CREB-mediated sensing of bacterial membrane vesicles unveils a conserved host defense pathway.

Bacterial membrane vesicles (MVs) are critical mediators of virulence factor delivery and intercellular communication, yet the mechanisms by which hosts detect and respond to these vesicles remain poorly characterized. Through transcriptional profiling, we found that MVs derived from the non-lethal pathogenic Erwinia carotovora carotovora 15 (Ecc15) robustly induce reactive oxygen species (ROS) production and systemically upregulate Jon genes-a family of immune-related genes-in the Drosophila intestine 24 h post-infection. Strikingly, these effects contrast with transcriptional changes observed upon gut-specific overexpression of CRTC, the coactivator of the conserved transcription factor cAMP response element-binding protein (CREB). Intriguingly, ingestion of OMVs from Ecc15 or from the Gram-positive bacterium Lactobacillus plantarum (L.plantarum) significantly suppresses CREB activity in enterocytes (ECs). Fractionation experiments revealed that proteinaceous components within bacterial MVs inhibited CREB activity by reducing apical Ca²⁺ levels in ECs. Mechanistically, the CRTC/CREB cascade promoted gut microbial load by transcriptionally repressing PGRP-SC2-dependent amidase activity, a pathway independent of the canonical Relish/Imd signaling axis. Furthermore, OMVs from E. coli (BL21) also potently suppressed expression of pro-inflammatory factors, such as IL-6 and CXCL10 in NIH3T3 by blocking the activity of CREB. Collectively, these findings demonstrated that CREB play a conserved role on sense bacterial MVs and trigger anti-infection defenses in both Drosophila and mammalian systems, unveiling a novel paradigm in host-microbe communication.