Structural transitions enable interleukin-18 maturation and signaling.

Several interleukin-1 (IL-1) family members, including IL-1ß and IL-18, require processing by inflammasome-associated caspases to unleash their activities. Here, we unveil, by cryoelectron microscopy (cryo-EM), two major conformations of the complex between caspase-1 and pro-IL-18. One conformation is similar to the complex of caspase-4 and pro-IL-18, with interactions at both the active site and an exosite (closed conformation), and the other only contains interactions at the active site (open conformation). Thus, pro-IL-18 recruitment and processing by caspase-1 is less dependent on the exosite than the active site, unlike caspase-4. Structure determination by nuclear magnetic resonance uncovers a compact fold of apo pro-IL-18, which is similar to caspase-1-bound pro-IL-18 but distinct from cleaved IL-18. Binding sites for IL-18 receptor and IL-18 binding protein are only formed upon conformational changes after pro-IL-18 cleavage. These studies show how pro-IL-18 is selected as a caspase-1 substrate, and why cleavage is necessary for its inflammatory activity.

Selenoprotein TXNRD3 supports male fertility via the redox regulation of spermatogenesis.

Thioredoxin/glutathione reductase (TXNRD3) is a selenoprotein composed of thioredoxin reductase and glutaredoxin domains. This NADPH-dependent thiol oxidoreductase evolved through gene duplication within the Txnrd family, is expressed in the testes, and can reduce both thioredoxin and glutathione in vitro; however, the function of this enzyme remains unknown. To characterize the function of TXNRD3 in vivo, we generated a strain of mice bearing deletion of Txnrd3 gene. We show that these Txnrd3 knockout mice are viable and without discernable gross phenotypes, and also that TXNRD3 deficiency leads to fertility impairment in male mice. We found that Txnrd3 knockout animals exhibited a lower fertilization rate in vitro, a sperm movement phenotype, and an altered thiol redox status in sperm cells. Proteomic analyses further revealed a broad range of substrates reduced by TXNRD3 during sperm maturation, presumably as a part of sperm quality control. Taken together, these results show that TXNRD3 plays a critical role in male reproduction via the thiol redox control of spermatogenesis.

A systematic screen for CDK4/6 substrates links FOXM1 phosphorylation to senescence suppression in cancer cells.

Cyclin D-dependent kinases (CDK4 and CDK6) are positive regulators of cell cycle entry and they are overactive in the majority of human cancers. However, it is currently not completely understood by which cellular mechanisms CDK4/6 promote tumorigenesis, largely due to the limited number of identified substrates. Here we performed a systematic screen for substrates of cyclin D1-CDK4 and cyclin D3-CDK6. We identified the Forkhead Box M1 (FOXM1) transcription factor as a common critical phosphorylation target. CDK4/6 stabilize and activate FOXM1, thereby maintain expression of G1/S phase genes, suppress the levels of reactive oxygen species (ROS), and protect cancer cells from senescence. Melanoma cells, unlike melanocytes, are highly reliant on CDK4/6-mediated senescence suppression, which makes them particularly susceptible to CDK4/6 inhibition.