Ignition of p53 bomb sensitizes tumor cells to granzyme K-mediated cytolysis.

Inactivation of tumor suppressor p53 results in loss of the apoptosis-regulating function of the p53 protein in tumor cells. Restoration of wild-type p53 expression in p53 mutant tumor cells increases tumor susceptibility to CTL-mediated cytolysis. However, the direct role of p53 in regulating tumor sensitivity to INK cell-mediated lysis and the functional relationship between p53 and granzymes in the control of tumor killing are still poorly documented. In this study, we found that p53 can sensitize tumor-killing susceptibility to NK and granzyme K-mediated cytolysis. Granzyme K is constitutively expressed in high levels in NK cells and induces rapid caspase-independent cell death. Granzyme K may exert a critical role in NK cell-mediated tumor clearance. p53 associates with granzyme K and is a physiological substrate of granzyme K. p53 was processed to three cleavage products of p40, p35, and p13 fragments at Lys(24) and Lys(305). These three cleavage products harbor strong proapoptotic activities that amplify the proapoptotic action of p53 to potentiate tumor-killing sensitivity. Therefore, p53 is as a cytotoxic bomb that can be triggered by granzyme K, leading to potentiating killing efficacy. The Journal of Immunology, 2009, 182: 2152-2159.