The multistage process of carcinogenesis in human esophageal epithelial cells induced by human papillomavirus

To investigate the multistage process of carcinogenesis, the progressive alteration of the morphology, telomerase, cytogenesis, oncogenes and tumorigenicity in the process of immortalization and malignant transformation of the human fetal esophageal epithelial cell (SHEE) was studied. The SHEE cells were immortalized by gene E6E7 of human papilloma virus (HPV) type 18 in our laboratory and continually cultivated over 100 passages, which had been malignantly transformed. Cells at the 11th, 35th, 65th and 100th passage were examined according to the following criteria: morphological changes of cell growth, contact-inhibition and anchorage-independent growth (AIG); the cell proliferative and apoptotic index; the modal number of chromosomes; c-myc, p53, bcl-2, ras; telomere length and activities of telomerase and tumorigenicity in nude mice or severe combined immunodeficient (SCID) mice. The cells of the 11th passage were well differentiated and the cells of 100th passage were relatively poorly differentiated with polymorphism, while the cells of 35th and 65th had two distinct differentiations. The proliferative indexes were 21.1%, 32.5%, 33.2%, and 40.9% and the apoptotic indexes were 3.3%, 2.7%, 3.5%, 2.7% in the 11th, 35th, 65th and 100th passage respectively. Karyotypes of four cell passages belonged to hyperdiploidy and hypotriploidy. C-myc, ras, p53 genes were low in the 10th and 35th, and high in the 65th and 100th passage, but bcl-2 was low in 4 passages. Telomere length sharply decreased from normal fetal esophagus cells until the 35th passage, but it was stably expressed in the 65th and 100th passage. The activities of telomerase were expressed in cells of the 35th, 65th and 100th passages. The efficiency of AIG varied in different passages of the SHEE cell and was absent in the 11th passage, low efficiency in the 35th passage and 65th passage, and high efficiency in the 100th passage. Transplanted cells of the 65th and 100th passage into SCID mice resulted in tumor formation, but only the 100th passage cells could grow in nude mice. All of these characteristic changes were in dynamic progressive process. These data demonstrate that carcinogenesis of esophageal epithelial cells induced by HPV is the multistage process, which goes through the initial, immortal, premalignant and malignant transformation stages. The generation of esophageal carcinoma is caused by the accumulation of cellular, genetic and molecular changes.