IMMORTALIZATION OF INBRED RABBIT KERATINOCYTES FROM A SHOPE PAPILLOMAAND TUMORIGENIC TRANSFORMATION OF THE CELLS BY EJ-RAS

An immortalized cell line of keratinocytes, named SPG1-3, was establis hed from a papilloma induced from cottontail rabbit papillomavirus (CR PV)-infected inbred rabbit skin. The cells have reached 60 passages in culture and are still growing well, but they are not tumorigenic in a thymic mice, Although CRPV DNA was present as extrachromosomal episome s in the papilloma from which the cell line was derived from a single colony of keratinocytes, there was no CRPV DNA detectable in the cells . Three sub-cell lines of SPG1-3EJ, SPG1-3EJ1 and SPG1-3EJ2 were then established from the EJ-ras transfected SPG1-3 cells. All of the three sub-lines contained both EJ-ras DNA and a 1.2 kb transcript of EJ-ras , and they are malignantly tumorigenic in athymic mice. These data ind icate that CRPV genome and its expression might be essential for the i nitiation and maintenance of neoplasia, but not for the maintenance of immortalization of the tumor-derived cells. In addition, some oncogen es such as EJ-ras may play an essential role in tumorigenic and malign ant conversion of the immortalized cells, These cell lines derived fro m inbred rabbit skin may provide a useful in vitro system for better u nderstanding of the oncogenic processes of papillomavirus-involved neo plastic progression by transfecting the cells with CRPV genes and seri al transplantation to the inbred rabbits for studying host immune resp onses to the viral oncogenic potential.