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. 2019 Apr 23;10:1897. doi: 10.1038/s41467-019-09810-w

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 8 — The sequential molecular events for the R-point decision. a, b Upon mitogenic stimulation, RUNX3 binds to inactive chromatin marked by H3K27-me3. pRB–E2F1 and p300 associate with RUNX3. p300 acetylates RUNX3 and histones. BRD2 binds to acetylated RUNX3 through its first bromodomain (BD1). c One hour after mitogenic stimulation, the second bromodomain (BD2) of BRD2 binds to H4K12-ac: BRD2 binds both acetylated RUNX3 and acetylated histone through its bromodomains. Subsequently, SWI/SNF, MLL1/5, and TFIID bind to the C-terminal region of BRD2. At this point, inhibitory histone marks (H3K27-me3) are erased, and activatory marks (H3K4-me3) are enriched at the locus. Soon thereafter, TAF7 (inhibitory TAF) is released from the large complex, and expression of ARF, p53, and p21 is induced. The large complex, of which RUNX3 is the core, was named as Rpa-RX3-AC. d Two hours after mitogenic stimulation, CDK4 (associated with p21) binds to RUNX3 and becomes an additional component of Rpa-RX3-AC. At this point, the Cyclin D1–PRC1 complex forms separately from Rpa-RX3-AC. e When the RAS–MEK signal is downregulated, the Cyclin D1–PRC1 complex matures into the Cyclin D1–HDAC4–PRC1 complex, which in turn binds to Rpa-RX3-AC through the interaction between Cyclin D1 and CDK4 (a component of Rpa-RX3-AC), yielding Rpa-RX3-TR. Activation of CDK4 through the association with Cyclin D1 is critical for the inactivation of the chromatin loci and the dissociation of the entire complex. If the RAS signal is constitutively activated, the Cyclin D1–PRC1 complex fails to mature into the Cyclin D1–HDAC4–PRC1 complex, and consequently cannot form Rpa-RX3-TR. Therefore, if R-point commitment is normal, cells expressing constitutively active RAS cannot progress through the R-point into S-phase. f If the mitogenic signal is downregulated in a normal manner, Rpa-RX3-TR dissociates (4 h after stimulation) into two pieces, RUNX3–Cyclin D1–HDAC4 and BRD2–PRC1–SWI/SNF–TFIID, which remain associated with chromatin. g Soon thereafter, EZH2 associates with RUNX3–Cyclin D1–HDAC4 to form Rpa-RX3-RE, which remains on the chromatin. EZH2 contributes to the enrichment of an inactive chromatin mark (H3K27-me3) at the locus