Analysis of genomic integrity and p53-dependent G(1) checkpoint in telomerase-induced extended-life-span human fibroblasts

Life span determination in normal human cells may be regulated by nucleopro tein structures called telomeres, the physical ends of eukaryotic chromosom es. Telomeres have been shown to be essential for chromosome stability and function and to shorten with each cell division in normal human cells in cu lture and with age in vivo. Reversal of telomere shortening by the forced e xpression of telomerase in normal cells has been shown to elongate telomere s and extend the replicative life span (H. Vaziri and S. Benchimol, Curr. B iol, 8:279-282, 1998; A. G. Bodnar et al., Science 279:349-352, 1998). Exte nsion of the life span as a consequence of the functional inactivation of p 53 is frequently associated with loss of genomic stability. Analysis of tel omerase-induced extended-life-span fibroblast (TIELF) cells by G banding an d spectral karyotyping indicated that forced extension of the life span by telomerase led to the transient formation of aberrant structures, which wer e subsequently resolved in higher passages. However, the p53-dependent G(1) checkpoint was intact as assessed by functional activation of p53 protein in response to ionizing radiation and subsequent p53-mediated induction of p21(Waf1/Cip1/Sdi1). TIELF cells were not tumorigenic and had a normal DNA strand break rejoining activity and normal radiosensitivity in response to ionizing radiation.