Telomerase activity in a specific cell subset co-expressing integrinβ1/EGFR but not p75NGFR/bcl2/integrin β4 in normal human epithelial cells

Telomerase activity is correlated with the immortality of various cultured cells and cancer cells. The activity, however, is also demonstrated in various normal regenerating cells which normally have a finite life span in vivo and in vitro, though its biological implication remains unclear. Using cultured normal human epithelial cells, we show that telomerase activity is associated with epithelial cell subsets which actively proliferate in vitro. Unlike in most cancer cell lines, telomerase activity was evidently up-regulated when the cells entered into S phase in primary human epithelial cells. To characterize the cells which have telomerase activity, the primary human epithelial cell population of uterine cervix was dissociated into several distinctive cellular subsets by means of immunocytochemical cell fractionation. Telomerase activity was found to be closely associated with the subset which expressed predominantly integrin pi and epidermal growth factor receptor. We further identified the telomerase-negative subpopulation which contained a small subset that strongly coexpresses p75(NGFR) low affinity nerve growth factor receptor, integrin beta 4 and bcl-2 protein. The location of the p75(NGFR)-expressing cells contrasts to that of the Ki-67 positive cells in vivo and is distinctive of telomerase positive cycling cells, indicating that these cells remain at the G0 phase, The present study supports the notion that telomerase activity is linked to cell cycle regulation, implying that telomerase is activated upon cell proliferation in regenerating normal human epithelial cells.