Resistance to apoptosis in human cells conferred by telomerase function and telomere stability

Cell senescence and programmed cell death (apoptosis) are two fundamental biological mechanisms that regulate proliferative capacity, survival potential, aging, and death of cells. Here we report several independent lines of experimental evidence that support the hypothesis that telomerase function and telomere length perform important roles in cell survival during apoptosis. First, with serum starvation and matrix-independent survival experiments, we found that young normal diploid cells were more resistant to apoptosis than their older counterparts. In addition, normal cells with stable telomere lengths caused by ectopic expression of telomerase maintained an increased resistance to serum starvation- and matrix-deprivation-induced programmed cell death compared with aged normal cells without telomerase. Second, we found that telomerase-positive immortalized SW39 cells had a higher survival ability and resistance to apoptosis than their telomerase-negative immortalized counterparts, SW13 and SW26. Third, we showed that telomerase-positive cells with experimentally elongated telomeres (GTR-IDH4 and GTR-DU145) acquired increased survival ability and higher resistance to apoptosis than the parental cell lines with shorter telomeres (IDH4 and DU145). Higher resistance to apoptosis of these cells was associated with a deficiency in two major apoptosis execution pathways: induction of nuclear calcium-dependent endonucleases and activation of the interleukin-1 beta-converting enzyme-family of proteases (caspases). Taken together, these results provide the first direct experimental evidence supporting the hypothesis that telomerase activity and maintenance of telomere stability are associated with increased cellular resistance to apoptosis.