Ribosome subunit attrition and activation of the p53-MDM4 axis dominate the response of MLL-rearranged cancer cells to WDR5 WIN site inhibition.

The chromatin-associated protein WD Repeat Domain 5 (WDR5) is a promising target for cancer drug discovery, with most efforts blocking an arginine-binding cavity on the protein called the 'WIN' site that tethers WDR5 to chromatin. WIN site inhibitors (WINi) are active against multiple cancer cell types in vitro, the most notable of which are those derived from MLL-rearranged (MLLr) leukemias. Peptidomimetic WINi were originally proposed to inhibit MLLr cells via dysregulation of genes connected to hematopoietic stem cell expansion. Our discovery and interrogation of small-molecule WINi, however, revealed that they act in MLLr cell lines to suppress ribosome protein gene (RPG) transcription, induce nucleolar stress, and activate p53. Because there is no precedent for an anticancer strategy that specifically targets RPG expression, we took an integrated multi-omics approach to further interrogate the mechanism of action of WINi in human MLLr cancer cells. We show that WINi induce depletion of the stock of ribosomes, accompanied by a broad yet modest translational choke and changes in alternative mRNA splicing that inactivate the p53 antagonist MDM4. We also show that WINi are synergistic with agents including venetoclax and BET-bromodomain inhibitors. Together, these studies reinforce the concept that WINi are a novel type of ribosome-directed anticancer therapy and provide a resource to support their clinical implementation in MLLr leukemias and other malignancies.

Ribosome subunit attrition and activation of the p53-MDM4 axis dominate the response of MLL-rearranged cancer cells to WDR5 WIN site inhibition.

The chromatin-associated protein WD Repeat Domain 5 (WDR5) is a promising target for cancer drug discovery, with most efforts blocking an arginine-binding cavity on the protein called the "WIN" site that tethers WDR5 to chromatin. WIN site inhibitors (WINi) are active against multiple cancer cell types in vitro, the most notable of which are those derived from MLL-rearranged (MLLr) leukemias. Peptidomimetic WINi were originally proposed to inhibit MLLr cells via dysregulation of genes connected to hematopoietic stem cell expansion. Our discovery and interrogation of small molecule WIN site inhibitors, however, revealed that they act in MLLr cell lines to suppress ribosome protein gene (RPG) transcription, induce nucleolar stress, and activate p53. Because there is no precedent for an anti-cancer strategy that specifically targets RPG expression, we took an integrated multi-omics approach to further interrogate the mechanism of action of WINi in MLLr cancer cells. We show that WINi induce depletion of the stock of ribosomes, accompanied by a broad yet modest translational choke and changes in alternative mRNA splicing that inactivate the p53 antagonist MDM4. We also show that WINi are synergistic with agents including venetoclax and BET-bromodomain inhibitors. Together, these studies reinforce the concept that WINi are a novel type of ribosome-directed anti-cancer therapy and provide a resource to support their clinical implementation in MLLr leukemias and other malignancies.

Structural basis of DNA binding by the WhiB-like transcription factor WhiB3 in Mycobacterium tuberculosis.

Mycobacterium tuberculosis (Mtb) WhiB3 is an iron-sulfur cluster-containing transcription factor belonging to a subclass of the WhiB-Like (Wbl) family that is widely distributed in the phylum Actinobacteria. WhiB3 plays a crucial role in the survival and pathogenesis of Mtb. It binds to the conserved region 4 of the principal sigma factor (σA4) in the RNA polymerase holoenzyme to regulate gene expression like other known Wbl proteins in Mtb. However, the structural basis of how WhiB3 coordinates with σA4 to bind DNA and regulate transcription is unclear. Here we determined crystal structures of the WhiB3:σA4 complex without and with DNA at 1.5 Å and 2.45 Å, respectively, to elucidate how WhiB3 interacts with DNA to regulate gene expression. These structures reveal that the WhiB3:σA4 complex shares a molecular interface similar to other structurally characterized Wbl proteins and also possesses a subclass-specific Arg-rich DNA-binding motif. We demonstrate that this newly defined Arg-rich motif is required for WhiB3 binding to DNA in vitro and transcriptional regulation in Mycobacterium smegmatis. Together, our study provides empirical evidence of how WhiB3 regulates gene expression in Mtb by partnering with σA4 and engaging with DNA via the subclass-specific structural motif, distinct from the modes of DNA interaction by WhiB1 and WhiB7.

Alternative food sources for Amblydromella caudiglans (Phytoseiidae) and effects on predation.

The addition of supplemental food sources for natural enemies is a growing component of conservation and augmentative biological control. Supplemental foods can be used to retain natural enemies when prey are scarce and to promote survival, fecundity, longevity, and development of natural enemy populations, especially generalist natural enemies. Amblydromella caudiglans (Schuster) (Acari: Phytoseiidae) is one of the most abundant predatory mites found in commercial apple orchards in Washington, USA, and contributes to spider mite control. However, because its widespread presence in commercial apple orchards was only recently discovered, how supplementary food sources affect its performance is unknown. In laboratory studies, we evaluated the performance (fecundity, retention, prey consumption) of the generalist phytoseiid A. caudiglans on commercially available supplemental food sources, including factitious prey (Ephestia eggs and Artemia brine shrimp cysts), and pollens of apple, pear, and cattail. We determined that A. caudiglans will not consume Ephestia eggs and performs best on cattail and pear pollens. Combinations of food sources did not enhance the performance of this predator compared to the best performing single-sources. The presence of alternative food sources did not decrease A. caudiglans predation of twospotted spider mite nymphs, except for Artemia brine shrimp cysts, which had a substantial handling time. These results lay the groundwork for identifying a way to promote and retain this natural enemy in tree fruit cropping systems through the use of food resource applications or floral plantings.