The MEF4-LoxPshBCCIP (passage 1) cells with the conditional BCCIP knockdown cassette were infected with control retro-viruses that express YFP, and the Cre-expressing retrovirus to activate the knockdown of BCCIP. Then, the cells were selected by puromycine, re-plated, and the numbers of cells were counted each day thereafter. Panel A shows the relative number of cells after Cre-expression. Panel B shows the expression of BCCIP, Cre-recombinase, total p53, Ser-15 phosphorylated p53 (p53-Ser15-P), p21, and PCNA in the MEF cells at different time after the virus infection. The p-value of t-test are indicated as (*): p<0.05 and (**): p<0.01.