Loss of function of the retinoblastoma protein, pRB, leads to lack of differentiation, hyperproliferation and apoptosis. Inactivation of pRB results in deregulated E2F activity, which in turn induces entry to S-phase and apoptosis. Induction of apoptosis by either the loss of pRB or the deregulation of E2F activity occurs via both p53-dependent and p53-independent mechanisms. The mechanism by which E2F induces apoptosis is still unclear. Here we show that E2F1 directly regulates the expression of Apaf-1, the gene for apoptosis protease-activating factor 1. These results provide a direct link between the deregulation of the pRB pathway and apoptosis. Furthermore, because the pRB pathway is functionally inactivated in most cancers, the identification of Apaf-1 as a transcriptional target for E2F might explain the increased sensitivity of tumour cells to chemotherapy. We also show that, independently of the pRB pathway, Apaf-1 is a direct transcriptional target of p53, suggesting that p53 might sensitize cells to apoptosis by increasing Apaf-1 levels.
ASJC Scopus subject areas
- Cell Biology