Analysis of genomic integrity and p53-dependent G1 checkpoint in telomerase-induced extended-life-span human fibroblasts.

Life span determination in normal human cells may be regulated by nucleoprotein structures called telomeres, the physical ends of eukaryotic chromosomes. Telomeres have been shown to be essential for chromosome stability and function and to shorten with each cell division in normal human cells in culture and with age in vivo. Reversal of telomere shortening by the forced expression of telomerase in normal cells has been shown to elongate telomeres and extend the replicative life span (H. Vaziri and S. Benchimol, Curr. Biol. 8:279-282, 1998; A. G. Bodnar et al., Science 279:349-352, 1998). Extension of the life span as a consequence of the functional inactivation of p53 is frequently associated with loss of genomic stability. Analysis of telomerase-induced extended-life-span fibroblast (TIELF) cells by G banding and spectral karyotyping indicated that forced extension of the life span by telomerase led to the transient formation of aberrant structures, which were subsequently resolved in higher passages. However, the p53-dependent G1 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.

Prostate-specific antigen induction by a steroid hormone in T47D cells growing in SCID mice.

Previous studies revealed that prostate-specific antigen (PSA) is present in > 30% of human breast tumor cytosols. Survival analysis showed that patients with PSA-producing tumors have a reduced risk for relapse, suggesting PSA to be an independent favorable prognostic marker for a large subset of breast cancer patients. The present investigation established an in vivo model for the induction of PSA in human breast cancer tumors growing as xenografts in severe combined immunodeficient (SCID) mice. The human mammary cancer cell-line T47D was grown i.m. in female mice. When the tumor and leg diameter reached 10 mm, the mice were stimulated daily with norgestrel for either 5 or 7 days to produce PSA, and sacrificed on day 8. The prostate cancer cell-line LNCaP was grown in male mice and functioned as a positive control for PSA production. After T47D and LNCaP mice were sacrificed, a highly sensitive immunofluorometric assay was used to analyze the PSA concentration in the tumor, muscle, liver, and kidney cytosols. Norgestrel-stimulated T47D mice showed significantly more PSA in the tumors compared to tumors of the control mice. However, PSA levels in tumors of the stimulated mice were significantly lower than those in the LNCaP xenografts. No PSA levels above background were present in the blood and normal tissue of the norgestrel-stimulated or control T47D xenografts. This mouse model will be a valuable tool for investigating and screening new therapies for a subgroup of breast cancer patients who have significant PSA concentrations in their tumors.