A chemical probe to modulate human GID4 Pro/N-degron interactions.

The C-terminal to LisH (CTLH) complex is a ubiquitin ligase complex that recognizes substrates with Pro/N-degrons via its substrate receptor Glucose-Induced Degradation 4 (GID4), but its function and substrates in humans remain unclear. Here, we report PFI-7, a potent, selective and cell-active chemical probe that antagonizes Pro/N-degron binding to human GID4. Use of PFI-7 in proximity-dependent biotinylation and quantitative proteomics enabled the identification of GID4 interactors and GID4-regulated proteins. GID4 interactors are enriched for nucleolar proteins, including the Pro/N-degron-containing RNA helicases DDX21 and DDX50. We also identified a distinct subset of proteins whose cellular levels are regulated by GID4 including HMGCS1, a Pro/N-degron-containing metabolic enzyme. These data reveal human GID4 Pro/N-degron targets regulated through a combination of degradative and nondegradative functions. Going forward, PFI-7 will be a valuable research tool for investigating CTLH complex biology and facilitating development of targeted protein degradation strategies that highjack CTLH E3 ligase activity.

Chemical tools for the Gid4 subunit of the human E3 ligase C-terminal to LisH (CTLH) degradation complex.

We have developed a novel chemical handle (PFI-E3H1) and a chemical probe (PFI-7) as ligands for the Gid4 subunit of the human E3 ligase CTLH degradation complex. Through an efficient initial hit-ID campaign, structure-based drug design (SBDD) and leveraging the sizeable Pfizer compound library, we identified a 500 nM ligand for this E3 ligase through file screening alone. Further exploration identified a vector that is tolerant to addition of a linker for future chimeric molecule design. The chemotype was subsequently optimized to sub-100 nM Gid4 binding affinity for a chemical probe. These novel tools, alongside the suitable negative control also identified, should enable the interrogation of this complex human E3 ligase macromolecular assembly.

Structure-Activity Relationship of a Pyrrole Based Series of PfPKG Inhibitors as Anti-Malarials.

Controlling malaria requires new drugs against Plasmodium falciparum. The P. falciparum cGMP-dependent protein kinase (PfPKG) is a validated target whose inhibitors could block multiple steps of the parasite's life cycle. We defined the structure-activity relationship (SAR) of a pyrrole series for PfPKG inhibition. Key pharmacophores were modified to enable full exploration of chemical diversity and to gain knowledge about an ideal core scaffold. In vitro potency against recombinant PfPKG and human PKG were used to determine compound selectivity for the parasite enzyme. P. berghei sporozoites and P. falciparum asexual blood stages were used to assay multistage antiparasitic activity. Cellular specificity of compounds was evaluated using transgenic parasites expressing PfPKG carrying a substituted "gatekeeper" residue. The structure of PfPKG bound to an inhibitor was solved, and modeling using this structure together with computational tools was utilized to understand SAR and establish a rational strategy for subsequent lead optimization.

TEP RNA: a new frontier for early diagnosis of NSCLC.

BACKGROUND: Non-small cell lung cancer (NSCLC) is the most common type of lung cancer (LC), which is the leading cause of tumor mortality. In recent years, compared with tissue biopsy, which is the diagnostic gold standard for tumor diagnosis, Liquid biopsy (LB) is considered to be a more minimally invasive, sensitive, and safer alternative or auxiliary diagnostic method. However, the current value of LB in early diagnosis of LC is not ideal, so it is particularly important to study the changes in blood composition during the process of tumorigenesis and find more sensitive biomarkers. PURPOSE: Platelets are a type of abundant blood cells that carry a large amount of RNA. In the LC regulatory network, activated platelets play an important role in the process of tumorigenesis, development, and metastasis. In order to identify predictive liquid biopsy biomarkers for the diagnosis of NSCLC, we summarized the development and function of platelets, the interaction between platelets and tumors, the value of TEP RNA in diagnosis, prognosis, and treatment of NSCLC, and the method for detecting TEP RNA of NSCLC in this article. CONCLUSION: The application of platelets in the diagnosis and treatment of NSCLC remains at a nascent stage. In addition to the drawbacks of low platelet count and complex experimental processes, the diagnostic accuracy of TEP RNA-seq for cancer in different populations still needs to be improved and validated. At present, a large number of studies have confirmed significant differences in the expression of TEP RNA in platelets between NSCLC patients and healthy individuals. Continuous exploration of the diagnostic value of TEP RNA in NSCLC is of utmost importance. The integration of NSCLC platelet-related markers with other NSCLC markers can improve current tumor diagnosis and prognostic evaluation systems, providing broad prospects in tumor screening, disease monitoring, and prognosis assessment.

