Phase Separation of RNA Helicase Triggers Stress-Responsive Translational Switch

Translation initiation or elongation inhibition triggers contrasting effects on Caenorhabditis elegans survival during pathogen infection

Diverse microbial pathogens are known to attenuate host protein synthesis. Consequently, the host mounts a defense response against protein translation inhibition, leading to increased transcript levels of immune genes. The seemingly paradoxical upregulation of immune gene transcripts in response to blocked protein synthesis suggests that the defense mechanism against translation inhibition may not universally benefit host survival. However, a comprehensive assessment of host survival on pathogens upon blockage of different stages of protein synthesis is currently lacking. Here, we investigate the impact of knockdown of various translation initiation and elongation factors on the survival of Caenorhabditis elegans exposed to Pseudomonas aeruginosa. Intriguingly, we observe opposing effects on C. elegans survival depending on whether translation initiation or elongation is inhibited. While translation initiation inhibition enhances survival, elongation inhibition decreases it. Transcriptomic studies reveal that translation initiation inhibition activates a bZIP transcription factor ZIP-2-dependent innate immune response that protects C. elegans from P. aeruginosa infection. In contrast, inhibiting translation elongation triggers both ZIP-2-dependent and ZIP-2-independent immune responses that, while effective in clearing the infection, are detrimental to the host. Thus, our findings reveal the opposing roles of translation initiation and elongation inhibition in C. elegans survival during P. aeruginosa infection, highlighting distinct transcriptional reprogramming that may underlie these differences.

IMPORTANCE

Several microbial pathogens target host protein synthesis machinery, potentially limiting the innate immune responses of the host. In response, hosts trigger a defensive response, elevating immune gene transcripts. This counterintuitive response can have either beneficial or harmful effects on host survival. In this study, we conduct a comprehensive analysis of the impact of knocking down various translation initiation and elongation factors on the survival of Caenorhabditis elegans exposed to Pseudomonas aeruginosa. Intriguingly, inhibiting initiation and elongation factors has contrasting effects on C. elegans survival. Inhibiting translation initiation activates immune responses that protect the host from bacterial infection, while inhibiting translation elongation induces aberrant immune responses that, although clear the infection, are detrimental to the host. Our study reveals divergent roles of translation initiation and elongation inhibition in C. elegans survival during P. aeruginosa infection and identifies differential transcriptional reprogramming that could underlie these differences.

Pharmacological inhibition of DEAD-Box RNA Helicase 3 attenuates stress granule assembly

Stress granules (SGs) are non-membranous cytosolic protein-RNA aggregates that process mRNAs through stalled translation initiation in response to cellular stressors and in disease. DEAD-Box RNA helicase 3 (DDX3) is an active target of drug development for the treatment of viral infections, cancers, and neurodegenerative diseases. DDX3 plays a critical role in RNA metabolism, including SGs, but the role of DDX3 enzymatic activity in SG dynamics is not well understood. Here, we address this question by determining the effects of DDX3 inhibition on the dynamics of SG assembly and disassembly. We use two small molecule inhibitors of DDX3, RK33 and 16D, with distinct inhibitory mechanisms that target DDX3's ATPase activity and RNA helicase site, respectively. We find that both DDX3 inhibitors reduce the assembly of SGs, with a more pronounced reduction from RK-33. In contrast, both compounds only marginally affect the disassembly of SGs. RNA-mediated knockdown of DDX3 caused a similar reduction in SG assembly and minimal effect on SG disassembly. Collectively, these results reveal that the enzymatic activity of DDX3 is required for the assembly of SGs and pharmacological inhibition of DDX3 could be relevant for the treatment of SG-dependent pathologies.