Role for caspase-mediated cleavage of Rad51 in induction of apoptosis by DNA damage

We report here that the Rad51 recombinase is cleaved in mammalian cells dur ing the induction of apoptosis by ionizing radiation (IR) exposure, The res ults demonstrate that IR induces Rad51 cleavage by a caspase-dependent mech anism, Further support for involvement of caspases is provided by the findi ng that IR-induced proteolysis of Rad51 is inhibited by Ac-DEVD-CHO. In vit ro studies show that Rad51 is cleaved by caspase 3 at a DVLD/N site. Stable expression of a Rad51 mutant in which the aspartic acid residues were muta ted to alanines (AVLA/N) confirmed that the DVLD/N site is responsible for the cleavage of Rad51 in IR-induced apoptosis. The functional significance of Rad51 proteolysis is supported by the finding that, unlike intact Rad51, the N- and C-terminal cleavage products fail to exhibit recombinase activi ty. In cells, overexpression of the Rad51 (D-A) mutant had no effect on act ivation of caspase 3 but did abrogate in Dart the apoptotic response to IR exposure. We conclude that proteolytic inactivation of Rad51 by a caspase-m ediated mechanism contributes to the cell death response induced by DNA dam age.