A unique binding pocket induced by a noncanonical SAH mimic to develop potent and selective PRMT inhibitors.

Protein arginine methyltransferases (PRMTs) are attractive targets for developing therapeutic agents, but selective PRMT inhibitors targeting the cofactor SAM binding site are limited. Herein, we report the discovery of a noncanonical but less polar SAH surrogate YD1113 by replacing the benzyl guanidine of a pan-PRMT inhibitor with a benzyl urea, potently and selectively inhibiting PRMT3/4/5. Importantly, crystal structures reveal that the benzyl urea moiety of YD1113 induces a unique and novel hydrophobic binding pocket in PRMT3/4, providing a structural basis for the selectivity. In addition, YD1113 can be modified by introducing a substrate mimic to form a "T-shaped" bisubstrate analogue YD1290 to engage both the SAM and substrate binding pockets, exhibiting potent and selective inhibition to type I PRMTs (IC50 < 5 nmol/L). In summary, we demonstrated the promise of YD1113 as a general SAH mimic to build potent and selective PRMT inhibitors.

The co-crystal structure of Cbl-b and a small-molecule inhibitor reveals the mechanism of Cbl-b inhibition.

Cbl-b is a RING-type E3 ubiquitin ligase that is expressed in several immune cell lineages, where it negatively regulates the activity of immune cells. Cbl-b has specifically been identified as an attractive target for cancer immunotherapy due to its role in promoting an immunosuppressive tumor environment. A Cbl-b inhibitor, Nx-1607, is currently in phase I clinical trials for advanced solid tumor malignancies. Using a suite of biophysical and cellular assays, we confirm potent binding of C7683 (an analogue of Nx-1607) to the full-length Cbl-b and its N-terminal fragment containing the TKBD-LHR-RING domains. To further elucidate its mechanism of inhibition, we determined the co-crystal structure of Cbl-b with C7683, revealing the compound's interaction with both the TKBD and LHR, but not the RING domain. Here, we provide structural insights into a novel mechanism of Cbl-b inhibition by a small-molecule inhibitor that locks the protein in an inactive conformation by acting as an intramolecular glue.

Discovery of a First-in-Class Small-Molecule Ligand for WDR91 Using DNA-Encoded Chemical Library Selection Followed by Machine Learning.

WD40 repeat-containing protein 91 (WDR91) regulates early-to-late endosome conversion and plays vital roles in endosome fusion, recycling, and transport. WDR91 was recently identified as a potential host factor for viral infection. We employed DNA-encoded chemical library (DEL) selection against the WDR domain of WDR91, followed by machine learning to predict ligands from the synthetically accessible Enamine REAL database. Screening of predicted compounds identified a WDR91 selective compound 1, with a KD of 6 ± 2 µM by surface plasmon resonance. The co-crystal structure confirmed the binding of 1 to the WDR91 side pocket, in proximity to cysteine 487, which led to the discovery of covalent analogues 18 and 19. The covalent adduct formation for 18 and 19 was confirmed by intact mass liquid chromatography-mass spectrometry. The discovery of 1, 18, and 19, accompanying structure-activity relationship, and the co-crystal structures provide valuable insights for designing potent and selective chemical tools against WDR91 to evaluate its therapeutic potential.

Discovery of a 53BP1 Small Molecule Antagonist Using a Focused DNA-Encoded Library Screen.

Methyl-lysine reader p53 binding protein 1 (53BP1) is a central mediator of DNA break repair and is associated with various human diseases, including cancer. Thus, high-quality 53BP1 chemical probes can aid in further understanding the role of 53BP1 in genome repair pathways. Herein, we utilized focused DNA-encoded library screening to identify the novel hit compound UNC8531, which binds the 53BP1 tandem Tudor domain (TTD) with an IC50 of 0.47 ± 0.09 µM in a TR-FRET assay and Kd values of 0.85 ± 0.17 and 0.79 ± 0.52 µM in ITC and SPR, respectively. UNC8531 was cocrystallized with the 53BP1 TTD to guide further optimization efforts, leading to UNC9512. NanoBRET and 53BP1-dependent foci formation experiments confirmed cellular target engagement. These results show that UNC9512 is a best-in-class small molecule 53BP1 antagonist that can aid further studies investigating the role of 53BP1 in DNA repair, gene editing, and oncogenesis.

