Abstract

Intestinal barrier function defects and dysregulation of intestinal immune responses are two key contributory factors in the pathogenesis of ulcerative colitis (UC). Phenazine biosynthesis-like domain-containing protein (PBLD) was recently identified as a tumor suppressor in gastric cancer, hepatocellular carcinoma, and breast cancer; however, its role in UC remains unclear. Therefore, we analyzed colonic tissue samples from patients with UC and constructed specific intestinal epithelial PBLD-deficient (PBLD IEC−/− ) mice to investigate the role of this protein in UC pathogenesis. We found that epithelial PBLD was decreased in patients with UC and was correlated with levels of tight junction (TJ) and inflammatory proteins. PBLD IEC−/− mice were more susceptible to dextran sulfate sodium (DSS)- and 2,4,6-trinitrobenzene sulfonic acid-induced colitis compared with wild-type (WT) mice. In DSS-induced colitis, PBLD IEC−/− mice had impaired intestinal barrier function and greater immune cell infiltration in colonic tissue than WT mice. Furthermore, TJ proteins were markedly reduced in PBLD IEC−/− mice compared with WT mice with colitis. Nuclear factor (NF)-κB activation was markedly elevated and resulted in higher expression levels of downstream effectors (C–C motif chemokine ligand 20, interleukin [IL]-1β, IL-6, and tumor necrosis factor [TNF]-α) in colonic epithelial cells isolated from PBLD IEC−/− mice than WT mice with colitis. PBLD overexpression in intestinal epithelial cells (IECs) consistently inhibited TNF-α/interferon-γ-induced intestinal barrier disruption and TNF-α-induced inflammatory responses via the suppression of NF-κB. In addition, IKK inhibition (IKK-16) rescued excessive inflammatory responses induced by TNF-α in PBLD knockdown FHC cells. Co-immunoprecipitation assays showed that PBLD may interact with IKKα and IKKβ, thus inhibiting NF-κB signaling, decreasing inflammatory mediator production, attenuating colonic inflammation, and improving intes