Unbiased location analysis of E2F1-binding sites suggests a widespread role for E2F1 in the human genome

The E2F family of transcription factors regulates basic cellular processes. Here, we take an unbiased approach towards identifying E2F1 target genes by examining localization of E2F1-binding sites using high-density oligonucleotide tiling arrays. To begin, we developed a statistically-based methodology for analysis of ChIP-chip data obtained from arrays that represent 30 Mb of the human genome. Using this methodology, we identified regions bound by E2F1, MYC, and RNA Polymerase II (POLR2A). We found a large number of binding sites for all three factors; extrapolation suggests there may be approximately 20,000-30,000 E2F1- and MYC-binding sites and approximately 12,000-17,000 active promoters in HeLa cells. In contrast to our results for MYC, we find that the majority of E2F1-binding sites (>80%) are located in core promoters and that 50% of the sites overlap transcription starts. Only a small fraction of E2F1 sites possess the canonical binding motif. Surprisingly, we found that approximately 30% of genes in the 30-Mb region possessed an E2F1 binding site in a core promoter and E2F1 was bound near to 83% of POLR2A-bound sites. To determine if these results were representative of the entire human genome, we performed ChIP-chip analyses of approximately 24,000 promoters and confirmed that greater than 20% of the promoters were bound by E2F1. Our results suggest that E2F1 is recruited to promoters via a method distinct from recognition of the known consensus site and point toward a new understanding of E2F1 as a factor that contributes to the regulation of a large fraction of human genes.