Discovery of a Novel DCAF1 Ligand Using a Drug-Target Interaction Prediction Model: Generalizing Machine Learning to New Drug Targets.

DCAF1 functions as a substrate recruitment subunit for the RING-type CRL4DCAF1 and the HECT family EDVPDCAF1 E3 ubiquitin ligases. The WDR domain of DCAF1 serves as a binding platform for substrate proteins and is also targeted by HIV and SIV lentiviral adaptors to induce the ubiquitination and proteasomal degradation of antiviral host factors. It is therefore attractive both as a potential therapeutic target for the development of chemical inhibitors and as an E3 ligase that could be recruited by novel PROTACs for targeted protein degradation. In this study, we used a proteome-scale drug-target interaction prediction model, MatchMaker, combined with cheminformatics filtering and docking to identify ligands for the DCAF1 WDR domain. Biophysical screening and X-ray crystallographic studies of the predicted binders confirmed a selective ligand occupying the central cavity of the WDR domain. This study shows that artificial intelligence-enabled virtual screening methods can successfully be applied in the absence of previously known ligands.

Discovery of Nanomolar DCAF1 Small Molecule Ligands.

DCAF1 is a substrate receptor of two distinct E3 ligases (CRL4DCAF1 and EDVP), plays a critical physiological role in protein degradation, and is considered a drug target for various cancers. Antagonists of DCAF1 could be used toward the development of therapeutics for cancers and viral treatments. We used the WDR domain of DCAF1 to screen a 114-billion-compound DNA encoded library (DEL) and identified candidate compounds using similarity search and machine learning. This led to the discovery of a compound (Z1391232269) with an SPR KD of 11 µM. Structure-guided hit optimization led to the discovery of OICR-8268 (26e) with an SPR KD of 38 nM and cellular target engagement with EC50 of 10 µM as measured by cellular thermal shift assay (CETSA). OICR-8268 is an excellent tool compound to enable the development of next-generation DCAF1 ligands toward cancer therapeutics, further investigation of DCAF1 functions in cells, and the development of DCAF1-based PROTACs.

From study abroad to study at home: Spontaneous neuronal activity predicts depressive symptoms in overseas students during the COVID-19 pandemic.

The objective of this study was to evaluate symptoms of depression and anxiety as well as changes in spontaneous neuronal activity in college students studying abroad during the coronavirus 2019 (COVID-19) pandemic. We examined functional brain changes using resting-state functional magnetic resonance imaging (fMRI), the amplitude of low-frequency fluctuations (ALFF), and regional homogeneity (ReHo) in overseas students with enforced isolation due to the COVID-19 pandemic. Additionally, emotional assessments were administered to determine the severity of depression and anxiety. The questionnaire results showed that anxiety and depressive symptoms differed between overseas students (i.e., those attending an overseas college virtually) and local students (i.e., those attending a local college in person). The fMRI data revealed higher ALFF values in the bilateral superior medial frontal gyrus, bilateral pre-central gyrus, left insula, and left superior temporal gyrus as well as lower ALFF values in the bilateral paracentral lobule (supplementary motor area) in overseas students. Moreover, ReHo analysis also revealed significant differences between overseas students and local students. Compared with local students, overseas students showed significantly increased ReHo in the right inferior frontal and superior temporal gyri and decreased ReHo in the bilateral paracentral lobule, bilateral superior medial frontal gyrus (supplementary motor area), and bilateral pre-central gyrus. In addition, in overseas students, altered ReHo in the cluster including the left superior and medial frontal gyri, pre-central gyrus, and paracentral lobule was significantly positively correlated with Self-Rating Depression Scale scores. Thus, spontaneous brain activity in overseas students changed during the COVID-19 pandemic. This change in brain function might be related to depression and anxiety symptoms. These results suggest that mental health services are needed to decrease the risk of anxiety and depression among college students studying abroad during the COVID-19 pandemic.

Cdyl Deficiency Brakes Neuronal Excitability and Nociception through Promoting Kcnb1 Transcription in Peripheral Sensory Neurons.

