Cooperation between p53 mutation and high telomerase transgenic expression in spontaneous cancer development

Abstract

Telomerase reintroduction in adult somatic tissues is envisioned as a way to extend their proliferative capacity. It is still a question, however, whether constitutive telomerase expression in adult tissues impacts the normal aging and spontaneous cancer incidence of an organism. Here, we studied the aging and spontaneous cancer incidence of mice with transgenic telomerase expression in a wide range of adult tissues, K5-Tert mice. For this, we maintained large colonies of K5-Tert mice for more than 2 years. K5-Tert mice showed a decreased life span compared to wild-type cohorts associated with a higher incidence of preneoplastic and neoplastic lesions in various tissue types. Neoplasias in K5-Tert mice were coincident with transgene expression in the affected tissues. These observations suggest that high telomerase activity may cooperate with genetic alterations that occur with age to promote tumorigenesis. Indeed, we demonstrate here that increased cancer incidence and the reduced viability of K5-Tert mice are aggravated in a p53(+/-) genetic background, indicating that telomerase cooperates with loss of p53 function in inducing tumorigenesis. Altogether, these results demonstrate that constitutive high levels of telomerase activity result in a decreased life span associated with an increased incidence of neoplasias as the organism ages.

FIG. 1.

(A) Decreased life span of K5-Tert transgenic mice compared to the wild-type controls. Survival curves for wild type (71 mice), T1 K5-Tert (79 mice), and T8 K5-Tert (46 mice). (B) Percentage of mice of each genotype that presented tumors at the time of spontaneous death. Preneoplastic lesions were not included as tumors. (C) Percentage of mice of each genotype that presented tumors at the time of sacrifice. Preneoplastic lesions were not included as tumors.

FIG. 2.

Examples of preneoplastic and neoplastic lesions in K5-Tert transgenics. Magnifications, ×20. (a) A skin section showing areas of hyperplasia and hyperkeratosis. (b) An esophagus section showing areas of hyperplasia and hyperkeratosis. (c) Forestomach showing areas of hyperplasia and hyperkeratosis. (d) Glandular stomach showing areas of hyperplasia. (e) Prostate showing hyperplasia. (f) Adenoma in the prepucial glands. (g) Hepatocellular carcinoma in the liver. (h) Hemangiosarcoma of the liver.

FIG. 3.

Scheme of the K5-Tert construct used for transgenesis. The primers used for PCR detection of both endogenous and transgenic Tert (A primers) or only transgenic Tert (B primers) are shown.

FIG. 4.

Specific detection of transgenic K5-Tert mRNA expression in tumors derived from K5-Tert mice. The primers used are shown in Fig. 3 (B primers). The K5-Tert mRNA-specific band is indicated with an arrow (522 bp in length). RNA was obtained from the indicated tumor as described (Materials and Methods). A K5-Tert skin sample was used as a positive control, and a tumor derived from a wild-type mouse was used as a negative control. The 522-bp band was cloned and sequenced to demonstrate that it amplified the specific product (not shown).

FIG. 5.

(A) Survival curves of wild-type and K5-Tert mice in the p53^−/− and p53^+/− genetic backgrounds. The number of mice of each genotype used in the analysis is indicated. (B) Percentage of mice of each genotype that presented tumors at the time of spontaneous death. Preneoplastic lesions were not included as tumors.