E2F4 deficiency promotes drug-induced apoptosis.

E2F1 and E2F4 are known to have opposing roles in cell cycle control. In the present work, we examine the role of both E2F1 and E2F4 in apoptosis induced by three cyclin-dependent kinase inhibitors (roscovitine, BMS-387032, and flavopiridol) as well as by three established chemotherapeutic drugs (VP16, cisplatin and paclitaxel). We find that E2F4 levels are diminished following treatment with cyclin dependent kinase inhibitors (flavopiridol, roscovitine and BMS-387032) or with DNA damaging drugs (cisplatin and VP16). In contrast, each of these drugs induced E2F1. We find that mouse fibroblasts nullizygous for the E2F4 gene are more sensitive to apoptosis induced by roscovitine, flavopiridol, cisplatin, and VP16, whereas E2F1-deficient fibroblasts are less sensitive. Likewise, we find that RNAi-mediated reductions in E2F4 in human cancer cells results in increased drug sensitivity. Taken together, these results support a model in which E2F1 and E2F4 play opposing roles during drug-induced apoptosis.