E2F transcriptional repressor complexes are critical downstream targets of p19ARF/p53-induced proliferative arrest

The p16INK4a/pRB/E2F and p19ARF/p53 tumor suppressor pathways are disrupted in most human cancers. Both p19ARF and p53 are required for the induction of senescence in primary mouse embryonic fibroblasts (MEFs), but little is known about their downstream targets. Disruption of E2F-mediated transcriptional repression in MEFs caused a general increase in the expression of E2F target genes, including p19ARF. We detected no contribution of E2F-mediated transactivation in this setting, indicating that a predominant role of endogenous E2F in asynchronously growing primary MEFs is to repress its target genes. Moreover, relief of transcriptional repression by E2F rendered MEFs resistant to senescence induced by either p19ARF, p53, or RASV12. Thus, E2F transcriptional repressor complexes are critical downstream targets of antiproliferative p19ARF/p53 signaling.