P111 TGFβ SIGNALING SUPPRESSES COLON EPITHELIAL INFLAMMATORY RESPONSES.

Abstract

It is well-established that microbiota and immune cells signal to colon epithelial cells to increase production of chemokines and pro-inflammatory cytokines that can accelerate inflammation, but we have found that TGFβ/SMAD4 signaling in colon epithelium can suppress inflammation by negatively regulating pro-inflammatory gene expression. TGFβ and related cytokines activate type I and type II receptors that then phosphorylate R-SMADs. When phosphorylated, R-SMADs must then form a complex with SMAD4 to act as transcriptional activators or repressors. Thus, loss of SMAD4 abrogates all canonical TGFβ family signaling. After conditional Smad4 gene deletion in adult murine colonic epithelium, we found striking evidence for increased inflammatory signaling within the epithelial compartment concomitant with an increase in inflammatory infiltrate. In cultured mouse and human colon epithelial cell lines and organoids, TGFβ1 and/or BMP2 inhibited transcriptional induction of multiple inflammatory genes by TNF, IL-1β, or LPS treatment. In vivo, DSS-induced colitis in mice with adult-onset deletion of the Smad4 gene in intestinal epithelium resulted in invasive mucinous adenocarcinomas of the distal colon, while no tumors were found without colitis or in the SMAD4+ controls. In humans, we found a much higher incidence of SMAD4 loss in colitis-associated carcinoma (CAC) than in sporadic colorectal cancer. We now present mechanistic data showing that SMAD4-mediated signaling represses chemokine/cytokine signaling by regulating transcription initiation and that SMAD complexes interact directly with NFκB-regulated genes, indicating that SMAD complexes serve as direct transcriptional repressors of epithelial pro-inflammatory genes. Transcriptional programs downstream of TGFβ vary greatly among different cell types. While TGFβ signaling can suppress inflammation in immune cells due, in part, to activation of FoxP3 expression in Treg precursors, TGFβ signaling utilizes transcriptional repression rather than activation in colon epithelium to suppress inflammatory responses. Understanding TGFβ-regulated gene expression programs in epithelial responses provides novel information on how to limit inappropriate pro-inflammatory cues in the colon.