Depolymerization of actin filaments by Cucurbitacin I through binding G-actin.

Cucurbitacins have high economic value as they are a major source of food and have pharmacological properties. Cucurbitacin I (CuI) is a plant-derived natural tetracyclic triterpenoid compound that shows an anticancer effect via inhibiting the JAK2-STAT3 signaling pathway. The actin cytoskeleton is the most abundant protein in cells and regulates critical events through reorganization in cells. In this study, it is aimed at determining the direct effect of CuI on actin dynamics. The fluorescence profile of G-actin in the presence of CuI (1-200 nM) shifted to a higher temperature, suggesting that G-actin binds CuI and that G-actin-CuI is more thermally stable than the ligand-free form. CuI dose-dependently inhibited the polymerization of F-actin in vitro and disrupted actin filaments in endothelial cells. Docking and MD simulations suggested that CuI binds to the binding site formed by residues I136, I175, D154, and A138 that are at the interface of monomers in F-actin. The migration ability of cells treated with CuI for 24 h was significantly lower than the control group (p < .001). This study reveals the molecular mechanisms of CuI in the regulation of actin dynamics by binding G-actin. More importantly, this study indicates a novel role of CuI as an actin-targeting drug by binding directly to G-actin and may contribute to the mode of action of CuI on anticancer activities.

Synthetic virology approaches to improve the safety and efficacy of oncolytic virus therapies.

The large coding potential of vaccinia virus (VV) vectors is a defining feature. However, limited regulatory switches are available to control viral replication as well as timing and dosing of transgene expression in order to facilitate safe and efficacious payload delivery. Herein, we adapt drug-controlled gene switches to enable control of virally encoded transgene expression, including systems controlled by the FDA-approved rapamycin and doxycycline. Using ribosome profiling to characterize viral promoter strength, we rationally design fusions of the operator element of different drug-inducible systems with VV promoters to produce synthetic promoters yielding robust inducible expression with undetectable baseline levels. We also generate chimeric synthetic promoters facilitating additional regulatory layers for VV-encoded synthetic transgene networks. The switches are applied to enable inducible expression of fusogenic proteins, dose-controlled delivery of toxic cytokines, and chemical regulation of VV replication. This toolbox enables the precise modulation of transgene circuitry in VV-vectored oncolytic virus design.