The infant mouse as a in vivo model for the detection and study of DNA damage–induced changes in the liver

Abstract

The present work describes the use of the infant (4-wk-old) mouse as an animal model for the study of DNA damage-induced G(1) checkpoint response, changes in p53 protein levels, and multiple gene expression changes after DNA damage has been induced in the liver. Hepatocytes in the infant B6C3F1 mouse had a proliferation index that was 27 times greater than that of the 12-wk-old B6C3F1 mouse (57.4 vs. 2.1%, respectively). Eight hours after infant mice were exposed to the DNA damaging agents bleomycin (100 mg/kg, i.p.) or 10 Gy of whole body gamma irradiation, the G(1)/S ratio significantly increased from 21 (control) to 66 and 75, respectively, because of the induction of the G(1)/S checkpoint response. One hour after whole body irradiation of infant mice the levels of the p53 protein, phosphoserine 18-p53 and phosphoserine 23-p53 increased dramatically and tended to peak at 1 h in the liver, whereas the p21(WAF1) protein increased more slowly and tended to peak at 2 h after irradiation. The mRNA expression of the p53-response genes p21, murine double minute clone 2 (mdm2), and cyclin G was increased at 2 h after irradiation but was decreased by 8 h postirradiation, relative to the 2-h time-point. The expression of insulin-like growth factor binding protein-1 (IGFBP-1) and growth-regulated oncogene 1 (GRO1) increased at 2 and 8 h postirradiation. This work characterizes various parameters in the infant mouse, thus validating the use of this model to study in vivo DNA damage-induced cell-cycle-related changes.

Telomerase activity is required for bleomycin-induced pulmonary fibrosis in mice

“…This is not unexpected, because it is unlikely that the in vivo dose used would cause DNA damage to cells to the degree achieved by in vitro doses (>20 μg/ml) (27). Moreover, 100 mg/kg of BLM is required in vivo to induce DNA damage in liver of mice (29), which would be greater than 65-fold the dose used in this study for induction of pulmonary fibrosis. Thus it is unlikely that the protective effect of TERT deficiency would be specific to fibrosis due to a genotoxic insult.…”

“…Because BLM is also known to cause DNA strand scission and damage (27)(28)(29), the protective effect of TERT deficiency in the BLM model may be specific only for genotoxic injury-induced pulmonary fibrosis. To examine this possibility, DNA damage was evaluated in the BLM model using the Comet assay.…”

“…Because BLM also has an effect on DNA damage (27)(28)(29), this protective effect of TERT deficiency may be specific to fibrosis induced by genotoxic injury. However, induction of fibrosis by the indicated dose of BLM (30 μg per 20-g mouse) did not cause detectable genotoxic injury using the standard Comet assay.…”

p53 Regulates the Ras Circuit to Inhibit the Expression of a Cancer-Related Gene Signature by Various Molecular Pathways

“…ATF3 represses CGS expression through direct binding to CGS promoters. Because ATF3 was found to be activated only following p53 stabilization, and both CXCL1 and IL-1β expressions are upregulated following stress (41,42), we treated Ras/shmNOXA and Ras/shp53 cells with cisplatinum, a DNA damage agent, and measured CGS expression. In agreement with others, we show that treatment of cells with cisplatinum induced CGS levels.…”

Serine 312 phosphorylation is dispensable for wild-type p53 functions in vivo

“…Furthermore, whole body g-irradiation led to increased S312A p53 levels to similar extends as WT p53 in thymus and liver tissues (Figure 2c), confirming that the induction of S312A protein is not compromised both in vitro and in vivo. It is noteworthy that p53 can be induced in livers of young mice 20 (Supplementary Figure 2B), unlike in the older mice which are found to be radioresistant. 21 To evaluate whether S312A p53 is truly a functional protein, we investigated the expression of some classical p53-target genes in various organs (thymus, spleen and liver) and MEFs, which showed p53-dependent transactivation to similar extends and with similar kinetics in both WT and p53 S312A/S312A tissues and cells on g-irradiation (Figure 2d).…”