Detection of p53 dysfunction by Western blotting.

CLL cells were analyzed for p53 and p21 expression 10 to 18 hours after exposure to ionizing radiation (5 Gy). BCL-2 was used as a control for protein loading. Type A p53 dysfunction (due to TP53mutation) is characterized by increased baseline levels of p53 and impaired radiation-induced up-regulation of p21. Type B p53 dysfunction (due to ATM mutation) is characterized by impaired up-regulation of both p53 and p21.