Oncogene-dependent regulation of caspase activation by p53 protein in a cell-free system

The mechanism by which p53 modulates apoptosis in cancer therapy is incompletely understood. Here, cell-free extracts from irradiated tumor cells are described in which endogenous p53 protein is shown to participate in caspase activation. This apoptotic activity is also oncogene dependent, but independent of transcription in general or the presence of Bax or cytochrome c. A general use for this system is as a cell-free screen for apoptosis modulators. In this way, profound effects of protein kinase A were identified and corroborated in vivo by the protection conferred by cAMP against diverse triggers of p53-dependent apoptosis, This system provides direct biochemical evidence that p53 protein can transduce apoptotic signals through protein-protein interactions and reveals a modulator kinase pathway capable of regulating p53-dependent caspase activation.