Characterization of primary human keratinocytes transformed by human papillomavirus type 18.

Primary human epithelial cells were cotransfected with pHPV-18 and pSV2neo, and cell strains were generated by selecting in G418. One cell strain (FE-A), which exhibits an extended life span, is currently in its 30th passage. In comparison, control cultures can only be maintained up to the seventh passage. Southern blot analysis revealed the presence of at least one intact, integrated viral genome in these cells. FE-A cells showed altered growth properties, characterized by a change in morphology, and clonal density. Differentiation markers analyzed by Western blotting (immunoblotting), such as cytokeratins and involucrin, indicated that the cells resembled a partially differentiated epithelial population. Increased expression of the 40-kilodalton cytokeratin was observed in FE-A cells, similar to that observed in simian virus 40-immortalized human keratinocytes (M. Steinberg and V. Defendi, J. Cell Physiol. 123:117-125, 1985). FE-A cells were also found to be defective in their response to terminal differentiation stimuli. Calcium and 12-O-tetradecanoyl-phorbol-13-acetate treatment induced normal epithelial cells to differentiate, whereas the human papillomavirus 18 (HPV-18)-containing keratinocytes were resistant to these signals, indicating their partially transformed nature. These cells were not able to induce tumors in nude mice over a period of up to 8 months. A second cell strain, FE-H18L, also generated by transfecting HPV-18, also exhibited an extended life span and similar alterations in morphology. Viral RNA transcribed from the early region of HPV-18 was detected in both cell strains by Northern (RNA) blot analysis. These cell strains should provide a useful model for determining the role of HPV in carcinogenesis.