SUMMARY The chromatin-associated protein WDR5 is a promising target for pharmacological inhibition in cancer. Drug discovery efforts center on the blockade of the “WIN site” of WDR5, a well-defined pocket that is amenable to small molecule inhibition. Various cancer contexts have been proposed to be targets for WIN site inhibitors, but a lack of understanding of WDR5 target genes and of the primary effects of WIN site inhibitors hampers their utility. Here, by the discovery of potent WIN site inhibitors, we demonstrate that the WIN site links WDR5 to chromatin at a small cohort of loci, including a specific subset of ribosome protein genes. WIN site inhibitors rapidly displace WDR5 from chromatin and decrease the expression of associated genes, causing translational inhibition, nucleolar stress, and p53 induction. Our studies define a mode by which WDR5 engages chromatin and forecast that WIN site blockade could have utility against multiple cancer types.

Author Contributions JT, KBT, JRA, JJM, KMM, RDG, CH, and JDM designed and synthesized compounds. ERA and LRT conducted mechanism of action studies featured in Figure 4,5 and 7. JS and JGS obtained the biochemical and cell-based data in Table 1-3. JLS conducted western blot and caspase assay in Figure 6. BZ, TAR, and WGP performed X-ray crystallography studies of complexes. JK, MI, andRJC conducted CTOSs assay in Figure 8. WJM GMS helped design experiments. WPT, SRS, TL, and SWF design and directed experiments and helped write the paper. All authors have given approval to the final version of the manuscript. Supporting Information. X-ray refinement statistics, MLL1 HMT assay details and titration curves of compound 16. This material is available free of charge via the internet at http://pubs.acs.org. Accession Codes. Atom coordinates and structure factors for WDR5-ligand complexes can be accessed in the PDB via the following accession codes: Compound 13/WDR5 complex (6UFX), Compound 16/WDR5 complex (6UCS). Authors will release the atomic coordinates upon article publication.

Background: PCNA mono-ubiquitination at stalled replication forks recruits translesion synthesis polymerases for fork restart. Results:The mono-ADP-ribosyltransferase PARP10 interacts with PCNA through a PIP-box. PARP10 knockdown results in DNA damage hypersensitivity and defective translesion synthesis. Conclusion: PARP10 participates in PCNA-dependent DNA damage tolerance. Significance: This is the first time that post-translational modification by mono-ADP-ribosylation is implicated in DNA repair.

WDR5 is a highly-conserved nuclear protein that performs multiple scaffolding functions in the context of chromatin. WDR5 is also a promising target for pharmacological inhibition in cancer, with small molecule inhibitors of an arginine-binding pocket of WDR5 (the ‘WIN’ site) showing efficacy against a range of cancer cell lines in vitro. Efforts to understand WDR5, or establish the mechanism of action of WIN site inhibitors, however, are stymied by its many functions in the nucleus, and a lack of knowledge of the conserved gene networks—if any—that are under its control. Here, we have performed comparative genomic analyses to identify the conserved sites of WDR5 binding to chromatin, and the conserved genes regulated by WDR5, across a diverse panel of cancer cell lines. We show that a specific cohort of protein synthesis genes (PSGs) are invariantly bound by WDR5, demonstrate that the WIN site anchors WDR5 to chromatin at these sites, and establish that PSGs are bona fide, acute, and persistent targets of WIN site blockade. Together, these data reveal that WDR5 plays a predominant transcriptional role in biomass accumulation and provide further evidence that WIN site inhibitors act to repress gene networks linked to protein synthesis homeostasis.