Figure 3.

Telomerase activity correlates with the rate of cell proliferation in immortal human cells. (A and B) Cells were rinsed and resuspended in medium without serum to obtain serum-free conditions and then plated in medium containing different concentrations of serum. Subconfluent cell cultures were harvested at 7 days, counted, and analyzed for telomerase activity. Serum-containing medium (10%) was added to a duplicate culture 0% serum plate for 2–3 days to test for reversibility of the quiescent block (0% + 10% rev). A gel from a representative experiment is shown, and the average number of cell divisions (population doubling) from several experiments is indicated below each lane. (A) HT1080 cells appear to undergo reversible quiescence in 0% serum. Telomerase activity appears proportional to growth rate. (B) DU145 cells are resistant to quiescence induced by serum-deprivation. The decrease in telomerase activity with decreased cell division may represent the combined effects of decreased growth rate and toxicity. (C) IDH4 cells were rinsed with medium without dexamethasone and plated in medium containing dexamethasone in a series of 2-fold dilutions. IDH4 cells also show a decrease in telomerase activity with the rate of proliferation. (D) Quantitation of telomerase activity and the rate of cell division are plotted showing a relatively linear relationship for each cell line tested. Data from several independent experiments have been combined.