Epigenetic modifications are involved in the onset, development, and maintenance of pain; however, the precise epigenetic mechanism underlying pain regulation remains elusive. Here it is reported that the epigenetic factor chromodomain Y-like (CDYL) is crucial for pain processing. Selective knockout of CDYL in sensory neurons results in decreased neuronal excitability and nociception. Moreover, CDYL facilitates histone 3 lysine 27 trimethylation (H3K27me3) deposition at the Kcnb1 intron region thus silencing voltage-gated potassium channel (Kv ) subfamily member Kv 2.1 transcription. Loss function of CDYL enhances total Kv and Kv 2.1 current density in dorsal root ganglia and knockdown of Kv 2.1 reverses the pain-related phenotypes of Cdyl deficiency mice. Furthermore, focal administration of a novel potent CDYL antagonist blunts nociception and attenuates neuropathic pain. These findings reveal that CDYL is a critical regulator of pain sensation and shed light on the development of novel analgesics targeting epigenetic mechanisms.

Survival­related DLEU1 is associated with HPV infection status and serves as a biomarker in HPV­infected cervical cancer.

Human papillomavirus (HPV) is the most common risk factor for the occurrence of cervical cancer (CC). In recent years, the important roles of long non­coding RNAs (lncRNAs) in CC have emerged, but studies on the relationship between lncRNAs and HPV­positive (HPV+) CC remain scarce. The present study aimed to investigate whether lncRNA deleted in lymphocytic leukemia 1 (DLEU1) is associated with HPV infection and explore the clinical significance of DLEU1 in HPV+ patients with CC. DLEU1 expression was detected by reverse transcription­quantitative PCR. The ability of DLEU1 to screen patients with CC from controls and differentiate individuals with different HPV infection status was evaluated by receiver operating characteristic analysis. The association of DLEU1 with the survival prognosis of patients with CC was assessed by Kaplan­Meier survival analysis and Cox regression analysis. The RNA Interactome Database was used to predict molecules interacting with DLEU1. The results indicated that DLEU1 expression was significantly upregulated in CC tissues and cell lines, particularly in those that were HPV+. In addition, DLEU1 had a high diagnostic value in discriminating patients with CC and differentiating between HPV+ and HPV­ patients with CC, and had a certain ability to screen HPV+ controls. DLEU1 was correlated with HPV infection in CC patients. Furthermore, DLEU1 was indicated to be associated with survival prognosis in both total patients with CC and HPV+ patients with CC, and independently predict the prognosis of patients with CC. Most of the molecules interacting with DLEU1 were microRNAs. In conclusion, abnormal DLEU1 expression is associated with HPV infection and may serve as a diagnostic and prognostic biomarker for HPV+ patients with CC.

A chemical probe targeting the PWWP domain alters NSD2 nucleolar localization.

Nuclear receptor-binding SET domain-containing 2 (NSD2) is the primary enzyme responsible for the dimethylation of lysine 36 of histone 3 (H3K36), a mark associated with active gene transcription and intergenic DNA methylation. In addition to a methyltransferase domain, NSD2 harbors two proline-tryptophan-tryptophan-proline (PWWP) domains and five plant homeodomains (PHDs) believed to serve as chromatin reading modules. Here, we report a chemical probe targeting the N-terminal PWWP (PWWP1) domain of NSD2. UNC6934 occupies the canonical H3K36me2-binding pocket of PWWP1, antagonizes PWWP1 interaction with nucleosomal H3K36me2 and selectively engages endogenous NSD2 in cells. UNC6934 induces accumulation of endogenous NSD2 in the nucleolus, phenocopying the localization defects of NSD2 protein isoforms lacking PWWP1 that result from translocations prevalent in multiple myeloma (MM). Mutations of other NSD2 chromatin reader domains also increase NSD2 nucleolar localization and enhance the effect of UNC6934. This chemical probe and the accompanying negative control UNC7145 will be useful tools in defining NSD2 biology.

Structural basis for the recognition of the S2, S5-phosphorylated RNA polymerase II CTD by the mRNA anti-terminator protein hSCAF4.

