Flow cytometric analysis of p53 expression during the cell cycle

Mutant p53 expressed in many types of carcinoma lacks an inhibitory function on cell growth, but its role has been unclear. We performed two-parameter flow cytometry (FCM) to elucidate the relationship between the expression of p53 and the cell cycle in A431 cells. Fluorescence in situ hybridization proved that an A431 cell had two p53 genes whereas chromosome 17 was tetraploid. FCM showed that A431 cells expressed constantly high levels of p53 during the cell cycle. Under conditions of both serum deprivation and presence of hydroxyurea, p53 expression was decreased throughout the cell cycle, and the bivariate DNA/p53 distribution pattern during the cell cycle did not change. The expression of p53 was reduced to 60% for the first 4 h after the addition of cycloheximide, and showed no significant changes at least for 20 h. Treatment with Triton X-100 increased p53 immunoreactivity throughout the cell cycle. These results indicate that mutant p53 differs from proliferative markers such as PCNA, Ki-67 and DNA polymerase-alpha, and that there are no links between the expression of p53 and the cell cycle in A431 cells.