The transcription factor E2F-1 induces both cell-cycle progression and, in certain settings, apoptosis. E2F-1 uses both p53-dependent and p53-independent pathways to kill cells. The p53-dependent pathway involves the induction by E2F-1 of the human tumour-suppressor protein p14ARF, which neutralizes HDM2 (human homologue of MDM2) and thereby stabilizes the p53 protein. Here we show that E2F-1 induces the transcription of the p53 homologue p73. Disruption of p73 function inhibited E2F-1-induced apoptosis in p53-defective tumour cells and in p53(-/-) mouse embryo fibroblasts. We conclude that activation of p73 provides a means for E2F-1 to induce death in the absence of p53.
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