Enterococcus faecalis-Induced Bystander Effect Drives Histone Acetylation Leading to Epithelial-Mesenchymal Transition via TGF-β Signaling

Murine macrophage RAW264.7 cells were treated with either superoxide-producing E. faecalis OG1RF or superoxide-deficient WY84. Conditioned medium (CM) was then collected and used to treat IEC-6 rat intestinal epithelial cells. Histone acetylation states and related signaling pathways were analyzed using immunoblotting, immunofluorescent staining, and chromatin immunoprecipitation sequencing (ChIP-seq).

Results: CM derived from E. faecalis-infected macrophages significantly induced histone H3 acetylation at lysine 27 and 9 (H3K27ac/H3K9ac) in IEC-6 cells compared to controls. Furthermore, this CM inhibited histone deacetylases, which contributed to the increased in H3 acetylation. ChIP-seq analysis revealed widespread alterations in H3K27ac across the genome in cells treated with E. faecalis-infected macrophage-derived CM.

Additionally, these changes were associated with aberrantly activated TGF-β signaling, leading to epithelial-mesenchymal transition (EMT). Targeted metabolomic analysis indicated that E. faecalis activated arachidonate lipoxygenase-12 (Alox12) in macrophages, resulting in the production of 12-hydroxyeicosatetraenoic acid (12-HETE), which induces H3 acetylation via the bystander effect (BSE). Conclusion: Infection with E. faecalis activates Alox12 in macrophages, leading to the production of 12-HETE that subsequently induces H3 acetylation through the BSE.

This aberrant H3 acetylation alters gene expression associated with TGF-β signaling, promoting EMT. These findings elucidate the mechanisms by which commensal bacteria may initiate and promote CRC, potentially providing insights for the development of novel strategies for CRC prevention and treatment.