Molecular analysis of episomal human papillomavirus type 16 DNA in a cervical carcinoma cell line

Integration of human papillomavirus type 16 DNA sequences into host DNA is a frequent event in cervical carcinogenesis. However, recent studies showing that HPV16 is present exclusively in an episomal form in many primary cervical cancers suggest that HPV16 can transform target cells by mechanisms that do not require viral integration. We have established a cervical carcinoma cell line that harbors episomal copies of HPV16 DNA of approximately 10 kb. Restriction enzyme and two-dimensional gel analysis confirmed that HPV16 DNA was extrachromosomal with both monomeric and multimeric forms present. HPV16 was maintained as episomes with passage both in culture and after subcutaneous growth in nude mice. The 10 kb viral genome, consisting of a full-length copy of HPV16 and a partial duplication of the long control region and the L1 open reading frame, exhibited transforming activity comparable to prototype HPV16. This cell line should provide a useful model system for studying the biological significance of the physical state of the HPV16 genome in cervical carcinoma cells.