The C-terminal domain (CTD) of RNA polymerase II serves as a binding platform for numerous enzymes and transcription factors involved in nascent RNA processing and the transcription cycle. The S2, S5-phosphorylated CTD is recognized by the transcription factor SCAF4, which functions as a transcription anti-terminator by preventing early mRNA transcript cleavage and polyadenylation. Here, we measured the binding affinities of differently modified CTD peptides by hSCAF4 and solved the complex structure of the hSCAF4-CTD-interaction domain (CID) bound to a S2, S5-quadra-phosphorylated CTD peptide. Our results revealed that the S2, S5-quadra-phosphorylated CTD peptide adopts a trans conformation and is located in a positively charged binding groove of hSCAF4-CID. Although hSCAF4-CID has almost the same binding pattern to the CTD as other CID-containing proteins, it preferentially binds to the S2, S5-phosphorylated CTD. Our findings provide insight into the regulatory mechanism of hSCAF4 in transcription termination.

Structure-Activity Relationship of USP5 Inhibitors.

USP5 is a deubiquitinase that has been implicated in a range of diseases, including cancer, but no USP5-targeting chemical probe has been reported to date. Here, we present the progression of a chemical series that occupies the C-terminal ubiquitin-binding site of a poorly characterized zinc-finger ubiquitin binding domain (ZnF-UBD) of USP5 and competitively inhibits the catalytic activity of the enzyme. Exploration of the structure-activity relationship, complemented with crystallographic characterization of the ZnF-UBD bound to multiple ligands, led to the identification of 64, which binds to the USP5 ZnF-UBD with a KD of 2.8 µM and is selective over nine proteins containing structurally similar ZnF-UBD domains. 64 inhibits the USP5 catalytic cleavage of a di-ubiquitin substrate in an in vitro assay. This study provides a chemical and structural framework for the discovery of a chemical probe to delineate USP5 function in cells.

Structural basis of the TAM domain of BAZ2A in binding to DNA or RNA independent of methylation status.

Bromodomain adjacent to zinc finger domain protein 2A (BAZ2A) (also called transcription termination factor-1 interacting protein 5), a key component of the nucleolar remodeling complex, recruits the nucleolar remodeling complex to ribosomal RNA genes, leading to their transcriptional repression. In addition to its tandem plant homeodomain-bromodomain that is involved in binding to acetylated histone H4, BAZ2A also contains a methyl-CpG-binding domain (MBD)-like Tip5/ARBP/MBD (TAM) domain that shares sequence homology with the MBD. In contrast with the methyl-CpG-binding ability of the canonical MBD, the BAZ2A TAM domain has been shown to bind to promoter-associated RNAs of ribosomal RNA genes and promoter DNAs of other genes independent of DNA methylation. Nevertheless, how the TAM domain binds to RNA/DNA mechanistically remains elusive. Here, we characterized the DNA-/RNA-binding basis of the BAZ2A TAM domain by EMSAs, isothermal titration calorimetry binding assays, mutagenesis analysis, and X-ray crystallography. Our results showed that the TAM domain of BAZ2A selectively binds to dsDNA and dsRNA and that it binds to the backbone of dsDNA in a sequence nonspecific manner, which is distinct from the base-specific binding of the canonical MBD. Thus, our results explain why the TAM domain of BAZ2A does not specifically bind to mCG or TG dsDNA like the canonical MBD and also provide insights for further biological study of BAZ2A acting as a transcription factor in the future.

The human pseudouridine synthase PUS7 recognizes RNA with an extended multi-domain binding surface.

The human pseudouridine synthase PUS7 is a versatile RNA modification enzyme targeting many RNAs thereby playing a critical role in development and brain function. Whereas all target RNAs of PUS7 share a consensus sequence, additional recognition elements are likely required, and the structural basis for RNA binding by PUS7 is unknown. Here, we characterize the structure-function relationship of human PUS7 reporting its X-ray crystal structure at 2.26 Å resolution. Compared to its bacterial homolog, human PUS7 possesses two additional subdomains, and structural modeling studies suggest that these subdomains contribute to tRNA recognition through increased interactions along the tRNA substrate. Consistent with our modeling, we find that all structural elements of tRNA are required for productive interaction with PUS7 as the consensus sequence of target RNA alone is not sufficient for pseudouridylation by human PUS7. Moreover, PUS7 binds several, non-modifiable RNAs with medium affinity which likely enables PUS7 to screen for productive RNA substrates. Following tRNA modification, the product tRNA has a significantly lower affinity for PUS7 facilitating its dissociation. Taken together our studies suggest a combination of structure-specific and sequence-specific RNA recognition by PUS7 and provide mechanistic insight into its function.