a novel ovine PV type within Deltapapillomaviruses 3 in a fibropapilloma of a ram is reported. In vitro transforming abilities of OaPV3 and OaPV4 E6 and E7 PV oncogenes are evaluated in a comparative study to investigate a potential role of Delta and Dyokappa viruses in non-melanoma skin cancer development. Both OaPV3 and OaPV4 E6 and E7 transduction alter cell growth profile of primary human and sheep keratinocytes, but while OaPV4-E6E7 determine a strong lifespan increase OaPV3-E6E7 are able to promote immortalization. Furthermore, pRB protein levels are altered upon E6 and E7 expression, and pulldown assays reveal stronger ability of OaPV3-E7 to efficiently associate with pRB leading to its destabilization. Results support the existence of peculiar in vitro transformation properties for ovine papillomaviruses reinforcing the thesis of a direct link between cutaneous papillomaviruses, cellular transformation, and NMSC progression.