DNA damage-associated dysregulation of the cell cycle and apoptosis control in cells with germ-line p53 mutation

Lymphoblastoid cell lines (LCLs) with heterozygous p53 mutations at residues 286A, 133R, 282W, 132E, and 213ter were established from five independent Li-Fraumeni syndrome families. When cell cycle regulation in response to γ-irradiation was studied, these LCLs showed an abnormal G₁ checkpoint associated with defective inhibition of cyclin F/cyclindependent kinase 2 activity in all eases except for 282W LCL which showed a normal G₁ checkpoint. On the other hand, the control of S-phase-G₂ as determined by cyclin A/cyclin-dependent kinase 2 activity was defective in all these LCLs. The mitotic checkpoint was also defective in the two LCLs analyzed as either competent or incompetent for G₁ arrest. When radiation-induced apoptosis, which requires wild-type p53 function under optimal conditions, was studied, all of these LCLs showed significant failure compared to normal LCLs. These findings indicate that although p53-dependent transactivation and G₁-S- phase cell cycle control are variably dysregulated, the induction of apoptosis and control of the cell cycle at S-phase-G₂ and the mitotic checkpoint in response to DNA-damaging agents are consistently dysregulated in heterozygous mutant LCLs. This suggests that these dysfunctions underlie, at least in part, the susceptibility of Li-Fraumeni syndrome families to cancer. Furthermore, the approach presented is a potentially useful method for studying individual carriers of different germ-line p53 mutations and different biological features.