Center for Integrative Chemical Biology and Drug Discovery, Division of Chemical Biology and Medicinal Chemistry, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
Department of Biochemistry and Molecular Medicine, Keck School of Medicine of the University of Southern California, Los Angeles, CA 90033, USA.
Cell Chem Biol. 2022 Apr 21;29(4):555-571.e11. doi: 10.1016/j.chembiol.2021.10.003. Epub 2021 Oct 28.
Canonical targeting of Polycomb repressive complex 1 (PRC1) to repress developmental genes is mediated by cell-type-specific, paralogous chromobox (CBX) proteins (CBX2, 4, 6, 7, and 8). Based on their central role in silencing and their dysregulation associated with human disease including cancer, CBX proteins are attractive targets for small-molecule chemical probe development. Here, we have used a quantitative and target-specific cellular assay to discover a potent positive allosteric modulator (PAM) of CBX8. The PAM activity of UNC7040 antagonizes H3K27me3 binding by CBX8 while increasing interactions with nucleic acids. We show that treatment with UNC7040 leads to efficient and selective eviction of CBX8-containing PRC1 from chromatin, loss of silencing, and reduced proliferation across different cancer cell lines. Our discovery and characterization of UNC7040 not only reveals the most cellularly potent CBX8-specific chemical probe to date, but also corroborates a mechanism of Polycomb regulation by non-specific CBX nucleotide binding activity.
多梳抑制复合物 1（PRC1）的规范靶向作用是通过细胞类型特异性的、同源盒（CBX）蛋白（CBX2、4、6、7 和 8）来抑制发育基因。基于它们在沉默中的核心作用，以及与人类疾病（包括癌症）相关的失调，CBX 蛋白是小分子化学探针开发的有吸引力的靶标。在这里，我们使用定量和靶向特异性细胞测定法来发现 CBX8 的有效正变构调节剂（PAM）。UNC7040 的 PAM 活性拮抗 CBX8 与 H3K27me3 的结合，同时增加与核酸的相互作用。我们表明，UNC7040 的治疗导致含有 CBX8 的 PRC1 从染色质中有效且选择性地逐出，沉默丧失，以及不同癌细胞系中的增殖减少。我们对 UNC7040 的发现和表征不仅揭示了迄今为止最具细胞活性的 CBX8 特异性化学探针，而且还证实了非特异性 CBX 核苷酸结合活性对 Polycomb 调节的机制。
