FIG. 2.

Loss of p53 improves growth of Cdk2^−/− MEFs. (A) Analysis of spontaneous immortalization of MEFs using a 3T3 assay. The five genotypes plotted are Cdk2^−/−, Cdk2^−/− p53^−/−, p53^−/−, p53^+/−, and Cdk2^−/− p53^+/−. The number of passages is plotted on the x axis, and cumulative growth is plotted on the y axis. (B) Proliferation assay performed on passage 6 for a period of 7 days for four genotypes: WT, Cdk2^−/− p53^−/−, Cdk2^−/−, and p53^−/−. Cdk2^−/− MEFs display a decreased growth rate, which is rescued by loss of p53. (C) Western blot (WB) analysis of protein extracts from MEFs using antibodies against Cdk2, p53, Cdk4, Emi1, Cdk1^pY15, and actin.