E6/E7 Genes of Human Papilloma Virus Type 18 Induced Immortalization of Human Fetal Esophageal Epithelium

To study the role played by human papilloma virus (HPV) in carcinogenesis, immortalized esophageal epithelial cells were induced by E6 and E7 genes of HPV type 18 and the biological behavior was studied. Human fetal esophageal epithelial cells were transfected with recombined HPV18E6E7AAV and were cultured and passaged in medium M199. In both the 10th passage (SHEE10) and the 31st passage (SHEE31), their proliferative rates by flow cytometry and their abilities to grow and form colonies in soft agar, or to form tumors in SCID mice were examined. The HPV18 genes of E6E7 and its expression were determined using PCR methods. Cellular telomerase activity was detected by TRAP and chromosomes were analyzed by standard method. Immortalized cell lines of esophageal epithelium induced by the HPV18E6E7 were successfully established and cultured for >100 passages over 4 years. The result of PCR showed that the E6E7 gene of HPV18 was detectable in both cell clones. Both of them were unable to grow in soft-agarose medium and failed to produce tumors in SCID mice. Flow cytometry demonstrated an average of 43% proliferation index in SHEE31, but 28% in SHEE10. Telomerase activity was clearly identified in SHEE31 but not in SHEE10. Cytogenetic analysis demonstrated progression of chromosomal abnormalities with increasing trisome. Our data indicated that genes E6/E7 of the HPV18 were capable of inducing immortalization in fetal esophageal epithelial cells. The immortal phenotype requires both activation of telomerase and genetic alterations that abrogate normal differentiation and promote cellular proliferation. This cell line can assist us to characterize the role played by HPV in carcinogenesis.