To search for potential biomarkers used to monitor the process of immortalization, we investigated the relative level of telomerase activity and other immortal phenotypes in the SHEE esophageal epithelial cell line. This human fetal esophageal epithelial cell line, induced by human papilloma virus (HPV) 18 E6E7, was continually propagated over 100 passages. Fourteenth passage cells (SHEE14) were cultured in a flask with a serum-free medium and continually cultured to the 30th passage (SHEE30). Cells of SHEE14, SHEE20 and SHEE30 were examined according to cell morphology, cell cycle, apoptosis, contact-inhibition growth, anchorage- dependency, dose-dependency to epithelial growth factors (EGF), telomerase activity and tumorigenicity. The SHEE14 cells exhibited good differentiation with contact-inhibition and anchorage-dependent growth. The SHEE20 cells exhibited increase of senescent and apoptotic cells, and difficulty in propagation. The SHEE30 cells exhibited a higher proliferative index and some undifferentiated cells, with weakened contact-inhibition and anchorage-dependent growth. The telomerase was activated in cells of SHEE30, but not in SHEE14 and SHEE20 cells. The different response to dose-dependency to EGF was not statistically different in SHEE14 and SHEE30. Three groups of cells displayed lack of tumor formation in nude mice. Compared with SHEE14 and SHEE20, SHEE30 cells were of immortalized status with immortal phenotype, which consisted of telomerase activity, increase of cell proliferation, weakened contact-inhibition and anchorage-dependent growth, dose dependency to EGF and lack of tumor formation. From passage 14 to 30th passage, SHEE cells went through cellular senescence, apoptosis and immortalization. With a view toward diagnostic and biological aspects, telomerase activity is a crucial step and a cardinal requirement for immortalization. The telomerase activity and other immortal phenotypes are potential markers for monitoring the process of immortalization.

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