Butyrate influences epithelial signaling via generation of reactive oxygen species

Abstract

Short chain fatty acids (e.g. butyrate) arise from bacterial fermentation of complex carbohydrates in the colon and are known to modulate innate immunity. We previously reported that commensal bacteria cocultured with intestinal epithelial cells stimulated generation of reactive oxygen species (ROS), with consequent suppression of ubiquitin‐mediated degradation of important signaling intermediates, including β‐catenin and the NF‐κB inhibitor IκB‐α. Ubiquitination of β‐catenin and IκB‐α is catalyzed by the SCFβ‐TrCP ubiquitin ligase, which itself requires regulated modification of the cullin‐1 subunit by the ubiquitin‐like protein NEDD8. Herein, we show that butyrate at physiological concentrations induced ROS in cultured intestinal epithelial cells within 30 minutes, transiently altering the intracellular redox balance. Butyrate induced ROS caused oxidative inactivation of Ubc12, the NEDD8‐conjugating enzyme, and resulted in loss of cullin‐1 neddylation and inactivation of the SCF‐βTrCPubiquitin ligase. Consistently, butyrate blocked TNF‐α induced nuclear translocation of the p65 subunit of NF‐κB and mediated the stabilization of β‐catenin. These data demonstrate how a natural product of the intestinal normal flora profoundly affects epithelial inflammatory and proliferative signaling pathways. This research was funded by NIH grant AI064462.