Altered protein synthesis in p53 null and hemizygous transgenic mouse embryonic fibroblasts

Embryonic fibroblasts derived from p53-deficient transgenic mice showed distinct phenotypic and biological changes in vitro. In this study, we investigated the possible impact of p53 on the synthesis of other cellular proteins by comparing the protein profiles of p53 null (-/-), hemizygous (+/-) and p53 positive homozygous (+/+) cells using high resolution two dimensional gel electrophoresis. A total of more than 850 proteins were detected in each cell line labeled with 35S-methionine by using computerized image analysis, and a number of proteins were detected with qualitative or quantitative changes in p53-/- cells and to a lesser extent in p53+/- cells. Specifically, seven proteins became undetectable, and no new proteins were detected in p53-/- cells. Neither newly expressed nor absent proteins were detected in p53+/- cell line. Quantitatively, a total of 97 and 59 proteins were detected with significant quantitative changes (3 fold or greater) in p53-/- and p53+/- cells, respectively. Generally, most protein changes fell into one of the following four patterns: 1) progressively decreased synthesis in cells from p53+/+ to p53+/- to p53-/- cells; 2) progressively increased synthesis in cells from p53+/+ to p53+/- to p53-/- cells; 3) decreased synthesis only in p53-/- cells; and 4) increased synthesis only in p53-/- cells. A 70 kD heat shock protein (Hsp 70) was identified and showed a greater than 1,000-fold increase in p53-/- cells compared to that in p53+/+ cells. Transferrin, tropomyosin, and proliferating cell nuclear antigen (PCNA) have also been identified and measured in this study. Synthesis of transferrin and tropomyosin was significantly increased or decreased, respectively in p53-/- cells, whereas expression of PCNA showed no significant change in p53-/- cells despite their much higher (3-4 times) proliferation rate than the other two cell lines (p53+/+ and p53+/- cells). We conclude that disruption of a single important gene, p53, results in a cascade of protein changes which are related to the loss of p53 mediated negative growth effects on cell cycle control.