Chromatin-bound RB targets promoters, enhancers, and CTCF-bound loci, and is redistributed by cell cycle progression.

Summary
RB’s interaction with chromatin is key to understanding its molecular functions. Here, for first time, we identify the full spectrum of chromatin-bound RB. Rather than exclusively binding promoters, as is often described, RB targets three fundamentally different types of loci (promoters, enhancers, insulators), which are largely distinguishable by the mutually exclusive presence of E2F1, c-Jun and CTCF. While E2F/DP facilitates RB association with promoters, AP-1 recruits RB to enhancers. Although phosphorylation in CDK-sites is often portrayed to release RB from chromatin, we show that the cell-cycle redistributes RB so that it enriches at promoters in G1, and at non-promoter sites in cycling cells. RB-bound promoters include the classic E2F-targets and are similar between lineages, but RB-bound enhancers associate with different categories of genes and vary between cell types. Thus, RB has a well-preserved role controlling E2F in G1, and it targets cell type-specific enhancers and CTCF-sites when cells enter S-phase.

Western blot data referring to Supplement figures S3, S4 and S5 are shown here.